液氦温区斯特林型脉管制冷机实际气体效应影响及性能优化研究

发布时间：2019-06-03 16:18

【摘要】：医疗、航天和科学研究等高科技领域对液氦及以下温区的制冷需求日益迫切,如用于医疗MRI、超导磁体和量子通讯器件的冷却以及低温环境维持等。斯特林型脉管制冷机具有长寿命、高效率、低电磁干扰、冷端温度波动小等优点,在越来越多的应用场合备受青睐,因此逐渐成为研究热点。近年来,尽管液氦温区斯特林型脉管制冷机研究虽然巳取得一定进展,但与G-M脉管制冷机相比在最低制冷温度和制冷效率方面仍有较大差距。液氦温区斯特林型脉管制冷机存在多级结构耦合复杂、高频回热效率低、实际气体效应损失、声功小调相困难及工质比热剧烈变化等问题,这些复杂问题严重制约了其发展。本文以进一步提高液氦温区斯特林型脉管制冷机的制冷性能为目标,揭示液氦温区实际气体效应对回热性能影响的机理,探索提高回热效率的新途径,采用多级脉管制冷机获得液氦温度,进而提高脉管制冷机在液氦温区的制冷效率。本文主要开展了以下三方面的研究工作：1.液氦温区斯特林型脉管制冷工质物性对制冷性能影响机理分析基于热力学定律,分析比较了脉管制冷机制冷工质He-4和He-3在液氦温区的热力学特性,并给出了两种工质下脉管制冷机的各种损失。结合Sage和REGEN3.3研究了使用两种工质在液氦温区脉管中的制冷性能,从冷端相位角、回热器损失等方面入手,定量研究了由工质变化引起的回热器冷端相位对最低制冷温度、制冷量和性能系数(COP)的影响关系,上述分析为液氦斯特林脉管制冷机不同工质(He-3、He-4)的实验优化提供了理论指导。2.采用He-3及He-4为工质的液氮温区脉管制冷性能对比实验与传统的观点普遍认为的氦-3工质更为优越不同,实验表明采用He-3直接替代He-4斯特林型脉管制冷机并不能获得更低制冷温度。随后分析了He-3优化前后实验结果及平均压力、预冷温度、运行频率和输入功等不同运行参数下的制冷性能,找出因工质物性变化而提高制冷机性能所需的运行参数优化规律。通过运行参数优化,He-3工质的最低制冷温度由5.4 K降至4.03 K,并在4.86 K获得20 mW制冷量。这是目前三级斯特林型脉管制冷机达到的最低制冷温度。为进一步了解工质物性下制冷机填料对制冷机性能影响,在此基础上初步实验研究了He-4为工质的4-20K温区不同组分多层回热填料优化实验,为后续与He-3工质的制冷机填料实验对比及填料优化积累经验。3.液氦温区直流(DC flow)对脉管制冷性能影响的理论与实验研究针对He-4工质在液氦温区高频脉管实际气体损失严重的问题,研究了液氦温区回热器内质量流和能量流规律,提出了液氦温区DC流辅助调节方案。结合焓流理论分析了DC流对液氦温区脉管回热器各部分损失的影响,以及DC结构下不同质量流量、运行频率、平均压力对制冷机性能影响规律。为了验证理论计算结果并探索在液氦温区斯特林型脉管制冷机采用DC流提高制冷性能的可行性,设计了不同结构的液氦温区DC流结构形式,开展了液氦温区多级斯特林脉管第三级DC流的实验研究。研究了不同DC结构对回热器温度分布、无负荷制冷温度以及预冷温度的影响,对DC流结构引入的优势和劣势进行了对比,在总结不同结构优缺点的基础上提出了加入DC流回路提高液氦温区制冷机性能的方案,在抑制实际气体效应不利影响的同时显著提升了制冷机的性能。实验结果表明,在相同的运行概况下采用DC流结构,液氦温区制冷机最低制冷温度在He-4临界温度以上时由7.8 K降至6.2 K；在液氦温区时冷端温度由4.76 K降至4.69 K。首次理论结合实验验证DC流用于多级斯特林脉管制冷机提升性能的可能性。
[Abstract]:The high-tech areas, such as medical, aerospace and scientific research, are becoming more and more urgent for liquid helium and the following temperature areas, such as for medical MRI, cooling of superconducting magnet and quantum communication devices, and low-temperature environment maintenance. The Stirling type pulse tube refrigerator has the advantages of long service life, high efficiency, low electromagnetic interference, small cold end temperature fluctuation and the like. In recent years, although some progress has been made in the research of the Stirling type pulse tube refrigerator in the liquid helium temperature region, there is still a great gap in the minimum refrigeration temperature and the cooling efficiency compared with the G-M pulse tube refrigerator. The multi-level structure coupling of the Stirling type pulse tube refrigerator in the liquid helium temperature region is complicated, the high-frequency heat-return efficiency is low, the real gas effect loss, the small-tone phase of the sound work and the severe change of the specific heat of the working medium are difficult, and the complex problems seriously restrict the development of the Stirling type pulse-type pulse-type pulse-type pulse tube refrigerator. In order to further improve the refrigeration performance of the Stirling type pulse tube refrigerator in the liquid helium temperature region, the mechanism of the effect of the real gas effect on the heat recovery performance of the liquid helium temperature region is revealed, a new way to improve the heat recovery efficiency is explored, and the liquid helium temperature is obtained by adopting the multi-stage pulse tube refrigerator, So as to improve the refrigeration efficiency of the pulse tube refrigerator in the liquid helium temperature region. In this paper, the following three aspects of research work are carried out:1. Based on the law of thermodynamics, the thermodynamic characteristics of the refrigeration working medium He-4 and He-3 in the liquid helium temperature range are compared and compared, and various losses of the pulse tube refrigerator under the two working fluids are given. The refrigeration performance of the two working fluids in the vessel of the liquid helium temperature zone is studied in combination with Sage and REGEN3. The minimum refrigeration temperature of the cold end phase of the regenerator