Centrifugal pump design and analysis

in this project, we will design a centrifugal pump and conduct a parametric study to understand the flow trajectories and pressure at the different outlet velocities. the main goal of this project was to analyze the max pressure created at the outlet.

Theory

Centrifugal pump is a device to create a pressure difference across the inlet and outlet. Surging is one of the criteria used for designing pumps. It may be explained in the following way. If we suppose that the compressor is operating at a point 'D' on the part of the characteristics curve (Figure 1) having a positive slope, then a decrease in mass flow will be accompanied by a fall in delivery pressure. If the pressure of the air downstream of the compressor does not fall quickly enough, the air will tend to reverse its direction and will flow back in the direction of the resulting pressure gradient. When this occurs, the pressure ratio drops rapidly causing a further drop in the mass flow until the point 'A' is reached, where the mass flow is zero. When the pressure downstream of the compressor has reduced sufficiently due to reduced mass flow rate, the positive flow becomes established again and the compressor picks up to repeat the cycle of events which occurs at high frequency.

This surging of air may not happen immediately when the operating point moves to the left of 'B' because the pressure downstream of the compressor may at first fall at a greater rate than the delivery pressure. As the mass flow is reduced further, the flow reversal may occur and the conditions are unstable between 'A' and 'B'. As long as the operating point is on the part of the characteristics having a negative slope, however, the decrease in mass flow is accompanied by a rise in delivery pressure and the operation is stable.

Figure 1 The theoretical characteristic curve

Priming:

Most centrifugal pumps are not self-priming. In other words, the pump casing must be filled with liquid before the pump is started, or the pump will not be able to function. If the pump casing becomes filled with vapors or gases, the pump impeller becomes gas-bound and incapable of pumping.priming can be seen in the animation above.(till fluid is not filled in casing the pumping doesn't start properly)

STEPS TO DESIGN:

• Create a 3D Model in Solidworks CAD Software.
• Modify the Components in the Components Control.
• The Computational Domain is created.
• The Rotating Region is selected and the speed is set to 100 rad/sec.
• The Inlet Boundary Condition is set as an Environmental Pressure of 1 bar.
• The Outlet Boundary Condition is the Exit Velocity of 10 m/s.
• The Surface Goal is set in the Outlet face.
• Then the Mesh is created for the model and the Automatic mesh level is set into 3 and Advanced Chanel refinement is selected.
• Run the Simulation and the cut plots are created for the Pressure and Velocity and get the values for the goals.

SIMULATION SETUP:

Every time we can't rely on the automatic convergence system by the software because it literally solves the L.H.S=R.H.S if any one of the conditions is satisfied then it terminates the calculation.

so, by keeping in this mind we are taking the 500 iterations as conditions need to be satisfied by the solver.

DESIGN POINTS:

Goal (Averaged Value)	Design Point 1	Design Point 2	Design Point 3	Design Point 4
Velocity normal to face (Outlet Velocity 1) [m/s]	10	12.5	17.5	20
SG Average Dynamic Pressure 1 [Pa]	54056.5221	82781.36409	163307.3098	212648.2783

DESIGN POINT 1:OUTLET VELOCITY = 10 m/sec:

DESIGN POINT 2:OUTLET VELOCITY = 12.5 m/sec:

DESIGN POINT 3:OUTLET VELOCITY = 17.5 m/sec:

DESIGN POINT 4:OUTLET VELOCITY = 20 m/sec:

CONCLUSION

by observing the above results we can able to say that the velocity and the pressure are inversely proportional to one another. so, the geometry is makeup the results are not accurate. by making real geometry we can get accurate results and better understanding.