发汗冷却多孔介质壁面内流动沸腾换热机理研究

Owing to the large specific heat transfer area in the porous media and the large latent heat absorbed by the liquid coolant, the transpiration cooling technique with phase change has a very high cooling efficiency and is possible to solve the high-heat-flux thermal protection problem in hypersonic aircrafts. The present project focuses on the fundamental investigation of the flow boiling heat transfer in porous media for the transpiration cooling with phase. The coupling of non-linear phase change, two-phase flow and local thermal non-equilibrium heat transfer in porous media will be investigated by experiment and mathematical modeling. In the present project, the flow boiling phenomenon and the two-phase flow pattern in porous media will be visualized and the temperature and pressure will be measured to support the macro-scale analysis. Based on the up-scaling tool of porous media, the macro-scale mathematical model of flow boiling in porous media will be developed and validated with the experimental data. The results of the project are to provide the theoretical basis for the transpiration cooling technique with phase change and make significant sense for the high-efficiency thermal protection technique.

相变发汗冷却技术凭借多孔介质壁面的高换热面积以及液体冷却剂吸收的大量汽化潜热实现高冷却效率，有望解决高超音速飞行器中的极高热流密度热防护问题。本项目的科学问题是高热流密度下多孔介质内流动沸腾的流动和传热规律与构建适用于相变发汗冷却的宏观尺度数学模型。本项目拟对多孔介质内流动沸腾换热过程进行可视化实验研究，观测和分析两相区的变化规律和流型特征，揭示多孔介质内流动沸腾的汽液两相共存区范围受加热条件、驱动条件以及流道结构的影响机理；基于多孔介质的上升尺度工具和理论，发展多孔介质内流动沸腾换热的局部非热平衡模型，进一步揭示多孔介质汽液两相共存区流动传热状态与多孔介质内局部非热平衡传热的相互影响机理。预期研究结果可为改进相变发汗冷却技术提供理论依据，对发展高效热防护技术有重要意义。

本项目围绕极高热流密度下热端部件的热防护问题，针对相变发汗冷却背景，立足于多孔介质内对流换热基础研究，通过可视化实验深入研究了多孔介质内的流动相变的流动与传热规律，发展了适用于描述相变发汗冷却的数学模型，与实验结果对照良好。指出相变区毛细作用是相变区域形成的主要原因，并发展了相变区厚度预测模型，通过理论分析获得毛细力效应的主要影响因素。基于相变区厚度预测模型得到忽略相变区的判据，发展了忽略相变区的耦合主流相变发汗冷却模型，揭示了耦合主流条件下可能产生传热恶化的机理，并可用于预测实际条件的相变发汗冷却性能。本项目为相变发汗冷却技术的预测和设计奠定了良好基础，得到一系列数学模型、判据以及多维耦合计算程序，其后续研究有望深化相变发汗冷却理论并指导其工程应用。