Interfacial shear stress has an important influence on the vapor downward condensation heat transfer in a smaller diameter condenser tube. At the present work, a volume of fluid (VOF) method based on the vapor-liquid interfacial capturing technique was used to numerically analyze the effects of interfacial shear stress on local condensation heat transfer coefficients (HTC) during the vapor downflow condensation. Because vapor condenses on the vapor-liquid interface, the condensation mass and energy source items were introduced into the volume fraction and energy governing equations of the VOF model. In addition, the condenser tube wall temperature was acquired by a coupling calculation of cooling water forced convection heat transfer. The parameters were obtained, including velocity, interfacial shear stress and local condensation HTC. The computations show that interfacial stress shear degrades along thetube length, obviously improving the condensation heat transfer at the condenser tube front. At the condenser tube rear, the vapor-liquid interfacial shear stress decreases, having a drag force to condensate. Therefore, the liquid-film gravity plays an important role in local condensation HTC at the condenser tube rear. Local condensation HTC obtained by the VOF method is compared with the Nusselt analytic solution. At the condenser tube front, the vapor-liquid interfacial shear stress is higher and has the same direction as condensate velocity, which enhances the condensation heat transfer by reducing the liquid film thickness. So local condensation HTC obtained by the VOF method is higher than the Nusselt analytic solution. However, at the condenser tube rear, the computing result is almost equal to the Nusselt analytic solution as a result of both lower interfacial shear stress and increasing the liquid film thickness. Furthermore, a comparison of local condensation HTC acquired by the VOF method to the experimental data of Goodykoontz et al. Was performed, good agreements were found for the condenser tube section from 0. 2 m to 0. 6 m, and their relative error is within ±35%.%界面剪切力对小径管中的蒸汽垂直下流凝结传热有重要影响.采用VOF模型数值模拟了蒸汽垂直下流凝结传热,分析了界面剪切力对局部凝结传热系数的影响.模拟中冷凝管壁面温度采用耦合计算冷却水的对流换热获得.计算得到了速度、界面剪切力和局部凝结传热系数的分布.计算结果表明:界面剪切力沿蒸汽流动方向逐渐减小,它对局部凝结传热系数的强化作用集中在垂直管前段,而在垂直管后段,液膜重力是影响局部凝结传热系数的重要因素.将VOF模型算得的局部凝结传热系数与Nusselt解析解进行了比较.在垂直管前段,由于汽-液界面剪切力的强化作用,VOF模型的计算结果大于Nusselt解析解；而在垂直管后段,汽-液界面剪切力逐渐减弱,VOF模型的计算结果接近Nusselt解析解.将VOF模型算得的局部凝结传热系数与Goodykoontz 等的实验数据做了比较,在0.2～0.6 m的垂直管段,VOF模型算得的局部凝结传热系数与Goodykoontz等的实验数据吻合较好,误差在±35％的范围内变化.
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