Stirling-type pulse tube refrigerator with slit-type heat exchangers for HTS superconducting motor

A cryogenic refrigeration system is one of the indispensable components for cooling superconducting motor or generator. Among various configurations of cryogenic refrigeration system, the on-board refrigeration system is considered to be attractive for compactness and small heat leak. In order to turn this concept into reality, we focus on two essential points; development of the specific structure for on-board refrigeration and optimal design of the refrigerator. Since the on-board refrigeration system should not create unbalanced vibration, the inline Stirling-type pulse tube refrigerator is considered as a good candidate and more concrete and efficient structure is developed under the design constraints. The dynamic absorber is used to maintain the dynamic stability of the single acting linear compressor. To increase thermal Carnot efficiency with the on-board Stirling-type pulse tube refrigerator, slit-type heat exchangers are implemented and flow straighteners are carefully designed by the three-dimensional CFD simulation. The overall configuration of the Stirling-type pulse tube refrigerator is designed and fabricated by the optimal process. The present on-board refrigerator has the cooling capacity of 7 W at 59.5 K with the Carnot efficiency of 10.9%. According to these experimental results, the pulse tube refrigerator as the on-board refrigeration system possesses a sufficient thermal efficiency despite the restricted design configuration. The on-board refrigeration is considered as a useful method for cooling HTS superconducting motor.     

Integration of superconducting magnets with cryogen-free dilution refrigerator systems

There has been much recent research interest into “cryogen-free” dilution refrigerators. Cryogen-free systems have some advantages from a safety and convenience point of view as liquid cryogens are unnecessary. However, this also makes integrating the low-temperature system with a high magnetic field environment much more challenging. Here we shall describe recent successes of integrating superconducting magnets and dilution refrigerators into one system requiring a single pulse tube cooler. The resulting environment provides experimental temperatures between 7 mK and 30 K and magnetic fields up to 12 T. We shall describe the effects of AC loss heating in such systems on the pulse tube refrigerator when the field is ramped and also the effects of eddy current heating on the mixing chamber in sweeping fields.     

A 128 kG 65.5 mm bore superconducting solenoid

The design, construction, and testing of commercial small high field superconducting magnets is described. A niobium—tin layer-wound solenoid with a 65.5 mm bore is used to give an example of practical applications of these techniques.     

Operation of superconducting magnet with dilution refrigerator insert in zero boil-off regime

The combination of high magnetic field and ultra-low temperatures has proved to be indispensable for a broad range of condensed matter physics experiments. However problems with the global helium supply have raised significant concern about affordability of conventional cryogenic equipment. The latest developments in cryo-cooler technology offer a new generation of cryogenic systems in which the cryogen consumption can be significantly reduced and in some cases completely eliminated. We have demonstrated a new high magnetic field - ultra-low temperature neutron scattering sample environment system based on re-condensing technology. In our tests we have shown that the 9 T superconducting magnet, built for the ISIS facility, can be run with a dilution refrigerator insert in continuous zero boil-off regime without any additional cooling.     

Thermoeconomic optimization of an irreversible Stirling cryogenic refrigerator cycle

This communication presents the thermoeconomic optimization of an irreversible Stirling cryogenic refrigerator cycle. The external irreversibility is due to finite temperature difference between the working fluid and the external reservoirs while the internal irreversibility is due to the regenerative heat loss. The thermoeconomic function is defined as the cooling load divided by the total cost of the system plus the running cost. The thermoeconomic function is optimized with respect to the working fluid temperatures and the values for various parameters at the optimal operating condition are calculated. The effects of different operating parameters on the performance of the cycle have been studied. It is found that the effect of regenerative effectiveness is more than those of the other parameters on all the performance parameters of the cycle, for the same set of operating condition.     

GM制冷机升降温特性与控制研究

设计了一套以GM制冷机作为冷源的实验系统,实现常温至液氦温区的升降温过程。分别从GM制冷机制冷量、自然升降温曲线、加热量、控制策略等方面对以GM制冷机为冷源的升降温系统进行可行性分析。通过搭建试验系统,最终在样品架上得到一个理想的线性升降温曲线。     

A closed cycle He-He dilution refrigerator insensitive to gravity

The cooling power and the lifetime of an open cycle dilution refrigerator as developed for the Planck mission (100 nW at 100 mK during 30 months) are limited by the quantity of the helium isotopes carried on the satellite at launch, because the helium mixture obtained after the dilution process is rejected into space. Future space missions require to increase the cooling power and lifetime significantly (1 μW at 50 mK during 5 years).Therefore we are extending the open cycle dilution refrigerator with a helium isotope separator operating at 1 K to close the cycle. A first prototype to demonstrate the principle of the closed cycle dilution refrigerator has been tested and a cooling power of 1 μW at temperatures below 60 mK has been obtained. We present the apparatus and the experimental results and give some elements for its integration in a complete cooling chain. The advantages (continuous operation, absence of magnetic field, less weight) of a closed cycle dilution refrigerator with respect to an adiabatic demagnetization refrigerator are also discussed.     

