Understanding Heat Exchangers

tehallchemist

Hi Physics Forum-ers, long time reader, first time poster.

I've been given the task to do a simulation for the cooling of a motor from 50C to 20C. The motor is cooled using a water cooling system, and a 3.5kW heat exchanger.

I've done some quick preliminary calculation, but I'm getting stuck on the limits of the heat exchanger. My current formula looks like:

Twater(1) = Twater(0) + Heat From motor(~2kW) - Heat Removed From exchanger (~3.5kW)

(I know I should use heat capacities and such, this is a simple model)

Now, the heat exchanger we are using is specced to remove 3.5kW of heat. I was told that using this value independent of temperature is an acceptable assumption, but if I were to assume that this will continuously remove 3.5kW, the water temperature would eventually drop below freezing, and I don't think this is correct. What type of function should I be using to describe the heat removed by the exchanger?

Other information:
Refrigerant Conditions BXD: 16bar, 52C
Refrigerant Conditions Suction: 3bar, 7K
Coolant temperature 35C