CFD simulation of a miniature coaxial Stirling-type pulse tube cryocooler operating at 128 Hz

A two-dimensional axis-symmetric CFD model of a miniature coaxial Stirling-type pulse tube cryocooler with an overall weight of 920 g operating at 128 Hz is established, and systematic simulations of the performance characteristics at different temperatures are conducted. Both thermal equilibrium and non-equilibrium mechanisms for the porous matrix are considered, and the regenerator losses including the gas and solid conduction, the pressure drop and the imperfect interfacial heat transfer are calculated, respectively. The results indicate that the pressure drop loss is dominant during the first 85% and 78% of regenerator length for the thermal equilibrium and non-equilibrium models, respectively, and it decreases monotonously from warm to cold end due to the steadily decreasing Darcy and Forchheimer terms, whereas other entropy generations share similar changing tendencies, going up gradually near the warm end, increasing dramatically from about 60% of length and then decreasing sharply near the cold end. The reasons for these entropy variations are discussed.     

斯特林型两级脉管制冷机的改进

在最近研制的1台直线压缩机驱动的两极脉管制冷机的初步试验的基础上,对直线压缩机的线圈重新进行了设计和制作,解决了由于绕制圈数过多而无法输入足够电功率的问题。对冷头的热端法兰及回热器热端热交换器进行了改进,采用了微槽式水冷却器,解决了压缩热无法得到充分冷却引起的制冷机热端温度过高的问题。改进后制冷机的性能得到了显著的提高,在2.0 MPa充气压力和40 Hz频率的条件下,该制冷机获得了14.2 K的最低制冷温度。并且,第一级和第二级在97.8 K和34.9 K时,分别具有2.5 W和1 W的制冷量。     

DC流对液氦温区斯特林型脉管制冷机的影响

理论研究表明DC流(Direct Current flow)存在于大多数双向进气结构的脉管制冷机中。开展了10 K以下多级斯特林脉管的实验研究,考察了在液氦温区斯特林脉管内直流流动对制冷机性能影响的规律。在采用双向进气结构对DC流流向及流量适当控制时,制冷机性能得到明显提升,在8—7 K温区适当的DC流下冷端由7.42 K降低至7.16 K。     

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.     

20K温区单级脉管制冷机漏热分析

漏热冷损是影响低温制冷机性能的一个重要因素.对1台工作在20 K温区的单级脉管制冷机进行了漏热计算,并对其进行了部分实验验证.结果表明:在系统总漏热中,脉管和回热器的壁面轴向导热所占的比例最大.     

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.     

Advances on a cryogen-free Vuilleumier type pulse tube cryocooler

This paper presents experimental results and numerical evaluation of a Vuilleumier (VM) type pulse tube cryocooler. The cryocooler consists of three main subsystems: a thermal compressor, a low temperature pulse tube cryocooler, and a Stirling type precooler. The thermal compressor, similar to that in a Vuilleumier cryocooler, is used to drive the low temperature stage pulse tube cryocooler. The Stirling type precooler is used to establish a temperature difference for the thermal compressor to generate pressure wave. A lowest no-load temperature of 15.1 K is obtained with a pressure ratio of 1.18, a working frequency of 3 Hz and an average pressure of 2.45 MPa. Numerical simulations have been performed to help the understanding of the system performance. With given experimental conditions, the simulation predicts a lowest temperature in reasonable agreement with the experimental result. Analyses show that there is a large discrepancy in the pre-cooling power between experiments and calculation, which requires further investigation.     

基于传输管的三级级联脉管制冷机实验研究

为提高脉管制冷机制冷效率,通过引入一根特殊设计的传输管,将本应在前一级脉管制冷机脉管热端耗散声功回收,理论上多级级联脉管制冷机制冷效率可达卡诺效率。基于该理论,在已有两级级联脉管制冷机基础上串入第三级制冷机。实验结果显示,该三级级联脉管制冷机最高可获得253.6 W@233 K制冷量,较单级制冷机制冷效率增加39.9%,制冷效率进一步趋于卡诺效率。     

热端温度对直线型脉冲管制冷机的影响分析

基于一台单级直线型脉冲管制冷机,研究分析了热端温度变化对制冷机性能的影响关系.建立了一维数值模型,分析了高频脉冲管制冷机内部相关热力学参数随热端温度变化的关系,从而揭示了热端温度变化影响整机性能的作用机理.最后通过实验数据和模拟值的比较研究,验证了模型的准确性.     

