Effect of pulse tube volume on dynamics of linear compressor and cooling performance in Stirling-type pulse tube refrigerator

In a Stirling-type pulse tube refrigerator (PTR), the pulse tube volume affects the dynamic behavior of a linear compressor as well as the cooling performance of PTR. In this study, PTRs which have different pulse tube volume are tested and simulated. The simulation code is verified with the experimental measurement of piston displacement, pressure wave, input power and cooling capacity. And then, the power transfer from the electric power input to the cooling capacity is explained with the simulation results. The smaller pulse tube increases the resonant frequency of a linear compressor and suppresses the piston motion because it imposes larger gas spring effect and also larger gas damping effect to the piston. The smaller one allows larger power transfer from electric power to expansion PV work despite the smaller piston displacement, but shows less cooling capacity due to larger thermal losses.     

A model for exergy analysis and thermodynamic bounds of Stirling refrigerators

A thermodynamic model based on exergy flow through a Stirling Refrigerator is developed. Important irreversibilities of the refrigerator due to external heat transfer with the reservoirs, heat leak, flow and heat transfer in regenerator are included in the model. Expansion and compression efficiencies are introduced in the model to account for the losses in these processes. The effect of a control phase shift between the mass flow rate and pressure across regenerator on the performance of the refrigerator is presented. Analytical solutions representing important quantities in the design of Stirling refrigerators such as the load curve, cooling power and efficiency in terms of basic system input parameters are developed. Thermodynamic bounds for the performance of Stirling refrigerators are obtained. Results indicating a compromise between cooling power and efficiency that are dependent on the constraint of the system are presented and discussed.     

谐振子耦合型热声驱动脉管制冷机研究

热声驱动脉管制冷机通常采用直接或者长管耦合的方式,但是因为耦合后的发动机和制冷机难以达到最佳的工作状态,耦合长管的损失也比较大,因此整体效率较低。本文提出一种热声驱动脉管制冷机结构,利用谐振子耦合热声发动机和脉管制冷机,能够显著减小声功传递损失,提升整机效率。全文针对在900 K加热温度、80 K空气液化温区下的热声驱动脉管制冷机展开理论研究,首先分析了谐振子耦合机理,并对谐振子参数进行了优化设计;其次,研究了加热温度、制冷温度和机械阻尼对系统性能影响;最后,将谐振子耦合型与长管耦合型两种方式的热声驱动制冷机进行了对比分析。结果表明:在平均压力为3MPa,加热温度为900 K,制冷温度为80 K时,谐振子耦合的热声驱动制冷机可获得整机22.5%的效率,而长管耦合的热声驱动脉管制冷机获得11.6%的效率。     

Investigation on the internal thermal link of pulse tube refrigerators

Within a pulse tube refrigerator (PTR) in coaxial configuration the pulse tube is located inside the regenerator matrix in axial direction. An internal thermal contact between these two main components of the coldfinger occurs. The experimental investigation of the direction and the quantity of transferred heat is in focus of this paper. Intermediate cooling of the regenerator by the corresponding part of its own pulse tube can improve the cooling performance of a PTR. Therefore, a well-adapted geometrical arrangement between the pulse tube and the regenerator is essential, considering the temperature distribution inside the coldfinger. We deduce design parameters to optimise the configuration of coaxial PTRs.     

Investigation on phase shifter of a 10 W/70 K inertance pulse tube refrigerator

A 10 W/70 K inertance pulse tube refrigerator (IPTR) has been developed for cooling infrared focal-plane array in a space mission. To investigate the influences of the phase shifter (inertance tube and reservoir) on the cooling performance, simulation models of the IPTR were built and experimental studies were conducted. The effects of reservoir volume and the surface roughness inside the inertance tube on cooling performance of the IPTR were investigated in detail. The optimized parameters of the phase shifter were developed to improve the cooling performance of the IPTR. The results show that a large reservoir volume reduces the optimal operating frequency, decreases the losses in the regenerator and improves the cooling performance of the IPTR. Because of the small surface roughness inside the stainless steel inertance tube, the input electric power of the IPTR is decreased, with a cooling power of 10 W at 70 K. The IPTR achieves 14.75% of the relative Carnot efficiency at 70 K by optimizing the inertance tube and reservoir.     

