散裂中子源低温系统的概念设计

为促进中子散射技术在中国的进一步发展,中国科学院和广东省政府将在广东省东莞市建设一座基于加速器的散裂中子源装置(CSNS).设计的低温系统主要包括氦制冷机、氢循环冷箱和氢安全系统,其中氢循环系统采用单相超临界氢循环工质,氢泵强制循环的技术模式.氦制冷系统提供低温氦气,通过换热器将氢循环回路的全部热负荷带走,氢安全系统采用了多重屏障隔绝措施来确保低温系统的安全.介绍了CSNs低温系统的基本原理和布局,并详细说明了其主要技术参数及工作过程.     

中国散裂中子源低温系统氦制冷系统的安装与调试

氦制冷系统是中国散裂中子源(CSNS)低温系统的重要组成部分,能够为氢循环系统提供2 200 W@20 K的冷源。介绍了CSNS氦制冷系统的组成及设备布局图及氦制冷系统的调试原理,完成了控制界面图及氦制冷系统的安装和调试准备工作,详细说明了调试的过程,获得了700 W/1 400 W/2 200 W 3种制冷功率下的状态参数。氦制冷系统调试顺利完成,结果满足了验收指标。     

PDHID检测器在冷中子源氦制冷系统氢杂质分析中的应用

针对氦中痕量氢难以分析的问题,应用高灵敏度的脉冲放电氦离子化检测器(PDHID),结合可调压进样装置,对冷中子源氦制冷系统中的氢杂质进行分析,结果精密度高,相对标准偏差RSD1%,总测量不确定度3%,测定氢的检出限达10μL/m3,比TCD检测器的检出限低4个量级。     

空间低温光学试验深低温背景环境的实现

为了实现空间低温光学试验的深低温背景条件,对实现深低温环模技术以及氦冷却系统进行了探讨.通过分析得到以氦循环方式建立的20 K稳定深低温冷黑背景是最为合适的低温光学试验背景环境.该系统是由氦液化系统配合相应冷氦分配装置以及终端冷舱组成密闭循环系统.氦液化系统是基于由布雷顿循环和焦耳-汤姆逊作用组合而成的克劳德循环,它能持续提供一定流量和压力的液氦或冷氦气作为循环系统中制冷工质,从而为试验提供稳定的深低温环境.     

散裂中子源超临界低温氢循环用氢氦换热器设计

中国散裂中子源工程(CSNS)采用氦制冷循环冷却超临界氢至20 K温区,进而用低温超临界氢慢化中子。根据冷却系统的运行工况和参数要求,使用MUSE软件对氢氦换热器进行设计计算,并分析了其压力、温度、传热系数的沿程分布。结果显示氦气侧的压降限制主导了换热器的主要结构尺寸。由于氦制冷机的氦气压力和质量流量较低,氦气侧的传热系数较低,研究表明这是该换热器性能提升的瓶颈。     

中国散裂中子源氢循环系统的氦降温调试试验研究

中国散裂中子源(CSNS)氢循环系统建成后,需要进行降温调试实验,以获得满足运行要求的温度、压力和流量参数。为了保证人员和设备的安全,先使用氦气替代氢气,成功后再使用氢气进行降温调试实验。介绍了氢循环系统及降温调试的原理,氦气降温调试的过程及相关的降温曲线,分析了降温过程中的异常现象。经过5轮调试实验,顺利完成了氢循环系统的氦降温调试,为氢循环系统的氢气降温调试实验奠定了基础。     

中国散裂中子源低温系统的氢安全方案设计

针对氢具有易燃、易爆的危险特性,设计了一套氢安全系统,以保障中国散裂中子源(CSNS)低温系统安全、稳定、可靠地运行.设计的氢安全系统包括配气系统、监控系统、排放系统和真空系统4部分.介绍了CSNS低温氢循环系统的原理,并根据纵深防御设计理念,详细阐述了CSNS氢安全系统的组成及设计方法.采用的多重屏障隔离措施是氢安全设计的一大特点,对今后其它系统的氢安全设计具有一定的指导意义.     

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.     

