高温超导磁储能(SMES)磁体直接冷却热输运过程研究

随着高温超导材料与低温技术的发展，采用制冷机直接冷却已经成为高温超导应用的发展方向，而界面热阻则直接影响着超导器件的冷却效率和运行可靠性，因此减小和控制低温界面热阻是实现超导系统直接冷却的技术关键。对直接冷却高温超导磁体从室温冷却到49K低温的热输运过程进行了理论分析和实验研究，磁体冷却实验结果和理论分析符合较好，通过直接冷却实验所达到的最低温度特性和过程分析，证实从微结构低温工程学的角度研究界面热阻、探索超导直接冷却最佳热耦合机制是高温超导应用基本而重要的科学问题之一。     

35 kJ高温超导磁储能(SMES)的热输运实验研究

研制了中国首台高温超导磁储能直接冷却系统,该系统不使用低温液体(液氦、液氮).在10-3Pa的真空度下,高温超导磁体线圈由1台单级GM制冷机从室温293 K冷却到19 K,Bi2223电流引线由另一台制冷机冷却到77 K以下.整个系统在通140 A直流电流的时候产生了4.5 T的磁场.系统连续运行480 h(20 d),磁体和低温系统各参数动态特性良好.实验研究表明,控制系统的漏热,优化磁体内部导冷结构,有效减少热传导部件的接触界面热阻是制冷机直接冷却高温超导磁体的关键技术.     

高温超导电机的冷却技术综述

重点探讨了高温超导电机关键技术之一的转子冷却技术的发展过程和各种冷却方式的特性分析,总结出了其优缺点.针对现有技术和结构提出了3种新型的冷却方式和结构:分布式旋转热管,分层开放式蒸发冷却和旋转管道两相流冷却,重新提出针对低速的电动机应用低温超导时代经常采用的浸泡式蒸发冷却方式,这4种方法都是基于相变传热的原理,传热效率高,具有自循环和自适应的特性.进一步提出在冷却系统方面需要深入研究的理论和工程方面的问题.针对各种超导电机的应用场合,提供了不同容量和转速下高温超导所能匹配的冷却方式.     

超导电力科学技术与低温技术研究的现状与进展

随着低温超导的发展,低温超导已在若干领域进入实际应用,而高温超导材料研究10余年来的巨大进步,高温超导的应用将步随其后。预计在21世纪前期,超导将进一步出现实用化、产业化契机,超导技术是通向未来高科技的道路。随着低温超导和高温超导技术的进一步发展,超导技术将进入一个新的应用超导的发展阶段,并对相应的低温技术提出了新的要求。超导技术的进步将进一步促进低温技术研究新热卢、的增长,并推动多学科的发展,从而迎接未来高科技发展的机遇与挑战。     

ITER 10kA高温超导电流引线测试装置低温系统的研究

为ITER CC 10 kA高温超导电流引线服务的低温性能测试装置已研制完成,并成功运行。其低温系统主要由500W/4.5 K氦制冷机,真空杜瓦,低温组件(低温阀门,过冷槽,管道加热器,热防护层),汽化器及低温传输管线等部分组成。本文对真空杜瓦和过冷槽进行设计,并讨论该低温系统的冷却流程方案,最后通过电流引线10 kA稳态实验结果对低温系统的运行效果进行分析,结果表明该低温系统运行稳定,能满足ITER CC电流引线的测试需要。     

高温超导直接冷却中AlN与Bi-2223间界面热阻的实验研究

基于微结构低温工程学，提出三维低温界面层的概念，指出界面热阻是制冷机直接冷却超导磁体需要解决的关键技术之一。以GM制冷机为冷源，按稳态热流法原理测量了Bi-2223、AIN的热导率及它们之间的低温界面热阻。在0.15MPa-0.55MPa压力范围内，AIN和Bi-2223间的界面热阻随界面层温度和接触压力的升高而降低，并随接触界面处温度的不同表现出不同的变化率。当界面层Bi-2223侧温度为55K时，在0.5469MPa的接触压力作用下，Bi-2223和AIN间的界面热阻是厚度为10mm的AIN垫片体积热阻的38.86倍，是接触压力0.2281MPa时界面热阻的38.7％。     

低温显微镜的研制

低温显微镜是低温生物医学研究中的重要工具,介绍了低温显微镜的历史和主要类型,并设计制作了一台采用液氮冷却的低温显微镜。该低温显微镜采用电子膨胀阀控制冷却介质的流量,最大升温速率可达100℃/min,最大降温速率可达50℃/min,控温精度为±1℃。     

