液氦输送技术

正确掌握液氦输送方法，对减少液氦预冷量，充分利用氦气冷量和提高液氦输送效率有着十分重要的经济意义，对液氦输送管的结构特点和使用要求及液氦预冷，液氦的输送方法和几种特殊容器的输送方法做了介绍。     

7.7 T超导磁体冷却液体理论与实际消耗量对比分析

以7.7 T超导磁体为载体,分析了其在采取液氮预冷、液氦浸泡的冷却方式时,冷却液体理论消耗量与实际消耗量的差别。结果表明预冷过程中液氮和液氦的实际消耗比理论计算值分别多140 L、48 L,主要与输液管道的保温效果和密封性、冷却液体焓变的利用率和满足实验的特别要求等因素有关。     

超导HWR腔垂直测试低温系统试验研究

中国科学院先导科技专项ADS(Accelerator Driven Suberitical,ADS)嬗变系统中超导HWR(half-wave resonator,HWR)腔垂直测试需低温系统维持4.2 K(液氦)的低温环境,低温系统降温过程包括氮气置换、液氮预冷、氦气置换和液氦冷却。通过实验建立了低温系统降温4个阶段不同测点温度随时间的变化规律,在此基础上,计算了液氦的消耗速率和杜瓦的静态热负荷,分析了低温系统在稳定工作状态时最佳的液氦补液时间间隔。结果表明:该低温系统满足超导HWR腔垂直测试需求,消耗液氮约175 kg、液氦约2 048 L,低温系统稳定工作时液氦体积消耗速率为32 L/h,杜瓦静态热负荷为21.36 W,液氦合理补液时间间隔为4 h,为后续超导HWR腔垂直测试提供了保障。     

600W／4．5K氦制冷－液化机初调

６００Ｗ／４．５Ｋ氦制冷－液化机是合肥超导托卡马克装置ＨＴ－７的低温供给系统核心设备。它具有液氮预冷，４台活塞式膨胀机，７级换热器，２个喷射器，４．５Ｋ温液氦槽和３．６Ｋ温过冷槽。１９９３年６月此机以液化模式运行，初调成功。最高液氦产量达１６０Ｌ／ｈ．     

低温管路系统预冷过程仿真研究

低温液体在通过管路系统传输前,需对管路系统进行充分预冷,以避免低温液体在输运过程中出现气液两相,造成潜在的危害。基于多学科仿真平台AMESim中的Steiner流动沸腾换热模型,采用液氮作为预冷工质分析管路系统的预冷过程,重点研究进口压力、脉冲流频率及脉冲比率对管路系统预冷效果的影响。分析表明,在计算范围内,随着进口压力的增大,管路的预冷效率逐渐降低。因此,实际预冷过程中在满足流体输送要求时可以适当降低进口压力来提高预冷效率;脉冲流的预冷效率随脉冲频率的增大,先增大后趋于稳定,随脉冲比率的增大而减小。研究结果对于提高预冷效率、降低资源消耗、确保预冷过程安全进行,具有一定的指导意义。     

苏联氦液化及制冷装置介绍

<正>苏联氦液化及制冷装置研究与生产,由氦机械科研生产联合体(НПО《Гелиймаш》)承担。1．低温氮装置КГУ-600/15-150/4.5-40该装置用于生产液氦或4.5K、15K温度水平的冷量。装置为带活塞式膨胀机的中压制冷循环,并有液氮预冷。技术参数如下:     

两级独立预冷的液氦温区小型JT制冷系统热力学分析及初步性能测试

空间液氦温区机械制冷技术是深空探测、量子导航等空间应用的关键技术之一。针对两级独立预冷的JT(Joule-Thomson)制冷循环系统,从热力学的角度探讨两级预冷所需的制冷量及JT侧压缩机所需的功耗。分析在不同的第二级预冷温度(18～22 K)下,高压压力对JT侧制冷机所需一二级预冷量及在液氦温区能够提供的最大制冷量的影响。搭建实验台进行性能测试,初步实验结果表明,该低温制冷系统在不同工况下可以在4.70 K提供约24 mW或者在4.18 K提供约12 mW的制冷量。     

液氦输送方法的改进

<正>在液氦使用中,通常的输送方法输液效率较低。每次输液都将损失30~40%液氦。提高输液效率关键在于回收液氦蒸发后冷气的冷量。国家低温中心采用液氦机外部节流的方法解决这部分冷量的回收问题。节流后的两相氦流体经过外节流输液管流入贮槽,未液化和汽化的冷氦气经     

液氦的输送

广义的液氦输送,不仪指两地间的输送,而且从容器到容器的转送及用管道进行的输送亦在此列。但本文就用船舶或槽车进行长距离输送液氦的历史,容器的结构,操作方法及输送的若干注意事项作一简述。     

高温超导材料的商业用途和开发现状

1987年2月,美国休斯敦大学制得临界温度超过77K 的稀土铜氧化物超导材料。新超导材料可用比液氦便宜得多的液氮作冷却剂。与在液氦温度冷却现有金属超导体消耗     

液氮冻结装置中液氮耗量与冷冻能力的分析

建立了焓法数学模型，利用数值诸方法计算了模拟对象黄瓜片冻结前后的能量变化量和冻结时间，分析了三种不同装置五种冻结条件下的液氮冷量利用量、液氮耗量、冷冻能力以及冻前预冷的影响作用，提出了更合理的装置使用方案和经济性措施。     

Design and experimental investigation of a cryogenic system for environmental test applications

This paper is concerned with the design, development and performance testing of a cryogenic system for use in high cooling power instruments for ground-based environmental testing. The system provides a powerful tool for a combined environmental test that consists of high pressure and cryogenic temperatures. Typical cryogenic conditions are liquid hydrogen (LH2) and liquid oxygen (LO2), which are used in many fields. The cooling energy of liquid nitrogen (LN2) and liquid helium (LHe) is transferred to the specimen by a closed loop of helium cycle. In order to minimize the consumption of the LHe, the optimal design of heat recovery exchangers has been used in the system. The behavior of the system is discussed based on experimental data of temperature and pressure. The results show that the temperature range from room temperature to LN2 temperature can be achieved by using LN2, the pressurization process is stable and the high test pressure is maintained. Lower temperatures, below 77 K, can also be obtained with LHe cooling, the typical cooling time is 40 min from 90 K to 22 K. Stable temperatures of 22 K at the inlet of the specimen have been observed, and the system in this work can deliver to the load a cooling power of several hundred watts at a pressure of 0.58 MPa.     

