Centrifugal pump design and analysis

Aim: 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 and outlet velocity.

Theory:

Centrifugal Pump

Centrifugal pumps are used to induce flow or raise the 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 a centrifugal force to the water particles, and water moves radially out. In Fig this process is illustrated.

Fig. 1 Centrifugal Pump

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 freshwater 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 speciality 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.

Design and Modelling

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

Parameters for Baseline Simulation:

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 rad/sec.
• The Inlet Boundary Condition is set as Environmental Pressure of 1 bar.
• The Outlet Boundary Condition is the Exit Velocity of 10 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.

Output:

Pressure Variation At 10m/sec

Velocity Trajectory at 10m/s

Results of Parametric Study:

Outlet Velocities: 10,15,20 m/sec

Graph of Comparision:

Pressure V/s outlet Velocity

Observation and Conclusion:

1. Pressure decrease as the velocity at outlet increases.
2. The velocity is less so the mass flow rate is less when the velocity increases the mass flow rate increases.
3. A pump does not create pressure it only creates flow. The pressure is a measurement of the resistance to flow.