Optimal defrost cycle for air coolers revisited: A study of fan-supplied tube-fin evaporators

The performance of fan-supplied tube-fin evaporators is assessed in the present paper aiming at identifying the key parameters which affect the cooling capacity under frosting conditions and defrost cycle performance. The analysis was carried out by means of a mathematical model comprised of a frost formation submodel, which was developed by the authors in a prior publication, together with an improved defrosting submodel. A performance evaluation criterion to account for the periodic defrosting, the so-called cooling cycle efficiency, was employed as an objective function for the defrost cycle optimization. The results pointed out that there does exist an optimal runtime which maximizes the evaporator performance even for variable air flow rate conditions. Moreover, it was observed that the optimal runtime rises either by increasing the heat transfer surface (while keeping the fin spacing) or the coil surface temperature, and diminishes by either increasing the power supplied to the heater, or the relative humidity of the inlet air.