旋转管内液膜流动与汽化传热机理研究

The flow and heat transfer characteristics of the liquid film inside a circular tube rotating about its own longitudinal are complex since it is influenced by many factors such as the centrifugal force, the Corioli force, surface tension, heat flux, scale of the liquid film, physical properties of the fluid, etc. The outstanding heat transfer performance of the liquid film inside a rotating pipe make it important for the efficient heat control for many rotating equipment. Until now, however, the flow and heat transfer mechanism of the liquid film inside a rotating pipe has not been clearly revealed yet. The mechanism of boiling suppression, the transition rule of the vaporization mode, and the three-dimensional flow feature of the liquid are still not clearly known, which makes it difficult to establish the design method for the thermal management system based on the heat transfer of the liquid film inside a rotating pipe and constrains its applications. .The present work is focused on (1) The flow and heat transfer mechanism of the liquid film inside a rotating pipe; (2) The vaporization heat transfer characteristic of the liquid film inside a rotating pipe, which are the two essential problems in the heat transfer processes of the liquid film inside a rotating pipe. Theoretical and experimental investigations are carried out on the fluid flow and heat transfer of the liquid film inside rotating pipes. The objective of the work is to explore the flow and vaporization heat transfer mechanism of the liquid film inside rotating pipes. It is expected to find the effects of different parameters on the heat transfer performance of the liquid film for achieving better performances, which may be helpful for the design of the thermal control systems based on the vaporization heat transfer of the liquid film inside rotating pipes.

当圆管绕中心轴做自转运动时，旋转管内的液膜受到惯性离心力、惯性科氏力、表面张力、热流密度、液膜尺度、物性参数、气液相互作用等多因素的影响，流动与传热规律比较复杂。旋转管内液膜的汽化传热热阻小，是很多高效旋转热控系统运行的关键环节，但是目前对旋转管内液膜的沸腾抑制机理、汽化模式的转变规律，以及三维流动特性等认识仍不清楚，因此无法构建其传热性能的完善设计方法，严重制约了基于旋转管内液膜汽化的旋转设备高效热控技术的发展。.本项目围绕旋转管内液膜传热过程中的两个关键科学问题：（1）旋转管内液膜的流动与传热机理；（2）旋转管内液膜的汽化传热规律开展理论和实验研究。研究目的旨在揭示各影响因素对旋转管内液膜流动与汽化传热特性的作用规律，明确旋转管内液膜传热性能的评价和调控方法，为基于旋转管内液膜汽化的热控系统设计提供科学的理论依据。

本项目围绕旋转管内液膜的流动与汽化传热机理开展了理论和实验研究。建立了描述旋转管内液膜流动与汽化传热过程的理论模型，揭示了向心加速度、热流、科氏力等因素对旋转管内液膜流动的作用规律，发现科氏力起到增加扰动并提高液膜流速的作用，相比于不考虑科氏力的情况下，液膜内部流速最大增加了18%至28%，即科氏力加强了不同流层之间的动量交换和热量交换；向心加速度从20g增大到120g，沿液膜厚度方向不同流层之间的速度差值增大了73.9%，向心加速度的提高显著增加了流体的对流强度。.在向心加速度较小（20g-60g）的情况下，液膜的汽化模式以核态沸腾为主，随着向心加速度的增大，气泡的数密度逐渐减小，直至核态沸腾被抑制（100g），汽化模式由液膜内部的核态沸腾转变为液膜的表面蒸发，其转变点随着热流密度的增大（1300W增大到1600W）会延后（100g变为120g）。考虑了科氏力影响后液膜中的气泡数密度增大，沸腾得到了强化，在向心加速度增大时，这种强化更加明显。随着热流的增大，液膜内部气泡数密度增大，核态沸腾更加剧烈。.液膜的换热系数随着向心加速度的增大先是显著增大，而后逐渐平稳或下降。热流的增大则导致了液膜换热系数的减小，例如向心加速度为40g时，加热膜功率由1300W提高到1600W，壁面过热度增大了约35%，而相同大小面积的水膜内汽泡个数增大了约14%，汽泡数量的增长率低于壁面过热度的增长率，壁面产生的汽泡数量有限，不能带走足够的热量，从而导致了换热系数下降。.通过研究获得了旋转管内液膜流动与汽化传热的基本规律，在此基础上开展了应用探索研究，设计了利用旋转管内液膜相变传热的发动机整流罩防冰装置，实验验证了其具有较好的传热性能。