Cryocooler Systems Research Articles

An Experimental Study of the Influence of Cold Head Displacement Speed on Single-Stage Gifford-McMahon Cryocooler System Performance

In positive displacement cryocooler systems, the cooling performance is generally driven by the interaction between the compressor’s displacement and the cold head’s displacement. An experimental investigation explored the relationship between performance and cold end displacement speed for a single-stage gas-driven GM-type cold head operated at different frequencies. As loss mechanisms can be frequency related, the investigation also compared varying the cold end displacement by changing stroke length instead of changing operating frequency. Results showing these relationships are presented, and their impact on seal wear and variable-speed operation are discussed.

Design and performance analysis of a Joule-Thomson cryocooler systems

The aim of the work is to develop a mathematical model which has capability to analyses the design parameters as a function of operations conditions for single and multi-stage Joule Thomson Cryocooler System JTCS. The operations conditions are inlet and outlet pressure, precooling temperature, and mass flow rate. The design parameters are expansion device (length, diameter, and Joule Thomson coefficient), heat exchanger (length, diameter, and effectiveness) and gas type (nitrogen, oxygen, and argon). Theoretical results for nitrogen, oxygen, and argon at initial pressure of 25 MPa, initial temperature of 20ºC, indicate that the final temperature equal to (-16.46ºC, −37.34ºC and −56.75ºC) respectively at single stage JTCS. It also shows the possibility of decreasing the final temperature to (-194ºC, −180.9ºC and −183.8ºC) respectively at multistage JTCS. The experimental rig has been constructed for satisfying mathematical model. The experimental results for nitrogen gas show a temperature drop of 6.5ºC when the initial pressure and temperature were 3 MPa and 20ºC respectively. Theoretical results were validated using experimental measurements on the other hand. The computer program has been built to carry out the analysis required for solving the parameters of JTCS under different operations conditions with good agreement compared to recent published researchers.

A research of micro-pulse tube cryocooler with displacer phase shifter

• The phase relationships in the whole displacer PTC system were analyzed. • Three different sizes of a displacer type micro PTCs have been designed. • A 2D CFD model was constructed and used to characterize the displacer micro PTC. • A displacer provides a good phase shifting for a small-cooling-power micro PTC. • A cooling power of 1.5 W@80 K and a COP of 20.96% is obtained by the second micro PTC. Investigations of phase shifters and power recovery mechanisms are of sustainable interest for developing Stirling pulse tube cryocoolers (SPTC) with more compact design and higher efficiency. The warm displacer type SPTC has been demonstrated with a very promising theoretical efficiency benefiting from its strong phase shifting and work recovery functions. Extending this same phase shifting approach to miniature pulse tube refrigerators may provide advantages over the other alternatives, since inertance tubes are severely limited in their phase shifting capability when the associated acoustic power decreases below 20 W. A comprehensive investigation regarding the micro-pulse tube cryocooler with a displacer phase shifter is carried out in this work, including the design of the major components of the cryocooler, theoretical analysis regarding the phase relationship in the whole displacer type cryocooler system, and 2D simulation work addressing the performance of the cryocooler systems. In the optimum phase angle conditions of the 3 mm pulse tube size cryocooler, the mass flow rate leads the pressure wave by 28.8° at the regenerator warm end, and lags the pressure wave by 27.7° at the regenerator cold end. A cooling power of 1.5 W at 80 K and a COP (Coefficient of Performance) of 20.96% is obtained with an input power of 7.4 W.

Sensitivity analysis on miniaturize pulse tube boundary layer losses

Miniaturized cryocooler systems are among the key components of state-of-art infrared sensing small satellites (SmallSats). To achieve small size, these cryocoolers need to operate at high frequencies, e.g., 200 to 300 Hz range. High frequency leads to lower compression and expansion swept volumes and hence a smaller cryocooler. Previously we showed that pulse tube cryocoolers have high boundary layer losses for small size pulse tube diameters, which results in low thermodynamic efficiency. In this follow-up study we present a sensitivity analysis on the pulse tube boundary layer losses and investigate the effects of the bounding temperatures, pulse tube aspect ratio, operating frequency and pulse tube diameter. Computational fluid dynamics (CFD) is used for this sensitivity analysis. The results allow us to find the threshold conditions beyond which a miniature pulse tube cryocooler can no longer be effective for use at high frequencies.

