Thermal design and tests of a subcooled superfluid helium refrigerator

Design methods for a subcooled superfluid helium refrigerator with high efficiency are studied. The design details are presented for a He I heat exchanger (perforated disk stack type), a He II heat exchanger (low fin tube type), an expansion valve, a safety valve, an initial filling valve and a pumping system. Heat loss, cooling capacity and cooldown time are also calculated. The test results for the trial-manufactured refrigeration system are presented in comparison with the designed values.     

过冷态超流氦恒温器的热力学分析

对过冷态超流氦恒温器的热力学过程进行分析,考察了不同的设计温度和J-T换热器热效率下恒温器的制冷性能,得到了理论制冷量的变化曲线.结果表明,理论制冷量与设计温度和J-T换热器的热效率密切相关.计算发现,160 L液氦在2W制冷量下从4.2K降至1.8K大约需要24 h.     

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.     

Efficiency improvements of a double acting reciprocating magnetic refrigerator

Continuing our work with gadolinium gallium garnet (GGG) after the previously obtained results of 1.2 W at 1.8 K and 45% of the Carnot cycle, we now have accomplished new steps using half of the volume of GGG, a more suitable field profile, improved heat transfer and we have obtained 0.9 W at 2.1 K with efficiency of 64%. We have also computed the competitive threshold values for a magnetic stage refrigerator.     

空间低温技术的新进展

对空间低温制冷技术的最新进展作了较为全面的综述 ,尤其是研讨了空间超流氦冷却的技术难点及解决方法 ,并对于各类较新的低温制冷机作了系统分析     

空间低温工程技术

综述国际上特别是美国的空间低温工程技术的最新技术进展，重点分析了超流氦，斯特林制冷机及脉管制冷机在空间中的应用现状及前景。     

Criterion for quantum turbulence onset after rectangular heat pulse in superfluid helium

On the basis of transient heat transfer measurements of the film boiling onset time in a He II bath, a criterion correlated to the bath temperature and pressure for quantum turbulence onset after a rectangular heat pulse in superfluid helium is shown. Using the criterion parameter α it is possible to determine the time τ needed to initiate quantum turbulence in the He II bath after a rectangular heat pulse. It is found that the criterion value in a He II bath is much smaller than that for He II confined in small channels. A strong pressure effect is also exhibited.     

ADS 2K低温系统超流氦换热特性研究

以ADS 2K低温系统为研究平台,分析了恒温器结构参数中上升管与峰值热量的关系,测量了超导腔液氦池中不同工作温度下的超流氦峰值热量,最后给出了恒温器上升管的设计方法,并验证了ADS低温恒温器上升管设计的合理性。     

A cryopump-operated rotating nuclear demagnetization cryostat for research on superfluid3He

We have constructed a rotating submillikelvin cryostat in which the dilution refrigerator can be operated in a continuous mode using two cryopumps. The⁴He pot is also equipped with similar pumps. The dilution unit is employed to precool a nuclear stage with 32 mol of copper in an 8-T field. In the design, special care was taken to make fast rotations possible. The apparatus is currently used to measure collective mode phenomena in superfluid³He-B.     

AMS-02超导磁体中超流氦加注过程研究

论述了AMS-02超导磁体中超流氦的加注过程,进行了各个环节压降和温降的计算分析,并用图表表示了在不同质量流量加注超流氦工况下管路系统中氦工质的速度、压力、温度和含气量的变化情况.计算结果表明,氦工质从液氦主杜瓦加注到磁体杜瓦的过程中,其压力和温度不断降低,而含气量不断增加.同时也表明在节流阀VVP9中实现了常流氦向超流氦的转变和质量流量的控制.     

A microprocessor controller for a nuclear demagnetization refrigerator

A microprocessor-based system controlling a nuclear demagnetization refrigerator is described. Magnetization, precooling, and demagnetization are software-controlled as are heat and persistent current switches. Although the system is fully automatic, the user maintains the ability to alter the process at any time. Some other applications of the microcomputer to low-temperature research are also described.     

