Question

A centrifugal pump delivers water against a net head of 14.5 m and a design speed of 1000 r.p.m. The vanes are curved back to an angle of 30° with the periphery. The impeller diameter is 300 mm and the outlet width is 50 mm. What is the tangential velocity of impeller at outlet ? 
1. 15.7 m/s 
2. 13.2 m/s
3. 9.7 m/s
4. 11.2 m/s

Answer 1

Correct Answer - Option 1 : 15.7 m/s 

Concept:

The tangential velocity of the impeller is given as:

U = πDN/60

Where

D is the diameter of the impeller

N is the speed in rpm

Calculation:

Given:

D = 300 mm = 0.3 m; N = 1000 rpm, H = 14.5 rpm

Curve back angle = 30 ° , Outlet width = 50 mm

Tangential Velocity (U) is:

\(U = \frac{{\pi\; \times \;0.3\; \times \;1000}}{{60}}\)

∴ U = 15.70 m/s

1. In the above equation if it is asked to find the tangential velocity at the inlet then we D as intlet diameter.

2. If both inlet and outlet diameters are given and it is asked to find out the tangential velocity of impeller & nothing is specified (inlet or outlet), then we should consider the average of inlet and outlet diameters.