空间用液氦温区高效复合型回热式低温制冷机理研究

The success applications of cooling technology at 80 K for space application indicate that Stirling coolers with moving parts at low temperature can be running for a long life as well as low vibration, while the advantage of no moving parts at low temperatures brings an intrinsic low efficiency as the expansion work is not recovered for pulse tube coolers. Can a high efficiency Stirling/pulse tube hybrid cooler combine the advantages of both of Stirling coolers and pulse tube coolers (PTCs) and avoid the disadvantages of them? Based on the research results of high frequency liquid helium temperature (4 K)pulse tube coolers in recent years of the applicant and a deep understanding of the key scientific problems that prevent high frequency PTCs working at 4 K efficiently and the latest research results of Stirling/pulse tube hybrid coolers, this proposal aims to investigate the following 3 key scientific problems by combining the theory of oscillating heat transfer, finite time thermodynamic and fluid mechanics and using Stirling/pulse tube hybrid cooler as a carrier. 1.Transient heat exchange characteristics of working fluid and matrixes at 4 K regenerators under finite heat transfer time and finite heat capacity of matrixes. Establishing real thermodynamic model of liquid helium temperature regenerator based on the finite time thermodynamic theory, and effects of finite heat exchange time and finite heat capacity on the performance of liquid helium temperature regenerator are investigated by introducing the time scale.Based on the energy equation of working gas and matrix, the effects of working frequency, heat capacity and temperature on the transient heat exchange characteristics of working fluid and matrixes in liquid helium temperature regenerators will be studied. 2.Pressure losses characteristics of oscillatory flow and high efficiency transmission of acoustic power in liquid helium temperature regenerators Based on the governing equations of oscillating gas, by applying the periodic boundary condition, the effect of mass flow rate, working frequency on the instantaneous and cycle-averaged friction coefficients will be investigated in theory. 3.High efficiency phase shifting method at low acoustic power condition. Effects of working parameters and geometry parameters on the phase shifting ability of inertance tube are calculated by theoretical analysis and experimental measurements. Comparisons and modifications of 3 inertance tube models will be carried out based on the experimental measurements. This research will get a better understanding of refrigeration mechanism of regenerative coolers at liquid helium temperature and lay a foundation for the manufacture of high efficiency and reliability long life hybrid regenerative cooler at liquid helium temperature, this kind of regenerative cooler would help to guarantee successful operation of national long term space exploration missions.

空间80K温区低温技术的实践证明，有运动部件的斯特林制冷技术可以实现长寿命和低振动，而无运动部件的脉管制冷技术存在膨胀功无法回收的本征低效率，能否结合两者的优点，避免两者的缺点，组合成更为高效更低温区的斯特林/脉管复合型液氦温区低温制冷技术？结合申请人近年来在高频液氦温区回热式制冷技术方面的研究基础和对相关关键科学问题的深入认识，以及国际上复合型回热式低温制冷技术的最新研究成果，本项目拟以斯特林/脉管复合型回热结构为载体，综合传热学、有限时间热力学和流体力学等相关理论，致力于解决液氦温区回热器在有限比热容有限时间条件下（高频）的高效换热、交变流动声功和压力的高效传输、小声功条件下高效调相等关键问题，最终实现在液氦温区下的高效高可靠长寿命回热式制冷方法。本项目的研究成果将为最终研制出满足空间应用特点的液氦温区回热式低温制冷技术奠定基础，以满足国家中长期空间探测计划的顺利实施。

液氦温区低温制冷技术在空间探测、国防军事、低温超导、能源、医疗等涉及国计民生等方面具有广泛的应用潜力。大部分探测器在液氦温区（或更低温度）下工作可获得高的敏感度和分辨率，而研制紧凑高效轻量长寿命的液氦温区低温制冷技术成为空间探测的根本保障！相比携带液氦或超流氦的杜瓦方式和吸附压缩驱动方式，本项目提出的斯特林/脉管复合型回热式制冷技术具有结构紧凑，可靠性高及长寿命的潜在优势，在本项目的支持下以斯特林/脉管复合型回热式制冷技术为核心开展了如下的研究：.1..液氦温区回热式制冷机理研究及结构创新.首次揭示了回热器在液氦温区和高温温区温度分布不同的内在机理，指明了非理想气体效应引起的时均压力焓流对回热器温度分布的决定性影响，为液氦温区高效回热器的优化设计提供了理论基础。基于理论分析结果，提出了一系列的可实现液氦温区回热式制冷的新结构，申请国家发明专利并获得授权。提出了一套包括回热器在内的脉管制冷机整机高效建模分析方法, 30 K温区脉管制冷机的相关实验结果已成功证明该模型的准确性。提出了带声功放大器的惯性管调相方式，获得美国专利授权。.2..斯特林/脉管复合型制冷机理理论及实验研究.从理论上研究了斯特林/脉管复合型制冷机的制冷机理和级间耦合匹配关系，首次提出了斯特林/脉管复合型制冷机的三种工作模式的判据(斯特林级制热模式、斯特林级制冷但净制冷量不足以及正常工作模式)。理论分析和实验测试结果表明，脉管级的引入使得原斯特林级的压力与排出器之间的相位和压力波动幅值均减小，从而导致斯特林级的制冷量减小或者不再制冷。基于该发现提出了一种斯特林/脉管制冷机的设计方法，后续将基于该设计方法完成液氦温区高效复合型回热式制冷机的研制。.3..可逼近卡诺效率的脉管级联制冷法研究.理论研究了惯性管(传输管)的相位调节特性，基于该研究提出了基于传输管的可逼近卡诺效率的声功回收型级联脉管制冷机新概念，该级联结构中每一级制冷机由回收自前一级制冷机脉管热端的声功来驱动，通过热力学分析表明，无穷级级联制冷效率等于卡诺效率。这一结论在脉管本征制冷效率[Tc/Th]和卡诺效率[Tc/(Th-Tc)]之间搭建了一座桥梁。实验结果表明，压缩机输入功为500 W时，两级级联较单级制冷效率提高约33.3%，三级级联提高39.9%，从实验上验证了脉管级联制冷法对能量回收再利用的能力。