LNG大型低温储罐冷却技术探讨

LNG大型低温储罐的冷却是储罐投用前最为关键的一步,充分的储罐冷却作业前准备、冷却过程中系统阀门的正确设置、储罐冷却速率的合理控制及安全措施的严格执行是LNG大型低温储罐冷却得以顺利实施的重要保证。以国内某一16万m3全容式LNG储罐为例,对LNG大型低温储罐的冷却技术进行了详细的论述。     

载人空间站系统中的低温冷却技术

论述了载入空间站系统中的低温冷却技术。以大量而翔实的资料为依据,说明载人空间站是航天书业发展的必然趋势.介绍了空间站系统和运输系统的组成以及它们对低温和冷却技术的需求;运输器飞行保障中的低温技术,包括电源系统中的低温技术和热控系统中的热沉,生命保障系统中的低温技术,包括氧的低温贮存供给技术和舱段环境的冷却。指出冷却散热是技术保障的关键技术之一,介绍了冷却散热的基本技术及装置,并用大量实例加以说明。     

直接冷却中高温超导电流引线的传热研究

降低高温超导电流引线向低温环境的漏热,以及实现电流引线与制冷机冷头导热不导电的直接接触冷却,是制冷机直接冷却超导系统走向应用的关键技术之一。本文提出了高温超导电流引线的基本结构,并对进入制冷机一、二级冷头的漏热进行了理论推导和数值模拟计算。     

Counter flow cooling characteristics with liquid nitrogen for superconducting power cables

Counter flow cooling is one of effective cooling systems for superconducting power transmission cables to save space. In designing of HTc superconducting power cables, investigating cooling characteristics with liquid nitrogen is important. We have conducted counter flow cooling tests of a 100-m long duplex-counter-flow tube with liquid nitrogen and obtained basic data of initial cooling and temperature distributions along the tube. Measured temperature distributions are compared with those calculated that are based on our previous study. They agree with temperature distributions of inner tube but not for outer tube. During cooling tests, mass flow rate oscillations are observed. Relation between oscillation period and tube length is discussed. Reservoir pressure dependence of measured initial cooling time is also shown and compared with analytically estimated time in this paper.     

Optimization and thermodynamic understanding of conduction-cooled Peltier current leads

Conduction-cooled Peltier current leads (PCLs) are optimized in a superconducting magnetic system. Optimum geometric factors, viz. the ratio of length to cross-sectional area, of both the copper lead and thermoelectric element, are simultaneously found to minimize the heat leak per PCL. A rigorous thermodynamic temperature-entropy (T-s) diagram is constructed. The heat leak as well as the total input power of both PCLs and converntional all-copper leads can be easily identified from the rectangular areas on the simple 2-D T-s plane.     

Peltier effect in metallic junctions with CPP structure

The bottom shift in a parabolic baseline of resistance-current (R--I) curves in trilayer current perpendicular to plane-giant magnetoresistance (CPP-GMR) elements is often observed in current induced magnetization reversal (CIMR) experiments. We fabricated CPP-metallic junction elements with various metal combinations (Co/Au, Cr/Au, Cr/Co, Cr/Cr), and measured the R-I curves. Our results reveal that the direction of the shift is coincident with the sign of the Peltier coefficient of the CPP structure, and the amount of the shift is proportional to the Peltier coefficient. We estimated the Peltier coefficients by using the current where the Joule heating and the Peltier cooling compensates, and found that the Peltier coefficients are larger than those obtained from bulk materials. The expected cooling power of the CPP-Co/Cr elements was about 100 /spl mu/W, which results in relatively large areal cooling power (/spl sim/10/sup 5/ W/cm/sup 2/) because of the large current density (/spl sim/10/sup 7/ A/cm/sup 2/).     

A novel cooling scheme for superconducting power cables

Long distance transmission of electrical power with superconducting cables is likely necessary for energy conservation and effective utilization of renewable energy sources. The performance and cost of such superconducting lines is as significantly influenced by cryogenic issues as by superconductor performance. One significant cryogenic issue is that in the usual method of cooling using sub-cooled cryogen flow there is a limited cable length before the cryogen needs to be re-cooled. This adds complexity and cost to the cable system. Here we address this problem by utilizing the latent heat of the cryogen without the complication of multi-phase flow. The cryogen is distributed to the superconducting components by spraying it through small holes in a pressurized line. The pressurized liquid exiting the holes turns into mixed liquid and vapor with a temperature near the boiling point of the cryogen at the pressure of the space surrounding the superconducting components. The pressure in the space surrounding the superconducting components is then kept near atmospheric by maintaining short distances to a vent. The sprayed liquid accumulates but rapidly vaporizes in response to the heat load, providing even cooling power at a fixed temperature for the entire length of the line. Our work indicates that it may be possible to implement a cooling system with much simplified cryogenic stations at the cable ends and allowing cable lengths of up to 100 km with no intermediate cooling stations.     

