Chapter 9 Flow In Closed Conduits 552e13

CHAPTER 9

Flow in Closed Conduits 9.1 Water at 10 °C flows in a 150-mm-diameter pipe at a velocity of 5.5 m/s. Is this flow laminar or turbulent?

i 92

N R = dv/v = (0.150)(5.5)/(1.30 X 10~6) = 634615. Since 634615 > 4000, the flow is turbulent.

SAE10 oil at 68 °F flows in a 9-in-diameter pipe. Find the maximum velocity for which the flow will be laminar,

f N R = pdv/fi. For laminar flow, assume N R ≤ 2000. 2000 = (1.68)(^)(u)/(1.70 x 10-3), v = 2.70 ft/s. 93

The accepted transition Reynolds number for flow past a smooth sphere is 250 000. At what velocity will this occur for airflow at 20 °C past a 10-cm-diameter sphere? N R = dv/v 250000= (0.10)(v)/(1.51 x 10“5) u = 37.8 m/s

I

9.4 Repeat Prob. 9.3 if the fluid is (a) water at 20° and (6) hydrogen at 20 °C (v = 1.08 x 104 m2/s).

f («) (6)

N R = dv/v N R = dv/v

250 000 = (0.10)(u)/(1.02 x 10-6) 250000 = (0.10)(u)/(l.08 x 10~4)

v = 2.55 m/s v = 270 m/s

93 A j-in-diameter water pipe is 60 ft long and delivers wafer at 5 gpm at 20 °C. What fraction of this pipe is taken up by the entrance region?

I G = (5)(0.002228) = 0.01114 ft3/s V = Q/A = 0.01114/[(^)(0.5/12)2/4] = 8.170 ft/s

N R = dv/v

From Table A-2, v = 1.02 x 10~6 m2/s at 20 °C, which equals 1.10 x 10-5 ft2/s; hence, N R = (0.5/12)(8.170)/(1.10 x 10~5) = 30 947. Since 30 947 > 4000, the flow is turbulent and for entrance length, LJd = 4AN r 6 = (4.4)(30 947)1/6 = 25. The actual pipe has L/d = 60/[(|)/12] = 1440; hence, L‘^d ] = Two = 0.017 or 1.7 percent L/d L An oil with p = 900 kg/m3 and v = 0.0002 m2/s flows upward through an inclined pipe as shown in Fig. 9-1. Assuming steady laminar flow, (a) that the flow is up and find the (6) head loss between section 1 and section 2, (c) flow rate, (<J) velocity, and (e) Reynolds number. Is the flow really laminar?

I (a)

HGL = z+p/pg HGL1 = 0 + 350000/[(900)(9.807)] = 39.65m HGL* = (10) (sin 40°) + 250 000/[(900)(9.807)] = 34.75 m Since HGLi > HGL2 , the flow is upward.

(6) (c)

h f = HGL, - HGL2 = 39.65 - 34.75 = 4.90 m p = pv = (900)(0.0002) = 0.180 kg/(m • s) npgd 4 h f (nr)(900)(9.807)(iso)4(4.90) ^ 128pL (128)(0.180)(10) =

(<0 (e)

= 0.00764 m3/s

v = Q/A = 0.00764/[(JT)(T®)2/4] = 2.70 m/s N R = dv/v = (,so)(2.70)/0.0002 = 810 This value of N R is well within the laminar range; hence, the flow is most likely laminar.

Fig. 9-1 197

198 D CHAPTER 9 9.7

For flow of SAE10 oil through a 100-mm-diameter pipe, for what flow rate in cubic meters per hour would we expect transition to turbulence at (a) 20 °C [#i = 0.104 Pa-s], and (ft) 100 °C [p = 0.0056 Pa • s]? # Assume transition to turbulence occurs at N R = 2300. N R = pdv/ft. (a) 2300 = (869)(0.100)(t;)/0.104 u = 2.753 m/s Q = Av = [(flr)(0.100)2/4](2.753) = 0.0216 m3/s or 77.76 m3/h (ft) 2300 = (869)(0.100)(u)/0.0056 v = 0.1482 m/s Q = Av = [(n:)(0.100)2/4](0.1482) = 0.00116 m3/s or 4.18m3/h

9.8

A fluid at 20 °C flows at 0.8 L/s through an 100-mm-diameter pipe. Determine whether the flow is laminar or turbulent if the fluid is (a) hydrogen (v = 1.08 x 10~ 4 m2/s), (ft) air, (c) gasoline (v = 4.06 x 10“7 m2/s), (d) water, (e) mercury (v = 1.15 x 10“7 m2/s), or (f) glycerin. NR = dv/v v = Q/A = (0.8 Xl0~3)/[(jr)(0.100)2/4]= 0.1019 m/s

f (a)

N R = (0.100)(0.1019)/(1.08 x 10“4) = 94

(ft) (c)

N R = (0.100)(0.1019)/(1.51 x 10“5) = 675 (laminar) N R = (0.100)(0.1019)/(4.06 x 10~7) = 25 099 (turbulent)

(d)

N R = (0.100)(0.1019)/(1.02 X 10“6) = 9990

(e)

N R = (0.100)(0.1019)/(1.15 X 10“7) = 88 609

(turbulent)

3

9.9

(laminar)

N R = (0.100)(0.1019)/(1.18 X 10~ ) = 9

(turbulent) (laminar)

Oil (s.g. = 0.9, v = 0.0003 m2/s) enters a 50-mm-diameter tube. Estimate the entrance length if the flow rate is 1 L/s.

f N R =dv/v v = Q/A = 0.001 / t(^r)(0.050)2/4] = 0.5093 m/s

N R = (0.050)(0.5093)/0.0003 = 85 (laminar)

L e /d = 0.061V* L e = (0.050)(0.06)(85) = 0.255 m 9.10

What is the Reynolds number for a flow of oil (s.g. = 0.8, ft = 0.00200 lb • s/ft2) in a 6-in-diameter pipe at a flow rate of 10 ft3/s. Is the flow laminar or turbulent?

f

v

= Q/A = 10/[(jr)(^)2/4] = 50.9 ft/s

N R = pdv/ft = [(0.8)( 1.94)](£)(50.9)/0.00200 = 19 749 9.11

(turbulent)

Gasoline at a temperature of 20 °C flows at the rate of 2 L/s through a pipe of inside diameter 60 mm. Find the Reynolds number. I

v = Q/A = (2 X 10-3)/[(nr)(0.060)2/4] = 0.707 m/s N R = pdv/ft = (719)(0.060)(0.707)/(2.92 X 10~4) = 104 452

9.12

The Reynolds number for fluid in a pipe of 10 in diameter is 2000. What will be the Reynolds number in a 6-in-diameter pipe forming an extension of the 10-in pipe? Take the flow as incompressible.

I N R = dv/v. Since v is constant, [lVR/(du)], = [N R /(dv)\ 2 , A 1 v 1 = A 2 v 2 , [(^r)(ii)2/4](t/i) = [(^)(R)2/4](U2), VI = 0.360U2, 2000/[(j§)(0.360U2)] = (AW2/[(£)(u2)], (A/*)2 = 3333. 9.13

Water is flowing through capillary tubes A and B into tube C, as shown in Fig. 9-2. If Q A = 3 mL/s in tube A, what is the largest Q B allowable in tube B for laminar flow in tube C? The water is at a temperature of 40 °C. With the calculated Q B , what kind of flow exists in tubes A and B1

I For laminar flow, assume N R ≤ 2300. N R = dv/v. In tube C, 2300 = (0.006)(vc)/(6.56 x 10“7), v c = 0.2515 m/s; Q c = A c v c = [(JT)(0.006)2/4](0.2515) = 7.11 X 10“6m3/s, or 7.11 mL/s, Q B = 7.11 - 3 = 4.11 mL/s. In tube A, v A = QJA A = (3 X 10“6)/[(TT)(0.005)2/4] = 0.1528 m/s, N R = (0.005)(0.1528)/(6.56 x 10“7) = 1165

(laminar)

FLOW IN CLOSED CONDUITS D 199 In tube B, v B = Q B /A B = (4.11 x 10’6)/[(JT)(0.004)2/4] = 0.3271 m/s, N R = (0.004)(0.3271)/(6.56 x 10"7) = 1995 (turbulent)

9.14

Incompressible steady flow of water occurs in a tube of constant cross section, as shown in Fig. 9-3. What is the head loss between sections A and B1

I

P A I Y + v\!2g + z A =p B /y +

V %/2

g + zB + hL

(90)(144)/62.4 + v 2 J2g + 0 = (30)(144)/62.4 + u|/2g + 100 + h L v\!2g = v%/2g

9.15

h L = 38.5 ft

Water flows through a pipe at 5 L/s, as shown in Fig. 9-4. If gage pressures Of 12.5 kPa, 11.5 kPa, and 10.3 kPa are measured for p u p 2 and p 3 , respectively, what are the head losses between 1 and 2 and 1 and 3?

f Pily + v\/2g + z, =p 2 /y + vl/2g + Z 2 + (h L ) 1_2

12.5/9.79 + v\/2g + 10 = 11.5/9.79 + v\/2g

+ 10 + (h L \- 2

vi/2g = vl/2g (AZ.)I-2 = 0.1021m p 1 /y + vl/2g + z 1 =p 3 /y+ vl/2g + z 3 +(h L )^ 3 Vi

= QIA t = (5 x 10~3)/[(JT)(0.050)2/4] = 2.546 m/s v3 = Q/A 3 = (5 x 10~3)/[(;r)(0.030)2/4] = 7.074 m/s

12.5/9.79 + 2.5462/ [(2(9.807)] + 10 = 10.3/9.79 + 7.0742/[(2)(9.807)] + 0 + (h L )^ 3

(h L )^ 3 = 8.00 m

Fig. 9-4 9.16

A large oil reservoir has a pipe of 3 in diameter and 7000-ft length connected to it, as shown in Fig. 9-5. Assuming laminar flow through the pipe, compute the amount of oil issuing out of the pipe as a free jet.

200 0 CHAPTER 9 Compute the velocity and Reynolds number to see if the flow is laminar. von = lX 10~4 ft7s. Neglect entrance losses to the pipe. I pjy + v\j2g + z 2 =pjy + v\Hg + z 3 +h L p 2 /62A + vl/2g +0 = 0 + vj/2g + 0 + A, v\J2g = v\llg pJ62A = h f

(1)

4

npgd h f U

128 juL

, 128QpL 128[(«P/4)(«J]pL 32V2VL (32)(U2)(1 X 1Q-4)(7000) „ f

npgd 4

xpgd 4

gd 2

Pi/y + w?/2g + z, = p 2 /y + t>l/2g + z2 + At

(32.2)(3/12)2

'

2

U

0 + 0 +10=p 2 /62A + u|/[(2)(32.2)] + 0 + 0

p 2 /62A—10 - u|/[(2)(32.2)]

(3)

Equating h f from Eqs. (1) and (2),. p2/62.4=11.13i/2 (4) Equatingp 2 /62A from Eqs. (3) and (4), 11.13u 2 = 10 - t>i/[(2)(32.2)], v\ + 716.8u2 - 644 = 0, t/2 = 0.8973 ft/s; Q=Av = [(zr)(^)2/4](0.8973) = 0.0440 ft3/s; N„ = dv/v = (£)(0.8973)/(l x 10~4) = 2243 (barely laminar).

Fig. 9-5

9.17

If 140 L/s of water flows through the system shown in Fig. 9-6, calculate the total head loss between 2 and 3.

I

p j y + vy2 g + z = p 3 / y + vl/2 g + Z + H L 2

3

v 2 = Q/A 2 = (140 x 10- )/[(*)(0.300)74] = 1.981 m/s v 3 = Q/A 3 = (140 x 10“ )/[(jr)(0.150)74] = 7.922 m/s 3

3

p2/9.79 + 1.9812/[(2)(9.807)] + 0 = 0 + 7.9227[(2)(9.807)] + 15 + h L

h L = p-J 9.79 - 18.00

P i / y + v\!2g + Zi = p 2 ly + v\/2g + z 2 + h L 0 + 0 + 30 =p2/9.79 + 1.98l7[(2)(9.807)] + 0 + 0 p2/9.79 = 29.80 m

9.18

h L = 29.80 - 18.00 = 11.80 m

Determine the maximum velocity for laminar flow for (a) medium fuel oil at 60 °F (v = 4.75 X 10 5 if Is) flowing through a 6-in pipe and (6) water at 60 °F flowing in the 6-in pipe.

f For laminar flow, assume N R ≤ 2000. N R = dv/v. (a)

2000 = (&)(u)/(4.75xl0-5) v = 0.190 ft/s

(A)

2000 = (£)(v)(1.21xl0-5) v = 0.0484 ft/s

FLOW IN CLOSED CONDUITS 0 201 9.19

Determine the type of flow occurring in a 12-in pipe when («) water at 60 °F flows at a velocity of 3.50 ft/s and {b) heavy fuel oil at 60 °F (v = 221 x 10~ 5 fP/s) flows at the same velocity.

f N R = dv/v (а)

N R = 0f)(3.50)/(1.21 x 10 s) = 289 256 (turbulent)

(б)

N R = (i)(3.50)/(221 x 10“5) = 1584 (laminar)

For laminar flow conditions, what size pipe will deliver 90 gpm of medium fuel oil at 40 °F (v = 6.55xl0“sft2/s)?

I Q = (90)(0.002228) = 0.2005 ft3/s. For laminar flow, assume N R ≤ 2000. N R = dv/v, v = Q/A = 0.2005/(JT d2/4) = 0.2553d“2, 2000 = (d)(0.2553d 2)/(6.55 x 10~5), d = 1.95 ft.

What is the Reynolds number of flow of 0.4 m3/s of oil (s.g. = 0.86, p = 0.025 Pa • s) through a 450-mm-diameter pipe?

I

v = Q/A = 0.4/ [( JT)(0.450)2/4] = 2.515 m/s N R = p dv/n = [(0.86)(1000)](0.450)(2.515)/0.025 = 38 932

9.22

An oil with s.g. = 0.85 and v = 1.8 x 10~ 5 m2/s flows in a 10-cm-diameter pipe at 0.50 L/s. Is the flow laminar or turbulent?

I

v = Q/A = (0.50)(1000)/[(n:)(^)2/4] = 0.06366 m/s N R = dv/v = (i&)(0.06366)/(1.8 x 10 5) = 354 (laminar)

9.23

Fluid with kinematic viscosity 0.00015 ft2/s flows through a pipe of diameter 9 in. What is the maximum velocity for laminar flow? 9.2 4

f For laminar flow, assume N R ≤ 2000. N R = dv/v, 2000 = C&)(v)/0.00015, v = 0.400 ft/s. An oil with v = 0.005 ft2/s flows through a 6-in-diameter pipe at 10 ft/sec. Is the flow laminar or turbulent?

I 9.2 5

N R = dv/v = (£)(10)/0.005 = 1000 (laminar)

Hydrogen at atmospheric pressure and 50 °F has a kinematic viscosity of 0.0011 ft 2/s. Determine the maximum mass flow rate for laminar flow in a 3-in-diameter pipe, y = 0.00540 lb/ft3. ≤ 2000. N R = dv/v, 2000 = Cn)(u)/0.0011, v = 8.80 ft/s; W = yAv = (0.00540)[(jr)(A)2/4](8.80) = 0.001037 lb/s.

f For laminar flow, assume N R 9.26

Air at 1500 kPa abs and 100 °C flows in a 20-mm-diameter tube. What is the maximum laminar flow rate? For laminar flow, assume N R ≤ 2000. N R = pdv/n, p = p/RT = (1.5 x 106)/[(287)(273 +100)] = 14.01 kg/m3, 2000 = (14.01)(0.020)(t>)/(2.17 X 10 5), v = 0.1549 m/s; Q=Av = [(nr)(0.020)2/4](0.1549) = 0.0000487 m3/s, or 0.0487 L/s.

f 9.27

What is the hydraulic radius of a rectangular air duct 8 in by 14 in?

I

R h = A/p w — [(8)(14)]/(8 + 8 +14 + 14) = 2.55 in or 2.55 ft

9.28 What is the percentage difference between the hydraulic radii of 30-cm-diameter circular and 30-cm square ducts? I

R h = A/p w (R H ) c^r = [(*)(30)2/4]/[(*)(30)] = 7.50 cm (R h )^ = (30)(30)/(30 + 30 + 30 + 30) = 7.50 cm

Since they are equal, the percentage difference is zero. Note that the hydraulic radius of a circular section is one-fourth its diameter. 9.29

Two pipes, one circular and one square, have the same cross-sectional area. Which has the larger hydraulic radius, and by what percentage?

202

a CHAPTER 9 f Let d = diameter of the circular pipe and a = the side of the square one. Since they have the same cross-sectional area, nd 2 /4 = a 2 , a = \nd/2; (R h = d/4 = 0.2500d, (/?*)*,„„„ = A/p w = a 2 /4a = a/4. Since a = y/ad/2, (/?*)«,»„«, = (Vnd/2)/4 = 0.2216d, hence, the circular pipe has the larger hydraulic radius by (0.2500 - 0.2216)/0.2216 = 0.128, or 12.8 percent.

9.30

Steam of weight density 0.26 lb/ft3 flows at 100 fps through a circular pipe. What is the shearing stress at the wall, if the friction factor is 0.015?

I 9.31

to = (f/4)(y)(v 2 /2g) = (0.015/4)(0.26){1007[(2)(32.2)]} = 0.151 lb/ft2

Glycerin at 68 °F flows 120 ft through a 6-in-diameter new wrought iron pipe at a velocity of 10.0 ft/s. Determine the head loss due to friction. f

h f = (f)(L/d)(v 2 /2g) N R = pdv/p = (2.44)(£)(10.0)/(3.11 x 10~2) = 392

Since N R < 2000, the flow is laminar and/ = 64/N R = ^ = 0.1633, h f = 0.1633[120/(£)]{10.07[(2)(32.2)]} = 60.9 ft. 9.32

SAE10 oil flows through a cast iron pipe at a velocity of 1.0 m/s. The pipe is 45.0 m long and has a diameter of 150 mm. Find the head loss due to friction.

I

h f = (f)(L/d)(v 2 /2g) N R = pdv/p = (869)®(1.0)/0.0814 = 1601

Since N R < 2000, the flow is laminar and/ = 64/N R = ^ = 0.0400, h f = 0.0400[45.0/(^)]{1.02/[(2)(9.807)]} = 0.612 m. 9.33

A 60-mm-diameter pipe (Fig. 9-7) contains glycerin at 20 °C flowing at 8.5 m3/h. that the flow is laminar. For the pressure measurements shown, is the flow ascending or descending? What is the head loss for these pressures?

I

v = Q/A = (8.5/3600)/[(TT)(0.060)2/4] = 0.835 m/s N R = pdv/p = (1258)(0.060)(0.835)/l .49 = 63 (laminar) HGL = z+p/pg HGL„ = 0 + (2.0)(101400)/[(1258)(9.807)] = 16.44 m

HGLB = 12 + (3.8)(101400) / [(1258) (9.807)] = 43.23 m Hence, the flow is from 15 to A (i.e., descending). Head loss = 43.23 — 16.44 = 26.79 m. 3.8 utin

9.34

For the data of Prob. 9.33, compute the theoretical head loss if the pipe length is 30 m between A and B. Compare with the head loss corresponding to the measured pressures.

f

npgdfhf 128/JL

8.5 3600 ~

=

(^)(1258)(9.807)(0.060)4(h/) (128)(1.49)(30)

h f = 26.89 m

which is only 10 cm greater than the value found in Prob. 9.33. 9.35 Two horizontal infinite plates keep a distance h apart as the upper plate moves at speed V, as in Fig. 9-8. There is a fluid of constant viscosity and constant pressure between the plates. If V = 5 m/s and h= 20 mm, compute the shear stress at the plates, given that the fluid is SAE 30 oil at 20 °C.

FLOW IN CLOSED CONDUITS 0 203 I N R = phV/p = (888)(0.020)(5)/0.440 = 202. Since the flow is laminar, du ay where u = (V/h)(y), r = (|u)(V/h) = 0.440[5/(2.0/100)] = 110 Pa. X\\\\\\\V,\\\\\\\\\|'\ ___________________ _

y

y

■ ► uh

{ *I “|—*

Fixed Rg. 9^

Find the head loss per unit length when a fluid of s.g. 0.86 and kinematic viscosity 0.008 ft 2/s flows in a 3-in-diameter pipe at a rate of 5 gpm. | Q = (5)(0.002228) = 0.01114 ft3/s h f = (f)(L/d)(v 2 /2g) v = Q/A = 0.01114/[(n:)(^)2/4] = 0.2269 ft/s N„ = dv/v = (^)(0.2269)/0.008 = 7.09 Since N„ < 2000, the flow is laminar and/ = 64/N R = 64/7.09 = 9.03, h f = 9.03[l/(^)]{0.22692/[(2)(32.2)]} = 0.0289 ft per foot of length. Tests made on a certain 12-in-diameter pipe showed that, when V = 10 fps, / = 0.015. The fluid used was water at 60 °F. Find the unit shear at the wall and at radii of 0,0.2, 0.3, 0.5, and 0.75 times the pipe radius. f

to = (//4)(y)(V2/2g) = (0.015/4)(62.4){102/[(2)(32.2)]} = 0.3634 lb/ft2

The stress distribution is linear; hence, r/r„

t, lb/ft2

0 0.2 0.3 0.5 0.75

0 0.0727 0.1090 0.1817 0.2726

If oil with a kinematic viscosity of 0.005 ft2/s weighs 54 lb/ft3, what will be the flow rate and head loss in a 3600-ft length of 4-in-diameter pipe when the Reynolds number is 800?

I N R = dv/v 800 = (£)(v)/0.005 v = 12.00 ft/s Q =Av = [(JT)(£)2/4](12.00) = 1.047 ft3/s / = 64/N R = 64/800 = 0.0800 h f = (f)(L/d)(v 2 /2g) = 0.0800[3600/(^)]{12.002/[(2)(32.2)]} = 1932 ft How much power is lost per kilometer of length when a viscous fluid (p = 0.20 Pa • s) flows in a 200-mm-diameter pipeline at 1.00 L/s? The fluid has a density of 840 kg/m 3.

f

v = Q/A = (1.00 X 10“3)/[(JT)(0.200)2/4] = 0.03183 m/s N R = pdv/p = (840)(0.200)(0.03183)/0.20 = 26.74 h,/L = (f)(l/d)(v 2 /2g)

Since N R < 2000, the flow is laminar and/ = 64/IV* = 64/26.74 = 2.393, h f /L = 2.393[l/(0.200)]{0.03183z/[(2)(9.807)]} = 0.0006180 m, P/L = Qyh,/L = Qpgh,/L = (1.00 x 10_3)(840)(9.807)(0.0006180) = 0.00509 W/m = 5.09 W/km. Calculate the discharge of the system in Fig. 9-9, neglecting all losses except through the pipe,

f Assume laminar flow and use the conversion 1.0 centipoise = 0.0002089 lb • s/ft 2. y Ah d 2 (55)(18)[(j)/12]2 = 4.017 ft/s (32)(0.0002089)(16) 32juL N R = pdv/p = (y/g)(d)(v)/p = (55/32.2)[(j)/12](4.017)/0.0002089 = 684 2

3

Q=Av = {(^)[(|)/12] /4}(4.017) = 0.00137 ft /s

(laminar)

204 0 CHAPTER 9

Y = 55 Ib/ft

18 ft

16 ft

diam

k=10 centipoise Fig. 9-9

9.41

In Fig. 9-10, H = 25 m, L = 40 m, 8 = 30°, 4 = 8 mm, y = 10 kN/m3, and fi = 0.08 Pa • s. Find the head loss per unit length of pipe and the discharge in liters per minute.

f Assuming laminar flow,

N R = pdv/fi = ( Y /g)(d)(v)/n = [1079.807](8 X 10 3)(0.1563)/0.08 = 16 (laminar) Q=Av = [(;r)(8 x 10_3)2/4](0.1563) = 7.857 x 10~6 m3/s = 0.471 L/min Ah/L = i = 0.625 m/m

Fig. 9-10

9.42

For the data of Prob. 9.41, find H if the velocity is 0.1 m/s. f By proportion, H = (0.1/0.1563)(25) = 16.0 m.

9.43

Water flows at 0.20 m3/s through a 300-mm-diameter, 120-m-long pipe, under a pressure difference of 280 mmHg. Find the friction factor. f h f = (f )(L/d)(v 2 /2g). From the pressure gradient, h f = (13.6/1)(0.280) = 3.808 m; v = Q/A = 0.20/[(JT)(0.300)74] = 2.829 m/s, 3.808 = (/)[120/(0.300)]{2.8292/[(2)(9.807)]}, / = 0.0233.

9.44

Use the Blasius equation for determination of friction factor to find the horsepower per mile required to pump 3.0 ft3/s of liquid (v = 3.3 x 10 4 ft2/s, y = 60 lb/ft3) through an 18-in pipeline.

I

h f = (f)(Lld)(v 2 /2g) f

= 0.316/JVr v = Q/A = 3.0/[(jr)(tf)2/4] = 1.698 ft/s

N R = dv/v = (TI)(1-698)/(3.3 x lO'4) = 7718

/ = 0.316/77181'4 = 0.03371

h f = 0.03371[5280/ (if)] {1.6982/[ (2) (32.2)]} = 5.312 ft P = Qyh f = (3,0)(60)(5.312) = 956.2 ft • lb/s per mile 956.2/550 = 1.74 hp per mile 9.45

Determine the head loss per kilometer required to maintain a velocity of 3 m/s in a 20-mm-diameter pipe, if v = 4 x 10~5 m2/s.

I

h f = (f)(L/d)(v 2 /2g) N R = dv/v = (0.020)(3)/(4 x 10~5) = 1500 (laminar) / = (A/N R = 64/1500 = 0.04267 h f = 0.04267[1000/(0.020)]{32/[(2)(9.807)]} = 979.0 m per km

FLOW IN CLOSED CONDUITS £7 205 Fluid flows through a 10-mm-diameter tube at a Reynolds number of 1800. The head loss is 30 m in a 120-m length of tubing. Calculate the discharge in liters per minute.

I h f = (J)(L/d)(v 2 /2g). Since N R < 2000, flow is laminar and/ = 64//V* = 64/1800 = 0.03556, 30 = 0.03556[120/(0.010)]{V2/[(2)(9.807)]}, V = 1.174 m/s; Q =Av = [(jr)(0.010)2/4](1.174) = 92.21 X 10~ m3/s = 5.53 L/min. 6

Oil of absolute viscosity 0.00210 lb • s/ft and specific gravity 0.850 flows through 10 000 ft of 12-in-diameter cast iron pipe at the rate of 1.57 cfs. What is the lost head in the pipe? 2

I

h f = (f)(L/d)(v 2 /2g) v = QIA = 1.57/[(;r)G!)74] = 1.999 ft/s N R = pdv/p = [(0.850)(1.94)](H)(1.999)/0.00210 = 1570 (laminar) / = 64/N R = iis = 0.04076 h f = 0.04076[10 000/G§)]{1.9992/[(2)(32.2)]} = 25.3 ft

When first installed between two reservoirs, a 4-in-diameter metal pipe of length 6000 ft conveyed 0.20 cfs of water, (a) If after 15 years a chemical deposit had reduced the effective diameter of the pipe to 3.0 in, what then would be the flow rate? Assume/remains constant. Assume no change in reservoir levels. (b) What would be the flow rate if in addition to the diamater change, / had doubled in value?

