微型低温节流制冷器热力过程与换热耦合调控机理研究

This study is aimed to resolve the critical issues of efficient and quick cooling and temperature stability at liquid nitrogen temperature of miniature Joule-Thomson cryocooler. The variable-mass thermodynamic analysis, numerical simulation of convective heat transfer in complicated micro-channels, and experimental tests will be performed to study the coupling mechanism of fast-changing thermodynamics and heat exchange in miniature Joule-Thomson cryocooler. An analytical model coupling the variable-mass thermodynamics and heat transfer processes will be proposed to study the fast cooling process and the nonlinear automodulation mechanism. The effects of ultra-high pressure, transcritical transition, large temperature difference, and small dimension can be properly considered including the distributed Joule-Thomson effect, compressibility, property variation, and axial conduction. Moreover, numerical simulations will be carried out to investigate the flow resistance and heat transfer in the complicated micro-channels of double helical finned tubes. The effects of small dimension, buoyant force, secondary flow pattern and fin parameters on the heat transfer characteristics will be analyzed in detail, and thereby the mechanism and method to enhance the heat transfer will be explored. The experimental tests will be also performed to investigate the fast cooling process and characteristics of flow and heat transfer in miniature Joule-Thomson cryocooler. The experimental results can be used to validate and calibrate the analytical model and numerical model. Based on the theoretical analysis and numerical results, the thermodynamic parameters, the structural parameters of the recuperator and the automodulation characteristics will be optimized, and multi-objective optimization method will be developed to improve the transient thermal performance of the cryocooler. The results and findings of this study can help to develop and enrich the mechanisms of fast-changing thermodynamics of Joule-Thomson refrigeration cycle, which provides theoretical guidelines to improve the technology of the miniature Joule-Thomson cryocoolers.

为解决液氮温区微型节流制冷器高效快速降温和稳定低温维持关键机理问题，本项目将从变质量热力学分析、微细复杂通道流动传热数值模拟和实验研究三个方面，围绕节流制冷开式循环中快速多变热力过程与流动传热耦合调控机理开展研究。考虑分布节流效应、可压缩性、变物性和轴向导热的影响，建立变质量热力学模型，对微型节流制冷循环快速降温过程和非线性自耦机制进行研究。通过双螺旋肋片管微细复杂通道内流动传热数值模拟，探讨尺寸效应、浮力、截面二次流、螺旋肋片结构等对流动阻力和换热特性的影响规律及强化传热机理。与此同时，开展微型节流制冷器快速降温和流动换热特性实验研究，进行理论模型和数值模型的校核。最后，对循环热力学参数、双螺旋肋片管结构和流量自调特性进行多目标优化分析，发展微型节流制冷循环瞬态热力性能调控设计理论。本项目在理论上可发展和丰富微型节流制冷循环快速多变热力学过程机理，为推进微型节流制冷技术进步提供科学依据。

微型节流制冷器是基于双螺旋翅片管换热器及微孔节流实现开式节流制冷热力学循环的装置，具有体积小、启动快和可靠性高的优点，在红外制导器件低温冷却和低温医疗领域有重要应用。本项目针对微型节流制冷器快速多变热力学过程和流动传热机理问题，深入开展了微型节流制冷器系统热力学过程耦合仿真、双螺旋肋片管微细复杂通道内流动传热特性和制冷器优化性能调控和优化设计方法研究。首先，建立了螺旋毛细管内部与横掠螺旋肋片管外翅片三维数学模型，对低温工质在管内及翅片侧复杂管道间的流动换热特性进行了数值研究，提出了螺旋肋片毛细管通道流动传热预测关联式，适用于节流制冷器系统非稳态仿真模型，流动摩擦因子和对流换热Nu数的拟合公式计算值95%的数据偏差在±5%范围内。其次，在微型节流制冷器热力学仿真模型中，将双螺旋毛细管内流动换热与快速多变微孔节流过程耦合，改进了模型求解收敛性和计算效率。采用本项目提出的拟合关联式进行计算时，启动阶段节流制冷器流量变化和降温参数的计算值与实验数据的误差由原来关联式时的±40%降低到±15%；稳态条件下流量预测偏差小于±5%、制冷温度预测偏差小于±2℃。进行了微型节流制冷器变质量热力学分析，在有限容积供气条件下节流制冷器在全工作周期内的制冷特性进行了仿真。最后，实现了微型节流制冷器多参数耦合优化，将变质量热力学模型与遗传算法结合，对不同工况条件下的结构参数进行优化，得到了微型节流制冷器设计性能图谱。研究工作对微型节流制冷器优化设计和性能提升提供了重要基础数据、仿真模型和优化方法。基于上述研究工作，发表学术论文17篇，其中，国际期刊学术论文9篇，国际会议论文2篇，中文期刊论文3篇，国内会议论文3篇。申请并获批发明专利4项，协助完成培养硕士研究生2名，博士研究生1名。