Stage Pulse Tube Cryocooler Research Articles

Two Stage Pulse Tube Cryocooler with Intermediate Heat Exchanger for accessing Regenerator Cooling Capacity

Conventional operation of closed-cycle two-stage GM-type Pulse Tube Cryocoolers (PTCs) usually relies on utilizing the cooling power of both the 1st and the 2nd stage. While the 1st stage is required to precool the 2nd stage to reach the lowest accessible temperature below 4K, it usually also provides enough cooling power to cool additional cryostat elements such as radiation shieldings. However, current applications in quantum physics have highlighted the need to additionally access heat sinks with intermediate temperatures and cooling powers, e.g. for cooling of superconducting wires. Here we will demonstrate a cooler configuration, where a third cooling stage is incorporated into the 2nd stage regenerator. This third intermediate cooling stage allows to extract 4-5 W of cooling power at temperatures between 8 K and 9 K for a standard two-stage PTC with a cooling capacity of 1.6 W at 4.2 K. Most importantly, this approach does not reduce the performance of the main stage but the added intermediate regenerator stage instead allows to tap into hidden cooling power of the PTC.

The simulation and experiments of a high frequency single stage pulse tube cryocooler with two cooled thermal sinks

In the application of infrared detectors, pulse tube cryocoolers are required to provide cooling power at different temperature ranges simultaneously with light weight and compact construction. In this paper, a single stage pulse tube cryocooler was designed to provide cooling power at different temperature ranges with an extra cooled thermal sink placed in the middle of the regenerator. The axial distribution of volume flow and pressure wave of cryocooler with middle heat exchanger and without middle heat exchanger were compared theoretically. To verify the simulation results, a series of experiments were carried out. As a result, the cooling power of cryocoolers with middle heat exchanger was decreased at 80 K, and 0.5 W @ 88.5 K & 0.5 W @ 195.8 K of cooling power was obtained simultaneously at 45 W input power.

Frequency response characteristics of a thermally coupled three-stage Stirling-type pulse tube cryocooler capable of achieving 110 mW@7 K

Long-life cryocoolers operating below 7 K are crucial for infrared astronomy projects, such as the hybrid cryocooler employed as the MIRI cryogenic system in the James Webb Space Telescope, which provides a cooling temperature of 6.2 K. A totally thermally-coupled three-stage Stirling-type pulse tube cryocooler was developed in SITP to obtain a relatively high cooling capacity at 6∼7 K. With the cold inertance tube as the phase shifter of the third stage pulse tube cryocooler, a no-load temperature of 3.96 K was reached with He-4. The operating frequency was 26.5 Hz, and the average pressure was 1.68 MPa at room temperature. Simulation results show that the frequency of the third stage SPTC has significant effects on the impedance characteristics of the cold inertance tube and the efficiency of the low-temperature regenerator. The effect of frequency on the cooling capacity has been verified experimentally, and the optimal frequency changes with cooling temperatures and precooling temperatures. When the precooling temperatures of the first stage and the second stage were 90 K and 24 K, the cooling capacity of 58.5 mW@6 K and 113.4 mW@7 K under 100 W input electric power of the third stage SPTC were obtained with the optimized operating frequencies of 24.5 and 23 Hz, respectively. The total input electric power was 510 W when achiveing 113.4 mW@7 K.

The effects of inclination on a two stage pulse tube cryocooler for use with a ground based observatory

Ground-based observatories across a wide range of wavelengths implement cryogenic cooling techniques to increase the sensitivity of instruments and enable low temperature detector technologies. Commercial pulse tube cryocoolers (PTCs) are frequently used to provide 40K and 4K stages as thermal shells in scientific instruments. However, PTC operation is dependent on gravity, giving rise to changes in cooling capacity over the operational tilt range of pointed telescopes. We present a study of the performance of a two stage PTC with a cooling capacity of 1.8W at 4.2K and 50W at 45K (Cryomech PT420-RM) from 0-55° away from vertical to probe capacity as a function of angle over a set of realistic thermal loading conditions. Our study provides a method to extract temperature estimates given predicted thermal loading conditions across the angular range sampled. We then discuss the design implications for current and future tilted cryogenic systems.

