Centrifugal pump design and analysis

CENTRIFUGAL PUMP DESIGN AND ANALYSIS

AIM – Design a centrifugal pump and run flow simulation analysis to obtain performance diagram.

OBJECTIVES-

1. Create 3D model of centrifugal pump.
2. Run a parametric study for different values of outlet velocity. Obtain outlet mass flow rate and outlet pressure.
3. Obtain pressure ratio vs. mass flow rate.

INTRODUCTION-

Centrifugal pumps are used to transport fluids by the conversion of rotational kinetic energy to the hydrodynamic energy of the fluid flow. The rotational energy typically comes from an engine or electric motor. They are a sub-class of dynamic axisymmetric work-absorbing turbomachinery The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from which it exits.

A portion of the energy goes into kinetic energy of the fluid. Fluid enters axially through eye of the casing, is caught up in the impeller blades, and is whirled tangentially and radially outward until it leaves through all circumferential parts of the impeller into the diffuser part of the casing. The fluid gains both velocity and pressure while passing through the impeller. The doughnut-shaped diffuser, or scroll, section of the casing decelerates the flow and further increases the pressure.

PROCEDURE-

1. Click on New > Part. Sketch two circles of diameter 0.025 m and 0.05m in top plane. Create two three point arcs between them to make vanes.
2. Use Power Trim to create 2d sketch. Exit sketch. Click on Extrude Boss/Base to create the impeller.
3. Create a circle in top plane for casing. Click on Extrude Boss/Base to create the casing. Uncheck the Merge result before clicking on ok.
4. Create another circle on top plane. Extrude again to generate inlet pipe of pump.
5. Create outlet pipe using Sweep Boss/Base. Uncheck the Merge result before clicking on ok.
6. Now, click on Direct Editing>Combine and select Boss extrude 2, Boss extrude 3 and Boss sweep.
7. Create a cylinder between impeller and casing. Save the part file.

8. Click on Wizard in Flow Simulation. Use SI units. Select flow type internal. Select water as working fluid.
9. In Physical features> Rotation. Use Local Averaging.
10. Now Right Click on Boundary conditions > Insert boundary conditions. Select inlet face and put environment pressure p=101325 Pa.
11. Insert one more boundary condition. Put outlet velocity at outlet face =10m/s.
12. Insert Rotating Region. Select the cylinder between impeller and casing. Set angular velocity to1000 rad/s.
13. Select Surface goal plot and select mass flow rate for outlet. Again select surface goal to calculate pressure at outlet.
14. Click on Calculation control option. In Finish section uncheck everything except Maximum iterations. Increase it to 500.
15. Click on Run. Wait for all iterations to finish.
16. Now start a New Parametric study. In input variables select add simulation parameter> Boundary conditions > Outlet velocity.
17. For values add range from 10m/s to 30m/s. Set number of values to 5. Select output parameters both goal plots.
18. Click on Run. Wait for all iterations to finish.
19. Click on Export button to draw all plots in Excel.

RESULTS:

Cut plot of velocity:

Cut plot of pressure:

Flow trajectory of centrifugal pump:

Results of parametric study-

Plot of outlet pressure:

Plot of mass flow rate:

Plot of Pressure Ratio vs. Mass flow rate

.

EXPLANATIONS AND CONCLUSIONS-

1. From plot we can easily see that mass flow rate increases with increase in outlet velocity.
2. Pressure drop becomes higher as outlet velocity varies from 10 m/s to 20m/s and again reduces from outlet velocity 20m/s to 30m/s.
3. With flow trajectory we can easily see swirl inside in the centrifugal pump. It helps to analyze flow in a better way.
4. Generally, the performance diagram of pressure ratio vs. mass flow rate is parabolic in nature, but due to random dimensions and less number of design points, our curves have peak and valleys.