Coaxial Pulse Tube Cryocooler Research Articles

High efficiency 40 K single-stage Stirling-type pulse tube cryocooler

A high efficiency single-stage Stirling-type coaxial pulse tube cryocooler (SPTC) operating at around 40 K has been designed, built and tested. The double-inlet and the inertance tubes together with the gas reservoir were adopted as the phase shifters. Under the conditions of 2.5 MPa charging pressure and 30 Hz operating frequency, the prototype has achieved a no-load temperature of 23.8 K with 330 W of electric input power at a rejection temperature of 279 K. When the input power increases to 400 W, it can achieve a cooling capacity of 4.7 W/40 K while rejecting heat at 279 K yielding an efficiency of 7.02% relative to Carnot. It achieves a cooling capacity of 5 W/40 K with an input power of 450 W. It takes 10 minutes for the SPTC to cool to its no-load temperature of 40 K from 295 K.

An efficient miniature 120 Hz pulse tube cryocooler using high porosity regenerator material

A 1.22 kg coaxial miniature pulse tube cryocooler (MPTC) has been fabricated and tested in our laboratory to provide cooling for cryogenic applications demanding compactness, low mass and rapid cooling rate. The geometrical parameters of regenerator, pulse tube and phase shifter are optimized. The investigation demonstrates that using higher mesh number and thinner wire diameter of stainless steel screen (SSS) can promote the coefficient of performance (COP) when the MPTC operates at 120 Hz. In this study, the 604 mesh SSS with 17 μm diameter of mesh wire is constructed as filler of regenerator. The experimental results show the MPTC operating at 120 Hz achieves a no-load temperature of 53.5 K with 3.8 MPa charging pressure, and gets a cooling power of 2 W at 80 K with 55 W input electric power which has a relative Carnot efficiency of 9.68%.

Development of a compact cryocooler system for high temperature superconductor filter application

Seeking a higher specific power of the pulse tube cryocooler is an important trend in recent studies. High frequency operation (100Hz and higher), combined with co-axial configuration, serve as a good option to meet this requirement. This paper introduces a high efficiency co-axial pulse tube cryocooler operating at around 100Hz. The whole system weighs 4.3kg (not including the radiator) with a nominal input power of 320W, namely, power density of the system is around 74W/kg. The envelop dimensions of the cold finger itself is about 84mm in length and 23mm in outer diameter. Firstly, numerical model for designing the system and some simulation results are briefly introduced. Distributions of pressure wave, the phase difference between the pressure wave and the volume flow rate and different energy flow are presented for a better understanding of the system. After this, some of the characterizing experimental results are presented. At an optimum working point, the cooling power at 80K reaches 16W with an input electric power of 300W, which leads to an efficiency of 15.5% of Carnot.

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 30–35K 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 27.2K and the cooling power of 0.78W at 35K, or 0.29W at 30K, with an input electric power of 220W and a reject temperature of 300K.

A novel coupled VM-PT cryocooler operating at liquid helium temperature

This paper presents experimental results on a novel two-stage gas-coupled VM-PT cryocooler, which is a one-stage VM cooler coupled a pulse tube cooler. In order to reach temperatures below the critical point of helium-4, a one-stage coaxial pulse tube cryocooler was gas-coupled on the cold end of the former VM cryocooler. The low temperature inertance tube and room temperature gas reservoir were used as phase shifters. The influence of room temperature double-inlet was first investigated, and the results showed that it added excessive heat loss. Then the inertance tube, regenerator and the length of the pulse tube were researched experimentally. Especially, the DC flow, whose function is similar to the double-orifice, was experimentally studied, and shown to contribute about 0.2K for the no-load temperature. The minimum no-load temperature of 4.4K was obtained with a pressure ratio near 1.5, working frequency of 2.2Hz, and average pressure of 1.73MPa.

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 920g operating at 128Hz 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.

Design, development and testing of coaxial pulse tube cryocooler and linear compressor

Cryocoolers, particularly pulse tube cryocooler, is playing a pivotal role in research. Three most important components of cryocooler are, pulse tube, regenerator and linear compressor. Based on the relative position of regenerator and pulse tube we have various configurations like, inline, u-shaped, coaxial and annular. The most important component of a cryocooler is a pulse/pressure generator, called linear motor compressor. These compressors use a current carrying wire within a magnetic field to impart a linear force in the axial direction to the piston while conventional rotary compressors use a crankshaft to provide this force. Our area of interest is designing and developing a stirling type, split coaxial pulse tube and suitable linear compressor (moving coil type). The model used for preliminary design is isothermal. The design and fabrication was done in Walchand College of Engineering and testing was done in Cryogenics lab, IIT, Mumbai. The results in hand show lowest temperature achieved is 105.2 K.