I (fl) (/0(L,/d )(v?/2g) = (fz)(L 2 /d 2 )(vl/2g). Since/, L, and g are constant and v = Q/A = <2/(JK/2/4), 1

Q\td\ = Qlldl 0.20 /4 = Ql/3.05, Q 2 = 0.0974 cfs. (ft) (/i)(Q 2 Jd\) = (fzKQl/dl). Since/ = 2fu Q\!d\ = (2)(Gl/d|), 0.20 /4 = (2)(Ql/3.05), Q 2 = 0.0689 cfs. 2

5

2

2

5

A liquid with y = 58 lb/ft flows by gravity through a 1-ft tank and a 1-ft capillary tube at a rate of 0.15 ft /h, as shown in Fig. 9-11. Sections 1 and 2 are at atmospheric pressure. Neglecting entrance effects, compute the viscosity of the liquid in slugs per foot-second. 3

I pjy + v\/2g +

Zj

3

=p 2 /y + v\/2g + z 2 + hL v 2 = Q/A 2

= (0. 15/3600)/[(JT)(0.004)2/4] = 3.316 ft/s

0 + 0 + (l + l) = 0 + 3.3162/[(2)(32.2)] + 0 + hf hf = 1.829 ft

Assuming laminar flow, 32 pLv

, h f

1 r.29 (^X^WC3-316)

p = 1.600 x 10 slug/(ft • s) 5

(58)(0.004)2

~~

N R = pdv/p = (y/g)(d)(v)/ju = (58/32.2)(0.004)(3.316)/(1.600 X 10“5) = 1493 (laminar) (l)

1 ft

1 rt

\

-£/=0.004 ft

(2 )

<2=0.15 ft3/h

Fig. 9-11

In Prob. 9.49, suppose the flow rate is unknown but the liquid viscosity is 2.1 x 10 slug/(ft • s). What will be the flow rate in cubic feet per hour? Is the flow still laminar? 5

I

p 1 /y + v\l2g + z i =p 2 ly + vll2g + z 2 + h L 0 + 0 + (l + l) = 0 + u2/[(2)(32.2)] + 0 + h f

h f = 2-0.01553D2

206 D CHAPTER 9 Assuming laminar flow, h, = 32 pLv/yd 2

2 - 0.01553v2 = (32)(2.1 x 10'5)(l)(u)/[(58)(0.004)2]

v 2 + 46.63u -128.8 = 0 v = 2.616 ft/s Q=Av = [(JT)(0.004)2/4](2.616) = 0.00003287 ft3/s = 0.118 ft3/h N R = pdv/p = (y/g)(d)(v)/p = (58/32.2)(0.004)(2.616)/(2.1 X 10 s) = 897 (laminar) 9.51 In the syringe of Fig. 9-12 the drug has p = 900 kg/m and p = 0.002 Pa • s. What steady force F is required to produce a flow of 0.4 mL/s through the needle? Neglect head loss in the larger cylinder. 3

I

pjpg

+ v 2 J2g + z A = p B /pg + v%/2g + z B + h L

v B = Q/A B = 0.4 x 10~6/[(JT)(0.25 X 10 3)2/4] = 8.149 m/s N B = pdv/p = (900)(0.25 x 10"3)(8.149)/0.002 = 917 32 pLv (32)(0.002)(0.020)(8.149) f pgd 2 (900)(9.807)(0.25 x 10 )

(laminar)

-3 2

p^/[(900)(9.807)] + 0 + 0 = pfl/[(900)(9.807)] + (8.149)2/[(2)(9.807)] + 0 + 18.91 P A ~ P B = 196 788 N/m

2

F= l P A -pa)(Apiston) = 196 788[(JT)(0.010)2/4] - 15.5 N = 10mm = 0.25 i

$ -20 mm—*+• --- 30 mm 9.52

Fig. 9-12

Paint issues from the tank in Fig. 9-13 at Q = 45 ft /h. Find the kinematic viscosity. Is the flow laminar? 3

I pjpg + v 2 J2g + z A =p B /pg + v\/2g + z B + h L v B = Q/A B = (^5O)/[(JT)(0.5/12)2/4] = 9.167 ft/s 0 + 0 + 9 = 0 + 9.167z/[(2)(32.2)] + 0 + h f

^ = 7.695 ft

Assuming laminar flow, hf =

128 vLQ ngd 4

(128Xv)(6)(jfe) (JT)(32.2)(0.5/12)4

v = 0.0002444 ft2/s

N R = dv/v = (0.5/12)(9.167)/0.0002444 = 1563 (laminar)

Fig. 9-13

9.53

In Prob. 9.52, what will the flow rate be if the paint properties are p = 1.78 slugs/ft and p = 0.00217 lb • s/ft2? 3

I

Pjpg + v\/2g + z A = p B lpg + v 2 B l2g + z B + h L 0 + 0 + 9 = 0 + u2/[(2)(32.2)] + 0 + h/

FLOW IN CLOSED CONDUITS 0 207 Assuming laminar flow, 32 pLv

(32)(0.00217)(6)(u)

2

' pgd ~ (1.78)(32.2)(0.5/12)2 _ 0 + 0 +9 = 0 + «7[(2)(32.2)]+ 0 + 4.187« v 2 + 269.6« - 579.6 = 0

« = 2.133 ft/s

Q = Av = [(;r)(0.5/12)2/4](2.133) = 0.002908 ft3/s or 10.47 ft3/h N R = pdv/p = (1.78)(0.5/12)(2.133)/0.00217 = 73 (laminar)

9.54

The smaller tank in Fig. 9-14 is 50 m in diameter. If the fluid is ethanol at 20 °C, find the flow rate.

I

pJy + v\l2g + z A =p B lY + v 2 B l2g + z B + h L 0 + 0 +(0.4+ 0.6) = 0 + 0 + 0 + ^ !2SpLQ xpgd*

h f = 1.000 m =

(128)(1.20 x 10 )(0.8 + 0.4)(Q) (jr)(788)(9.807)(0.002)4 3

1.000 =

Q=2.107 x 10~6 m3/s or 7.59 L/h

Fig. 9-14

9.55

For the system in Fig. 9-14, if the fluid has density of 920 kg/m and the flow rate is unknown, for what value of viscosity will the capillary Reynolds number exactly equal the critical value 2300? 3

#

h, = 1.000 m =

(from prob 9.54) pgd 2

1 000

(32)00(0-8+ 0.4)(«) (920)(9.807)(0.002)2

0.0009398 p

N R = pdv/p 2300 = (920)(0.002)(0.0009398/jU)/f* p = 0.000867 Pa • s

9.56

For the pressure measurements shown in Fig. 9-15, determine (a) whether the flow is up or down, and (6) the flow rate. Use p = 917 kg/m and p = 0.290 Pa • s. 3

I HGL = z + plpg HGL„ = 15 + (200)(1000)/[(917)(9.807)] = 37.24 m

(a)

HGL^ = 0 + (600)(1000)/[(917)(9.807)] = 66.72 m Since HGLX > HGLB, the flow is from A to B (i.e., up). (A) Assume flow is laminar. 12SuLQ h f = ----npgd = 66.72 - 37.24 = 29.48 m 4

L = Vl5 + 20 = 25.00 m “ 2

2

29.48 =

(128)(0.290)(25.00)(Q) ( JT)(917)(9. 807)(0.030)4

Q = 0.000727 m3/s or 2.617 m3/h « = Q/A = 0.000727/[(JT)(0.030)2/4] = 1.028 m/s N K = pdv/p = (917)(0.030)(1.028)/0.290 = 98 (laminar)

208 0 CHAPTER 9 PB =200kPa

Fig. 9-15 9.57 Repeat Prob. 9.56 if the pressures are the same but there is a pump between A and B which adds a 10-m head rise in the flow direction. Is the flow still laminar?

I h f = HGLA - HGL„ + hpump. Using values of HGLA and HGLB from Prob. 9.56, L — 25.00 m (from Prob. 9.56)

h f = 66.72 — 37.24 + 10 = 39.48 m = npgd* 39.48 =

(128)(0.290)(25.00)Q3) (JT)(917)(9.807)(0.030)4

Q = 0.000974 m3/s or 3.51 m3/h

v = Q/A = 0.000974/ [(JT)(0.030)2/4] = 1.378 m/s N R = pdv/p = 9.58

= 131 Water at 40 °C flows from tank A to tank B as shown in Fig.(917)(0.030)(1.378)/0.290 9-16. Find the volumetric flow, neglecting entrance losses to the capillary tube as well as exit losses. (laminar)

f PA/ Y

+ VAl2g + z A =p B lY + v2Bl2g + z B + h L 0 + 0 + (0.22 + 0.1) = 0 + 0 + 0 + h f h f = 0.32

Assume laminar flow. 128 pLQ f zgd

(128)(6.51 X 10~ )(0.22 + 0.08)(Q) (w)(992)(9.807)(0.001)4 4

4

Q = 3.912 x 10~ m3/s = 1.41 L/h 7

v = Q/A = 3.912 x 10~7[(jr)(0.001) /4] = 0.4981 m/s 2

N„ = pdv/p = (992)(0.001)(0.4981)/(6.51 x 10 4) = 759 (laminar)

0.1 m

7

cL = 1 mm.

0.22 m

•_

B-

0.08 m

1

Fig. 9-16 9S9

In Prob. 9.58, what should the internal diameter of the tube be to permit a flow of 2.16 L/h?

f Assuming laminar flow, Q «
16\1/4 (1 mm) = 1.534mm

(

FLOW IN CLOSED CONDUITS 0 209

9.60 A hypodermic needle has an inside diameter of 0.3 mm and is 60 mm in length, as shown in Fig. 9-17. If the piston moves to the right at a speed of 18 mm/s and there is no leakage, what force F is needed on the piston? The medicine in the hypodermic has a viscosity ju of 0.980 x 10 ~ Pa • s and its density p is 800 kg/m3. Consider flows in both needle and cylinder. Neglect exit losses from the needle as well as losses at the juncture of the needle and cylinder. 3

f For cylinder: Q =Av = [(;r)(0.005)2/4](0.018) = 3.534 X MT m3/s 7

N R = pdv/n = (800)(0.005)(0.018)/(0.980 X 10~3) = 73 (laminar) USfiLQ P=

ltd*

(128)(0.980 x 10“3)(0.050)(3.534 X 10~7) -=1.129 Pa Pi = (*r)(0.005)4

For needle: v = Q/A = 3.534 X 10~ /[(*r)(0.3/1000)74] = 5.000 m/s 7

N R = (800)(0.3/1000)(5.000)/ (0.980 X 10~ 3) = 1224 (laminar) (128X0.980 x 10-3)(0.060)(3.534 X 10 7) =

..............

----------------- (nr)(0.3/1000) ----------------4

= 104 525 Pa

F = (Ap)(AcyUnder) = (104 525 - 1.129)[(*r)(0.005)74] = 2.05 N

z

Cylinder

AT=

*

18 mm/s

, Needle

5 mm

= 0.3 mm ----- 60 mm

-—50 mm—►

9.61

Q,

128pLQ _________ (128X0.980 X 10 3)(0.060)(ema>) Jtd* (*r)(3 X 10' ) 4 4

3

= 3.27 X HT m /s = 0.327 mL/s 7

In Prob. 9.60, it took a force of 2.05 N to move the piston to the right at a speed of 18 mm/s. What should the inside diameter be for the cylinder if the force needed is only 1.2 N for the same piston speed? Neglect losses in cylinder. PF

1.2 A (*r)(0.005)74

= 61116 Pa

d = 0.343 mm

9.63

Fig. 9-17

In Prob. 9.60, suppose that medicine is drawn from a bottle at atmospheric pressure. What is the largest flow of fluid if the fluid has a vapor pressure of 4.8 kPa abs? Neglect losses in the cylinder. Ap = 101400 - 4800 = 96 600 Pa =

9.62

----- ►

P=-

128 pLQ nd*

61116 =

(128)(0.980 x 10~3)(0.060)(3.534 x 10~7) nd'*

N R = pdv/p = (800)(0.343/1000)(0.018)/(0.980 x 10 3) = 5

(laminar)

Water at 70 °F flows through a new cast iron pipe at a velocity of 9.7 ft/s. The pipe is 1200 ft long and has a diameter of 6 in. Find the head loss due to friction.

I

h f = (f)(L/d)(v 2 /2g) N R = dv/v = (£)(9.7)/(1.05 x 10 5) = 461905

From Table A-9, e = 0.00085 ft for new cast iron pipe; e/d = 0.00085/(£) = 0.0017. From Fig. A-5, / = 0.0230; h f = 0.0230[1200/(£)]{9.77[(2)(32.2)]} = 80.6 ft.

9.64

A 96-in-diameter new cast iron pipe carries water at 60 °F. The head loss due to friction is 1.5 ft per 1000 ft of pipe. What is the discharge capacity of the pipe?

I

h f = (f)(L/d)(v 2 /2g)

1.5= (/)[1000/(f|)]{t;7[(2)(32.2)]} fv 2 = 0.7728

Assume/ = 0.0150; (0.0150)(v2) = 0.7728, u = 7.178 ft/s; N„ = dv/v = (§)(7.178)/(1.21 x 10“5) = 4.75 x 106.

210 0 CHAPTER 9 From Table A-9, e = 0.00085 ft for new cast iron pipe, e/d = 0.00085/(?§) = 0.000106. From Fig. A-5, / = 0.0124. Evidently, the assumed value of/of 0.0150 was not the correct one. Try a value of/of 0.0124. (0.0124)(t>2) = 0.7728, v = 7.894 ft/s; N R = (ff)(7.894)/(1.21 x 10~5) = 5.22 x 106. From Fig. A-5,/ = 0.0124. Hence, 0.0124 must be the correct value of/, and v = 7.894ft/s. Q = Av = [(JT)(T|)2/4](7.894) = 397 fP/s. 9.65

Water at 70 °F is being drained from an open tank through a 24-in-diameter, 130-ft-long new cast iron pipe, as shown in Fig. 9-18. Find the flow rate at which water is being discharged from the pipe. Neglect minor losses. I

PJ Y

+ v] /2g + z, =p 2 /y + v\!2g + z 2 + h L

h L = h f = (f)(L/d)(v 2 /2g) = (/)[130/(f|)]{v|/[(2)(32.2)]} = 1.009M 0 + 0 + 150.5 = 0 + ul/[(2)(32.2)] + 98.4 + 1.009/u| Assume / = 0.0240. 150.5 = u!/[(2)(32.2)] + 98.4 + (1.009)(0.0240)(n|) v 2 = 36.21 ft/s N R = dv/v = (f|)(36.21)/(1.05 x 10“5) = 6.90 X 10 From Table A-9, e = 0.00085, e/d = 0.00085/(i) = 0.000425. From Fig. A-5,/ = 0.0162. Evidently, the assumed value of/of 0.0240 was not the correct one. Try a value of/of 0.0162. 6

150.5 = u|/[(2)(32.2)] +98.4+ (1.009)(0.0162)(nl) v 2 = 40.43 ft/s N R = (f|)(40.43)/(1.05 X 10-5) = 7.70 x 10

6

From Fig. A-5, / = 0.0162. Hence, 0.0162 must be the correct value of/, and v = 40.43 ft/s. Q = Av = [(jr)(f§)2/4](40.43) = 127 ft /s. 3

JZ.

CD

E!ev. 130.5 ft

Water

©

Elev. 98.4 ft

Fig. 9-18 9.66

Gasoline is being discharged from a pipe, as shown in Fig. 9-19. The pipe roughness (e) is 0.500 mm, and the pressure at point 1 is 2500 kPa. Find the pipe diameter needed to discharge gasoline at a rate of 0.10 m /s. Neglect any minor losses. 3

I Pi/y + vl/2g + z 1 =p 2 /y + v\/2g + z 2 + h L h L = h f = (f)(L/d)(v 2 /2g) = (/)(965.5/d){oi/[(2)(9.807)]} = 49.23fv\/d 2.500/7.05 + v\/2g + 82.65 = 0 + v\/2g + 66.66 + 49.23ful/d 2

v\/2g = v\/2g

fv 2 /d = 0.3320 v 2 = Q/A 2 = 0.10/(nrd /4) = 0.1273/d (/)(0.1273/d ) /d = 0.3320 d = (0.04881/)1'5 Assume/ = 0.0200. d = [(0.04881)(0.0200)]1/5 = 0.2500 m, v 2 = 0.1273/0.25002 = 2.037 m/s; N R = pdv/p = (719)(0.2500)(2.037)/(2.92 x 10”4) = 1.25 x 106. From Table A-9, e = 0.00050 m. e/d = 0.00050/0.2500 = 0.0020. From Fig. A-5,/ = 0.0235. Evidently, the assumed value of/of 0.0200 was not the correct one. Try a value of/of 0.0235. 2

2

2 2

d — [(0.04881)(0.0235)]l/s = 0.2582 m v = 0.1273/0.25822= 1.909 m/s N R = (719)(0.2582)(1.909)/(2.92 X 10~4) = 1.21 x 10

6

e/d = 0.00050/0.2582 = 0.00194

/ = 0.0235

Hence, 0.0235 must be the correct value of/, and d = 0.2582 m.

FLOW IN CLOSED CONDUITS 0 211 Elev. 82.65 m

9.67

Water at 20 °C flows through a new cast iron pipe at a velocity of 4.2 m/s. The pipe is 400 m long and has a diameter of 150 mm. Determine the head loss due to friction.

I

h f = (f)(L/d)(v 2 /2g) N R = dv/v = ®)(4.2)/(1.02 x 10~6) = 6.18 x 10

5

From Table A-9, e = 0.00026 m. e/d = 0.00026/0.150 = 0.00173. From Fig. A-5,/ = 0.0226. h f = 0.0226[400/®)]{4.27[(2)(9.807)]} = 54.20 m. 9.68

SAE10 oil at 68 °F is to be pumped at a flow rate of 2.0 ft3/s through a level 6-in-diameter new wrought iron pipe. Determine the pressure loss in pounds per square inch per mile of pipe and compute the horsepower lost to friction.

I

h f = (f)(L/d)(v 2 /2g) v = Q/A = 2.0/[(?r)(£) /4] = 10.19 ft/s 2

N R = pdv/p = (1.68)(&)(10.19)/(1.70 x 10"3) = 5035 (turbulent) From Table A-9, e = 0.00015 ft. e/d = 0.00015/(£) = 0.00030. From Fig. A-5, / = 0.038. h f = 0.038[5280/(£)]{10.197[(2)(32.2)]} = 647 ft of oil; p = yh = (54.2)(647)/144 = 244 psi/mile. 9.69

Water at 20 °C flows in a 100-mm-diameter new cast iron pipe with a velocity of 5.0 m/s. Determine the pressure drop in kilopascals per 100 m of pipe and the power lost to friction.

I

h f = (f)(L/d)(v 2 /2g) N R = dv/v = (S)(5.0)/(1.02 x 10"6) = 4.90 x 10

5

From Table A-9, e = 0.00026 m. e/d = 0.00026/®) = 0.0026. From Fig. A-5, / = 0.0252. h f = 0.0252[100/®)]{5.07[(2)(9.807)]} = 32.12 m p = (9.79)(32.12) = 314 kN/m per 100 m of pipe 2

3

Q=Av = [(nr)®) /4](5.0) = 0.03927 m /s 2

Power lost = Qyh f = (0.03927)(9.79)(32.12) = 12.35 kW per 100 m of pipe 9.70

Determine the discharge capacity of a 150-mm-diameter new wrought iron pipe to carry water at 20 °C if the pressure loss due to friction may not exceed 35 kPa per 100 m of level pipe.

I

N R = dv/v = (i«jo)(tO/(1.02 x 10~6) = 1.47 X 105!;

Trial No. 1 Assume v = 3.0 m/s: N R = (1.47 x 10 )(3.0) = 4.41 x 10s, e/d = 0.000046/®) = 0.000307. From Fig. A-5, / = 0.0164, h f = (f)(L/d)(v 2 /2g) —p/y - 35/9.79 = 3.575 m, 3.575 = 0.0164[100/®)]{u 2/[(2)(9.807)]}, v = 2.53 m/s. 5

Trial No. 2 Assume u = 2.53 m/s: N R = (1.47 x 10 )(2.53) = 3.72 x 105, / = 0.0166, 3.575 = 0.0166[100/®)]{U2/[(2)(9.807)]}, t; = 2.52m/s; Q=Av = [(jr)®)2/4](2.52) = 0.0445 m /s. 5

3

9.71

SAE30 oil at 68 °F is to be pumped at a flow rate of 3.0 ft3/s through a level new cast iron pipe. Allowable pipe friction loss is 10 psi per 1000 ft of pipe. What size commercial pipe should be used? p = yh

I

(10)(144) = 55.4h f

h f = 26.0 ft of oil per 1000 ft of pipe

212 0 CHAPTER 9 Trial No. 1 Assume v = 5.0 ft/s: Q=A/v 3.0 = (jtd 2 /4)(5.0) d = 0.874 ft N R = pdv/p = (1.72)(0.874)(5.0)/(9.2 x 10“3) = 817 (laminar) h, = (f)(L/d)(v 2 /2g) f = 64/A/* = & = 0.0783 26.0 = (0.0783)(1000/0.874)(u2/[(2)(32.2)]} v = 4.32 ft/s Trial No. 2 Assume u = 4.32 ft/s: 3.0 = (*rd74)(4.32) d = 0.940 ft N R = (1.72)(0.940)(4.32)/(9.2 X 10“3) = 759 (laminar) /= = 0.0843 26.0 = (0.0843)(1000/0.940){y2/[(2)(32.2)]} u = 4.32 ft/s Hence, a pipe diameter of 0.940 ft, or 11.28 in, would be required. A 12-in-diameter commercial pipe should be used, which would result in a pipe friction loss somewhat less than the allowable 10 psi per 1000 ft of pipe. 9.72

SAE10 oil at 20 °C is to flow through a 300-m level concrete pipe. What size pipe will carry 0.0142 m3/s with a pressure drop due to friction of 23.94 kPa? I

p-yh 23.94 = 8.52hr /tr = 2.81m

Trial No. 1 Assume v = 1.5 m/s: Q=A/v 0.0142 = (jrd74)(1.5) d = 0.110m N R = pdv/p = (869)(0.110)(1.5)/(8.14 x 10“2) = 1761

(laminar)

2

h f = (f){L/d)(v /2g) f = 64/A/* = T^I = 0.0363 2.81 = (0.0363)(300/0.110){u7[(2)(9.807)]} v = 0.746 m/s Trial No. 2 Assume v = 0.746 m/s: 0.0142 = 7rd74)(0.746) d = 0.156 m N R = (869)(0.156)(0.746)/(8.14/10~2) = 1242 (laminar) / = 1^2 =

0.0515

2.81 = (0.0515)(300/0.156){i;7[(2)(9.807)]} o = 0.746 m/s

Hence, a pipe diameter of 0.156 m, or 156 mm, would be required. 9.73

Compute the friction factor for flow having a Reynolds number of 5 x 10 and relative roughness (e/d) of 0.015 (transition zone). Use the Colebrook formula, the Swamee-Jain formula, and the Moody diagram. 3

f Colebrook formula: l/y/f= 1.14 - 2.0 log [e/d + 9.35/(A7\//)] = 1.14 - 2.0 log [0.015 + 9.35/(5 x lOV/)] / = 0.0515 (by trial and error) Swamee-Jain formula: / = 0.25/[log (e/3.7 d) + (5.47/A^ )] = 0.25/{log (0.015/3.7) + [5.47/(5 x 10 ) 9

Moody diagram (Fig. A-5): 9.74

2

3 09

]}2

= 0-0438

y _ Q 0512

Repeat Prob. 9.73 for flow having a Reynolds number of 4 x 10 s and relative roughness (e/d) of 0.0001 (rough-pipe zone).

f Colebrook formula: / = 1/[1.14 - 2.0 log (e/d)] 2 = 1/[1.14 - 2.0 log (0.0001)]2 = 0.0120 Swamee-Jain formula: f = 0.25/[log (e/3.7 d) + (5.74/A^9)]2 = 0.25/(log (0.0001/3.7) + [5.74/(4 X 10 6)09]}2 = 0.0120 Moody diagram (Fig. A-5): / = 0.0125

FLOW IN CLOSED CONDUITS 0 213 We have oil of kinematic viscosity 8 x 10~5 ft2/s going through an 80-ft horizontal pipe. If the initial pressure is 5.0 psig and the final pressure is 3.5 psig, compute the mass flow if the pipe has a diameter of 3 in. At a point 10 ft from the end of the pipe a vertical tube is attached to be flush with the inside radius of the pipe. How high will the oil rise in the tube? p = 50 lbm/ft3. Pipe is commercial steel (e = 0.000145 ft). I

pjy + v\/2g + z 1 =p 2 ly + vl/2g + z 2 + h L (5.0)(144)/(50/32.2) + v\/2g + 0 = (3.5)(144)/(50/32.2) + vl/2g + 0 + h f

v\/2g = vl/2g h f = 139.1 ft = (f)(L/d)(v 2 /2) 139.1 = (/)[80/(£)](«72) fv 2 = 0.8694 2 Try/ = 0.020: 0.020t/ = 0.8694, v = 6.593 ft/s; 1V* = dv/v = (^)(6.593)/(8 x 10“5) = 2.06 x 104; e/d = 0.000145/(^) = 0.000580. From Fig. A-5,/ = 0.0265. Try/ = 0.0265: 0.0265u 2 = 0.8694, v = 5.728 ft/s; N R = (A)(5.728)/(8 x 10~5) = 1.79 x 104;/ = 0.0267, 0.0267u2 = 0.8694, v = 5.706ft/s; M = pAv = 50[(JT)(^)2/4](5.706) = 14.0 lbm/s. To find the pressure at the point 10 ft from the end of the pipe (call it point A), apply the Bernoulli equation between point 1 and point A: (5.0)(144)/(50/32.2) + v\/2g + 0 = p A /(50/32.2) + vl/2g + 0 + h f h f = 463.7 - 0.6440\p A = 0.0267[70/(^)](5.7062/2) = 121.7 ft 121.7 = 463.7 — 0.6440/7,4 p A = 531.1 lbm/ft2 h =p/p = 531.1/50= 10.62ft How much water is flowing through the pipe shown in Fig. 9-20? Take v = 0.114 x 10~5 m2/s and e = 0.0000442 m. I

PJ Y

+ vl/2g + z t =p 2 /y + vl/2g + z 2 + h,_ v\/2g = vl/2g

1.6 + v\/2g + 0 = 0.3 + v\/2g + 0 + h f

h f = 1.3 m = (f)(L/d){v 2 /2g)

Try/= 0.015: 1.3 = 0.015[10/(0.150)]{u2/[(2)(9.807)]} v = 5.050 m/s N K = dv/v = (0.150)(5.050)/(0.114 x 10 5) = 6.64 X 10s e/d = 0.0000442/(0.150) = 0.000295 From Fig. A-5, / = 0.016. 1.3 = 0.016[10/(0.150)]{u2/[(2)(9.807)]} v = 4.889 m/s M = pAv = 1000{(jr)(0.150)2/4](4.889) = 86.4 kg/s

Fig. 9-20 Whiskey (s.g. = 0.6, v = 5.0 x 10“7 m2/s) is drawn from a tank through a hose of inside diameter 25 mm (see Fig. 9-21). The relative roughness for the hose is 0.0004. Calculate the volumetric flow and the minimum pressure in the hose. The total length of hose is 9 m and the length of hose to point A is 3.25 m. Neglect minor losses at head entrance.

f pjy

+ wf/2g + zi =/>2// + vl/2g + Z2 + h L 0 + 0 +(5- 1.5) = 0 + u|/[(2)(9.807)] + 0 + h f h f = 3.5 - 0.05098«! = (f)(L/d)(v 2 /2g)

214 0 CHAPTER 9 Try/ = 0.016: h f = 0.016[9/(0.025)]{i/|/[(2)(9.807)]} = 0.2937v!

0.2911 v\ = 3.5 - 0.05098t>!

