Mathcad Tool For Design Of Volute Of Centrifugal Air Compressor 3m2un

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Mathcad Tool for Design of Volute of Centrifugal Air Compressor Article in International Journal of Scientific and Engineering Research · November 2013

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Mathcad Tool for Design of Volute of Centrifugal Air Compressor P V Shyam, Vithuraj T Abstract— This paper presents a project work aimed at developing a Mathcad tool capable of deg different types of industrial centrifugal air compressor volutes. Six different volutes are designed in this project with the help of suitable algorithms, which are Rectangular Cross Sectional External and Semi-External volutes; Elliptical Cross Sectional External and Semi External volutes; Circular Cross Sectional External and Semi-External volutes. The geometry generated incorporates the manufacturing and performance requirements necessary for a practical volute design. The Mathcad tool capability is validated by comparing with the prediction of an © established Commercial Tool called COMPAERO . Thus, this project ultimately looks in introducing a volute design tool compatible to the industry. Index — Algorithms for Mathcad, CAM design, Circular Cross Sectional External and Semi-External Volutes, Elliptical Cross Sectional External and Semi External Volutes, Rectangular Cross Sectional External and Semi-External Volutes, Validation with © COMPAERO , Volute or Scroll

——————————  ——————————

1 INTRODUCTION

T

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HE main objective of the project is to generate the cross sectional profiles of the volute and hence arrive at the 3D structure of the volute. The tool is developed as a Mathcad script using the commercially available design software called “Mathcad-14”. Design methodology adopted is to establish the area distribution in the volute from the principles of Conservation of Angular momentum and Mass (CAM Designs) [1].

II. III. IV. V. VI.

Rectangular Cross sectional Semi-External Volute Elliptical Cross sectional External Volute Elliptical Cross sectional Semi-External Volute Circular Cross sectional External Volute Circular Cross sectional Semi-External Volute

2 DESIGN ALGORITHMS

The algorithms used for deg the Elliptical and Circular cross sectional volutes are done in such a way that 3/4th of the volute profile is an ellipse or circle and the rest is rectangle for manufacturability. The equations used for the design can be referred in the Appendix A.

Fig. 1 Full Collection Plane of the Volute

The tool developed is capable of deg six types of commonly used industrial volutes which are as follows:I. Rectangular Cross sectional External Volute ————————————————

• P V Shyam is currently pursuing B.E. Hons. Mechanical Engineering in Birla Institute of Technology and Science Pilani Hyderabad Campus, India E-mail: [email protected]

2.1 Algorithm for Rectangular External Volute a) Algorithm for Geometrical properties for the Full Collection Plane.  Input Values:- Volute Inlet Radius; Volute inlet Width; Sizing parameter; Aspect Ratio; Inlet Flow angle; Number of Stations for Volute generation  Equations for finding Variables like Height, Width, Area, Mean Radius and Maximum Radius for the Volute age cross section are derived from CAM designs and Geometrical concepts  If Width ≤ Volute inlet width then, Width = Volute inlet width and continue solving the equations by keeping this value in finding other variables  Otherwise, continue with the value obtained for Width from CAM design equations and use that to find further variables  This process is continued for the corresponding number of Stations  Display Values of Variables in a table format b) Algorithm for 3D Co-ordinates for Full Collection Plane  Input Values:- Height, Width, Mean Radius and

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Maximum Mean Radius of the Volute age, Number of Stations for Volute Generation  Equations for finding the 3D Coordinates(X, Y, Z) at 5 points of the Rectangle which are Volute inlet Point; the three Corner points of the Rectangle and the Volute inlet width point derived from mathematical modeling concepts  The process is continued for all the stations specified  Display the coordinate values in a table format c) Algorithm for Geometrical Properties of the Exit Cone  Input Values:- Ideal Divergence angle needed for the Exit cone; the geometric properties of the rectangle at 3600 of the Full Collection Plane; Number of sections for Exit cone generation  Equations derived from basic geometrical concepts of frustum to find the height, width and area of the Exit cone Cross section at each section after giving a fixed value to the Exit Flange Area  All the parameters of the Exit cone are calculated and displayed in the Output d) Algorithm for Coordinates of the Exit Cone  Input Values:- Geometrical Properties & Coordinates of the Rectangle at 3600 of the Full Collection Plane; Geometrical Properties of the Exit Cone at each section  Equations are derived from Mathematical Modeling concepts for finding the 3D spacing of the Exit Cone at each section  Results are displayed in Array format showing the Coordinate values of the Exit cone

