Free Convection Condensation of Multi-component Vapor Mixture on a Horizontal Smooth Tube (Surface Shape and Heat Transfer Characteristics of Condensate)

本课题研究的是多组分蒸汽混合物在水平光滑管上的自由对流冷凝实验。以甲醇/水、乙醇/水、正丙醇/水、再乙醇/乙醇和甲醇/正丙醇五种二元混合物作为试验液。在体积蒸汽质量分数、压力和壁面热流密度等不同条件下，对冷凝液的表面形状进行了观察，并对其传热特性进行了测量。结果表明：(1)再乙醇/乙醇和甲醇/正丙醇混合物表面呈光滑膜状。(2)对于甲醇/水、乙醇/水和正丙醇/水的混合物，观察到四种类型的表面形状。在低醇质量分数的情况下，表面形状总是呈滴状。在高酒精质量分数的情况下，随着壁面热流的增加，表面形状由滴状变为膜状，通过条纹和环状。接近共沸体时，表面形状总是光滑的。(3)采用无量纲冷凝膜厚度delta/ROO< >sigma/(rhog)对表面形状进行分类。(4)非膜状表面形状是由表面张力不均匀性引起的。(5)根据表面形状的不同，冷凝物的传热系数比光滑膜状冷凝理论值高1.1 ~ 7倍。

This research project deals with the experiment of free-convection condensation of multi-component vapor mixtures on a horizontal smooth tube. Five kinds of binary mixtures of methanol/water, ethanol/water, n-propanol /water, reethanol/ethanol and methanol/n-propanol were used as test fluids. The observation of the surface shape of condensate and the measurement of the heat transfer characteristics were performed under various conditions of bulk vapor mass fraction, pressure and wall heat flux. The results are as follows :(1) For reethanol/ethanol and methanol/n-propanol mixtures the surface shape is smooth filmwise.(2) For methanol/water, ethanol/water and n-propanol/water mixtures four types of the surface shape are observed. In case of low alcohol mass fraction the surface shape is always dropwise. In case of high alcohol mass fraction the surface shape changes from drop to filmwise through streak and ringwise as the wall heat flux increases. Near azeotrope the surfaced shape is always smooth filmwise.(3) The surface shapes is classified by using the dimensionless condensate film thicknessdelta/ROO< >sigma/(rhog).(4) Non-filmwise surface shapes are induced by the surface tension inhomogeneity.(5) The heat transfer coefficient of condensate is 1.1 to 7 times higher than the theoretical values for smooth filmwise condensation, depending on the surface shapes.