Combination of thermal and electric properties' measurement techniques in a single setup suitable for radioactive materials in controlled environments and based on the 3ω approach.

We have designed and developed a new experimental setup, based on the 3ω method, to measure thermal conductivity, heat capacity, and electrical resistivity of a variety of samples in a broad temperature range (2-550 K) and under magnetic fields up to 9 T. The validity of this method is tested by measuring various types of metallic (copper, platinum, and constantan) and insulating (SiO2) materials, which have a wide range of thermal conductivity values (1-400 W m-1 K-1). We have successfully employed this technique for measuring the thermal conductivity of two actinide single crystals: uranium dioxide and uranium nitride. This new experimental approach for studying nuclear materials will help us to advance reactor fuel development and understanding. We have also shown that this experimental setup can be adapted to the Physical Property Measurement System (Quantum Design) environment and/or other cryocooler systems.

Role of size on the relative importance of fluid dynamic losses in linear cryocoolers

Thermodynamic modeling results for a novel small satellite (SmallSat) Stirling Cryocooler, capable of delivering over 200 mW net cooling power at 80 K for less than 6 W DC input power, are used in this paper as the basis for related pulse tube computational fluid dynamics (CFD) analysis. Industry and government requirements for SmallSat infrared sensors are driving the development of ever-more miniaturized cryocooler systems. Such cryocoolers must be extremely compact and lightweight, a challenge met by this research team through operating a Stirling cryocooler at a frequency of approximately 300 Hz. The primary advantage of operating at such a high frequency is that the required compression and expansion swept volumes are reduced relative to linear coolers operating at lower frequencies, which evidently reduces the size of the motor mechanisms and the thermodynamic components. In the case of a pulse tube cryocooler, this includes a reduction in diameter of the pulse tube itself. This unfortunately leads to high boundary layer losses, as the presented results demonstrate. Using a Stirling approach with a mechanical moving expander piston eliminates this small pulse tube loss mechanism, but other challenges are introduced, such as maintaining very tight clearance gaps between moving and stationary elements. This paper focuses on CFD modelling results for a highly miniaturized pulse tube cooler.

Fabrication of high sensitivity 3D nanoSQUIDs based on a focused ion beam sculpting technique

In this paper a nanofabrication process, based on a focused ion beam (FIB) nanosculpting technique, for high sensitivity three-dimensional nanoscale superconducting quantum interference devices (nanoSQUIDs) is reported. The crucial steps of the fabrication process are described, as are some peculiar features of the superconductor–normal metal–insulator–superconductor (SNIS) Josephson junctions, which may useful for applications in cryocooler systems. This fabrication procedure is employed to fabricate sandwich nanojunctions and high sensitivity nanoSQUIDs. Specifically, the superconductive nanosensors have a rectangular loop of 1 × 0.2–0.4 μm2 interrupted by two square Nb/Al–AlOx/Nb SNIS Josephson junctions with side lengths of 0.3 μm. The characterization of a typical nanoSQUID has been carried out and a spectral density of magnetic flux noise as low as 0.8 μΦ0 Hz–1/2 has been measured.

Stability test of conduction-cooled LTS/HTS composite coil

A small LTS/HTS composite coil made of NbTi/Cu and YBCO, with an inner diameter of 80 mm, an outer diameter of 88mm, a height of 50 mm, and an inductance of 5.5 μH, was designed to test its heat disturbance performance in a GM cryocooler. For comparison, a conventional LTS coil of a similar size made of NbTi/Cu wire was also tested. Transport current was applied from 50 A to 700 A at 8 K and 8.5 K, respectively. The two coils’ heat disturbance, minimum quench energy and quench propagation velocity performance were investigated and simulated. The results indicate that the LTS/HTS composite coil shows better thermal stability and is more fit for operation in conductive cryocooler systems compared to LTS coils.

