E=Q-W Application Question

kvk1962

Some guidence would be great on this one...

I have a submersible pump 20 m below ground. The 15kW motor sits below the intake screen of the pump.

Normally in these applications the ground water flows past the motor when operating and into the screen. The ground water passing the motor is what cools it.

However for this application the water will be drawn down into the screen from holes in the well casing located above the motor.

With this operation the risk is overheating the pump.

What I would like to try and calculate is how hot the ground water between the casing and the motor actuallys get. (+/- 20 C accuracy would be fine)

A potentially big flaw in my thinking is that as the ground water heats up around the motor, that heat will dissipate at a microscopic level into the colder water above and to a lesser extent into the casing beside the pump. Can this heat dissipation occur when water pressure a the top of the motor is 15m head (150kPa) or so (ie pressure from water depth acting down on water at this level? Also can the heat dissipation occur quick enought to prevent the motor from overloading.

So in summary the question I am trying to answer is will the heat generated by the motor dissipate quickly enough via the cooler water above to maintain a safe motor temperature?

The data I have is:
Pump power 15kW
Ground Water Temperature 8 C.
Pump Diameter 250 mm
Well Casing Diameter 300 mm
Water Pressure at top of motor about 150kPa
Depth of water below motor to bottom of casing 5m.

Thanks
Kevin