Many heat transfer textbooks have a derivation showing that the log mean temperature difference is the right average temperature to use for heat exchanger calculations. Of average temperature difference is needed. For heat exchangers, there are two fluids involved, with the temperatures of both changing as they pass through the heat exchanger, so some type The driving force for any heat transfer process is a temperature difference. Each of those parameters will now be discussed briefly. U is the overall heat transfer coefficient in Btu/hr-ft 2– oF,Ī is the heat transfer surface area in ft 2,Īnd ΔT lm is the log mean temperature difference in oF, calculated from the inlet and outlet temperatures of both fluids.įor design of heat exchangers, the basic heat exchanger design equation can be used to calculate the required heat exchanger area for known or estimated values of the other three parameters, Q, U, and ΔT lm.
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