多层绝热和支撑辐射对低温传输管线的影响分析

为了确保低温传输管线的设计质量,采用高真空多层绝热方式减少管线的漏热。通过分析多层绝热和支撑表面辐射,对低温传输管线进行了传热模拟研究,得到了内管道壁面间的辐射换热量和支撑总体漏热量。分析了三角形和正方形支撑漏热量的不同;同时对比了不同发射率支撑表面下,支撑辐射换热量、导热量和温度分布的变化。结果表明:在满足支撑强度条件下,应当增大热传导距离,减小支撑的接触面积以及辐射换热面积;随着支撑表面发射率增大,支撑表面辐射换热量增加,导热量减少,总体漏热量增大,当发射率为1时,模拟得到的漏热量仍小于1 W/m。     

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。     

微型制冷机做冷源的固体材料导热系数测量装置设计

基于一维轴向稳态热流法,采用微型脉冲管制冷机作为冷源,研究建立了一台可连续测量60—300 K下固体材料的导热系数的装置。该装置采用集成化设计,各组件密集排布,整体结构精简有序,其测量方法采用两探针形式,适用于测量导热系数较小的样品。在高真空的环境下,进一步对该装置制冷机冷头的漏热和样品的漏热进行了分析和计算,得出样品测量时的总漏热约为472.3μW,制冷机及样品台组件的总漏热约为760.0 mW。最后,通过标样测量和误差分析,证明装置具有较小的误差和较高的精度,该装置所测量得不锈钢标准样的导热系数与标准数据仅存在4%左右的偏差。     

合肥光源超导波荡器用二元电流引线的设计研究

电流引线作为连接室温电源与低温超导磁体的部件,温度跨越范围大,是低温恒温器的最主要热负荷之一。超导波荡器(SCU)用高温超导电流引线主要采取小型制冷机直接传导冷却的形式,通过对合肥光源超导波荡器(HLS-2 SCU)用400 A高温超导二元电流引线铜段的长度、截面等几何参数进行理论优化,以减小小型低温制冷机的热负荷。考虑室温端热阻以及铜段低温端的温度对最小漏热的影响,得出铜段最佳值参数。通过有限元仿真计算结果进行验证,得出的结果吻合的较好。最终确定了400 A高温超导电流引线的设计参数。     

制冷机做冷源的低温热导率测量装置研制

设计研制了1套以4.2 K制冷机为冷源的低温热导率快速测量装置.该装置采用可拆卸的具有独立真空环境的样品测试杆,使得样品测试部件与低温冷源部件分离,从而实现不破坏制冷机冷源真空环境及制冷机不复温的情况下快速更换样品.高真空绝热恒温样品杆通过高导热柔性热桥与制冷机冷头良好热耦合.热导率测试采用稳态绝热纵向热流法.除快速测...     

热声系统高温段的漏热分析与防护结构的优化设计

对热声系统高温段的漏热进行理论分析,建立高温段真空防护结构的物理模型,并基于fluent中S2S模型,对模型进行了稳态数值模拟,得到了辐射散热量、导热量、外表面的热流量随加热温度的变化,以及辐射和导热占总漏热量的比值;在此基础上,对防护结构进行优化,提出防护结构2,对比分析了两种热防护结构的防漏热效果。结果表明,真空防护结构会有效的减少系统的漏热,增大系统的热声转换效率,且优化后的结构2较结构1更能有效的减少系统漏热。     

高真空多层绝热低温容器整体热分析及试验验证

对35 m'高真空多层绝热低温容器在满载液氧的状态下进行热分析,得到标准状态下该容器漏热量的分布范围及相应的静态蒸发率分布,分析了导热和辐射漏热在总漏热的比重.将计算结果和静态蒸发率试验进行对比,结果符合较好,说明计算的准确性和有效性.进而分析了冷态下玻璃钢支承件和罐体的接触情况.结果可为高真空多层绝热低温容器的设计、...     

