The thermodynamic characteristics of a Stirling/pulse tube hybrid cryocooler

A Stirling/pulse tube hybrid cryocooler (SPC), comprised of a Stirling cryocooler as the first stage and a pulse tube cryocooler as the second stage, features the ability of shifting cooling capacity between stages by adjusting the movement of the displacer in the first stage. Such an ability allows an SPC to accommodate itself to time-varying heat loads at different temperatures, which makes it a competitive candidate in space applications. However, due to the gas coupling, there exists a significant mutual effect between stages which endows an SPC with special thermodynamic characteristics and has a significant effect on the SPC’s capability of shifting cooling capacity between stages. With the phasor analysis and the thermodynamic analysis, this paper establishes an idealized model of an SPC. The model is then used to study the effect of the second stage on the first stage and reveal the condition that an SPC is able to shift cooling capacity between stages. Also, the model is compared with a Sage numerical model and the two models are consistent on the overall trend. Though it is unable to reflect reality precisely, the idealized model can interpret the mechanism and highlight some of the essential nature of an SPC, which will eventually benefit the appropriate design of an SPC.     

Study on a high frequency pulse tube cryocooler capable of achieving temperatures below 4 K by helium-4

High-frequency pulse tube cryocooler (HPTC) has advantages of compact structure, low vibration, high reliability and long operation time. In this study, Theoretical analysis and experimental tests have been conducted in four aspects based on a developed 4 K HPTC. Firstly, a compressor with larger power output capability was employed and the impedance match between the cold head and the compressor was discussed. Secondly, simply using inertance tube configuration to replace the traditional inertance tube-gas reservoir structure. Then, the type and the size of the regenerator materials working at 4–20 K have been experimentally optimized. Finally, the performance of double-inlet working at as low as 20 K has also been tested for the first time for the HPTC. The present prototype achieved a no-load temperature of 3.6 K, which is the lowest temperature record ever reported for HPTC using helium-4 as working gas. A cooling power of 6 mW/4.2 K was also obtained with 250 W input power and a precooling power of 12.1 W/77 K.     

基于斯特林制冷机的文物恒湿展柜设计及实验研究

博物馆文物保存过程中相对湿度对文物的影响尤其重要，因此针对目前小型展柜广泛采用的半导体制冷存在制冷量小的缺点，结合斯特林制冷机制冷量大、寿命长、安全可靠等优点，设计并搭建了一台基于斯特林制冷的文物恒湿展柜装置，实现对微环境中相对湿度的精确调节。将斯特林制冷机的冷头置于优化设计的水槽中用于控制水温，采用空气与水直接接触的方式控制展柜内空气湿度。结果表明：使用散热片以及小型循环水泵可以大幅提升冷头与水之间的换热效率；合理的风机控制策略可以有效提升展柜湿度调节速度，维持湿度稳定，降低系统能耗；展柜内的相对湿度在45.0%～65.0%之间连续可调，并能保持稳定。     

Design,development and testing twin pulse tube cryocooler

The design and development of Twin Pulse Tube Cryocooler (TPTC) is presented. Both the coolers are driven by a single Linear Moving Magnet Synchronous Motor (LMMSM) with piston heads at both ends of the mover shaft. Magnetostatic analysis for flux line distribution was carried-out during design and development of LMMSM based pressure wave generator. Based on the performance of PWG, design of TPTC was carried out using Sage and Computational Fluid Dynamics (CFD) analysis. Detailed design, fabrication and testing of LMMSM, TPTC and their integration tests are presented in this paper.     

A non-lumped dynamic simulation method of sorption compressor for sorption cryocooler

A dynamic analysis of sorption compressor is motivated by the design of a practical sorption compressor. In this paper a non-lumped dynamic simulation method based on a non-isothermal parameter has been developed. An algorithm for simulating the dynamic behaviors of sorption compressor involving mass and energy transport is described and is calculated using Computational Fluid Dynamics (CFD). The calculated time-dependent pressure and temperature across the sorption compressor are obtained and verified by experiments. Then, the effects of thermal gradient and non-equilibrium adsorption–desorption on the net gas outflow from the sorption compressor are also investigated. It is shown that thermal gradient and non-equilibrium adsorption–desorption can significantly affect the net gas outflow with the same total heat input.     