Theoretical analysis of two coupling modes of a 300-Hz three-stage thermoacoustically driven cryocooler system at liquid nitrogen temperature range

Highly reliable, compact, and efficient cryocoolers with a cooling power of several watts to several hundred watts at liquid nitrogen temperatures around 77K are indispensable for cooling superconducting devices and infrared detectors, especially in aerospace applications. This paper introduces three-stage traveling-wave thermoacoustically driven cryocooler systems operating around 300Hz that meet the demand. In addition to the potential reliability due to the lack of moving components in a thermoacoustically driven cryocooler, this configuration has the potential for both compact size and high efficiency owing to the slim resonance tube and acoustic power recovery. Numerical simulations are performed to investigate two coupling modes: coupling the cooler at the branch of the engine (BR-coupling) or coupling the cooler parallel to the engine (PA-coupling). First, the two topologies are carefully designed to obtain high total exergy efficiency and the optimal dimensions are presented. Then, the axial distributions of the phase difference and the acoustic power are further provided to better illustrate the coupling characteristics. Furthermore, a theoretical analysis is performed on the influence of the two acoustic tubes in the PA-coupling mode and the result shows the importance of the tube dimensions. With a heating temperature of 850K, total exergy efficiencies of 11.4% and 14.8% have been achieved in the BR-coupling and PA-coupling modes, respectively. The PA-coupling mode’s higher efficiency is due to recycling the acoustic power entering the pulse tube cryocooler, whereas BR-coupling fails to recycle any acoustic power. However, the energy feedback in PA-coupling may cause structural complexity. Generally speaking, both coupling mode systems show encouraging prospects for aerospace applications.

A Dual Operational Refrigerator/Flow Cryostat with Wide Bore Medium Field Magnet for Application Demonstration

Since stand alone cryocooler systems have become more widely available, there has been increased commercial interest in superconductor applications in the temperature range intermediate to liquid helium and liquid nitrogen. There are however few facilities that have large in-field bore size with variable temperatures. A large bore system can reduce costs associated with full scale demonstration magnets by testing smaller coils and qualify medium length (up to meters) conductors. A 5 T, wide bore, (170 mm) Nb3Sn Oxford Instrument magnet has been integrated into a custom built dual mode refrigerator/helium flow cryostat with 600A HTS current leads. In one mode the system can be used with zero field without cost of liquid helium relying for cooling on a Sumitomo GM cryocooler with 1.5W at 4.2K: (no He) this can be used either as the sole characterisation method, or as a preliminary check before more expensive and extensive measurements are taken. The first measurements using MgB2 wire from 10 to 20K were made using a transient current step of ∼5s duration, as opposed to a DC measurement. This has the advantage of not requiring thermal equilibrium to be achieved at nominal current. The feasibility of this technique for determining critical transport properties is discussed.

Focus on cryogenics and vacuum

Focus on cryogenics and vacuum

Air Liquide space cryocooler systems

After successful developments these last 3 years, AL/DTA is now in position to propose two pulse tube cryocooler systems for space applications in the 40–80 K temperature range. The two pulse tube cryocoolers are yet qualified against stringent thermal and mechanical environmental constraints. AL/DTA also develops associated Cooler Drive Electronic at QM level implementing launch locking and vibrations cancellation. This paper presents these complete cryocooler systems available for space applications.

Focus on vacuum and cryogenics

Focus on vacuum and cryogenics

98/01560 Effective use of mobile air-conditioners in deep mines: Yakovenko, A. K. and Martynov, A. A. Ugol' Ukr., 1996, (10–11), 16–20. (in Russian)