Numerical investigation on parameter influence in double-stage Vuilleumier type pulse tube cryocooler (VM-DPTC)

The double stage Vuilleumier type pulse tube cryocooler (VM-DPTC) is a modified 4 K-class pulse tube cryocooler form the Vuilleumier hybrid pulse tube cryocooler in TIPC, CAS. Besides its compact size and low-frequency working pattern eliminating the moving parts in cryogenic temperature (<77 K) will improve the working stability and reduce the inherited losses. To design a proper double stage pulse tube cryocooler under a certain thermal compressor to work below 5 K, a numerical model based on Sage 10 software was established and the geometry of phase shifter was optimized firstly. Then the influence of working parameters on no-load temperature, cooling power and the heat rejection of the thermal compressor were studied.

Design and investigations on rotary valve for GM type pulse tube cryocooler

The rotary valve is one of the key components of GM-type pulse tube cryocooler and the cooling performance of GM-type pulse tube cryocooler depends on the rotary valve performance. In order to get better cooling power during steady-state operation of GM-type pulse tube cryocooler, the pressure ratio should be sufficiently high. The efficient rotary valve design should provide such a high-pressure ratio during the operation at steady state condition. The investigations are aimed at getting better pressure ratio and hence better cooling power. The present work involves the design of a rotary valve for two stage pulse tube cryocooler for 20 K applications based on the mass requirements at steady state operation and valve timing with the help of numerical modeling. With 3.65 pressure ratio,18.52 K no load temperature and 1 W cooling power at 19.51 K was obtained at optimum valve timing without using any rare earth materials in second stage regenerator.

A cryogen-free Vuilleumier type pulse tube cryocooler operating below 10 K

Vuilleumier (VM) type pulse tube cryocooler (PTC) utilizes the thermal compressor to drive the low temperature stage PTC. This paper presents the latest experimental results of a cryogen-free VM type PTC that operates in the temperature range below 10 K. Stirling type pre-coolers instead of liquid nitrogen provide the cooling power for the thermal compressor. Compared with previous configuration, the thermal compressor was improved with a higher output pressure ratio, and lead and HoCu2 spheres were packed within the regenerator for the low temperature stage PTC for a better match with targeted cold end temperature. A lowest no-load temperature of 7.58 K was obtained with a pressure ratio of 1.23, a working frequency of 3 Hz and an average pressure of 1.63 MPa. The experimental results show good consistency in terms of lowest temperature with the simulation under the same working condition.

Development status of a high cooling capacity single stage pulse tube cryocooler

High temperature superconducting (HTS) applications require high-capacity and high-reliability cooling solutions to keep HTS materials at temperatures of approximately 80 K. In order to meet such requirements, Sumitomo Heavy Industries, Ltd.(SHI) has been developing high cooling capacity GM-type active-buffer pulse tube cryocooler. An experimental unit was designed, built and tested. A cooling capacity of 390.5 W at 80 K, COP 0.042 was achieved with an input power of approximately 9 kW. The cold stage usually reaches a stable temperature of about 25 K within one hour starting at room temperature. Also, a simplified analysis was carried out to better understand the experimental unit. In the analysis, the regenerator, thermal conduction, heat exchanger and radiation losses were calculated. The net cooling capacity was about 80% of the PV work. The experimental results, the analysis method and results are reported in this paper.