An electrical circuit analogy model for analyses and optimizations of the Stirling-type pulse tube cryocooler

The existing electrical circuit analogy (ECA) models are mainly used to optimize the inertance tube and to analyze the crude phase of the dynamic pressure and the volume flow rate. The specific analyses and optimizations of other components or the whole Stirling-type pulse tube cryocooler (SPTC) with the ECA model have not been carried out. In this paper, a new ECA model including the main components of the SPTC such as regenerator, pulse tube, phase shifter and reservoir has been developed. To improve the practicability of the ECA model, based on the basic governing equations, calculation expressions of the above components are worked out, and their equivalent analogical electrical elements are defined according to the analogy theory. Through the developed ECA model, the specific pressure and volume flow rate at any position can be acquired. Further optimizations on the SPTC based on the ECA model show that, with the same pressure and PV power at the warm end of the regenerator, there exists an optimal phase angle between the pressure and the volume flow rate for the SPTC to achieve the highest gross cooling capacity. In addition, with the same ratio of the pressure to the volume flow rate and the same phase angle between them at the warm end of the regenerator, when the regenerator ineffectiveness loss is neglected, the SPTC efficiency keeps constant with variations of the PV power, however, the efficiency will increase with the increase of the PV power if the loss is considered.     

Design and experimental investigation of the high efficiency 1.5 W/4.2 K pneumatic-drive G-M cryocooler

The development of a high cooling power and high efficiency 4.2 K two stage G-M cryocooler is critically important given its broad applications in low temperature superconductors, MRI, infrared detector and cryogenic electronics. A high efficiency 1.5 W/4.2 K pneumatic-drive G-M cryocooler has recently been designed and developed by ARS. The effect of expansion volume rate and operation conditions on the cooling performance has been experimentally investigated. A typical cooling performance of 1.5 W/4.2 K has been achieved, and the minimum temperature of the second stage is 2.46 K. The steady input power of the compressor at 60 Hz is 6.8 kW, while the operation speed of the rotary valve is 30 rpm. A maximum cooling power of 1.75 W/4.2 K has been obtained in test runs.     

Investigation on phase shifting for a 4 K Stirling pulse tube cryocooler with He-3 as working fluid

He-3 is generally recognized for its ability to provide more excellent thermophysical performance than He-4, especially in the 4 K temperature range. However, this was not always the case in our preliminary experiments on a three-stage Stirling-type pulse tube cryocooler (SPTC). Our ongoing studies, as reported in this paper, demonstrate that the different working fluids also affect the performance through their phase shifting capability. This feature has been passed over in large part by researchers considering refrigerant substitution. Unlike previous theoretical analyses that focus primarily on regenerator losses, this report investigates the effects of the working fluid on the phase angle at the cold end in order to quantitatively reveal the relationship between the lowest attainable temperature and the cooling capacity. The analysis agrees well with our experimental results on a three-stage SPTC. While running with the operating parameters optimized for He-3, the lowest temperature of the SPTC decreased from 5.4 K down to 4.03 K. This is the lowest refrigeration temperature ever achieved with a three-stage SPTC.     

双级斯特林制冷机热力分析

基于热力学第一定律,分析了双级斯特林制冷机两级之间冷量分配的关系式,以及冷量与压缩机功耗之间的关系.通过商业计算软件,对制冷机内部能量流进行模拟计算,结合实例定量给出制冷机各部分的损失.     

混合填充式回热器单级脉管制冷机性能研究

回热器为回热式低温制冷机的关键部件,其性能对系统的影响甚大。为探索回热器内金属丝网混合填充对回热器性能的影响,文章基于回热器模拟软件REGEN3.3仿真结果的基础上,制作了单级脉管制冷装置,采用#300SS,#400SS和#500SS的金属丝网混填了四组回热器,并在不同输入功率下进行了系统制冷性能实验。实验结果表明,较之低目数丝网填充的回热器制冷机,采用高目数丝网填充的回热器制冷机性能较优;在回热器热端填充低目数,冷端填充高目数的丝网,可提高回热器冷端压比,提高整机制冷性能。