NBI低温冷凝泵液氦杜瓦的热力分析与工程设计

降低中性束注入器低温冷凝泵的LHe消耗率,是进行低温冷凝泵设计时应考虑的核心问题之一。通过对NBI低温冷凝泵的LHe杜瓦进行热力分析,确定了影响杜瓦内LHe蒸发率的关键参数。探讨了降低LHe蒸发率的措施,依此确定了在工程设计中为达到减小LHe蒸发率、提高泵运行经济性可采用的结构形式。     

Compact,ultra-low vibration,closed-cycle helium recycler for uninterrupted operation of MEG with SQUID magnetometers

A closed-cycle helium recycler was developed for continuous uninterrupted operation for magnetometer-based whole-head magnetoencephalography (MEG) systems. The recycler consists of a two stage 4 K pulse-tube cryocooler and is mounted on the roof of a magnetically shielded room (MSR). A flexible liquid helium (LHe) return line on the recycler is inserted into the fill port of the MEG system in the MSR through a slotted opening in the ceiling. The helium vapor is captured through a line that returns the gas to the top of the recycler assembly. A high-purity helium gas cylinder connected to the recycler assembly supplies the gas, which, after it is liquefied, increases the level of LHe in the MEG system during the start-up phase. No storage tank for evaporated helium gas nor a helium gas purifier is used. The recycler is capable of liquefying helium with a rate of ∼17 L/d after precooling the MEG system. It has provided a fully maintenance-free operation under computer control for 7 months without refill of helium. Although the recycler is used for single-orientation operation at this initial testing site, it is designed to operate at ±20° orientations, allowing the MEG system to be tilted for supine and reclining positions. Vibration of the recycler is dampened to an ultra-low level by using several vibration isolation methods, which enables uninterrupted operation during MEG measurements. Recyclers similar to this system may be quite useful even for MEG systems with 100% magnetometers.     

Design analysis of a solid nitrogen cooled “permanent” high-temperature superconducting magnet system

Potential performance advantages of a solid nitrogen cooled “permanent” high-temperature superconducting (SN2/HTS) magnet system over a liquid helium cooled low-temperature superconducting (LHe/LTS) system are explored. The SN2/HTS system design includes a second solid heat capacitor that cools a radiation shield. Recooling of the heat capacitors is performed with a demountable cryocooler. The SN2/HTS system offers both enhanced stability and improved portability over a LHe/LTS system.Design codes are constructed to compare the SN2/HTS system design with a LHe/LTS design for a general permanent superconducting magnet system employing a room temperature bore. The codes predict the system volume and mass that should be expected for a given set of design requirements, i.e. field strength and bore size, and a given set of conductor properties. The results indicate that present HTS conductor critical current and index are not yet sufficient for producing SN2/HTS systems of a size that is comparable with that expected for a LHe/LTS system; however, the conductor properties of Bi2223/Ag have been consistently improving, and new HTS conductors are expected to be developed in the near future. The codes are used to determine the minimum Bi2223/Ag conductor performance required for a SN2/HTS system to be competitive with a LHe/LTS system.     

A self-circulation helium liquefaction system with five 4 K G-M cryocoolers

A self-circulation helium liquefaction system (SCHLS) with five 4 K G-M cryocoolers is developed to supply liquid helium (LHe) for SECRAL (a superconducting ECR ion source used in Lanzhou city, China). LHe is vaporized in SECRAL and warmed up to room temperature. SCHLS will re-liquefy the helium gas at a rate of 83.2 L/day under normal atmosphere pressure. With SCHLS, SECRAL system can run online without any interruption of refilling LHe.     

Characterisation and optimisation of flexible transfer lines for liquid helium. Part I: Experimental results

The transfer of liquid helium (LHe) into mobile dewars or transport vessels is a common and unavoidable process at LHe decant stations. During this transfer reasonable amounts of LHe evaporate due to heat leak and pressure drop. Thus generated helium gas needs to be collected and reliquefied which requires a huge amount of electrical energy. Therefore, the design of transfer lines used at LHe decant stations has been optimised to establish a LHe transfer with minor evaporation losses which increases the overall efficiency and capacity of LHe decant stations. This paper presents the experimental results achieved during the thermohydraulic optimisation of a flexible LHe transfer line. An extensive measurement campaign with a set of dedicated transfer lines equipped with pressure and temperature sensors led to unique experimental data of this specific transfer process. The experimental results cover the heat leak, the pressure drop, the transfer rate, the outlet quality, and the cool-down and warm-up behaviour of the examined transfer lines. Based on the obtained results the design of the considered flexible transfer line has been optimised, featuring reduced heat leak and pressure drop.     

失超引起的气泡对超导体绝缘特性的影响

综述了超导设备在失超情况下液氦中气泡的形成,以及气泡对超导设备的绝缘特性的影响,分析了在均匀和不均匀电场中热传导率、压强及电极表面状况对击穿特性的影响,并探讨了提高失超情况下液氦击穿电压的方法.