double pipe exchanger design

[epoh0303]

From 80 ?C, water is cooled down to 40 ?C using double pipe exchanger, with the hot water in the inside concentric pipe. I have scanned all the books and available resources here but i can't still figure how to go over. My problem is the length of the concentric annular pipe and the flow rate. I understand that there is a need to get an estimated area using the heat lost/gained in the system. When i use the area im getting high Reynolds number (is it okey to use it? might be that the area im using is heated surface area) when i continue i get the coefficient of heat transfer. Now, im figuring out how would i move to find the length and flow rate of the system. Can anybody help.

-epoh0303 (mechanical)
-neophyte

 

[srfish]

You asked about the length and flow rate. I don't see the length problem since you have an area calculated. The flow rate should be known since you have calculated a Reynolds number.