Upward branching of two-phase refrigerant in a parallel flow minichannel heat exchanger

Brazed aluminum heat exchangers are recently considered as evaporators of automotive or residential air conditioners. In this case, it is very important to distribute the two-phase refrigerant (especially the liquid) evenly into each tube. In this study, R-134a flow distribution was experimentally studied for a round header-ten flat tube test section simulating a brazed aluminum heat exchanger. Three different inlet orientations (parallel, normal, vertical) were investigated. Tests were conducted with upward flow for the mass flux from 70 to 130 kg m−2 s−1 and quality from 0.2 to 0.6. Tubes were protruded to center of the header. Results show that better distribution (both for liquid and gas) is obtained for vertical inlet configuration. Possible explanation is provided based on flow visualization results. Efforts were made to develop correlations to predict the liquid or gas distribution in a header with limited success. Refined correlations should consider both geometric and operating variables. Header pressure drop data are also provided.