柯氏力作用下旋转热管内工质流动与传热特性研究

Rotating heat pipes employ centrifugal force to drive the working liquid circulating, having profound heat transfer performance, and having great potential on the thermal or cold protection for rotating equipment. But their heat transfer principle and the mechanical stability are still uncertain, which constricted their utilization on that important energy conversion equipment such as generators and gas turbines. In this research, the possibility of the existence of Coriolis Force under high rotating speed was considered, and the Coriolis Force and its impact on the performance of rotating heat pipes were aimed to be studied. By solving the 3D velocity field of the two phases of liquid and vapor, the dimension of the Coriolis Force and the impact of the circumferential shear force caused by Coriolis Force on the thickness of the liquid film was to be obtained, and the mechanism of the condensation heat transfer process would be revealed. By studying the stability of the vapor liquid interface and the flow of the vapor, the transition critical parameters and the transition law of the heat transfer and the mechanical performance would be obtained. By studying the entrainment limit and the dry out limit, the operating limits and their influencing factors would be obtained. In order to ensure the convergence of the calculating process, the initial values of the flow field and the source terms would be set according to the analytical potential flow solution, and the research on the flow stability would be based on the small perturbation theory. During the experiments, the temperature would be measured contacted by the slipping ring, and the visualization of the flow would be realized by the wireless endoscope, and the construction of experiment model and the data processing would be performed according to the similarity theory. This research would make sense for extending the utilization of rotating heat pipes and maximizing its advantage of energy conservation and thermal protection.

旋转热管依靠离心力驱动液体回流，具有良好的传热性能，对回转设备具有较大的冷热防护潜力，然而其在高转速下的传热规律及力学稳定性尚不明确，限制了其在发电机、燃气轮机等重要能量转化设备中的应用。本课题考虑到高转速下柯氏力存在的可能，拟对旋转热管内柯氏力及其对旋转热管性能的影响展开研究，通过求解汽液两相三维速度场，得到柯氏力大小及其引起的周向剪切对液膜厚度的影响，揭示旋转热管内凝结换热机理；通过研究汽液界面及汽相内部流动的稳定性，得到传热及力学性能的转变规律及临界参数；通过研究携带极限及干涸极限得到旋转热管的运行界限及其影响因素。为保证计算过程收敛性，流场初值及源项根据势流解析解进行预设，流动稳定性采用小扰动理论进行分析，实验过程中通过滑环进行温度的接触测量，通过无线内窥镜实现流场的可视化，根据相似理论进行实验建模及数据处理。本研究对于扩展旋转热管的应用，充分发挥其节能与热防护优势是有意义的。

工程中大量回转设备存在过热、过冷以及热应力问题，比如钻头、磨床、发电机、燃气轮机叶片等，需要进行冷热防护。旋转热管是一种依靠离心力驱动液相回流的热管，具有驱动力强、传热能力强等优点，可用于回转设备散热及热应力消除。本项目主要研究了热管内蒸发凝结过程中温度场、速度场以及柯氏力分布、稳态工况下旋转热管的传热性能、非稳态工况下旋转热管动态特性、旋转热管的传热极限及其失效、流动稳定性以及流型的转变等内容。得出热管内的耦合蒸发凝结过程为非平衡相变，存在温度跳变，相变过程中，温度、干度、速度、压力等参数在相变边界层内实现剧烈变化。柯氏力在汽液界面上最大，在蒸发段与冷凝段方向相反。旋转热管正常工况下具有较高的传热性能，热阻可达0.1～0.4K/W量级。水平旋转热管存在分层流与环状流两种流型，转速小于760rpm时为层状流，大于1000rpm时为环状流，中间为过渡区。旋转热管热阻在分层流下，随转速的升高而增加，在环状流下随转速的升高而降低。旋转热管启动时，热阻明显减小，其中蒸发段热阻下降尤为明显，冷凝段热阻的变化具有一定的滞后性。旋转热管在静止状态下易出现温度脉动现象，旋转后，温度脉动明显被抑制。旋转热管的失效形式主要为干涸极限。在低充液率、高加热功率以及低冷却温度下，旋转热管容易发生干涸，提高转速能够抑制干涸。旋转热管的干涸失效不仅与边界条件有关，还与初始条件有关，表现出一定的惯性与非线性。旋转热管液膜分布对其稳态与动态性能有重要的影响，分层流下粘性剪切的作用会使液体向一端聚集，诱发干涸，为稳定液体分布，强化回流，需要在其内部加装泵流结构。本项目研究结果在理论上可进一步完善蒸发、凝结相变理论。得到的重力、离心力、柯氏力、粘性剪切、表面张力的作用规律为旋转热管的理论研究与结构优化提供了重要参考。旋转热管较高的传热性能也为其在回转设备中的应用提供数据支撑。