Regarding physical quantities necessary to evaluate performance of air coolers under the condition that both heat and mass are transferred at the same time, there are an enthalpy transfer coefficient, a mass transfer coefficient and many other items. In the case of the cross-finned tube heat exchanger, however, it is very difficult to estimate, or measure the performance of the air coolers experimentally, due to their complicated structures. Therefore, an equivalent enthalpy transfer coefficient is generally utilized. As the equivalent enthalpy transfer coefficient is less significantly influenced by air temperature and humidity than the equivalent mass transfer coefficient, air coolers are very often designed by utilizing the equivalent enthalpy transfer coefficient. The equivalent enthalpy transfer coefficient of air coolers, however, has not been predictable without experimental measurements.

This paper presents a method for predicting the equivalent enthalpy transfer coefficient by utilizing only the surface heat transfer coefficient of the fin of the air cooler, and also discusses the influence of air temperature, air humidity and the tube surface temperature on the equivalent enthalpy transfer coefficient.