frost, defrost cycle, optimization, evaporator, fan
Frost accretion on a tube-fin evaporator surface raises its thermal and hydraulic resistances, which in turn deteriorates the cooling capacity of the refrigeration system. For this reason, periodic defrost operations are required to recover the initial performance of the system. Most defrost techniques rely on supplying heat to the frost layer. Due to technological and thermodynamic limitations, only part of the heat supply is effectively used to melt the frost built-up on the evaporator, while the rest increases the refrigerator thermal load. Therefore, the amount of heat dissipated, the duration of a defrost operation, and the time between two consecutives defrost operations must be considered for properly designing the defrost system. The present paper assesses, by means of a simulation model that considers the airflow reduction with frost accretion, the effects of evaporator operating and geometric conditions, and defrost cycle parameters on the time-averaged cooling capacity. The results pointed out the existence of an optimum time for the defrost operation, indicating that short intervals between two defrost operations increase the thermal load by frequent heat supply, whilst long intervals promote severe capacity depletion by frost clogging.