一种用于飞秒激光实验的柔性真空低温系统

为满足某飞秒激光实验需要,研制了一套低温系统,该系统由真空腔体和制冷系统组成,制冷系统冷源为液氮或液氦。在实验晶体样品的周围使用4个并联电阻加热片提供加热功率,通过PID控制策略,可以将晶体温度控制在5—300 K范围内的任何点。除此之外,该低温系统引入了柔性的输液和排气管路,能够保证晶体在二维移动平台控制下实现一定范围内的移动和转动。介绍了整个真空低温系统的组成,并对系统漏热和晶体温度分布进行了数值模拟,完成了温度测量与控制实验。实验结果表明,通过采用冷气体调节与PID组合的控制策略,当在5—80 K内使用液氦作为冷源时,晶体温度的波动小于0.9 K,当在80—300 K内使用液氮作为冷源时,晶体温度波动小于1.3 K。     

制冷机作冷源的低温气体吸附测量装置研制

为研究气体在低温下的吸附特性,设计并搭建了低温气体吸附测试平台,其测温范围为5—300 K,测压范围为真空至20 MPa。该装置以G-M制冷机为冷源,摆脱了对低温液体的依赖,可以稳定地维持所需的低温环境,具有可靠性高、维护方便、结构紧凑等优点。利用所述装置,在活性炭样品上测量了氮气和氦气在20—160 K温区内的吸附等温线,并且对吸附等温线方程进行了拟合。     

半导体功率器件测试用脉冲高压源的设计与实现

为满足精密测温需求,解决标准光电高温计测温结果易受环境温度影响的问题,设计多点控温系统,该系统通过多点布控的方式实现内层壳体整体控温,应用薄膜加热片作为控温元件,并采用自主设计的控温电路。开展试验对该系统的控温稳定性、重复性以及标准光电的测温稳定性进行了验证,结果表明多点控温系统稳定后2.5 h波动0.09 ℃,三天控温重复性0.1 ℃。室温环境下,应用标准光电高温计测试银固定点黑体辐射源,使用多点控温系统与不使用多点控温系统时的测温波动分别为0.1 ℃和0.7 ℃。本文研制的标准光电高温计多点控温系统具有稳定性好、体积小、重量轻、易于控制等优点,能够有效满足标准光电高温计的精密测温需求,为促进国产精密测温仪器的性能提升起到推动作用。     

基于低温制冷机的低温流体电容式密度测量

设计并搭建了一套基于G-M低温制冷机的电容式密度测量实验装置,由平行板电容器、样品流体测试腔、充排气体管路、低温制冷机、温度测量与控制单元、压力测量单元、真空绝热保护腔以及高真空排气系统八个部分组成。该系统适用温度测量范围为15—300 K,压力测量范围0.01—0.3 MPa。实验中的低温液体由常温气体经低温制冷机冷却液化得到,并蓄存在装有平行板电容器的样品测试腔内。该测试腔上开有视窗,可用于观察冷却过程中低温液体的形成及其液位。对受控压力及温度下的液氮、液氩两种低温流体的密度进行了测量,所得数据与文献实验值及美国NIST标准数据吻合良好,液相区相对偏差小于±0.5%。该密度测量系统今后可用于测量其他流体(包括混合物)在低温下的p-ρ-T数据,还有望经过改进和集成化设计后实现LNG和空分等工业领域的低温流体密度在线实时监测。     

4.2—280K宽温区低温电磁驱动式热开关实验研究

为了在低温温度标定系统中实现超宽温区控温,研制了一种以电磁力驱动的主动机械式热开关,相比常规的气隙式或者材料热胀冷缩式热开关,具有工作温区宽、响应速度快等优点。以一台两级G-M低温制冷机为冷源,搭建了温度低至4.2 K的低温热开关性能试验台。通过升降温过程中的控温对比实验,测得该热开关在50 K时闭合热导为1.5 W/K,断开热导为1.2 m W/K,开关比为1 250;在240 K时闭合热导为0.4 W/K,断开热导为0.5 m W/K,开关比为80。     

20—80K低温压力传感器校准系统的研制

针对低温压力传感器的精确测量,设计并搭建了一套20-80 K低温压力传感器校准系统,介绍了系统中恒温试验腔的原理、结构及连接方式,验证了恒温试验腔内温度场的均匀分布。恒温试验腔完全浸没在液氢中,通过温度控制系统调节腔内电加热丝功率,来实现对测试环境温度的控制。试验结果表明,该系统结构紧凑,安全可靠性高,性能稳定,测试温区内变温有良好的温度梯度,温控精度在±0.2 K以内,可通过压力标准源对安装在恒温试验腔内的低温压力传感器进行精确校准。     

