地热利用超长热管相变传热及强化机理

Super-long heat pipes (SLHPs) can significantly lift the efficiency of geothermal utilization system. However, due to the super-long structure, SLHPs face the extreme difficulties in fabrication, transportation, and installation. Particularly, the excessively high liquid column in SLHPs lead to large static pressure at the bottom, inhibiting the boiling of liquid and thus decreasing their heat transfer performance. These problems limit the further development of SLHPs in geothermal applications. This project will fabricate SLHPs using flexible metal bellows, or referred to as super-long flexible heat pipes (SLFHPs), to overcome the problems of fabrication, transportation, and heat transfer efficiency. The combination of experimental tests, theoretical analysis, and CFD simulation will be used to reveal the phase-change heat transfer and enhancement mechanism of SLFHPs. The key influencing factors on heat transfer characteristics of SLFHPs will be explored. And the semi-empirically predictive methods of thermal performance and optimum filling quantity of working fluid of SLFHPs will be developed by coupling the theories of dimensional analysis, drift model, and thermal resistance model. The pressure-based vapor/liquid phase-change model with self-adaptive balance of vaporization and condensation will be proposed, by which a dynamic phase-change CFD (Computational Fluid Dynamic) model for SLHPs will be established. And then, investigation of the relevance of inner heat transfer behaviors to thermal performance of SLHPs and the inhibiting effect of ripple structure on high liquid column will be carried out. The structure optimization methods by regulating ripple form, designing inner components or wick, and employing variable diameter structure will be examined, and the corresponding heat transfer enhancement mechanism will be explored as well. This project will provide theoretical and technical support for the penetration and highly efficient application of SLHPs in the geothermal application.

超长热管可大幅提高地热利用系统的整体效率，但由于其结构过长，加工、运输和安装极其不便，特别是，在大长径比和高液柱作用下，热管底部工质静压大，难以沸腾，无法有效传热，限制了超长热管传热技术的发展。项目拟采用金属波纹管构建超长柔性热管，破解其加工、运输和高效传热等难题，并通过实验测试、理论分析和仿真模拟协同分析手段，揭示其相变传热及强化机理：探讨地热利用超长柔性热管的传热特性关键影响因素，耦合量纲分析、漂移流理论、热阻模型等分析方法，建立其传热性能与最佳充液量半经验计算方法；提出基于压力触发的汽化-冷凝自适应平衡相变模型，进而开发超长热管相变传热动态仿真CFD模型，揭示其内部相变传热机制与传热特性的关联规律，探究波纹结构对液柱高度的抑制作用；探寻调控波纹形式、设计内置插件或吸液芯、采用变径结构等结构优化方法，阐明其强化传热机理。为超长热管在地热利用领域的推广和稳定高效应用提供理论和技术支撑。

超长热管可大幅提高地热利用系统的整体效率，但因其存在的难以加工、运输和高效传热等难题限制了其商业化进程。本项目采用金属波纹管构建超长柔性热管破解以上难题，并通过实验测试、理论分析和仿真模拟协同分析手段，揭示其相变传热及强化机理，主要研究内容和结果如下：.分别开展了总长32m和52m地热利用超长柔性热管的真实工况野外试验，探讨了不同操作工况对其传热特性的影响，阐明了关键影响因素，建立了传输功率半经验计算公式，验证了其应用前景。提出了基于压力触发的汽化-冷凝自适应平衡相变模型，构建了超长热管相变传热动态仿真CFD模型，揭示了内部相变传热机制及其与传热特性的关联规律。结合可视化实验和CFD仿真研究，分别考察了波纹结构（U型和螺旋形）、内插件（柔性钢丝绳和吸液芯）和变径结构对波纹管柔性热管内传热特性的影响，阐明了其强化机理。本项目研究结果可为超长热管在地热利用领域的推广和稳定高效应用提供理论和技术支撑。本项目实施期间共发表期刊SCI论文6篇（均为中科院大类二区/top期刊），参与国内外学术会议、交流4次，完成了预定目标。