Stirling-type Pulse Tube Cryocooler Research Articles

Thermodynamic characteristics of a single-stage stirling-type pulse tube cryocooler capable of 1220 W at 77 K with two cold fingers driven by one linear compressor

This paper conducts the thermodynamic analysis and experimental verification of a single-stage Stirling-type pulse tube cryocooler (SPTC) with the configuration of two cold fingers driven by one linear compressor, achieving the kW-class cooling capacity at 77 K. The internal oscillating mass and flow, heat transfer, and phase variation characteristics are analyzed for the design with the aid of CFD. Meanwhile, the regenerator filled with mixed matrices for optimizing the uniformity of its internal temperature distribution is also theoretically and experimentally investigated. Thermodynamic features of gas parcels oscillating in different parts of the cold finger are studied to clarify the internal working mechanism from the perspectives of movement, p–v, and T–s characteristics. The developed SPTC typically provides a cooling power of 1220 W at 77 K with a relative Carnot efficiency of 16.7%. The experimental and simulation results are compared, and fairly good consistencies are observed.

Investigations on a 2.2 K five-stage Stirling-type pulse tube cryocooler. Part A: Theoretical analyses and modeling

This paper conducts systematic theoretical analyses and modeling of a five-stage Stirling-type pulse tube cryocooler (SPTC) which is expected to directly reach a temperature of around 2 K and also to simultaneously achieve the cooling capacities at five temperatures varying from 2.2 K to 80 K for multiple uses. At the fourth stage it uses an active phase compressor (APC) to obtain the optimal phase relationship at the low temperatures below 12 K. A further improved electrical circuit analogy (ECA) model with the APC is developed to investigate the phase characteristics, loss mechanisms, and cooling performance of the last two stages. The structural design of the five-stage SPTC is described, in which a waveform synthesis method based on the impedance and phase analysis is proposed to clarify the effects of APC parameters on the pressure and flow in the regenerators of the last two stages. The impedance and dimensional parameters of both stages are optimized according to the system exergetic efficiency. The simulation results indicate that, with He-3, the system exergetic efficiency of the last two stages is expected to reach 2.39 %. It also indicates a five-stage SPTC alone has potential of reaching 2.2 K with simultaneously having the cooling capacities at five temperatures.

Investigations on a 2.2 K five-stage stirling-type pulse tube cryocooler. Part B: Experimental verifications

In this part, a five-stage Stirling-type pulse tube cryocooler (SPTC) is worked out to verify the theoretical analyses conducted in Part A. The experimental setup is described in detail, and the operating frequency, charge pressure and input electric power of the last two stages are optimized with He-3. Relevant experiments are also conducted with He-4 for comparison. The experimental results show that a no-load temperature of 2.28 K is reached with He-3, and the cooling capacities of 2.5 W at 80 K, 0.15 W at 30 K, 0.05 W at 12 K, 16.9 mW at 6 K, and 12.2 mW at 3.5 K are simultaneously achieved, respectively, with a total system exergetic efficiency of 2.25 %. Satisfactory agreements are observed between theoretical and experimental studies.

Theoretical and experimental investigations on the piston offset characteristics in a four-stage DC linear compressor unit for a 1.8 K hybrid cryocooler

A four-stage DC linear compressor (DCLC) unit with high reliability, long life and lightweight is developed for a Joule-Thomson cooler (JTC), which is the final cooling stage of a 1.8 K hybrid cryocooler using a four-stage Stirling-type pulse tube cryocooler (SPTC) as the precooler. A dynamic model is built to analyze the physical mechanism of piston offset, in which the influence of the resistance on the mean piston position is emphasized. An approach to optimizing the piston offset is proposed by changing the resistance characteristics of both suction and discharge flows. Experimental results show that through the optimization the piston offset can decrease up to 65.4%, and the ultimate pressure ratio (UPR) increases from 4.1 to 4.9 while the motor efficiency slightly decreases by 2.7%. The similar variation tendencies of experimental and theoretical results are observed, and the experimental results generally meet the theoretical expectation. The measured suction pressure of the optimized four-stage DCLC unit is reduced to 1.5 kPa, which makes an important contribution to the hybrid cryocooler in achieving a 1.8 K cooling temperature with He-4 as the only working medium.

