关键词:

珠状凝结, Marangoni, 水-酒精混合蒸气, 相变

Abstract:

The condensation heat transfer of the water-ethanol vapor mixture on vertical tubes with different radii was studied experimentally at the same vapor velocity and different vapor pressures. A wide range of ethanol concentration was used. The results indicated that the condensation heat transfer of water-ethanol vapor mixture on vertical tubes was extremely intensified in the low ethanol concentration range. The maximum heat transfer coefficient was 150 kW·m^-2·K^-1 at p=84. 52 kPa，U=2 m·s^-1，C=1%，on the tube with 5 mm radius，which was around 8 times of that of pure water vapor. With the increase of ethanol concentration，the condensation heat transfer coefficient decreased notably. Moreover，with the increase of vapor-to-surface temperature difference，the condensation curves of heat flux and heat transfer coefficient revealed nonlinear characteristics and had peak values. The nonlinear condensation characteristic curves were caused by the complex changes in condensation mode and the diffusion resistance inherent as vapor-side thermal resistance in the condensation of the binary vapor mixtures. The condensation heat transfer characteristics were also different when different tube radii were adopted. Under the same conditions，the maximum heat transfer coefficient of the vapor mixture on the vertical tube with 5 mm radius was at a higher degree of super-cooling of surface compared with that of the tube with 10 mm radius，and the value was higher than that of the tube with 10 mm radius. In addition，according to the condensation modes recorded，dropwise condensation occurred over a wide range of ethanol concentration and vapor-to-surface temperature difference.

Key words:

珠状凝结, Marangoni, 水-酒精混合蒸气, 相变