DESIGN AND ANALYSIS OF CENTRIUGAL PUMP
1 AMIT H. BHUPTANI, 2 PROF. RAVI K. PATEL, 3 K.M. BHUPTANI
1M.Tech.[CAD/CAM] Student, Department Of Mechanical Engineering, U.V. Patel College of Engineering And Technology, Kherva, Gujarat
2 Asst.Professor, Department Of Mechanical Engineering, U.V. Patel college of Engineering And Technology, Kherva, Gujarat
3 PhD Scholar, Mech. Engg.,J.J.T. University, Jhunjhunu, Rajasthan
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Keywords- Pump impeller, SolidWorks 2009, Computational fluid dynamics, Fluid flow (CFX), Efficiency
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I: INTRODUCTION
Pump is a mechanical device generally used for raising liquids from a lower level to a higher one. This is achieved by creating a low pressure at the inlet and high pressure at the outlet of the pump. However, work has to be done by a prime mover to enable it to impart mechanical energy to the liquid which ultimately converts into pressure energy. It is widely in used in industries and residential applications. Centrifugal pumps are the machines, which employ centrifugal force to lift from a lower level to a higher level by developing pressure. The centrifugal pump moves liquid by rotating one or more impellers inside a volute casing. The liquid is introduced through the casing inlet to the eye of the impeller where it is picked up by the impeller vanes. [1, 2].
II: LITERATURE REVIEW
E.C. Bacharoudis, A.E Filios, M.D. Mentzos, D.P. Margaris [3] presented the influence of the outlet blade angle on the performance with the help of CFD simulation. He studied that as the outlet blade angle increases the performance curve becomes smoother and flatter. In this study, the performance of impeller with same outlet diameter having different outlet blade angles is evaluated and concluded that, when pumps operate at nominal capacity, the gain in the head is more than 6%, when outlet blade angle increases from 20° to 50°. A. Manivannan [4] had studied about the CFD analysis of mixed flow impeller is done and the results are compared with the existing impeller having head H = 19.24 m and efficiency = 55%. In the analysis three modified model of the impeller were created by changing the inlet and outlet vane angles and concluded that by varying the outlet angle performance is effected the most. Swapnil Urankar, Dr. H S Shivashankar, Sourabh Gupta [5] had presented the impeller and volute designed by Walter K Jekat method and error triangle method, which was modified during this work by taking equal divisions and varying vane inlet angle from hub to shroud. The model prepared is been analyzed in CFD tool CFX and its performance is analyzed at different flow rates. At, inlet the boundary conditions was 0 pa, and at outlet 500 m3/hr, 1800 rpm. Finally, concluded that increase in efficiency is due to little twist provided at the leading edge of the vane by varying the leading edge angle from hub to shroud, and small modification in the vane can give very good results. S.RAjendran and Dr. K. Purushothaman [6] presented the work that describes the simulation of flow in the impeller of a centrifugal pump having head H = 10m and discharge Q = 0.0125 m3/sec. The flow pattern, pressure distribution in the blade passage, blade loading plot at 50% span, stream wise variation of mass averaged total pressure was presented. He also concluded that CFD predicted value of head at the design flow rate is approximately H =9.4528 m, and pressure contours show a continuous pressure rise from leading edge to the trailing edge of the impeller due the dynamic head developed by the rotating pump impeller. Mitul G. Patel, Subhedar Dattatraya, Bharat J. Patel [7] carried out the analysis of the impeller used in the mixed flow submersible pump. Fluid flow (CFX) was used for the analysis purpose and due to constant mass flow rate, same boundary condition, i.e. the mass flow rate at the inlet and outlet was applied, the hub and shroud was defined as a wall. And obtained (1) pressure and velocity distribution in meridional view of impeller and in blade to blade view of impeller and concluded that the head generated by the CFX showed good agreement with the experimental head.
III: CONVENTIONAL DESIGN OF PUMP
The following are the duty point parameters, required for the designing of pump. 1) Head (H) = 21.5m, 2) Discharge (Q) = 0.016m3s, 3) Speed (n) = 1450 rpm. The design steps are as follows: [8]
1. Calculation of Shape Number (Nsh):
Nsh =103*n'*Q(gh)34
Where n’ is in rps
2. Calculation of Power (P):
· Power input to the pump, Pc is given by,
PC =ρ*g*H*Qηov
The calculation of overall efficiency is done from the figure 1.
Figure.1 Efficiency as a function of shape number
· Calculation of power to be supplied by the Motor PCm,
Pcm=Molf*PC
Where Molf is overloading factor.
