低温绝热气瓶真空寿命模拟试验研究

提出了对绝热气瓶真空夹层逐次充入模拟气体进行绝热气瓶漏气和材料放气的真空寿命模拟试验评价方法。试验实例表明:低温绝热气瓶静态蒸发率在低温下夹层压力>5×10^-2Pa后迅速上升,即5×10^-2Pa可视为夹层真空寿命终结的拐点(或阈值)。5A分子筛在液氮温度下对氮具有巨大的吸附潜力,对氢表现出弱的吸附能力。真空绝热夹层的材料放气对真空寿命的影响远远大于漏气的影响,提高绝热气瓶真空寿命的技术途径是减小夹层材料的放气率和改善内置吸附剂对氢的吸附能力。模拟试验能直观、实际、准确地研究漏气和放气对真空寿命诸因素的影响,为确定切合实际的设计参数和工艺提供参考数据,进而推广用于各类真空绝热型低温容器的真空寿命评价和应用。     

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。     

多层绝热低温容器真空夹层中的残余气体质谱分析

介绍了多层绝热低温容器进行真空夹层残余气体质谱分析的目的、方法和装置,分别测出被测低温容器在注入液氮之前、之后的残余气体质谱图。分析结果表明:容器经过抽真空封口后,因多层绝热材料放气,夹层真空逐渐降低,其放气的主要成份是氢,其次是H_2O和CO、N_2等;装入液氮后,夹层真空会有较大幅度地提高,这时残气成份几乎全是氢。认为材料放气中的氢是获得和长期维持更好真空的主要限制因素。最后提出减少氢气量的三点技术措施。     

在用LNG低温真空绝热容器漏热量监测

LNG低温真空绝热容器在使用过程中因真空绝热夹层内材料放气、漏气以及夹层材料的老化、松散等原因,可导致低温容器真空绝热性能下降,致使低温容器内的低温液体的蒸发量增加,造成液体的浪费,此时储罐蒸发率可能超过要求,使得储罐不能继续使用。论文介绍了一种简单的方法对低温容器的漏热量进行实时监测,若储罐漏热量超过限定值时报警提醒,确保低温容器的使用安全、人员安全。     

玻璃钢及多层绝热材料真空放气速率试验研究

在低温储运时，由于真空夹层中材料的放气，夹层真空度会下降，热量从外界导入使得低温容器的蒸发率加大，低温液体损耗增加，真空寿命缩短。因此，对真空夹层中材料放气性能的研究非常重要。本文基于静态升压测量法，搭建了真空下材料放气率测试装置，进行了低温储罐用多层绝热材料和玻璃钢真空下放气速率测试研究，得到了多层绝热材料和D3848玻璃钢的单位面积放气速率分别为4.93×10^-8Pa·m³/(s·m²)和1.13×10^-7Pa·m³/(s·m²)，该结果可以为真空夹层吸附剂量的设计提供可靠依据。     

高真空多层绝热低温容器真空丧失后的传热试验

利用一个工业化的高真空多层绝热低温量热器,以液氮为介质研究了真空突然丧失对高真空多层绝热低温容器漏热量的影响.主要研究了低温量热器绝热层的变化及破空气体(空气和干燥氮气)的不同对真空丧失后低温容器漏热量的影响,指出绝热层数和破空气体种类都是影响真空丧失后低温容器漏热量的重要因素.     

高真空多层绝热低温容器完全真空丧失后传热及绝热夹层内温度分布规律实验

在搭建了高真空多层绝热低温容器完全真空丧失传热研究实验台的基础上,分别利用干燥氮气、二氧化碳、氧气、氦气及空气为破空介质,进行了高真空多层绝热低温容器发生完全真空丧失事故后的传热实验研究.实验中通过流量计和温度采集系统测得了高真空多层绝热低温容器在发生完全真空丧失事故后的排放率和绝热夹层内的温度分布规律.实验结果表明,...     

