Heat transfer calculation in heat exchangers is a long and difficult process. Luckily, we've had a few engineers put together a program based on experimental data we've derived from testing on our plate heat exchangers. If you'd like us to perform an analysis for you, you can visit our site and enter in your information. We do this on a sizing basis, but can also tell you performance for different models if you'd like. Submission forum is half way down.

http://www.dudadiesel.com/heat_exchangers.php

Required surface area is based on the equation U=Q/AΔTlm where U = heat transfer coefficient, Q = BTU, A = area, and ΔTlm = log mean temperature difference.

U (the opposite of R factor like in insulation) is the tricky bit and is specific to any single heat exchanger. Many manufacturers use an overall heat transfer coefficient when calculating required area. We have tested each exchanger we make and have found that the U factor actually varies dependent on flow rates, specific heat, and specific gravity.

A sizing calculator for the Carlson Heat Exchanger (fully welded plate heat exchanger) can be found here:
http://carlsonhx.com/index.php?item=calc&view=size

It is available free of charge with no registration and allows you to see the amount of heat transfer capacity (area) needed per model based on any set of conditions.

Ryan
Carlson Heat Exchanger
carlsonhx.com