大口径低温管道变工况漏热特性分析与优化

建立了一个包含辐射漏热、固体导热和残余气体导热分析的复合热力学模型,对高真空绝热低温管道在热边界温度(环境温度)变化、冷边界温度变化(压力变化或者改变流体)和真空度变化等变工况的漏热特性开展了研究。结果表明,热边界温度(环境温度)对漏热量的影响显著高于冷边界温度改变(流体种类改变或者管道内压力变化)导致的影响;当真空度为10—10~(-2) Pa区间,随着真空的改善,漏热量明显变小,不过当真空度优于10~(-3) Pa时,真空的进一步改善对漏热量的影响不再显著。     

20K温区单级脉管制冷机漏热分析

漏热冷损是影响低温制冷机性能的一个重要因素.对1台工作在20 K温区的单级脉管制冷机进行了漏热计算,并对其进行了部分实验验证.结果表明:在系统总漏热中,脉管和回热器的壁面轴向导热所占的比例最大.     

300kVA高温超导变压器电流引线漏热损耗的测量分析

高温超导变压器是利用高温超导材料替换铜线制作导线圈,用液氨替换变压器油当做超导线圈的冷却介质。相对于传统的变压器和低温超导变压器在性能上具有很大优势。电流引线是高温超导变压器的主要漏热源,其漏热大小能够直接对超导设备运行的稳定性以及经济性造成影响。因此,电流引线的设计和漏热测量对高温超导变压器的生产和使用均具有很大意义,也一直是变压器方面研究的重点。本文主要以300kVA高温超导变压器为例,采用量热法对其不同电流下的漏热损耗进行了简介测量,分析和探讨了电流导线漏热损耗的测量方法和相关因素。     

Optimal cool-down time of a 4 K superconducting magnet cooled by a two-stage cryocooler

A cool-down time is one of the major factors in many cryocooler applications, especially for the design of conduction-cooled superconducting devices. Cool-down time means a time cooling a thermal mass from a room-temperature to cryogenic-temperature within a stipulated amount of time. The estimation of cool-down time seeks the elapsed time to cool the thermal object by a cryocooler during initial cool-down process. This procedure includes the dimension and properties of thermal object, heat transfer analysis for cryogenic load, thermal interface between cold mass and cryocooler, and available refrigeration capacity of cryocooler. The proposed method is applied to the specific cooling system for 3 T superconducting magnet cooled by a two-stage GM cryocooler. The result is compared with that of experiment, showing that proposed method has a good agreement with experiment. In addition, the initial cool-down time can be shortened by employing thermal link between the cold mass and first-stage of cryocooler. Through a rigorous modeling and analysis taking into account the effect of thermal link size, it is concluded that there exists an optimal cool-down time during initial cooling in conduction-cooled superconducting magnet system.     

Experimental investigation on the detachable thermosiphon for conduction-cooled superconducting magnets

A detachable thermosiphon, as a transient thermal switch for conduction-cooled superconducting magnet, is designed, fabricated and tested. A thermosiphon between the first and second stages of a cryocooler can reduce the cool-down time of a conduction-cooled superconducting magnet by using the large cooling capacity of the first stage. The thermosiphon is a very efficient heat transfer device until all the working fluid in it freezes (off-state). After the working fluid freezes and the second stage temperature becomes lower than that of the first stage, however, the thermosiphon then becomes a conduction heat leak path between two stages of the cryocooler. Considering a very small cooling capacity of the second stage of the cryocooler around 4.2 K, the conduction heat loss is not negligible. Therefore, a detachable thermosiphon, made of a metal bellows, is considered to be able to eliminate such a conduction heat leak. The mock-up magnet is cooled down with the thermosiphon and the thermodynamic states of the thermosiphon and the mock-up magnet are precisely examined during the whole cool-down process. At off-state, the thermosiphon is detached mechanically from the magnet. In this way, the conduction heat leak path through the thermosiphon wall is completely eliminated. This paper describes the detailed transient operation of the detachable thermosiphon using nitrogen as the working fluid.     

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.     

EAST托卡马克装置冷屏的真空要求与受热分析

冷屏是EAST超导托卡马克核聚变实验装置的重要部件之一。对冷屏系统的氦泄漏漏率做了计算,介绍了其检漏实践;采取有限元法对内冷屏的受热状况进行了计算分析,以验证内冷屏氦冷却管道设计方案的可靠性。     

EAST超导托卡马克冷屏的结构设计及受热分析

EAST是一个拥有全超导磁体系统的托卡马克实验装置.为有效减少来自真空室和外真空杜瓦的辐射热以及支撑的传导热等各项热负荷,超导纵场磁体和极向场磁体被约80 K的真空室冷屏(内冷屏)和外真空杜瓦冷屏(外冷屏)所包容,从而保证磁体运行的稳定可靠.运用大型有限元分析程序ANSYS和FLUENT,对冷屏的受热状况进行了数值分析,为其结构设计和低温制冷方案的制定提供可靠的理论依据.     