Development and experimental investigation of Stirling-type pulse tube refrigerator (PTR) below 20 K; cold compressor and colder expander

This research paper focuses on the experimental investigation of the Stirling-type pulse tube refrigerator with cold compression concept. Due to this innovative feature, the pulse tube refrigerator can reach lower temperature effectively other typical single-stage Stirling-type pulse tube refrigerators. The experiment as a proof of concept is carried out to demonstrate the capability of the pulse tube refrigerator operating between 80 K and 20 K. The cold linear compressor, which is submerged in a liquid nitrogen bath, produces cold mass flow with the efficiency of 85% for all the frequencies. At the lowest temperature part of the pulse tube refrigerator, the no-load temperature of 18.7 K is recorded and the cooling power of 0.4 W is measured at 20 K. The experimental results are analyzed in dynamic and thermal aspects by using the numerical model. The model can well explain how much losses are distributed in the system.     

High-efficiency 3 W/40 K single-stage pulse tube cryocooler for space application

Temperature is an extremely important parameter for space-borne infrared detectors. To develop a quantum-well infrared photodetector (QWIP), a high-efficiency Stirling-type pulse tube cryocooler (PTC) has been designed, manufactured and experimentally investigated for providing a large cooling power at 40 K cold temperature. Simulated and experimental studies were carried out to analyse the effects of low temperature on different energy flows and losses, and the performance of the PTC was improved by optimizing components and parameters such as regenerator and operating frequency. A no-load lowest temperature of 26.2 K could be reached at a frequency of 51 Hz, and the PTC could efficiently offer cooling power of 3 W at 40 K cold temperature when the input power was 225 W. The efficiency relative to the Carnot efficiency was approximately 8.4%.     

Wave-shaping of pulse tube cryocooler components for improved performance

The method of wave-shaping acoustic resonators is applied to an inertance type cryogenic pulse tube refrigerator (IPTR) to improve its performance. A detailed time-dependent axisymmetric experimentally validated computational fluid dynamic (CFD) model of the PTR is used to predict its performance. The continuity, momentum and energy equations are solved for both the refrigerant gas (helium) and the porous media regions (the regenerator and the three heat-exchangers) in the PTR. An improved representation of heat transfer in the porous media is achieved by employing a thermal non-equilibrium model to couple the gas and solid (porous media) energy equations. The wave-shaped regenerator and pulse tube studied have cone geometries and the effects of different cone angles and the orientation (nozzle v/s diffuser mode) on the system performance are investigated. The resultant spatio-temporal pressure, temperature and velocity fields in the regenerator and pulse tube components are evaluated. The performance of these wave-shaped PTRs is compared to the performance of a non wave-shaped system with cylindrical components. Better cooling is predicted for the cryocooler using wave-shaped components oriented in the diffuser mode.     

Theoretical and experimental study of a gas-coupled two-stage pulse tube cooler with stepped warm displacer as the phase shifter

A compact and high efficiency cooler working at liquid hydrogen temperature has many important applications such as cooling superconductors and mid-infrared sensors. This paper presents a two-stage gas-coupled pulse tube cooler system with a completely co-axial configuration. A stepped warm displacer, working as the phase shifter for both stages, has been studied theoretically and experimentally in this paper. Comparisons with the traditional phase shifter (double inlet) are also made. Compared with the double inlet type, the stepped warm displacer has the advantages of recovering the expansion work from the pulse tube hot end (especially from the first stage) and easily realizing an appropriate phase relationship between the pressure wave and volume flow rate at the pulse tube hot end. Experiments are then carried out to investigate the performance. The pressure ratio at the compression space is maintained at 1.37, for the double inlet type, the system obtains 1.1 W cooling power at 20 K with 390 W acoustic power input and the relative Carnot efficiency is only 3.85%; while for the stepped warm displacer type, the system obtains 1.06 W cooling power at 20 K with only 224 W acoustic power input and the relative Carnot efficiency can reach 6.5%.     