控温包装控温时间预测模型研究

目的建立控温包装控温时间预测模型,保护温度敏感产品在一定时间内不受外界温度变化的影响。方法以典型长方体产品的控温包装为研究对象,通过计算控温包装系统热阻及控温包装内蓄冷剂的吸热量,建立控温包装控温时间预测模型。同时,基于2种典型控温包装产品在296,308,318 K等3个温度环境中的储藏试验,进行理论与实验验证。结果实际控温时间比模型预测时间长,但偏差均小于10%。结论该理论模型能准确地预测控温包装控温时间,研究成果为控温包装设计提供了理论依据。     

采用低温流体氘和氧的介电常数测量流体的密度

为测量低温流体在不同受控状态下的密度,设计了一套基于G-M低温制冷机的介电常数法低温流体密度测量实验装置,该实验装置适用温度测量范围为15~300 K,压力测量范围0.01~0.30 MPa。实验中的低温液体由常温气态流体经低温制冷机冷却液化得到,蓄流在装有平行板电容器的样品流体测试腔内。该测试腔上开有视窗,可用于观察冷却过程中低温液体的形成及其液位情况。对受控压力及温度下的液氘、液氧的密度进行了测量,所得数据与文献实验值及美国NIST标准数据吻合良好,液相区相对偏差小于±0.5%,满足高精度p-ρ-T热物性参数的需要。     

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。     

电涡流式位移传感器低温标定系统及其误差分析

介绍了一种能在20 K～300K温度范围内对电涡流式位移传感器进行静态标定的系统,着重分析了该系统的温度及位移误差,并对传感器进行了20 K,90 K的标定实验.该标定系统具有多通道数据采集与处理、自动温控、观察窗可视操作等特点,工作区温控精度优于±1 K,位移给定精度0.001 mm.经适当改进后还可对其它原理位移传感器进行低温标定.     

Liquid helium free mechanical property test system with G-M cryocoolers

In the present work, a cryogenic mechanical property testing system conduction-cooled by two G-M cryocoolers was developed. The testing sample can be cooled from room temperature to 2.7 K within 7.5 h. The sample was first cooled down to 11.1 K directly by the two G-M cryocoolers and then cooled down to 2.7 K by decompressing the chamber. Instead of liquid helium, the cooling process is characterized by cooling with recycled helium gas as heat transfer medium. The heat load of the system was analyzed and optimizations were adopted in terms of material selections and design. The static load capacity of the system reaches 200 kN and the fatigue load capacity can reach 50 kN. This system can be installed onto an electronic universal testing machine or a fatigue testing machine to characterize static tension, fracture mechanics or fatigue properties at tunable low temperatures. Tensile properties of 316L austenitic stainless steels at 4.2 K were tested with the system and the results were compared with those obtained by cooled using liquid helium, which demonstrates high reliability.     

温度、应变率对航空PMMA压缩力学性能的影响研究

本文利用INSTRON试验机和分离式Hopkinson压杆测试了航空有机玻璃在试验温度为299K～373K之间,两种准静态应变率(10-3,10-1 1/s)和一种动态应变率(550 1/s)下的压缩力学行为.试验结果表明:在准静态载荷下,随着温度的升高,材料的弹性模量和流动应力减小,在应变率为10-1 1/s时表现出明显的应变软化行为;在高应变率(550 1/s)下,随着温度的升高,材料的流动应力逐渐减小而破坏应变增大,当温度超过333K时也有应变软化现象发生;在相同温度下,随着应变率的升高,材料的流动应力增大,但破坏应变减小.通过观察变形后试样的形貌,可以认为试样内部的微裂纹是应变软化的主要原因.最后,ZWT粘弹性本构模型被用来对试验数据进行拟合,结果表明该模型能够较好地预测这种材料在应变8%以内的力学行为.     

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.     

Cooling cycle effects on low temperature cracking characteristics of asphalt concrete mixture

The effect of cooling cycles on the low temperature behavior of asphalt concrete mixtures is investigated using a recently developed acoustic emission (AE) test device. In an attempt to link the local AE response of the asphalt mixtures to the pavement global response obtained through mechanical tests, the AE-based results were validated using traditional mechanical pavement performance testing methods namely, the disk-shaped compact tension [DC(T)] test and the indirect tensile test (IDT) method. Field-aged pavement cores, which were expected to have a gradient in binder aging properties (more aging near the surface of the pavement), were collected and tested. Test results revealed that significant damage resulted from cyclic cooling, effecting the fracture energy and stress relaxation ability of the asphalt mixture. The AE results collected were consistent with the results obtained using the DC(T) and the IDT test methods. The so-called Felicity effect was observed by evaluating AE activity occurring in a sample subjected to multiple cooling cycles and an AE based healing index was introduced to evaluate the amount of healing that resulted from warming cycles. Low temperature induced microdamage was also investigated using X-ray computer micro-tomography, in an effort to better understand the physical nature of microcracking in asphalt mixtures at low temperatures and the source of AE emissions detected.     