低于4K温度工作的二级脉管制冷机研制

介绍最近研制的一台双向进气带第二小孔阀型二极脉管制冷机实验情况。该机采用计算机时序控制，脉管热端均处于室温。文中给出了二级脉管制冷机的基本结构尺寸以及试验结果；一级脉管达到４５Ｋ；二级脉管无负荷最低制冷温度达到３．１Ｋ。能稳定，长期工作，讨论了制冷机性能的主要因素。     

多路旁通型高频脉冲管制冷机及固定调相装置比较实验

研制了一台低于40 K温区的单级同轴型高频脉冲管制冷机,采用多路旁通结构,在输入功率为222 W时,其最低温度达到34.22 K,并比较了惯性管、惯性管加双向进气、惯性管加多路旁通以及惯性管加双向进气加多路旁通4种固定调相装置的差异(其中双向进气采用喷嘴结构).实验结果表明:惯性管、喷嘴、多路旁通组合方式是一种非常有效的降低制冷温度的方式,是应用深低温区单级脉冲管制冷机调相方式的最佳选择;而惯性管则是应用于较高温区大冷量的最佳的调相方式.实验还表明,多路旁通加喷嘴结构能够降低脉冲管内部的直流,有效地提高脉冲管制冷机的性能.     

Theoretical and experimental investigations on the three-stage Stirling-type pulse tube cryocooler using cryogenic phase-shifting approach and mixed regenerator matrices

Theoretical analyses and experimental verification for a three-stage Stirling-type pulse tube cryocooler (SPTC) expected to operate at 5–12 K are conducted. Cryogenic phase-shifting and mixed regenerator matrices are employed to improve the performance at the third stage. Simulations of the phase relationship, dynamic pressure and mass flow rate are presented with third-stage phase-shifters at 40 K, 50 K and 293 K, respectively. Mixed regenerator matrices of conventional stainless steel meshes and rare-earth materials such as Er₃Ni, HoCu₂ and Er_0.6Pr_0.4 are optimized theoretically. Different ratios and combinations are analyzed and compared, and the quantitative analyses by the entropy analysis are made. A three-stage SPTC without external precooling is developed based on the theoretical analyses, and experiments were conducted. The results show a good agreement between simulations and experiments. With an overall input electric power of 370 W, the three-stage SPTC has experimentally reached a no-load temperature of 6.82 K and achieved a cooling capacity of 112 mW at 10 K.     

两级同轴型脉管制冷机回热器与脉管壁换热影响的模拟与实验

针对同轴型结构的两级脉管制冷机,采用热力学方法分析了回热器与脉管壁间换热作用对制冷机性能的影响。发现当脉管内热量通过壁面传向回热器时,脉管冷端焓流将增大,进而提升脉管冷指的制冷量。对设计的一台两级同轴型高频脉管冷指进行了数值模拟。模拟结果表明相同结构参数及输入下,引入回热器与脉管壁间的径向换热作用,低温级制冷量由原先的0.55 W@30 K提升至1.39 W@30 K,而对高温级的影响却小到可以忽略。     

10W/80K高频同轴脉冲管制冷机的实验性能

介绍了一款大冷量高频单级同轴脉冲管制冷机的基本结构、数值模拟和实验性能。其线性压缩机采用Redlich动磁式直线电机驱动,压缩活塞对置布置,使用板弹簧支撑和间隙密封技术,80 K温区工作时的电机效率在83%以上。膨胀机的蓄冷器和脉冲管为同轴型布置,这种结构使冷头与器件之间的耦合非常方便。使用数值软件对制冷机整机和调相部件进行数值模拟,并对模拟结果进行实验验证。对制冷机的运行频率和制冷性能进行实验研究,制冷机在210.3 W输入电功时能获得10 W/80 K的制冷性能,比卡诺效率为12.66%,运行频率为62 Hz,整机重量小于5.5 kg。     

Theoretical and experimental investigations on the cooling capacity distributions at the stages in the thermally-coupled two-stage Stirling-type pulse tube cryocooler without external precooling

The two-stage Stirling-type pulse tube cryocooler (SPTC) has advantages in simultaneously providing the cooling powers at two different temperatures, and the capacity in distributing these cooling capacities between the stages is significant to its practical applications. In this paper, a theoretical model of the thermally-coupled two-stage SPTC without external precooling is established based on the electric circuit analogy with considering real gas effects, and the simulations of both the cooling performances and PV power distribution between stages are conducted. The results indicate that the PV power is inversely proportional to the acoustic impedance of each stage, and the cooling capacity distribution is determined by the cold finger cooling efficiency and the PV power into each stage together. The design methods of the cold fingers to achieve both the desired PV power and the cooling capacity distribution between the stages are summarized. The two-stage SPTC is developed and tested based on the above theoretical investigations, and the experimental results show that it can simultaneously achieve 0.69 W at 30 K and 3.1 W at 85 K with an electric input power of 330 W and a reject temperature of 300 K. The consistency between the simulated and the experimental results is observed and the theoretical investigations are experimentally verified.     

