竖直管内蒸汽完全冷凝换热特性的理论研究

Nusselt模型是静止蒸汽在竖直平壁上层流膜状冷凝换热的理论模型。蒸汽在竖直管内冷凝时，受管内蒸汽流速的影响，冷凝界面存在剪切应力，导致直接采用Nusselt模型计算冷凝换热系数会引入较大偏差。以非能动余热排出换热器冷凝换热工况为研究背景，考虑界面剪切力的影响，对Nusselt冷凝换热模型进行修正。分别采用Nusselt模型和修正模型对竖直管内蒸汽完全冷凝时的换热特性进行分析并与实验结果比较。研究表明，蒸汽在竖直管内完全冷凝时界面剪切力会改变蒸汽和冷凝液膜的流动状态，其对冷凝换热的影响不能忽略。修正模型合理地考虑了冷凝界面剪切力的影响，计算结果与实验结果吻合较好。

Heat Transfer Characteristics of Complete Condensation in Vertical Tube

Nusselt model is the theory model for predicting the film condensation of a quiescent vapor along an isothermal vertical plate.When the steam condenses inside a vertical,the interfacial shear stress due to the steam flow tends to accelerate the liquid film and to make it thinner which would induce the prediction by Nusselt theory deviating from the measured heat transfer coefficient.Considering the effect of interfacial shear stress,the Nusselt model for film condensation was modified in this paper.By using the Nusselt model as well as the modified model,the heat transfer characteristics of complete condensation in a vertical tube passive condenser were studied.The results show that the interfacial shear stress can change the flow state of vapor and liquid film inside tube and its influence on condensation can not be neglected.The modified model considers the interfacial shear stress appropriately,so the calculated values agree well with the experimental results.