Improvement of two-phase refrigerant distribution in a parallel flow minichannel heat exchanger using insertion devices

Abstract

In this study, various insert devices (wire mesh, perforated plate, perforated tube) were investigated to obtain an improved flow distribution in a round header/ten flat tube test section using R-134a. To simulate an actual brazed aluminum heat exchanger, tubes were protruded to center of the header. Tests were conducted both for downward and upward flow for the mass flux from 70 to 130 kg m−2 s−1 and quality from 0.2 to 0.6. Of the investigated insert devices, perforated tube significantly improved the flow distribution both for downward and upward flow when the holes were located facing tubes. Preferred hole geometry was dependent on the flow direction. For downward flow, non-uniform hole configuration with decreasing hole sizes in flow direction yielded better flow distribution than uniform hole configuration. For upward flow, however, uniform hole configuration yielded better flow distribution. Possible reason was provided based on flow visualization results. Header pressure drop was obtained from the measured pressure drop by subtracting appropriate pressure drops. For no-insert configuration, header pressure drops were mostly negative, which implied that the pressure was recovered in the header. With insertion of the perforated tube, however, the header pressure drop increased significantly. Other insert devices (wire mesh, perforated plate) were not effective in improving the flow distribution.