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

冷表面结霜是低温工况下运行的空气冷却器的一个固有现象，从热效率的角度来看，也是一种负面现象。为了开发高性能的热泵系统，必须研究以下几个基本问题：（1）换热器在结霜条件下的运行特性;（2）以换热器为复合元件的热泵系统的特性。去年，主要通过使用简单的结霜模型对第二个问题进行了分析研究。在今年，第一个问题将在实验和理论上进行讨论，作为寻求换热器最佳设计和操作条件的基础研究。即，使用四排翅片管型换热器研究了霜沉积对每排传热和传质以及压力损失的影响。霜层的生长被发现取决于行的位置，因为在空气流动的方向上的水蒸气浓度的减少。预测了每一排的传热效率和换热器中的压力损失与每一排霜层的生长的关系。通过预测发现，逆流式换热器的性能优于平行流式换热器，这是因为逆流式换热器的结构更致密，霜层在换热器表面的沉积更均匀。

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.