Study on the Coupling Characteristics of Sub-Kelvin Sorption Cooler and 4 K Stirling-type Pulse Tube Cryocooler with Small Cooling Capacity

Study on the Coupling Characteristics of Sub-Kelvin Sorption Cooler and 4 K Stirling-type Pulse Tube Cryocooler with Small Cooling Capacity

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.

A Long-Life, High-Capacity and High-Efficiency Cryogenic System Developed for High-Tc Superconducting Magnet Applications

Cryogenic system plays a vital role in the field of high-Tc superconducting (HTS) magnet applications. For a variety of HTS magnet applications in energy storage devices, current limiters, generators, and maglevs, the technology itself is relatively mature. However, the problems associated with the used cryocoolers have hampered the advancement of their practical applications. At present, China is developing a new generation of electrodynamic suspension prototype train with HTS magnets. Compared with the existing commercial electromagnetic suspension technology, it has better suspension stability, larger suspension gap, and lower energy consumption. To meet the aimed cooling requirement of the vehicle-mounted HTS magnet, a long-life, high-capacity and high-efficiency cryogenic system based on the Stirling-type pulse tube cryocooler (SPTC) is designed and developed in the authors’ laboratory. The SPTC driven by the linear compressor without any moving component in the cold head has the intrinsic merits of long life and high reliability. The cryogenic system can achieve a minimum no-load cooling temperature of 12 K. Multiple SPTCs will provide a cooling capacity of 100 W at 45 K with the relative Carnot efficiency of 10.8 % to cool the HTS coils inside the magnet. This paper will describe and analyze the overall design approach, integration with the HTS magnet and the arrangement in maglev of the developed cryogenic system, together with the performance characteristics of the SPTC during the laboratory test.

Theoretical Analyses and Design of a 4 K Gas-Coupled Multi-Bypass Stirling-Type Pulse Tube Cryocooler

Theoretical Analyses and Design of a 4 K Gas-Coupled Multi-Bypass Stirling-Type Pulse Tube Cryocooler

Design and optimization of the four-stage recuperative coiled tube-in-tube heat exchanger for a 1.8 K hybrid cryocooler

The recuperative coiled tube-in-tube heat exchanger (RCTTHE) is a key component of the hybrid cryocooler formed by a four-stage Stirling-type pulse tube cryocooler and a JT cooler, and its heat exchanger effectiveness and pressure drop of low-pressure side play an important role in enhancing the overall performance of the hybrid cryocooler. This paper develops a finite difference model to systematically investigate the four-stage RCTTHE. The flow and heat transfer characteristics in the temperature range of 4–300 K under different dimensional and operating parameters are investigated in detail. The heat exchanger effectiveness and pressure drop of the low-pressure side are optimized to meet the requirements of the 1.8 K hybrid cryocooler with He-4 as the only working medium. The experimental investigations of the hybrid cryocooler based on the optimized four-stage RCTTHE are conducted. Satisfactory agreements are observed between the theoretical and experimental data, and thus verify the proposed model. The experimental results show that the pressure drop of the low-pressure side of the RCTTHE reaches a considerably low value of 518 Pa and an effectiveness of higher than 97.1 % is achieved for the four-stage RCTTHE, both of which make a significant contribution to the hybrid cryocooler in achieving 1.8 K.