Numerical Study of a 10 K Two Stage Pulse Tube Cryocooler with Precooling Inside the Pulse Tube

High efficiency cryocoolers working below 10 K have many applications such as cryo-pump, superconductor cooling and cryogenic electronics. This paper presents a thermally coupled two-stage pulse tube cryocooler system and its numeric analysis. The simulation results indicate that temperature distribution in the pulse tube has a significant impact on the system performance. So a precooling heat exchanger is put inside the second stage pulse tube for a deep investigation on its influence on the system performance. The influences of operating parameters such as precooling temperature, location of the precooling heat exchanger are discussed. Comparison of energy losses apparently show the advantages of the configuration which leads to an improvement on the efficiency. Finally, the cryocooler is predicted to be able to reach a relative Carnot efficiency of 10.7% at 10 K temperature.

A 63 K phase change unit integrating with pulse tube cryocoolers

This article presents the design and computer model results of an integrated cooler system which consists of a single stage pulse tube cryocooler integrated with a small amount of a phase change material. A cryogenic thermal switch was used to thermally connect the phase change unit to the cold end of the cryocooler. During heat load operation, the cryogenic thermal switch is turned off to avoid vibrations. The phase change unit absorbs heat loads by melting a substance in a constant pressure-temperature-volume process. Once the substance has been melted, the cryogenic thermal turned on, the cryocooler can then refreeze the material. Advantages of this type of cooler are no vibrations during sensor operations; the ability to absorb increased heat loads; potentially longer system lifetime; and a lower mass, volume and cost. A numerical model was constructed from derived thermodynamic relationships for the cooling/heating and freezing/melting processes.

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 15.1K is obtained with a pressure ratio of 1.18, a working frequency of 3Hz and an average pressure of 2.45MPa. 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.

Investigation on thermal coupled three stage pulse tube cryocooler

Pulse Tube Cryocoolers (PTCs) have been investigated in recent times with the focus on achieving much lower temperature and reliable operation. Lower temperatures can be obtained by cascading the stages of the PTC. These stages can either be gas coupled or thermal coupled. This paper presents the design and development of two different configurations of three stage thermal coupled PTC, one with room temperature phase shifting mechanism (PSM) and the other with cold phase shifting mechanism. For room temperature PSM, the first and second stage are provided with inertance tube, while that for the third stage is provided with inertance tube and a double inlet valve. For the cold PSM, only an inertance tube is used as a phase shifter. In case of PTC with room temperature PSM, a minimum temperature of 19.61 K is achieved with a refrigerating effect of 220 mW at 30 K at the cold end of the third stage pulse tube, with an input power of 600 W. While for the PTC with cold PSM, a minimum temperature of 32.41 K is achieved. A reliability test is carried out; the PTC performed well during the entire operation and the repeatability is established.

Transient analysis of single stage GM type double inlet pulse tube cryocooler

Transient analysis of single stage GM type double inlet pulse tube cryocooler is carried out using a one dimensional numerical model based on real gas properties of helium. The model solves continuity, momentum and energy equation for gas and solid to analyse the physical process occurring inside of the pulse tube cryocooler. Finite volume method is applied to discretize the governing equations with realistic initial and boundary conditions. Input data required for solving the model are the design data and operating parameters viz. pressure waveform from the compressor, regenerator matrix data, and system geometry including pulse tube, regenerator size and operating frequency for pulse tube cryocooler. The model investigates the effect of orifice opening, double inlet opening, pressure ratio, system geometry on no load temperature and refrigeration power at various temperatures for different charging pressure. The results are compared with experimental data and reasonable agreement is observed. The model can further be extended for designing two stage pulse tube cryocooler.

Study on a cascade pulse tube cooler with energy recovery: new method for approaching Carnot

A pulse tube cryocooler (PTC) can not achieve Carnot efficiency because the expansion work must be dissipated at the warm end of the pulse tube. How to recover this amount of dissipated work is a key for improving the PTC efficiency. A cascade PTC consists of PTCs those are staged by transmission tubes in between, these can be a two-stage or even more stages, each stage is driven by the recovered work from the last stage by a well-designed long transmission tube. It is shown that the more stages it has, the closer the efficiency will approach the Carnot efficiency. A two-stage cascade pulse tube cooler consisted of a primary and a secondary stage working at 233 K is designed, fabricated and tested in our lab. Experimental results show that the efficiency is improved by 33% compared with the single stage PTC.