3. Calculation of Shaft Diameter (dsh):-
dsh=316*Pcmω*π*τtor
4. Calculation of Hub Diameter (dh):-
dh=1.4*dsh
5. Calculation of Eye Diameter (de):-
de=4.5*3Qn
6. Impeller inlet diameter (Di):-
Di=1.05 to 1.02 de
7. Calculation of inlet vane angle (β1):-
β1=tan-1(Cm1u1)
8. Tangential velocity at inlet (U1):-
U1=π*Di*n60
9. Calculation of number of Vanes (Z):-
10. Calculation of Suction Pipe Diameter (DS):-
Cm1=CO,
Where Cm1= Flow velocity at inlet
But, CO = 0.06 to 0.08*3Qn2
11. Inlet width at the impeller (B1):-
· The flow area just inside the vane passage at the inlet, is
A1=Ф1*Q'Cm1
· Vane contraction factor at the inlet,
Ф1=t1t1-Su1
Where, t1= Pitch of vanes
Su1= Peripheral vane thickness at the inlet
t1=π*DiZ
· Peripheral Vane thickness at inlet,
Su1=S1Sinβ1
Where, S1= Vane thickness at inlet 5 to 8 mm.
B1=A1π*Di
12. Vane angle at the outlet (β2):-
β2=35-Nsh8
13. Calculation of outlet diameter (DO):-
U2=Cm22tanβ2 +((Cm2 2tanβ2)2 + gHb1∞)12
· Hydraulic efficiency ηhy,
ηhy = 1− 0.42(logde-0.172)2
· Theoretical Head Hb1,
Hb1= Hηhy
· Flow velocity at outlet, Cm2 = 0.8 to 0.9Cm1
Substituting the value of U2, Do = U2*60π*n . Similar steps can be applied for obtaining the outlet width of blade (B2) as for inlet width (B1).
14. Relative velocity at inlet and outlet (Vr):-
Vr1,2=Cm1,2Sinβ1,2
The calculated parameters are as below.
1. / Shape Number Nsh = 562. / Power input to the pump, Pc = 4.68 kw
3. / Power to supplied by motor, Pcm = 6.09 kw
4. / Shaft Diameter, dsh = 17.94 mm
5. / Hub diameter, dh = 25.11 mm
6. / Eye Diameter, de = 104.06 mm
7. / Impeller inlet diameter, Di = 109.26 mm
8. / Impeller outlet diameter, Do = 254.20 mm
9. / Impeller inlet width, B1 = 37.89 mm
10. / Impeller outlet width, B2 = 14.54 mm
11. / Number of vanes, Z = 8
12. / Inlet vane angle, β1 = 13.98°
13. / Outlet vane angle, β2 = 28°
14. / Tangential velocity at inlet, U1=8.29 m/s
15. / Tangential velocity at outlet, U2=19.2 m/s
16. / Flow velocity at inlet, Cm1 = 2.07 m/s
17. / Flow velocity at outlet, Cm2 = 1.65 m/s
18. / Relative velocity at inlet, Vr1 = 8.64 m/s
19. / Relative velocity at outlet, Vr2 = 3.51 m/s
20. / Hydraulic efficiency, hy = 87.7%
21. / Theoretical head, Hb1 = 24.51 m
IV: MODELING AND ANALYSIS
The model of closed impeller was created using SolidWorks 2009, as shown in figure 2, and figure 3, shows meshed cavity model in ANSYS 13.0 Workbench. Computational Fluid Dynamics (CFD) is the process of solving fluid flow equations of mass, momentum, and energy on computer as applied to a particular geometry and flow conditions. For, the analysis Fluid Flow (CFX) was used as simulation tool. Boundary conditions: Centrifugal pump impeller is considered as rotating frame of reference and the working fluid through the pump is water at 25°c. Also, the K- ε turbulence model with turbulence intensity of 5%. At inlet, mass flow rate of 16 kg/s and at outlet, static pressure (atm), also hub and shroud are considered as walls. No of nodes = 10546, No of elements = 44630.
Figure 2. CAD model of impeller
Figure 3. Meshed model of impeller
V: RESULTS AND DISCUSSION
The flow conditions inside the impeller can be varied by changing the geometric features of the impeller. The table 1 and table 2, below shows vane angles of modified impeller and existing and optimum vane angles.
Table 1. Vane angles of modified impeller
IMPELLER DESIGN / INLET ANGLE (°) / OUTLET ANGLE (°)Existing / 13.98° / 28°
Impeller 1 / 11.98° / 28°
Impeller 2 / 15.98° / 28°
Impeller 3 / 13.98° / 26°
Impeller 4 / 13.98° / 30°
Table 2. Existing and optimum vane angles
IMPELLER DESIGN / INLET ANGLE (°) / OUTLET ANGLE (°)Existing / 13.98° / 28°
Impeller 4 (Optimum) / 13.98° / 30°
Fig 4. 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. Fig 5. Shows pressure at outlet of impeller, before entering the casing.