N R = dv/v = (0.025)(3.187)/(5.0 x 10” ) = 1.59 x 10 7

v = 3.187 m/s

5

From Fig. A-5 with e/d = 0.0004, / = 0.019. Try / = 0.019: h f = 0.019[9/(0.025)]{ui/[(2)(9.807)]} = 0.3487u|

0.3487v? = 3.5 - 0.05098u| 7

A/R = dv/v = (0.025)(2.959)/(5.0 X 10' ) = 1.48 x 10 Q=Av =

[(JT)(0.025)2/4](2.959)

= 1.45 L/s

5

v = 2.959 m/s

/ = 0.019

pjy + w?/2g + z, = pjy + v\/2g + z A + h L 2

0 + 0 + (5 - 1.5) = JPA/[(0.6)(9.79)] + 2.959 /[(2)(9.807)] + 5 + h f

p A = -11.43 - 5.874^

h f = 0.019[3.25/(0.025)] {2.9592/[(2)(9.807)]} = 1.103 m p A = -11.43 - (5.874)(1.103) = -17.91 kPa

Fig. 9-21 9.78

In using the Darcy-Weisbach equation for flow in a pressure conduit, what percentage error is introduced in Q when/is misjudged by 20 percent? f

h f = (f)(L/d)(v 2 /2g) = KtfQ 2 (where K t is a constant)

Assume h f is constant. Q = K 2 /Vf= K 2 f~ m , dQ = ~l(K 2 )(f~ 3,2 )(df) -10 percent 9.79

For the system in Fig. 9-13, find the flow rate if the liquid is water at 68 °F. f Assume smooth-wall turbulent flow. p A /y + v\/2g + z A =p B /y + v%/2g + z B + h L , 0 + 0 + 10 = 0 + u|/[(2)(32.2)] + 0 + h f , h f = 10 - 0.01553t/| = {f)(L/d)(v 2 /2g). Try/ = 0.02: h f = 0.02[6/(0.5/12)]{v|/[(2)(32.2)]} = 0.04472v|

10 - 0.01553u| = 0.04472u| v B = 12.88 ft/s

N R = pdv/p = (1.93)(0.5/12)(12.88)/(2.04 x 10"5) = 5.08 x 104 (turbulent) From Fig. A-5, / = 0.0208. Try / = 0.0208: h f = 0.0208[6/(0.5/12)]{u|/[(2)(32.2)]} = 0.04651u|

10 - 0.01553u| = 0.04651u| v B = 12.70 ft/s

N R = pdv/p = (1.93)(0.5/12)(12.70)/(2.04 x 10“5) = 5.01 x 104 (turbulent) / = 0.0208 9.80

Q=Av = [(JT)(0.5/12)2/4](12.70) = 0.0173 ft3/s

If 1 mile of 3-in-diameter wrought iron pipe carries water at 68 °F and v=23 ft/s, compute the head loss and the pressure drop. f

h f = (J)(L/d)(v 2 /2g)

N R = pdv/p = (1.93)(H)(7/0.3048)/(2.04 X 10"5) = 5.43 x 10s e/d = 0.00015/(£) = 0.000600

FLOW IN CLOSED CONDUITS 0 215 From Fig. A-5, / = 0.0182. h f = 0.0182[5280/(n)] {(23)2/[(2)(32.2)]} = 3157 ft

p = yh f = (62.4)(3157)/144 = 1368 lb/in2

Ml Mercury at 20 °C flows through 3 m of 6-mm-diameter glass tubing with average velocity 2.0 m/s. Compute the head loss and the pressure drop. |

h f = (f)(L/d)(v 2 /2g) N R = pdv/p = (13 570)(0.006)(2.0)/(1.56 x 10 3) = 1.04 x 105

From Fig. A-5, / = 0.0180 (assuming glass to be “smooth”). h, = 0.0180[3/(0.006)] (2.02/[(2)(9.807)]} = 1.835 m 9.82

p = yh f = [(13.6)(9.79)](1.835) = 244 kPa

Gasoline at 20 °C is piunped at 0.2 m3/s through 16 km of 180-mm-diameter cast iron pipe. Compute the power required if the pumps are 75 percent efficient. I

h f = (f)(L/d)(v 2 /2g) v = Q/A = 0.2/[(ac)(0.180)2/4] = 7.860 m/s N R = pdv/p = (719)(0.180)(7.860)/(2.92 x 10 4) = 3.48 x 106 e/d = 0.00026/(0.180) = 0.00144

From Fig. A-5 ,/ = 0.0216. h f = 0.0216[(16)(1000)/ (0.180)] {7.860 2/[(2)(9.807)]} = 6048 m P = pgQhf/ri = (719)(9.807)(0.2)(6048)/0.75 = 11.37 X 106 W or 11.37 MW 9.83

Vinegar (s.g. = 0.86, v = 0.00003 ft2/s) flows at 1 ft3/s through a 6-in asphalted cast iron pipe. The pipe is 2000 ft long and slopes upward at 10° in the flow direction. Compute the head loss and the pressure change. f

h f = (f)(Lld)(v 2 l2g) v = Q/A = l/[(*)(4)2/4] = 5.093 ft/s N R = dv/v = (f5)(5.093)/0.00003 = 8.49 X 104 e/d = 0.0004/(£) = 0.000800

From Fig. A-5,/ = 0.0219. hf = 0.0219[2000/(TJ)]{5.0932/[(2)(32.2)]} = 35.28 ft h,, = 35.28 + 2000 sin 10° = 382.6 ft p = yh f = [(0.86)(62.4)](382.6)/144 = 142.6 lb/in 2 9^4 The pipe flow in Fig. 9-22 is driven by pressurized air in the tank. What gage pressure p, is needed to provide a flow rate of 50 m3/h of water? Assume a “smooth” pipe. f Pi/y + v\/2g + Z! = p 2 /y + v\/2g + z 2 + h L v 2 = Q/A 2 = (50/3600)/[(;r)(0.050)2/4] = 7.074 m/s h L = h f = (f)(L/d)(v 2 /2g) N R = pdv/p = (998)(0.050)(7.074)/(1.02 X 10“3) = 3.46 x 105 From Fig. A-5,/ = 0.0140. h L = 0.0140[(40 + 80 + 20)/0.050]{7.0742/[(2)(9.807)]} = 100.0 m Pt/9.79 + 0 + 10 = 0 + 7.0742/[(2)(9.807)] + 80 + 100.0 Pl = 1689 kPa gage

Open jet

[*- 40m

Fig. 9-22

216 0 CHAPTER 9 9.85

In Fig. 9-22 suppose the fluid is methanol at 20 °C and p, = 900 kPa gage. What flow rate Q results? I P i / y + v\Hg + z, = p 2 /y + vl/2g + z 2 + h L 900/7.73 + 0+ 10 = 0 + u|/[(2)(9.807)] + 80 + h L = 46.43 - 0.05098t>i = h f = (f)(L/d)(v 2 /2g) Try/= 0.02: h L = 0.02[(40 + 80 + 20)/0.050]{t>i/[(2)(9.807)]} = 2.855u|

2.855uf = 46.43 - 0.05098v 2 = 4.000 m/s

N R = pdv/ft = (788)(0.050)(4.000)/(5.98 x 10~4) = 2.64 x 105 From Fig. A-5, / = 0.0150. Try / = 0.0150: h L = 0.0150[(40 + 80 + 20)/0.050]{u|/[(2)(9.807)]} = 2.141ul

2.141u^ = 46.43 - 0.05098^ 4

N R = (788)(0.050)(4.602)/(5.98 x 10~ ) = 3.03 x 10

t/2 = 4.602m/s

s

Try/= 0.0145: h L = 0.0145[(40 + 80 + 20)/0.050]{v2/[(2)(9.807)]} = 2.070t/l

2.070ul = 46.43 - 0.05098u|

N R = (788)(0.050)(4.679)/(5.98 x 10~4) = 3.08 x 105

/ = 0.0145

3

At this Reynolds number, Q—Av = = 0.00919 m /s or 33.1 m3/h. In Fig. 9-22 suppose the fluid is carbon tetrachloride at 20 °C and p t = 1300 kPa. Calculate the pipe diameter needed for a volumetric flow of 5.555 L/s. [(JT)(0.050)2/4](4.679)

9.86

u2 = 4.679m/s

I

Pi/y + v\/2g + Zj =p 2 /y + vl/2g + z 2 + h L pjy + 0 + z, = 0 + vl/2g + z2 + (f)(L/d)(vl/2g)

_ (2g)(Pi/y + Z, - z2) (2)(9.807)(1300/15.57 + 10 - 80) 264.7 _ 1+fL/d ~ 1+ (/>(40 + 80 + 20)/d 1 + 140//d = (QIA 2 ) 2 = [(5.555 x 10“3)/(jrd2/4)]2 = 0.00005004/d4 u2 = 0.007074/d2 0.00005004 264.7 (1 + 140//d)1M 4_ d 1 + 140//d " 47.96 Try d = 50 mm, or 0.050 m: N R = pdv/p = (1588)(0.050)(0.007074/0.0502)/(9.67 x 10 4) = 2.32 x 105. From Fig. A-5, / = 0.0151. d = [1 + (140)(0.0151/0.050)] 1M/47.% = 0.0535 m. Try d = 0.0535 m: 2

Vz

N R = (1588)(0.0535)(0.007074/0.0535 2)/ (9.67 x 10"4) = 2.17 x 10s

/ = 0.0155

d = [1 + (140)(0.0155/0.0535)] 1/4/47.96 = 0.0529 m Try d = 0.0529 m: N R = (1588)(0.0529)(0.007074/0.0529 2)/(9.67 x 10“4) = 2.20 x 105

/ = 0.0155

d = [1 + (140)(0.0155/0.0529)]1M/47.96 = 0.0531 m Try d = 0.0531m: N R = (1588)(0.0531)(0.007074/0.0531 2)/(9.67 x 10“4) = 2.19 X 105

/ = 0.0155

1,4

d = [1 + (140)(0.0155/0.0531)] /47.96 = 0.05301 m Hence, use d = 0.053 m, or 53 mm. 9.87

The reservoirs in Fig. 9-23 contain water at 20 °C. If the pipe is smooth, with L = 7 km and d = 50 mm, what will the flow rate be for Az = 98 m?

1 PI/Y

+ v\/2g + z, = pjy + vl/2g + z2 + hi 0 + 0+100 = 0 + 0 + 0 + /^ 98 = (/)[7000/0.050]{V2/[(2)(9.807)]} V = 0.1172/V/

h/=98m = (f)(L/d)(y 2 /2g)

Try/ = 0.02: v = 0.1172/V002 = 0.8287 m/s, N„ = pdv/p = (998)(0.050)(0.8287)/(1.02 x 10“3) = 4.05 x 104. From Fig. A-5, / = 0.022. Try / = 0.022: v = 0.1172/V0.022 = 0.7902 m/s N R = (998)(0.050)(0.7902)/(1.02 x 10“3) = 3.87 x 104 / = 0.022

(O.K.)

Q = Av = [(n:)(0.050)2/4](0.7902) = 0.00155 m3/s or 5.58 m3/h

FLOW IN CLOSED CONDUITS 0 217

Fig. 9-23

9.88

Repeat Prob. 9.87 to find Q if L = 2500 ft, d = 3 in, and Az = 82 ft.

I Pi/Y + v\Hg + z, =p 2 /y + v\/2g + z 2 + h L 0 + 0 +82 = 0 + 0 + 0 +/i, h f =82 ft = (f)(L/d)(v 2 /2g) 82 = (/)[2500/(£)]{u2/[(2)(32.2)]}

„ = 0.7267/Vf

Try/= 0.02: v = 0.7267/vfr02 = 5.139 ft/s N R = pdv/p = (1.93)(&)(5.139)/(2.04 X 10“5) = 1.22 x 10s From Fig. A-5,/ = 0.0175. Try/ = 0.0175: v = 0.7267/V0.0175 = 5.493 ft/s

AT* = (1.93)(£)(5.493)/(2.04 x 10“5) = 1.30 x 10s

/ = 0.0170

Try/= 0.0170: v = 0.7267/VO.0170 = 5.574 ft/s / = 0.0170

= (1.93)(^)(5.574)/(2.04 X 10~5) = 1.32 X 10s

(O.K.) Q=Av = [(jr)(^)2/4](5.574) = 0.2736 ft3/s or 985ft3/h

9it9 Repeat Prob. 9.88 if the pipe has a roughness of 0.2 mm. I From Prob. 9.88, v = 0.7267/y/f. Try / = 0.02: N„ = 1.22 x 105 eld = 0.2/[(3)(25.4)] = 0.00262 From Fig. A-5, / = 0.0265. Try / = 0.0265: v = 0.7267/V0.0265 = 4.464 ft/s / = 0.0265

= (1.93)(^)(4.464)/(2.04 x 10 5) = 1.06 x 105

(O.K.) Q= Av = [(^)(^)2/4](4.464) = 0.2191 fP/s or 789ft3/h

This is (985 - 789)/985 = 0.199, or 19.9 percent less than when the pipe is smooth. 9.90

Water at 20 °C flows through a 598-m pipe 150 mm in diameter at 60 L/s. Determine the pipe roughness if the head loss is 49 m.

I

h L = (f)(L/d)(v 2 /2g) v = Q/A = 0.06/[(nr)(0.150)2/4] = 3.395 m/s 49 = (/)[598/(0.150)]{3.395z/[(2)(9.807)]}

/ = 0.0209

N„ = pdv/n = (998)(0.150)(3.395)/(1.02 x ftT3) = 4.98 x 10s From Fig. A-5 with/ = 0.0209 and N R = 4.98 x 10s, e/d = 0.0012; e = (150)(0.0012) = 0.180mm. 9.91

A 4-in-diameter commercial steel pipe is to be sloped so that 198 gpm of water at 20 °C es through it in gravity flow. Find the declination 6 of the pipe.

I

Q = (198)(0.002228) = 0.4411 f^/s v = Q/A = 0.4411/[(nr)(^)2/4] = 5.055 ft/s e/d = 0.00015/((j) = 0.00045 N R = dv/v = (£)(5.055)/(1.05 x 10“5) = 1.60 x 10s

218 0 CHAPTER 9 From Fig. A-5, / = 0.0190. sin 6 = Az/L = h f IL = (/)(l/d)(u2/2g), sin 6 = 0.0190[l/(£)]{5.0552/[(2)(32.2)]}, 0 = 1.30°. 9.92

In Prob. 9.91 find the volume flow corresponding to 0 = 3°. f From Prob. 9.91, (/)(l/d)(u2/2g) = sin 6, (/)[l/(£)]{u2/[(2)(32.2)]} = sin 3°, v = 1.060/Vf. Try / = 0.02: v = 1.060/V5!02 = 7.495 ft/s TV* = du/v = (£)(7.495)/(1.05 X 10“ 5) = 2.38 x 105 e/d = 0.00045 (from Prob. 9.91) From Fig. A-5, / = 0.0182. Try / = 0.0182: v = 1.060/V0.0182 = 7.857 ft/s W* = (T2)(7.857)/(1.05/10 5) = 2.49 X 105 / = 0.0182

9.93

(O.K.) Q=Av = [(JT)(£)7 4](7.857) = 0.6857 ft3/s = 0.6857/0.002228 = 308 gpm

A tank containing 1 m3 of water at 20 °C has an outlet tube at the bottom, as shown in Fig. 9-24. Find the instantaneous volume flux Q, if the roughness of the tank is e = 1.5 nm. f

pjy + v\/2g +

Zj=

pjy + v\!2g + z 2 + h L

h L = h f = (f)(L/d)(v 2 /2g) = (/)[0.82/0.04]{u2/[(2)(9.807)]} = 1.045/u2 0 + 0 + (1 + 0.82) = 0 + u|/[(2)(9.807)] + 0 + 1.045\fv\

v 2 = 1.349/V0.05098+ 1.045/

Try/= 0.02: v 2 = 1.349/V0.05098 + (1.045)(0.02) = 5.032 m/s N R = du/v = (0.04)(5.032)/(1.02 x 10 6) = 1.97 x 105 e/d = 0.0000015/0.04 = 0.0000375 From Fig. A-5, / = 0.016. Try / = 0.016: v 2 = 1.349/V0.05098 + (1.045)(0.016) = 5.185 m/s N R = (0.04)(5.185)/(1.02 x 10“6) = 2.03 x 105 / = 0.016

(O.K.)

Q =Av = [(nr)(0.04)2/4](5.185) = 0.006516 m3/s = 6.516 L/s

VI

L = 82 cm "* cL = 4 cm

ol

9.94

2.

Fig. 9-24

Repeat Prob. 9.93 for a fluid with p = 917 kg/m3 and ju = 0.29 Pa • s.

I PitY + u?/2g + z,= p 2 /y + v\/2g + z 2 + h L . Assume laminar flow. 32 pLv (32) (0.29)(0.82) (v) h L — hf — 2 = 0.5288u. pgd ~ (917)(9.807)(0.04)2 0 + 0 + (1 + 0.82) = 0 + u?/[(2)(9.807)] + 0 + 0.5288u 2 v\ + 10.37u2 - 35.70 = 0 N R = pdv/p = (917)(0.04)(2.726)/0.29 = 345 (laminar)

J

Q-Av = [(JT)(0. 04)2/4](2.726) = 0.003426 m3/s = 3.426 L/s

v = 2.726 m/s

FLOW IN CLOSED CONDUITS D 219 What depth of water behind a dam (Fig. 9-25) will yield a flow rate of 0.02 ft3/s through the 0.5-in commercial steel exit pipe? pjy + v 2 J2g + z, = p 2 /y + vl/2g + Z2 + h L

I

v 2 = Q/A = 0.02/[(JT)(0.5/12)2/4] = 14.67 ft/s

h L = h f = (f)(L/d)(v 2 /2g) N R = dv/v = (0.5/12)(14.67)/(1.05 x 10"5) = 5.82 X 104 e/d = 0.00015/(0.5/12) = 0.00360 From Fig. A-5, / = 0.0295: h L = 0.0295[100/(0.5/12)]{14.672/[(2)(32.2)]} = 236.6 ft, 0 + 0 + H = 0 + 14.672/[(2)(32.2)] + 0 + 236.6, H = 239.9 ft.

^7 1

Water 20 *C

/y

L=

< '5 L1 =

1

*

Fig. 9-25

In Fig. 9-25, imagine the fluid to be benzene at 20 °C and H = 100 ft. What pipe diameter is required for the flow rate to be 0.02 ft3/s? f

pjy + v\/2g + z x =pjy + vl/2g + z 2 + h L h L = h f = (f)(L/d)(v 2 /2g) = (/)(100/d){t;|/[(2)(32.2)]} = 1.553fvl/d 0 + 0+100 = 0+ vl/[(2)(32.2)] + 0 + 1.553fvl/d

v 2 = Q/A 2 = 0.02/(jrd2/4) = 0.02546/d2

100 = (0.02546/d 2 ) 2 /[(2)(32.2)] + (1.553)(/)(0.02546/d 2)2/d d = [(1.007 X 10"7) + (1.007 x 10 5//rf)],/4 2 5 Try d = 0.05 ft: N R = pdv/p = (1.70)(0.05)(0.02546/0.05 )/(1.36 x lO" ) = 6.36 x 104, e/d = 0.00015/0.05 = 0.00300. From Fig. A-5, / = 0.028. d = [(1.007 x 10“7) + (1.007 x 10-5)(0.028)/0.05]1/4 = 0.0489 ft. Try d= 0.00489 ft: N R = (1.70)(0.0489)(0.02546/0.04892)/(1.36 X 10-5) = 6.51 X 104

/ = 0.028

(O.K.)

d = 0.0489 ft or 0.59 in Water at 70 °F flows through 102 ft of 0.5-in-diameter piping whose roughness is 0.01 in. Find the volumetric flow if the pressure drop is 60 psi. pjy + v 2 J2g + z, = pjy + v 2 j2g + z 2 + h L

f

h L = h f = (f)(L/d)(v 2 /2g) = (/)[102/(0.5/ 12)]{u2/[(2)(32.2)]} = 38.01/u2 (60)(144)/62.3 + vl/2g + 0 = 0 + v\/2g + 0 + 38.01/u2

v\/2g = v\/2g v 2 = 1.910/V/

Try/= 0.05: v 2 = 1.910/V005 = 8.542 ft/s N R = dv/v = (0.5/12)(8.542)/(1.05 x 10“5) = 3.39 x 104 e/d = 0.01/0.5 = 0.0200 / = 0.050

(O.K.) Q = Av = [(JT)(0.5/12)2/4](8.542) = 0.0116 ft3/s

Ethanol at 20 °C flows at 3.2 m/s through a 10-cm-diameter pipeline (e = 1.5 pm). Compute (a) the head loss per kilometer of tube and (ft) the wall shear stress. I (a)

h f = (J){L/d)(v 2 /2g)

NR

= pdv/p = (788)(0.10)(3.2)/(1.20 x 10-3) = 2.10 x 105 e/d = 0.0000015/0.10 = 0.0000150

From Fig. A-5, / = 0.0158. h f = 0.0158[1000/0.10]{(3.2)2/[(2)(9.807)]} = 82.5 m per 1000 m. (h) u* = uV/78 = (3.2)V0.0158/8 = 0.1422 m/s rwal, = (p)(u*f = (788)(0.1422)2 = 15.9 Pa

220 0 CHAPTER 9 9.99

In Fig. 9-26, the 50-m duct is 60 mm in diameter. Compute the flow rate if the fluid has p = 917 kg/m 3 and fi = 0.29 Pa • s.

f Assume laminar flow from 1 to 2. pjpg + v\!2g + Z i = pjpg + v\l2g + z 2 + h L h,=h,=

128 pLQ (128)(0.29)(50)((2) ; = 5069(2 npgd 4 (JT)(917)(9.807)(0.060)4

0 + 0 + 12 = (205)(1000)/[(917)(9.807)] + 0 + 0 + 5069Q Q = -0.002130 m3/s or

-7.67 m3/h

Since Q is negative, flow is from 2 to 1. v = Q/A = 0.002130/[(jr)(0.060)2/4] = 0.7533 m/s N R = pdvlp = (917)(0.060)(0.7533)/0.29 = 143 (laminar)

Fig. 9-26

9.100

Compute the diameter of duct in Fig. 9-26 required to maintain a flow rate of 25 m3/h. f P i . u ? _£i , w? , Pg 2g 22 pg 2g 2‘

,.

. f

128pL<2 (128)(0.29)(50)(25/3600) 4.5621 x 10~4 npgd 4 (jr)(917)(9.807)(d)4 d*

(205)(1000)/[(917)(9.807)] + 0 + 0 = 0 + 0+12 + 4.5621 X 10 4/d4 d = 0.0806 m v = Q/A = (25/3600)/[(JT)(0.0806)2/4] = 1.361 m/s Af„ = pdv/p = (917)(0.0806)(1.361)/0.29 = 347 (laminar)

9.101

A 40-ft-long conduit, having an annular cross section with a = 1 in and b = 0.5 in, connects two reservoirs which differ in surface height by 21 ft. Compute the flow rate if the fluid is water at 20 °C and the conduit is made of commercial steel. f Hydraulic diameter = D h = (2)(a — b) = (2)(1 — 0.5) = 1.00 in

pj y + v\/2g + z x = p 2 / y + v\/2g + z 2 + h L

0 + 0 + 21 = 0 + 0 + 0 + h L h L = 2\ft = h f = {f)(L/d)(v 2 /2g) 21 = (/)[40/(1.00/12)]{»7[(2)(32.2)]} u = 1.679fy/f Try/= 0.02: v = 1.679/^02 = 11.87 ft/s N R = dv/v = (1.00/12)(11.87)/(1.05 x 10“5) = 9.42 X 104 e/d = 0.00015/(1.00/12) = 0.00180 From Fig. A-5, / = 0.0246. Try / = 0.0246: v = 1.679/Vo.0246 = 10.70 ft/s

N R = (1.00/12)(10.70)/(1.05 x 10 5) = 8.49 x 104

Try/ = 0.0250: v = 1.679/V0.0250 = 10.62 ft/s N R = (1.00/12)(10.62)/(1.05 x 10 5) = 8.43 x 104 / = 0.0250

(O.K.) Q = Av = {(jr)[(1.00/12)2 - (0.5/12)2]}(10.62) = 0.174 ft3/s

/ = 0.0250

FLOW IN CLOSED CONDUITS D 221 i 9.102 An annular capillary causes a very large pressure drop and is useful in an accurate measurement of viscosity. If a smooth annulus 1 m long with a = 50 mm and b — 4 9 mm carries an oil flow at 0.0012 m3/s, what is the oil viscosity if the pressure drop is 260 kPa? Q = (jr/8p)(Ap/L)[a4 — b * — (a2 — b2)2/ln (a / b )]

I

|

0.0012 = (jt/8p)(260 000/l)[0.0504 - 0.0494 - (0.0502 - 0.0492)2/ln (0.050/0.049)] p = 0.0738 Pa • s 9.103 A metal ventilation duct (e = 0.00015 ft) carries air at 20 °C and 1 atm. The duct section is an equilateral triangle 1 ft on a side, and its length is 100 ft. If a blower can deliver 1 hp to the air, what flow rate can occur? I

f From Fig. 9-27, A = i(l)GV3) = 0.4330 ft2

| ■

P = Q yh f Q = A v= 0.4330« h f = (J) (L / d ) (v 2 / 2 g ) d = D h = 4 A/ p „

1

D h = (4)(0.4330)/[(12 + 12 + 12)/12] = 0.5773 ft h f = (/)(100/0.5773){t/7[(2)(32.2)]} = 2.69fv 2 (1)(550) = (0.4330u)(0.0750)(2.69/u 2) v = 18.47//,/3 Try/= 0.02: v = 18.47/0.021'3 = 68.04 ft/s N R = d v/ v = (0.5773)(68.04)/(1.64 X 10 4) = 2.40 x 105 e/ D h = 0.00015/0.5773 = 0.000260 From Fig. A-5, / = 0.0176. Try / = 0.0176: v = 18.47/0.01761/3 = 71.00 ft/s N R = (0.5773)(71.00)/(1.64 X 10"4) = 2.60 x 10s (O.K.) Q = (0.4330)(71.00) = 30.7 ft3/s

/ = 0.0176

1 ft - - - - -

' Fig. 9-27 9.104

A fluid with p = 917 kg/m3 and p = 0.29 Pa • s flows between two smooth parallel plates 5 cm apart (h = 5 cm) at an average velocity of 3 m/s. Compute the pressure drop, centerline velocity, and head loss for each 100 m of length. f d = D h =2 h = (2)(0.05) = 0.1000 m N R = p d v/ p = (917)(0.1000)(3)/0.29 = 949 (laminar) v = (h 2 / \ 2 f t )( Ap / L )

3 = {(0.05)2/[(12)(0.29)]}(Ap/100)

h f = Ap l p g = 417 600/[(917)(9.807)] = 46.44 m 9.105

Ap=417 600Pa

u ^ = 1 . 5 v = (1.5)(3) = 4.50 m/s

Air at STP is forced at 25 m/s through a 30-cm-square steel duct 148 m long. Compute the head loss, pressure drop, and power required if the blower efficiency is 60 percent. Use e = 0.000046 m. I

d = D h = 4 A / p w = (4)[(0.30)(0.30)]/[(4)(0.30)] = 0.3000 m h f = (f ) (L l d ) (v 2 / 2 g ) = (/)(148/0.3000) (252/[(2)(9.807)]} = 15720f

N R = p d v/ p = (1.20)(0.3000)(25)/(1.81 x 10 5) = 4.97 X 10s e/ d = 0.000046/0.3000 = 0.000153 From Fig. A-5, / = 0.0150. h f = (15 720)(0.0150) = 235.8 m

Ap = p g h f = (1.20)(9.807)(235.8) = 2775 Pa

3

Q = A v = [(0.30)(0.30)](25) = 2.25 m /s P = PS Qh f ! V = (1.20)(9.807)(2.25)(235.8)/0.60 = 10406W or 10.4 kW

222 0 CHAPTER 9 9.106

A 50-m-long wind tunnel has a wooden (e = 0.0001 m) rectangular section 40 cm by 1 m. The average flow velocity is 45 m/s for air at STP. Compute the pressure drop, assuming fully developed conditions, and the power required if the fan has 70 percent efficiency.

f

d = D h = 4A/ p w = (4)[G&)(l)]/(& + ift + 1 + 1) = 0.5714 m h f = (f ) (L / d ) (v 2 / 2 g ) = (/)(50/0.5714){452/[(2)(9.807)]} = 9034/ N R = p d v/ p = (1.20)(0.5714)(45)/(1.81 x 10 5) = 1.70 x 106 e/ d = 0.0001/0.5714 = 0.000175

From Fig. A-5, / = 0.0140. h f = (9034)(0.0140) = 126.5 m

Ap = p g h f = (1.20)(9.807)(126.5) = 1489 Pa

Q = Av = [(ujg)(l)](45) = 18.00 m3/s P = PgQh f /r} = (1.20)(9.807)(18.00)(126.5)/0.70 = 38 281W or 38.3 kW 9.107

A smooth rectangular duct 82 m long, of aspect ratio 6:1, is designed to transport 0.6 m 3/s of hydrogen at STP. If the pressure drop is 75 Pa, calculate the dimensions of the cross section. For hydrogen, p = 0.0838 kg/m3 and p = 9.05 j«Pa • s.

f Let h = height of duct; then duct width = 6h . d = D h = 4 A / p „ = (4)[(6A)(A)]/(6A + 6h +h +h ) = 1.714h

v = Q / A = 0.6/[(6A)(A)] = 0.1000/A2

h f = (f ) (L / d ) (y 2 / 2 g ) = (/)(82/l.714ft ){(0.1000/h 2)2/ [(2)(9.807)]} = 0.02439//ft5 Ap = p g h f

75 = (0.0838) (9.807)(0.02439/ /ft5)

ft = 0.1929/1'5

Try/ = 0.02: A = (0.1929)(0.02)1'5 = 0.08821 m, N R = p d v/ p = 0.0838[(1.714)(0.08821)](0.1000/0.088212)/(9.05 x 10~6) = 1.80 x 104. From Fig. A-5, / = 0.0265. Try / = 0.0265: ft = (0.1929)(0.0265)1'5 = 0.09332 m, N „ =0.0838[(1.714)(0.09332)1(0.1000/0.09332 2)/(9.05 x 10“6) = 1.70 x 104, / = 0.0267. Try / = 0.0267: ft = (0.1929)(0.0267) 1/s = 0.09346 m, N R = 0.0838[(1.714)(0.09346)] (0.1000/0.09346 2) / (9.05 x 10 6) = 1.70 x 104. / = 0.0267

(O.K.)

Hence, ft = 9.35 cm and width = 6ft = 56.1 cm. 9.108

Kerosene at 10 °C flows steadily at 15 L/min through a 150-m-long horizontal length of 5.5-cm-diameter cast iron pipe. Compare the pressure drop of the kerosene flow with that of the same flow rate of benzene at 10 °C through the same pipe. At 10 °C, p = 820 kg/m3 and p = 0.0025 N • s/m2 for kerosene, and p = 899 kg/m3 and p = 0.0008 N • s/m2 for benzene.

f For kerosene: v = Q t A = [(iMs)/60]/[(jr)(5.5/100)74] = 0.1052 m/s N R = p d v/ p = (820)(5.5/100)(0.1052)/0.0025 = 1898 (laminar) Ap = 8 p vL / r l = (8)(0.0025)(0.1052)(150)/[(5.5/100)/2] 2 = 417 Pa For benzene: N R = (899)(5.5/100)(0.1052)/0.0008 = 6502 2

Ap = (f ) (L / d ) (p ) ( v / 2 )

(turbulent)

e/ d = 0.00026/(5.5/100) = 0.00473

From Fig. A-5, / = 0.040: Ap — (0.040)[150/(5.5/100)](899)(0.1052 2/2) = 543 Pa. The pressure drop is greater for the benzene than the kerosene, although the benzene has a lower viscosity. If both flows had been laminar or both turbulent, the lower-viscosity fluid, benzene, would have had the lower pressure drop. However, the viscosity of the kerosene is high enough to give laminar flow, while the lower viscosity of the benzene causes a high enough Reynolds number for turbulent flow. 9.109

Water at 60 °F flows through a 250-ft length of horizontal 2-in-diameter drawn tubing. If the pressure drop across the tubing is 10 psi, what is the flow rate?

f Assume turbulent flow. h f = (f ) (L / d ){ v 2 / 2 g ),

h f = (10)(144)/62.4 = 23.08 ft, 23.08 = (/)[250/(£)]{U2/[(2)(32.2)]}, V = 0.9954/7/ Try v = 5 ft/s: N R = p d v/ p = (1.94)(£)(5)/(2 35 x IQ"5) . 6.88 x 104 (turbulent), e/ d = 0.000005/(£) = 0.000030. From Fig. A-5,/ = 0.0195. v = 0.9954/V0.0195 = 7.13 ft/s.

FLOW IN CLOSED CONDUITS 0 223 Try v = 7.13 ft/s: N R = (1.94)(&)(7.13)/(2.35 x 10“5) = 9.81 x 104, / = 0.0180, v = 0.9954/VO.0180 = 7.42 ft/s. Try v = 7.42 ft/s: A* = (1.94)(&)(7.42)/(2.35 X 10“5) = 1.02 X 105, / = 0.0180 (O.K.); Q = Av = tOOCs)2/4](7.42) = 0.162 ft2/s. 9.110

Air at 200 °F and 15 psig is to be ed through a 150-ft length of new galvanized iron pipe at a rate of 15 ft3/s. If the maximum allowable pressure drop is 5 psi, estimate the minimum pipe diametei.

