超临界氦增压系统及试验研究

为了对超临界氦增压技术在运载火箭中的应用可行性进行验证,研究超临界氦增压系统设计参数的匹配特性,本文对比分析了不同增压方式的效率,开展了超临界氦增压系统试验.在试验中通过分析比对超临界氦增压系统的各项参数,获得了超临界氦增压系统的增压性能,同时验证了超临界氦的置换、预冷、加注等流程.试验表明,在适当的参数匹配条件下,超临界氦增压系统增压性能稳定,是一种具有较高效率和可靠性的液体火箭的增压方案.     

超临界氦循环泵的设计方法

超临界氦循环泵用于超导磁体的迫流冷却.从普通离心泵的基本理论出发,分析了低比转速超临界氦循环泵的特性,从提高效率的角度比较了多种设计方法.得出最理想的方法是提高泵的转速,同时也证明了超临界氦循环泵采用高速全流泵和高速部分流泵设计的可行性.     

超临界氦增压系统仿真与优化设计

采用基于集总参数法的AMESim两相流库及32参数的MBWR物性方程,针对超临界氦增压的地面预增压过程及箭上增压过程,构建了超临界氦增压系统仿真模型,实现了从亚临界的气液两相流到临界流、超临界流状态的全过程仿真。以某超临界氦增压系统为算例进行了超临界氦增压仿真分析,并建立了超临界氦增压系统优化模型,以增压完成后挤压气瓶剩余质量和液氦贮罐内剩余质量最小为优化目标,以挤压气瓶容积,液氦贮罐容积为优化变量,采用多目标遗传算法对该超临界氦增压系统参数进行了优化设计,在满足增压要求的情况下减轻了系统的总质量。     

稳态混合磁体装置低温系统过冷槽的设计与优化

40 T稳态混合磁体装置的外超导磁体需要4.5K、5×105Pa、18 g／s超临界氦迫流冷却,拟采用盘管换热器将从制冷机出来的氦冷却至超临界状态.首先对氦制冷机进行混合模式的热力学分析,确定过冷槽中盘管换热器的进口压力及温度,进而提出阶梯管径理论,根据工程要求设计并优化盘管换热器,得出盘管换热器的盘绕方式及尺寸;最后...     

部分流超临界氦循环泵特性分析

通过将大型超导托卡马克装置中用于超导磁体冷却的超临界氦循环泵与传统离心泵进行比较,对BNI(Barber-Nichols Inc.)部分流超临界氦循环泵进行了结构特点和性能特点分析,重点讨论了叶轮、叶片和蜗壳的结构差异,以及由于这些结构的不同决定的流量、扬程和效率差异,为部分流超临界氦循环泵的设计及试验研究提供了理论依据.     

超临界氦增压与排放过程的压力温度特性

为了探讨超临界氦增压技术在中国运载火箭和航天器上实现的可行性,进行了超临界氦增压排放实验研究。分析了低温杜瓦内的超临界氦的热分层稳定性;讨论了温度计引线两端大温差引起热声振荡和漏热现象;此外,由于节流微分效应和换热器管壁轴向导热,换热器出口温度在排放过程出现大幅温度波动。实验结果证明超临界氦增压过程中增压压力平稳、可靠,压力容易控制。但后续改进实验中应消除换热器节流微分效应导致的出口温度波动,并且减小杜瓦以及支撑结构的漏热。     

液浴氦低温泵

叙述了无液氮槽的液浴氦低温泵，介绍了其结构和试验结果的详细情况.     

氦制冷机节流级的最佳工作点

在氦制冷机/液化器中,最末级的冷却一般采用节流方式.节流级的各参数的选择必然会影响氦制冷机的制冷量或氦液化率.讨论了节流级节流前压力、末级换热器的热端温度及其效率对制冷量或液化率的影响,得出了不同模式下的节流级的最佳工作点.     

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.     

EAST超导托卡马克热负荷波动对低温系统液氦槽的影响

EAST超导托卡马克的纵场和极向场磁体均采用NbTi超导材料,由3.8 K超临界氦冷却.在托卡马克实验运行时,极向场的放电脉冲和等离子体破裂产生的交流损耗带来的热负荷增加,经过超临界氦流带到低温系统控制阀箱内的液氦槽和过冷槽,造成槽内的液氦蒸发量增加.蒸发的氦回到制冷机中,从而影响制冷机的稳定运行.通过对实际超临界管道和液氦槽、过冷槽中换热过程建立换热模型,进行热工分析,分析液氦槽和过冷槽中的压力等参数的变化,指导低温系统的设计.     

Cryogenic leak test procedure for a large superconducting cyclotron helium vessel

A procedure for testing the vacuum integrity of very large stainless steel weldments used at cryogenic temperatures has been developed at Michigan State University. This development, which uses large quantities of liquid nitrogen, is a modification of a technique commonly applied to small devices and involves cooling the cryostat's liquid helium vessel (bobbin) to liquid nitrogen temperature, and then proceeding immediately with leak testing. This method was applied to the K800 superconducting magnet helium vessel, which seemed leak tight at room temperature, but was found to have an easily detectable helium leak when cooled. After repairing the leak, retesting revealed no leaks, where upon the K800 cryostat construction was completed; i.e. the bobbin was wrapped with superinsulation, a liquid nitrogen radiation shield was added, and the assembly was inserted into the vacuum jacket. The final leak test occurred when the cryostat was cooled to liquid helium temperature and was found to be helium leak tight.     