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.     

Cold storage characteristics of mobile HTS magnet

A cold storage system specialized in mobile high-temperature superconducting (HTS) magnets (e.g. for magnetically levitated (maglev) vehicles) has been proposed. In this system, a cooling source is detachable and a HTS coil is capable of maintaining superconducting state with its heat capacity. This system allows a considerably lightweight HTS magnet.An apparatus was constructed to evaluate the possibility of using cold storage systems in maglev vehicles. The thermal characteristic of this apparatus was based on a magnet for previous maglev test vehicles [1]. The operational temperature range of the magnet was assumed from 20 K to 50 K. Some experiments indicated that heat conduction by residual gas was not negligible. Especially over 30 K, gas conduction took a large part of heat input. This phenomenon is attributable to reduction of cryopumping effect. However, activated carbon in the apparatus compensates cryopumping effect. A unique heat capacitor was also used to enhance the cold storage effect. Water ice was chosen as a heat capacitor because water ice has a higher heat capacity than metallic materials at cryogenic temperatures. A small amount of water ice also prolonged cryogenic temperature condition. These results indicate 1 day of cold storage is probable in a magnet for maglev vehicles.     

Model for transient behavior of pulse tube cryocooler

This article describes an investigation of the transient behavior of a small (2.0 W at 85 K) pulse tube cryocooler operating at 120 Hz with an average pressure of 3.5 MPa, capable of relatively fast cool-down from ambient to about 60 K. In a series of experiments, the cold end temperature was measured as a function of time in a complete cool-down and subsequent warm-up cycle, with no heat load and different quantities of excess mass at the cold end. A transient heat transfer model was developed, that considers the effects of the cooling power extracted at the cold end and that of the heat gain at the warm end on the cool-down time. The heat gain factor was calculated from warm-up data, and found to be approximately the same for all experiments. Using the same model with cool-down data enables a determination of both the gross and net cooling power as functions of time, but more importantly – as functions of the cold end temperature. An expression was derived for the cold end temperature as a function of time for any amount of excess mass, including zero. The cool-down time of the “lean” cryocooler (with no excess mass) was found to be less than 50 s.This cool-down/warm-up method for evaluating the cooling power of a cryocooler seems simpler than steady-state experiments with a heater simulating load at the cold end. Use of the heat transfer model with data from one or two good experiments conducted in the above manner, can yield both the gross and net cooling powers of a cryocooler as functions of the cold end temperature, and allow the determination of cool-down time with any amount of excess thermal mass. While the net cooling power during cool-down differs somewhat from that under steady-state operation, the former can serve as a good measure for the latter.     

Cryogenic helium gas circulation system for advanced characterization of superconducting cables and other devices

A versatile cryogenic test bed, based on circulating cryogenic helium gas, has been designed, fabricated, and installed at the Florida State University Center for Advanced Power Systems (FSU-CAPS). The test bed is being used to understand the benefits of integrating the cryogenic systems of multiple superconducting power devices. The helium circulation system operates with four sets of cryocooler and heat exchanger combinations. The maximum operating pressure of the system is 2.1 MPa. The efficacy of helium circulation systems in cooling superconducting power devices is evaluated using a 30-m-long simulated superconducting cable in a flexible cryostat. Experiments were conducted at various mass flow rates and a variety of heat load profiles. A 1-D thermal model was developed to understand the effect of the gas flow parameters on the thermal gradients along the cable. Experimental results are in close agreement with the results from the thermal model.     

电子倍增CCD相机制冷绝热设计

对电子倍增CCD(EMCCD)相机制冷的必要性以及热电制冷器(TEC)的特点进行了说明,阐述了真空绝热的优势,分析了真空绝热失效条件,提出了真空绝热的难点及真空保持方案,分析了相机芯片发挥其性能所需的制冷温度,对制冷相机漏热途径进行了分析,计算了克服漏热所需的制冷功率,并设计了制冷绝热方案,对相机进行了稳态热分析建模,将多级热电制冷器进行了参数化转化并将其带入模型边界中,经过迭代拟合得到了相机杜瓦及芯片温度分布,分析了绝热制冷方案的可行性。