A Study of Two-Phase Refrigerant Behavior in Flattened Tubes

摘要

The purpose of this study was to observe refrigerant behavior in flattened coppertubes. A round, smooth tube with an internal diameter of 8.91 mm is taken as the basecase. 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-phaserefrigerant side pressure drop, heat transfer, and void fraction were experimentallydetermined for each tube and flattening height, at several flow conditions.An analysis of the experimental data, leads to interesting discoveries in the twophaseflow data as the tube is flattened. Shifts in the void fraction data from a continuoustrend line suggest a flow regime change at low mass flux and low quality. As the tube isflattened to 0.974 mm high, a completely different void fraction trend is observed. Theheat transfer data suggests that an optimal tube configuration may exist for refrigerantside heat transfer. Attempts at fundamental modeling provide an interesting view of theexperimental data.Lastly, a computer simulation is used to determine the effect of flattening a tubeon total heat exchanger performance. Benefits of flattening the tube include a substantialdecrease in refrigerant mass, and a slightly decrease in overall tube length.