Determination of Heat and Mass Transfer Coefficients by Condensation in an Air Cooler

Abstract

This paper describes an improved class of heat and mass transfer air cooler model. The model is based on the approach of Green [1]. It delivers a compact and fast model that is appropriate for year round simulations of air conditioning systems. The model is validated through a set of experiments in the laboratory with an air cooler of eight rows. The heat transfer coefficients have been derived from the standard relations. For a good agreement between the measurements of a wet cooler and the model solutions, a substantial correction in the heat transfer coefficients is needed. In addition, the results obtained from the measurements indicated that the heat transfer coefficient itself and the correlation between heat and mass transfer had to be adapted. Acceptable results were obtained when mass transfer coefficient was adjusted by a correction factor. The decrease in heat transfer has been observed with an increase in dehumidification and the same could be concluded from the coupling of heat and mass transfer. The fins are not completely wet, which implies that an analogy between sensible and latent heat only partly exists. The model does not take wetness of the pipe into account. To overcome this problem, the Lewis number is modulated, based on the degree of dehumidification. In other words, the smaller mass transfer coefficient, there is the higher the dehumidification.