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Analysis of stagnant non condensable gases effects on condensation heat transfer in a vertical tube

机译：滞留的不可冷凝气体对立管中冷凝热传递的影响分析

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In a vertical condenser tube installed at the cold end of a non-vacuum separate type heat pipe, non condensable (NC) gases in the system is pushed by continuous vapor flowing from the hot end into the condenser tube at the cold end, gathering above condensate at the outlet of the condenser tube. Therefore, condensation heat transfer of vapor with the stagnant NC gases occurs in the condenser tube. It is necessary to comprehend the effects of stagnant NC gases on condensation heat transfer. A VOF method was adopted to analyze how stagnant NC gases affect condensation heat transfer, a mass fraction equation of NC gases was used to solve diffusion between NC gases and vapor, a Hertz-Knudsen-Schrage model was applied to deal with condensation rate of vapor on the surface of liquid film. Parameters, including volume fraction, velocity, pressure, mass fraction of NC gases and condensation heat transfer coefficients (HTC), were obtained. Results show that a lot of NC gases deposits in the condenser tube rear, leading a lot of vapor to condense at the condenser tube front. NC gases slightly affect condensation HTC of the tube front, and severely degrade condensation HTC of the tube rear. Furthermore, an increase in mass of NC gases causes a rise in pressure and velocity, improving condensation heat transfer.
机译：在安装在非真空分离式热管冷端的立式冷凝器管中，系统中的不可冷凝（NC）气体被从热端流入冷端冷凝器管的连续蒸汽推动，并聚集在上方冷凝器管出口处的冷凝水。因此，在冷凝器管中发生蒸气与滞留的NC气体的冷凝热传递。有必要了解停滞的NC气体对冷凝传热的影响。采用VOF法分析了停滞的NC气体如何影响凝结传热，利用NC气体的质量分数方程求解了NC气体与蒸汽之间的扩散，采用Hertz-Knudsen-Schrage模型处理了蒸汽的凝结率。在液膜的表面上。获得了包括体积分数，速度，压力，NC气体的质量分数和冷凝传热系数（HTC）在内的参数。结果表明，大量的NC气体沉积在冷凝器管的后部，导致大量蒸汽在冷凝器管的前部冷凝。 NC气体会轻微影响管前冷凝HTC，并严重降低管后冷凝HTC。此外，NC气体质量的增加导致压力和速度的提高，从而改善了冷凝传热。

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