Numerical Investigations about Flow Resistance Values for Stirling Type Pulse Tube Cryocooler

Pulse tube cryocoolers are extensively used for space application because of simplicity and reliability in operation. Many researchers have attempted the numerical analysis of the oscillatory flow inside the cryocooler, however, the precise predictions of the exact behavior of the gas inside the cryocooler using CFD has not yet been reported. While performing the CFD analysis of cryocooler, the values of inertial and viscous resistance coefficients play vital role and highly contributes to the pressure drop taking place in porous media. The prime objective of present work is to analyze the effect of these resistance values on performance of cryocooler. A single stage Stirling type pulse tube cryocooler model from literature is employed to perform the CFD analysis and the results obtained from the analysis are validated to ensure that methodology used for analysis is correct. The resistance values mentioned in the literature are applicable for steady and unidirectional flows. The model is further modified for the values of resistances for oscillating flow at room temperature and oscillating flow at cryogenic temperature. It is observed that performance predictions for oscillating flow at cryogenic temperature resistance values yields substantially lower temperature than all other cases. As experimental validation of this model is still not reported in literature, the reliability of accurate resistance values is not confirmed. Hence, another model of single stage Stirling type pulse tube cryocooler from literature is numerically analyzed for various operating conditions and is compared with its experimental performance, and found to be in fair agreement.

The effect of the aftercooler on the regenerator temperature non-uniformity in a high-capacity pulse tube cryocooler

High-power Stirling-type pulse tube cryocoolers (SPTC) are expected to be an ideal candidate for cooling high temperature superconductivity (HTS) for its advantages of compact structure, low maintenance and long service life. However, the regenerator temperature non-uniformity is still a key problem needs to be solved since it significantly deteriorates the cooling performance. As a main heat exchanger, the insufficient and asymmetric heat exchange in the aftercooler may be one of the factors affecting the temperature inhomogeneity inside the regenerator. However, it has been seldom investigated. In this study, the relationship between the performance of the aftercooler and the temperature non-uniformity of the regenerator was investigated based on a high-power SPTC working at ∼ 80 K. With the help of Sage simulation, it is found that the inlet temperature of the regenerator has a large effect on its inside temperature distribution. Even an inapparent temperature inhomogeneity at the inlet of the regenerator will induce a large temperature difference in the middle of the regenerator, due to an obvious DC flow generated in the regenerator. By changing the water inlet and outlet directions of the aftercooler, the temperature non-uniformity of the regenerator will consequently change, which means the uneven heat transfer of aftercooler can be one of the main inducements to the temperature non-uniformity inside the regenerator. Further, methods of using copper wire mesh filling at the hot end of the regenerator, and optimizing heat exchange tubes inside the aftercooler were studied to reduce the temperature non-uniformity.

Development of a 20K two-stage Stirling type pulse tube cryocooler with pre-cooling inside second-stage pulse tube

Cryocoolers working in the liquid hydrogen temperature are important for applications such as cryo-pump, superconductor cooling and cryogenic electronics. This paper analyzes and compares the 20K gas-coupled two-stage Stirling type pulse tube cryocooler with and without pre-cooling. The pre-cooling uses some of the cooling power generated by the first stage cold head to pre-cool the middle of the second stage pulse tube. Given the same input acoustic power, the simulation results show that the cooling capacity of the second stage increase from 0.64 W to 2 W@20 K while the first stage available cooling capacity decrease from 5.84 W to 3 W@77 K when the pre-cooling is used. Meanwhile, the cryocooler relative Carnot Efficiency in terms of acoustic power increases from 10.3% to 14.6%.

Numerical analysis and experimental research of a 2W/35 K Stirling-type pulse tube cryocooler

Cooling to the temperature of liquid nitrogen to liquid hydrogen is a necessary working prerequisite for some infrared detectors. The development of compact and efficient miniature cryocoolers is of great significance for the space application of the detectors. The pulse tube cryocooler driven by a dual-opposed linear compressor is prospective in space applications due to the advantages of no low-temperature moving parts, compact structure, and high reliability. In this paper, a 2W/35K Stirling-type pulse tube cryocooler with a single-stage structure has been designed and tested. The influences of structural parameters of the phase shifters such as inertance tube, as well as the operating parameters such as operating frequency and charging pressure, on the cooling performance were investigated through numerical calculations and experiments.

