heat exchanger efficiency calculation

[nani09]

Hi,

I am trying to calculate the heat exchanger calculation for spiral reactor.But,I am not sure what the equation to calculate the heat exchanger..the flow in temperature for the water is about 25C. the water will be heated at the middle part of the reactor and the temperature is about 400C.and then the water will be cooled down when flow out from the middle part.the tube for flow in water is beside the flow out water.so,the hot water will be cooled down because of the heat transfer.i also want to know if the length effect the process.please help me..

 

I know this might be quite simple but i really don't have any idea to calculate the efficiency..

thank you in advance.

nani09