Question

If the manometric efficiency and mechanical efficiency of a centrifugal pump are 70% and 80%, respectively. Determine the overall efficiency of the pump.
1. 0.1
2. 0.56
3. 0.53
4. 0.6

Answer 1

Correct Answer - Option 2 : 0.56

Concept:

The following are the important efficiencies of a centrifugal pump:

1) Manometric Efficiency (ηman): It is the ratio of the manometric head to head imparted by the impeller to the water.

\({\eta _{man}} = \frac{{{H_m}}}{{\frac{{{V_{w2}}{u_2}}}{g}}} = \frac{{g{H_m}}}{{{V_{w2}}{u_2}}}\)

2) Mechanical Efficiency (ηm): It is the ratio of the power available at the impeller to the power at the shaft of the centrifugal pump.

\({\eta _m} = \frac{{{\rm{Power\;at\;the\;impeller}}}}{{{\rm{Power\;at\;the\;shaft}}}} = \frac{{\frac{W}{g}\left( {\frac{{{V_{w2}}{u_2}}}{{1000}}} \right)}}{{{\rm{SP}}}}\)

3) Overall Efficiency (ηo): It is defined as a ratio of the power output of the pump to the power input to the pump.

ηo = ηman × ηm

Calculation:

Given:

ηman = 0.7, η_m = 0.8

ηo = ηman × η_m = 0.7 × 0.8 = 0.56 

The overall efficiency of the pump is 0.56.