In this paper, a theoretical model of filmwise condensation of steam on three-dimensional pin fins fabricated by selective laser melting (SLM), an additive manufacturing (AM) technique, is developed. The model considers the effects of surface tension and gravity on the liquid film flow over the pin fin surface. The three-dimensional nature of the liquid film flow over the fin flank and the unique features of the fin structures as a result of the laser melting process are modeled. Visualization studies are performed to verify the assumptions made in the model. From the modeling results, the local heat transfer coefficient and length-averaged heat transfer coefficient are obtained. The liquid film thickness at various locations of the pin fin is analyzed. The effects of fin tip dimensions, fin stem radius and fin pitch on the liquid film characteristics and heat transfer coefficient are systematically investigated. Our results showed that a thin film region exists in the flat and circular segments of the fin tip which cover approximately 25 – 30% of the fin surface. For a fixed fin diameter, it is found that the length-averaged heat transfer coefficient can be optimized by varying the dimensions of the flat and circular segments. A locally thin film region resulting from the suction effect is observed near the fin base for small fin spacings. However, the suction effect reduces with increasing fin spacing. Due to the three-dimensional nature of the pin fins which induces surface tension in the circumferential direction, the liquid film distribution is uniform. The differences in the length-averaged heat transfer coefficient at different circumferential locations are smaller than 5%. Finally, a comparison with existing experimental results demonstrates that a relatively accurate prediction of the average heat transfer coefficient can be achieved by our model with a maximum deviation of 8.3%.

在本文中，建立了通过选择性激光熔化（SLM），增材制造（AM）技术制造的三维针状鳍片上蒸汽薄膜冷凝的理论模型。该模型考虑了表面张力和重力对流过针鳍表面的液膜的影响。对液膜在翅片侧面流动的三维特性以及由于激光熔化过程而形成的翅片结构的独特特征进行了建模。进行可视化研究以验证模型中所做的假设。根据建模结果，获得局部传热系数和长度平均传热系数。分析针状鳍片的各个位置处的液膜厚度。鳍尖尺寸的影响，系统地研究了翅片杆半径和翅片间距对液膜特性和传热系数的影响。我们的结果表明，在鳍尖的平坦和圆形部分中存在一个薄膜区域，覆盖了鳍表面约25 – 30％。对于固定的翅片直径，发现可以通过改变扁平段和圆形段的尺寸来优化长度平均传热系数。对于较小的翅片间距，在翅片基部附近观察到了由抽吸效应产生的局部薄膜区域。但是，随着翅片间距的增加，抽吸效果会降低。由于针状翅片的三维特性在周向上引起表面张力，所以液膜分布是均匀的。在不同圆周位置的长度平均传热系数之差小于5％。最后，与现有实验结果的比较表明，通过我们的模型可以实现相对准确的平均传热系数预测，最大偏差为8.3％。