Hi,

I'm a little stuck on this issue and wondered if someone could help.

I want to design a shell and tube heat exchanger that takes a cool liquid, and heats it up to boiling temperature, then boils it. There is also a small bleed stream outlet. The hot side is also liquor so the temperature will change accordingly.

In this situation we have two functions, heating the liquor, then the evaporation. For the first part the LMDT is larger, and with the second part it's smaller. So I believe it's not valid to use the LMDT over the entire head exchanger. Is this correct?

How should one go about calculating the LMDT in this situation? Would it be a matter of calculating the sum of two separate areas for the separate functions (heating and evaporating) and summing them together for the total area?

The basic concept is a shell and tube with multiple passes.

Thank you!

Blaghness