氢燃料“氢浆”

美国国家航空与航天管理局的路易斯研究中心(克利夫兰市)协同对用于宇宙飞船和超音速“国家航天飞机”(正在设计一种普通飞机那样进入轨道和着陆的飞行器)的氢燃料进行研究。研究中的氢燃料是“氢浆”氢,一种体积为液氢体积15％的高能氢悬浮物,可使用小箱供给飞机燃料。“氢浆”是液氢通过一个由氦冷却的容器,把在容器壁     

中国散裂中子源氢循环系统的氢排放方案设计

为保障中国散裂中子源(CSNS)氢循环系统停机时,顺利、安全地将低温氢排放至大气中,设计一套可靠的氢排放系统非常重要。设计的氢排放系统包括氢排放管道、氢放空管、净化吹扫管道以及排放控制阀、阻火器、止回阀等装置。介绍了CSNS氢循环系统流程,CSNS氢排放方式和氢排放系统的流程,详细阐述了氢排放管道的设计和允许排放流量的计算。CSNS氢排放系统的设计考虑了CSNS装置的现场环境、风向、风速及居民区的距离,并通过计算确定了氢排放管道的长度,氢排放的最小流量和最大流量。     

A very light and thin liquid hydrogen/deuterium heat pipe target for COSY experiments

A liquid hydrogen/deuterium heat pipe (HP) target is used at the COSY external experiments TOF, GEM and MOMO. The target liquid is produced at a cooled condenser and guided through a central tube assisted by gravitation into the target cell. An aluminum condenser is used instead of copper, which requires less material, improves conductivities and provides shorter cooling down time. Residual condenser temperature fluctuations in the order of ≈0.4 K are reduced by using thermal resistances between the cooling machine and the condenser of the heat pipe combined with a controlled heating power. A new design with only a 7-mm-diameter HP has been developed. The diameter of the condenser part remains at 16 mm to provide enough condensation area. The small amount of material ensures short cooling down times. A cold gas deuterium HP target has been designed and developed which allows protons with energy ?1 MeV to be measured. A 7-mm-diameter HP is used to fill a cooling jacket around the D₂ gas cell with LH₂. The D₂ gas is stabilized at 200 mbar to allow for thin windows. Its density is increased by factor 15 compared to room temperature.     

Performance measurements of a 7 mm-diameter hydrogen heat pipe

A gravity assisted heat pipe with 7-mm diameter has been developed and tested to cool a liquid hydrogen target for extracted beam experiments at COSY. The liquid flowing down from the condenser surface is separated from the vapor flowing up by a thin wall 3 mm diameter plastic tube located concentrically inside the heat pipe. The heat pipe was tested at different inclination angles with respect to the horizontal plane. The heat pipe showed good operating characteristics because of the low radiation heat load from the surroundings, low heat capacity due to the small mass, higher sensitivity to heat loads (to overcome the heat load before the complete vaporization of the liquid in the target cell) due to the higher vapor speed inside the heat pipe which transfers the heat load to the condenser.     

Non-equilibrium two-phase refrigerant flow at subcooled temperatures in an R600a refrigeration system

A refrigeration system is typically designed such that the refrigerant reaches a subcooled state at the condenser outlet. A series of experiments are conducted to investigate the refrigerant state at the condenser outlet and the capillary tube inlet. The refrigeration system used in the present experiment is operated with R600a. The visual observations, as well as temperature and pressure measurements, demonstrate that R600a flows in a non-equilibrium two-phase state at highly subcooled temperatures. Furthermore, a set of equations is proposed for calculating the specific enthalpy of the refrigerant in a non-equilibrium two-phase state, and this calculation method is verified using experimental measurements. It is found that the thermodynamic property table does not provide an appropriate value of specific enthalpy in non-equilibrium conditions, while the enthalpy calculation method proposed in this work is in good agreement with the experimentally measured values.     

A novel special distributed method for dynamic refrigeration system simulation

A novel dynamic mathematical model based on spatially distributed approach has been developed and validated in this paper. This model gives good agreement in predicting the system COP and other parameters. The validated model has been used to enhance the prediction of the micro variations of superheat and sub-cooling. The novel spatial distributed model for the condenser and evaporator in refrigeration system, calculates the two-phase region in gas and liquid field separately since the gas and liquid in the two-phase region have different velocities. Previous researchers have used a pre-defined function of the void fraction in their spatially distributed model, based on experimental results. This approach results in the separate solution of the mass and energy equations, and less calculation is required. However, it is recognized that the mass and energy equations should be coupled during solving for more accurate solution. Based on the energy and mass balance, the spatial distribution model constructed here solves the velocity, pressure, refrigerant temperature, and wall temperature functions in heat exchangers simultaneously. A novel iteration method is developed and reduces the intensive calculations required. Furthermore, the condenser and evaporator models have shown a parametric distribution along the heat exchanger surface, therefore, the spatial distribution parameters in the two heat exchangers can be visualised numerically with a two-phase moving interface clearly shown.     