equations This process is continued for the corresponding number of Stations  Display the Values in a table format b) Algorithm for 3D Co-ordinates for Full Collection Plane  Input Values:- Height, Width, Mean Radius and Maximum Mean radius of the Volute Cross sectional age; Number of Stations for Volute generation; Thickness between the annular age and the Volute age  Equations derived from the basic concepts of Mathematical modeling to get the values for X, Y, Z Coordinates for 6 points in the rectangle which include Volute inlet point, Volute width + thickness point, Volute inlet width point and the rest of 3 corner points of the Rectangle  The process is continued for all the stations specified  Display the coordinate values in a table format c) Algorithm for Geometrical Properties of the Exit Cone  Input Values:- Ideal Divergence angle needed for the Exit cone; the geometric properties of the rectangle at 3600 of the Full Collection Plane; Thickness between the annular and Volute age; Number of sections for Exit cone generation  Equations derived from basic geometrical concepts of frustum to find the height, width and area of the Exit cone Cross section at each section providing a fixed value to the Exit Flange Area  All the parameters of the Exit cone are calculated and displayed in the Output

2.2 Algorithm for Rectangular Semi-External Volute a) Algorithm for Geometrical Properties of Full Collection Plane  Input Values:- Volute Inlet Radius; Volute inlet Width; Sizing parameter; Aspect Ratio; Inlet Flow angle; Number of Stations for Volute generation; Thickness between the annular age and the Volute age  Equations for finding the Height, Width, Area, Mean Radius and Maximum Mean Radius of the Volute age Derived from the CAM design and geometrical concepts  If Aspect Ratio (Width/Height) > 1 then take the Equation of Height and check for all the stations and if Height ≤ 2*Volute inlet width then Height =2* Volute inlet width and continue solving the equations by keeping this value in finding other Variables. Otherwise continue with the value obtained from CAM design equations  If Aspect Ratio (Width/Height) < 1 take the Equation of Width and check for all the stations and if Width ≤ 2*(Volute inlet width +Thickness) then Width = 2*(Volute inlet width +Thickness) and continue solving the equations by keeping this value in finding other Variables. Otherwise continue with the value obtained from CAM design

d) Algorithm for Coordinates of the Exit Cone  Input Values:- Geometrical Properties & Coordinates of the Rectangle at 3600 of the Full Collection Plane; Geometrical Properties of the Exit Cone at each section; Thickness between the annular and Volute age  Equations are derived from Mathematical Modeling concepts for finding the 3D spacing of the Exit Cone at each section  Results are displayed in Array format showing the Coordinate values of the Exit cone

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2.3 Algorithm for Elliptical External Volute a) Algorithm for Geometrical properties of Full Collection Plane  Input Values:- Volute Inlet Radius; Volute inlet Width; Sizing parameter; Aspect Ratio; Inlet Flow angle; Number of Stations for Volute generation  Equations for finding Variables like Total Height, Width, Area, Mean Radius and Maximum Radius for the Volute age are derived from CAM designs and Geometrical concepts  If Width ≤ Volute inlet width then Width = Volute inlet width and continue solving the equations using this value to find values of other variables

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International Journal of Scientific & Engineering Research, Volume 4, Issue 11, November-2013 ISSN 2229-5518