Figure 4. Inlet pressure contour of existing impeller
Figure 5. Outlet pressure contour of exisitng impeller
Figure 6. Inlet pressure contour of impeller 4
Figure 7. Outlet pressure contour of impeller 4
Similarly, fig 6 and fig 7, shows the inlet and outlet pressure contour of impeller 4, having maximum pressure as compared to existing impeller, which ultimately increases the head then the existing impeller.
a) Head variation
The characteristic curve between head and discharge is shown in figure 8. It shows that for the existing impeller, that as the discharge increases the head decreases. Also the discharge rate increases the velocity of fluid also increases. The characteristic curve between head and discharge for the modified impeller 1 shows that the head is increased by 24.10 % at best efficiency point. The characteristic curve between head and discharge for the modified impeller 2 shows that the head is decreased by 11.45 % at best efficiency point. The characteristic curve between head and discharge for the modified impeller 3 shows that the head is decreased by 34.12 % at best efficiency point. The characteristic curve between head and discharge for the modified impeller 4 shows that the head is increased by 28.85 % at best efficiency point. Table 3. shows head at various flow rate.
b) Efficiency variation
The characteristic curve between efficiency and discharge is shown in figure 9, it shows that the efficiency for the existing impeller starts decreasing after 16 lps. Thus efficiency is decreasing while operating in higher discharge rate. The characteristic curve between efficiency and discharge for the modified impeller 1 shows that the efficiency is increased by 24.50 %. The characteristic curve between efficiency and discharge for the modified impeller 2 shows that the efficiency is decreased by 10.93 %. The characteristic curve between efficiency and discharge for the modified impeller 3 shows that the efficiency is decreased by 33.46 %. The characteristic curve between efficiency and discharge for the modified impeller 4 shows that the efficiency is increased by 29.30 % as compared to the existing impeller, which is maximum compared to all the other impellers at same duty point.
Table 3. Head at various discharge
Discharge (lps) / Head (m) of impellerExisting / 1 / 2 / 3 / 4
10 / 26.86 / 34.51 / 25.89 / 21.95 / 35.82
13 / 24.40 / 31.60 / 22.31 / 18.66 / 33.12
16 / 21.5 / 28.33 / 19.29 / 16.03 / 30.22
19 / 17.18 / 22.63 / 14.49 / 12.42 / 24.33
22 / 14.19 / 18.48 / 11.69 / 9.71 / 20.24
Figure 8. Head vs. Discharge
Figure 9. Efficiency vs. Discharge
VI: CONCLUSION
Based on the detailed design and analysis of impeller, following conclusions were derived:
· The best efficiency point of the pump is found to be 16 lps.
· The existing impeller, the head, and efficiency are found out to be 21.5 m and 55%.
· The impeller 1, the percentage increase in the head, and efficiency are 24.10% and 24.50%.
· The impeller 2, the percentage decrease in the head, and efficiency are 11.45% and 10.93%.
· The impeller 3, the percentage decrease in the head, and efficiency are 34.12% and 33.46%.
· The impeller 4, the percentage increase in the head, and efficiency are 28.85% and 29.30%.
Based on the above analysis one can conclude that impeller4 gives better performance as compared to the existing impeller as well as other modified impellers. Thus CFD is an effective tool to calculate quickly and inexpensively the effect of design parameter of pump.
REFERENCES
[1] / G.K. Sahu., Pumps, New Age International Publishers, First edition, 2000.[2] / Ross Mackay., The Practical Pumping Handbook, Elsevier Science and Technology Books, 2004.
[3] / E.C. Bacharoudis, A.E. Filios, M.D. Mentzos, D.P. Margaris. “Parametric study of a centrifugal pump impeller by varying the outlet blade angle”. The Open Mechanical Engineering Journal; 2, pp.75-83; 2008.
[4] / A. Manivannan. “Computational fluid dynamics analysis of a mixed flow pumps impeller”. International Journal of Engineering, Science and Technology, vol.2, no.6, pp.200-206, 2010.
[5] / Swapnil Urankar, Dr. H.S. Shivashankar. “Design and CFD analysis of single stage, end suction, radial flow centrifugal pump for mine dewatering application”. IJREAS, vol.2, issue 2, pp.6-18, Feb. 2012.
[6] / S. Rajendran, Dr.K. Purushothaman. “Analysis of a centrifugal pump impeller using ANSYS-CFX”. International Journal of Engineering Research and Technology, vol.1, issue 3, May. 2012.
[7] / Mitul G. Patel, Subhedar Dattatraya, Bharat J. Patel. “CFD analysis of mixed flow submersible pump impeller”. Indian Journal of applied research, vol.1, issue 9, pp.97–100, June. 2012.
[8] / Prof. S. Kumaraswamy. “Databook for design of Centrifugal Pumps”. Center for Industrial Consultancy and Sponsored Research, IIT Madras.
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