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.     

Progress on a novel VM-type pulse tube cryocooler for 4 K

VM type pulse tube cryocooler is a new type pulse tube cryocooler driven by the thermal-compressor. This paper presented the recent experimental results on a novel single-stage VM type pulse tube cryocooler with multi-bypass. The low temperature double-inlet, orifice and gas reservoir, and multi-bypass were used as phase shifters. With the optimal operating frequency of 1.6 Hz and optimal average pressure of 1.4 MPa, a no-load temperature of 4.9 K has been obtained and 30 mW@5.6 K cooling power has been achieved. It was the first time for the single-stage VM-PTC obtaining liquid helium temperature reported so far. Moreover, it was also the first time for the multi-bypass being used in the low-frequency Stirling type pulse tube cryocooler.     

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%.     

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.     

Experimental study on the coupling characteristics of 100 Hz inertance tube pulse tube cryocooler working under optimal frequcency

Miniature pulse tube cryocooler is one of the main developing trends of pulse tube cryocooler. Four pulse tube cold fingers, two compressors and a series of inerance tube assemblies are employed to carry out the experimental investigation of coupling characteristic of miniature pulse tube cryocooler. It is concluded that the cooling performance of miniature pulse tube cryocooler is determined by the match conditions among its compressor, cold finger and inertance tube. If the three parts of cooler match well, the cold finger can achieve nearly same cooling performance under two totally different working conditions.     

CFD modeling and experimental verification of oscillating flow and heat transfer processes in the micro coaxial Stirling-type pulse tube cryocooler operating at 90–170 Hz

This paper presents the CFD modeling and experimental verifications of oscillating flow and heat transfer processes in the micro coaxial Stirling-type pulse tube cryocooler (MCSPTC) operating at 90–170 Hz. It uses neither double-inlet nor multi-bypass while the inertance tube with a gas reservoir becomes the only phase-shifter. The effects of the frequency on flow and heat transfer processes in the pulse tube are investigated, which indicates that a low enough frequency would lead to a strong mixing between warm and cold fluids, thereby significantly deteriorating the cooling performance, whereas a high enough frequency would produce the downward sloping streams flowing from the warm end to the axis and almost puncturing the gas displacer from the warm end, thereby creating larger temperature gradients in radial directions and thus undermining the cooling performance. The influence of the pulse tube length on the temperature and velocity when the frequencies are much higher than the optimal one are also discussed. A MCSPTC with an overall mass of 1.1 kg is worked out and tested. With an input electric power of 59 W and operating at 144 Hz, it achieves a no-load temperature of 61.4 K and a cooling capacity of 1.0 W at 77 K. The changing tendencies of tested results are in good agreement with the simulations. The above studies will help to thoroughly understand the underlying mechanism of the inertance MCSPTC operating at very high frequencies.     

Investigation of ejector-equipped Joule–Thomson refrigerator operating below 77 K

The lowest attainable refrigeration temperature of a nitrogen based Joule–Thomson refrigerator is generally limited to 77 K since the compressor suction pressure is usually higher than atmospheric pressure. The Joule–Thomson process with an ejector is proposed to achieve a refrigeration temperature as low as 68 K by adjusting the evaporation pressure down to 28 kPa and boosting the return stream pressure up to 147 kPa. A one-dimensional numerical model is developed to predict the performance of the ejector at cryogenic temperature, and its accuracy is compared with experimental data. The analysis results show that the addition of the ejector in the Joule–Thomson refrigeration cycle increases up to 5 times the overall efficiency, where the maximum achievable COP and exergy efficiency are 0.0195 and 6.65%, respectively. Other featured advantages of the proposed Joule–Thomson refrigeration cycle with ejector are the simplicity of cycle, minimization of mechanical moving components, cost effectiveness, and high reliability compared to other cryogenic refrigeration methods using pumps or cold compressors in Joule–Thomson cycles.     

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.     

CFD modeling and experimental verification of a single-stage coaxial Stirling-type pulse tube cryocooler without either double-inlet or multi-bypass operating at 30–35 K using mixed stainless steel mesh regenerator matrices

This paper presents the CFD modeling and experimental verifications of a single-stage inertance tube coaxial Stirling-type pulse tube cryocooler operating at 30–35 K using mixed stainless steel mesh regenerator matrices without either double-inlet or multi-bypass. A two-dimensional axis-symmetric CFD model with the thermal non-equilibrium mode is developed to simulate the internal process, and the underlying mechanism of significantly reducing the regenerator losses with mixed matrices is discussed in detail based on the given six cases. The modeling also indicates that the combination of the given different mesh segments can be optimized to achieve the highest cooling efficiency or the largest exergy ratio, and then the verification experiments are conducted in which the satisfactory agreements between simulated and tested results are observed. The experiments achieve a no-load temperature of 27.2 K and the cooling power of 0.78 W at 35 K, or 0.29 W at 30 K, with an input electric power of 220 W and a reject temperature of 300 K.     

Dynamic and thermodynamic characteristics of the moving-coil linear compressor for the pulse tube cryocooler: Part B – Experimental verifications

Experimental investigations are carried out to verify the theoretical analyses and modeling conducted in Part A. Some empirical corrections are made and two sets of experiments are arranged based on the same compressor coupled with two different coaxial cold fingers typically operating at 80 K and 60 K, respectively. The variations of φ, ΔP, I, θ; the input electric power, η_motor; the cooling capacity and ηCarnot with the operating frequency at the given cooling temperatures are tested and compared with the simulation results, and fairly good agreements are found in both cases. The effects of the cooling temperature on these characteristics are also tested and discussed. Experimental results verify the validity of the theoretical investigations in Part A. The results also indicate that the theoretical studies can apply to wide ranges of both the operating frequency and the cooling temperature.     

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.     

Thermodynamic Properties of Liquid 3He-4He Mixtures Between 0–10 bar below 1.5 K

The thermodynamic properties of liquid ³He-⁴He mixtures at pressures of up to 10 bar and temperatures below 1.5 K are determined. The calculations are based on previously determined thermodynamic properties of ³He-⁴He mixtures at saturated (zero) pressure, and available experimental measurements of the molar volume, which are used to determine an expression for the molar volume. Since available experimental data for mixtures at higher pressures are restricted to low temperatures (below about 0.7 K), the calculated molar volumes at high pressure and high temperature are largely based on pure ³He and pure ⁴He data.