A Study of Two-Phase Refrigerant Behavior in Flattened Tubes

The purpose of this study was to observe refrigerant behavior in flattened copper tubes. A round, smooth tube with an internal diameter of 8.91 mm is taken as the base case. This tube is then successively flattened to heights of 5.74 mm, 4.15 mm, 2.57 mm, and 0.974 mm. Experiments were also performed with two microfin tubes, one with a 0?? helix micro fin helix angle, and the other with an 18?? microfin helix angle. Two-phase refrigerant side pressure drop, heat transfer, and void fraction were experimentally determined for each tube and flattening height, at several flow conditions. An analysis of the experimental data, leads to interesting discoveries in the twophase flow data as the tube is flattened. Shifts in the void fraction data from a continuous trend line suggest a flow regime change at low mass flux and low quality. As the tube is flattened to 0.974 mm high, a completely different void fraction trend is observed. The heat transfer data suggests that an optimal tube configuration may exist for refrigerant side heat transfer. Attempts at fundamental modeling provide an interesting view of the experimental data. Lastly, a computer simulation is used to determine the effect of flattening a tube on total heat exchanger performance. Benefits of flattening the tube include a substantial decrease in refrigerant mass, and a slightly decrease in overall tube length