Frost Formation on An Air-Cooler and characteristics in Heat Pump System

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Frost formation on a cold surface is an inherent feature for air coolers operating under low temperature circumstances, and is also anegative phenomenon from the standpoint of thermal efficiency. In order to develop high-performance heat pump system, the following fundamental problems should be studied: (1) the characteristic of heat exchanger operating with frost formation, (2)the characteristic of heat-pump system, in which a heat exchanger is include as a compo-site element. In last year, analytical studies were performed mainlyfor the second problem by using a simple frost formation model. In this year, the first problem will be discussed experimentally and theoretically as a basic study to pursue the optimum design and operating conditions for heat exchangers. Namely, the effect of frost deposition on heat and mass transfer for each row and pressure loss were investigated using a four rows finned tube type heat exchanger. The growth of a frost layer was found to depend on the location of the row because of the decrease in water vapor concentration toward the direction of air flow. The efficiency of heat transfer for each row and the pressure loss in the heat exchanger were predicted in relation with the growth of a frost layer for each row. By this prediction, it was found that the performance of heat exchanger operating in counter flow type was higher in comparison with that in parallel flow type, because of a denser structure and a uniform deposition of frost layer on the surface of the heat exchanger.