I ft, = (f ) (L / d ) (v 2 / 2 g ) = p l y y = p / RT = (15 +14.7)(144)/[(53.3)(200 + 460)] = 0.1216 lb/ft 3 v = Q/ A = 15/(jrd2/4) = 19.10/d2

ft, = (5)(144)/0.1216 = 5921 ft

5921 = (/)(150/d){(19.10/d2)2/[(2)(32.2)]} d = 0.6782f ' s Try d = 0.5 ft: N R = p d v/ p = (y/ g ) (d v )/ p = (0.1216/32.2)(0.5)(19.10/0.5 2)/(4.49 x HT7) = 3.21 x 10s e/d = 0.0005/0.5 = 0.0010 From Fig. A-5, / = 0.0205; d = (0.6782)(0.0205)1/5 = 0.3117 ft. Try d = 0.3117 ft: N R = (0.1216/32.2)(0.3117)(19.10/0.3117 2)/(4.49 x 10~7) = 5.15 x 105 e/ d = 0.0005/0.3117 = 0.0016 / = 0.0225 d = (0.6782)(0.0225)1/s = 0.3175 ft Try d = 0.3175 ft: N R = (0.1216/32.2)(0.3175)(19.10/0.3175 2)/(4.49 x 10~7) = 5.06 x 10s e/d = 0.0005/0.3175 = 0.0016 Hence, d = 0.3175 ft, or 3.81 in. 9.111

/ = 0.0225

(O.K.)

Compute the loss of head and pressure drop in 200 ft of horizontal 6-in-diameter asphalted cast iron pipe carrying water with a mean velocity of 6 ft/s.

I hf

= (f ) (L / d ) (v 2 / 2 g ) N R = d v/ v = (£)(6)/(1.05 x 10~5) = 2.86 x 105 e/d = 0.0004/(£) = 0.00080 From Fig. A-5, / = 0.020: h f = (0.020)[200/(£)]{67[(2)(32.2)]} = 4.47 ft 9.112

Ap = yh f = (62.4)(4.47) = 279 lb/ft2

Oil with p = 900 kg/m3 and v = 0.00001 m2/s flows at 0.2 m3/s through 500 m of 200-mm-diameter cast iron pipe. Determine (a) the head loss and (ft) the pressure drop if the pipe slopes down at 10° in the flow direction.

I (a)

h f = (/)(L/d)(u2/2g) v = Q / A = 0.2/[(^)(^)2/4] = 6.366 m/s N R = d v/ v = (TO5O)(6.366)/0.00001 = 1.27 x 105 e/d = 0.00026/®) = 0.00130

(ft)

From Fig. A-5, / = 0.0225, h f = 0.0225[500/®)](6.3662/[(2)(9.807)]} = 116.2 m. h f = Ap / (p g ) + L sin 10° 116.2 = Ap/[(900)(9.807)] + (500)(sin 10°) Ap = 259 300 Pa or 259.3 kPa

9.113

Oil with p = 950 kg/m3 and v = 0.00002 m2/s flows through a 30-cm-diameter pipe 100 m long with a head loss of 8 m. The roughness ratio e/d is 0.0002. Find the average velocity and flow rate.

I

h f = (f ) (L / d ) (v 2 / 2 g )

8 = (/)[100/®]{u2/[(2)(9.807)]}

u= 0.6861/ y/ f

4

Try v = 5 m/s: N R = d v/ v = ®)(5)/0.00002 = 7.50 x 10 . From Fig. A-5,/ = 0.020, v = 0.6861/V0.020 = 4.851 m/s. Try v = 4.851 m/s: N R = ®(4.851)/0.00002 = 7.28 x 104, / = 0.020 (O.K.). Q = Av = [(*)®2/4](4.851) = 0.343 m3/s. 9.114

Fluid flows at an average velocity of 6 ft/s between horizontal parallel plates a distance of 2.4 in apart (h = 2.4 in). Estimate the head loss and pressure drop for each 100 ft of length for p = 1.9 slugs/ft3 and v = 0.00002 fP/s. Assume smooth walls.

I

h f = (f ) (L / d ) (v 2 / 2 g ) d = Z>* = 2ft D* = (2)(2.4/12) = 0.400 ft N R = d v/ v = (0.400)(6)/0.00002 = 1.20 x 10 5 (turbulent)

224

a CHAPTER 9 From Fig. A-5,/ = 0.0173. h f = (0.0173)(100/0.400) {62/[(2)(32.2)]} = 2.42 ft

9.115

Ap = p g h f = (1.9)(32.2)(2.42) = 148 lb/ft2

Repeat Prob. 9.114 if v = 0.002 ft2/s. f

N K = d v/ v = (0.400)(6)/0.002 = 1200 (laminar) / = 96/A/* =

= 0.0800

h f = (f ) (L / d ) (v 2 / 2 g ) = (0.0800)(100/0.400){67[(2)(32.2)]} = 11.18 ft Ap = p g h f = (1.9)(32.2)(11.18) = 684 lb/ft2 9.116

Estimate the reservoir level h needed to maintain a flow of 0.01 m3/s through the commercial steel annulus 30 m long shown in Fig. 9-28. Neglect entrance effects and take p = 1000 kg/m3 and v = 1.02 x 10-6 m2/s for water. f p j y + ”i/2g + 2, = p 2 / y + vl / 2 g + Z 2 + hf

v = Q/ A = 0.01/{(jr)[(^)2 - (flb)2]} = 1.989 m/s

d = D h = (2) (a -b ) D„ = (2 )(4 s - 40 = 0.0400m

h f = (f )( L / d )( v 2 / 2 g )

h f = (/)(30/0.0400) {1.9892/[(2) (9.807)]} = 151.3/

0 + 0 + A= 0 +1.9892/[(2)(9.807)] + 0 +151.3/

h = 0.2017 +151.3/ N R = d v/ v = (0.0400)(1.989)/(1.02 x 10“6) = 7.80 x 104 e/ d = 0.000046/0.0400 = 0.00115 From Fig. A-5,/ = 0.0232, h = 0.2017 + (151.3)(0.0232) = 3.71 m.

(!)

h-?

V

s a = 5 cm y b = 3 cm

y

^ Water

9.117

mZZZZZZZZZZZ L = 30 m ZZZZEZL

(2)

~Q , ir Fig. 9-28

Air with p = 0.00237 slug/ft3 and v = 0.000157 ft2/s is forced through a horizontal square 9-in by 9-in duct 100 ft long at 25 ft3/s. Find the presssure drop if e = 0.0003 ft. f

h f = (f ) (L / d ) (v 2 / 2 g ) N R = d v/ v D h = 4 A/ p w = 4[(£)(£)]/[(4)(£)] = 0.7500 ft

From Table A-10, for b / a = % , or 1.0, the effective diameter is d = D c B = (64/56.91){ D h ) = (64/56.91)(0.7500) = 0.8434ft, v = Q / A = 25/[(^)(^)] = 44.44ft/s, N R = (0.8434)(44.44)/0.000157 - 2.39 x 105, e/ d = 0.0003/0.8434 = 0.000354. From Fig. A-5, / = 0.0177; h f = (0.0177)(100/0.7500){44.442/[(2)(32.2)]} = 72.37 ft, Ap = p g h f = (0.00237)(32.2)(72.37) = 5.52 lb/ft2. 9.118

Find the head loss in 1 ft of 6-in-diameter pipe (e = 0.042 in) when turpentine (s.g. = 0.86) having a viscosity of 0.0008 lb ■ s/ft2 flows at a rate of 16 cfs. Also find the shear stress at the wall of the pipe.

I

h f = (f ) (L / d ) (v 2 / 2 g ) v = Q/ A = 16/[(JT)(£)2/4] = 81.49 ft/s N R = p d v/ p = [(0.86)(1.94)](^)(81.49)/0.0008 = 8.50 x 10 4

e/ d = 0.042/6 = 0.00700

FLOW IN CLOSED CONDUITS D 225 From Fig. A-5, f = 0.0324. h , = 0.0324il/^)K81.4^/l(2X32.2)\> = 6.68 ft r„ =f p v 2 / 8 = 0.0324[(0.86)(1.94)] (81.49)2/8 = 44.9 lb/ft2 9.119

When water at 150 °F flows in a 0.75-in-diameter copper tube at 1.0 gpm, find the head loss per 1000 ft. Also find the centerline velocity. f Q = (1.0)(0.002228) = 0.002228 ft3/s v = Q / A = 0.002228/[(jr)(0.75/12)2/4] = 0.7262 ft/s h f = (f ) (L / d ) (v 2 l 2 g ) N R = d v/ v = (0.75/12)(0.7262)/(4.68 x 10“*) = 9.70 x 10 3 el d = 0.000005/(0.75/12) = 0.0000800 From Fig. A-5, / = 0.030. h f = (0.030)[1000/(0.75/12)]{0.7262 2/[(2)(32.2)]} = 3.93 ft Mmax = (u)(l + 1.33f 1 1 2 ) = 0.7262[1 + (1.33)(0.030)1/2] = 0.893 ft/s 8i = 32.8v|(vfV2r) = (32.8)(4.68 x \0-6)|((0.m2X0M)H * 0.00122 ft

9.120

Refer to Prob. 9.119. How thick is the viscous boundary layer for a flow of 20 gpm? I The Reynolds number is now (20/1.0)(9.70 x 10 3) = 1.94 x 10s. From Fig. A-5,/ = 0.016. Then,

8 X = 32.8 v/(uf *) = (32.8)(4.68 x 10-6)/((20)(0.7262)(0.016)l/2] « 8.36 x 10“5 ft 9.121

Find the maximum velocity in a 100-mm-diameter pipe (e = 0.00085 m) when oil (s.g. = 0.84), of viscosity 0.0052 Pa • s flows at a rate of 40 L/s. |

v

= Q / A = (40 x 10~3)/[(JT)(0. 100)2/4] = 5.093 m/s

N R = p d v/ n = [(0.84)(1000)](0.100)(5.093)/0.0052 = 8.23 x 10 4 e/ d = 0.00085/(0.100) = 0.0085 From Fig. A-5, / = 0.0365. Hence, Mmax = (t»)(l +1.33f 1 2 ) = 5.093[1 + (1.33)(0.0365)1/2] = 6.387 m/s

9.122

The head loss in 240 ft of 6-in-diameter pipe is known to be 30 ft when oil (s.g. = 0.90) flows at 2.0 ftVs. Determine the shear stress at the wall of the pipe.

I

v

= Q / A = 2.0/[(;r)(£)74] = 10.19 ft/s

N R = p d v/ f i = [(0.90)(1.94)](£)(10.19)/0.0008 = 1.11 x 10 4 (turbulent) h f = (f ) (L / d ) (v 2 / 2 g )

30 = (/)[240/(^)]{10.192/(2)(32.2)]}

/ = 0.0388

To =f p v 2 l 8 = 0.0388[(0.90)(1.94)](10.19)78 = 0.879 lb/ft 2

9.123

If, in a 1-m-diameter pipe, velocities are 5.03 m/s on the centerline and 4.85 m/s at r = 100 mm, what is the flow rate? I

« = Mm« - (5.75)(r0/ p Y 2 log [ r j (r 0 - /■)] 4.85 = 5.03 - (5.75)(T0 / p ) 1 / 2 log [500/(500 - 100)]

v = Mmax - (l)(2.5 VWp) = 5.03 - (§)(2.5)(0.3230) = 3.819 m/s

(T0 / p )' / 2 = 0.3230

Q = A v = [(JT)(1)2/4](3.819) = 3.00 m3/s

226 D CHAPTER 9 9.124

The velocities in a 30-in-diameter pipe are measured as 15.0 and 14.5 ft/s at r = 0 and r = 4 in, respectively. Approximate the flow rate. u = «max - (5.75)(r0/p)1/2 log [fb/(r0 - r)]

#

(r0/p)1/2 = 0.6456 r„/p =/u2/8 umax = (u)(l + 1.33/1/2)

14.5 = 15.0 - (5.75)(T„/P)1/2 log [15/(15 - 4)] (T0/P),/2 = (/u2/8)1/2 = 0.6456

15.0 = (u)(l + 1.33/1/2)

/ = 3.3344/u2

15.0 = (u)[l + (1.33)(3.3344/t;2)1/2]

15.0 = v + 2.4286 u = 12.57 ft/s Q= Av = [(jr)(f§)74](12.57) = 61.7 ft3/s 9.125

With turbulent flow in a circular pipe, prove that the mean velocity occurs at a distance of approximately 0.78r 0 from the centerline of the pipe. I u = (1 + 1.33/',2)(u) - (2.04)(/1,2)(t>) log \ r j (r a - r)] log [r0/(r0-r)]= 0.65196

9.126

0 = 1.33/1/2u - (2.04/1/2u){log [r0/(r0 - r)]}

r0/(r0 - r ) = antilog 0.65196 = 4.487 r = 0.776ro

The flow rate in a 12-in-diameter pipe is 8 cfs. The flow is known to be turbulent, and the centerline velocity is 12.0 fps. Determine the velocity profile, and determine the head loss per foot of pipe. 12.0 = (10.19)(1 +1.33/“)

f v = Q / A = 8/[(^)(i)2/4] = 10.19 ft/s «max = (w)(l + 1.33f 1 1 2 )

/ = 0.01784 h f = ( f ) (L / d ) (v 2 / 2 g ) = 0.01784[l/(j§)]{10.192/[(2)(32.2)]} = 0.0288 ft per foot r0 = (//4)(p)(u2/2) = (0.01784/4)(p)(10.192/2)

(r0/p)1/2 = 0.4812

U = «ma* - 5.75(r0/p)1/2 log [ r 0 / (r u - r)] For r = 0, u = 12.0 - (5.75)(0.4812) log [6/(6 - 0)] = 12.0 ft/s. For r = 2, u = 12.0 - (5.75)(0.4812) log [6/(6 2)] = 11.5 ft/s. For r = 4, u = 12.0 - (5.75)(0.4812) log [6/(6 - 4)] = 10.7 ft/s. For r = 5, u = 12.0 (5.75)(0.4812) log [6/(6 - 5)] = 9.85ft/s. For r = 5 . 5 , u = 12.0- (5.75)(0.4812) log [6/(6-5.5)] = 9.01 ft/s. For r = 5.9, u = 12.0 - (5.75)(0.4812) log [6/(6 - 5.9)] = 7.08 ft/s. For r = 5.99, u = 12.0 - (5.75)(0.4812) log [6/(65.99)] = 4.31 ft/s. 9.127

Tung oil (s.g. = 0.82) flows at a temperature of 80 °F (v = 2.21 x 10 -5 ft2/s) in a 2-in-diameter smooth brass pipeline at 10 gpm. Find the head loss per mile. Q = (10)(0.002228) = 0.02228 ft3/s v = Q/ A = 0 . 02228/[(JT)(£)2/4] = 1.021 ft/s

f

h f = (f ) (L / d ) (v 2 / 2 g ) N R = d v/ v = (£)(1.021)/(2.21 X 10”5) = 7.70 x 103 From Fig. A-5 for smooth pipe, / = 0.0333. h f = 0.0333[5280/(n)]{1.0212/[(2)(32.2)]} = 17.1 ft per mile. 9.128

Water at 40 °C flows in a 20-cm-diameter pipe with v = 5.1 m/s. Head loss measurements give / = 0.022. Determine the value of e and find the shear stress at the wall of the pipe and at r = 3 cm. I N R = d v/ v = (0.20)(5.l)/(6.56 x 10 7). From Fig. A-5, e/ d = 0.0015, e = (20)(0.0015) = 0.0300 cm; r0 = f p v 2 / 8 = (0.022)(992)(5.l)2/8 = 71.0 Pa; r = (r0)(r/r0) = (71.0)(0.03) = 21.3 Pa.

9.129

Water at 15 °C flows through a 200-mm-diameter pipe with e = 0.01 mm. (a) If the mean velocity is 3.6 m/s, what is the nominal thickness 6, of the viscous boundary layer? (b ) What will be the boundary layer thickness if the velocity is increased to 6.0 m/s? f (a)

^ = 32.8v/ (vf 1 1 2 ) N R = d v/ v = (0.200)(3.6)/(1.16 x 10~6) = 6.21 x 10s

e/ d = (0.01/10)/20 = 0.0000500 From Fig. A-5, / = 0.0133. 6, = (32.8)(1.16 x 10"6)/[(3.6)(0.0133)1/2] = 9.16 x 10“5 m, or 91.6 pm.

(b )

N R = (0.200)(6.0)/(l. 16 x 10"6) = 1.03 x 106 6

I/2

/ = 0.0126

<51 = (32.8)(1.16xlO- )/[(6.0)(0.0126) ] = 5.65xlO-5m or 56.5 pm

FLOW IN CLOSED CONDUITS D 227 9.130

When water at 50 °F flows at 3.2 cfs in a 2-ft pipeline, the head loss is 0.0004 ft per foot. What will be the head loss when glycerin at 68 °F flows through the same pipe at the same rate? h f = (f ) (L / d ) (v 2 / 2 g ) v = Q/ A = 3.2/[(jr)(f|)2/4] = 1.0186 ft/s

f For water:

0.0004 = (/)[1/(2)]{1.01867[(2)(32.2)]} f = 0.04966 N R = p d v/ p = (1.94)(2)(1.0186)/(2.72 x 10-5) = 1.45 x 105 (turbulent) From Fig. A-5, e/ d = 0.021. For glycerin: N R = (2.44)(2)(1.0186)/(3.11 x 10“2) = 160 (laminar) / = 6 4 / N R = 64/160 = 0.4000 h f = 0.4000[l/(2)]{1.01862/[(2)(32.2)]} = 0.00322 ft per ft 9.131

Air flows at 50 lb/min in a 4-in-diameter welded steel pipe (e = 0.0018 in) at 100 psia and 60 °F. Determine the head loss and pressure drop in 200 ft of this pipe. Assume the air to be of constant density.

I hf

= (f ) (L / d ) (v 2 / 2 g )

NR =

p d v/ p p = p / RT = (100)(144)/[(1716)(460 + 60)] = 0.01614 slug/ft 3

W = y Av = p g Av § = (0.01614)(32.2)[(JT)(£)74](U) V = 18.37 ft/s NR

= (0.01614)(£)(18.37)/(3.74 X 10~7) = 2.64 x 105 e/ d = 0.0018/4 = 0.00045

From Fig. A-5, / = 0.018. h f = 0.018[200/(£)]{18.372/[(2)(32.2)]} = 56.6 ft of air, Ap = p g h f = (0.01614)(32.2)(56.6) = 29.4 lb/ft2, or 0.204 lb/in2. 9.132

Air flows at an average velocity of 0.5 m/s through a long, 3.2-m-diameter, circular tunnel. Find the head-loss gradient at a point where the air temperature and pressure are 16 °C and 109 kPa abs, respectively. Assume e = 2 mm. Find also the shear stress at the wall and the thickness of the viscous sublayer.

I

h f / L = (f / d ) (v 2 / 2 g ) p =p / R T = (109)(1000)/[(287)(273 + 16)] = 1.314 kg/m3 N R = p d v/ p = (1.314)(3.2)(0.5)/(1.79 X HT5) = 1.17 x 10s e/ d = (0.002)/3.2 = 0.000625

From Fig. A-5,/ = 0.021. h f IL = (0.021/3.2){0.52/[(2)(9.807)]} = 8.36 x 10-5 m/m or 83.6jum/m To

=f p v 2 / 8 = (0.021)(1.314)(0.5)2/8 = 0.862 mPa

6, = 32.8v/(iO = (32.8)(p / p )/ ( vf m ) = (32.8)(1.79 x 10-5/1.314)/[(0.5)(0.021)1/2] = 0.00620 m or 6.20 mm

9.133

Repeat Prob. 9.132 for the average velocity 5.0 m/s.

I From Fig. A-5, for N R = (5.0/0.5)(l. 17 x 10s) = 1.17 x 106 and e/ d = 0.000625, / = 0.018. h f IL = (f / d ) ( v 2 / 2 g ) = (0.018/3.2){5.02/[(2)(9.807)]} = 7.17 X HT3 m/m T0 = f p v 2 / 8 = (0.018)(1.314)(5.0)2/8 = 73.9 mPa

6 1 = 3 2 . 8 v/ (vf m ) = (3 2 . 8 ) ( f i / p ) / ( vf m ) = (32.8)(1.79 x 10 5/1.314)/[(5.0)(0.018)1/2] = 6.66 x 10“4 m or 0.660 mm 9.134

Air at 20 °C and atmospheric pressure flows with a velocity of 6 m/s through a 50-mm-diameter pipe. Find the head loss per meter of pipe if e = 0.0025 mm.

I

h f / L = (f )( l / d )( v 2 / 2 g )

NR =

d v/ v = (0.050)(6)/(1.51 x 10-5) = 1.99 x 104

e/ d = 0.0025/50 = 0.000050 From Fig. A-5,/ = 0.026. h f / L = 0.026[l/0.050]{62/[(2)(9.807)]} = 0.954m/m.

228

a CHAPTER 9

9.135

What is the head loss per foot of pipe when oil (s.g. = 0.88) having a viscosity of 1.9 x 10 4 lb • s/ft2 flows in a 2-in-diameter welded steel pipe at 0.15 cfs? f

h f / L = (f / d )( v 2 / 2 g ) v — Q / A = 0. 15/[(*)(£)74] = 6.875 ft/s N R = p d v/ p = [(0.88)(1.94)](H)(6.875)/(1.9 X 10“4) = 1.03 X 104 e/d = 0.00015/(ft) = 0.00090

From Fig. A-5, / = 0.033. h f / L = [0.033/(£)]{6.8752/[(2)(32.2)]} = 0.145 ft/ft.

9.136

Water at 50 °F flows in a 36-in-diameter concrete pipe (e = 0.02 in). For a flow rate of 202 cfs, determine N R and Toil v = Q/ A = 202/[(*r)(ff)74] = 28.58 ft/s N R = du/v = (f|)(28.58)/(1.40 x 10'5) = 6.12 X 106 r 0 = f p v 2/8

e/ d = 0.02/36 = 0.000556

From Fig. A-5,/= 0.0175. T0

9.137

= (0.0175)(1.94)(28.58)78 = 3.47 lb/ft2

What is the flow regime in Prob. 9.136?

f

6, = 32.8v/(tO = (32.8)(1.40 x 10-5)/[(28.58)(0.0175),/2] = 0.000121 ft

Since [6! = 0.000121] < [0.3e = (0.3)(0.02/12) = 0.000500], regime is “rough.” 9.138

Find the flow rate if water at 60 °F experiences a head loss of m ft/ft in 6-in cast iron pipe.

I

h f / L = (f ) (l / d ) (v 2 / 2 g ) *«(/)[ l/(£)]{«7[(2)(32.2)]}

K=

0.2809/V/

Try t/ = 2 ft/s: N R = d v/ v = (n)(2)/(1.21 x 10'5) = 8.26 x 104, e/d = 0.00085/(£) = 0.00170. From Fig. A-5, / = 0.0245. v = 0.2809/VO.0245 = 1.79 ft/s. Try t> = 1.79 ft/s: N R = (^)(1.79)/(1.21 X 10~5) = 7.40 X 104, / = 0.025, v = 0.2809/V0.025 = 1.78 ft/s. Try v = 1.78 ft/s: N R = (£)(1.78)/(1.21 X 10'5) = 7.40 X 104, / = 0.025 (O.K.); Q = Av = [(jr)(£)2/4](1.78) = 0.350 ft7s. 9.139

Kerosene with kinematic viscosity 5.1 x 10~7 m2/s flows in a 30-cm-diameter smooth pipe. Find the flow rate when the head loss is 0.4 m per 100 m.

I

h f = (J) (L / d ) (v 2 / 2 g )

0.4 = (/)[100/(^)]{n2/[(2)(9.807)]}

u = 0.1534/ \ f f

Try u = 1 m/s: N R = d v/ v = (^)(l)/(5.1 X 10'7) = 5.88 X 10s. From Fig. A-5,/ = 0.0128. t; = 0.1534/V0.0128 = 1.36 m/s. Try v = 1.36 m/s: N R = (^)(1.36)/(5.1 x 10'7) = 8.00 x 105 , f = 0.0122, v = 0.1534/V0.0122 = 1.39 m/s. Try t; = 1.39 m/s: N R = (i&)(1.39)/(5.1 x 10'7) = 8.18 x 105, / = 0.0122 (O.K.); Q= Av = [(*)(t&)74](1.39) = 0.0983 m7s. 9.140

A pipe with e = 0.00015 ft is required to carry fluid of kinematic viscosity 0.00021 ft 2/s at the rate of 8.0 cfs. If the head loss is to be 0.004 ft/ft, calculate the pipe diameter.

I hf/L

= (f / d ) (v 2 / 2 g ) v = Q / A = 8.0/(jrd2/4) = 10.19/d2 d = 3.320/1/5

0.004= (//d){(10.19/d2)7[(2)(32.2)]}

N R = d v/ v = (d)(10.19/d2)/0.00021 = 48 524/d

Try d = 1 ft: N R = 48 524/1 = 4.85 x 104, e/ d = 0.00015/1 = 0.00015. From Fig. A-5, / = 0.0215. d = (3.320)(0.0215)1/s = 1.54 ft. Try d = 1.54ft: TV* = 48 524/1.54 = 3.15 X 10 4, e/ d = 0.00015/1.54 = 0.0000974, / = 0.0235, d = (3.320)(0.0235)1/s = 1.57 ft. Try d = 1.57 ft: N R = 50 950/1.57 = 3.25 x 104, e/ d = 0.00015/1.57 = 0.0000955,/ = 0.0235 (O.K.). Hence, d = 1.57 ft, or 18.8 in.

FLOW IN CLOSED CONDUITS 0 229

9.141

(a) Find the shear stress on 40-in-diameter asphalted iron pipe if the fluid is water at 72 °F and the average

velocity is 10 fps. (b ) What will be the shear stress if the average velocity is reduced to 5 fps?

I (a)

r0=/pu2/8 N R = d v/ v N R = (T§)(10)/(1.02 X 10~5) = 3.27 x 106 e/ d = 0.0004/(ff) = 0.00012 From Fig. A-5, / = 0.0127. r0 = (0.0127)(1.93)(10)2/8 = 0.306 lb/ft2 N R = (ff)(5)/(1.02 X 10~5) = 1.63 x 106

(ft)

/ = 0.0132

r„ = (0.0132)(1.93)(5)2/8 = 0.07% lb/ft2

9.142

A straight steel pipeline (e = 0.00015 ft) slopes downward at a small angle 6 , where sin 8 * 0 = 0.01523. For gravity flow of oil (v = 0.0006 ft2/s) at 10 ft3/s, what pipe size is needed? f

sin 0 = h f / L = (f / d ) (v 2 / 2 g ) v = Q / A = 10/(n:d2/4) = 12.73/d2 0.01523 = (//d){(12.73/
d = 2.777/1'5 N R = d v/ v = 00(12.73/d2)/0.0006 = 21 217Id Try d = 1 ft: N R = 21217/1 =2.12 X 10\ e/ d = 0.00015/1 = 0.00015. From Fig. A-5, / = 0.0265. d = (2.777)(0.0265)1/s = 1.34 ft. Try d = 1.34 ft: N R = 21217/1.34 = 1.58 x 104, e/ d = 0.00015/1.34 = 0.00011, / = 0.0284, d = (2.777)(0.0284)1/5 = 1.36 ft. Try d = 1.36ft: N R = 21 217/1.36 = 1.56 x 104, e/ d = 0.00015/1.36 = 0.00011, / = 0.0284 (O.K.). Hence, d = 1.36 ft, or 16.3 in.

9.143

Water at 140 °F flows in a 0.824-in-diameter iron pipe (e = 0.00015 ft) of length 400 ft between points A and B. At point A the elevation of the pipe is 104.0 ft and the pressure is 8.50 psi. At point B the elevation of the pipe is 100.3 ft and the pressure is 9.00 psi. Compute the flow rate. P A / Y + v \ / 2 g + z A =p B / y + v 2 B / 2 g + z B + h L

f

(8.50)(144)/61.4 + v 2 J2 g + 104.0 = (9.00)(144)/61.4 + v% / 2 g + 100.3 + h L v \ / 2 g = u|/2g h L = 2.52ft h f = h , . = (f ) (L / d )( v 2 / 2 g ) 2.52 = (/)[400/(0.824/12)] (u2/[(2)(32.2)]} u = 0.1669/Yf Try v = 1 ft/s: N R = dv/v = (0.824/12)(l)/(5.03 x 10"6) = 1.37 x 104, e/d = 0.00015/(0.824/12) = 0.0022. From Fig. A-5,/ = 0.0325. v = 0.1669/V0.0325 = 0.926 ft/s. Try v = 0.926ft/s: N R = (0.824/12)(0.926)/(5.03 x 10'6) = 1.26 x 104, / = 0.0330, u = 0.1669/VO.0330 = 0.919 ft/s. Try v = 0.919 ft/s: N R = (0.824/12)(0.919)/(5.03 X lO'6) = 1.25 x 104, / = 0.0330 (O.K.); Q = Av = [(jr)(0.824/12)2/4](0.917) = 0.00339 ft3/s.

9.144

Air at 50 psia and 160 °F flows in a 1-ft by 1.5-ft by 1000-ft duct at the rate of 1 lb/min. Find the head loss if e = 0.0005 in.

I

h f =(f )( L / d )( v 2 / 2 g ) d = 4 R h R*=A/p; = (l)(1.5)/(l + l + 1.5 + 1.5) = 0.300 ft d = (4) (0.300) = 1.20 ft

W = y Av y = p / RT = (50)(144)/[(53.3)(460 + 160)] = 0.2179 lb/ft3

1/60 = 0.2179[(l)(1.5)](u) v = 0.05099 ft/s h f = (/)(1000/1.20){0.050992/[(2)(32.2)]} = 0.03364/ N R = d v/ v = (1.20)(0.05099)/(2.06 x 10“4) = 297 (laminar) / = 64/ N R = 64/297 = 0.2155 h f = (0.03364)(0.2155) = 0.00725 ft

9.145

Find the approximate rate at which 60 °F water will flow in a conduit shaped in the form of an equilateral triangle if the head loss is 2 ft per 100 ft. The cross-sectional area of the duct is 120 in2, and e = 0.0018 in.