Otherwise, continue with the value obtained for Width from CAM design equations and use that to find further variables  This process is continued for the corresponding number of Stations  Display Values of Variables in a table format b) Algorithm for Co-ordinates of Full Collection Plane  Input Values:- Height, Width, Mean Radius and Maximum Mean radius of the Volute Cross sectional age; Number of Stations for Volute generation; Number of points for Ellipse Generation  Equations derived from the basic concepts of Mathematical modeling to get the values for X, Y, Z Coordinates for ‘n+3’ points in the Cross section which are Volute inlet point, first corner point of 1/4th rectangle portion, ’n’ points for 3/4th Ellipse and Volute inlet width point  The process is continued for all the stations specified  Display the coordinate values in a table format 

2.4 Algorithm for Elliptical Semi-External Volute a) Algorithm for Geometrical properties of Full Collection Plane  Input Values:- Volute Inlet Radius; Volute inlet Width; Sizing parameter; Aspect Ratio; Inlet Flow angle; Number of Stations for Volute generation; Thickness between the annular age and the Volute age  Equations for finding the Height, Width, Area, Mean Radius and Maximum Mean Radius of the Volute age Derived from the CAM design and geometrical concepts  If Aspect Ratio (Width/Height) > 1 then take the Equation of Height and check for all the stations and if Height ≤ Volute inlet width then Height = Volute inlet width and continue solving the equations by keeping this value in finding other Variables. Otherwise continue with the value obtained from CAM design equations  If Aspect Ratio (Width/Height) < 1 take the Equation of Width and check for all the stations and if Width ≤ (Volute inlet width +Thickness) then Width = (Volute inlet width +Thickness) and continue solving the equations by keeping this value in finding other Variables. Otherwise continue with the value obtained from CAM design equations  This process is continued for the corresponding number of Stations  Display the Values in a table format b) Algorithm for 3D Co-ordinates for Full Collection Plane  Input Values:- Height, Width, Mean Radius and Maximum Mean radius of the Volute Cross sectional age; Number of Stations for Volute generation; Number of points for Ellipse Generation; Thickness between the annular age and the



 

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Volute age Equations derived from the basic concepts of Mathematical modeling to get the values for X, Y, Z Coordinates for ‘n+3’ points in the Cross section which include Volute inlet point, Volute width + thickness, Volute inlet width point, the rest of n points for the Ellipse and an inside corner point of the 1/4th rectangle The process is continued for all the stations specified Display the coordinate values in a table format

2.5 Algorithm for Circular External Volute a) Algorithm for Geometrical Properties of Full Collection Plane  Input Values:- Volute Inlet Radius; Volute inlet Width; Sizing parameter; Inlet Flow angle; Number of Stations for Volute generation  Equations for finding Variables like Total Height, Width, Area, Mean Radius and Maximum Radius for the Volute age are derived from CAM designs and Geometrical concepts  If Width ≤ Volute inlet width then Width = Volute inlet width and continue solving the equations using this value to find values of other variables  Otherwise, continue with the value obtained for Width from CAM design equations and use that to find further variables  This process is continued for the corresponding number of Stations  Display Values of Variables in a table format b) Algorithm for Co-ordinates of Full Collection Plane  Input Values:- Height, Width, Mean Radius and Maximum Mean radius of the Volute Cross sectional age; Number of Stations for Volute generation; Number of points for Circle Generation  Equations derived from the basic concepts of Mathematical modeling to get the values for X, Y, Z Coordinates for ‘n+3’ points in the Cross section which are Volute inlet point, first corner point of 1/4th of rectangle portion, ’n’ points for 3/4th of Circular portion and Volute inlet width point  The process is continued for all the stations specified  Display the coordinate values in a table format

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2.6 Algorithm for Circular Semi-External Volute a) Algorithm for Geometrical properties of Full Collection Plane  Input Values:- Volute Inlet Radius; Volute inlet Width; Sizing parameter; Aspect Ratio; Inlet Flow angle; Number of Stations for Volute generation; Thickness between the annular age and the Volute age  Equations for finding the Height, Width, Area, Mean Radius and Maximum Mean Radius of the Volute age Derived from the CAM design and