Subcooled liquid nitrogen refrigerator for HTS power systems

Subcooled liquid nitrogen is a good cooling medium of high temperature superconducting (HTS) electric power systems such as an electric power line and a power transformer. To produce subcooled liquid nitrogen, a cryocooler is used and a circulation pump is installed in the system. Several subcooled liquid nitrogen circulation systems were constructed and tested. Those are used as a refrigerator for HTS power systems. The pressure of subcooled liquid nitrogen is maintained at atmospheric pressure (0.108 MPa) and the working temperature is 68 K. One system of HTS power transformer was tested in distribution power line. In each case, the temperature of the cold head of the cryocooler is kept at 64 K little above nitrogen freezing temperature. For the stable operation, the system must work even in the case of shaking condition by earthquake, the pressure must be stable and be kept at atmospheric pressure.     

The design and fabrication of a reverse Brayton cycle cryocooler system for the high temperature superconductivity cable cooling

A high temperature superconductivity cable must be cooled below the nitrogen liquefaction temperature to apply the cable to power generation and transmission systems under superconducting state. To maintain the superconducting state, a reliable cryocooler system is also required. The design and fabrication of a cryocooler system have been performed with a reverse Brayton cycle using neon gas as a refrigerant. The system consists of a compressor, a recuperator, a cold-box, and control valves. The design of the system is made to have 1 kW cooling capacity. The heat loss through multilayer insulators is calculated. Conduction heat loss is about 7 W through valves and access ports and radiation heat loss is about 18 W on the surface of a cryocooler. The design factors are discussed in detail.     

A “permanent” high-temperature superconducting magnet operated in thermal communication with a mass of solid nitrogen

A new design for a portable “permanent” superconducting magnet system is explored. The design involves a persistent-mode high-temperature superconducting (HTS) magnet that is cooled by a solid heat capacitor. The system is an alternative to permanent low-temperature superconducting (LTS) magnet systems where the magnet is cooled by a bath of liquid helium.An apparatus was constructed to demonstrate stable operation of a permanent magnet wound with Bi2223/Ag conductor while in thermal communication with a mass of solid nitrogen. The apparatus includes a room-temperature bore and can function while it stands alone, detached from its cooling source, power supply, and vacuum pump. The magnet is operated in the 20–40 K temperature range. This apparatus is the first to demonstrate the operation of a superconducting magnet with a permissible temperature variation exceeding a few degrees kelvin. Models are developed to predict the experimental system's warming trend and magnetic field decay. The models are validated with a good agreement between simulations based on these models and experimental results. The results indicate that present HTS conductor critical current and index are not yet sufficient to provide field strengths and field decay time constants that are required for typical persistent-mode applications.     

Research and development of superconducting cable in Super-ACE project

Research and development of fundamental technologies for superconducting AC power equipments (called Super-ACE) project started as a national project in 2000 fiscal year by Ministry of Economy, Trade and Industry and New Energy and Industrial Technology Development Organization. This project is to research and develop the basic technology of high temperature superconducting cable (HTS cable), fault current limiter, and transformer. Main subjects of the cable in this project are to study the 3 kA superconducting cable conductor, cooling technology of 500 m HTS cable, and power system analysis of cable and AC equipments. The present paper describes the background of this project, target of each research subject, schedule of research and development, and major results of research activity in 2001.     

Thermal regulator for IC temperature characterization using a microprobe station

This paper presents a thermal regulator conceived to allow the electrical characterization of integrated circuits (ICs) over a wide temperature range. The main feature, as compared to conventional thermal chambers, is the possibility to reach test points on the IC surface by means of a microprobe station. The thermal regulator is based on a Peltier cell, which is placed close to the bottom side of the device under test (DUT). This way, the cooling/heating power needed to reach the required IC temperature, is supplied directly through the thermal conduction of the package and the chip substrate. The main advantages of the proposed solution are low cost, small size, accurate temperature control, and fast settling time. The measured temperature range is from -40/spl deg/C up to +120/spl deg/C with a settling time of about 4 min. The maximum power consumption is about 30 W (during startup transients).     

Progress of technology for superconducting generator

In this special edition, the results of Japanese national project on development of superconducting generators (SCGs) are reported. Before the reports, the history of developing conventional generators, (that is, larger generator requests higher technology of cooling) motivation of developing SCGs (which is on way of higher cooling technology for larger generator), key technologies of SCGs except superconducting technology, features of SCGs, (that is, larger capacity, small size, high efficiency, good characteristics for power system operation) and so on, present situation of the development and some comments of real application are described.