定壁温水平传热管外降膜对流显热换热特性理论研究

A Theoretical Study of the Forced Convection Heat Transfer of a Falling Subcooled Water Film on Horizontal Tubes under the Condition of Constant Wall Temperatures

采用层流模型对定壁温边界条件时水平管外垂降液膜的强制对流显热换热性能进行了数值计算。计算中对管顶部的冲击滞止区和管侧部的自由绕流区分别采用不同的坐标变换方法进行微分方程组简化。根据滞止区计算结果确定自由绕流区的初始边界条件。计算结果证明管径对平均换热系数的影响不容忽视。定壁温条件时的平均换热系数比定热通量时约高 12 %到 2 0

With the help of a laminar flow model a numerical calculation was conducted of the forced convection heat transfer of a falling subcooled water film on horizontal tubes under the condition of constant wall temperatures. During the calculation a liquid flow region has been divided into a shock stagnation zone at the tube top portion and a free surface flow one at the tube lateral portion. Two kinds of coordinate transformation methods are used to simplify the differential equations of the above mentioned two zones. On the basis of the stagnation zone calculation results determined were the initial boundary conditions of the free surface flow zone. The calculation results show that the tube diameter has a significant influence on the average heat transfer factor. The average heat transfer factor under the condition of constant wall temperatures has been found to be higher by approximately 12% 20% than in the case of a constant heat flux.