高汇聚太阳热流边界两相环路热虹吸管耦合传热及强化机理

The two-phase loop thermosiphons (TPLTs) have great potential for application in highly concentrated solar thermal (non-uniform, unsteady, and intensive heat flux) systems. However, their heat transfer performance and thermal stability are not high, and the conjugated heat transfer mechanism is still indistinct. This project aims to develop the visualized experiment, theoretical and numerical heat transfer models, as well as to explore the heat transfer enhancement method & mechanism of the TPLT in above complex and unsteady heat flux boundary conditions: ①By integrating glass-to-metal sealing, glass self-cleaning and antireflection technologies, an "endoscopic" visualized experimental system will be developed to directly reveal the phase-change and two-phase flow regimes in the TPLT; ②Based on the lumped parameter method, two-phase flow regimes and the thermodynamic analysis, a theoretical heat transfer model which conjugates the dynamic radiation/conduction/convection/phase-change processes will be constructed; afterward, a regulation strategy for the phase-change time relaxation parameters will be developed to improve both accuracy and efficiency of the general CFD/VOF model; ③The high-parameter heat transfer enhancement components, e.g. nano-coated metal foam, will be fabricated for the confined spaces in TPLT, and then both the heat transfer enhancement mechanism and performance of the TPLT will be further investigated by the above experimental, theoretical and numerical methods. This research will deeply reveal the heat transfer & enhancement mechanisms of the TPLT in highly concentrated solar heat fluxes, and obtain the best technical scheme for optimizing the heat transfer performance. Therefore, this research has great theoretical and practical significance.

两相环路热虹吸管（TPLT）在高汇聚太阳能热利用（非均匀、非稳态和极强热流）系统中应用潜力巨大，但传热性能和热稳定性不高，耦合传热机理尚不明晰。基于该复杂非稳态热流边界，项目拟构建TPLT可视化实验、传热理论和数值仿真模型，探究其强化传热方法和机理：①集成金属-玻璃封接和玻璃自洁、增透技术，创新TPLT“内窥式”可视化实验手段，直观揭示工质相变和两相流机制；②基于集总参数法、两相流机制和热力学分析，构建TPLT辐射-传导-对流-相变相耦合的动态传热理论模型；并开发CFD/VOF模型多参数优化的相变时间松弛因子调控策略，建立其真实高效的通用仿真模型；③开发TPLT受限空间内纳米涂层泡沫金属等高参数强化传热元件，基于上述实验、理论和数值模拟手段，研究其强化传热机理和特性。本研究能够深度揭示TPLT在高汇聚太阳热流下的传热及强化机理，并获得传热特性最优化的技术方案，因此具有重要的理论和实践意义。

两相环路热虹吸管（TPLT）在高倍聚光式太阳能热利用（非均匀、非稳态和极强热流）系统中应用潜力巨大，但传热性能和热稳定性不高，动态传热机理尚不明晰。项目构建了TPLT可视化实验、传热理论和数值仿真模型，探讨了其强化传热方法和机理，获得如下结论：1）研制了热虹吸管“内窥式”可视化实验平台，直观揭示了热管工质在金属壁面下的相变传热和两相流动机制，结果表明，间歇沸腾源自于壁面-液体过热度（壁面生成）、液体-气泡过热度（池内生成），分别造成了壁温的强脉动和弱震荡两种波动现象。2）构建了TPLT的稳态传热理论数学模型，计算值与实验值误差<5%，获得了高热流下TPLT内部温度和压降分布及传热极限（9.4~19.7 kW）；此外构建了TPLT动态传热预测模型，预测了突变功率（30~75 W）下TPLT动态响应特性，预测精度控制在±6%以内。3）开发了基于压力系数、相变界面汽相工质导热系数等多参数优化的相变时间松弛因子调控策略，建立了真实高效的热虹吸管CFD/VOF仿真模型，实现了相变温度与工作压力的平衡，预测了不同热流下的总热阻变化规律，误差在5.4～10%之间，揭示了TPLT内部流型与相变传热的关联机制。4）获得了高参数强化传热元件；表征显示改性后的泡沫铜表面形貌呈现“花椰菜状”结构，其内部润湿性呈现梯度变化，其中30 PPI泡沫铜经12 h溅射后的HTC和CHF分别提高了75.6%和17.3%；此外，建立了改性样品结构参数与传热系数的关联式，预测平均误差≤11.2%；另外，泡沫金属显著强化了TPLT的传热性能和流动稳定性。论文深度揭示了热虹吸管在复杂非稳态热流下的强化传热机理，可为其在高倍聚光式太能热利用领域的应用提供理论和技术支撑。