Design And Flow Through CFD Analysis Of Enclosed Impeller

Design And Flow Through CFD Analysis Of Enclosed Impeller

Ashish J. Patel1, Bhaumik B. Patel2

1 M.E (Machine Design) Student, Mechanical Engineering,

Kalol Institute of Technology and Research Centre, Kalol, Gujarat, India

2 Assistant Professor, Mechanical Engineering Department, Kalol Institute of Technology and Research

Centre, Kalol, Gujarat, India,

Gujarat Technological University

Abstract — The Impeller of Centrifugal Pump is one of most Critical Component to be designed. The Flow through Centrifugal Pump impeller is three dimensional and fully turbulence model. The present work describes the design and flow through CFD analysis of enclosed impeller of the centrifugal Pump. The model of impeller was generated using SOLIDWORKS and analyzed in ANSYS (Workbench) Fluid Flow (CFX). The numerical solution of the discredited three dimensional, incompressible Navier-Stokes equations over an unstructured grid is accomplished with an ANSYS-CFX. The design of enclosed impeller is done by using various input data, the value of head is determined by theoretical as well as CFD value. The CFD analysis of Enclosed impeller has been carried out at various inlet and outlet blade angles of the impeller and number of blades of impeller to investigate the changes in head as well as efficiencies.

Keywords Impeller Design, Solid Works, CFD, Pressure Distribution, Efficiency

1. INTRODUCTION

   A pump is a machinery or device for raising, compressing or transferring fluid. A fluid can be gasses or any liquid. Pumps are one of the most often sold and used mechanical devices and can be found in almost every industry. Pumps alone do not create pressure; they only displace fluid, causing a flow. Adding resistance to flow causes pressure. Pumps fall into five major groups: direct lift, velocity, buoyancy and gravity pumps.

   A centrifugal pump is a kinetic device. Liquid entering the pump receives kinetic energy from the rotating impeller. The centrifugal action of the impeller accelerates the liquid to a high velocity, transferring mechanical (rotational) energy to the liquid. That kinetic energy is available to the fluid to accomplish work. The centrifugal pumps act as a reversed of an inward radial flow reaction turbine. Centrifugal pumps consist of a set of rotating vanes, enclosed within a housing or casing, used to impart energy to a fluid through centrifugal force.

2. OBJECTIVE

   To Perform Design and Flow through CFD analysis of the Enclosed impeller in Ansys software with modification in inlet and outlet blade angles of the impeller and number of

   blades of the impeller to investigate the changes in head as well as efficiencies.

3. LITERATURE REVIEW

   E.C. Bcharoudis et. al. [1] have contributed to reveal the flow mechanisms inside centrifugal impellers and studied performance by varying outlet blade angle. They observed a gain in head more than 7 % with increase in outlet blade angle from 20 degree to 45 degree.

   K. M. Pandey et. al. [2] have performed two-dimensional steady numerical analysis for centrifugal pumps with impeller blades 7, 8 and 9 using Ansys Fluent 6.3 software for inlet diameter 80 mm and outlet diameter 168 mm at 2500 rpm rotational speed also to investigate the changes in head as well as efficiencies with the increase of blade number.

   S.Rajendran et. al. [3] have performed the simulation of the flow in the impeller of a centrifugal pump. The flow pattern, pressure distribution in the blade passage, blade loading and pressure plots are discussed.

4. Design of Enclosed Impeller

For design calculation, the design Parameters of CROMPTON SRAM-400 Pump are taken as follows:

Table 4.1 Design Data for Pump

The design steps are as follows: [4]

1. Calculation of Shape Number (N ):

   • The flow area just inside the vane passage at the inlet, is

     1 Q

     sh A1 =

     Cm 1

     Nsh

     103 n Q

     3

     • Vane contraction factor at the inlet,

   t1

   =

   (gh)4

   1 = t1

   Where, t1= Pitch of vanes

   • Su1

     Su1= Peripheral vane thickness at the inlet

2. Calculation of Power (P):

   • Power input to the pump, Pc is given by,

     t = Di

     1

     Z

     • Peripheral Vane thickness at inlet,

       P = g H Q

       C ov

       Su1

       = S1

       Sin1

       Where, S1= Vane thickness at inlet 5 to 8 mm.