Experimental Investigation on Stirling Type Thermally Coupled Three Stage Pulse Tube Cryocoolers with ‘U’ Type Configuration

Research on Stirling type Pulse Tube Cryocooler (PTC) is focused on achieving lower temperatures by cascading the stages or by multi-staging. Multi-staging can be done either by gas coupling or by thermal coupling of the stages. In the thermal coupling option, either a two stage cooler can pre-cool a single stage PTC to reach lower temperatures or a single stage PTC can cool a two stage PTC. In the present work, both these configurations are tested experimentally keeping the same two stage PTC. In case-1, the two stage PTC is used as a pre-cooling stage while in case-2, the single stage PTC is used as a pre-cooling stage. Length of the single stage is required and to be increased to match the two stages PTC for effective thermal coupling in case-1. The lowest temperature achieved in case-1 is 50.07K where as in case-2 the lowest temperature achieved is 19.61K at 17bar charge pressure and 68Hz frequency. The pressure drop in both the PTCs is compared to analyze the difference in performance.

Indigenous development of a table top batch liquefaction for nitrogen using pulse tube crycooler

Cryogenic recondensation devices present considerable challenges towards condensing helium in systems such as MRI, NMR and SQUID cryostats etc. Normally refilling of cryogens is costly and also troublesome. To replace the standard refilling system, there is a need of small scale recondensing system. In a typical recondensation system, the evaporating gas is initially pre-cooled by the cooling power of the first stage cold head. Subsequently, it is passed on to the second stage cold head, where a special heat exchanger is mounted with large surface area for cooling. The gas when passing over this cold surface gets condensed into a liquid and returns back to the cryostat dewar. This paper presents the design and development of a simple experimental setup for batch liquefaction of nitrogen and is based on the two stage pulse tube Cryocooler already developed in our laboratory. The details of the system and the preliminary experimental results are presented here. This setup serves as a pre-runner for our subsequent development of re-condensation system for helium gas.

Performance improvement of 2 stage GM-type pulse tube Cryocooler for cryopump

This paper describes experimental study and performance improvement of 2 stage Gifford-McMahon (G-M) type pulse tube cryocooler for cryopump. The objective of this study is to improve the efficiency of 2 stage pulse tube cryocooler for substituting 2 stage G-M cryocooler used in cryopump. The target cooling capacities are 5 W at 20 K and 35 W at 80 K for the <TEX>$1^{st}$</TEX> and the <TEX>$2^{nd}$</TEX> stage, respectively. These values are good cooling capacities for vacuum level in medium size ICP 200 cryopump. Design of the 2 stage pulse tube cryocooler is conducted by FZKPTR(Forschungs Zentrum Karlsruhe Pulse Tube Refrigerator) program. In order to improve the performance of 2 stage pulse tube cryocooler, U-type pulse tube cryocooler is fabricated and connecting tubes are minimized for reducing dead volumes and pressure losses. Also, to get larger capacities, orifice valves and double inlet valves are optimized and the compressor of 6 kW is used. On the latest unit, the lowest temperatures of 2 stage pulse tube cryocooler are 42 K (<TEX>$1^{st}$</TEX> stage) and 8.3 K (<TEX>$2^{nd}$</TEX> stage) and the cooling capacities are 40 W at 82.9 K (<TEX>$1^{st}$</TEX> stage) and 10 W at 20.5 K (<TEX>$2^{nd}$</TEX> stage) with 6.0 kW of compressor input power. This pulse tube cryocooler is suited for commercial medium size cryopump. In performance test of cryopump with 2 stage pulse tube cryocooler, pumping speed for gaseous nitrogen is 4,300 L/s and the ultimate vacuum pressure is <TEX>$7.5{\times}10^{-10}$</TEX> mbar.