真空保温杯常用材料放气特性研究北大核心CSCD

材料放气是真空保温杯真空度保持和寿命的重要技术指标。本文利用新型基于转换气路法材料放气率测试系统,对钛合金钢、304不锈钢和银等三种真空保温杯常用材料在室温、200℃、400℃真空条件下的放气率和放气成分等特性进行了研究。结果表明,室温下三种材料的放气率由小到大依次为钛合金钢、304不锈钢和银,放气成分均主要以H2分子和H2O分子为主;在温度升高过程中,三种材料放出的H2O分子含量均会缓慢减少,但是放出的H2分子含量的变化趋势却有所不同,304不锈钢和银的H2分子含量随温度升高呈现先增大后减小的趋势,而钛合金钢中H2分子含量则快速增大。因此,在真空除气工艺中,304不锈钢和银的烘烤温度设置400℃以下即可,而钛合金钢内部H2分子含量较高,较难除去,除气工艺应高于400℃。     

液位高度对低温绝热气瓶漏热量的影响分析

为了研究低温液体在存储过程中由于蒸发和使用造成的容器传热面积和传热路径变化问题,考虑了瓶外的自然对流换热、瓶内的液体温度以及气瓶沿轴向、径向的固体导热,利用数值模拟的方法建立了低温绝热气瓶的稳态传热模型,分析计算了不同液位高度下的温度场与漏热量,获得了液位高度与低温绝热气瓶漏热量之间的关系。研究结果表明:当气瓶容积一定时,随着液位升高,气瓶的漏热量逐渐增大。     

真空下非金属材料放气模型与研究综述

总结了放气研究在工业领域的各种应用．分析了真空环境下非金属材料放气的三种模型：Schram模型、扩散模型和基于马列夫理论吸附扩散模型。对国内外非金属材料放气的研究状况进行了论述。     

Increased strength and related mechanisms for mortars at cryogenic temperatures

Properties of cement-based materials at cryogenic temperatures are quite different from those at room temperatures. The strength of mortars at cryogenic temperatures was experimentally studied and an empirical model was established. The freezing thermodynamic process of pore water and pore size distribution in mortars were characterized by differential scanning calorimeter (DSC) and thermoporometry (TPM), respectively. The relationship between the increased cryogenic strength and pore ice formation was discussed. The results showed that flexural strength of mortars increased at a higher rate than compressive strength. Water content and initial strength at room temperatures were the main factors influencing the cryogenic strength. Higher water content and higher initial strength resulted in higher cryogenic strength. Ice formation in pores is one of the main reasons for the mortar’s cryogenic strength increase. Nearly half of the water remained unfrozen in pores with radius less than 40 nm at −40 °C. Both ice formed in capillary pores and gel pores contributes to the strength increase observed at cryogenic temperatures.     

车载LNG储罐蒸发率的理论与试验

为研究车载LNG低温绝热气瓶内液体的蒸发规律,以200 L高真空多层绝热气瓶为例,采用液氮(LN2)为工质,进行了一系列LN2日蒸发率试验。列出根据实验系统结构参数得到的相关传热学计算结果,包括试验系统分别贮存LN2和LNG各项漏热及理论蒸发率。对理论计算与实验结果进行比较,通过理论计算结果与LN2蒸发率实验结果对LNG试验蒸发率作了预测。根据大气压力下进行的各种充满率的LN2蒸发率实验,拟合出了系统蒸发率与充满率的关系曲线,并分析了系统中环境温度和压力对蒸发率的影响规律。     

Effect of cryogenic treatment on the tensile behaviour of En 52 and 21-4N valve steels at room and elevated temperatures

This experimental study investigates the effects of cryogenic treatment on the tensile behaviour of En 52 and 21-4N valve steels at room and elevated temperatures. The materials are subjected to shallow cryogenic treatment (SCT) at 193 K and deep cryogenic treatment (DCT) at 85 K and the tensile behaviour is compared with that of the conventional heat treatment (CHT). The high temperature tensile test is conducted at 673 K (400 °C) and 923 K (650 °C) for the En 52 and 21-4N valve steels respectively. The ultimate tensile strength of the En 52 and 21-4N DCT samples show an enhancement of 7.87% and 6.76% respectively, over the CHT samples tested at the elevated temperature. The average yield strength of the En 52 DCT samples has an improvement 11% than that of the CHT samples when tested at room and elevated temperatures. The deep cryogenic treatment conducted at the optimized condition shows 7.84% improvement in the tensile strength for the En 52 valve steel and 11.87% improvement for the 21-4N valve steel when compared to the strength of the samples without the cryogenic treatment. A scanning electron microscopic analysis of the fracture surface indicates the presence of dimples and microvoid coalescence on the grain facets and interfaces of the cryo-treated specimens. The fracture surface of the deep cryo-treated 21-4N valve steel specimen shows a complete intergranular fracture with deep secondary cracks between the grains. On comparing the results of the percentage elongation, the cryo-treated samples show a smaller reduction in the elongation than that of the CHT samples. It is concluded that the precipitation of fine secondary carbide through cryogenic treatment is the reason for the improved strength and the reduction in elongation.     

