How to calculate the average temperature difference for phase change in a heat exchanger

In heat exchangers with phase changes, the logarithmic mean temperature difference formula (LMTD) is commonly used to calculate the average temperature difference. If a fluid undergoes a phase change, such as boiling or condensation, its temperature can be considered constant, that is, equal to its phase transition temperature. Suppose one fluid in a heat exchanger rises or falls from temperature T1 to the phase transition temperature T2 (such as the condensation temperature or boiling point), while another fluid changes from T3 to T4. The temperature during the phase transition can be considered constant (T2). Based on this information, the average temperature difference ΔTlm can be calculated using the following logarithmic mean temperature difference formula: \ where T2 is the phase transition temperature, T3 is the inlet temperature of the other fluid, and T4 is its outlet temperature. This formula applies to the case where phase change occurs at one end of the heat exchanger. .

I’ve studied a bit… It’s been so long since I’ve worked on engineering projects that I’ve forgotten quite a lot

What if there is phase change on both sides? What about a state where one side condenses while the other side evaporates? Is it just a simple calculation of Ti-ti? Because Ti=To ti=to

It’s still necessary to review old material to gain new insights; I leave all of this to the teacher: lol