Cryogenic refrigeration using a low temperature heat source

A non mechanical gas sorption refrigeration system which could be powered by a low temperature heat source was designed and analysed. The system involved no sealing, no mechanical moving parts and no active control. The system was analysed using a 1 W cooling load at 74 K as an example. It was found that the new system was competitive with a passive radiator and superior to a solid cryogen system.     

热加工对管线用低碳钢性能的影响

通过热模拟实验,研究了一种管线钢相变组织的形成规律,在此基础上,进行两阶段多道次控轧和在适度冷却速度下控冷的控制热加工实验,分析了工艺参数对钢的组织结构和力学性能的影响。结果表明,开轧温度、终轧温度、终冷温度和冷却速度对管线钢的力学性能有强烈的影响。通过优化工艺,获得了以针状铁素体为主的混合组织,针状铁素体的含量越多,材料的力学性能越好。     

Design and performance of a 4He-evaporator at <1.0 K

A helium evaporator for obtaining 1 K temperature has been built and tested in laboratory. This will function primarily as the precooling stage for the circulating helium isotopic gas mixture. This works on evaporative cooling by way of pumping out the vapour from the top of the pot. A precision needle valve is used initially to fill up the pot and subsequently a permanent flow impedance maintains the helium flow from the bath into the pot to replenish the evaporative loss of helium. Considering the cooling power of 10 mW @1.0 K, a 99.0 cm³ helium evaporator was designed, fabricated from OFE copper and tested in the laboratory. A pumping station comprising of a roots pump backed by a dry pump was used for evacuation. The calibrated RuO thermometer and kapton film heater were used for measuring the temperature and cooling power of the system respectively. The continuously filled 1 K bath is tested in the laboratory and found to offer a temperature less than 1.0 K by withdrawing vapour from the evaporator. In order to minimize the heat load and to prevent film creep across the pumping tube, size optimization of the pumping line and pump-out port has been performed. The results of test run along with relevant analysis, mechanical fabrication of flow impedance are presented here.     

基于液氮冷源超导磁体氦气循环预冷系统设计

为了提高超导磁体300-80 K预冷过程中的降温效率和安全性,开发了一种新的预冷方法.设计了一台以液氮为冷源、氦气为循环介质的可控温预冷装置,对其内部结构进行了优化设计,包括低温风机、板式换热器、气动调节阀、翅片换热器等主要组成部分,整个装置与磁体构成一个闭合循环系统.在预冷装置的作用下,该超导磁体从300 K到80 ...     

道间温度对10CrNi5MoV钢气体保护焊接头力学性能的影响

通过屈服强度和冲击韧性测试、组织分析,研究了两种焊接热输入条件下道间温度对10CrNi5MoV钢气体保护焊接头力学性能的影响。结果表明,随着道间温度从40℃提高到300℃,焊接热输入为8 kJ/cm和18 kJ/cm的焊缝金属屈服强度分别从868 MPa和855 MPa单调下降至728 MPa和693 MPa,-50℃冲击韧性分别从70 J和69 J升高至117 J和72 J(道间温度分别为200℃和100℃),然后降低至67 J和43 J;焊缝金属的组织差异是不同道间温度下焊接接头力学性能不同的原因。随着道间温度从40℃提高到300℃,焊缝金属中马氏体组织逐渐消失,粒状贝氏体组织逐渐增多,针状铁素体组织比例先增加再减少,含量最高时的道间温度与冲击韧性峰值水平相一致。     

Tensile properties and thermal expansion of discontinuously reinforced aluminium composites at subambient temperatures

The effects of temperature on the mechanical properties and thermal expansion of two discontinuously reinforced aluminium composites have been determined over the range 300–100 K. Silicon carbide particulate-reinforced 2009 and 6092 aluminium alloys were studied by tensile testing, in which both longitudinal and transverse strains were recorded, and by thermal expansion measurements. The test results clearly show that cooling to 100 K induces plastic flow in the aluminium alloy matrices due to the thermal expansion difference between aluminium and silicon carbide. At very low temperatures, the linear region of the stress-strain curve is greatly reduced or eliminated and the Poisson’s ratio, ν, increases. For the higher yield strength 2009 matrix composite, ν increases from a room-temperature value of 0.28 to 0.35 at 100 K. For the lower-strength 6029 matrix composite, ν increases from a room-temperature value of 0.33 to a value of 0.5 at 100 K. A Poisson’s ratio of 0.5 is the value characteristic of plastic flow in an incompressable material. Changes in yield strength, Young’s modulus and thermal expansion with decreasing temperature are also consistent with thermally induced plastic flow in the composite matrix. This revised version was published online in November 2006 with corrections to the Cover Date.