Experimental Study of an Aerospace Low Temperature Refrigerator Cooled by a Pulse-tube Cryocooler

Asingle-stage coaxial pulse tube cryocooler (PTC) has been designed, manufactured and tested at ShanghaiInstitute of Technical Physics (SITP), Chinese Academy of Sciences (CAS) for cooling an aerospace low temperature refrigerator (LTR), whose volume is 20 liters. The LTR system and the PTC system are introduced. Lots of simulations are carried out by CAD/FLUENT for verifying the LTR structure rationality and predicting the inside walls temperature uniformity. Some performance experiments of the LTR have been carried out and analyzedafter coupling with the PTC. The experimental results show that the PTC is capable of cooling the LTR to about average -100oC, so the PTC has a great potential for cooling aerospace LTRs. Some cooling curves are presented and discussed in detail for a thorough understanding of the LTR system.

A high-efficiency coaxial pulse tube cryocooler with 500 W cooling capacity at 80 K

High-temperature superconductivity power-grid technologies require a highly reliable and efficient cryocooler with cooling power of 100W to kilowatt level at liquid-nitrogen temperatures to produce cryogenic environments. This paper describes the design of a coaxial Stirling-type pulse tube cryocooler to meet this need. In the designed cryocooler, the regenerator and pulse tube are lengthened to avoid possible temperature inhomogeneity. In an experiment, the azimuthal temperature difference at the middle of the regenerator was less than 30K. With 7.6kW electric power input, the cryocooler offers more than 520W cooling power at 80K corresponding to a relative Carnot efficiency of 18.2%. When the cooling power was less than 370W, the efficiency is higher than 20%.

Theoretical and experimental investigation of two pulse tube cryocoolers driven by a single opposed linear compressor

In order to achieve low temperature at different positions, two coaxial pulse tube cryocoolers driven by one linear compressor have been designed, built and tested at Shanghai Institute of Technical Physics (SITP), Chinese Academy of Sciences. The performances of two coupled pulse tube cryocoolers were investigated at different operating frequencies from 50Hz to 60Hz and different charging pressures from 2.0MPa to 3.2MPa and its reject temperature dependence was observed in the range of 290–320K by the test bench. Experimental results showed that the performances of the two pulse tube cryocoolers, which were designed identically, were different. After being coupled, the differences of the performance between the two pulse tube cryocoolers were more obvious. These two pulse tube refrigerators could obtain a low-noise cooling capacity of more than 1.79W at 60K and 1.38W at 60K, respectively.

18.6 K single-stage high frequency multi-bypass coaxial pulse tube cryocooler

A single-stage high frequency multi-bypass coaxial pulse tube cryocooler (PTC) has been developed for physical experiments. The performance characteristics are presented. At present, the cooler has reached the lowest temperature of 18.6K with an electric input power of 268W, which is the reported lowest temperature for single-stage high frequency PTC. The cooler typically provides 0.2W at 20.6K and 0.5W at 24.1K with the input power of 260W at 300K ambient temperature. The cooperation phase adjustment method of multi-bypass and double-inlet shows its advantages in experiments, they might be the best way to get temperature below 20K for single-stage high frequency PTC. The temperature stability of the developed PTC is also observed.

Fabrication of Taper Gap Warm End Heat Exchanger in Coaxial Pulse Tube Cryocooler

Coaxial pulse tube cryocooler (PTC) acquires a perfect substitute for the existing Stirling cryocooler for providing reliable low-noise cooling for the given infrared detector system. The challenging work is the exacting requirement on its dimensions which have to adapt to the given Dewar.Warm end heat exchanger is the key assembly of the pulse tube cryocooler,and the coupling effect especially the heat exchange of the gas and solid in warm end heat exchanger directly affects the performance of the pulse tube cryocooler ,this paper briefly analyzes the differences of warm end heat exchangers in the form of cylinder gap,cylinder copper screen and taper gap.The status of every type of warm end heat exchanger are outlined, including the fabricating material and technique kernel , and especially introduce the taper gap warm end exchanger.In the end of the paper we conclude that the taper gap warm end exchanger can apparently improve the performance and minish the volume of the of the pulse tube cryocooler

High frequency pulse tube cryocooler with nonmetallic cold head

For some special applications, such as SQUID cooling, an entirely nonmetallic coaxial pulse tube cryocooler (PTC) was designed and tested, and the performance of nylon mesh as a regenerator matrix was also investigated. The study of nylon mesh in metallic PTCs shows that nylon mesh is suitable as regenerator matrix in the cold head at temperatures around 80 K. However, the measured performances of cryocoolers using nylon mesh are found to be significantly worse than that using stainless steel mesh. The distorted nylon mesh is considered to be one of the main reasons for the loss in performance. A lowest temperature of 74 K and a cooling capacity of 0.14 W at 80 K has been obtained by our nonmetallic cryocooler. Although the losses of nonmetallic PTC are bigger than the original prediction, there is still a large room for improvement. Such an entirely nonmetallic PTC is an alternative choice for SQUID-cooling without cryogenic liquids.

10 W/90 K single-stage pulse tube cryocoolers

A single-stage 10W/90K coaxial pulse tube cryocooler has been developed for space-borne optics cooling. The design considerations are described, and the optimizations on the double-segmented inertance tubes are presented. The preliminary engineering model (EM) of the cooler has been worked out, which typically provides the cooling of 10W at 90K with the input power of 175.6W at 310K reject temperature, and achieves around 14% of Carnot efficiency at 90K. The reject temperature dependence experiments on the EM show a smaller slope of 10.2W/10K and indicate a good adaptability to the reject temperature range from 290K to 333K.