Design of non-flammable mixed refrigerant Joule-Thomson refrigerator for precooling stage of high temperature superconducting power cable

A cryogenic Joule-Thomson (JT) refrigerator has many advantages for large industrial applications, including easy cooling power adjustability and high reliability because there are no moving parts at low temperature. In this paper, a single stage and a cascade type of non-flammable (NF) mixed refrigerant (MR) JT refrigerators have been proposed for the precooling process of a neon/nitrogen mixed refrigerant JT refrigerator. The neon/nitrogen MR JT refrigerator is used to maintain a subcooled state of liquid nitrogen coolant for an HTS (high temperature superconductor) cable.Both selected MRs for the 1st stage (low temperature cycle) of the cascade MR JT refrigerator and the single MR JT refrigerator are composed of Nitrogen (N₂), Argon (Ar), Tetrafluoromethane (CF₄, R14) and Octafluoropropane (C₃F₈, R218). R410A is selected as the refrigerant for the 2nd stage (high temperature cycle) of the cascade MR JT refrigerator, of which the cooling temperature is approximately 240 K. A commercial software with Peng-Robinson equation of state (EOS) is utilized to design the non-flammable MR JT refrigerator. The optimal design is discussed with consideration for various parameters such as the temperature staging, the operating pressure of the compressor and the mass flow rate of the working fluid. The maximum coefficient of performance (COP) and Carnot efficiency of the cascade MR JT refrigerator are obtained as 0.216 and 40%, respectively at 105 K. Exergy analysis is also carried out in this paper to reveal the irreversibility of the refrigeration cycle.     

Thermodynamics of a self-pumping cooling cycle for superconducting generator applications

The helium supply and outlet lines of a rotating superconducting magnet can be arranged so that the self-pumping mechanism due to the centrifugal forces effects a pressure and temperature decrease in the rotor. Several parameters such as speed of rotation, diameter of the rotor, outlet pressure, and quality of the helium supplied to the rotor have been modified in a computer study. The calculation shows that the self-pumping mechanism is so effective that even the temperature at the periphery of a large scale rotor decreases with increasing speed of rotation. This refrigeration cycle appears to have a strong self-regulating characteristic.     

Optimal gas discharge through cryogenic flow inlets in refrigerator cooling of superconducting magnetic systems

A relationship connecting the discharge of the gas-cooling cryogenic flow inlets to the discharge of the gas returning in the reverse flow is obtained, for which the cold-productivity of the refrigerator, which is required, is a minimum.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 35, No. 2, pp. 266–271, August, 1978.     

Performance analysis of air cycle refrigerator integrated desiccant system for cooling and dehumidifying warehouse

In this paper, the performance of air cycle refrigerator integrated desiccant system used to cool and dehumidify warehouse is analyzed theoretically. Simulation analysis is carried out to calculate the system coefficient of performance, cooling effects and the humidity change under different values of pressure ratio, storage zone temperature inside dock and outdoor air conditions. Also, the effect of the air cycle and the rotor parameters on the system performance is evaluated. From the simulation result it is found that, the desiccant system has the ability to supply air to the dock area at very low humidity. The system coefficient of performance increases due to the exhaust heat recovery on the desiccant system, and this enhancement can be more than 100%. The coefficient of performance of the proposed system is greater than that of a conventional system under the same operating conditions.     

Compact dilution refrigerator with a cryogenic circulation cycle of He3

A He³-He⁴ dilution refrigerator has been constructed which circulates He³ by using two alternately operating adsorption pumps which are in the same cryostat as the dilution refrigerator. The scheme described here organised the low temperature circulation cycle such that the construction and cryostat communications were essentially simplified, the dimensions of the arrangement were decreased which resulted in a circulation velocity of 10^?4 mole s^?1, which was sufficient to obtain a temperature in the order of 10 mK.     

Development of a thermodynamic model for a cold cycle 3He-4He dilution refrigerator

A thermodynamic model of a ³He-⁴He cold cycle dilution refrigerator with no actively-driven mechanical components is developed and investigated. The refrigerator employs a reversible superfluid magnetic pump, passive check valves, a phase separation chamber, and a series of recuperative heat exchangers to continuously circulate ³He-⁴He and maintain a ³He concentration gradient across the mixing chamber. The model predicts cooling power and mixing chamber temperature for a range of design and operating parameters, allowing an evaluation of feasibility for potential ³He-⁴He cold cycle dilution refrigerator prototype designs. Model simulations for a prototype refrigerator design are presented.     

Improvements of a room-temperature magnetic refrigerator combined with Stirling cycle refrigeration effect

A high pressure hybrid refrigerator that combines the active magnetic refrigeration effect with the Stirling cycle refrigeration effect at room temperature is studied here. In the apparatus, a helium-gas-filled alfa-type Stirling refrigerator uses Gd sheets as the regenerator and the regenerator is put in a magnetic field varying from 0 to 1.4 T, which is provided by a Halbach-type rotary permanent magnet assembly. With an operating pressure of 5.5 MPa and a frequency of 2.5 Hz, a no-load temperature of 273.8 K was reached in 9 minutes, which is lower than that of 277.6 K for pure Stirling cycle. For the hybrid operation, cooling powers of 40.3 W and 56.4 W were achieved over temperature spans of 15 K and 12 K, respectively. For the latter case, the cooling power improves by 28.5% if compared with that exploiting only the Stirling cycle refrigeration effect.     

90K低温下带预冷的林德制冷机的系统设计

为了获得90K的低温,提出1套带预冷循环的林德制冷系统,并分别对该系统的预冷循环和制冷循环进行了设计.预冷系统和制冷循环的制冷剂分别为R404A 和 R740.无热负荷时,设定低温箱的温度90 K,制冷量为140 W.该系统整体结构简单,获取温度低,在低温领域有较广泛的应用.