Centrifugal pump design and analysis

Abstract:

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

1. Introduction:

1.1 Centrifugal Pump:

Centrifugal pumps are used to induce ow 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 tted inside the shroud plates. The impeller is always immersed in the water. When the impeller is made to rotate, it makes the uid 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 lled 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 ow direction. Such increasing area will help to accommodate newly added water stream, and will also help to reduce the exit ow velocity. Reduction in the ow 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 ow rate of a system is a measure of the mass of uid passing a point in the (m) system per unit time. The present study aims to analyze the fluid flow in a owbench 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 ow 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.

3. Parameters for Baseline Simulation:

4. Procedure:

1. Create a 3D Model in Solidworks CAD Software.
2. Modify the Components in the Components Control.
3. The Computational Domain is created.
4. The Rotating Region is selected and the speed is set to 1000 rpm.
5. The Inlet Boundary Condition is set as Environmental Pressure of 1 bar.
6. The Outlet Boundary Condition is the Exit Velocity of 10 m/s.
7. The Surface Goal is set in the Inlet and the Outlet faces.
8. Then the Mesh is created for the model and the Automatic mesh level is set into 3 and Advanced Chanel re nement is selected.
9. 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.

Goal (Value)	Design Point 1	Design Point 2	Design Point 3	Design Point 4	Design Point 5
Velocity normal to face (Outlet Velocity 2) [m/s]	10	15	20	25	30
inlet total pressure [Pa]	111008.1074	109034.8846	101325	101337.5316	101325
outlet total pressure [Pa]	1535736.603	1408315.141	1068537.797	974117.9613	915280.3292
mass flow rate at outlet [kg/s]	-0.484246239	-0.726385492	-0.968848913	-1.210794692	-1.453659743
mass flow rate at inlet [kg/s]	-0.404036465	-0.27386767	0.952775936	1.011519333	1.580670624

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 plot @ 10m/s

velocity trajectory @ 10m/s

ii. Design point 2 @ velocity 15m/s

Velocity Plot @ 15m/s

pressure plot @ 15m/s

velocity trajectory @ 15m/s

iii. Design point 3 @ velocity 20m/s:

Velocity Plot @ 20m/s

pressure plot @ 20m/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

Velocity normal to face (Outlet Velocity 2) [m/s]	inlet total pressure [Pa]	outlet total pressure [Pa]	preasure ratio
10	111008.1074	1535736.603	13.83445
15	109034.8846	1408315.141	12.91618
20	101325	1068537.797	10.54564
25	101337.5316	974117.9613	9.6126
30	101325	915280.3292	9.03311

GOAL PLOTS:

Goal (Value)	Design Point 1	Design Point 2	Design Point 3	Design Point 4	Design Point 5
Velocity normal to face (Outlet Velocity 2) [m/s]	10	15	20	25	30
inlet total pressure [Pa]	111008.1074	109034.8846	101325	101337.5316	101325
outlet total pressure [Pa]	1535736.603	1408315.141	1068537.797	974117.9613	915280.3292
mass flow rate at outlet [kg/s]	-0.484246239	-0.726385492	-0.968848913	-1.210794692	-1.453659743
mass flow rate at inlet [kg/s]	-0.404036465	-0.27386767	0.952775936	1.011519333	1.580670624

total pressure at inlet:

total pressure at outlet:

Mass flow rate at inlet:

Mass flow rate at outlet:

Graph of pressure ratio and mass flow rate:

8. Observation and Conclusion

1. From the First plot we can see that initially, the velocity is less so the mass ow rate is less when the velocity increases the mass ow 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 gure 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 out ow velocity as assigned.Show in the plots above.

5. A pump does not create pressure it only creates ow. Pressure is a measurement of the resistance to flow.

6. It is evident from other similar studies pressure ratio decrease as the velocity at outlet increase but in my case, the pressure ratio varied due to technical failure of my laptop which did not perform accurately as expected.