基于场协同机制,对强化含有不凝气体的蒸汽冷凝过程的速度场与浓度梯度场协同作用进行了理论分析,提出利用冷凝液动态行为所产生的气液界面效应来强化混合蒸汽冷凝传热特性新思路。为进一步验证界面效应对气相传质扩散过程的影响,在不凝气摩尔含量为10%以内的混合蒸汽层流流动条件下,对冷凝液沿冷凝表面流动的常规膜状冷凝和冷凝液以液滴滴落方式定向脱离表面的两种排液方式下的膜状冷凝、冷凝液脉动的锯齿形滴膜共存冷凝和完全滴状冷凝四种模式下的冷凝传热特性进行了对比实验,比较分析了冷凝液运动行为影响传热特性的实质。实验结果表明,在不需要增加能耗的情况下,利用重力作用下冷凝液的运动行为产生的剪切作用和附加速度场,对气相边界层内的扩散传质过程能够产生协同作用,可以达到传热传质的无源强化效果。
Based on the field synergy mechanism, the relationship between velocity field and concentration gradient field of the mass transfer process in the presence of non-condensable gas was analyzed, An idea of utilization of the interfacial effects gained from the condensate liquid movement was put forward to enhance the heat and mass transfer of the condensation process. The experiments of four condensation modes possessing different interfacial effects, such as the perfect dropwise condensation mode, general filmwise condensation mode, specially designed filmwise condensation mode and dropwise-filmwise coexisting condensation mode, were carried out respectively on a vertical tube surface with using the steam containing air as non-condensable gas, in which the air molar concentration is in the range of 0% to 10%. During the experiments of designed filmwise condensation mode or dropwise-filmwise condensation mode, it was found that the condensate liquid is converged to pulsating droplets which fall off or fall along the condensing surface in different directions and can provide falling movement in the gas boundary layer. The results indicate that the heat and mass transfer process of the gas side can be enhanced by the condensate falling movement in gravity field without additional energy consumption. As a passive enhancement method, the falling movement which results in the well synergy of flow field and concentration gradient field on gas side has a noticeable effect on heat and mass transfer characteristics.