Log Mean Temperature Difference

In heat exchanger applications, the inlet and outlet temperatures are generally specified depend on the fluid in the tubes. The temperature change, which takes place across the heat exchanger from the entrance to the exit, is not linear. The precise temperature change among two fluids across the heat exchanger is best symbolized by the log mean temperature difference (i.e., LMTD or ΔT_lm), stated in equation shown below:

Here:

ΔT₂ = the larger temperature difference among the two fluid streams at either the entrance or the exit to the heat exchanger.

ΔT₁ = the smaller temperature difference among the two fluid streams at either the entrance or the exit to the heat exchanger.