I First, find the length of each side (s ) of the cross section (see Fig. 9-29): A = b h / 2 120 = (x +X)(V3T)/2 x = 8.324 in 5 = 2x = (2)(8.324) = 16.65 in h f = (f ) (L / d ) (v 2 / 2 g )

R h = A/ p „ = 120/[(3)(16.65)] = 2.402 in or 0.2002 ft

d = 4 R h = (4)(0.2002) = 0.8008 ft 2 = (/)(100/0.8008){u 2/[(2)(32.2)]}

u = 1.016/v7

230

a CHAPTER 9 Try v = 10 ft/s: N R = d v/ v = (0.8008)(10)/(1.21 x 10~5) = 6.62 x 105, e/ d = (0.0018/12)/0.8008 = 0.000187. From Fig. A-5, / = 0.0150. v = 1.016/V0.0150 = 8.30 ft/s. Try v = 8.30 ft/s: N R = (0.8008)(8.30)/(1.21 x 10“5) = 5.49 X 105, / = 0.0155, v = 1.016/V0.0155 = 8.16 ft/s. Try t> = 8.16 ft/s: N R = (0.8008)(8.16)/(1.21 X HT5) = 5.40 x 105,/ = 0.0155 (O.K.); Q = A v = (]fj)(8.16) = 6.80ft3/s.

Fig. 9-29

9.146

When fluid of weight density 50 lb/ft3 flows in a 6-in-diameter pipe, the frictional stress between the fluid and the pipe wall is 0.5 lb/ft2. Calculate the head loss per mile of pipe. If the flow rate is 2.5 cfs, how much power is lost per mile?

f Rh= d / 4 = (£>/4 = 0.1250 ft h f = (r 0 ) (L / R h y ) = 0.5{5280/[(0.1250)(50)]} = 422.4 ft per mile p = Q y h { = (2.5)(50)(422.4) = 52 800 ft • lb/s per mile = 52 800/550 = 96.0 hp per mile

9.147

Prove that for a constant rate of discharge and a constant value of / the friction head loss in a pipe varies inversely as the fifth power of the diameter.

f v = Q/ A = 4 Q / xd 2 h f = (f )( L / d )( v 2 / 2 g ) = (f ) (L / d )[ (4 Q/ xd 2 ) 2 / 2 g] = (f ) (L / d 5 ) (8 Q 2 / : z 2 g ) Thus for constant/and constant Q , h f «1/d5.

9.148

Two long pipes are used to convey water between two reservoirs whose water surfaces are at different elevations. One pipe has a diameter twice that of the other. If both pipes have the same value of / and if minor losses are neglected, what is the ratio of the flow rates through the two pipes?

h f = (f )( L / d )( v 2 / 2 g ) = A elevation h f «Q 2 / d 5 (from Prob. 9.147)

f

Q 1 /) i = {hf)i Therefore, Q \ / d \ = Q \ J d \ , Q J Q , = (d 2 / d 1)5/2 = 2 s n = 5.66. Thus the flow in the larger pipe will be 5.66 times that in the smaller one.

9.149

Points C and D , at the same elevation, are 500 ft apart in an 8-in pipe and are connected to a differential gage by means of small tubing. When the flow of water is 6.31 cfs, the deflection of mercury in the gage is 6.43 ft. Determine the friction factor/. I P c / Y + v c/ 2 g + z c = P D / Y + V 2 d / 2 g + z D + h f . Since v 2 c / 2 g = v 2 J2 g and z c = z D , Pj y - p D / Y = h f = (6.43)(13.6 - 1) = 81.02 ft, v = Q / A = 6.31/[(n:)(^)2/4] = 18.08 ft/s, h f = (f ) (L / d ) (v 2 / 2 g ) = (/)[500/(£)]{18.082/[(2)(32.2)]} = 3807/, 81.02 = 3807/, / = 0.0213.

9.150

Oil flows from tank A through 500 ft of 6-in new asphalt-dipped cast iron pipe to point B, as shown in Fig. 9-30. What pressure in pounds per square inch will be needed at A to cause 0.450 cfs of oil to flow? (s.g. = 0.840; v = 2.27 x 10“5 ft2/s; e = 0.0004 ft.) I P A I Y + v 2 J2 g +

- P B I Y + vi/2g + z B + h L v B = Q/ A B = 0.450/[(^)(^)2/4] = 2.292 ft/s

h L = h f = (f ) (L / d ) (v 2 / 2 g ) = (/)[500/(£)]{2.2927[(2)(32.2)]} = 81.57/ />„/[(0.840X62.4)] + 0 + 80.0 = 0 + 2.292 2/[(2)(32.2)] + 100.0 + 81.57/ p A = 1053 + 4276/ N R = d v / v = (£)(2.292)/(2.27 x 10~5) = 5.05 x 10“ e/ d = 0.0004/(£) = 0.000800 From Fig. A-5, / = 0.0235. p A = 1053 + (4276)(0.0235) = 1153 lb/ft2, or 8.01 lb/in2.

FLOW IN CLOSED CONDUITS

0 231

Fig. 9-30

9.151

An old 12-in by 18-in rectangular duct carries air at 15.2 psia and 68 °F through 1500 ft with an average velocity of 9.75 ft/s. Determine the loss of head and the pressure drop, assuming the duct to be horizontal and the size of the surface imperfections is 0.0018 ft.

I

R h = A/p w = (T§)(T§)/(H +1§ + H + H) = 0.300 ft d = 4f?, = (4)(0.300) = 1.20ft h f = (f)(L/d)(v 2 /2g) = (/)(1500/1.20){9.752/[(2)(32.2)]} = 1845/

N R = d v/ v = (1.20)(9.75)/[(14.7/15.2)(1.64 x 10“4)] = 7.38 x 104 (turbulent) el d = 0.0018/1.20 = 0.00150 From Fig. A-5, / = 0.024. h f = (1845)(0.024) = 44.28 ft of air

9.152

Ap = yh , = [(15.2/14.7)(0.0750)](44.28)/144 = 0.0238 lb/in 2

What size of new cast iron pipe, 8000 ft long, will deliver 37.5 cfs of water at 70 °F with a drop in the hydraulic grade line of 215 ft?

I

PA l Y + v 2 A l 2 g + z A =p B l y + v l l 2 g + z B + h L [ (P A / Y + z A ) ~ (P B / Y + z B )] = h L [(P A / 7 + Z A ) ~ (P B I Y + z B )] = HGL = 215 ft

v = Q / A = 37.5/(nrd2/4) = 47.75/d2

h L = h f = (f )(L / d ) ( v 2 / 2 g ) = (/)(8000/d){(47.75/d2)2/[(2)(32.2)]} = 283 238f i d 5 215 = 283 238f / d s 6

d = 4.207f v s

N R = d v/ v = (d)(47.75/d2)/(1.05 x 10"5) = 4.55 X 106 / d

6

Try d = 2 ft: N R = (4.55 x 10 )/2 = 2.28 x 10 , e/d = 0.00085/2 = 0.000425. From Fig. A-5, / = 0.0164. d = (4.207X0.0164)1'5 = 1.85 ft. Try d = 1.85 ft: N R = (4.55 X 106)/1.85 = 2.46 x 106, e/d = 0.00085/1.85 = 0.000459,

/ = 0.0164 (O.K.). Hence, d = 1.85 ft, or 22.2 in.

9.153

What rate of flow of air at 68 °F will be carried by a new horizontal 2-in-diameter steel pipe at an absolute pressure of 3 atm and with a drop of 0.150 psi in 100 ft of pipe? Use e = 0.00025 ft. f At 68 °F and standard atmospheric pressure, y = 0.0752 lb/ft3 and v = 1.60 x 10”4 ft2/s. At a pressure of 3 atm, y = (0.0752)(3) = 0.2256lb/ft3 and v = (1.60 x 10“4)/3 = 5.333 x 10 5 ft2/s. h , = (f )( L / d )( v 2 / 2 g ), (0.150)(144)/0.2256 = (/)[100/(^)]{u2/[(2)(32.2)]}, v = 3.206/V/. Try v = 10 ft/s: N R = d v/ v = (£)(10)/(5.333 x IQ"5) = 3.13 x 104, e/d = 0.00025/(i|) = 0.00150. From Fig. A-5, / = 0.027. u = 3.206/VO.027 = 19.51 ft/s. Try v = 19.51 ft/s: N R = (£)(19.51)/(5.333 X 10“5) = 6.10 x 104, / = 0.0248, v = 3.206/V0.0248 = 20.36 ft/s. Try v = 20.36 ft/s: N R = (£)(20.36)/(5.333 x 10~5) = 6.36 X 104,

/ = 0.0248 (O.K.); Q = Av = [(/r)(/2)2/4](20.36) = 0.444 ft3/s.

9.154

Determine the nature of the distribution of shear stress at a cross section in a horizontal, circular pipe under steady flow conditions. f For the free body in Fig. 9-31a, since the flow is steady, each particle moves to the right without acceleration. Hence, the summation of the forces in the * direction must equal zero. (p , )(j r r 2 ) - (p 2 ) (n r 2 ) (r)(2jrrL) = 0 or

z = { P \- P2 )(r )/ {2 L )

(1 )

When r = 0, the shear stress r is zero; and when r = r0, the stress r0 at the wall is a maximum. The variation is linear and is indicated in Fig. 9-31f>. Equation (1) holds for laminar and turbulent flows as no limitations concerning flow were imposed in the derivation. Since (p, -p2)/y represents the drop in the energy line, or the lost head h L , multiplying Eq. (1) by y/ y yields r = (yr / 2 L )[ (p 1 -p 2 )/ y] or *

=

(yh J 2 L ) (r ) (2

)

9.155

Develop the expression for shear stress at a pipe wall. I h L = (f ) (L / d ){ v 2 / 2 g ). From Prob. 9.154, h L = 2r0 L / yr 0 = 4r0 L / yd , 4r0 L / yd = (f ) ( L / d ) (v 2 / 2 g ) , r0 = f yv 2 / S g =/pu2/8.

232 0 CHAPTER 9 Lost head HL

9.156

For steady, laminar flow (a) what is the relationship between the velocity at a point in the cross section and the velocity at the center of the pipe, and (6) what is the equation for velocity distribution? r = —(n ) (d v/ d r ) = (p, —p 2 ) ( r )/ (2 L ) (from Prob. 9.154)

I (a )

~ (p ) (d v/ d r ) = (p, — p 2 )( r ) / (2 L ) Since (pt — p2)/L is not a function of r ,

-o—v-

(JP I -

Pi V 4/iL (i)

But the lost head in L feet is h L = (p l — p 2 )/ y , hence, V

yhLr2 ~ *~ 4pL

(2)

V

( b ) Since the velocity at the boundary is zero, when r = r „ , v = 0 in Eq. (1 ), we have _ i p l P z ) r o (at centerJjne) 4 pL

(2)

Thus, in general,

(4 ) 9.157

Develop the expression for the loss of head in a pipe for steady, laminar flow of an incompressible fluid. Refer to Fig. 9-3Id. _

f vd A f (v ) (2 Jirdr)

t^avQ, j

A

_JO dA

/_(2Jv)(p

1-p2) p

nrl

(j r r 2 0 )(4 f i

f°

(r l -r 2 )(r d r )

Jo

L) (i) ,, _ (P i - P 2)(r l ) av 8 pL Thus for laminar flow, the average velocity is half the maximum velocity v , . in Eq. (3) of Prob. 9.156. Rearranging Eq. (1), we obtain , P1-P2 8pLvay 32pLvay n Lall —fluids — = and conduits. 35 These expressions apply for laminar flow of in all pipes y yn yd 2

9.158

Determine (a) the shear stress at the walls of a 12-in-diameter pipe when water flowing causes a measured head loss of 15 ft in 300 ft of pipe length, (6) the shear stress 2 in from the centerline of the pipe, (c) the shear velocity, («f) the average velocity for an/value of 0.50, and (e) the ratio v/ v t .

(2 )

FLOW IN CLOSED CONDUITS 0 233 I (a) T 0 = yh L r J2 L = (62.4)(15)[({|)/2]/[(2)(300)] = 0.780 lb/ft 2, or 0.00542 lb/in2. (ft) Since T varies linearly from centerline to wall, r = (0.00542)(|) = 0.00181 lb/in 2. (c) v , = V U p = V0.780/1.94 = 0.634ft/s. i d ) T „ = f p v 2 / 8 , 0.780 = (0.050)(1.94)(u2)/8, v = 8.02 ft/s. (e ) r„ = ( p ) ( v / y ) , v — p i p , T 0 = p v ( v / y ) , T0 / p = ( v ) ( v / y ) = v l = ( v ) ( v / y ) , v / v l = y / v , v / v * = v*y/v. 9.159

If in Prob. 9.158 the water is flowing through a 3-ft by 4-ft rectangular conduit of the same length with the same lost head, what is the shear stress between the water and the pipe wall? f

R h = A/ p w = (3)(4)/(3 + 3 + 4 + 4) = 0.8571 ft =

r (yh L / L )( R H ) = [(62.4)(15)/300](0.8571) = 2.67 lb/ft2 or 0.0186 lb/in2 9.160

Medium lubricating oil (s.g. = 0.860) is pumped through 1000 ft of horizontal 2-in pipe at the rate of 0.0436 cfs. If the drop in pressure is 30.0 psi, what is the absolute viscosity of the oil? f Assuming laminar flow,

Pi ~ Px 32p L v „ n . — n_ S / I I I .11 y yd2

(from Prob. 9.157)

i>av = Q l A = 0.0436/[(nr)(n)2/4] = 1.998 ft/s (30.0)(144)/[(0.860)(62.4)] = (32)(ju)(1000)(1.998)/{[(0.860)(62.4)](^) 2} p = 0.00188 lb • s/ft2 » N R = p d v/ p = [(0.860)(1.94)](f2)(1.998)/0.00188 = 296 (laminar) 9.161

A horizontal wrought iron pipe, 6-in inside diameter and somewhat corroded, is transporting 4.50 lb of air per second from A to B. At A the pressure is 70 psia and at B the pressure must be 65 psia. Flow is isothermal at 68 °F. What is the length of pipe from A to B? Use e = 0.0013 ft. |

Pi ~ P 2_ 2[2 In j vj vi ) + {f Yi

)(LI dj ) (v 2 J2 g )

I+P2/P1 3

y, = (0.0752)(70/14.7) = 0.3581 lb/ft y2 = (0.0752)(65/14.7) = 0.3325 lb/ft 3 W = y Av 4.50 = (0.3581)[(JT)(^)2/4](U,) V2 = 64.00 ft/s 4.50 = 0.3325[(;r)(£)2/4](u2)

v t = 68.93 ft/s

N R = d v / v = (£)(64.00)/[(14.7/70.0)(1.60 x lO"4)] = 9.52 x 105 e/ d = 0 . 0 0 1 3 / ( &) = 0.0026 From Fig. A-5, / = 0.025. (70 - 65)(144) 2(2 In (68.93/64.00) + 0.025[L/(^)]}{64.00 2/[(2)(32.2)]} 1 + 65 1 + 70 0.3581 9.162

Heavy fuel oil flows from A to B through 3000 ft of horizontal 6-in steel pipe. The pressure at A is 155 psi and at B is 5.0 psi. The kinematic viscosity is 0.00444 ft 2/s and the specific gravity is 0.918. What is the flow rate?

f

Assuming laminar flow, from Eq. (2) of Prob. 9.157, P 1-P 2 32pLv, y (32)(vp)(Luav)

(155 - 5.0)(144) 32{(0.00444)[(0.918)(1.94)]}(3000)(uav) (0.918)(62.4) ~ [(0.918)(62.4)](£)2

y ~ yd 2 ~ yd 2

uav = 7.11 ft/s

N R = dv/v = (^)(7.11)/0.00444 = 808 Q=Av~

9.163

L = 607 ft

[(TT)(£)2/4](7. 11)

(laminar)

3

= 1.40 ft /s

What size pipe should be installed to carry 0.785 cfs of heavy fuel oil (v = 0.00221 ft 2/s, s.g. = 0.912) at 60 °F if the available lost head in the 1000-ft length of horizontal pipe is 22.0 ft?

f

Assuming laminar flow, h f = ~^ V v

= Q / A = 0.785/(^d2/4) = 0.9995/d 2

p = pv = [(0.912)(1.94)](0.00221) = 0.003910 lb ■ s/ft 2

22.0 = (32)(0.003910)(1000)(0.9995/d2)/{[(0.912)(62.4)](d2)}

d = 0.562 ft or 6.75 in N R = dv/v = (0.562)(0.9995/0.5622)/0.00221 = 805 (laminar)

234 0 CHAPTER 9 9.164

Determine the head loss in 1000 ft of new, uncoated 12-in-ID cast iron pipe when water at 60 °F flows at 5.00 ft/s. Use e/ d = 0.0008. h f = (f )( L / d )( v 2 / 2 g )

I

N R = d v / v = (j§)(5.00)/(1.21 x 10~5) = 4.13 x 105

From Fig. A-5, f = 0.0194. h f = 0.0194[1000/(H)]{5.007[(2)(32.2)]} = 7.53 ft. 9.165

Rework Prob.

9.164 if the liquid is medium fuel oil at 60 °F (v = 4.75 x 10~5 ft2/s) flowing at the same velocity,

f

hf

N R = d v/ v = (||)(5.00)/(4.75 x 10-5) = 1.05 x 105

= (f XL / d X v^g )

From Fig. A-5,/ = 0.0213. h f = 0.0213[1000/(H)]{5.007[(2)(32.2)]} = 8.27 ft. 9.166

Points A and B are 4000 ft apart along a new 6-in-ID steel pipe. Point B is 50.5 ft higher than A and the pressures at A and B are 123 psi and 48.6 psi, respectively. How much medium fuel oil at 70 °F will flow from A to B? Use s.g. = 0.854, v = 4.12 X 10“5 ft2/s, e = 0.0002 ft. I

PA/Y +

V2a/2g

+ z A =p B / y + vl / 2 g +z B + h L

(123) (144) / [(0.854) (62.4)] + v \ ! 2 g + 0 = (48.6)(144)/[(0.854)(62.4)] + u|/2g + 50.5 + h L v 2 J2 g = v% / 2 g h L = 150.5 ft = h f = (f )( L / d )( v 2 / 2 g ) 150.5 = (/)[4000/(£)]{u2/[(2)(32.2)]} v = 1.1 0 1 / Vf Try v = 10 ft/s: N R = d v / v = (£)(10)/(4.12 x 10~5) = 1.21 x 105, e / d = 0.0002/(£) = 0.000400. From Fig. A-5, / = 0.0195. v = 1.101/V0.0195 = 7.884 ft/s. Try v = 7.884 ft/s: N R = (H)(7.884)/(4. 12 x 10~5) = 9.57 x 104, / = 0.0195 (O.K.); G = A u = [(^)(^)2/4](7.884) = 1.55ft3/s. 9.167

How much water (60 °F) would flow under the conditions of Prob. 9.166. p A / y + v A / 2 g + z A =p B / Y + v 2 B / 2 g + z B + h L

I

(123)(144)/62.4 + v \ / 2 g + 0 = (48.6)(144)/62.4 + u|/2g + 50.5 + h L v \ / 2 g = vl / 2 g h L = 121.2 ft = h f = (f )( L / d )( v 2 / 2 g ) 121.2 = (/)[4000/(£)]{u2/[(2)(32.2)]} v = 0.9878/V/

9.168

Try v = 10 ft/s: N R = d v / v = (£)(10)/(1.21 x 10~5) = 4.13 x 105, e/ d = 0.0002/(£) = 0.000400. From Fig. A-5, / = 0.0172. v = 0.9878MT0172 = 7.532 ft/s. Try v = 7.532 ft/s: N R = (£)(7.532)/(1.21 x 10~5) = 3.11 x 105, / = 0.0176, v = 0.9878/V0.0176 = 7.446 ft/s. Try v = 7.446ft/s: N R = (£)(7.446)/(1.21 x 10~5) = 3.08 x 105, / = 0.0176 (O.K.); Q = A v = [(jr)(£)74](7.446) = 1.46ft3/s. To transport 300 cfs of air, p = 16 psia, T = 68 °F, with a head loss of 3 in of water per 1000 ft, what size galvanized pipe is needed? (e = 0.0005 ft.)

I

d = 0 . 6 6 [ (e 1 2 5 ) (L Q 2 / g h f y 7 5 + (v ) (Q ) 9 \ L / g h f ) 5 2 f M Y

= p / R T = (16)(144)/[(53.3)(460 -I- 68)] = 0.08187 lb/ft3 h f = (£0(62.4/0.08187) = 190.5 ft of air i J (1000)(300)21475 d = 0.66 {(°- 0005125) L(32.2)(190.5) ]

r

475

9.169

mno

-ISZ-.OIM

t ( 1. 64xlO( 300r[

] } -2.84 ft

Two tanks of a solvent (p = 0.05 Pa • s, y = 8 kN/m3) are connected by 300 m of commercial steel pipe. What size must the pipe be to convey 50 L/s, if one tank is 4 m higher than the other?

I

d = 0.66[(e,25)(LG7g^)4 75 + (v ) (Q ) 9 A (L / g h f ) 5 2 ] 0 0 4 v = p / p = p g / y = (0.05)(9.807)/[8 x 103] = 6.129 x HT5 m2/s 0.( d = 0.66 {((0.000046

xi.25\f

(300)(T^O)214'75

1 (9.807)(4) J

OAA 15.210.04

[ wm*)} 1 -a

222 m

9.170 Calculate the diameter of a wooden conduit (e = 0.006 ft) that is to carry 300 ft3/s of water at 60 °F a distance of 1000 ft with a head loss of 1.1 ft. I

d = 0.66[(e'25)(LQ2/g/i/)4 75 + (v )( Q ) 9 \ L / g h f ) 5 2 ] 0 0 4 = 7.59 ft

FLOW IN CLOSED CONDUITS 0 235 f.171 An old pipe 2 m in diameter has a roughness of € = 30 mm. A 12-mm-thick lining would reduce the roughness to e = 1 mm. How much would pumping costs be reduced per kilometer of pipe for water at 20 °C with discharge of 6 m3/s? The pumps are 75 percent efficient, and the cost of energy is $1 per 72 MJ. u, = Q / A x = 6/[(JT)(2)2/4] = 1.910 m/s N R = d v/ v

I

(N R ) X = (2)(1.910)/(1.02 x 10~6) = 3.75 X 106 e x / d x = (0.030)/2 = 0.015 From Fig. A-5, / = 0.044. d 2 = [2 — (2)(0.012)] = 1.976 m v 2 = Q/ A 2 = 6/[(nr)(1.976)2/4] = 1.957 m/s (N r ) 2 = (1.976)(1.957)/(1.02 X 10“6) = 3.79 x 106

e 2 / d 2 = (0.001)/1.976 = 0.000506

f 2 = 0.017 h f = (f )( L / d )( v 2 / 2 g ) (h f ) x = 0.044[1000/2] {1.9102/[(2)(9.807)]} = 4.902 m (h f ) 2 = 0.017[1000/1.976]{1.9572/[(2)(9.807)]} = 1.680 m Saving in head = 4.092 -1.680 = 2.412 m P = Q yh f / r ) = (6)(9.79 x 103)(2.412)/0.75 = 0.1889 MJ/s Savings per year = (0.1889)[(365)(24)(3600)]/72 = $82 738 9.172 What size of new cast iron pipe is needed to transport 0.5 m3/s of water at 25 °C for 1000 m with head loss of 2 m? d = 0.66[(ei25)(LQ2/ghfy75 + (v){Q)9\L/ghf)52]00*

713 m

9.173 Pure water at 70 °F runs at 2.778 lb/s through a smooth tube between two reservoirs 30 ft apart and having a difference in elevation of 4.1 ft. What size tubing is needed? I

Q = 2.778/62.3 = 0.04459 ft3/s h f = (f ) (L / d ) (v 2 / 2 g ) v = Q/ A = 0.04459/(^/74) = 0.05677/d2

4.1 = (/)(30/d){(0.05677/d2)2/[(2)(32.2)]} d = 0.2055/1'5

N R = d v/ v = (d)(0.05677/d2)/(1.05 X 10~5) = 5.41 x 103/d Try/ = 0.020: d = (0.2055)(0.020)1/s = 0.09398 ft, N R = 5.41 x 1070.09398 = 5.76 x 104. From Fig. A-5, / = 0.0205. Try/ = 0.0205: d = (0.2055)(0.0205)1/5 = 0.09444 ft, N R = 5.41 x 103/0.09444 = 5.73 x 104, / = 0.0205 (O.K.). Hence, d = 0.09444 ft, or 1.13 in. 9.174 In Fig. 9-10, H = 20 m, L = 150 m, d = 50 mm, s.g. = 0.85, f i = 0.400 N • s/m2, and e = 1 mm. Find the newtons per second flowing. Neglect minor losses. I

h f = (f ) (L / d ) (v 2 / 2 g ) 20 = (/)[150/(i®o)]{t;2/[(2)(9.807)]} u = 0.03616/v7 N R = p d v/ n = [(0.85)(1000)](iis)(w)/0.004 = 10 625u

Try/ = 0.050: v = 0.3616/V0.050 = 1.617 m/s, N R = (10 625)(1.617) = 1.72 x 10 4, e/d = (4B)/(^O) = 0.0200. From Fig. A-5, / = 0.051. v = 0.3616/V0.051 = 1.601 m/s N R = (10 625)(1.601) = 1.70 x 104

/ = 0.051

(O.K.)

2

W = yA v = [(0.85)(9.79)][(jr)(j§jo) /4](1.601) = 0.0262 kN/s or 26.2 N/s 1.175 Determine the head loss for flow of 140 L/s of oil, v = 0.00001 m2/s, through 400 m of 200-mm-diameter cast iron pipe. f

h f = (f ) (L / d ) (v 2 / 2 g ) v = Q/ A = (^)/[(^)(^)74] = 4.456 m/s N R = d v/ v = (wi)(4.456)/0.00001 = 8.91 x 104 e/d = 0.00026/®) = 0.00130

From Fig. A-5, / = 0.023. h f = 0.023[400/®)]{4.4562/[(2)(9.807)]} = 46.6 m. U76 Water at 15 °C flows through a 300-mm-diameter riveted steel pipe, e = 3 mm, with a head loss of 6 m in 300 m. Determine the flow.

236 0 CHAPTER 9

I hf =

(f ) (L / d ) (v 2 / 2 g ). Try / = 0.040: 6 = 0.040[300/(^)]{t>2/[(2)(9.807)]}, v = 1.715 m/s; A* = dv/v = 1 (^i)(1.715)/(1.16 x 10"6) = 4.44 x 105; e/ d = ^ = 0.0100. From Fig. A-5, / = 0.038. Try / = 0.038: 2

6

s

6 = (0.038)[300/(t^gs)]{v /[(2)(9.807)]}, v = 1.760 m/s; /V« = ®)(T760)/(1.16 X 10~ ) = 4.55 x 10 ; / = 0.038 (O. K. ); e= A v = [(nr)®)2/4](1.760) = 0.124 m3/s. 9.177

1

I 1

Determine the size of clean wrought iron pipe required to convey 4000 gpm of oil, v = 0.0001 ft 2/s, 10 000 ft < with a head loss of 75 ft.

I

Q = (4000)(0.002228) = 8.912 ft3/s h f = (f ) (L / d ) (v 2 / 2 g ) v = Q / A = 8 . 9 1 2 / ( j t d 2 / 4 ) = 11.35/d2

75 = (/)(10 000/d){(11.35/d2)2/[(2)(32.2)]} d = 3.056/1/5

Try/ = 0.020: d = (3.056)(0.020)1/5 = 1.398ft, N R = d v/ v = (1.398)(11.35/1.3982)/0.0001 = 8.12 x 104, e/ d = 0.00015/1.398 = 0.000107. From Fig. A-5,/ = 0.019. Try/ = 0.019: d = (3. 0 5 6 )(0 . 0 1 9 )' / s = 1 . 3 8 3 ft, N R = (1.383)(11.35/1.3832)/0.0001 = 8.21 x 104, / = 0.019 (O.K.). Hence, d = 1.383 ft, or 16.6 in. 9.178

In Prob. 9.177, for d = 16.6 in, if the specific gravity is 0.85, p, = 40 psi, z, = 200 ft, and z 2 = 50 ft, determine the pressure at point 2. I

p l l y + v \ l 2 g +z 1 =p 2 l y + v l l 2 g + z 2 + h L (40)(144)/[(0.85)(62.4)] + v \ / 2 g + 200 = (p2)(144)/[(0.85)(62.4)] + v \ / 2 g + 50 + 75 v \ / 2 g = v \ / 2 g p 2 = 67.6 lb/in2

9.179

What size galvanized iron pipe is needed to be “hydraulically smooth” at N R = 3.5 x 105? (A pipe is said to be hydraulically smooth when it has the same losses as a smoother pipe under the,same conditions.)

f From Fig. A-5, e/d = 0.00001 is equivalent to smooth pipe. 0.0005/d = 0.00001, d = 50.0 ft. 9.180

Above what Reynolds number is the flow through a 3-m-diameter riveted steel pipe, e = 30 mm, independent of the viscosity of the fluid?

f e/d = 0.030/3 = 0.010. From Fig. A-5, N R = 1.0 x 105 at complete turbulence. 9.181

Determine the absolute roughness of a 1-ft-diameter pipe that has a friction factor of 0.032 when N R = 1.0 x 10*.;

I From Fig. A-5, e/d = 0.006. e/1 = 0.006, e = 0.006 ft. 9.182

Galvanized iron pipe of diameter d has the same friction factor for N R = 100 000 as 400-mm-diameter cast iron pipe. Evaluate d.

f For cast Iron: e/d = 0.00026/0.400 = 0.00065. For galvanized iron: e/d = 0.00015/d = 0.00065, d = 0.231 m, or 231 mm. 9.183

Calculate the friction factor for atmospheric air at 80 °F, flowing at v = 40 ft/s in a 2-ft-diameter galvanized pipe.

