Centrifugal pump design and analysis Using SOLIDWORKS

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Abstract

In this Project, Creating a 3D model of a Centrifugal pump, run a baseline flow simulation where inlet flow takes place and then perform a parametric study for different velocities. Showing the Performance diagram and Obtain the relationship between Pressure ratio and mass flow rate and explaining the results. 

1. Introduction

1.1 Centrifugal Pump

Centrifugal pumps are used to induce flow or raise pressure of a liquid. Its working is simple. At the heart of the system lies impeller. It has a series of curved vanes fitted inside the shroud plates. The impeller is always immersed in the water. When the impeller is made to rotate, it makes the fluid surrounding it also rotates. This imparts centrifugal force to the water particles, and water moves radially out. In Fig this process is illustrated.

Since the rotational mechanical energy is transferred to the fluid, at the discharge side of the impeller, both the pressure and kinetic energy of the water will rise. At the suction side, water is getting displaced, so a negative pressure will be induced at the eye. Such a low pressure helps to suck fresh water stream into the system again, and this process continues

From foregoing discussions, it is clear that the negative pressure at the eye of the impeller helps to maintain the flow in the system. If no water is present initially, the negative pressure developed by the rotating air, at the eye will be negligibly small to suck fresh stream of water. As a result, the impeller will rotate without sucking and discharging any water content. So the pump should be initially filled with water before starting it. This process is known as priming.

The impeller is fitted inside a casing. As a result, the water moves out will be collected inside it, and will move in the same direction of rotation of the impeller, to the discharge nozzle.

From the illustrations of the pump so far, one specialty of the casing is clear. It has an increasing area along the flow direction. Such increasing area will help to accommodate newly added water stream, and will also help to reduce the exit flow velocity. Reduction in the flow velocity will result in an increase in the static pressure, which is required to overcome the resistance of the pumping system.

1.2 Mass Flow Rate

The mass flow rate of a system is a measure of the mass of fluid passing a point in the (m) system per unit time. The present study aims to analyze the fluid flow in a flowbench and perform the grid dependency and valve lift test and observe the results.

1.3 Pressure Ratio

Pressure ratio is the ratio between the outlet pressure and the inlet pressure.

Pressure ratio = Outlet total pressure/ Inlet total pressure

The present study aims to analyze the performance diagram and Obtain the relationship between Pressure ratio and mass flow rate and explain the results.

2. Geometry and Modelling

In this Project, a 3D model of centrifugal pump is created using Solidworks CAD software. In this model, I have made some changes in the Impeller.

Fig. 1     ISOMETRIC VIEW OF CENTRIFUGAL PUMP

Fig. 2 ISOMETRIC VIEW OF THE IMPELLER

3. Parameters for Baseline Simulation

4. Procedure

•  Create a 3D Model in Solidworks CAD Software. 
• Modify the Components in the Components Control. 
• The Computational Domain is created. 
• The Rotating Region is selected and the speed is set to 1000 rpm. 
• The Inlet Boundary Condition is set as Environmental Pressure of 1 bar. 
• The Outlet Boundary Condition is the Exit Velocity of 15 m/s. 
• The Surface Goal is set in the Inlet and the Outlet faces. 
• Then the Mesh is created for the model and the Automatic mesh level is set into 3 and   Advanced Chanel refinement is selected.    
• Run the Simulation and the cut plots are created for the Pressure and Velocity and get the values for the goals.

5. Results-Grid Dependency test

For this test, I have set the input variables as output velocity and the values are 10 m/s, 15 m/s, 20 m/s, 25 m/s, 30 m/s. The Level of mesh is set as 3. The number of Iteration for the solver is set as 500 in the calculation control option. The mesh is refined to advanced channel refinement.

 6. Output

Inlet pressure remains the same for all the cases but the outlet pressure varies. When the flow rate at the outlet is high the pressure reduces at outlet which results in the decrease in the pressure ratio.

i. Design point 1 @ velocity 10m/s

• Velocity Plot @ 10m/s

• Pressure Trajectory @ 10m/s

• Velocity Trajectory @ 10m/s

ii. Design point 2 @ velocity 15m/s

• Velocity Plot @

• Pressure Trajectory @ 15m/s

• Velocity Trajectory @ 15m/s

iii. Design point 3 @ velocity 20m/s

• Velocity Plot @ 20 m/s

• Pressure Trajectory @ 20 m/s

• Velocity Trajectory @ 20m/s

iv. Design point 4 @ velocity 25m/s

• Velocity Plot @ 25m/s

• Pressure Plot @ 25m/s

• Velocity Trajectory @ 25m/s

v. Design point 5 @ velocity 30m/s

• Velocity Plot @ 30m/s

• Pressure Plot @ 30m/s

• Velocity Trajectory @ 30m/s 

7. Graphs and comparison

• Pressure Ratio

1. Pressure Ratio Graph

• Mass Flow Rate [Kg/s]

1. Mass Flow Rate Graph

• Relationship between Pressure ratio and Mass flow rate

1. Graph of pressure ratio and mass flow rate

8. Conclusion

• Outlet pressure decreases due to increased outlet velocity according to Burnouli's principle and mass flow rate increases.
• With increase in mass flow rate there is decrease in pressure ratio which suggests that the pumping capacity decreases with increased flow rate.
• With increased flow rate the height upto which water can be pumped decreases.