caused by the change of the working medium is quantitatively studied from the aspects of the cold end phase angle and the heat regenerator loss. The influence of the cooling capacity and the performance coefficient (COP) is the theoretical guidance for the experimental optimization of the different working fluid (He-3, He-4) of the liquid helium Stirling pulse tube refrigerator. He-3 and He-4 are used as the working medium, and the experimental results show that He-3 is used to replace the He-4 type pulse tube refrigerator, and the lower refrigeration temperature can not be obtained. The experimental results, the average pressure, the pre-cooling temperature, the operating frequency and the input power of He-3 were then analyzed to find out the optimization of the operating parameters needed to improve the performance of the refrigerator due to the change of the physical properties of the working medium. The minimum cooling temperature of He-3 working medium is reduced from 5.4K to 4.03K by operating parameters, and 20 mW of cooling capacity is obtained at 4.86K. This is the lowest cooling temperature reached by the current three-stage Stirling type pulse tube refrigerator. In ord to further understand that effect of the refrigerator filler on the performance of the refrigerator under the physical property of the working medium, a multi-layer re-thermal packing optimization experiment of the different components of the 4-20K temperature zone of He-4 as a working medium is studied. The theoretical and experimental study of the effect of the direct current (DC flow) in the liquid helium temperature zone on the performance of the vessel's cooling performance is to study the problem of the serious loss of the real gas in the high-frequency vessel in the liquid helium temperature zone of the He-4 working medium. The law of the mass flow and the energy flow in the regenerator of the liquid helium temperature zone is studied, and the auxiliary regulation scheme of the liquid helium temperature zone DC flow is proposed. The effect of the DC current on the partial loss of the tube heat regenerator in the liquid helium temperature zone and the influence of different mass flow, operating frequency and average pressure on the performance of the refrigerator under the DC structure are analyzed in combination with the current flow theory. In order to verify the theoretical calculation results and to explore the feasibility of using the DC flow to improve the refrigeration performance of the Stirling type pulse tube refrigerator in the liquid helium temperature region, the DC flow structure of the liquid helium temperature zone with different structure is designed, and the experimental study of the third stage DC flow of the multi-stage Stirling vessel in the liquid helium temperature region is carried out. The effects of different DC structures on the temperature distribution of the heat regenerator, the no-load cooling temperature and the pre-cooling temperature are studied, and the advantages and disadvantages introduced in the structure of the DC flow are compared. On the basis of summarizing the advantages and disadvantages of different structures, the scheme of adding the DC current loop to improve the performance of the liquid helium temperature zone refrigerator is put forward, and the performance of the refrigerator is obviously improved while suppressing the adverse effect of the real gas effect. The experimental results show that the minimum refrigeration temperature of the liquid helium-temperature-zone refrigerator is reduced from 7.8 K to 6.2 K at the time of the critical temperature of He-4 by adopting the DC current structure under the same operation condition. The temperature of the cold end is reduced from 4.76K to 4.69K in the liquid helium temperature zone.
【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TB651

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