Two-phase refrigerant distribution in a parallel flow minichannel heat exchanger having horizontal headers

The refrigerant R-134a flow distributions are experimentally studied for a round header-ten flat tube test section simulating a brazed aluminum heat exchanger. Three different inlet orientations (parallel, normal, vertical) are investigated. Tests are conducted with downward flow for the mass flux from 70 to 130 kg/m2 s and quality from 0.2 to 0.6. Tubes are protruded to the center of the header. It is shown that the preferred inlet configuration is dependent on mass flux or quality. At low mass flux or quality, vertical inlet yields the best flow distribution, followed by normal and then parallel inlet. As mass flux or quality increases, the optimum configuration switches to normal inlet configuration. As compared with the flush-mounted configuration, more uniform flow distribution is obtained for the present protruded configuration. Possible explanation is provided based on flow visualization results. Correlations are developed to predict the fraction of liquid or gas taken off by downstream channel as a function of header gas Reynolds number at immediate upstream.