       • Calculation of power to be supplied by the Motor

         PCm ,

         B = A1

         1 Di

         P = M

         P

         12. Vane angle at the outlet (2 ):

         Where M

         olf

         cm

         is overloading factor.

         olf C

         = 35 Nsh 2 8

3. Calculation of Shaft Diameter (dsh ):

13. Calculation of outlet diameter (DO ):

3 16 Pcm

U = Cm 2 +(( Cm 2 )2 + gH

)1

dsh =

tor

2 2tan 2 2tan 2

b1 2

1. Calculation of Hub Diameter (dh):

   dh = 1.4 dsh

   • Hydraulic efficiency hy,

2. Calculation of Eye Diameter (de ):

   3 Q

   hy

   = 1 0.42

   (log 0.172 )2

   de = 4.5 n

   • Theoretical Head Hb1,

3. Impeller inlet diameter (Di):

   Di = 1.05 to 1.02 de

   Hb1= H

   hy

   • Flow velocity at outlet, Cm2 = 0.8 to 0.9Cm1

4. Calculation of inlet vane angle (1 ):

   Substituting the value of U2, Do

   = U260 . Similar steps

   n

   = tan1(Cm 1)

   1 u1

5. Tangential velocity at inlet (U1):

can be applied for obtaining the outlet width of blade (B2) as for inlet width (B1).

14. Relative velocity at inlet and outlet (Vr):

1

U = Di n

60

Vr1,2

= Cm 1,2

Sin1,2

1. Calculation of number of Vanes (Z):

   6.5*(D2 +D1)*sin(1+2 )

   Sr.	Parameters	Value
   1	Impeller inlet diameter	402 mm
   2	Impeller outlet diameter	630 mm
   3	Impeller inlet width	120 mm
   4	Impeller outlet width	70 mm
   5	Blade thickness	15 mm
   6	Inlet vane angle	140
   7	Outlet vane angle	200
   8	Number of vanes	4

   The Calculated Parameters are as below:

   Z=

   (D2 -D1)

   2

2. Calculation of Suction Pipe Diameter (DS ): Cm1 = CO ,

   Where Cm1= Flow velocity at inlet But, CO = 0.06 to 0.08*3 Qn2

3. Inlet width at the impeller (B1):

   1. CFD ANALYSIS OF ENLOSED IMPELLER

      Computational Fluid Dynamic is a branch of fluid mechanics that uses numerical methods and algorithms to solve and analyze problem that involve fluid flows.

      Figure 5.1 CFD methodology

   2. BOUNDARY CONDITIONS

      Centrifugal pump impeller domain is considered as rotating frame of reference with a rotational speed of 735 rpm. The working fluid through the pump is water at 27 0C. k- turbulence model with turbulence intensity of 5% is considered. Inlet and outlet Pressure and mass flow rate of

      0.5 m3 /s are given as boundary conditions. Three dimensional incompressible N-S equations are solved with Ansys-CFX Solver.

   3. PROCEDURE OF CFD ANALYSIS Step1. 3D Model of Impeller is generated in SOLIDWORKS 2009 as per above given Drawing.

Figure 7.1 3D Model of Impeller

Step2. Our CFD Analysis method is Cavity Patten so we have to create Cavity model of above impeller.

Step3. Save above Cavity model in *. IGES Format for Importing into ANSYS Workbench Mesh Module for Meshing.

Figure 7.2 Cavity Model of Impeller

Step4. Import above Cavity model in ANSYS Workbench Mesh Module.

