Abstract: The condenser performance deteriorates sharply with the reduction of gravity.An order of magnitude increase in tube length is required to achieve complete condensation in a tube under microgravity as compared with a tube under normal gravity.The phase distribution and heat transfer are not coordinated under microgravity so that the heat transfer is deteriorated.The new phase separation condenser tube proposed using the passive phase separation concept to modulate flow patterns and enhance heat transfer is suitable for different gravities.This paper focuses on the numerical simulation of the air-water flow pattern modulation process in the vertical phase separation condenser tube under normal gravity,low gravity and microgravity.Three conclusions could be drawn.(1)The phase distributions of “gas near the tube wall and liquid in the tube core” are obtained under the three gravitational conditions.Under microgravity,the annular region is completely occupied by the gas and almost all liquid flows in the core region.(2)Smaller gravity makes the liquid film thickness much less by the flow pattern modulation.Under microgravity,the thickness is decreased to 1/32.(3)Smaller gravity enhances the condensation heat transfer dominated by the thin liquid film more greatly by the flow pattern modulation.Under microgravity,the condensation heat transfer is enhanced 57.4 times.In general,the flow pattern modulation is more helpful to enhance the condensation heat transfer at smaller gravity.

Key words: flow pattern modulation, condensation heat transfer, gravity

摘要： 随着重力的降低,冷凝换热性能急剧恶化,特别在微重力条件下,流型与传热极不协同,所需的冷凝长度要比地面常规重力情况大一个数量级。基于非能动相分离概念的适用于不同重力条件的新型相分离冷凝管,促进了流型与传热的协同,极大强化了冷凝换热。在地面常规重力、小重力和微重力情况下,数值研究了新型冷凝管内垂直上升的空气-水两相流型的调控过程。通过研究得出:在三种不同重力条件下,均呈现“气在壁面,液在中心”的全新分布模式,特别是在微重力情况下,环隙区域内完全被气体占据,液体完全在核心区域内流动;重力越小,调控后液膜厚度减小幅度越大,特别在微重力条件下,减薄到1/32;重力越小,调控后薄液膜主导的冷凝换热量提高幅度越大,特别在微重力条件下,调控后提高到57.4倍,极大地强化了冷凝换热。总体来说,重力越小,流型调控过程越有利于强化冷凝换热。

关键词: 流型调控, 冷凝换热, 重力