study of impeller design considerations of a aa a ... 3 study of impeller design...jss academy of...

Volume – II, Issue – I, (January – June, 2016) SANKALAN: - The Journal of Science, Technology And Humanities I.S.S.N. (Online): 2455-3557

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Study of Impeller Design Considerations of Study of Impeller Design Considerations of Study of Impeller Design Considerations of Study of Impeller Design Considerations of

a a a a Centrifugal Pump and Investigate its Centrifugal Pump and Investigate its Centrifugal Pump and Investigate its Centrifugal Pump and Investigate its

effect on Pump Performance using ANSYSeffect on Pump Performance using ANSYSeffect on Pump Performance using ANSYSeffect on Pump Performance using ANSYS

1Rudra Pratap Singh, 2Sonali Singh 3Nishi Chauhan 4Manul Rastogi, 5Navneet Kumar Pandey

1, 2, 3, 4 B.Tech, 5Assistant Professor, Department of Mechanical Engineering, JSS Academy of Technical Education, Noida, Uttar Pradesh, India

E-mail:- [email protected]

Abstract: An impeller is a rotor used to increase the pressure and flow of a fluid in pumps. The most critical parameters which affect the performance of centrifugal pumps are number of blades, impeller outlet diameter and the blade angle. To evaluate the results, CFD analysis is carried out using ANSYS CFX Workbench. The model pump with a rotation speed of 1450 rpm and an impeller having 5 number of blades has been considered. The number of blades are varied as 4, 6, 7 and 8. Similarly the effect of outer diameter on head values and efficiency has been studied. On the basis of which, the characteristics of centrifugal pump with different blade numbers and at different outer diameter are simulated and predicted by using ANSYS software. The best pump design parameters have been selected after evaluating and comparing the results.

Keywords: Pump Impeller, ANSYS CFX, CFD, Meridional Velocity, Pressure, Efficiency.

I. INTRODUCTION

A centrifugal pump is a mechanical device which converts available mechanical energy into kinetic and pressure energy of fluid. It is a roto-dynamic device in which initially the kinetic energy of the fluid increases and then this kinetic energy of the fluid converted into pressure energy.

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. When

velocity is reduced due to resistance encountered in the system, pressure increases. The actual energy available for work at any point in a system is a combination of the available velocity head and pressure head at that point.

At present, single and multistage centrifugal

pumps are widely used for agricultural, sewage, industrial and mining purposes. One of the most important components of a centrifugal pump is the impeller. The performance characteristics related to the pump comprising the head and the overall efficiency rely a great deal on the impeller.

To achieve better performance for a centrifugal pump, design parameters are:

1. The number of blades 2. Impeller outlet diameter 3. Impeller outlet blade angle 4. Blade height 5. Blade width

Liquid flow is quite complex due to its three

dimensional behavior and turbulence. Hence the parameters governing the behavior fluid flow through impeller and affects its performance must be accurately determined. A) Effect of Number of Blades

The pump head as a function of the volume flow rate, illustrating that the pump head increases with a greater blade number. This is explained by the decrease in the liquid pressure drop in the flow passage with an augmented impeller blade number, keeping the same total volume flow rate. The pump brake horsepower


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increases relatively with the augmented blade number. This is due to the increase in the request pump shaft torque, as the pump blade number also increases.

B) Effect of Impeller Diameter

The pump head increases with increasing impeller diameter, which can be explained by the fact that the liquid static pressure drop in impeller decreases with increasing impeller diameter. In other words, for a given volume flow rate, the pressure difference between the volute outlet and the impeller inlet is higher for an impeller with a greater diameter.

The brake horsepower increases relative to the increasing impeller diameter, due to the requested augmented impeller shaft torque relative to the size of the impeller diameter. Hence the efficiency decreases at greater diameter.

II. PUMP SPECIFICATIONS

The specifications of centrifugal pump undertaken in the current analysis are shown in Table 1.