Figure 7.3 Cavity model of impeller in ANSYS Workbench

Step5. Meshing of Impeller Meshing Type: 3D

Type of Element: Tetrahedral

No. of Nodes: 46403 No. of Elements: 241146

Figure7.4 Meshed Model of Impeller Cavity

Step6. Save above model in *.CMDB Format for importing into ANSYS CFX Pre.

Step7. Import above .CMDB File in ANSYS CFX Pre.

Step9. Define Heat Transfer and Turbulence model.

Figure 7.7 Heat Transfer and Turbulence Model

Heat Transfer Model: Total Energy Turbulence Model: k- epsilon

Where k is the turbulence kinetic energy and is defined as the variance of the fluctuations in velocity. It has dimensions of (L2 T-2); for example, m2 /s2.

is the turbulence eddy dissipation (the rate at which the velocity fluctuations dissipate), as well as dimensions of k per unit time (L2 T-3) (e.g., m2 /s3).

The k- model introduces two new variables into the system of equations. The continuity equation is then:

+ U = 0

t

and the momentum equation becomes

U + U U

U

Figure 7.5 Impeller Cavity in ANSYS CFX Pre

Step8. Define Water + Particle Domain. Domain Type: Fluid

Domain Fluid: Water + 5 mm Particle Domain motion: Rotating

Domain RPM: 735 rpm Rotating about: Y Axis

Figure 7.6 Water + Particle Domain

t ef f

= P + ef f U T + B

Step10. Define Hub as a Rotating Wall Wall Roughness: Smooth Wall

Heat Transfer: Adiabatic

Figure 7.8 Hub as a Rotating Wall Step11. Define Shroud as a Rotating Wall.

Figure 7.9 Shroud as a Rotating Wall

Step12. Define inlet for Impeller Define inlet mass Flow Rate: 0.5 m3 /s

Static Frame to Total Temperature: 300 K

Step14. Define Solver Control Criteria.

Figure 7.12 Solver Control Criteria

Number of Outer loop iteration: 100 Convergence Criteria:

Residual Target: 1e-4 Step15. Run the Analysis

Inlet Angle: 140

1. Results of Analysis:

   Figure 7.10 Inlet for Impeller

   Step13. Define Outlet for Impeller Define Outlet mass Flow Rate: 0.5 m3 /s

   Figure 7.11 Outlet for Impeller

   Outlet Angle: 200

   Figure 7.13 Velocity Contour

   Figure 7.13 shows minimum velocity is 1.035*101 m/s and maximum velocity is 4.051*101 m/s.

   Figure 7.14 Inlet Pressure Contour

   Figure shows pressure contours at inlet, it helps one in identifying the maximum and minimum pressure at the inlet when the fluid comes in contact with the blade. Here minimum inlet pressure is 1.625*105 Pascal and maximum inlet pressure is 1.752*105 Pascal.

   Figure 7.15 Outlet Pressure Contour

   Figure shows that pressure at outlet of impeller, before entering the casing. Here minimum outlet pressure is 4.825*105 Pascal and maximum outlet pressure is 4.925*105 Pascal.

   Outlet Pressure Inlet Pressure

   Figure 7.16 Outlet Pressure Contour

   Here minimum outlet pressure is 5.401*105 Pascal and maximum outlet pressure is 5.426*105Pascal. Figure 4.29 shows inlet pressure contour at inlet blade angle 140 and outlet blade angle 180 at which fluid leave the impeller and pump get maximum efficiency (approximately 96%).

   Figure 7.17 Inlet Pressure Contour

   Here minimum inlet pressure is 1.613*105 Pascal and maximum inlet pressure is 1.690*105Pascal. Figure 4.30 shows inlet pressure contour at inlet blade angle 140 and outlet blade angle 180 which indicate maximum pressure at which fluid comes in contact with the impeller and the head is maximum(approximately 36 m).