Application of Stirling pulse tube cryocoolers in high temperature superconducting filters subsystems

The application of high temperature superconducting(HTS)filter has penetrated into various fields. In recent decades, GM-type pulse tube cryocooler and Stirling-type pulse tube cryocooler (SPTC) are two common cryocoolers. Due to the advantages of PTCs, such as no moving parts at the cold end, simple structure, small mechanical vibration and longer lifetime, pulse tube cryocoolers is gradually replacing oil-lubricated Stirling-coolers and G-M cryocoolers to cool down HTS magnets. In this paper, the development of PTC in HTS magnet cooling in the past 20 years is summarized firstly. Secondly, the development of HTS cooling system in our lab are reported. At last, the further development direction of HTS’s cooling system is discussed.

An 880 mW@15 K thermal coupled pulse tube cryocooler with active phase shifter

A two-stage Stirling-type pulse tube cryocooler (SPTC) operating in 15 K is developed in our lab for cooling infrared detectors and precooling helium JT cryocooler. For easy adjustment, the driven compressor of the SPTC is designed as two independent linear compressors. The second stage cold finger uses an active warm displacer (AWD) as phase shifter to maximize the cooling performance. The variation of pre-cooling temperature and swept volume of the AWD will influence the cooling capacity of the SPTC. The cooling performance are experimentally tested and analyzed. With the pre-cooling temperature of 80 K, the second stage cold finger can obtain 470 mW at cooling temperature of 15 K with a total electric input power of 363 W. It can also obtain 880 mW at cooling temperature of 15 K with full input power of 527 W. A no-load temperature of 9.9 K can be obtained with an electric power of 180 W and 170 W for first and second stage. The experimental results also show that there exists an optimal pre-cooling temperature and swept volume of the AWD to achieve the maximum cooling capacity for 20 K applications.

Investigations on a 1 K hybrid cryocooler composed of a four-stage Stirling-type pulse tube cryocooler and a Joule-Thomson cooler. Part B: Experimental verifications

In this part, a hybrid cryocooler composed of a four-stage Stirling-type pulse tube cryocooler (SPTC) and a Joule-Thomson cryocooler (JTC) is worked out to verify the theoretical analyses carried out in Part A. The heat loss on each precooling stage is calculated to evaluate the feasibility of thermal coupling between the SPTC and the JTC. The JT compressors are tested and then the compression capacity is studied. A bypass-accelerated-cooling approach is adopted to speed up the cool-down process. The experimental results show that with He-4 in the SPTC and He-3 in the JTC, a no-load temperature of 1.36 K is reached when the three precooling temperatures are kept at 71.2 K, 40.5 K and 8.12 K, respectively. The cooling capacity of 13.9 mW at 1.8 K is measured with the JT loop high pressure and the last stage precooling temperature being at 0.5 MPa and 8.1 K, respectively. Satisfactory agreements are observed between theoretical and experimental studies.

Study on the impedance characteristics of a high-capacity pulse tube cryocooler

Stirling-type pulse tube cryocoolers are used in many applications such as military facilities, aerospace devices and superconductive systems. A major problem in improving its energy conversion efficiency is how to achieve a better impedance matching. In this study, a pulse tube cryocooler is investigated based on the impedance analyses. A group of impedance maps is proposed to analyze the energy conversion performance of the compressor. The velocity map, the efficiency map, the acoustic power map and the phase angle map are provided under the total equivalent impedance. These maps offer a visualized guidance of the maximum performance a compressor could reach and in which direction to optimize. Experiments on a high capacity pulse tube cryocooler are conducted to verify the theoretical analyses. The results show that it is of great help in using the proposed maps to analyze and improve the energy conversion performance of the cryocooler. A cooling capacity of 300W@80K is finally achieved. The study clearly reveals the influence of the impedance on the energy conversion efficiency and it is quite useful in improving the performance of the pulse tube cryocooler.

