CFD - Project 1 - Centrifugal Pump Design and Analysis.

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 Performancediagram 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 hasa series of curved vanes fitted inside the shroud plates. The impeller
is always immersed in the water. When the impeller is made to rotate, itmakes the fluid surrounding it also rotates. This imparts centrifugalforce to the water particles, and water moves radially out. In Fig thisprocess is illustrated.

Since the rotational mechanical energy is transferred to the fluid, atthe discharge side of the impeller, both the pressure and kinetic energyof 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 pressurehelps to suck fresh water stream into the system again, and this processcontinues

From foregoing discussions, it is clear that the negative pressure atthe eye of the impeller helps to maintain the flow in the system. If nowater is present initially, the negative pressure developed by therotating air, at the eye will be negligibly small to suck fresh streamof water. As a result, the impeller will rotate without sucking anddischarging any water content. So the pump should be initially filledwith water before starting it. This process is known as priming.

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

From the illustrations of the pump so far, one specialty of the casingis clear. It has an increasing area along the flow direction. Suchincreasing area will help to accommodate newly added water stream, andwill also help to reduce the exit flow velocity. Reduction in the flowvelocity will result in an increase in the static pressure, which isrequired 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 passinga point in the (m) system per unit time. The present study aims toanalyze the fluid flow in a flowbench and perform the grid dependencyand valve lift test and observe the results.

1.3 Pressure Ratio

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

Pressure ratio = Outlet total pressure/ Inlet total pressure

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

2. Geometry and Modelling

In this Project, a 3D model of centrifugal pump is created usingSolidworks CAD software. In this model, I have made some changes in theImpeller.

Fig. 2 ISOMETRIC VIEW OF CENTRIFUGAL PUMP

Fig. 3ISOMETRIC VIEW OF 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 15 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 levelis set into 3 and Advanced Chanel refinement is selected.
9. Run the Simulation and the cut plots are created for the Pressureand 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 channerefinement.

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

8. Observation and Conclusion

1. From the First plot we can see that initially, the velocity is lessso 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
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.