Question

A pump is used to pump oil to a tank located 10-m high at room temperature. The oil flow is laminar. Now, if the oil is pre-heated while the oil flowrate is maintained, discuss whether the pumping power of the pump will increase or decrease.

Answer 1

Power of a pump depends on the 4 factors i.e. Density of fluid, height, flow rate, acceleration due to gravity.

Since, in the above case height, flow rate and acceleration due to gravity remains constant, therefore only variable is density of fluid.

When the oil is pre-heated its density decreases (density decreases with increase in temperature for liquids), if density decreases then power of pump also decreases because both are directly proportional to each other keeping all other terms constant.

pumping power of pump will decrease.