I 9.184

/ = 1.325/[ln (e/3.7d + 5.74/A^9)]2 N R = d v/ v = (3)(40)/(1.69 X 10~4) = 710 059 / = 1.325/(In [0.0005/(3.7)(2) + 5.74/710 059° 9]}2 = 0.0156

Atmospheric air at 92 °F is conducted through a 4-ft-diameter, 1000-ft-long wrought iron pipe. Find the head loss corresponding to a flow of 266.7 cfs. I

h f = (f ) (L / d ) (v 2 / 2 g ) p = p / R T = (14.7)(144)/[(1716)(460 + 92)] = 0.002234 slug/ft 3 v = Q / A = 266.7/[(zr)(4)2/4] = 21.22 ft/s N R = p d v/ p = (0.002234)(4)(21.22)/(3.90 x 10 7) = 4.86 x 105 e/d = 0.00015/4 = 0.0000375

From Fig. A-5, / = 0.013. h f = (0.013)(1000/4){21.222/[(2)(32.2)]} = 22.72 ft.

FLOW IN CLOSED CONDUITS D 237

9.185

A smooth toroidal wind tunnel is 60 m around at the centerline and has cross-sectional diameter 2 m; the fluid is air at 1 atm and 20 °C. Determine the horsepower rating of a fan that will produce a 500-km/h airstream. h f = (f ) (L / d ) (v 2 / 2 g )

v = 5 x 1073600 = 138.9 m/s

N „ = d v/ v = (2)(138.9)/(1.46 x 10 5) = 1.90 x 10

7

From Fig. A-5, / = 0.0072 (extrapolated). h f = (0.0072)(60/2){138.97[(2)(9.807)]} = 212.5 m Q = Av = [(jr)(274)](138.9) = 436.4 mVs P = Q y h f = (436.4)(11.8)(212.5) = 1.09 x 10 IV or 1460 hp 6

9.186

Assume that 2.0 cfs of oil (p . = 0.0003342 slug/ft • s, p = 1.677 slug/ft3) is pumped through a 12-in pipeline of cast iron. If each pump produces 100 psi, how far apart can they be placed? I

h f = (f ) (L / d ) (v 2 / 2 g ) =p / p g =

(100

x 144)/(1.677)(32.2) = 266.7ft

v = Q / A = 2.0/[(*r)(}§)74] = 2.546 ft/s N R = p d v / p = (1.667)(yf)(2.546)/0.0003342 = 1.27 x 10 e/ d = 0.00085/(H) = 0.00085 4

From Fig. A-5, / = 0.031. 266.7 = 0.031[L/(;f)]{2.5467[(2)(32.2)]}, L = 85 473 ft, or 16.2 miles.

9.187

A 60-mm-diameter smooth pipe 160 m long conveys 36 m 3/h of water at 25 °C from a sidewalk hydrant to the top of a building 25 m tall. What pressure can be maintained at the top of the building, if the hydrant pressure is 1.6 MPa? I

Pi/ Y + v 2 /2g + z, = P ? J Y + v\!2g + z 2 + h L h L = h f = (f)(L/d)(v 2 /2g) v = Q/A = (36/3600)/[(yr)(0.060)74] = 3.537 m/s N R = dv/v = (0.060)(3.537)/(9.10 X 10 *7) = 2.33 x 105

From Fig. A-5, f = 0.016.

h L = 0.016[160/0.060] {3.5377[(2)(9.807)]} = 27.21 m (1.6)(1000)/9.79 + v \ / 2 g + 0 = (p )(1000)/9.79 + v \ / 2 g + 25 + 27.21 2

v\/2g = v22/2g

p 2 = 1.09 MPa

9.188 Calculate the discharge for the pipe of Fig. 9-32; the fluid is water at 150 °F. f

h , = h f = (f ) (L / d ) (v 2 / 2 g ) 258 = (/)[238/(f2)]{u22/[(2)(32.2)]} v = 3 . 4 M / V f

Try/ = 0.019: v = 3.411/V0.019 = 24.74 ft/s, e/ d = 0.00015/(ft) = 0.000900, N R = d v/ v = (^)(24.74)/(4.68 x 10“6) = 8.81 x 105. From Fig. A-5,/ = 0.019 (O.K.); Q =A v = [(JT)(^)2/4](24.74) = 0.540ft /s. 3

238ft

1258 ft

2in -diam wrought iron

1.189

Fig. 9-32

In Fig. 9-32 how much power would be required to pump 160 gpm of water at 60 °F from a reservoir at the bottom of the pipe to the reservoir shown? f

Q = (160)(0.002228) = 0.3565 ft3/s

p x / y + v 2 / 2 g + Z i = p 2 / y + vl / 2 g + Z 2 + hL

v ! = Q / A , = 0.3565/[(;r)(i)74] = 16.34 ft/s

hL = hf = (f ) (L / d ) (v 2 / 2 g )

N R = d v/ v = (H)(16.34)/(1.21 X lO^5) = 2.25 x 10 e/ d = 0.00015/(ft) = 0.000900 5

238 D CHAPTER 9 From Fig. A-5,/ = 0.0205. h L = 0.0205[238/(n)] {16.342/[(2)(32.2)]} = 121.4 ft

p j y + 16.342/[(2)(32.2)] + 0 = 0 + 0 + 260 + 121.4

Pi / Y = 377.3 ft P = Q y(Ap l y ) = (0.3565)(62.4)(377.3) = 8393 ft • lb/s = 15.3 hp 9.190

A 12-mm-diameter commercial steel pipe 16 m long is used to drain an oil tank. Determine the discharge when the oil level in the tank is 2 m above the exit end of the pipe, (p = 0.10 Pa • s, y = 8 kN/m3.)

f Assuming laminar flow, h L y d 2 2[(8)(1000)](0.012)2 = 0.4500 m/s 32 p L (32)[(0.1)(0.10)](16)

v=

N R = p d vl p = (y/ g ) (d v )/ p = [(8)(1000)/9.807](0.012)(0.4500)/[(0.1)(0.10)] = 440

(laminar)

Q = A v = [(JT)(0.012)2/4](0.4500) = 0.0000509 m3/s or 0.0509 L/s 9.191

Two liquid reservoirs are connected by 198 ft of 2-in-diameter smooth tubing. What is the flow rate when the difference in elevation is 50 ft? (v = 0.001 ft2/s).

I

p Jy + v \ l 2 g +z i =p z l y + v \ l 2 g + z 2 + h L h L = h f = (f ) ( L / d ) (v 2 / 2 g )

Assuming laminar flow, f = 64/ N R N R = d v/ v = C&)(«)/0.001 = 166.7« h L = (64/166.7«)[198/(i|)]{u7[(2)(32.2)]} = 7.082« 0 + 0 + 50 = 0 + 0 + 0 + 7.082«

«=7.060 ft/s N R = (£)(7.060)/0.001 = 1177 (laminar)

Q = Av = [(JT)(T|)741(7.060) = 0.154 ft3/s 9.192

Atmospheric air at 16 °C flows for 200 m through a 1.25-m-diameter duct (e = 1 mm). Calculate the flow volume, if the head loss measures 80 mmH20. I hf = (f ) (L / d ) (v 2 / 2 g ) 0.01197 kN/m3

(yhfU = (yh f ) „ 2 o

yair =p / RT = 101.4/[(29.3)(273 + 16)] =

(0.01197)(^)air = (9.79)(0.080) (/t/)air = 65.43 m 65.43 = (/)(200/1.25){«z/[(2)(9.807)]} 2.832/ \ f f

«

Try / = 0.020: « = 2.832/V0.020 = 20.03 m/s, N R = d v/ v = (1.25)(20.03)/(1.46 xlO^f) = 1.71 x 10 6, e/ d = 0.001/1.25 = 0.000800. From Fig. A-5,/ = 0.0205. Try/ = 0.0205: « = 2.832/V0.0205 = 19.78 m/s, N R = (1.25)(19.78)/(1.46 x 10“5) = 1.69 x 106, / = 0.0205 (O.K.); Q = Av = [(JT)(1.252/4)](19.78) = 24.3 m3/s. 9.193

Water at 20 °C is to be pumped through 2 km of 200-mm-diameter wrought iron pipe at the rate of 60 L/s. Compute the head loss and power required. f

h f = (f ) (L / d ) (v 2 / 2 g )

« = QM = (60 x 10~3)/[(jr)(0.200)74] = 1.910 m/s

N R = d v/ v = (0.200)(1.910)/(1.02 x 10~6) = 3.75 X 105 e/ d = 0.000046/(0.200) = 0.000230 From Fig. A-5, / = 0.016. h f = 0.016[2000/0.200] {1.9102/[(2)(9.807)]} = 29.76 m 9.194

P = Q y h f = (60 x 10“3)(9.79)(29.76) = 17.48 kW

An industrial ventilation system contains 4000 ft of 12-in-diameter galvanized pipe. Neglecting minor losses, what head must a blower produce to furnish 3 ton/h of air at p = 14 psia, T = 90 °F? I h f = (f ) (L / d ) (v 2 / 2 g ) N R = p d v/ p p = p / RT = (14)(144)/[(1716)(460 + 90)] = 0.002136 slug/ft 3 Af = p Av 6000/3600 = t(0.002136)(32.2)][(^r)(]i)74](«)

« = 30.85 ft/s

N R = (0.002136)(]!)(30.85)/(3.90 x 10~7) = 1.69 X 105 e/ d = 0.0005/(i) = 0.000500 From Fig. A-5, / = 0.019. h f = 0.019[4000/(]§)]{30.852/[(2)(32.2)]} = 1123.2 ft of air or 1.24 ft of water

=

FLOW IN CLOSED CONDUITS 0 239 9.155

A 2.0-m-diameter pipe of length 1560 m for which e = 1.5 mm conveys water at 12 °C between two reservoirs at a rate of 8.0 m3/s. What must be the difference in water-surface elevations between the two reservoirs? Neglect minor losses.

I

PIIY + v\/2g +

Zi=

pjy + v\/2g +

Z2

+ h L O + O + z^O + O + Zz + fy

z 1 -z 2 = h f = (f )( L / d )( v 2 2 g ) v = Q / A = 8.0/[(JT)(2.0)2/4] = 2.546 m/s N R = d v/ v = (2.0)(2.546)/(1.24 x 10~6) = 4.11 x 106 el d = (1.5/1000)/2.0 = 0.000750 From Fig. A-5,/ = 0.018. h f = (0.018)(1560/2.0){2.5462/[(2)(9.807)]} = 4.64 m. Hence, the difference in water-surface elevations between the two reservoirs is 4.64 m. 9.196

Water flows from reservoir 1 to reservoir 2 through a 4-in-diameter, 500-ft-length pipe, as shown in Fig. 9-33. Assume an initial friction factor (/) of 0.037 and a roughness (e) of 0.003 ft for the pipe. Find the flow rate.

I Pi / Y + v 2 1 / 2 g +z 1 =p 2 / y + v l / 2 g + z 2 + h L 0 + 0 + 700.6 = 0 + 0 + 655.5 + h L h L = 4 5 . 2 f t = h f + h m (I) Friction loss:

h f = (f ) (L / d ) (v 2 / 2 g ) = 0.037[500/(£)](v2/2g) = 55.50u2/2g .

(II) Minor losses: (a ) Due to entrance: From Fig. A-7, take = 0.45. (b ) Due to globe valve: From Table A-ll, K o p c n = 5.7. From Table A-12, take K 2 / K o p c n = 1.75. Hence, K 2 = (5.7)(1.75) = 9.98. (c ) Due to bend: R ID =f = 3.0, e/ D = 0.003/(£) = 0.00900. From Fig. A-12, K 3 = 0.45. (d ) Due to elbow: From Table A-ll, K 4 = 0.23. (e ) Due to exit: From Fig. A-7, K s = 1.0. Thus, h f + h m - (U2/[(2)(32.2)]}(55.50 + 0.45 + 9.98 + 0.45 + 0.23 + 1.0) = 1.050u2 1.050u2 = 45.2 u = 6.561 ft/s

N R = D v / v = (^)(6.561)/(1.90 x 10~5) = 1.15 X 105 e/ D = 0.003/(£) = 0.00900 From Fig. A-5,/ = 0.037. (Assumed value of/O.K.) Q =A v = [(JT)(£)2/4](6.561) = 0.573 ft3/s.

Elev. 700.6 ft

12-in-bend radius Elev. 655.5 ft

Sharp-edged entrance

©

Globe valve, 25 closed

Vfl Sharp-edged exit 90° long-radius elbow

Fig. 9-33

240 0 CHAPTER 9 9.197

Determine the head loss in the system shown in Fig. 9-34 and the discharge in the pipe. f

p j y + v \ / 2 g + z t =p 2 / y + vl / 2 g +

Z2

+ h L 0 + 0-t-100 = 0 + ul/[(2)(32.2)] + 0 + hi

2

h L = h f +h m h f = (J )( L / D ) ( v / 2 g ) =/[500/(4)]{v|/[(2)(32.2)]} = 15.53/v! h m = (K ) (v 2 / 2 g ) K = 0.5 h m = 0.5{«!/[(2)(32.2)]} = 0.007764«! h L = 15.53/«! + 0.007764«! 100 = 0.01553«! + 15.53/«! + 0.007764«! u 2 = Vl00/(0.02329 + 15.53/) Try v 2 = 10 ft/s: N R = D v / v = (4)(10)/(1.21 x 10~5) = 4.13 x 105, e/ D = 0.00015/(4) = 0.00030. From Fig. A-5, / = 0.0165. v 2 = Vl00/[(0.02329 + (15.53)(0.0165)1 = 18.91 ft/s. Try v 2 = 18.91 ft/s: N R = (4)(18.91)/(1.21 x 10~5) = 7.81 x 105, f = 0.0157, v 2 = Vl00/[0.02329 + (15.53)(0.0157)] = 19.35 ft/s. Try v 2 = 19.35 ft/s: = (4)(19.35)/(1.21 x lO^5) = 8.00 x 10s , f = 0.0157 (O.K.); h L = (15.53)(0.0157)(19.35)2 + (0.007764)(19.35)2 = 94.2 ft of water, Q= Av = [(jr)(4)2/4](19.35) = 3.80 fP/s.

Fig. 9-34 9.198

Figure 9-35 shows two reservoirs containing water at 60 °F. The water in the upper reservoir is to be drained to the other reservoir at a lower level as shown. The total length of commercial steel pipe is 100 ft, and the diameter of the pipe is 4 in. What will be the flow rate of water through the pipe when the water surface elevations are as shown in Fig. 9-35? f

p j y + v l l 2 g + z 1 =p 2 l y + v l l 2 g + z 2 + h L 0 + 0 + 335 = 0 + 0 + 300 + A*. h L = h f + h m h f = (f ) (L / D ) ( v 2 l 2 g ) =/[100/(4)]{«I/[(2)(32.2)]} = 4.658/«! h m = (K ) (v 2 / 2 g )

Due to entrance, take K 2 = 0.45. Due to elbow, K 2 = 0.64. Due to gate valve, K o p c n = 0.11. Take K JK 0 ^ n = 17. Hence, K 3 = (0.11)(17) = 1.87. Due to exit, K t = 1.0. h m = (0.45 + 0.64 + 1.87 + 1.0){w2/[(2)(32.2)]} = 0.06149u2

h L = 4.658f v 2 + 0.06149u2

335 = 300 + 4.658/u2 + 0.06149«2 u = V35/(4.658f + 0.06149) Try / = 0.019: « = V35/[(4.658)(0.019) + 0.06149] = 15.28 ft/s, N R = D v / v = (4)(15.28)/(1.21 X 10~5) = 4.21 x 105. From Fig. A-5, / = 0.0175. Try / = 0.0175: « = V35/[(4.658)(0.0175) + 0.06149] = 15.64 ft/s, N R = (4)(15.64)/(1.21 x 10“5) = 4.31 X 105, / = 0.0175 (O.K.); Q= Av = [(jr)(4)2/4](15.64) = 1.36 ft*/». 9.199

A 15-in-diameter new cast iron pipe connecting two reservoirs as shown in Fig. 9-36 carries water at 60 °F. The pipe is 120 ft long, and the discharge is 20 ft/s. Determine the difference in elevation between water surfaces in the two reservoirs. I

p 1 / y + vl / 2 g + z 1 =p 2 / y + vl / 2 g + z 2 + h L O + O + z^O + O + Zz + At

Since Z \ — z 2 — H and h L = h f + h m , H = h f + h m , h f = (f )( L / D) ( v 2 / 2 g ). v = Q / A = 20/[(JT)(X§)2/4] = 16.30 ft/s N R = D v / v = 0f)(16.30)/(1.21 x 10~5) = 1.68 x 10* e/ D = 0.00085/Of) = 0.00068 From Fig. A-5, / = 0.018. h f = 0.018[120/(H)]{16.302/[(2)(32.2)]} = 7.13 ft, h m = (K ) (v 2 / 2 g ). For entrance, take K x = 0.45. For exit, K 2 = 1.0. h m = (0.45 +1.0){16.302/[(2)(32.2)]} = 5.98 ft, H = 7.13 + 5.98 = 13.11 ft.

FLOW IN CLOSED CONDUITS D 241

Elev. 300 ft

Fig. 9-35

Fig. 9-36

Repeat Prob. 9.87 by including losses due to a sharp-edged entrance, the exit, and a fully open flanged globe valve. f For entrance, K x = 0.5. For exit, K 2 = 1.0. For globe valve, K 3 = 8.5. From Prob. 9.87, h L = h f +h f = [ (f ) (L l d ) + K X + K 2 + K 3 ] (v 2 / 2 g ) , 98 = {/[7000/0.050] + 0.5 + 1.0 + 8.5}(v2/[(2)(9.807)]}, 1922 = (140 000/ + 10.0)(v2), v = [1922/(140 000/ + 10.0)],/2. Try/ = 0.02: v = {1922/[(140 000)(0.02) + 10.0]},/2 = 0.8270 m/s, AT* = p d vl i i = (998)(0.050)(0.8270)/(1.02 x 10 3) = 4.05 x 104. From Fig. A-5, / = 0.022. Try / = 0.022: v = {1922/[(140000)(0.022) + 10.0]}1/2 = 0.7887 m/s, N R = (998)(0.050)(0.7887)/(1.02 x 10 3) = 3.86 x 104, / = 0.022 (O.K.); Q = Av = [(rr)(0.050)2/4](0.7887) = 0.001548m3/s, or 5.57m3/h. Repeat Prob. 9.95 by including losses due to a sharp entrance and a fully open screwed swing-check valve.

f For sharp entrance, K t = 0.5. For swing-check valve, K z = 5.1. h m = (AT, + K 2 ) (y 2 / 2 g ). From Prob. 9.95, v = 14.67 ft/s. h m = (0.5 + 5. l){14.672/[(2) (32.2)]} = 18.71 ft. From Prob. 9.95, 0 + 0 + /t=0 + 14.672/[(2)(32.2)] + 0 + (236.6 + 18.71), h = 258.7 ft. Two lakes (Fig. 9-37) communicate via two 20-ft-long wrought iron pipes ed abruptly. The entrance and exit are sharp-edged. Including minor losses, compute the flow rate if lake 1 stands 59 ft higher than lake 2, and the average temperature of the system is 20 °C. I

Pi/y + t>?/2g + Zi=p2/y + v l / 2 g + 2

Z2

+ hL hL = hf + hm

2

h f = (f ) (L / D )( v / 2 g ) = (/a)[20/(^)]{u /[(2)(32.2)]} +/fc[20/(*)]{tr|/[(2)(32.2)]> A„ v a = A„ v h [(JT)(R)2/4](U„) = [(jr)(A)2/4](ufc) v „ = vJ A h f = 3.727f . vl + (1.863)(/i>)(ua/4)2 = 3.727/, u2 + 0.01164f b v 2 a

242 0 CHAPTER 9 For sharp entrance, = 0.5. For sharp exit, K 2 = 1.0. For sudden expansion, K 2 = (1 — 0.5)2 = 0.5625. h m = (0.5 + 0.5625) (u2/[(2)(32.2)]} + (1.0){u?/[(2)(32.2)]} = 0.01650u 2 + (0.01553)(uo/4)2 = 0.01747u2, 0 + 0 + 59 = 0 + 0 + 0 + [(3.727/,u2 + 0.1164/, u2) + 0.01747u2]. Try/. =/, = 0.020: 59 = (3.727)(0.020)(u2) + (0.1164)(0.020)(u2) + 0.01747u2

v a = 25.01 ft/s

v „ = 25.01/4 = 6.253 ft/s

(e/D)„ = 0.00015/(£) = 0.00180

N R = D v/ v (N R ) a = (i)(25.01)/(l.ll x 10~s) = 1.88 x 105

From Fig. A-5,/„ = 0.024. (N R ) b = (£)(6.253)/(l.ll x 10" ) = 9.39 X 10 , (e/ D) b = 0.00015/(^) = 0.000900, f „ = 0.022. Try/. = 0.024 and/, = 0.022: 5

4

59 = (3.727)(0.024)(u2) + (0.1164)(0.022)(u2) + 0.01747u2

u. = 23.21 ft/s

(AW. = (S)(23.41)/(1. 11 x 10“ ) = 1.76 x 10 5

(.N r )„ = (n)(5.852)/(l.ll x 10" ) = 8.79 x 10 5

5

v „ = 23.21/4 = 5.803 ft/s

f „ = 0.024 f „ = 0.022

4

2

Therefore,/. = 0.024 and/, = 0.022 is O.K. Q =A v = [(jr)(£) /4](23.21) = 0.127 ft3/s.

Fig. 9-37 9.203

Two reservoirs containing water at 20 °C are connected by 800 m of 180-mm cast iron pipe, including a sharp entrance, a submerged exit, a gate valve 75 percent open, two 1-m-radius bends, and six regular 90° elbows. If the flow rate is 9 m3/min, find the difference in reservoir elevations. f

pjy + v\f2g + zt= p2/Y v

+

v l / 2 g + z 2 + h L h L = h f +h m h f = (f )(L / D ) (v 2 l 2 g )

= Q / A = (9/60)/[(JT)(0. 180>2/4] = 5.895 m/s N R = Dv / v = (0.180)(5.895)/(1.02 x 10~6) = 1.04 x 106

e/ D = 0.00026/0.180 = 0.00144 From Fig. A-5,/ = 0.0217. h f = 0.0217(800/0.180]{5.8952/[(2)(9.807)]} = 170.9 m. For sharp entrance, K t = 0.5. For exit, K 2 = 1.0. For gate valve 75 percent open, K 3 = 0.3. For bends, = (2)(0.15) = 0.30. For elbows, K s = (6)(0.27) = 1.62. h m = (0.5 + 1.0 + 0.3 + 0.30 + 1.62)(5.895 2/[(2)(9.807)]} =6.6m, h L = 170.9 + 6.6 = 177.5m, 0 + 0 + Zi = 0+ 0 + z2 + 177.5, z, — z 2 = 177.5m. 9.204

The system in Fig. 9-38 consists of 1000 m of 50-mm cast iron pipe, two 45° and four 90° flanged long-radius elbows, a fully open flanged globe valve, and a sharp exit into a reservoir. What gage pressure is required at point 1 to deliver 5 L/s of water at 20 °C into the reservoir, whose free surface lies 100 m above point 1? I

Pi/y + v \ / 2 g + Zj =p 2 l y + v \ / 2 g + z 2 + h L h L = h f +h m h f = (f ) (L / D )( v 2 / 2 g ) v

= Q / A = 0.005/[(JT)(0.050)2/4] = 2.546 m/s N R = Dv/ v = (0.050)(2.546)/(1.02 X 10“6) = 1.25 x 105

e/ D = 0.00026/0.050 = 0.00520 From Fig. A-5,/ = 0.0315. h f = 0.0315[1000/0.050]{2.5462/[(2)(9.807)]} = 208.2 m. For 45° elbows, K x = (2)(0.20) = 0.40. For 90° elbows, K 2 = (4)(0.30) = 1.20. For the open valve, K 3 = 8.5. For exit, K 4 = 1.0. h m = (0.40 + 1.20 + 8.5 + 1.0){2.546 2/[(2)(9.807)]} = 3.7 m, h L = 208.2 + 3.7 = 211.9 m, p j 9.79 + 2.5462/[(2)(9.807)] + 0 = 0 + 0+100 + 211.9, p, = 3056kPa gage.

SL Sharp exit

45° Open globe

0

45'

Fig. 9-38

FLOW IN CLOSED CONDUITS 0 243 9.205

A 1-in-diameter smooth water pipe slopes upward at 30° (Fig. 9-39); the flanged globe valve is fully open. Calculate the flow rate. I

p j y + v 2 J2 g + z l =p 2 / y + v \ ! 2 g + z 2 + h L v \ ! 2 g = v \ / 2 g h L = h f + h m

Therefore, p j y + z x = p j y + z z + h f + h m , (P i - P 2 ) / Y = z 2 -z 1 + h f +h m

(1 )

From manometer, Pi ~ Pi = (/ng — yH2o)(n) + (yH2o)(z2 —

(-2) 2

Combining Eqs. (1 ) and (2), [(yHg - yH o)/yH o](n) = h f + h m , h f = (f ) (L / D )( v / 2 g ) = (/)[(9/cos 30°)/ (£)]{v2/[(2)(32.2)]} = 1.936/u2, h m = { K )( v 2 l 2 g ). For globe valve, K = 13. h m = 13{u2/[(2)(32.2)n = 0.2019U2, {[(13.6)(62.4) - 62.4]/62.4}(^) = 1.936/t>2 + 0.2019t;2, v = V7.350/(1.936/ + 0.2019). Try/ = 0.02: u = \/7.350/[(1.936)(0.02) + 0.20191 = 5.527 ft/s, N R = Du/v = (^)(5.527)/(1.05 x 10”5) = 4.39 X 104. From Fig. A-5,/ = 0.0217. Try / = 0.0217: v = V7.350/[(1.936)(0.0217) + 0.2019] = 5.489 ft/s, N R = (^)(5.489)/(1.05 x 10"5) = 4.36 X 104, / = 0.0217 (O.K.); Q= Av = [(JT)(^)2/4](5.489) = 0.0299 fp/s. 2

2

Fig. 9-39 9J06 A pipe system carries water from a reservoir and discharges it as a free jet, as shown in Fig. 9-40. How much flow is to be expected through a 200-mm steel commercial pipe with the fittings shown? I

p j y + v \ ! 2 g +z 1 =p 2 / y + v \ / 2 g + z 2 + hL hL = hf + hm h f = (/)(L/D)(u2/2g) =/[(60 + 20 + 60)/®)]{ui/[(2)(9.807)]> = 35.69/t; 22 hm = (K )( v 2 / 2 g ) = [0.05 + (2)(0.40)]{u|/[(2)(9.807)]} = 0.04334u 2

0 + 0 + 30 = 0 + wl/[(2)(9.807)] + 20 + (35.6 9 f v 2 2 + 0.04334u|) v 2 = Vl0/(35.69/ + 0.09432) Try/ = 0.014: u2 = Vl0/[(35.69)(0.014) + 0.09432] = 4.103 m/s, N R = D v / v = ®)(4.103)/(0.0113 x 10“4) = 7.26 x 105, e/ D = 0,000046/(^1 = 0.000230. From Fig. A-5,/ = 0.0152. Try/ = 0.0152: v 2 = Vl0/[(35.69)(0.0152) + 0.09432] = 3.963 m/s, N R = ®)(3.963)/(0.0113 x 10“4) = 7.01 x 105, / = 0.0152 (O.K.); Q = A v = [(JT)®)2/4](3.963) = 0.125 m3/s.

v = .0113 X 10-4 m2/s p = 999 kg/m3 9.207

Fig. 9-40

A pipe system having a given centerline geometry as shown in Fig. 9-41 is to be chosen to transport a maximum of 1 ft3/s of oil from tank A to tank B. What is a pipe size that will do the job? p d y + vl / 2 g + z c —p p / y + v 2 / 2 g + z p +h L h L = h f +h m

I hf

=

(f )( L / D ) (v 2 / 2 g ) =/[(100 + 130 + 300)/D]{Up/[(2)(32.2)]} = 8.230 f v 2 p / D h m = (K )( v 2 / 2 g ) = (0.05 + 0.5 + 0.5 + l){t/2/[(2)(32.2)]} = 0.03183i/2

244 D CHAPTER 9 (100Xl44)/50 + 0 + 130 = (50)(144)/50 + t> 2/[(2)(32.2)] + 0 + 8.230f v 2 p / D + 0.03183v2 0.04736i»p + 8.230f v 2 p / D = 274 v ; = 274/(0.04736 + 8.230f / D )

v p = Q/ A p =

1/(JID2/4)

= 1.273/D2

(1.273/ D 2 ) 2 = 274/(0.04736 + 8.230f / D ) Try/ = 0.015: (1.273/D2)2 = 274/[0.04736 + (8.230)(0.015)/D]. By trial and error, D = 0.240ft. v = 1.273/0.2402 = 22.1 ft/s

N R = p D v/ p = (Y / g ) (D v) / p = (50/32.2)(0.240)(22. l)/(50 x 10‘ 5) = 1.65 x

104

e/ D = 0.00015/0.240 = 0.000625 From Fig. A-5,/ = 0.0285. Try/ = 0.0285: (1.273/D2)2 = 274/[0.04736 + (8.230)(0.0285)/D]. By trial and error, D= 0.272 ft. v = 1.273/0.2722 = 17.2 ft/s

N R = (50/32.2)(0.272)(17.2)/(50 x 10“5) = 1.45 x 104 / = 0.0285

(O.K.)

Hence, D = 0.272 ft, or 3.26 in.