Numerical investigation on a 300 Hz pulse tube cryocooler driven by a three-stage traveling-wave thermoacoustic heat engine

A 300 Hz pulse tube cryocooler (PTC) driven by a three-stage traveling-wave thermoacoustic heat engine (TSTHE) has been proposed and studied in this paper. In the configuration, three identical thermoacoustic heat engine units are evenly incorporated in a closed traveling-wave loop, in which three pulse tube cryocoolers are connected to the branch of each thermoacoustic heat engine. Compared with the conventional thermoacoustic heat engine which involves a traveling-wave loop and a long resonator, it has advantages of compact size and potentially high thermal efficiency. A TSTHE–PTC system was designed, optimized and studied in detail based on the thermoacoustic theory. Firstly, numerical simulation was conducted to design the system thus the optimum structure parameters of the system were obtained. With the operating condition of 4 MPa mean pressure and high working frequency, a cooling power of 7.75 W at 77 K and an overall relative Carnot efficiency of 11.78% were achieved. In order to better understand the energy conversion characteristics of the system, distributions of key parameters such as acoustic work, phase difference, dynamic pressure, volume flow rate and exergy loss were presented and discussed. Then, the coupling mechanism of the system was investigated. In addition, influence of coupling position on the system performance was further studied.     

空间用3 W@80 K脉冲管制冷机实验研究

为冷却某空间用红外探测器,研制了一台斯特林型脉冲管制冷机。该制冷机为单级同轴型结构,整机重量4.5 kg,设计寿命5年。系统介绍了脉冲管制冷机系统结构及实验装置,测试了制冷机性能及其与杜瓦耦合后的降温特性曲线,实验结果表明,脉冲管制冷机在80 K可提供0—3 W制冷量,比卡诺效率11%,其制冷量可充分满足杜瓦组件的低温和长寿命的工程需求。     

Valve timing effect on the cooling performance of a 4 K pulse tube cooler

Generally, a compressor together with a rotary valve system generates the pressure oscillation in GM-type cryocoolers. The timing of the rotary valve, which is one of the key operating parameters for cryocoolers, determines the relationship between intake and exhaust processes. A systematic investigation of valve timing effects on cooling performance of a two-stage 4 K pulse tube cooler (PTC) is reported. The experiments show that the optimization of valve timing can considerably improve the cooling performance for both stages. For the same PTC, a performance comparison for operation on different compressors with various input powers ranging from 0.5 to 6.0 kW is also presented.     

Innovative phase shifter for pulse tube operating below 10 K

Stirling type pulse tubes are classically based on the use of an inertance phase shifter to optimize their cooling power. The limitations of the phase shifting capabilities of these inertances have been pointed out in various studies. These limitations are particularly critical for low temperature operation, typically below about 50 K. An innovative phase shifter using an inertance tube filled with liquid, or fluid with high density or low viscosity, and separated by a sealed metallic diaphragm has been conceived and tested. This device has been characterized and validated on a dedicated test bench. Operation on a 50–80 K pulse tube cooler and on a low temperature (below 8 K) pulse tube cooler have been demonstrated and have validated the device in operation. These developments open the door for efficient and compact low temperature Stirling type pulse tube coolers. The possibility of long life operation has been experimentally verified and a design for space applications is proposed.     

Efficient helium recondensing using a 4 K pulse tube cryocooler

This paper introduces helium recondensing in a 4000 l dewar using a 4 K pulse tube cryocooler at Amundsen-Scott research station at the South Pole. The helium dewar has a normal boil-off rate of 14 l/day. Two features of cooling the dewar neck by helium vapor and precooling helium gas to be liquefied ensured high efficiency of the pulse tube recondenser in this application. The liquefier/recondenser has being successfully operating in the dewar at South Pole station since February 2005. It not only maintains zero boil-off of the dewar, but also liquefies helium gas supplied from outside of the dewar with a rate around 2.7 l/day.