Numerical simulation of a GM-type pulse tube cryocooler system: Part II. Rotary valve and cold head

A simplified model to characterise a rotary valve is proposed. This model is used inside a complete GM-type pulse tube cryocooler (GMPTC) simulation including the compressor, rotary valve and cold head. The verification of the model is presented including the pressure wave, cooling power and COP by comparing the simulation results to the experimental data of an existing GMPTC system. The exergy losses produced by the compressor, rotary valve and cold head are discussed. This paper is aimed to propose a simulation method which can be applied to analyse and optimise a GMPTC cold head by using the characteristics of a specific compressor and rotary valve.     

有阀型小孔脉管制冷机的深入研究

为了克服第三代脉管制冷机存在的制冷温度不稳定的缺陷,本文从提高脉管制冷效率,进一步降低制冷温度的角度,对有阀型小孔脉管制冷机进行了研究。通过理论计算和实验改进,有阀型单级脉管制冷机取得了３４Ｋ的无负荷制冷温度,在８０Ｋ获得３０Ｗ以上的制冷功率,其制冷效率达到国外同类商品型有阀脉管制冷机的水平。     

Experimental study of a cascade pulse tube cryocooler with a displacer

Recovering the expansion power in pulse tube cryocooler is of great utility in improving cooling efficiency. Using a second-stage cooler after a primary cooler to produce extra cooling power is an effective way especially when the cooling temperature is not very low. In the configuration, the two coolers are connected by a displacer which is used as a phase shifter. In this paper, experimental investigations were conducted to study this system. Firstly, the performance of the overall system and separated cooler was respectively presented. To better understand the displacer, phase relation, mechanical resistance and displacement were then clarified. In addition, the power consumption distribution of the cascade cryocooler was discussed. Finally, both numerical and experimental comparisons were made on the displacer-type and tube-type cryocooler. The experimental results show that the displacer-type cryocooler has superior performance due to the better phase-modulation capability and less power loss. With the input electric power of 1.9 kW and cooling temperature of 130 K, the overall system achieved a cooling power of 371 W and a relative Carnot efficiency of 24.5%.     

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。     

混合工质脉管制冷的热力学性能预测

提出了用于预测混合工质脉管制冷热力学性能的改进型Brayton制冷循环,建立了制冷系统制冷量和制冷系数COP的理论表达式。在对多种低温流体的预测计算的基础上,提出了具有应用潜力的混合工质对。计算结果表明,如果用10%氮与90%氦的混合工质对代替纯氦,脉管制冷机在80K温度下的制冷系数和制冷量分别可以提高9.5%和6.7%。此外还讨论了其它可能用于80K温区脉管制冷的混合工质对,如氢-氦、氩-氦、氖-氦混合物等。     

A high efficiency coaxial pulse tube cryocooler operating at 60 K

In recent years, improved efficiency of pulse tube cryocoolers has been required by some space infrared detectors and special military applications. Based on this, a high efficiency single-stage coaxial pulse tube cryocooler which operates at 60 K is introduced in this paper. The cryocooler is numerically designed using SAGE, and details of the analysis are presented. The performance of the cryocooler at different input powers ranging from 100 W to 200 W is experimentally tested. Experimental results show that this cryocooler typically provides a cooling power of 7.7 W at 60 K with an input power of 200 W, and achieves a relative Carnot efficiency of around 15%. When the cooling power is around 6 W, the cryocooler achieves the best relative Carnot efficiency of around 15.9% at 60 K, which is the highest efficiency ever reported for a coaxial pulse tube cryocooler.     

On the performance of copper foaming metal in the heat exchangers of pulse tube refrigerator

As key components in pulse tube refrigerators (PTRs), heat exchangers have great influence on the performance of the PTRs, especially the cold end heat exchangers which dominate the cooling effect between the cold gas and heat load. Filling copper screens are widely used to improve the performance of heat exchange and laminar flow. Whereas, the heat transfer rate of copper screens is still not good enough for the actual requirements of PTRs. Furthermore, the flow resistance of the copper screen is growing up quickly with the increase of screen mesh. In this paper, we propose a new type of copper foaming metal with high heat transfer area and low flow resistance in the heat exchanger instead of the copper screens. The heat transfer performances of the copper screens and the copper foaming metal are firstly compared by theoretical calculation, which shows that the performance of the copper foaming metal with 600 μm pore size is better than that of 20 and 80 mesh copper screens, verified by experimental results. A four valve pulse tube refrigerator (FVPTR) with copper foaming metal of 600 μm pore size as filling material of the heat exchanger achieved 69.5 K, 2.5 K lower than that of using 20 mesh copper screens, 1.7 K lower than that of using 80 mesh copper screens.     

