Centrifugal pump design and analysis

AIM - Creating a 3D model of a Centrifugal pump, run a baseline flow simulation

OBJECTIVES -

1) To carry out analysis on made up centrifugal pump

2) To understand relationship between pressure ratio and mass flow rate

THEORY

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.

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 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

1.	Analysis Type	Internal
2.	Fluid Type	Water
3.	Rotation Type	Local area Averaging
4.	Boundary condition at Inlet	101325 Pa
5.	Boundary condition at Outlet	10 m/s

Results

Parametric Study

Analysis Results

Analysis Plots

Relationship b/w Mass Flow Ratio and Pressure Ratio

Performance Diagram

Flow Trajectories

Explanation

1. From the First plot we can see that initially, the velocity is less so the mass flow rate is less when the velocity increases the mass flow rate increases.
2. From the Second plot, we can see that the pressure ratio is high for low velocity and pressure ratio starts to decrease when the velocity increases.
3. From the graphs, I can figure out that due to performance failure of the laptop the pressure ratio curve varied but later on it showed study decrease in pressure ratio.
4. Velocity plots have proper indication of outflow velocity as assigned.Show in the plots above.
5. A pump does not create pressure it only creates flow. Pressure is a measurement of the resistance to flow.

Conclusion

Hence, the questions requirements are met and the inferences are drawn.

1) Relationship between pressure ratio and mass flow rate is parabolic in nature.

2) Pressure ratio becomes almost constant on further increasing velocity.