Fig. 9-41 9.208

What gage pressure p, is required to cause 5 ft3/s of water to flow through the system shown in Fig. 9-42? Assume that the reservoir is large, that minor losses are negligible, and that v = 2.11 x 10~5 ft2/s.

f

pJY + v\l2g + z l =p 2 lY + v\l2g + z 2 + h L v 2 = Q/ A 2

= 5/[(nr)(^)2/4] = 25.46 ft/s

h L = h f = (f ) (L / D )( v 2 / 2 g ) N R = d v/ v = (^)(25.46)/(2.11 x KT5) = 6.03 X 10s e/ d = 0.00015/(^) = 0.00030 From Fig. A-5, / = 0.016. h L = 0.016[(400 + 160 + 250)/(^)]{25.46 2/[(2)(32.2)]} = 260.9 ft (p,)(144)/62.4 + 0 + 120 = 0 + 25.46 z/[(2)(32.2)] + 160 + 260.9 p, = 135 lb/in 2 gage

Fig. 9-42 9.209

In Prob. 9.208, let 6 in be the n o m i n a l diameter of the pipe. For the entrance fitting, r / d = 0.06. Calculate the pressure p,. The elbows are screwed elbows and there is now an open globe valve in the pipe system. Include minor losses.

I Use d = 6.065 in Pi/y + v \ / 2 g + hL = hf+ hm

Zi= PJY

+ v\/2g +

h f = (f )( L / d )( v 2 / 2 g )

Z2

+ hL

V 2 =Q / A 2

= 5/[(JT)(6.065/12)2/4] = 24.92 ft/s

N R = d v/ v = (6.065/12)(24.92)/(2.11 X 10 5) = 5.97 X 10s

e/ d = 0.00015/(6.065/12) = 0.000297

FLOW IN CLOSED CONDUITS 0 245

ff

From Fig. A-5,/ = 0.016. h f = 0.016[(400 + 160 + 250)/(6.065/12)]{24.92 2/[(2)(32.2)]} = 247.3 ft, h m = (K )( v 2 / 2 g ). For entrance, K x = 0.15. For elbows, K 2 = (2)(0.45) = 0.90. For globe valve, K 3 = 5.1. h m = (0.15 + 0.90 + 5.1) (24.922/[(2)(32.2)]} = 59.3 ft

h L = 247.3 + 59.3 = 306.6 ft

(Pi)(144)/62.4 + 0 + 120 = 0 + 24.922/[(2)(32.2)] + 160 + 306.6 p x = 154 lb/in2 gage 9.210

The industrial scrubber B of Fig. 9-43 consumes water (v = 0.113 x 10 5 m2/s) at the rate of 0.1 m3/s. If the pipe is 150-mm commercial pipe, compute the necessary tank pressure p x . I P A / Y + v 2 J2 g + z A = p B / y + v % / 2 g +z B + h L v B = Q/ A B = 0. l/[(jr)(0.150)2/4] = 5.659 m/s h L = h f + h m h f = (f ) (L / d ) ( v 2 / 2 g ) N p = d v/ v = (0.150)(5.659)/(0.113 x 10 5) = 7.51 x 105 e/ d = 0.000046/0.150 = 0.000307 From Fig. A-5, / = 0.016. h f = 0.016[(300 + 150 + 295)/0.150] (5.659 2/[(2)(9.807)]} = 129.7 m h m = (K ) (v 2 / 2 g ) = (0.4 + 0.9 + 0.9 + l){5.6592/[(2)(9.807)]> = 5.2 m h L = 129.7 + 5.2 = 134.9 m p,/9.79 + 0 + 25 = 40/9.79 + 5.659 2/[(2)(9.807)] + 150 + 134.9 p x = 2600 kPa gage

p2=40kPa gauge

K = 0.9

295 m

1:

1K= 1

P1

B

1=0

Air

150 m

1--Water

25 m

J

9.211

A

: K = 0.4

m

3001

K = 0.9

Fig. 9-43

What pressure p x is required in Fig. 9-44 to cause 1 ft3/s of water to flow, given p 2 = 5 psig? Take p = 2 . 1 l x 10“5 lb • s/ft2 for water. I P A / Y + v 2 J2 g + z A = p B / Y + v % / 2 g + z B + h L

p j y = (p,)(144)/62.4 + (10)(0.8) = 2.308p, + 8.00

v B = Q ! A B = l/[(^r)(^)2/4] = 5.093 ft/s h L = h f + h m h f = (f )( L / d ) (v 2 / 2 g ) N R = p d v/ p = (1.94)(£)(5.093)/(2.11 x 10"5) = 2.34 x 10s e/ d = 0.00015/(£) = 0.00030 From Fig. A-5,/ = 0.0175. h f = 0.0175[2800/(£)]{5.0932/[(2)(32.2)]} = 39.47 ft h m = (K ) (v 2 / 2 g ) = (0.5 + l){5.0932/[(2)(32.2)]} = 0.60 ft h L = 39.47 + 0.60 = 40.07 ft (2.308p, + 8.00) + 0 + 25 = (5)(144)/62.4 + 5.093 2/[(2)(32.2)} + 0 + 40.07 p, = 8.2 psig

i10 ft H Himir Oil, specific gravity; 0,8v.w.-.

t 25 ft

— Water -»■

2800 ft

C-I-I-I Reservoir

1\ f P i - Device .

1 K = 0.5

6-in new commercial steel pipe

I Fig. 9-44

246

a CHAPTER 9

9.212

Find the flow through the system of Fig. 9-45. Use e = 0.00015 ft. f P A /Y + v 2 J2 g + Z A =P B /Y + v% / 2 g +z s + h L 0 + 0 + (100 + 100) = 0 + 0 + 100 + h L h L = 100 ft = h f + h„

h , = (f ) (L / D )( v 2 / 2 g ) =/[(500 + 100 + 102)/(£)]{U2/[(2)(32.2)]} = 21.80/u2 h m = (K ) (v 2 / 2 g ) = (0.4 + 0.8 + 0.8 + l){u2/[(2)(32.2)]} = 0.04658t/2 h L = 21.80/u2 + 0.04658v2 100 = 21.80/u2 + 0.04658U2 v = Vl00/(21.80/ + 0.04658) Try/ = 0.015: v = Vl00/[(21.80)(0.015) + 0.04658] = 17.49 ft/s, N „ = Dv/ v = (£)(17.49)/(1.21 X lO"5) = 7.23 x 10s, e/ D = 0.00015/(£) = 0.00030. From Fig. A-5,/ = 0.016. Try / = 0.016: v = Vl00/[(21.74)(0.016) + 0.04658] = 15.92 ft/s, N R = (£)(15.92)/(1.21 X 10“5) = 6.58 x 105 , f = 0.016 (O.K.); Q = A v = [(^)(^)2/4](15.92) = 3.13 ft3/s.

Fig. 9-45

9.213

A flow of 170 L/s is to go from tank A to tank B in Fig. 9-46. If v = 0.113 x 10 5 m2/s, what should the diameter be for the horizontal section of pipe? I p A / Y + v A / 2 g + z A =p B / y + v % / 2 g + z B + h L 0 + 0 + (35 + 35) = 0 + 0+ \ 6 + h L h L = 5 4 m = h f +h „ V i = GMi = ®)/(*D2/4) = 0.2165/D2

v 2 = Q / A = (^/[(tf)®^] = 9.620 m/s 2

2

h f = (J) (L / D ) ( v / 2 g ) = (/1)(65/D){(0.2165/D2)2/[(2)(9.807)]} +/2[35/(^)]{9.6202/[(2)(9.807)]} = 0.1553f JD 5 + 1101/2 h m = (K ) (v 2 / 2 g ) = (0.4 + 0.9) {(0.2165/D2)2/[(2)(9.807)]} + 1.0{9.6202/[(2)(9.807)]} = 0.003107/D4 + 4.718 h L = 0.1553//D5 + U01/2 + 0.003107/D4 + 4.718 54 = 0.1553/,/D5 + U01/2 + 0.003107/D4 + 4.718 Try/, =/2 = 0.015: 54 = (0.1553)(0.015)/DS + (1101)(0.015) + 0.003107/D4 + 4.718. By trial and error, D = 0.154 m. u, = 0.2165/0.1542 = 9.129 m/s N R = Dv/ v (N r ) i = (0.154)(9.129)/(0.113 x 10“5) = 1.24 x 106 (e/D), = 0.000046/0.154 = 0.00030 From Fig. A-5,/, = 0.0155. (N R ) 2 = (^)(9.620)/(0.113 x 10'5) = 1.28 X 106, (e/D)2 = 0.000046/(^) = 0.00031, f 2 = 0.0155. Try/, =/2 = 0.0155: 54 = (0.1553)(0.0155)/D5 + (1101)(0.0155) + 0.003107/D4 + 4.718. By trial and error, D = 0.155 m. Vi

= 0.2165/0.1552 = 9.011 m/s

(A*), = (0.155)(9.011)/(0.113 x HT5) = 1.24 x 106

(e/D), = 0.000046/0.155 = 0.00030 -5

(h f R ) 2 = (t555)(9.620)/(0.113 x 10 ) = 1.28 x 10 Therefore, D = 0.155 m, or 155 mm.

/, = 0.0155 6

/2 = 0.0155

(O.K.)

FLOW IN CLOSED CONDUITS 0 247

A 35 m , K = 0.4

,D = ?' 65 m

K = 0.9

ry^

. 35 m

D = 150 mm

£ 16 m K= 1 q = 170 L/s = 0.113 X 10“5 m2/s commercial steel pipe

9.214

V/////////////Z Fig. 9-46

In Prob. 9.208, if p x = 200 lb/in2 gage, what should the inside pipe diameter be to enable transport of 12 ft 3/s of water? Again neglect minor losses.

I

p Jy + v 2 J2 g + z 1 =p 2 l y + v 2 2 / 2 g + z 2 + h L v 2 = Q / A 2 = 12/(nrd2/4) = 15.28/d2 h L = h f = (f ) (L / d ) (v 2 / 2 g ) h f = (/)[(400 + 160 + 250)/d] {(15.28/d 2)2/[(2)(32.2)]} = 2937f / d 5

(200)(144)/62.4 + 0 + 120 = 0 + (15.28/d 2)2/[(2)(32.2)] + 160 + 2937f / d 5 421.5 = 3.625/d4 + 2937f / d 5 4 5 Try/ = 0.015: 421.5 = 3.625/d + (2937)(0.015)/d . By trial and error, d = 0.643 ft. v = 15.28/0.6432 = 36.%ft/s, N R = d v/ v = (0.643)(36.96)/(2.11 x 10“5) = 1.12 x 106, e/d = 0.00015/0.652 = 0.00023. From Fig. A-5, / = 0.015 (O.K.). Therefore, d = 0.643 ft, or 7.72 in. 9.215

Under the pressures established in Prob. 9.210, what size pipe is needed to double the flow?

I

p Jy + v 2 A l 2 g + z A =p B l y + v 2 B / 2 g + z B + h L v B = Q/ A B = 0.2/(^td2/4) = 0.2546/d2 h f = (f ) (L / d ) (v 2 / 2 g ) =/[(300 + 150 + 295)/d] {(0.2546/d2)2/[(2)(9.807)]} = 2.462//d5 h m = (K ) (v 2 / 2 g ) = (0.4 + 0.9 + 0.9 + l){(0.2546/d2)2/[(2)(9.807)]} = 0.01058/d4 h L = h f + h m =2 . 462f / d 5 + 0.01058/d4 2600/9.79 + 0 + 25 = 40/9.79 + (0.2546/d 2)2/[(2)(9.807)] + 150 + 2.462f i d 5 + 0.01058/d4

136.5 = 2.462f i d 5 + 0.01388/d4 Try/ = 0.015:136.5 = (2.462)(0.015)/d + 0.01388/d4. By trial and error, d = 0.196 m. v = 0.2546/0.1962 = 6.627 m/s, N R = dv/v = (0.196)(6.627)/(0.113 x 10“5) = 1.15 x 106, e/d = 0.000046/0.196 = 0.000235. From Fig. A-5,/= 0.015 (O.K.). Therefore, d = 0.196 m, or 196mm. 5

9.216

A 12-in-diameter pipe with a friction factor of 0.02 conducts fluid between two tanks at 10 fps. The ends of the pipe are flush with the tank walls. Find the ratio of the minor losses to the pipe friction loss if the length of the pipe is («) 10 ft, (6) 250 ft, and (c) 1500 ft. f («)

h f = (/)(L/d)(v2/2g) h m = ( K ) (v 2 / 2 g ) h f = 0.02[(10/|§)](v2/2g) = 0.20v2/2g

h m = (0.5 -I- 1.0)(v2/2g) = 1.5v2/2g

h j h f = (1.5v2/2g)/(0.20v2/2g) = 7.5 (61

h f = 0.02[250/G|)](v2/2g) = 5.0v2/2g

h m = (0.5 + 1.0)(v2/2g) = 1.5v2/2g

h j h f = (1.5v2/2g)/(5.0v2/2g) = 0.3 (c)

2

h f = 0.02[1500/(il)](v /2g) =

30V2/2g

(7.5:1)

(0.3:1)

h m = (0.5 + 1.0)(v2/2g) = 1.5v2/2g

h j h f = (1.5v2/2g)/(30v2/2g) = 0.05

(0.05:1)

248 0 CHAPTER 9 9.217

A smooth pipe 30 cm in diameter and 100 m long has a flush entrance and a submerged discharge. The velocity is 3 m/s. If the fluid is water at IS °C, what is the total loss of head?

I

h L = h f + h m h f = (f )( L / d ) (v 2 / 2 g ) N R = d v/ v = (0.30)(3)/(l. 16 x 10") = 7.76 x 10 5

From Fig. A-5,/ = 0.0122. h f = 0.0122[100/0.30]{32/[(2)(9.807)]} = 1.87 m, h m = (K ){ v 2 / 2 g ) = (0.5 + 1.0){32/[(2)(9.807)]} = 0.69 m, h L = 1.87 + 0.69 = 2.56m. 9.218

The water of Prob. 9.217 is replaced by oil with kinematic viscosity 9.3 x 10 5 m2/s and specific gravity 0.925. Determine the pressure loss. h L = h f + h „ h f = (f )( L l d )( v 2 / 2 g ) N R = d v/ v = (0.30)(3)/(9.3 x 10") = 9.68 x 10’

I

From Fig. A-5,/= 0.031. h f = 0.031 [100/0.30] {32/[(2) (9.807)]} = 4.74 m h m = (K )( v 2 / 2 g ) = (0.5 + 1.0){32/[(2)(9.807)]} = 0.69 m h L = 4.74 + 0.69 = 5.43 m of oil Ap = y h L = [(0.925)(9.79)](5.43) = 49.2 kPa 9.219

A smooth pipe consists of 100 ft of 8-in pipe followed by 200 ft of 24-in pipe, with an abrupt change of cross section at the junction. It has a flush entrance and a submerged exit. If it carries water at 60 °F in the smaller leg with a velocity of 18 fps, what is the total head loss? f h L = h f +h m h f = (f )( L / d )( y 2 / 2 g ) N „ = d u / v

(TV*)—a = (*)(18)/(1.21 x 105) = 9.92 x 105

From Fig. A-5, (/)d_g = 0.0117. A l V l =A 2 v

2

A, = [(7r)(£)2/4] = 0.3491 ft2 A 2 = [(jr)(f|)74] = 3.142 ft2

(0.3491)(18) = (3.142)(U2) V 2 = 2.000 ft/s (N K ) d = 2 4 = (f|)(2.000)/(1.21 x 10") = 3.31 x 10 5 (f h -2 4 = 0.0142

h f = 0.0117[100/(£)]{182/[(2)(32.2)]} + 0.0142[200/(f|)]{2.000 2/[(2)(32.2)]} = 8.92 ft

h m = (K ) (v 2 / 2 g ) For entrance, K t = 0.5. For abrupt change, K 2 = (1 — A 1 / A 2 ) 2 = (1 — 0.3491/3.142)2 = 0.7901. For exit, K 3 = 1.0. h m = (0.5 + 0.7901){182/[(2)(32.2)]} + 1.0(2.0002/[(2)(32.2)]} = 6.55 ft, h L = 8.92 + 6.55 = 15.47 ft. 9.220

A 6-in-diameter pipe (f = 0.032) of length 110 ft connects two reservoirs whose water-surface elevations differ by 10 ft. The pipe entrance is flush, and the discharge is submerged, (a) Compute the flow rate, (b ) If the last 10 ft of pipe were replaced with a conical diff with a cone angle of 10°, compute the flow rate.

I {a)

Pi l Y + v \ l 2 g + z l =p 2 l Y + v \ / 2 g + z 2 + h L h f = (f ) (L / d ) (v 2 / 2 g ) = 0.032[110/(£)]{u7[(2)(32.2)]} = 0.1093u 2 h m = (K ) (v 2 / 2 g ) = (0.5 + 1.0){t>2/[(2)(32.2)]} = 0.02329u2 h L = h f + h m = 0. 1093D2 + 0.02329u2 = 0.1326t/2 0 + 0+10 = 0 + 0 + 0 + 0.1326u2

v = 8.684 ft/s

Q = Av = [(JT)(^)2/4](8.684) = 1.71 ft3/s (b ) h f = 0.032[(110 - 10)/(E)](D2/[(2)(32.2)]} = 0.09938v2 h L = 0.09938U2 + 0.01398U2 = 0.1134u2

h m = (0.5 + 0.40){u2/[(2)(32.2)]} = 0.01398u2 0 + 0+10 = 0 + 0 + 0 +0.1134u2

v = 9.391 ft/s Q =Av = [(^T)(H)2/4](9.391) = 1.84 ft3/s 9^21 Given two pipes in series with a diameter ratio of 1:2 and flow velocity of 15 fps in the smaller pipe, find the loss of head due to abrupt (a) contraction and (b ) enlargement. I (a ) (A) 9.222

h m = (K ) (v 2 / 2 g ) d / D =0 . 5 K = 0.33 h m = 0.33{152/[(2)(32.2)]} = 1.15 ft K = 0.55 h m = 0.55 {152/[(2)(32.2)]} = 1.92 ft

In a 50-ft length of 4-in-diameter wrought iron pipe there are one open globe valve (K = 10), one 45° regular elbow (K = 0.75), and one pipe bend with a radius of curvature of 40 in (K = 0.10). The bend is 90°, and its

FLOW IN CLOSED CONDUITS 0 249 length is not included in the 50 ft. No entrance or discharge losses are involved. If the fluid is water at 72 °F and the velocity is 6 fps, what is the total head loss?

I

h L = h f + h m h f = (f ) (L / d ) ( v 2 / 2 g ) N R = d vl v = (n)(6)/(1.02 x 10~5) = 1.96 x 10s e/ d = 0.00015/(£) = 0.00045

From Fig. A-5,/ = 0.0185. L = 50 + M(2)(*)(f§)] = 55.2 ft h f = 0.0185[55.2/(£)]{62/[(2)(32.2)]} = 1.71 ft h m = { K ){ v 2 / 2 g ) = (10 + 0.75 + 0.10){62/[(2)(32.2)]> = 6.07 ft h L = \ J \ + 6.07 = 7.78 ft 9.223

Compute the friction head per 1000 ft of pipe for laminar flow at Reynolds number 50 000 (the empirical upper limit). Consider two situations: one where the fluid is water at 60 °F, the other where the fluid is SAE10 oil at 150 °F (v = 0.00016 ft2/s). Pipe diameter is 2.0 in.

I

h f = (f ) (L / d ) (v 2 / 2 g ) f = 64/A/* = 64/50 000 = 0.00128 N R = d v / v

For water: 50 000 = (2.0/12)(v)/(1.21 x 10~5) v = 3.630 ft/s h f = 0.00128(1000/(2.0/12)] {3.630 z/[(2)(32.2)]} = 1.57 ft For oil: 50 000 = (2.0/12)(v)/0.00016 u = 48.00 ft/s h f = 0.00128(1000/(2.0/12)] {48.00 2/[(2)(32.2)]} = 275 ft 9.224

Repeat Prob. 9.223 if the flow is turbulent in a smooth pipe.

I h f = (J) (L / d ) (v 2 / 2 g ). From Fig. A-5, / = 0.0207. For water: From Prob. 9.223, v = 3.630 ft/s. h f = 0.0207[1000/(2.0/12)]{3.6307[(2)(32.2)]} = 25.4 ft. For oil: From Prob. 9.223, v = 48.00 ft/s. h f = 0.0207[1000/(2.0/12)]{48.007[(2)(32.2)]} = 4443 ft. 9.225

Repeat Prob. 9.223 if the flow is turbulent in a rough pipe with e/ d = 0.05.

I h , = (f ) (L / d ) (v 2 / 2 g ). From Fig. A-5, f = 0.072. For water: From Prob. 9.223, v = 3.630 ft/s. h f = 0.072[1000/(2.0/12)]{3.6302/[(2)(32.2)]} = 88.4 ft. For oil: From Prob. 9.223, v = 48.00 ft/s. h f = 0.072[1000/(2.0/12)]{48.007[(2)(32.2)]} = 15 455 ft. 9.226

Water at 60 °F flows through 10 000 ft of 12-in-diameter pipe between two reservoirs whose water-surface elevation difference is 200 ft. Find the flow rate if e = 0.0018 in. f

p j y + v \ ! 2 g +z x =p z l y + v \ l 2 g + Z2 + h L 0 + 0 + 200 = 0 + 0 + 0 + /:*. h L = 200 ft = h f = (f )( L / d )( v 2 / 2 g ) =/[10 000/(j§)]{t/2/[(2)(32.2)]} = 155.3f v 2

200 = 155.3f v 2 v = 1.135 /V/ Try/ = 0.03: v = 1.135/VO03 = 6.553 ft/s, N R = d v/ v = (d)(6.553)/(1.21 x 10~5) = 5.42 x 105, e/ d = 0.0018/12 = 0.00015. From Fig. A-5, / = 0.015. Try/ = 0.015: v = 1.135/1/0.015 = 9.267 ft/s, N R = (H)(9.267)/(1.21 x 10~5) = 7.66 x 105, / = 0.0145. Try/ = 0.0145: v = 1.135/V0.0145 = 9.426ft/s, N R = (i§)(9.426)/(1.21 x 10"5) = 7.79 x 105, / = 0.0145 (O.K.); Q= Av = [(jr)0i)2/4](9.426) = 7.40 ft7s. 9.227

Repeat Prob. 9.226 if e is twenty times larger than in Prob. 9.226.

Iv

= 1.135/ \ / f (from Prob. 9.226). Try/ = 0.03: v = 1.135/Vfr03 = 6.553 ft/s, N R = d v/ v = (i§)(6.553)/(1.21 x 10’5) = 5.42 x 105, e/ d = (20)(0.0018)/12 = 0.00300. From Fig. A-5, / = 0.027. Try/ = 0.027: v = 1.135/VO.027 = 6.907 ft/s, N R = (H)(6.907)/(1.21 x 10“5) = 5.71 x 103, / = 0.027 (O.K.); Q = Av = [(jr)(i§)2/4](6.907) = 5.42 ft3/s.

250 0 CHAPTER 9 9.228

How large a wrought iron pipe is required to convey oil (s.g. = 0.9, p = 0.0008 lb • s/ft2) from one tank to another at a rate of 1.0 cfs if the pipe is 3000 ft long and the difference in elevation of the free liquid surfaces is 40ft?

I

p JY + v 2 J2 g + z 1 * =p 2 / y + vl / 2 g + z 2 + h L

0 + 0 + 40 = 0 + 0 + 0 + 6*.

2

h L = 40 ft = h f = (f ) (L / d ) (v / 2 g ) v = Q/ A = 1.0/(jrd2/4) = 1.273/ d 2 h L = (/)(3000/d){(1.273/
If the diameter of a pipe is doubled, what effect does this have on the flow rate for a given head loss if the flow is laminar?

f

h L = (32 )( v )( L / g d 2 ) (v ) = (constant)(v/d2)

v = k d 2 Q =A v = k ' d 4

Thus, doubling the diameter will increase the flow rate by a factor of 2 4, or 16. 9.230

If the diameter of a pipe is doubled, what effect does this have on the flow rate for a given head loss if the flow is turbulent? If/ = constant (complete turbulence): h L = k t v 2 l d , v = k 2 d V 2 , Q — A v = k 3 d 5 ' 2 . Thus, doubling the diameter will increase the flow rate by a factor of 25/2, or 5.66. For smooth pipe with N R < 100 000: / = 0.316/A^25, h L = (f )(L / d ) (v 2 / 2 g ) = (fca)(u7,4/d5/4), v = k 2 d s n , Q= Av = k 3 d 1 9 1 7 . Thus, doubling the diameter will increase the flow rate by a factor of 2 19/7, or 6.56.

f

9.231

A 150-mm-diameter pipeline 100 m long discharges a 50-mm-diameter jet of water into the atmosphere at a point 60 m below the water surface at intake. The entrance to the pipe is a projecting one, with K = 0.9, and the nozzle loss coefficient is 0.05. Find the flow rate and the pressure head at the base of the nozzle, assuming / = 0.03.

I

p Jy + v 2 J2 g + z l =p 2 l y + v 2 2 / 2 g + z 2 + h L h f = (f ) (L / d ) (v 2 / 2 g ) = 0.03[100/0.150]{u2/[(2)(9.807)]} = 1.020u2 h m = (K ) (v 2 / 2 g ) = (0.9){u2/[(2)(9.907)]} + (0.05){u2et/[(2)(9.907)]} = 0.04589u2 + 0.002549u2et h , =h f + h m = 1 . 0 2 0 v 2 + 0.04589u2 + 0.002549V2,, = 1.066u2 + 0.002549V2,,

0 + 0 + 60 = 0 + v?e,/[(2)(9.807)] + 0 + 1.066v2 + 0.002549v2e, Since velocity varies as the square of the diameter, vje, = ('|)2(v) = 9v, 60 = (9v)2/[(2)(9.807)] + 1.066v2 + (0.002549)(9v)2, v = 3.333 m/s; Q = Av = [(?r)(0.150)2/4](3.333) = 0.0589 m3/s. Applying Eq. (1) to the nozzle, p j 9.79 + 3.3332/[(2)(9.807)] + 0 = 0+ [(9)(3.333)] 2/[(2)(9.807)] + 0 + 0.05{[(9)(3.333)] 2/[(2)(9.807)]}, p, = 46.9 kPa. 9.232

A 2.0-m-diameter, 1600-m-long concrete pipe (e = 1.5 rrnn) carries water at 12 °C between two reservoirs at 8.0 m3/s. Find the difference in water-surface elevation between the two reservoirs, considering minor losses at entrance and exit.

f

p 1 / y + v 2 J2 g + z 1 =p 2 l y + v 2 2 / 2 g + z 2 + h L h L = h f + h m h f = (/)(L/d)(v2/2g) v

= Q/ A = 8.0/[(TT)(2.0)2/4] = 2.546 m/s N R = d v/ v = (2.0)(2.546)/(1.24 x 10^6) = 4.11 x 106 e/ d = 0.0015/2.0 = 0.00075

From Fig. A-5, / = 0.0185.

hf = (0.0185)(1600/2.0) {2.5462/[(2)(9.807)]} = 4.89 m hm = (K )(v 2 / 2 g ) = (0.5 + 1.0) {2.5462/[(2) (9.807)]} = 0.50 m hL = 4.89 + 0.50 = 5.39 m 0 + 0 + z,=0 + 0 + Z2 + 5.39 m z, - z2 = 5.39 m

(1 )

FLOW IN CLOSED CONDUITS 0 251 9.233

A pipe of mean diameter 5 ft and length 6000 ft delivers water to a facility 1300 ft below the water surface at intake. Assume / = 0.025. When the pipe delivers 300 cfs, what is the horsepower delivered?

I

v 2 = Q / A 2 = 300/[(JT)(?§)2/4] = 15.28 ft/s h f = (f ) (L / d ) (v 2 / 2 g ) = 0.025[6000/(“)]{15.28z/[(2)(32.2)]} = 108.76 ft h m = (K ) (v 2 / 2 g ) = 0.50 {15.282/[(2) (32.2)]} = 1.81 ft h L = h f + h m = 108.76 + 1.81 = 110.57 ft P = Gr(Az - h L ) = (300)(62.4)(1300 - 110.57) = 2.227 x 107 ft • lb/s = (2.227 x 107)/550 = 40 491 hp

9.234

Find the kilowatt loss in 500 m of 50-cm-diameter pipe for which e = 0.05 mm when dye at 45 °C (s.g. = 0.86, v = 4.4 x 10-6 ft2/s) flows at 0.22 m3/s. Neglect minor losses.

I

h f = (/)(L/d ) ( v 2 / 2 g )

v = Q / A = 0.22/[(zr)(^,)2/4] = 1.120 m/s

N R = d v/ v = (0.50)(1.120)/(4.4 x 10~6) = 1.27 x 105 el d = (5 x 10“5)/(5 x 10“') = 0.0001 From Fig. A-5,/ = 0.018. h , = 0.018[500/0.50]{1.1202/[(2)(9.807)]} = 1.151 m, P = Q y h f = 0.22[(0.86)(9.79)](1.151) = 2.13 kW. 9.235

Linseed oil, of kinematic viscosity 0.0005 ft2/s and weight density 59.8 lb/ft3, is pumped through a 3-in pipe (e = 0.001 in), (a) At what maximum velocity would the flow still be laminar? (6) What would then be the loss in energy head per 1000 ft of pipe? f (a) Assume laminar flow exists for N R ≤ 2000. N R = d v/ v, 2000 = (T!)(V)/0.0005, V = 4.00 ft/s. (6) / = 64/NR = 5555 = 0.032 h f = (f )( L / d )( v 2 / 2 g ) = 0.032[1000/(£)]{4.002/[(2)(32.2)]} = 31.80 ft P — yh f = (59.8)(31.80)/144 = 13.2 psi per 1000 ft

9.236

Repeat Prob. 9.235 if the velocity is three times the maximum velocity for laminar flow.