Table 1. Analysis of Design Parameters

S No. DESIGN PARAMETER

(variables)

SET 1

1. Number of Vanes

5

2. Rotational Speed 1450 rpm

3. Volume Flow Rate

280 m3/hr

4. Pump Head 20 m

5. Inlet Flow Angle 90o

6. Blade Angle 22.5o

III. MESHING

The geometry and the mesh of a six bladed pump impeller domain are generated using Ansys Workbench. An unstructured mesh with tetrahedral cells is also used for the zones of impeller of meshed data:

Total Nodes: 559878 Total Elements: 515858

Geometry Plot: - The geometry plot of impeller with 5 blades has been shown as:

Figure 1. Surface Geometry of Impeller

IV. OBSERVATIONS

After generating the model set and running various sets, the following observations regarding blade loading, pressure contours at inlet and outlet span, stream-wise variation of Pt and Ps has been made:

A) Blade loading of Sample Set

Blade loading at 20%, 50% and 80% are obtained with maximum pressure drop at 80% span and minimum pressure drop at 20% span is observed at 10% stream wise and trailing edge. Similarly blade loading for 4, 5, 7, 8 blades are also obtained.

Figure 2. Blade Loading at 20% Span for Blade 5.


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B) Pressure Contour at Inlet and Outlet Span of Sample Set

As fluid flows across the inlet of blade, it is observed that pressure is maximum at low periodic and decreases towards high periodic across the inlet span.

As fluid flows across the outlet of blade, it is observed that pressure is maximum at high periodic and decreases towards low periodic across the outlet span.

Figure 5. Pressure Variation at Inlet Span of Blade.

Figure 6. Pressure Variation at Outlet Span of Blade.

C) Pressure Variation on Meridional Surface

The variation of pressure on the meridional surface has been shown for different blade numbers as 4, 5, 6, 7, 8.

The pressure at the inlet is minimum and it increases towards the outlet. But there are certain regions of high pressure in between.

Figure 7. Pressure Variation along Meridional Surface at Blade Number 4.



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Figure 11.Pressure variation along meridional surface at Blade number 8.

D) Stream wise Variation of Mass Averaged Total Pressure and Static Pressure

Stream wise variation of mass averaged total pressure and static pressure is shown in respective figures.

Figure 12. Stream wise Pressure Variation (Pt & Ps) at Blade Number 4.


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Figure 13. Stream wise Pressure Variation (Pt &

Ps) at Blade Number 5.


Figure 15. Stream wise pressure variation (Pt. & Ps) at blade number 7.


Here total pressure is always more than the static pressure because it also comprises of dynamic head. The behavior of total and static pressure is studied and a gradual increase is observed from inlet to outlet. The total and static pressures are observed constant at low stream wise locations due to the inlet duct before the impeller.

Since at higher stream-wise locations there is a dynamic energy transfer from the rotating impeller to the fluid, the pressures are observed to be increasing from 35% stream wise location till 80%. From 90% stream wise location slight increase in mass averaged total pressure is observed due to the absence of energy transfer in outlet duct.

Whereas static pressure keeps on rising at the end of stream wise location due to diffusion of fluid in the outlet duct.

V. RESULT AND ANALYSIS

A) Effect of Variation of Number of Blades

First of all the effect of variation of number of blades on the characteristics of pump has been studied and the plots are obtained.

B) Variation of Head and Efficiency vs. Mass Flow Rate

Head and efficiency output are obtained with different mass flow rate as shown in table as shown below.


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C) Diameter

For blade 6, outer diameter 270, 275, 280, 285 (all in mm) are selected and analyzed for performance evaluation. Maximum head varied from 22.662 to 21.021 at 77.8 kg/s with drop of head from 3.927 for OD 270 to 0.678 for OD 285 at 200 kg/s.

The head and efficiency variations v/s mass flow rate at different outer diameter has been shown as:

Figure 17. Head vs. Mass Flow at Outer Tip Diameter 270, 275, 280, 285 mm.