SiO2/环氧树脂基纳米复合材料的室温和低温力学性能

利用溶胶-凝胶法制备了SiO₂/环氧树脂基复合材料,研究了材料的室温与低温(77 K)下的力学性能。结果表明,适量SiO₂的引入提高了室温与低温下材料的拉伸强度、断裂伸长率和冲击强度,即SiO₂含量在2%时可同时起到增强、增韧作用。采用扫描电镜(SEM)和透射电镜 (TEM)分别对复合材料的断口形貌和高温焚烧后残留物纳米颗粒进行了观察。还利用动态力学分析(DMA)研究了二氧化硅的引入对复合材料的影响。      

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。     

二氧化硅/ 聚酰亚胺纳米杂化薄膜室温及低温力学性能

利用溶胶-凝胶技术制备了不同SiO₂ 含量的二氧化硅/ 聚酰亚胺(SiO₂ / PI) 纳米杂化薄膜。采用红外光谱( IR) 和扫描电镜(SEM) 手段对该体系的分子结构和断裂形貌进行了表征, 研究了聚酰亚胺薄膜室温和低温(77K) 力学性能。结果表明: 室温和低温(77 K) 下, SiO₂ / PI 杂化薄膜的拉伸强度开始时均随SiO₂ 含量的增加而增加, 在含量为3 %时达到最大值, 低温下杂化薄膜的拉伸强度明显高于室温。室温下, 杂化薄膜的断裂伸长率在含量为3 %时达到最大值, 而低温(77 K) 下, 薄膜的断裂伸长率的变化没有呈现明显的规律性。      

Dielectric and piezoelectric properties of perovskite materials at cryogenic temperatures

Dielectric and piezoelectric properties of perovskite materials including La modified Pb(Zr, Ti)O3 (PZT's), (Ba, Sr)TiO3 (BST) polycrystalline ceramics and Pb(Zn1/3 Nb2/3)O3-PbTiO3 (PZN-PT) single crystals were investigated for capacitor and actuator applications at cryogenic temperatures. PZTs were compositionally engineered to have decreased Curie temperatures (Tc) by La and Sn doping in order to compensate for the loss of extrinsic contributions to piezoelectricity at cryogenic temperatures. Enhanced extrinsic contributions resulted in piezoelectric coefficients (d33) as high as 250 pC/N at 30 K, superior to that of conventional DOD Type PZT's (d33~100 pC/N). This property enhancement was associated with retuning to the MPB at cryogenic temperatures. 5/95 BST with a dielectric maximum at 57 K was investigated to obtain high electrostrictive properties or E-field induced piezoelectricity. Coupling coefficients (k31) 25% comparable to those of the cryogenic PLZT piezoelectrics were observed at d.c. bias of 1.5 kV/cm and 50 K. Though significantly lower than the room temperature values, PZN-PT rhombohedral single crystals exhibited d33> 500 pC/N at 30 K.     

Metallurgical effects in niobium-titanium alloys

The effects of metallurgical treatments on some of the physical, metallurgical, and mechanical properties of commercial purity Nb-34-wt % Ti, Nb-45-wt % Ti, and Nb-55-wt % Ti, were studied by measuring properties of annealed and metallurgically processed materials at both room and cryogenic temperatures. Processing strengthens all three materials, but significantly changes the electrical resistivity of only Nb-55-wt % Ti. The behaviour of the electrical resistivity of Nb-55-wt % Ti upon deformation at 76 K suggests the occurence of a systematic transformation (twinning or martensitic phase transformation).     

低温绝热气瓶的有限元热分析与试验研究

通过有限元方法对充满低温液体的气瓶进行传热分析,与试验的结果相结合,分析气瓶的颈管、支撑结构和绝热结构的漏热量并对产品结构进行优化设计,来保证达到优良的绝热性能.