The thermal-hydraulic performance of folded-fin, flat-tube heat exchangers is experimentally studied for conditions of an initial frost growth on the air-side surface and for subsequent “refrosting” after a defrost period. Typically, the performance under refrosting conditions becomes periodic and repeatable after the third or fourth refrosting cycle. This behavior is caused by the need to reach a periodic distribution of water liquid at the end of a defrost, and the roles of frost growth and water retention on the surface are explored in this context. The allowable frost growth period (before a defrost is required), the defrost requirement, and the thermal-hydraulic performance are seen to depend on heat exchanger geometry for the two specimens used in this study. The performances for two heat exchangers are compared in the paper to explore geometry effects.

Units: SI