空间环境中闭式回路自适应微流道相变换热技术研究

Microchannel boiling technology is regarded as an optimum scheme for high heat flux chip cooling in aerospace owing to their integration advantage of microchannel cooling and flow boiling cooling. The project will fabricate the microchannel heat sink by micromachining processes, conduct the visualization experimental investigation on microchannel boiling heat transfer, and develop a theoretical model of flow boiling process in microchannel. Combining with the visualization experiment and theoretical model, the flow boiling heat transfer mechanisms and vapor-liquid two-phase flow dynamics in microchannels are investigated. The start-up characteristics and steady-state operating performance, temperature uniformity and flow instability mechanisms are explored and analyzed. The scale effect, bubble dynamics and flow regimes of microchannel boiling in micro-gravity environment are revealed. These investigations aim to develop the heat transfer enhancement technology of microchannel boiling and suppression method of flow instability. Based on the understanding of microchannel boiling performance, the project will construct and develop the space two-phase flow loop system with a focus on the high heat flux chip cooling in aerospace. The performance test and automatic control study on the piezoelectric-pump-driven two-phase flow loop system, where the microchannel boiling and condensation radiation is coupled, are conducted to develop the independent innovation capability of the self-adaptive microchannel technology for high heat flux chip cooling. The project is closely integrated with the aerospace thermal control requirements, which will provide theoretical guidance and technical support for the independent research and development of space two-phase flow loop system. Furthermore, it is also of significant scientific value in the basic theory development for microgravity two phase flow and microscale heat transfer.

微流道沸腾技术集成了微通道和流动沸腾的双重优势，是航天高热流密度芯片冷却散热的优选方案。本项目将研制微流道热沉，开展微流道沸腾可视化实验，并结合微流道沸腾过程的理论模型，研究微流道沸腾相变传热机理和两相流动力学行为，探明微流道沸腾的启动及稳态运行特性、均温性能及其不稳定机理，揭示微重力环境下微流道沸腾的尺度效应、气泡动力学行为以及流型演化机制，发展微流道沸腾传热强化技术和不稳定性抑制方法。在掌握微流道沸腾性能的基础上，本项目将针对航天高热流芯片的冷却散热需求，构建研制空间两相流回路系统，开展泵驱动的微流道沸腾-冷凝辐射相耦合的两相流回路系统的性能测试及自动控制研究，形成高热流芯片用自适应微流道技术的自主创新能力。项目紧密结合航天热控需求，将为我国自主研发空间两相流系统提供理论指导和技术支撑，同时对微重力两相流、微尺度传热基础理论的发展也具有重要科学价值。

自适应微流道沸腾相变技术是解决航天高热流密度芯片的冷却散热问题的一种优选方案。本项目针对航天高热流芯片冷却散热需求，结合可视化实验和数值模拟方法研究了微尺度气液两相流动行为和沸腾相变传热机理。在此基础上，设计搭建了高热流密度芯片用泵驱两相流回路系统，研究了闭式回路自适应微流道相变换热系统的启动和稳态运行特性、动态热响应特性及不稳定机理，揭示微流道沸腾的尺度效应、气泡动力学行为以及流型演化机制，实现了回路系统的微流道蒸发器温度的自适应主动调控，发展了微流道沸腾传热强化技术。.研究结果表明：（1）随热流密度增加，微结构内依序出现池表面蒸发、间歇性核态沸腾、充分发展核态沸腾、过渡沸腾和膜态沸腾等气液相变传热机理，在微流道蒸发器内依序出现单相流动、泡状流、塞状流、搅拌流、环状流等气液两相流型，微流道传热系数依序经历快速上升阶段、均匀上升阶段和下降阶段，启动模式则依次呈现渐进启动和超调启动；（2）微流道毛细-重力蒸发过程出现独特的角膜蒸发模式，伴随壁面温度超调和气液界面不稳定脉动现象；垂直状态下微槽道内存在池状流、脉动流和环状流三种流态，当表面张力与重力相当时在微槽道内产生气液两相脉动流，脉动流是流道小型化过程出现的独特机理；（3）针对微流道蒸发器温控而提出的基于过冷度、储液罐温度及泵流量的自适应控制策略在温度设定值跟踪和扰动抑制方面均表现更好，相较于PI控制，具有跟踪速度更快、对扰动和耦合的鲁棒性更高等特点。.本项目的研究不仅对完善微尺度两相流动和沸腾相变基础理论具有重要的科学意义，也将为我国自主研发微流道相变换热系统提供重要的理论指导和技术支撑。基于本项目研究成果，共在国内外期刊发表论文16篇，其中SCI论文14篇、EI论文2篇(不含SCI、EI双收录)；申请发明专利5项（其中已授权2项）；培养已毕业研究生5名，项目负责人入选国家优青。