Heat transfer characteristics of condensing flow in plate heat exchanger (effect of condensate on flow distribution).

In the case where a brazed plate heat exchanger (BPHE) is used for a water heater in a heat pump system using a high critical point refrigerant, the refrigerant is supplied as a superheated vapor, and condensed to be subcooled liquid with large subcooling. In this case, although both the inlet and exit flow conditions of the refrigerant are single-phase flow, the effect of the refrigerant flow distribution on the heat transfer performance should be considered. In this study, experiments for two BPHEs with 10 paths of refrigerant and the different wave 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 evaluate the flow distribution. Moreover, to understand the flow behaviors in each path, single path experiments were performed. From the results, the larger wave height lead to non-uniform liquid distribution in each path, and the flow structure enhanced maldistribution of refrigerant flow which caused the deterioration of the heat transfer rate. The tendency became quite large for the horizontally placed BPHE.