Centrifugal pump design and analysis

OBJECTIVES

• To create a geometry of a centrifugal pump and perform flow simulation using Solidworks
• To Obtain the relationship between Pressure ratio and mass flow rate.

INTRODUCTION

Centrifugal pumps are used to transport fluid by conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy basically comes from the engine or electric motor. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber, from which it exits.

GEOMETRY:

Parts of a Centrifugal Pump:

1. Impeller
2. Casing (Volute)
3. Delivery pipe
4. suction pipe

Working of Centrifugal Pump

The first step in the operation of a centrifugal pump is priming. Priming is the operation in which suction pipe casing of the pump and the position of fluid with the liquid which is to be pumped so that all the air from the position of pump is driven out and no air is left. The necessity of priming of a centrifugal pump is due to the fact that the pressure generated at the centrifugal pump impeller is directly proportional to the density of fluid that is in contact with it.

After the pump is primed the delivery valve is still kept closed and the electric motor is started to rotate the impeller. The delivery valve is kept closed in order to reduce valve is opened the liquid is made to flow in an outward radial direction thereby vanes of the impeller at the outer circumference with high velocity at outer circumference due to centrifugal action vacuum is created.

This cause liquid from the sump to rush through the suction pipe to the eye of impeller thereby replacing long discharge from the center circumference of the impeller is utilized in lifting liquid to required height through delivery pipe.

PROCEDURE:

1. Create a 3D model of centrifugal pump
2. Start the flow simulation by defining the lids
3. Specify inlet boundary condition as inlet pressure = 1 bar
4. Specify outlet boundary condition as outlet velocity = 10 m/sec.
5. Select the required surface goals that need to be computed
6. Converge the simulation based on the number of iterations and run it.
7. Create flow trajectories and cut plots for the velocity and pressure.

RESULTS:

1. Velocity cut plots at different velocities:

2.Pressure cut plots at different velocities:

3. Flow Trajectory

PARAMETRIC STUDY

A study has been carried out to understand the variation of mass flow rate and pressure ratio with respect to outlet velocity in a centrifugal pump. Here, the velocity has been varied from 10 m/sec to 30m/sec in 5 steps. Pressure ratio is the ratio of outlet pressure to the inlet pressure.

Goal (Value)	Design Point 1	Design Point 2	Design Point 3	Design Point 4	Design Point 5
Velocity normal to face (Outlet Velocity 1) [m/s]	10	15	20	25	30
SG Av Total Pressure 1 [Pa](outlet)	8562915.154	7547558.766	2984517.712	2758733.303	4537474.485
SG Mass Flow Rate 1 [kg/s]	-0.427180994	-0.692138324	-0.985329015	-1.23538344	-1.438651023
SG Av Total Pressure 2 [Pa](inlet)	1012310.386	924469.1175	339993.5671	378583.8262	865246.386
Pressure Ratio	8.458	8.164	8.778	7.286	5.244

Note: Mass flow rate is negative because the flow is leaving the boundary.

Performance curve:

Explanation: From the curve, it is clear that the mass flow rate increases with an increase in velocity.

Explanation: fluctuation in the pressure is due to the interaction of fluid (water) with impeller and casing.

CONCLUSION: Hence from performance curve it is clear that the mass flow rate increases with an increase in velocity and mass flow rate increases with an increase in velocity.