I

v = (3)(4.00) = 12.00 ft/s h f = (f ) (L / d ) (v 2 / 2 g ) N R = d v/ v = (^)(12.00)/0.0005 = 6000 e/ d = 0.001/2 = 0.00050

From Fig. A-5, / = 0.036. h f = 0.036[1000/(^)]{12.002/[(2)(32.2)]} = 322.0 ft p = yh f = (59.8)(322.0)/144 = 134 psi per 1000 ft 9.237

Water flows upward at 3 m/s through a vertical 150-mm-diameter pipe standing in a body of water with its lower end 1.0 m below the surface. Considering all losses and with / = 0.022, find the pressure at a point 3 m above the surface of the water. f p j y + v\ / 2 g + Zi = p 2 / y + v \ / 2 g + z 2 + h L . Let point 1 be at the water surface and point 2 be 3 m above the water surface. h L = h f + h m , h f = (f ) (L / d ) (v 2 / 2 g ) = 0.022[(3 + 1.0)/0.150]{32/[(2)(9.807)]} = 0.269 m, h m = (K )( v 2 / 2 g ). For entrance loss, assume K = 0.8. h m = 0.8{32/[(2)(9.807)]} = 0.367 m, h , = 0.269 + 0.367 = 0.636 m, 0 + 0 + 0 = p 2 / 9.79 + 32/[(2)(9.807)] + 3 + 0.636, p 2 = -40.1 kPa.

9.238

Work Prob. 9.237 if the flow is downward.

I

p 2 / y + vl / 2 g + z 2 =p Jy + v 2 j 2 g + z i + h L h L = h f + h m h f = 0.269 m (from Prob. 9.237) h m = (K ) (v 2 / 2 g )

For exit loss, assume K = 1.0. h m = 1.0{32/[(2)(9.807)]} = 0.459 m h L = 0.269 + 0.459 = 0.728 m p2/9.79 + 32/[(2)(9.807)]+ 3 = 0 + 0 + 0 + 0.728

p2= -26.7kPa

252 0 CHAPTER 9 9.239

A horizontal pipe 20cm in diameter and for which/ = 0.030 projects into a pond 1 m below the surface. Considering all losses, find the pressure at a point 4 m from the end of the pipe if the flow is at 3 m/s from the pipe into the pond. f pi/y + v 2 J2 g + z, = p 2 / y + uf/2g + z 2 + h L . Let point 1 be 4 m from the end of the pipe and point 2 be at the water surface. h L = itf + h m , h f = (f )( L / d )( v 2 / 2 g ) = 0.030[4/0.20]{32/[(2)(9.807)]} = 0.275 m, h m = (K ) (v 2 / 2 g ). For exit loss, K = 1.0. h m = 1.0{32/[(2)(9.807)]} = 0.459 m, h L = 0.275 + 0.459 = 0.734 m, />,/9.79 + 32/[(2)(9.807)] + 0 = 0 + 0+ l+ 0.734, />, = 12.5 kPa.

9.240

Repeat Prob. 9.239 if the flow is from the pond into the pipe.

f

p 2 / y + vl / 2 g +z 2 =p l / y + v \ / 2 g + z t +h L

hL = hf + hm

h f = 0.275 m (from Prob. 9.239) h m = (K ) (v 2 / 2 g ) For entrance, K = 0.8. h m = 0.8{32/[(2)(9.807)]} = 0.367 m h L = 0.275 + 0.367 = 0.642 m 0 + 0 + 1 = />,/9.79 + 32/[(2)(9.807)] + 0 + 0.642 9.241

/>, = -0.99 kPa

A pipe runs from one reservoir to another, both ends of the pipe being under water. The intake is nonprojecting; the length of pipe is 480 ft; its diameter is 10.25 in; and the difference in the two water levels is 106 ft. If / = 0.02, what will be the pressure at a point 300 ft from the intake and 120 ft below the surface of the water in the upper reservoir? I

p Jy

+

v\l2g

+

Z i =p 2 l y

+

vl l 2 g

+

z2

+

hL

(1 ) Let points 1 and 2 be at the water surface in the upper and lower reservoirs, respectively. h f = (f )( L / d )( v 2 / 2 g ) = 0.02[(480)/(10.25/12)] { u 2/[(2)(32.2)]} = 0.1745i/2 h m = (K ) (v 2 / 2 g ) = (0.5 + 1.0){i>2/[(2)(32.2)]} = 0.02329v2 h L = h f + h m = 0.1745t>2 + 0.02329u2 = 0.1978t>2 0 + 0+106 = 0 + 0 + 0 +0.1978i>2 v = 23.15 ft/s Now apply Eq. (1) between the upper reservoir (point 1) and the point 300 ft from the intake (point 2). h f =0.02[(300)/(10.25/12)]{23.152/[(2)(32.2)]} =58.46 ft h L = 58.46 + 4.16 = 62.62 ft 9.242

h m = 0.5 {23.152/[(2)(32.2)]} = 4.16 ft

0 + 0 + 120 = (/>2)(144)/62.4 + 23.152/[(2)(32.2)] + 0 + 62.62 p 2 = 21.3 lb/in2

A 9.5 -in-diameter pipeline runs from one reservoir to another, both ends being under water, and the intake end is nonprojecting. The difference in water levels between the two reservoirs is 110 ft, and the length of pipe is 1000 ft. What is the discharge if / = 0.06?

I

p Jr + v 2 i l 2 g + z 1 =p 2 / y + vl / 2 g + z 2 + h L h f = (f ) (L / d ) (v 2 / 2 g ) = 0.06[(1000) / (9.5/12)] {v2/[(2)(32.2)]} = 1.1769t/2 h m = (K ) (v 2 / 2 g ) = (0.5 + 1.0){t>2/[(2)(32.2)]} = 0.02329t>2 h L = h f + h m = 1.1769t>2 + 0.02329u2 = 1.200i>2

0 + 0 +110 = 0 + 0 + 0 + 1.200t> 2

v = 9.57 ft/s Q = A v = [(nr)(9.5/12)2/4](9.57) = 4.71 ft3/s

9.243

A jet of water is discharged through a nozzle at a point 200 ft below the water level at intake. The jet is 4 in in diameter, and the loss coefficient of the nozzle is 0.15. If the pipeline is 12 in in diameter, 600 ft long, with a

FLOW IN CLOSED CONDUITS 0 253 nonprojecting entrance, what is the pressure at the base of the nozzle? Assume / = 0.0125.

I

p Jy + v 2 1 l 2 g + z l =p 2 l y + vl l 2 g + z 2 + h L

(1)

h f = (f ) (L / d ) (v 2 / 2 g ) = 0.0125[600/(ji)]{v7[(2)(32.2)]} = 0.1165u 2 h m = (K ) (v 2 / 2 g ) = 0.5{V7[(2)(32.2)]} + (0.15){ )2, v = 11.28 ft/s. Applying Eq. (1 ) to the nozzle, (p,)(144)/62.4 + 11.287[(2)(32.2)] + 0 = 0 + [(9)(11.28)]2/[(2)(32.2)] + 0 + (0.15){[(9)(11.28)]7[(2)(32.2)]}, p x = 78.9 lb/in2. 2

9.244

Compute the losses due to flow of 25 m3/min of air, p = 1 atm, T — 20 °C, through a sudden expansion from 300-mm pipe to 900-mm pipe. How much head would be saved by using a 10° conical diff?

I For sadden expansion: h m ~ [ \ - (ZVA) ] (i>?/2g), u, = Q / A x 2 2

= (®)/[(^r)(^) /4] = 5.895 m/s, 2

h m = [1 - (fo5)2]2{5.8952/1(2)(9.807)]} = 1.400 m. For conical diff: h m = 0.152[(u1 - v 2 ) 2 / 2 g] , v 2 = Q / A 2 = (i)/[(^r)(^) /4] = 0.655 m/s, h m = 0.152{(5.895 - 0.655)2/[(2)(9.807)]} = 0.213 m. 2

Saving in head = 1.400 — 0.213 = 1.187 m or 1.187N-m/N or 1.187 J/N 9.245

Calculate the value of H in Fig. 9-47 for 125 L/s of water at 15 °C through commercial steel pipe. I

p Jy + v 2 J2 g + z l =p 2 l Y + vl / 2 g + z 2 + h L h L = h f + h m h f = ( J )( L / d )( v 2 / 2 g ) v = Q / A = (125 x 10“3)/[(JT)(0.30)2/4] = 1.768 m/s

N „ = d v/ v = (0.30)(1.768)/(1.16 x 10~6) = 4.57 x 10 e/ d = 0.000046/0.30 = 0.00015 5

From Fig. A-5,/ = 0.015. h f = 0.015[50/0.30] {1.7682/[(2)(9.807)]} = 0.398 m h m = (K)(v 2 /2g) = (0.5 + 1.0){1.7682/[(2)(9.807)]} = 0.239 m h L = 0.398 + 0.239 = 0.637 m 0 + 0 + z, = 0 + 0 + z 2 + 0.637 z, - z = H = 0.637 m 2

—1 ----H ->

9.246

+

*

- -J

. ' ----- * Fig. 9-47 _*

L—

J

In Fig. 9-47, for W = 3m and a fluid with s.g. = 0.8 and ju = 0.007 Pa • s, calculate the discharge through smooth pipe. p x / y + v \ / 2 g + z, = p 2 / y + v 2 / 2 g + z 2 + h L

I

h f = (f ) (L / d ) (v 2 / 2 g ) = (/)[50/0.30]{u2/[(2)(9.807)]} = 8.497fv 2 h m = (K ) (v 2 / 2 g ) = (0.5 + 1.0) {u2/[(2)(9.807)]} = 0.07648u2 h L = h f + h m = 8.497/u + 0.07648u2 2

+ 0 + 3 = 0 + 0 + 0 + 8.497/u + 0.07648v2 v = V3/(8.497/ + 0.07648) Try/ = 0.02: v = V3/[(8.497)(0.02) + 0.07648] = 3.489 m/s, N R = p d v/ p = [(0.8)(1000)](0.30)(3.489)/ 0.007 = 1.20 x 105. From Fig. A-5,/ = 0.017. Try/ = 0.017: v = V3/[(8.497)(0.017) + 0.07648] = 3.685 m/s, NR = [(0.8)(1000)](0.30)(3.685)/0.007 = 1.26 x 10 5, / = 0.017 (O.K.); Q = A v = [(^)(0.30)2/4](3.685) = 0.260 m /s. 2

0

3

254 9.247

a CHAPTER 9 Evaluate K for a valve that, placed in the line in Prob. 9.246, would reduce the discharge by 50%. f From Prob. 9.246, H = 3 = [(/)(50)/0.30 + 0.5 + 1.0 + /Cvalve]{(3.685/2)7[(2)(9.807)]}, Kvalve = 15.83 166.7/, N R = p d v/ f i = [(0.8)(1000)](0.30)(3.685/2)/0.007 = 6.32 X 104. From Fig. A-5, / = 0.0197. tfvalve = 15.83 - (166.7)(0.0197) = 12.5.

9.248

A water line connecting two reservoirs at 70 °F has 4860 ft of 24-in-diameter steel pipe, three standard elbows (K = 0.9), a globe valve (K = 10), a re-entrant pipe entrance (K = 1.0), and a submerged pipe exit (K = 1.0). What is the difference in reservoir elevations for 20 cfs?

I

p JY + v \ l 2 g + Z i =p 2 l Y + v \ l 2 g + Z 2 + h L h L = h f +h m h f = (J) (L / d ) (v 2 / 2 g ) v = Q / A = 20/[(jr)(ff) /4] = 6.366 ft/s N R = d v/ v = (f|)(6.366)/(1.05 x 10“5) = 1.21 x 10 2

6

e/ d = 0.00015/(f|) = 0.000075 From Fig. A-5, / = 0.013. h f = 0.013[4860/(ff)] (6.3662/[(2)(32.2)]} = 19.88 ft h m = (K ) (v 2 / 2 g ) = [(3)(0.9) + 10 + 1.0 + 1.0]{6.366 2/[(2)(32.2)]} = 9.25 ft h L = 19.88 + 9.25 = 29.13 ft 0 + 0 + 2, = 0 + 0 + Zj + 29.13 9.249

z, - z = 29.13 ft 2

For the conditions given in Prob. 9.248, determine the discharge if the difference in elevations is 40 ft.

I From Prob. 9.248,40 = h f

+ h m = (u7f(2)(32.2)l| Uf ) \ 4 8 6 0 / (% ) \ + f(3)(0.9) + 10 + 1.0 + 1.0]}, v = V2576/(2430/ + 14.7). Try/ = 0.013: v = V2576/[(2430)(0.013) + 14.7] = 7.46 ft/s, N R = d v/ v = (fj)(7.46)/(1.05 X 10-5) = 1.42 x 106, e/ d = 0,000075 (from Prob. 9.248). From Fig. A-5, / = 0.0125. Try / = 0.0125: v = V2576/[(2430)(0.0125) + 14.7] = 7.560 ft/s, N R = (f|)(7.560)/(1.05 x 10“5) = 14.4 x 106, / = 0.0125 (O.K.); Q =A v = [(nr)(f|)74](7.560) = 23.8 ft /s. 3

9.250

What size commercial steel pipe is needed to convey 200 L/s of water at 20 °C a distance of 5000 m with a head drop of 4 m? The line connects two reservoirs, has a re-entrant (K = 1.0), a submerged outlet (K = 1.0), four standard elbows (K — 0.9), and a globe valve (K = 10). f

p j y + v \ / 2 g + 2t = p 2 / y + v \ / 2 g + z 2 + h L 0 + 0 + 4 = 0 + 0 + 0 + 112. h L = h f +h m v = Q / A = ® )/(nrd /4) = 0.2546/d2 2

h f = (f ) (L / d ) (v 2 / 2 g ) = (/)(5000/d){(0.2546/d2)2/[(2)(9.807)]} = 16.52f / d 5 h m = (K ) (v 2 / 2 g ) = [1.0 +1.0 + (4)(0.9) +10] {(0.2546/d 2)2/[(2)(9.807)]} = 0.05156/d4 4 =16.52//d5 +0.05156/d4 Try/ = 0.02: 4 = (16.52)(0.02)/d5 + 0.05156/d4. By trial and error, d = 0.619 m. v = 0.2546/0.6192 = 0.6645 m/s N R = d v/ v = (0.619)(0.6645)/(1.02 x 10~6) = 4.03 x 10

5

e/ d = 0.000046/0.619 = 0.000074 From Fig. A-5,/ = 0.0145. Try/ = 0.0145: 4 = (16.52)(0.0145)/d 5 + 0.05156/d4, d = 0.588 m, v = 0.2546/0.5882 = 0.7364 m/s, N R = (0.588)(0.7364)/(1.02 x 10“6) = 4.25 x 105, / = 0.0145. Therefore, d = 0.588 m, or 588 mm. 9.251

Find the equivalent lengths of 167-mm-diameter pipe, / = 0.024, for (a) a re-entrant pipe entrance (K = 1.0), (b) a sudden expansion from 167 mm to 334 mm diameter, and (c) a globe valve and a standard tee?

I

L t = K D/ f

(а ) (б) (c)

L e = (1.0)(0.167)/0.024 = 6.94 m K = [1 - (D,/D ) ] = [1 - (}) ] = 0.5625 L e = (0.5625)(0.167)/0.024 = 3.91 m 2

2 2

2 2

K = 10 +1.8 = 11.8 L e = (11.8)(0.167)/0.024 = 81.9 m

FLOW IN CLOSED CONDUITS 0 255 9.252

Find H in Fig. 9-48 for 200 gpm of oil (p = 1 , y = 60 lb/ft3) for the angle valve wide open (K = 5.0). f

p 1 /Y + v 2 i / 2 g + z l =p 2 lY + v l / 2 g + z 2 + h L h L = h f +h m h f = (f ) (L / d ) (v 2 / 2 g )

Q = (200)(0.002228) = 0.4456 ft3/s t, = Q/ A= 0.4456/[(rr)(^)2/4] = 9.078 ft/s By Prob. 9.40, p = 0.0002089 lb • s/ft2; N R = (yl g ) (d v )l p = (60/32.2)(^)(9.078)/0.0002089 = 2.02 x 10 4, e/ d = 0.00015/(^) = 0.000600. From Fig. A-5, / = 0.0275. h f = 0.0275[212/ (fi)] {9.0782/ [(2)(32.2)]} = 29.84 ft h m = (K ) (v 2 / 2 g ) = [0.5 + 5.0 + 1.0]{9.078z/[(2)(32.2)]} = 8.32 ft /1^ = 29.84+ 8.32 = 38.16 ft 0 + 0 + z, = 0 + 0 + Zz + 38.16 z,-z2 = tf = 38.16ft

+)+

Angle

212-ft 3-in.-diam

valve

.-----Hr-----

steel pipe

------------------J

Fig. 9-48 9.253

Find K for the angle valve in Prob. 9.252 for a flow of 10 L/s at the same H . y = Q / A = [(i®o)/0.30483] /[(?r) (TI) /4] = 7.194 ft/s

f

2

N R = p d v/ p = (Y / g )(d v) / p = (60/32.2)(f5)(7.194)/0.0002089 = 1.60 x 10

4

e/ d = 0.000600 (from Prob. 9.252) From Fig. A-5, / = 0.0285. From Prob. 9.252, H = [ (f ) (L / d ) + K , + K 2 + K 3 ] (v 2 l 2 g ), 38.16 = {(0.0285)[212/(^)] + 0.5 + K 2 + 1.0}{7.1942/[(2)(32.2)]}, K 2 = 21.8. 9.254

Calculate the discharge through the system of Fig. 9-48 for water at 25 °C and H = 8 m. I

PJY

+ v \ ! 2 g + Zi = P J Y + vl / 2 g + z 2 + hL

In British Engineering units, we have h f = (f ) (L / d ) (v 2 / 2 g ) = (/)[212/(^)]{U2/[(2)(32.2)]} = 13.17/u2 h m = (K ) (v 2 / 2 g ) = (0.5 + 5.0 + 1.0){u2/[(2)(32.2)]> = 0.1009u2 0

+ 0 + 8/0.3048 = 0 + 0 + 0+13.17/u2 + 0.1009u2

hL = h f +h m = 13.17f v 2 + 0.1009u2

v = V26.25/(13.17/ + 0.1009)

Try / = 0.02: v = V26.25/[(13.17)(0.02) + 0.1009] = 8.489 ft/s, N R = d v/ v = (j|)(8.489)/(9.56 X 10"6) = 2.22 x 10s, e/ d = 0.00015/(^) = 0.000600. From Fig. A-5, / = 0.019. Try / = 0.019: v = V26.25/[(13.17)(0.019) + 0.1009] = 8.646 ft/s, N R = (£)(8.677)/(9.56 x 10“6) = 2.27 x 105, / = 0.019 (O.K.); Q =A v = [(zr)(^)2/4](8.646) = 0.4244 ft3/s = (0.4244)(0.3048)3 = 0.0120 m /s, or 12.0 L/s. 3

9.255

Find the discharge through the pipeline in Fig. 9-49 for H = 10 m, as shown. Use minor loss coefficients for the entrance, elbows, and globe valve of 0.5, 0.9 (each), and 10, respectively. I

Pt/y + w i/2g + Zj = p 2 l

Y

+ vl / 2 g + z 2 + h L

2

h f = (f ) (L / d ) (v / 2 g ) =/[(30 + 12 + 60)/®)]{uI/[(2)(9.807)]> = 34.67/t;2 h m = (K ) (v 2 / 2 g ) = [0.5 + (2)(0.9) + 10]{u!/[(2)(9.807)]} = 0.6271u 2 h L = h f + hm = 34.67f v \ + 0.6271u|

0 + 0 +10 = 0 + u|/[(2)(9.807)] + 0 + 34.67/u| + Q. 6 2 1 \ v \

v = Vl0/(34.67/ + 0.6781) Try / = 0.02: v = Vl0/[(34.67)(0.02) + 0.6781] = 2.700 m/s, N R = d v/ v = (^)(2.700)/(1.02 x 10“6) = 3.97 x 105, e/ d = 0.00026/(^1) = 0.00173. From Fig. A-5,/ = 0.023. Try/ = 0.023: v = V 10/[(34.67)(0.023) + 0.6781] = 2.603 m/s, N R = (^)(2.603)/(1.02 x 10“6) = 3.83 x 105, / = 0.023 (O.K.); Q = Av = [(^r)(i7®i)2/4](2.603) = 0.0460 m /s, or 46.0 L/s. 3

256 0 CHAPTER 9

Fig. 9-49 9.256

Rework Prob. 9.255 to find H if Q = 60 L/s. p j y + v 2 , / 2 g + z, =p 2 / y + v l l l g + z + h L h L — h f + h m h f = (f ) (L / d ) (v 2 / 2 g )

f

2

v = Q/ A = (T&)/l(*)(d&)74] = 3.395 m/s N R = d v/ v = (t^)(3.395)/(1.02 x 10~6) = 4.99 x 10

5

e/ d = 0.00173 (from Prob. 9.255) From Fig. A-5,/ = 0.0225. hf = 0.0225[(30 +12 + 60)/(t^)]{3.3952/[(2)(9.807)]} = 8.99 m h m = (K ) (v 2 / 2 g ) = [0.5 + (2)(0.9) +10] {3.3952/[(2)(9.807)]} = 7.23 m h L = 8.99 + 7.23 = 16.22 m 0 + 0 + 2j = 0 + 3.3952/[(2)(9.807)] + z* + 16.22 z, - z* = H = 16.81 m 9.257

Assume that water at 10 °C is to be conveyed at 300 L/s through 500 m of commercial steel pipe with a total head drop of 6 m. Minor losses are 1 2 v 2 / 2 g . Determine the required diameter.

I

(1 )

N R = R 5 /D 9

f = R 7 / [ l n (R 3 / D+ R 2 / N ° R ) ]

2

(2 )

x = R 6 + R + D/ f D = (R )(z + R x 475

0

l 25

9 5 004

h25

1

(3 ) (4)

52 0 04

)

OA

where R 0 = (0 . 6 6 ) ( e Q ) , R, = v/ e Q , R 2 = 5.74, R 3 = e/3.7, R, = K / g h f , R s = 4Q / n v, R 6 = L/ghf, R 7 = 1.325, e = 0.000046 m, Q = 300 L/s, or 0.300 m /s, v = 1.30 x 10“ m /s. 3

K = 12

h f = 6 mm

6

2

R 0 = (0.66)(0.000046'250.30095)004 = 0.25351

R 3 = 1.30 x 10“7(0.0000461250.300O1) = 0.38707 R 3 = 0.000046/3.7 = 1.2432 x 10~ R 4 = 12/[(9.807)(6)] = 0.20394 R s = (4)(0.300)/[(^)(1.30 x 10 6)] = 2.9382’x 10 R 6 = 500/[(9.807)(6)] = 8.4973

5

5

Assume l) = lm. Substituting into Eqs. (1), (2), (3), and (4), N R = 2.9382 x 1071 = 2.9382 x 10 f = 1.325/{ln [(1.2432 x 10"5)/1 + 5.74/(2.9382 x 10 ) 5

5 09

]}2

= 0.014938

x = 8.4973 + (0.20394)(l)/0.014938 = 22.150 D = (0.25351)[22.1504 + (0.38707)(22.1505 2)]° = 0.47418 m Try D — 0.47418 m: N R = 2.9382 x 1070.47418 = 6.1964 x 10 5 , f = 1.325/{ln [(1.2432 x 10-5)/0.47418 + 5.74/(6.1964 x 10 ) ]} = 0.014086, x = 8.4973 + (0.20394)(0.47418)/0.014086 = 15.363, D = (0.25351)[15.3634 + (0.38707)(15.3635 )]° = 0.44063 m. Try D = 0.44063 m: N R = 2.9382 X 1070.44063 = 6.6682 x 105 , f = 1.325/{ln [(1.2432 x 10 5)/0.44063 + 5.74/(6.6682 x 10 ) ]} = 0.014075, x = 8.4973 + (0.20394)(0.44063)/0.014075 = 14.882, D = (0.25351)[14.8824 + (0.38707)(14.8825 2)]° = 0.43783 m. Try D = 0.43783 m: N R = 2.9382 x 105/0.43783 = 6.7108 x 105, / = 1.325/{ln [(1.2432 x 10~5)/0.43783 + 5.74/(6.7108 x 4 10 ) ]} = 0.014074, x = 8.4973 + (0.20394)(0.43783)/0.014074 = 14.842, D = (0.25351)[14.842 + (0.38707)(14.8425 )]° = 0.43759 m. Therefore, D = 0.438 m, or 438 mm. 75

5 09

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9.258

2

04

One equation for determining the friction factor is 1 / Vf = 0.869 In (N R y / f ) — 0.8. Compare the smooth pipe curve on the Moody diagram (Fig. A-5) with results from the equation above for values of Reynolds number of 6 7 10 ,10 , and 10 . 5

f For N R = 105, from Fig. A-5,/ = 0.0178. From the equation, l / \ ^f = 0.869{ln [(105)(\//)]} - 0.8. By trial and error,/ = 0.0183. For N R = 106, from Fig. A-5,/ = 0.0116. From the equation, l / V f = 0.869{ln [(106)(v7)]} — 0.8. By trial and error, / = 0.0116. For N R = 107, from Fig. A-5, / = 0.0082. From the equation, l / V f = 0.869{ln [(10 )(V/)]} - 0.8. By trial and error, / = 0.00810. 7

FLOW IN CLOSED CONDUITS D 257 9.259

An equation for determining the friction factor developed by Colebrook is 1 / Vf = -0.869 In [ (e / D )/ 3.7 + 2 . 5 2 3 / (N K y/ f )] . Check the location of line e/ D = 0.0002 on the Moody diagram (Fig. A-5) with the equation above for a Reynolds number of 10 s. I From Fig. A-5, / = 0.0190. From the equation, 1 / Vf = -0.869 In {0.0002/3.7 + 2.523/[(10 5)(v7)]}- By trial and error, / = 0.0192.

9.260

Find the head loss in a pipeline consisting of 200 ft of 4-in steel pipe, a 90° bend on 24-in radius (K = 0.15), 4-in gate valve (fully open) (K = 0.20), 100 ft of 4-in steel pipe, expansion to 6 in with a 20° taper (K = 0.4), 300 ft of 6-in steel pipe, abrupt contraction to 3-in diameter (K = 0.35), and 50 ft of 3-in steel pipe. The discharge rate is 1.5 cfs. I h f = (f ) (L / d ) (v 2 / 2 g ), h m = (K ) ( v 2 / 2 g ). For 200 ft of 4-in pipe: v x = Q / A = 1.5/[(nr)(£) /4] = 17.19 ft/s, N R = d v x / v = (15)(17.19)/(1.05 x 10~5) = 5.46 x 105, e/ d . = 0.00015/(£) = 0.00045. From Fig. A-5, / = 0.0175. h f = 0.0175[200/(£)]{17. 19Z/[(2)(32.2)]} = 48.2 ft. 2

For bend: h m = 0.15{17.192/[(2)(32.2)]} = 0.7 ft. For gate valve: h m = 0.20(17.192/[(2)(32.2)]} = 0.9 ft. For 100 ft of 4-In pipe: h f = 0.0175[100/(£)]{17.192/[(2)(32.2)]} = 24.1 ft. For expansion: v 2 = 1.5/[(*)(&) /4] = 7.639 ft/s, h m = 0.4(17.19 - 7.639)2/[(2)(32.2)]} = 0.6ft. For 300 ft of 6-in pipe: N R = (£)(7.639)/(1.05 x 1(T5) = 3.64 x 10s, e/ d = 0.00015/(£) = 0.00030, / = 0.0170, h f = 0.0170[300/(fj) ] (7.6392/[(2)(32.2)]} = 9.2 ft. 2

For abrupt contraction: v 3 = 1.5/[(;r)(tl) /4] = 30.56 ft/s, h m = 0.35(30.562/[(2)(32.2)]} =5.1 ft. 2

For 50 ft of 3-in pipe: N R = (£)(30.56)/(1.05 x 10“5) = 7.28 x 105, e/ d = 0.00015/(^) = 0.00060, / = 0.0180, h f = 0.0180(50/({5)](30.56 /[(2)(32.2)]} = 52.2ft, h L = 48.2 + 0.7 + 0.9 + 24.1 + 0.6 + 9.2 + 5.1 + 52.2 = 141.0ft. 2

9.261

Using the Darcy-Weisbach formula, find the head loss in 1000 ft of 6-ft-diameter smooth concrete pipe carrying 80 cfs of water at 50 °F. h f = (f ) (L / D ) ( v 2 / 2 g ) v = Q / A = 80/[(JT)(6)2/4] = 2.829 ft/s

f

N R = D v / v = (6)(2.829)/(1.40 x 1(T5) = 1.21 x 10 e/ D = 0.001/6 = 0:000167 6

From Fig. A-5, / = 0.014. h f = (0.014) (^p) (2.8292/ [ (2) (32.2)]} = 0.290 ft 9.262

Solve Prob. 9.261 using the Manning formula. I

v = (1.486/rt)(R)2,3(s)1/2 = 2.829 ft/s (from Prob. 9.261) n = 0.013 (from Table A-13) R = D /4 = | = 1.500 ft 2.829 = (1.486/0.013)(1.500)2/3(s)1/2

9.263

Solve Prob. 9.261 using the Hazen-Williams formula.

f

v = 1.3180?° “s = 2.829 ft/s (from Prob. 9.261) C = 120 (from Table A-14) R = 1.500 ft (from Prob. 9.262) 0 54

2.829 = (1.318)(120)(1.500)O63(s)° 9.264

s = 0.0003567 h , = (0.0003567)(1000) = 0.357 ft

s = 0.0003618 h f = (1000)(0.0003618) = 0.362 ft

Using the Darcy-Weisbach formula, find the head loss in 100 ft of 3-ft-diameter welded steel pipe carrying 15 cfs of water at 60 °F.

I

h f = ( f ) (L / D ) (v 2 / 2 g ) v = Q/ A

= 15/[(JT)(3)2/4] = 2.122 ft/s

N R = D v/ v = (3)(2.122)/(1.21 x 10“5) = 5.26 x 10 e/ D = 0.00015/3 = 0.000050 5

From Fig. A-5, / = 0.0135. h f = (0.0135)(1§a){2.1222/[(2)(32.2)]} = 0.031 ft.