Figure 18. Efficiency vs. Mass Flow at Different Outer Tip Diameter 270, 275, 280, 285 mm

VI. CONCLUSION

A centrifugal pump impeller is modeled and analyzed using computational fluid dynamics. The performance results, blade loading plot at span wise, stream wise variation of mass averaged total pressure and static pressure for designed flow rate are presented.

To investigate the effect of the impeller blade number on the pump head and the overall pump efficiency, impeller with number of blades 4, 5, 6, 7 and 8 were selected, while the other parameters were kept constant.

The variation of efficiency is complex. It initially increases till a certain value of mass flow rate and then decreases. But it is found maximum at blade number 6.

Afterwards for maximum efficiency of blade 6, outer diameter 270, 275, 280, 285(all in mm) were selected and analyzed for performance evaluation.

Efficiency is best for blade 6 of OD 270 mm at mass flow 100 kg/s for given sets of blade number and outer diameter.

VII. REFERENCES

[1] Frank M White, “Fluid Mechanics”, Tata McGraw-Hill, Sixth Edition, 2008.

[2] Fox W Robert, McDonald T .Alan, “Introduction to Fluid Mechanics”, Eighth Edition, John Wiley & Sons, 2011.

[3] Yunus A.Cengel, John M.Cimbala, “Fluid Mechanics-Fundamentals and Applications”, Mcgraw Hill Higher Education, 2006.

[4] K.M. Pandey, A.P. Singh and Sujoy Chakraborty, “Numerical studies on effects of blade number variations on performance of centrifugal pumps at 2500 rpm”, Journal of Environmental Research And Development Vol. 6 No. 3A, Jan-March 2012.

[5] LIU Houlin, WANG Yong, YUAN Shouqi, TAN Minggao, and WANG Kai,“Effect of Blade number on characteristics of centrifugal pumps”, Research Center of Fluid Machinery Engineering and Technology, Jiangsu University, Zhenjiang212013, China.

[6] S.Chakraborty and K.M.Pandey, “Numerical Studies on Effects of Blade Number Variations on Performance of Centrifugal Pumps at 4000 RPM” IACSIT International Journal of Engineering and Technology, Vol.3, No.4, August 2011.

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70 120 170 220

He

ad

(in

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)

Mass flow (in kg/s)

OD 270 OD 275 OD 280 OD 285

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70 85 100 115 130 145 160 175 190 205

eff

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ncy

mass flow OD 270 OD 275

OD 280 OD 285


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Rudra Pratap is pursuing B.Tech in Mechanical Engineering from JSS Academy of Technical Education Noida, (Affiliated to Dr. A.P.J Abdul Kalam Technical

University, Lucknow, Uttar Pradesh).

He has interest in various technical projects in his concerned domains.

Sonali Singh is B.Tech in Mechanical Engineering from JSS Academy of Technical Education Noida, (Affiliated to Dr. A.P.J Abdul Kalam Technical University, Lucknow, Uttar Pradesh).

She has interest in various technical projects in his concerned domains.

Nishi Chauhan is B.Tech in Mechanical Engineering from JSS Academy of Technical Education Noida, (Affiliated to Dr. A.P.J Abdul Kalam

Technical University, Lucknow, Uttar Pradesh).

She has interest in various technical projects in his concerned domains.

Manul Rastogi is B.Tech in Mechanical Engineering from JSS Academy of Technical Education Noida, (Affiliated to Dr. A.P.J Abdul Kalam Technical University, Lucknow, and Uttar Pradesh).

He has interest in various technical projects in his concerned domains.

Mr. Navneet Kumar Pandey is working as an Assistant Professor in the Department at JSS Academy of Technical Education, Noida, Uttar Pradesh. His areas of Interest include design of

systems.

He has vast experience in the field of teaching and research in past many years.

study of impeller design considerations of a aa a ... 3 study of impeller design...jss academy of...

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