Highly reliable, compact, and efficient cryocoolers with a cooling power of several watts to several hundred watts at liquid nitrogen temperatures around 77 K are indispensable for cooling superconducting devices and infrared detectors, especially in aerospace applications. This paper introduces three-stage traveling-wave thermoacoustically driven cryocooler systems operating around 300 Hz that meet the demand. In addition to the potential reliability due to the lack of moving components in a thermoacoustically driven cryocooler, this configuration has the potential for both compact size and high efficiency owing to the slim resonance tube and acoustic power recovery. Numerical simulations are performed to investigate two coupling modes: coupling the cooler at the branch of the engine (BR-coupling) or coupling the cooler parallel to the engine (PA-coupling). First, the two topologies are carefully designed to obtain high total exergy efficiency and the optimal dimensions are presented. Then, the axial distributions of the phase difference and the acoustic power are further provided to better illustrate the coupling characteristics. Furthermore, a theoretical analysis is performed on the influence of the two acoustic tubes in the PA-coupling mode and the result shows the importance of the tube dimensions. With a heating temperature of 850 K, total exergy efficiencies of 11.4% and 14.8% have been achieved in the BR-coupling and PA-coupling modes, respectively. The PA-coupling mode’s higher efficiency is due to recycling the acoustic power entering the pulse tube cryocooler, whereas BR-coupling fails to recycle any acoustic power. However, the energy feedback in PA-coupling may cause structural complexity. Generally speaking, both coupling mode systems show encouraging prospects for aerospace applications.

Small-scale liquefaction of hydrogen

Hydrogen may be stored compactly as a cryogenic liquid at low pressure and temperature, i.e. 20 K at atmospheric pressure. Gaseous hydrogen at normal temperature may be liquefied on a small scale using a cryogenic refrigerator (cryocooler). Stirling refrigerators are well suited to this duty. These machines operate on a closed thermodynamic regenerative cycle with compression and expansion of the working fluid (helium) at different temperature levels. Very low temperature Stirling refrigerators have several stages of expansion, typically two or three for a hydrogen liquefier. A concept for an electrically driven Stirling hydrogen liquefier of low capacity is described. Stirling machines can also be used as power systems converting heat to work. A second concept is described for a combustion heated Stirling — Stirling hydrogen liquefier. Conceptual design studies for both units have been carried out including computer simulation of the power system and cryocooler systems. These indicate the net energy flow and principal dimensional parameters permitting first order estimates of costs for prototype manufacture and the unit costs in series production.

Cryocoolers for the new high-temperature superconductors

Compact, reliable, low-cost cryocoolers operated simply by closing a switch are an essential requirement for the coming age of superconductivity and cold electronic systems. The advent of high-temperature superconductors has substantially eased the task of those seeking to fill the above need. This article reviews some recent developments in cryocooler systems and examines some prospects for the future.

Mounting a 10 K cooling device without rotating seals on a four-circle diffractometer

Instrumentation has been developed for collection of three-dimensional X-ray and neutron diffraction data at temperatures below the boiling point of liquid nitrogen. A closed-cycle two-stage refrigerator has been mounted on the ϕ shaft of a four-circle goniometer. The sample crystal is attached to the nominal 10 K station. The refrigerator mount functions as a goniometer head without arcs. The x−y−z centering device has a range of ± 5 mm for the z direction along the ϕ axis and ± 2 mm along x and y. Dovetails and eccentrics with narrow tolerances allow a precise firmly lockable centering of the crystal. The whole refrigerator unit undergoes all the normal ϕ, χ and ω movements during data collection without any rotating vacuum seals. These are usually integral vulnerable parts of existing liquid-helium-temperature cryocoolers. When refrigeration is not required, the cryo-unit can be dismounted in a few minutes and replaced by a device for mounting an ordinary goniometer head for room-temperature data collection. Thus, the system is simple, robust and easy to operate, both at room temperature and at cryogenic temperatures. Furthermore, the use of a closed-cycle refrigerator makes the system more economical than comparable cryocooler systems based on flow cryostats.

小型ヘリウム冷凍機

This paper reviews the recent progress of the small cryocoolers operating near 4K, for the application of small scale superconducting magnets or superconducting devices.The research and development scheme of cryocoolers can be classified into two categories. The first one is related to the investigation of reliability, compactness and cutting costs of the well known cryocooler systems. Stirling or G-M cycle cryocoolers with a J-T loop and small scale claude cycle also belong in this category. The second one is a fundamental approach to the novel refrigeration systems such as a magnetic refrigerator or regenerative cryocoolers which can be cooled down to liquid Helium temperature without J-T loop. A cascade J-T system using gas adsorption compressor is also included.