A two-stage thermally-coupled pulse tube cryocooler working at 35 K for space application

The attainment and maintenance of a low temperature environment is essential for aerospace cryogenic detectors to achieve their required performance. Developing cryocoolers with features of high efficiency, compact structure, and long lifetime is the main challenge for cryogenic detector cooling. In this paper, a high efficiency thermally-coupled two-stage Stirling type pulse tube cryocooler working at 35 K for HgCdTe long wave infrared detector cooling is designed and tested. The thermally-coupled type avoids gas distribution at cold side which minimizes the inter-stage influence. The whole cryocooler is driven by one linear compressor which enables compact structure. The influence of operation frequency and mean pressure is studied by numerical calculation and experiments to determine the optimum operation condition. Acoustic impedance characteristics of both stages and the whole cold finger are also analyzed by comparing performance of cryocooler with different frequency, mean pressure and structure dimensions. The distributions of acoustic power and phase angle are presented to study the relation between impedance characteristic and the cooling performance. Impedance match between compressor and cold finger is also discussed by analyzing the efficiency of the linear compressor and the performance of cryocooler with different pulse tubes. Under optimum impedance match and operation condition of a working frequency of 39.2 Hz and a mean pressure of 2.45 MPa, the cryocooler provides a cooling power of 1 W at 35.1 K with an input electrical power of 150 W, which indicates a relative Carnot efficiency of 5%. This is a rather high efficiency for developed Stirling type multi-stage pulse tube cryocooler working at 35 K with only inertance tubes as phase shifter. The development of this cryocooler lays a solid base for the further optimization to realize a competitive candidate for aerospace cooling requirements.

Cooling performance improvement of a two-stage pulse tube cryocooler with Er-plated screen as regenerator material

• A new regenerator material called Er-plated screen was proposed. • Comparision between Er-plated screen and stainless steel screen were involved. • Pre-cooling temperature, no-load temperature and cooling capacity were experimentally studied. • A lowest temperature of 15.29K with 235W input can be achieved while using Er-plated screen. As one of the key component in the pulse tube cryocooler (PTC), a regenerator needs to reduce losses for performance improvement. Thus, a good regenerator material should have large volumetric specific heat capacity and heat exchange area with small flow resistance. At present, high-mesh stainless steel screen and magnetic materials such as Er 3 Ni are commonly used as regenerator materials in the low temperature range. However, with the cooling temperature decreasing to lower than about 20K, the volumetric specific heat capacity of stainless steel decreases significantly, increasing the irreversible heat transfer losses of the regenerator. This paper proposes a new regenerator material which coats a magnetic material (Er) with high volumetric heat capacity at low temperature on the surface of stainless steel screen. The two-stage Stirling type pulse tube cryocooler (SPTC) with Er-plated screen filled in the cold end of the second-stage regenerator is investigated. The cooling performance of the SPTC filling with stainless steel screen and Er-plated screen is compared numerically and experimentally. A no-load temperature of 14.95 K can be obtained with an electric power of W when Er-plated screen is used. The relative Carnot efficiency (rCOP) of the cryocooler with Er-plated screen at 20K is 3.32 %, which is higher than with stainless steel screen. Another interesting phenomenon found in the research is that the rCOP of the SPTC with Er-plated screen reverses to be lower than with stainless steel screen when the temperature exceeds 30 K.

Investigation on the cool-down speed of Stirling type pulse tube cryocooler with inertance tube

In some applications, the cool-down speed obtainable with a cryocooler is important besides the high efficiency at the working temperature. Because of the difference in configurations, the design and the control strategies for various cryocoolers may be different. This work numerically studies the cool-down characteristics of a Stirling-type pulse tube cryocooler (PTC), which uses inertance tube and reservoir as the phase shifter and work at the temperature region of liquid nitrogen. The cryocooler is predicted to provide a nominal cooling power of 18.7 W at 77 K. Three cool-down strategies, namely, cool-down with constant voltage at 66 Hz, cool-down with constant piston displacement by tuning the voltage at 66 Hz, and cool-down with constant piston displacement by tuning voltage and frequency simultaneously during the cool-down process, are investigated. The corresponding calculated cool-down time from the ambient temperature to 77 K of these strategies are 340, 275, and 260 s, respectively. Using the third strategy, the cool-down time can be reduced by 23%.