HEAT TRANSFER CHARACTERISTICS OF CONDENSING FLOW IN PLATE HEAT EXCHANGER (EFFECT OF CONDENSATE ON FLOW DISTRIBUTION)

摘要

In the case where a brazed plate heat exchanger (BPHE) is used for a water heater in a heat pump system usinga high critical point refrigerant, the refrigerant is supplied as a superheated vapor, and condensed to besubcooled liquid with large subcooling. In this case, although both the inlet and exit flow conditions of therefrigerant are single-phase flow, the effect of the refrigerant flow distribution on the heat transfer performanceshould be considered. In this study, experiments for two BPHEs with 10 paths of refrigerant and the differentwave configurations were performed for condensing heat exchange using HFC-134a as the working fluid.Refrigerant temperatures at the exit of each path were measured by inserted sheathed thermocouples to evaluatethe flow distribution. Moreover, to understand the flow behaviors in each path, single path experiments wereperformed. From the results, the larger wave height lead to non-uniform liquid distribution in each path, andthe flow structure enhanced maldistribution of refrigerant flow which caused the deterioration of the heattransfer rate. The tendency became quite large for the horizontally placed BPHE.