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Flow and heat transfer characteristics of ambient air condensation on a horizontal cryogenic tube

机译：水平低温管上环境空气冷凝的流动和传热特性

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Ambient air condensation on a cryogenic horizontal tube is investigated using a newly built mathematical model, in which the liquid film and the vapor boundary layer are coupled together with a major emphasis on the effect of buoyancy. Based on the model, the heat transfer coefficients and the film thickness as well as the interfacial shear are obtained under different conditions to investigate the effects on the flow and heat transfer characteristics of the superheating between vapor and film, the buoyancy in the boundary layer and the subcooling between wall and film. In addition to the flow and heat transfer characteristics of air, the other four different vapors, i.e. H_2O, R134a, methane (CH_4), argon (Ar), are also discussed. The results show that the superheating has a more significant contribution to the increase of heat transfer coefficient for air comparing to the other vapors, e.g. in the cases of superheating ΔT_∞= 100 and 200 K the mean heat transfer coefficient increases by 10.3% and 24.3% for air, while it increases by only 1.8% and 3.9% for H_2O. In contrast to superheating, the subcooling has a negative effect on the increase of heat transfer coefficient. Noteworthy, the buoyancy plays a non-negligible role on the flow and heat transfer characteristics of superheated air condensation. The analytical results are of great importance in the design and improvement of ambient-heated cryogenic vaporizer (AHCV),
机译：使用新建立的数学模型研究了低温水平管上的环境空气凝结，其中液膜和蒸汽边界层耦合在一起，并且主要强调浮力的影响。在该模型的基础上，获得了不同条件下的传热系数和膜厚以及界面剪切，以研究蒸汽和膜之间的过热，边界层和表面的浮力对流动和传热特性的影响。墙和膜之间的过冷。除了空气的流动和传热特性外，还讨论了其他四种不同的蒸气，即H_2O，R134a，甲烷（CH_4），氩气（Ar）。结果表明，与其他蒸气（例如，蒸汽）相比，过热对空气的传热系数的增加具有更大的贡献。在过热ΔT_∞= 100和200 K的情况下，空气的平均传热系数分别增加10.3％和24.3％，而H_2O的平均传热系数仅增加1.8％和3.9％。与过热相反，过冷对传热系数的增加有负面影响。值得注意的是，浮力在过热空气冷凝的流动和传热特性中起着不可忽略的作用。分析结果对于环境加热的低温蒸发器（AHCV）的设计和改进非常重要，

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