多孔径复合吸液芯微小型均热板蒸发-冷凝相变传热机理及性能强化

Miniature vapor chamber has been recognized as one of the effective ways for the uniform cooling of electronics with high heat flux density in a confined micro-space. In this project, the composite metal foam with multi-scale pore structure is introduced as a wick for the miniature vapor chamber, and a visualized miniature vapor chamber with this design will be fabricated, then the visualization experimental investigation on the vapor-liquid two-phase flow and phase change heat transfer will be conducted. In addition, an unsteady state model of vapor-liquid two-phase flow and phase change heat transfer in porous media will be developed based on lattice Boltzmann method, with the comprehensive consideration of the vapor-liquid interface evolution as well as the coupled evaporation, condensation and heat conduction. By the combined numerical simulation and visualization experiment, the coupled evaporation-condensation phase change heat transfer mechanisms in the porous media is studied, the effects of pore and bulk parameters of wicks, as well as the working parameters, on the characteristics of vapor-liquid phase change heat transfer are clarified, the cooperating optimization mechanisms of metal foams with multi-scale pore structure for gas-liquid two-phase heat transfer in vapor chamber will be revealed. In addition, the fractal tree-shaped micro-grooves will be introduced into the design of evaporation surface structure. An enhancement method for the heat and mass circulation efficiency of working medium will be developed on the basis of co-packaging fractal tree-shaped micro-grooves evaporation surface with composite metal foam with multi-scale pore. This study not only has important scientific significance for the development of the microscale heat and mass transfer theory, but also provides key technical support for the development of high performance ultra-thin phase change heat transfer devices.

微小型均热板是解决受限微小空间内高热流密度电子器件/设备散热及均温问题的理想工具。本项目拟提出一种多孔径复合泡沫金属吸液芯设计，研制微小型均热板样件，开展板内气液流动相变传热特性可视化实验研究；建立考虑蒸发-冷凝-导热耦合及界面演化的多孔介质内气液流动相变传热过程的格子Boltzmann非稳态理论模型并进行数值模拟。结合可视化实验和数值模拟，揭示均热板特别是吸液芯内蒸发-冷凝耦合相变传热机制，阐明吸液芯孔结构参数、体结构参数和均热板工作参数对板内气液流动相变传热特性的影响规律，揭示吸液芯多孔径复合结构对板内工质能质输运的协同优化机理。在此基础上，引入分形树状微槽道结构蒸发面与多孔径复合泡沫金属吸液芯联配，提升板内工质能质循环输运效率，发展微小型均热板传热性能强化新方法。本项目研究不仅对于完善微尺度相变传热传质基础理论具有重要的科学意义，也将为高性能超薄相变传热器件的研发提供关键技术支撑。

微小型均热板是解决受限微小空间内高热流密度电子器件/设备散热及均温问题的理想工具。本项目提出了一种多孔径复合吸液芯设计，研制了微小型均热板样件，搭建了均热板传热性能测试平台以及可视化观测平台，开展了板内气液流动相变传热特性可视化实验研究，建立了考虑蒸发-冷凝-导热耦合及界面演化的气液流动相变传热过程的格子Boltzmann非稳态理论模型并进行了数值模拟。结合可视化实验和数值模拟，本项目对均热板内蒸发-冷凝耦合相变传热传质机理开展了深入研究，在此基础上，引入分形树状微槽道结构蒸发面与多孔径复合泡沫金属吸液芯联配，研制了性能强化型微小型均热板并开展了传热性能测试实验。研究结果表明：（1）梯度孔径吸液芯所提供的毛细驱动力由外向内逐级递增，有利于冷凝液从四周向中心汇聚，可及时补充中心热源处蒸发的液态工质；因此，梯度孔径吸液芯均热板的热质输运效率更高，传热性能更好。（2）与均匀吸液芯均热板相比，梯度孔径吸液芯的孔径尺寸从内向外逐级递增，蒸汽从中心向外扩散时阻力逐渐减小，蒸汽向四周铺展情况得到改善，热量能够及时地分散至整个均热板表面，蒸发面与冷凝面温度分布更加均匀。（3）梯度孔径吸液芯均热板在逆重力下运行时，其传热性能和均温性能均下降。在热流密度达到160W/cm2时，梯度孔径吸液芯均热板仍未达到传热极限。（4）具有壁面分形槽道的梯度孔径吸液芯均热板与其他类型均热板相比，具有更低的传热热阻，说明分形槽道结构可促进蒸发面冷凝工质向热源汇聚，均热板内气液循环效率得到进一步提升，传热性能更好。（5）随着热负荷增加，均热板内蒸发面依序经历池表面蒸发、液桥蒸发、膜态沸腾。薄液膜蒸发是受限高度微小化作用下封闭腔体内沸腾冷凝共同作用下而出现的独特气化机理。本项目研究不仅对于完善微尺度相变传热传质基础理论具有重要的科学意义，也将为高性能超薄相变传热器件的研发提供关键技术支撑。