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International Journal of Scientific & Engineering Research, Volume 4, Issue 11, November-2013 ISSN 2229-5518

geometrical concepts If Aspect Ratio (Width/Height) > 1 then take the Equation of Height and check for all the stations and if Height ≤ Volute inlet width then Height = Volute inlet width and continue solving the equations by keeping this value in finding other Variables. Otherwise continue with the value obtained from CAM design equations  If Aspect Ratio (Width/Height) < 1 take the Equation of Width and check for all the stations and if Width ≤ (Volute inlet width +Thickness) then Width = (Volute inlet width +Thickness) and continue solving the equations by keeping this value in finding other Variables. Otherwise continue with the value obtained from CAM design equations  This process is continued for the corresponding number of Stations  Display the Values in a table format b) Algorithm for 3D Co-ordinates for Full Collection Plane  Input Values:- Height, Width, Mean Radius and Maximum Mean radius of the Volute Cross sectional age; Number of Stations for Volute generation; Number of points for Circle Generation; Thickness between the annular age and the Volute age  Equations derived from the basic concepts of Mathematical modeling to get the values for X, Y, Z Coordinates for ‘n+3’ points in the Cross section which include Volute inlet point, Volute width + thickness, Volute inlet width point, the rest of n points for the Ellipse and an inside corner point of the 1/4th rectangle  The process is continued for all the stations specified  Display the coordinate values in a table format The algorithm for the generation of Exit cone for Elliptical and circular cross sectional External as well as Semi-External volutes are not mentioned because the existing algorithm used for rectangular cross sectional External as well as Semi-External volutes are repeated over there. 

v. vi. vii. viii. ix. x. xi. xii.

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Coordinates for the Exit Cone Area Variation of Full Collection Plane Circumferential Area Increase of Full Collection Plane Radial Orientation of Full Collecton Plane Variation of Full Collection plane around Diff 3D Contour Plot of the Volute Variation of the Exit Cone Radial Orientation of the Exit cone

4 VALIDATION WITH COMPAERO© In this section, the comparison results are reported for all the External volutes which were previously generated by Mathcad software. The procedure is repeated for Semi-External Volutes so, it’s immaterial to report those results here. In COMPAERO© sofware the properties generated for internal volutes are basically the properties for Semi-External volutes. Thus, the results obtained in Mathcad for Semi-External volutes are directly compared with the internal volutes. The process used for comparison of geometrical properties is COMPAERO© results were subtracted from the Mathcad outputs. For matching the cross sectional shapes a separate mathcad file was created for each volute. In this program 5 angles were taken on a symmetric basis and the cross sectional shapes of the Volute were compared at each of these angles. In this section the cross sectional shape at the exit of the full collection plane of the Volute is shown.

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3 MATHCAD OUTPUTS The algorithms which are made above are converted into programs in Mathcad software so that a new tool could be created for deg the Volutes. The programs were created such that each algorithm produced an individual program for each volute. So, a total of 24 programs were created for the design of all the six volutes and all programs were clubbed together in another fresh Mathcad file. An additional program called Choice was added to it so that a could choose between any of the six volutes and model the selected one. The Output of the combined programs consists of 12 parts which are:i. Full Collection Plane Geometrical Properties ii. Coordinates for the Full Collection Plane iii. Exit Cone Geometrical Properties iv. Length of the Exit Cone

4.1 Rectangular External Volute Comparison of Full Collection Plane’s Geometries Avg% Area Error 0.4

Avg%R Error

-0.1

Avg% Rmax Error -0.1

Avg% Wmax Error -0.4

These values are procured by subtracting the COMPAERO© result values from Mathcad result values. A small difference is seen while comparing the results because COMPAERO© software has reduced the area by filleting the corner part of the rectangle with the radius having the magnitude of volute inlet width as shown in fig.2. The properties taken here for validating are the Area of the Full Collection Plane, Mean Radius Variation of the Volute age (R), Maximum Mean Radius Variation of the Volute age (Rmax), Maximum Width of the Cross Section of the Volute (Wmax).

