Centrifugal pump design and analysis

Aim –

1)To perform CFD analysis on hypothetical centrifugal pump

2)To obtain relation between pressure ratio and mass flow rate.

Introduction-

The three important parts of centrifugal pumps are impeller, volute casing and diffuser.

A) Impeller

Whirling motion is imparted to the liquid by means of backward curved blades mounted on a wheel known as the impeller. As the impeller rotates, the fluid that is drawn into the blade passages at the impeller inlet or eye is accelerated as it is forced radially outwards. In this way, the static pressure at the outer radius is much higher than at the eye inlet radius.

B) Volute Casing –

A volute or scroll collector consists of a circular passage of increasing cross-sectional area.

C) Vaneless diffuser -

For the diffusion process, the vaneless diffuser is reasonably efficient and is best suited for a wide range of operations. It consists simply of an annular passage without vanes surrounding the impeller.

D) Vaned diffuser –

The vaned diffuser is advantageous where small size is important.

The effect of impeller blade shape on performance –

Blade shape can be classified as backward curved, forward curved, radial blade.

Centrifugal pump outlet velocity triangle for varying blade outlet angle -

Charecteristics for varying outlet blage angle-

Here H is manometric head from this it can be observed that theoretically as mass flow rate increases head decreases.

CASE SETUP –

Objective of this project is to analyse hypothetical model of centrifugal pump.

Assigned boundary conditions are –

Inlet: environmental pressure -101325 pa

Outlet: velocity – 10m/s to 30 m/s

Fluid: water

Speed of impeller : 3500 rpm

CFD analysis is performed for six cases by varying flow rate and obtain relationship between pressure ratio and mass flow rate.

Results –

Behaviour for different case-

Effect of increasing mass flow rate on pressure ratio –

Plot of mass flow rate and pressure ratio-

Flow trajectory -

Contour plots for different Cases –

Case 1)

Case2)

Case3)

Case4)

Case5)

Case6)

Conclusion –

From results it can be concluded that as mass plow ratre increase pressure ratio increses initiallly and then decreases with further increase in mass flow rate.