Velocity Variation through Pipeline

[discreet544]

Hi

Imagine there is a closed-loop pipeline which we are pumping pure water. Reasonably, we expect the pressure-drop to increase towards the end, due to friction and minor losses. My question, however, is about the velocity.

When you half the length of the loop, at the same pump power, velocity increases, as there will be less total friction and maybe less pump slippage. However, at the same pump power, should we expect pressure drop/length to be different through pipeline?

In my experiment, I am experiencing different kPa/m at various positions. As the D and f is the same everywhere through pipeline, it can happen only if the velocity is different from point to point. But, when the pump power is kept fixed, the fixed amount of water is expected to be pumped and the velocity should be the same everywhere. Am I right ? If not, and the velocity reduces as well through pipeline, how do you justify the continuity of fluid ?

Thanks;

 

[Navin A S]

The pressure drop throughout the pipeline should remain almost constant. The reason for this is that the energy loss associated with friction is usually proportional to the square of the velocity. Thus, when you reduce the length of the loop, the same amount of energy is lost, but the velocity increases so that the total energy losses are the same. This means that the pressure loss stays the same, as long as the pipe diameter and friction coefficient remain constant. The continuity of the fluid is maintained by the conservation of mass. Since the same amount of water is being pumped through the pipeline, the flow rate will stay the same even if the velocity changes slightly.