Study On Condensation Flow Regime And Heat Transfer Of R152a In Micro-tubes

Micro-channel heat exchanger has compact structure and high performance, andnowadays becomes the main developing trend for the heat exchangers in refrigeratorand air conditioning. As an environment friendly refrigerant with low GWP and zeroODP, R152a has a great advantage in substituting R22. Experiment study oncondensation flow regime and heat transfer of R152a in micro-tubes is an indispensablepart to discover the condensation mechanism inside micro-channels. It also provides theimportant theoretical basis for the substitution of R22.Test setup was built to study the condensation heat transfer at microscale.Condensation flow regime of R152a under low mass fluxes in a0.75mm quartzglass tube was obtained by a visualization section. Annular, annular-wavy,intermittent, bubbly were observed. Gravity is not dominative in this tube. Theannular flow was restrained as the heat transfer temperature difference increased,while the intermittent flow with the opposite trend. The variation of coolantflow rate affect the regime transition little and can be ignored. The existing flowpattern map and transition lines based on macro-scale or adiabatic flow cannotpredict the experimental result, while the others based on micro-scale anddiabatic flow agree with the experimental data well.Heat transfer coefficient inside stainless steel tubes with inner diameter of1mm and0.6mm were obtained. The saturation temperature was between40and50℃. The mass fluxes varied from200to1200kg/m~2-s, and the quality variedfrom0.1to0.9. The heat transfer is enhanced remarkably as the mass fluxesincreased, especially in high quality region. The heat transfer coefficient wouldincrease a little as the saturation temperature and heat fluxes decreased. Theeffect of diameter and inclination angle can be observed under low mass fluxesat high quality region. Compared to the experimental data, the existingcondensation heat transfer correlative could not predicte the heat transfercoefficient under this experiment condition well. A correlative was modified bythe experimental date with accuracy of±30%, but great divergences.