Condensation Heat Transfer from Humid Air to a Horizontal tube

本课题对湿空气在水平管内的传热传质进行了实验研究，并对平板上湿空气中水蒸气的层流膜凝结过程进行了数值分析。本研究旨在建立一种对潮湿空气进行冷却除湿的小温差式换热器的设计方法。实验和数值分析的主要结果总结如下：(1)冷却试验中的膜状、滴状和混合型冷凝模式在很大程度上取决于试管的表面状况，但由于含汽量小，对换热影响不大。(2)传质的Sherwood数和对流换热的Nusselt数在图中表示为雷诺数的函数。(3)从汽-空气混合边界层温度和质量浓度分布分析可知，在边界层附近存在超饱和状态，但实际上会由于雾的形成而趋于饱和状态。(4)界面与壁面温差很小，凝结对对流换热的影响很小。(5)由相似解得到传热传质的无量纲相关性，然后将两者结合估算总传热；

The present project deals with both the experimental study of heat and mass transfer from humid air to a horizontal tube and numerical analysis of laminar film condensation of water vapor in humid air flowing on a flat plate. The study aims at the establishment of the design method of a small temperature difference type heat exchanger in which humid air is cooled and dehumidified. Main results obtained in experiments and numerical analysis are summerized as follows:(1) Condensation pattern such as film, drop and mixed wise in the cooling test much depends on surface condition of test tube, however, little effect on heat transfer due to small amount of vapor content.(2) Sherwood number for mass transfer and Nusselt number for convective heat transfer are shown as function of Reynolds number in the figure.(3) From the analysis of temperature and mass concentration distributions in the boundary layer of vapor -air mixtures, there exists thermodynamically a supper saturated state near the interface, but it actually will tend to a saturation state by formation of fog.(4) It became clear that temperature difference between the interface and the wall is so small and little ffect of condensation on convective heat trasfer is recognized.(5) Nondimentional correlations on heat and mass transfer are obtained from similarity solutions, then total heat transfer is to be estimated by combining them,