R290冷凝器的设计与制造

针对R290的性能特点和管内两相流的冷凝换热特性，设计并制造了R290／CO2复叠式制冷循环中的R290水冷式冷凝器，为自然工质R290／CO2复叠式制冷循环系统的研究和实际应用奠定基础。     

Visualization of refrigerant flow at the capillary tube inlet of a high-efficiency household refrigerator

The subcooled condition at the condenser outlet ensures complete condensation, which is necessary in vapor compression systems to increase the cooling capacity and ensure the liquid conditions at the expansion device inlet. However, in household refrigerators, recent works indicate the presence of two-phase flow at the capillary tube inlet. These systems behave quite differently from other refrigeration systems due to the extremely low capacity. In the present work, a test bench was built to visualize the refrigerant flow at the condenser outlet and at the capillary tube inlet of a commercial household refrigerator. A transparent tube replaced the end of the condenser and three transparent filters were installed with different orientations. Different positions of the capillary tube within the filters were also tested. Despite measuring a certain subcooling, all the reported visualizations showed that the capillary tube was steadily drawing in two-phase flow.     

R404A直接接触凝结制冷循环的性能分析

提出R404A直接接触凝结换热的制冷循环,分析R404A直接接触凝结制冷循环的热力性能,并与常规双级压缩制冷循环的性能进行对比。得出结论:在一定的冷凝温度、蒸发温度和过冷液体的过冷度下,直接接触凝结制冷循环存在最佳的饱和液体温度,并在此最佳的饱和液体温度下,获得最优的性能和最小的冷凝热负荷,随着过冷液体的过冷度增大和蒸发温度升高,直接接触凝结制冷循环的性能系数增加、冷凝热负荷减少,获得最优性能的最佳饱和液体温度值提高。过冷液体的过冷度为25℃时,直接接触凝结制冷循环的最佳性能系数较双级压缩制冷循环的最佳性能系数提高6.2%。直接接触凝结制冷循环的最小冷凝热负荷较双级压缩制冷循环的最小冷凝热负荷减小1.8%。     

Potential energy benefits of integrated refrigeration system with microturbine and absorption chiller

This paper presents and analyzes the performance potential of a refrigeration system that is integrated with a microturbine and an absorption chiller (RMA). The waste heat from the microturbine operates the absorption chiller, which provides additional cooling. This additional cooling capacity can be utilized either to subcool the liquid exiting the condenser of the refrigeration system or to precool the air entering the condenser in the refrigeration system. Moreover, any surplus cooling capacity not utilized in the subcooler can be utilized to precool the microturbine intake air. The additional assistance to the refrigeration system enhances the efficiency of the refrigeration cycle, which in turn reduces the required microturbine size. The smaller size of the microturbine enhances the part load efficiency, especially in lower ambient temperatures. With increased microturbine efficiency, RMA with subcooler, RMA with subcooler and microturbine intake air precooler, and RMA with condenser air precooler can reduce the annual energy consumption by 12, 19, and 3%, respectively, as compared to a refrigeration system operating without any waste heat utilization from the microturbine. Therefore, RMA with subcooler and microturbine intake air precooler has the best potential of energy savings. The payback period of RMA with subcooler and microturbine intake air precooler is estimated in 3 years, which facilitates it as an economically feasible solution among the options investigated.     

Investigation of helium injection cooling to liquid oxygen under pressurized condition

Sub-cooling of cryogenic propellant by helium injection is one of the most effective methods for suppressing bulk boiling and keeping sub-cooled liquid oxygen before rocket launch. Compared with the helium injection cooling under atmospheric condition, helium injection cooling under pressurized condition has advantage that it can greatly reduce re-warming time of the sub-cooled liquid oxygen. Helium injection cooling under pressurized condition is characterized by cooling of initially sub-cooled cryogenic liquid, which is significantly different from that of the atmospheric condition where liquid oxygen usually exists at saturated condition. In this paper, we discuss the characteristics of helium injection cooling under pressurized condition, with the associated physical understanding of the process. Experimental results are presented along the simulations of variously combined system parameters based on the finite heat transfer and instantaneous diffusion mass transfer model. A non-dimensional parameter for identifying the cooling regime is conceived. The critical values of the non-dimensional parameters and injected helium temperatures are also estimated.     

Measurements of the Nuclear Spin Relaxation Times for Small Grains of Solid Hydrogen Suspended in Liquid Helium

Measurements of the nuclear spin-lattice relaxation times (T ₁) and the nuclear spin-spin relaxation times (T ₂) are reported for suspensions of small grains of solid hydrogen in liquid helium. The measurements have been carried out for temperatures 1.8>T>4.9 K and for a nuclear Larmor frequency of 4.0 MHz. The samples were prepared by rapid condensation of hydrogen and helium gas in a precooled cell. The hydrogen pressure was maintained below the triple point to prepare a “slush” of hydrogen particles in liquid helium. The characteristic relaxation times are much shorter, typically by an order of magnitude for T ₂, than those observed and reported previously for bulk samples of solid hydrogen for the same ortho-hydrogen concentrations and applied magnetic fields. Possible origins for this difference between the relaxation in bulk and micro-geometries are discussed.