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Mathcad.

Comparison of Cross sectional shape At 3600 Polar Angle

Comparison of Cross sectional shape At 3600 Polar Angle

Fig. 2 Comparison of Rectangular Cross sectional shapes gen© erated in Mathcad and COMPAERO

Fig. 4 Comparison of Circular Cross sectional shapes generated © in Mathcad and COMPAERO

4.2 Elliptical External Volute

5 END SECTIONS

Comparison of Full Collection Plane’s Geometries

5.1 Appendix A Equations involved in Design of each volute are presented in this section. These equations are directly derived from the CAM design concepts of centrifugal air compressor.

Avg% Area Error 0.0

Avg%R Error 0.0

Avg% Rmax Error 0.0

Avg% Wmax Error 0.0

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Elliptical cross sectional Volutes showed a great similarity between the results produced in both the soft wares. This tells about the authenticity of the programming algorithm used by the Mathcad software to design the Volutes.

For all the below volutes the equation for Area calculation is TABLE 1 NOMENCLATURE

Variables r

Comparison of Cross sectional shape At 3600 Polar Angle

R Rmax b t H W A ρ ɵ

Fig. 3 Comparison of Elliptical Cross sectional shapes generated © in Mathcad and COMPAERO

4.3 Circular External Volute Comparison of Full Collection Plane’s Geometries Avg% Area Error 0.0

Avg%R Error 0.0

Avg% Rmax Error 0.0

Avg% Wmax Error 0.0

Circular Cross Sectional Volutes also gave a great similarity between the results obtained from COMPAERO© and from

Vf Vw V α β L SP 4 5 6 7 C E

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Representation

Volute Radius Measured from the center of the compressor Radius of the Mean age flow Volute Outer Radius Measured from the Centre of the Compressor Volute Inlet Width or Minimum width of the volute Thickness between the Annular age and the age flow inside the volute Height of the Cross section of the volute Width of the Cross section of the volute Area of the Cross section of the volute Density of the air flow in the volute Polar angle representing the sections of volute age Meridional velocity of the air Swirl component of the velocity of the air Absolute Velocity of the air Flow angle with respect to the volute cross section Divergence angle required for the Exit Cone Length of the Exit Cone Sizing Parameter for performance Volute Inlet Position Full Collection Plane’s maximum radial position Tongue Position Position of the Exit Flange Area Mean age Flow position of the volute Intermediate Exit cone position

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taken from the CAM design concept [1] as, (rV)c = (rVw )4 (ρV)c A = θ(ρrbVf )4 A = SP ∗ θ ∗ rc ∗ b4 ∗ tanα4

(1) (2) (3)

Rectangular Cross Sectional External Volute For Rectangular Cross sectional External Volute, 1

𝑆∗𝜃

𝑊= � 2

2

𝑆∗𝜃 2

+ ��

(4)

� + 4 ∗ 𝐴𝐴 ∗ 𝑟4 ∗ 𝑆𝑆�

2

Where S = SP ∗ b4 ∗ tanα4

Rectangular Cross sectional Semi-External Volute For Aspect Ratio Greater than 1 (AR > 1) 1

H=

2∗AR

t2

t

(5)

�− + � 4 + 4 ∗ (S ∗ θ + b24 ∗ AR)� 2

For Aspect Ratio Less than 1 (AR < 1) 1

W= � 2

b4 −t 2

+�

(b4 −t)2 4

(6)

+ 4 ∗ θ ∗ S�

Where S = SP ∗ AR ∗ r4 ∗ b4 ∗ tanα4

Elliptical Cross sectional External Volute For Elliptical Cross sectional External Volute, W = �S ∗

θ

3 1+ ∗π 4

+ ��S ∗

Where S = SP ∗ b4 ∗ tanα4

3 4

1

�1+ π�∗AR

2

� + 4 ∗ AR ∗ r4 ∗ S ∗

3 1+ ∗π 4

θ

3 4

� (7)

