蒸汽冷凝型态的表面自由能差判据

提出了蒸汽在固体表面上冷凝方式的表面自由能差判据 ,即冷凝温度下液体表面自由能与固体表面的表面自由能差大于 33.3mJ·m^-2 时蒸汽在该表面上呈现滴状冷凝的必要条件 .当表面自由能差在 0与 33.3mJ·m^-2范围内 ,表面强化冷凝传热的效果将取决于表面自由能差值的大小 ,差值越大 ,强化效果越明显 .这对深化表面涂层强化冷凝传热的机理以及选择传热表面涂层材料具有指导意义 .通过与文献报道实验结果的比较证实 ,该判据排除了静态接触角判据中测量温度的影响 .

SURFACE FREE ENERGY DIFFERENCE CRITERION FOR CONDENSATION MODES

A surface free energy difference criterion,i.e.the surface free energy difference between condensate liquid at condensation temperature and solid surface, was proposed to predict whether filmwise or dropwise condensation of a vapor occurs on a solid surface.The critical surface free energy difference was considered to be 0.0333J·m ^-2 .The surface free energy of a solid can be calculated from the measured contact angles at room temperature for low surface-free-energy solid surfaces like polymer films.Consequently,it is more convenient and accurate to use the surface free energy rather than the contact angle to predict condensation mode because the surface free energy difference is independent of the temperature for contact angles measurement.It is of considerable significance to get more insights into the mechanism of condensation heat transfer enhancement by means of surface coatings.Meanwhile, the criterion is much helpful to choosing the coating materials that promote dropwise or dropwise-film coexisting condensation modes according to the condensing vapor.