   Head = Outlet Pressure Inlet Pressure

   g

   = (5.426 e5 – 1.69 e5)/(1050 * 9.81)

   = 36.27 m

   Head =

   g

   Sr. No	Inlet Angle	Outlet Angle	Head (m)	(%)
   1	160	220	33.52	90.86
   2	160	200	34.59	93.76
   3	160	180	35.27	95.60
   4	140	220	28.34	76.82
   5	140	200	30.80	81.00
   6	140	180	36.27	96.68
   7	120	220	26.15	70.88
   8	120	200	28.96	78.50
   9	120	180	36.12	95.94

   Table 7.1 Generated Head at Various

   = 4.925e5 1.752 e5

   1050 9.81

   Head = 30.804 m

2. Modification in Inlet and Outlet Blade Angles of Impeller

   Here we took various inlet and outlet blade angles to show pressure distribution at inlet and outlet of impeller before entering the casing. Among them the best result was taken and discussed below.

   Inlet Angle: 140

   Outlet Angle: 180

   Blade Angles

   100

   80

   Efficiency

   60

   40

   20

   0

   Figure 7.21 Inlet Pressure Contour at Number of Blades 4

   Generated Head

   Figure7.18 Generated Head Vs. Efficiency

3. Modification in Number of Blades of Impeller

Figure 7.19 Outet Pressure Contour at Number of Blades 3

Figure 7.20 Inlet Pressure Contour at Number of Blades 3

Figure 7.22 Outlet pressure Contour at Number of Blades 4

Figure 7.23 Outlet pressure Contour at Number of Blades 5

Figure 7.24 Inlet pressure Contour at Number of Blades 5

Figure7.25 Number of Blades Vs. Head CONCLUSION

The CFD predicted value of the head at the designed flow rate is approximately H=30.804 m. There is 8.04% of difference between the theoretical head and the predicted numerical head.

From the CFD analysis of centrifugal pump impeller, the maximum generated head is 36.27m at inlet blade angle 140 and outlet blade angle 180 respectively and the pump efficiency is approximately 96%.

With modification in number of blades of impeller, it is conclude that head is decreases at number of blades 3 and

5. So number of 4 blade impeller is suitable for this pump.

REFERENCES

1. E. C. Bacharoudis, A. E. Filios, M. D. Mentzos and D. P. Margaris, Parametric Study of a Centrifugal Pump Impeller by Varying the Outlet Blade Angle, The open Mechanical Engineering Journal, 2008, 2, 75-83.

2. K. M. Pandey, A. P. Singh and Sujoy Chakraborty, Numerical studies in effect of Blade number variations on perforance of Centrifugal Pumps at 2500 rpm, Journal of Environmental Research and Development, Vol.6 No. 3A, Jan-March 2012.

3. S.Rajendran and Dr.k.Purushothaman, Analysis of a centrifugal pump impeller using ANSYS-CFX, International Journal of Engineering Research & Technology (IJERT) Vol. 1 Issue 3, May 2012, ISSN: 2278-0181.

4. Prof. S. Kumaraswamy. Databook for design of Centrifugal Pumps. Center for Industrial Consultancy and Sponsored Research, IIT Madras.

5. Sujoy Chakraborty, Kishan Chaudhary, Prasenjit Dutta, Performance prediction of Centrifugal pumps with variations of blade number, Journal of science and Industrial research, vol.72, June 2013, pp. 373-378.

6. Weidong zhou, Zhimei Zhao, T. S. Lee, and S. H. Winoto, Investigation of flow through Centrifugal Pump Impellers using Computational Fluid Dynamics, International Journal of Rotating Machinery, 9(1): 49-61, 2003.

7. C. P. Kothandaraman, R. Rudramoorthy, Fluid Mechanics And Machinery (Second Edition), Handbook, New Age International (P) Limited, Publishers.

[9] John D. Anderson Jr., Joris Degroote, G´erard Degrez, Erik Dick, Computational Fluid Dynamics an Introduction, Handbook, Springer.