Centrifugal pump design and analysis

AIM:

To design and then perform Flow Simulation on a Centrifugal pump using SOLIDWORKS.

THEORY:

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. 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. Centrifugal pumps are often chosen for their flow rate capabilities, abrasive solution compatibility, mixing potential, as well as their relatively simple engineering.

Centrifugal pump converts rotational energy, often from a motor, to energy in a moving 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 of the casing decelerates the flow and further increases the pressure. It is important to note that the fluid is not pushed radially outward by centrifugal force, but rather by inertia, the natural tendency of an object to continue in a straight line when traveling around circle. This can be compared to the way a spin-cycle works in a washing machine.

Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid with surfaces defined by boundary conditions.

PROCEDURE:

• Create a 3D model of the Centrifugal Pump by first designing the impeller and then the casing provide uncheck the mesh results option and then design the inlet and delivery pipe and combine it with the casing geometry. After this create a bound region which will be used for providing the rotation to the impeller. After this convert it into a shell.

• Now for the flow simulation firstly create lids at both the openings. Now with the help of wizard set an internal flow simulation with rotation as a parameter.

• Now by right clicking on the input data and then select component control and from there uncheck the bound that was created for setting the rotational speed. And then select the calculation control option and there set only iteration and give a value of 500.
• Now select the rotational regions and here insert the bound that was left above.
• Now set the boundary conditions starting with the inlet face here prove an environment pressure and then at the delivery face provide an outlet velocity of 10 m/s.
• Now set surface goals, average total pressure at inlet and outlet of the casing and mass flow rate at the delivery face and also provide an equation goal for calculating the pressure ratio.
• Now set the mesh level and then run the simulation.

• Now for parametric study select the outlet velocity as the input variable.
• Now for output parameters select all the plots and also the goals. Then run the study.

RESULTS:

FOR 10 m/s OUTLET VELOCITY

FOR 20 m/s OUTLET VELOCITY

FOR 30 m/s OUTLET VELOCITY

FOR 40 m/s OUTLET VELOCITY

PARAMETRIC STUDY

NOTE : THE NEGATIVE SIGN IN MASS FLOW RATE ONLY SIGNIFIES THAT THE FLUID IS BEING DISCHARED FROM THE PUMP

NOTE : PRESSURE RATIO = TOTAL OUTLET PRESSURE / TOTAL INLET PRESSURE

CONCLUSION:

• We can see from the pressure contour that at the periphery the pressure is the highest in all the cases and also as the outlet velocity increases area of this contour also increases, but at 30 m/s the pressure is the high in almost full volume whereas at 40 m/s outlet velocity there is a slight decrease in pressure at the center of the impeller.
• We can see that there in not much difference in the velocity contour as the outlet velocity increases, the noticeable difference are at the delivery pipe. The velocity of the fluid is seen to be low near the center of the impeller whereas it is high at the end of the vanes.
• The average total pressure at the inlet increases as the velocity increases but it can be seen that it suddenly decreases at 40 m/s outlet velocity. Same is the case with the average total pressure at the outlet.
• The mass flow rate increases linearly as the outlet velocity increases.
• It can be seen that at low velocity the pressure ratio is quite high and it decreases as the outlet velocity increases, and we can also say that that as the pressure ratio decreases the mass flow rate increases but at 30 m/s outlet velocity there can be seen a rise in the pressure ratio.