1+ ∗π

3

�−t + �t 2 + 4 ∗ �1 + π� ∗ (S ∗ θ + b24 ∗ AR)� (8) 4

For Aspect Ratio Less than 1 (AR < 1) W=

1

3 4

�1+ π�

�

b4 −t 1

(b4 −t)2

+�

1

3

(9)

+ 4 ∗ θ ∗ S ∗ �1 + π�� 4

Where S = SP ∗ AR ∗ r4 ∗ b4 ∗ tanα4 θ

3 1+ ∗π 4

+ ��S ∗

Where S = SP ∗ b4 ∗ tanα4 1

3 �1+ π� 4

�

b4 −t 1

+�

The primary project goal of development of a volute design tool using the Mathcad was successfully completed. The new tool is capable of deg centrifugal compressor volute profiles of six different types which were mentioned all along the project. The main aim was the consideration of ease of manufacturability and performance which are of prime concern for industry which was attained with the help of this tool. The main reason for this is that the output of the tool is in a format which could be easily imported to any CAD software for modeling the same and for further manufacturing process. The Mathcad results obtained are authenticated and validated with commercially approved software called COMPAERO©, which is used in most of the major centrifugal compressor production industries. All these comparison results are reported and it has been observed that the results produced were greatly matching with the results of COMPAERO© software. Performance validation module could be taken up as a future work. Thus, it can be concluded that the Mathcad tool generated volute designs could be used in the manufacturing industries for the Centrifugal compressors.

θ

2

� + 4 ∗ r4 ∗ S ∗

3 1+ ∗π 4

(b4 −t)2 1

Where S = SP ∗ r4 ∗ b4 ∗ tanα4

7 REFERENCES

[2] θ

�

3 1+ ∗π 4

(10)

3

+ 4 ∗ θ ∗ S ∗ �1 + π�� 4

[3] [4] [5]

Circular Cross Sectional Semi-External Volute For Circular Cross sectional Semi-External Volute, W=

6 CONCLUSION

[1]

Circular Cross Sectional External Volute For Circular Cross sectional External Volute, W = �S ∗

5.2 Acknowledgments This Project has been done during the Practice School II course conducted by Birla Institute of Technology and Science, PILANI. Hence, special acknowledgement is given to the Practice school division for the background given in completion of the project successfully. The authors are thankful to Mr. Pavan Kumar Reddy and Dr. Swaminathan Gopalakrishnan at ELGI EQUIPMENTS LIMITED for their valuable during the course of the project. A special gratitude is shown to the Learning and Development Department of ELGI EQUIPMENTS LIMITED for providing the opportunity to do the project.

IJSER θ

Elliptical Cross sectional Semi-External volute For Elliptical Cross sectional Semi-External Volute, For Aspect Ratio Greater than 1 (AR > 1) H=

1385

(11)

[6]

R..H. Aungier Volute design. In Centrifugal compressors: a strategy for aerodynamic design and analysis (pp. 195-200). New york: ASME. Cohen, H., & Rogers, G. (1996). Centrifugal Compressors. In Gas Turbine Theory (pp. 141-151). England: Longman Group Limited. Meherwan. (2003). Centrifugal Compressors: a basic guide. In Boyce, Compressor Selections (pp. 1-30). Oklahoma: PennWell Corporation. PMFM_Lecture_Slides. (2011, February). Centrifugal compressor. Hyderabad, Andhra, India: BITS-Pilani. Reunanen, A. (2001). “Experimental and Numerical Analysis of different volutes in a centrifugal compressor”. High Speed Technology Research Program, 152. Ronald. (n.d.). Turbomacinery Aerodynamic Technology. Retrieved 2013, from Design and Analysis software and Consulting services: http:// www.turboaero.com/documents/CompAero.aspx

For the calculation of Exit Cone cross sectional parameters the equation used is as follows, WE =2*W360 *tan(β/2) (12) Where, W 360 is the Width of the Cross section of the full collection plane. IJSER © 2013 http://www.ijser.org