40 K single-stage coaxial pulse tube cryocoolers

Several 40K single-stage coaxial high frequency pulse tube cryocoolers (PTCs) have been developed to provide reliable and low-noise cooling for GaAs/AlGaAs Quantum-Well infrared photodetectors (QWIPs). The inertance tubes together with the gas reservoir become the only phase shifter to guarantee the required long-term stability. The mixed regenerator consisting of three segments has been developed to enhance the overall regenerator performance. At present, the cooler prototype has achieved a no-load temperature of 29.7K and can typically provide 860mW cooling at 40K with 200W electric input power rejecting at 300K. The performance characteristics such as the temperature stability and ambient temperature adaptability are also presented.

High-capacity 60 K single-stage coaxial pulse tube cryocoolers

A high-capacity single-stage coaxial pulse tube cryocooler operating at around 60K has been developed to provide the appropriate cooling for the next-generation very-large-scale long wave infrared focal plane arrays under development. The application background and cooler design process are described, and the performance characteristics are presented. At present, the cooler typically provides 4.06W at 60K with the input power of 180W at 300K reject temperature. 4.72W can also be achieved when the input power increases to 200W, and over 9.4% of Carnot efficiency at 60K has been realized. The larger pulse tube diameter of 14.2mm is used and the evident orientation sensitivity is observed in the range of 55–65Hz. The experiments also observe the obvious reject temperature dependence.

Investigation on the Ultra-high Frequency Coaxial Pulse Tube Cryocooler

With compact size and low mass,the ultra-high frequency pulse tube has got big attention for space application and has become the frontier of the pulse tube research.For simple configuration and easy to debug,the in-line type pulse tube cryocooler is fabricated and optimized on the basis of simulation calculation firstly.Then the coaxial pulse tube with same dimension of the in-line pulse tube is fabricated.The cold finger of the coaxial pulse tube has 9 mm outer diameter,40 mm length and mass of 250 g mass.After the match of compressor and the optimization of the double inlet,driven by a liner compressor designed for 50 Hz operating at 90 Hz,the no-load temperature reaches to 46.4 K,and the cooling power is 2.1 W at 80 K with 80 W electric power input.Because of the low mass and the high operating frequency,the temperature of the cold end can decrease to working temperature 80 K from room temperature 300 K in two minutes and the gravity has little effect on the performance.

Performances investigation of two parallel PTCs driven by one linear compressor

To achieve refrigeration at different positions, we tried out pairs of different coaxial pulse tube cryocoolers (PTCs) driven in parallel by a single compressor and set up an experimental apparatus. The refrigerating performances of different PTC combinations are investigated through simulation and experiments. The distribution of output PV power between the PTCs is analysed by comparing the refrigeration performance for single PTC operation to that of two PTCs operated in parallel. Experiments and simulation results show that a typical combination consisting of PTC1 (diameter of cold finger: 14 mm) and PTC2-1 (diameter of cold finger: 10 mm) can simultaneously achieve refrigeration capacities of around 0.5 W at 60 K and 0.5 W at 80 K. The combination of two samples (PTC2-1 + PTC2-2) of the same type of PTC shows a non-uniformity of refrigerating performances. Power distribution among the PTCs depends mainly on the size of the pulse tubes and the phase change. The length of the connection tube has significant influence on the refrigeration performances of two parallel PTCs in the experiments.

Single-stage high frequency coaxial pulse tube cryocooler with base temperature below 30K

This paper introduces two single-stage high frequency coaxial pulse tube cryocoolers (PTCs) with base temperature below 30 K. One has reached the lowest temperature of 26.1 K with an electric power of 250 W, which is the reported lowest temperature for single-stage high frequency PTC without multi-bypass. Using nozzle for double-inlet instead of need valves, the second PTC has achieved the temperature of 28.6 K with an electric power of 235 W. The analysis result is coinciding with experiments in general. The paper shows the advantage of the cooperated phase adjustment method of inertance tube and double-inlet, they might be the best choice when low temperature PTC is required.

Detection of micro-flaws on thin copper tubes using SQUID-NDI system based on eddy current technique

We constructed a SQUID-NDI system for inspection of micro-flaws on heat exchanger copper tubes employing HTS-SQUID gradiometer and Helmholtz-coil-type inducer. The HTS-SQUID gradiometer was cooled using a coaxial pulse tube cryocooler. The detection of artificial flaws several tens of μm in depth on copper tubes, 6.35mm in outer diameter and 0.825mm in thickness, was demonstrated using the SQUID-NDI system. With excitation field of 1.6μT at 5kHz, the system could detect a 30-μm-depth flaw with SN ratio of about 20, where conventional NDI methods should fail to detect. The amplitude of the magnetic signal due to the flaw was in proportion to the square of flaw depth. Taking into account of the system’s noise level, the results suggest that the SQUID-NDI system has a potential to detect sub-10-μm-depth flaws on copper tubes.