An efficient continuous flow helium cooling unit for mossbauer experiments

A Mossbauer continuous flow cooling unit for use with liquid helium over the temperature range 4.2–300 K is described. The cooling unit can be used for either absorber or source studies in the horizontal plane and it is positioned directly on top of a helium storage vessel. The helium transfer line forms an integral part of the cooling unit and feeds directly into the storage vessel so that helium losses are kept to the minimum. The helium consumption is 0.12 / h^-1 itat 4.2 K decreasing to 0.055 / h-1 at 40 K. The unit is top loading and the exchange gas cooled samples can be changed easily and quickly.     

Electro-magnetic stress-induced degradation of insulation vacuum of a large cryo-magnetic system

In superconducting magnets, the cold mass is placed in a vacuum vessel to reduce heat load to the liquid helium system. Helium leaks into the vacuum vessel can degrade the insulation vacuum, which can, in turn, cause an increase in the heat load to the liquid helium system. These leaks are called cold leaks, as they show up when the coil is cooled with liquid helium. K500 superconducting cyclotron magnet at Variable Energy Cyclotron Centre, Kolkata has such cold leaks in the helium vessel that developed during cool down. The leak rate increases with the increase of current in the superconducting coils. This paper describes a series of experiments carried out on the superconducting cyclotron magnet to find the level of degradation of insulation vacuum and measure the increase in heat load with magnet current. The leak rate was also measured and the leak size was estimated analytically. Detail magneto-structural analysis was done using Finite Element Method (FEM) to identify highly stressed zones in the helium vessel and found out that highly stressed zones coincide with the weld zones. The magneto-structural stress was applied on an estimated size of single crack and found that crack tip stress could reach beyond elastic limit of the material. We can predict that the full design current may be unachievable in this situation. Mitigation of increased heat load was also done using an additional vacuum pump for the insulation vacuum space.     

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.     

低温绝热容器氦质谱检漏方法探讨

漏率是低温绝热容器产品的主要技术参数之一,利用氦质谱检漏技术对漏孔进行定位、定量检测可以起到控制产品质量的目的。文章首先对低温绝热容器用两种氦质谱检漏系统进行了比较和试验分析。结果表明：在测试条件一致的情况下,标准漏孔安装在系统中的不同位置,将对系统最小可检漏率、系统反应时间、漏率测算值产生影响。在对影响结果进行分析的基础上,对实际检漏工作提出相应建议。其次对分流和无分流两种检漏方法的选择原则进行了探讨。然后以53m^3液化天然气储运容器为例,对容器制造过程中的角焊缝、对接焊缝、夹层内存在的漏孔、阀门及容器整体的检漏方法进行了详述。最后对检漏过程中应注意的事项进行了说明。     

Application of gas oscillation in a tube to pressurization in a liquid helium storage vessel

A novel application of gas oscillation in a tube connected between room and liquid helium temperatures is described. The apparatus is designed to increase the internal pressure in a liquid helium storage vessel, in order to transfer the liquid from the storage vessel to an individual cryostat. The apparatus includes a liquid level meter which can be used even under pressure.     

Theoretical and experimental investigation of magnetic field related helium leak in helium vessel of a large superconducting magnet

The helium vessel of the superconducting cyclotron (SCC) at the Variable Energy Cyclotron centre (VECC), Kolkata shows a gradual loss of insulation vacuum from 10⁻⁷ mbar to 10⁻⁴ mbar with increasing coil current in the magnet. The insulation vacuum restores back to its initial value with the withdrawal of current. The origin of such behavior has been thought to be related to the electromagnetic stress in the magnet. The electromagnetic stress distribution in the median plane of the helium vessel was studied to figure out the possible location of the helium leak. The stress field from the possible location was transferred to a simplified 2D model with different leak geometries to study the changes in conductance with coil current. The leak rate calculated from the changes in the leak geometry was compared with the leak rate calculated from the experimental insulation vacuum degradation behavior to estimate the initial leak shape and size.     

不同种类破空气体对高真空多层绝热低温容器真空丧失后传热的影响

通过实验,分别利用氮气、空气、氧气和氦气作为破空气体,对高真空多层绝热低温容器在真空完全丧失后的漏热进行了研究。结果表明,多层绝热结构对于绝热真空完全丧失后的低温容器能够起到一定的保护作用,初始和最终漏热和渗入到绝热真空夹层中气体的性质密切相关。     

Design and development of a helium injection system to improve external leakage detection during liquid nitrogen immersion tests

The testing of assemblies for use in cryogenic systems commonly includes evaluation at or near operating (therefore cryogenic) temperature. Typical assemblies include valves and pumps for use in liquid oxygen-liquid hydrogen rocket engines. One frequently specified method of cryogenic external leakage testing requires the assembly, pressurized with gaseous helium (GHe), be immersed in a bath of liquid nitrogen (LN₂) and allowed to thermally stabilize. Component interfaces are then visually inspected for leakage (bubbles). Unfortunately the liquid nitrogen will be boiling under normal, bench-top, test conditions. This boiling tends to mask even significant leakage.One little known and perhaps under-utilized property of helium is the seemingly counter-intuitive thermodynamic property that when ambient temperature helium is bubbled through boiling LN₂ at a temperature of −195.8 °C, the temperature of the liquid nitrogen will reduce.This paper reports on the design and testing of a novel proof-of-concept helium injection control system confirming that it is possible to reduce the temperature of an LN₂ bath below boiling point through the controlled injection of ambient temperature gaseous helium and then to efficiently maintain a reduced helium flow rate to maintain a stabilized liquid temperature, enabling clear visual observation of components immersed within the LN₂. Helium saturation testing is performed and injection system sizing is discussed.     

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.