Performance analysis and optimization of high capacity pulse tube refrigerator

High capacity pulse tube refrigerator (HCPTR) is a new generation of cryocoolers tailored to provide more than 250 W of cooling power at cryogenic temperatures. The most important characteristics of HCPTR when compared to other types of pulse tube refrigerators are a powerful pressure wave generator, and an accurate design. In this paper the influence of geometrical and operating parameters on the performance of a double inlet pulse tube refrigerator (DIPTR) is studied. The model is validated with the existing experimental data. As a result of this optimization, a new configuration of HCPTR is proposed. This configuration provides 335 W at 80 K cold end temperature with a frequency of 50 Hz and COP of 0.05.     

声功回收型脉管制冷机的分析与研究

对所有的回热式低温制冷机,压力小与质量流之间的相位控制是达到制冷效果的关键。在斯特林制冷机中,这一相位是由压缩活塞和冷头排出器的相对运动来提供来;而在脉管制冷机中,这一相角是由构成脉管制冷机的各个部件：回热器、换热器、脉管、小孔,气库,连管等在几何空间上的合理拓扑结构来实现达到适宜的热声网络阻抗,从而最终实现压力波与质量流之间的适配相角。脉管制冷机的这一结构上的简化及由此带来的寿命长,可靠性高等优     

Stirling-type pulse tube refrigerator with slit-type heat exchangers for HTS superconducting motor

A cryogenic refrigeration system is one of the indispensable components for cooling superconducting motor or generator. Among various configurations of cryogenic refrigeration system, the on-board refrigeration system is considered to be attractive for compactness and small heat leak. In order to turn this concept into reality, we focus on two essential points; development of the specific structure for on-board refrigeration and optimal design of the refrigerator. Since the on-board refrigeration system should not create unbalanced vibration, the inline Stirling-type pulse tube refrigerator is considered as a good candidate and more concrete and efficient structure is developed under the design constraints. The dynamic absorber is used to maintain the dynamic stability of the single acting linear compressor. To increase thermal Carnot efficiency with the on-board Stirling-type pulse tube refrigerator, slit-type heat exchangers are implemented and flow straighteners are carefully designed by the three-dimensional CFD simulation. The overall configuration of the Stirling-type pulse tube refrigerator is designed and fabricated by the optimal process. The present on-board refrigerator has the cooling capacity of 7 W at 59.5 K with the Carnot efficiency of 10.9%. According to these experimental results, the pulse tube refrigerator as the on-board refrigeration system possesses a sufficient thermal efficiency despite the restricted design configuration. The on-board refrigeration is considered as a useful method for cooling HTS superconducting motor.     

Development of a 30–50 K dual-stage pulse tube space cooler

There has been a trend towards increasing heat loads for cryogenically cooled Earth Observation instruments in recent years.This is the case at both the current operational temperature levels (∼50K), as well as at lower operational temperature levels (30–50 K). One solution to meet this trend is to use existing pulse tube technology in a double stage configuration. With such technology increased cooling power at a lower temperature can be achieved at the payload detector. Another advantage of such a system is the possibility to increase overall system efficiency by cooling an intermediate shield to avoid parasitic heat losses towards the detector.Therefore a consortium consisting of Thales Cryogenics B.V. (TCBV), Alternative Energies and Atomic Energy Commission (CEA) and Absolut System (AS) is working on the development of a space cryostat actively cooled by a 2-stage high reliability pulse tube cryocooler. This work is being performed in the frame of an European Space Agency (ESA) Technical Research Program (TRP) (refer 4000109933/14/NL/RA) with a target TRL of 6.This paper presents the design of the overall equipped cryostat and cryostat itself but is mainly focused on the 2-stage cryocooler. Design, manufacturing and test aspects of cryocooler and its the lower level components such as the compressor and cold finger are discussed in detail in this paper. The cryocooler test campaign is meanwhile in final stages of completion and the obtained test results are in line with program objectives.