超流氦气液相分离器实验装置研制

外太空科学探测系统需要4 K以下制冷系统的支持,超流氦(HeII)是在此温度区间的一种理想冷却剂,超流氦空间制冷系统的关键部件超流氦相分离器是利用超流氦的超流特性和热机械效应实现气液相分离的.根据超流氦相分离器研究的需要,研制了一套超流氦多孔塞气液相分离器的实验装置及其测量系统.利用该实验装置成功地完成了多批多孔塞样品的特性实验,获得了丰富的实验数据.介绍了实验装置方案选择、结构组成、实验方法及调试结果.     

Peak and recovery heat flux densities in bath of subcooled superfluid helium

This paper describes the measurement of the peak and recovery heat flux densities (q_P, q_R) in a bath of subcooled superfluid helium. A RhFe wire (d = 51 μm, L = 34.8 mm) was horizontally immersed in a He Ilp cryostat, which served as the sample, the heater and the temperature sensor. For the steady state measurement a programmed voltage method with a triangular waveform of 20 s was applied. The measured q_P and q_R values cover the temperature range 1.81–2.1K at a pressure of 0.1 MPa. On the basis of the heat and mass transfer through phase interfaces, theoretical relations (without geometrical parameters) of q_P and q_R are derived, which have very wide application range due to the relative critical heat flux density method used for the calculations. The theoretical results fit the experimental results well for both q_P and q_R.     

超流氦低温系统发展及涡轮冷压缩机的应用

2 K下大型氦低温系统已采用离心式涡轮冷压缩机在低温低压下对饱和液氦槽减压操作,以获得超流氦或过冷氦.介绍了2K温度级超流氦制冷机发展情况和涡轮冷压缩机在氦制冷系统中的应用,以及中国科学院等离子体物理研究所EAST超导托卡马克氦低温制冷机中过冷氦的制取过程.     

A low temperature 35 T and 20 kJ cryomagnetic set for far infrared transmission experiments

An experimental set up associating a 20 kJ, 35 T pulsed electromagnet with a helium cryostat and laser beam excitation of a semiconducting sample is described. Besides the known advantages of low cost of high field production by means of a pulsed magnet, simplicity and compactness, this system is shown to yield performances similar to that of much more elaborated sets, and has additional operating conveniences, such as mounting or changing the sample while the experiment is under way. Its efficiency and reliability are exemplified by the quality of a typical recording of cyclotron resonance absorption in InSb.     

The prediction of steady state heat flux and related temperature profiles in pressurized superfluid helium II

To design superconducting magnets cooled by pressurized superfluid helium II, it is necessary to know the heat transfer characteristics of steady state heat flux in the cryogen. This study shows the calculation used to obtain these characteristics using the universal Gorter-Mellink equation proposed by Soloski et al. The calculated results agree fairly well with the data obtained in this study.     

Numerical study of flow and heat transfer of superfluid helium in capillary channels

A modified two-fluid model is adopted to study flow and heat transfer of superfluid helium in a microchannel with a diameter as small as that of a superleak in a fountain effect pump. Variable properties of superfluid helium and energy dissipations due to the two-fluid mutual friction and the friction at the channel wall are fully taken into consideration. It is found that the normal fluid component flow is not trivial even in a channel with diameter of a micrometre, and that there exists an optimum diameter for the maximum mass flow rate. The flow of superfluid helium through a channel with different temperatures at the ends differs considerably from that of a Newtonian fluid. The strong dependence of the thermodynamic properties on temperature and pressure, as well as the internal-convection mechanism are found to be the causes of the unique flows.     

Method for measuring a vacuum in an environment at liquid helium temperatures

The experimental results of a new method to measure a vacuum in an environment at liquid helium temperatures are presented. The method uses a thin superconducting wire suspended in the vacuum vessel, the wire is heated by a current pulse > l_c. The cool down time, which depends on the heat transfer into the rest gas and on the axial heat conductance of the wire, is a measure of the vacuum and it is detected by the recovery of the wire to superconductivity. The results exhibit good resolution in the range of pressures from 5 × 10^?3 to 5 Pa (5 × 10^?5 to 5 × 10^?2 mbar).     

Special arrangement for specimen cooling to 50 mK using liquid He4 for heat exchange

We propose a new arrangement for specimen cooling to 50 mK using liquid He⁴ for heat exchange. This arrangement avoids some of the disadvantages of the standard system.     

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.