共查询到19条相似文献,搜索用时 125 毫秒
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该装置由11T超导强磁体;ф_内=30mm室温孔径的金属内杜瓦瓶;80升液氦金属外杜瓦瓶;JWL-150A超导磁体电源以及防辐射屏、吊杆、引线等五部分构成。金属内杜瓦瓶直接插在磁体内径中,其实验空间与外界相通,它可在4.2—400K之间变温,在0—10T之间改变磁场强度,也可随时更换测试样品。金属外杜瓦瓶采用气冷多屏绝热的结构。它自身的蒸发率为0.21升/小时。在内杜瓦瓶温度~70K、场强为10T时,液氦蒸发率为1.3—1.6升/小时之间。 相似文献
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低温液体蒸发气再液化系统漏热引起的储罐内低温液体蒸发气(BOG)蒸发速率和压力有效控制是试验正常进行的关键,通过对储罐内低温液体的热响应分析,建立罐内低温液体和BOG计算模型,对制冷机关闭情况下储罐内压力(BOG压力)和BOG蒸发速率随储存时间的变化过程进行数值计算。结果表明:随着储存时间的增大,储罐内压力升高、压力增长速率加快、BOG蒸发速率减小;液氮和BOG温度升高对储罐内压力升高速率具有显著的影响;制冷机可以实现对罐内压力和BOG量的调节控制。为制冷机控制方案的制定和后续开展低温液体BOG再液化试验研究提供理论基础。 相似文献
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由我们研制的几种杜瓦瓶表明,将多层绝热结构应用于低温液氦实验杜瓦瓶,代替液氮保护,可以得到良好的效果. 我们研制的口径为φ5120mm、φ150mm、φ200mm,内胆容积分别为10升、27升、38升,用铝箔和玻璃纤维纸作多层绝热结构的液氦实验杜瓦瓶液氦平均蒸发率分别为100毫升/小时、120毫升/小时、180毫升/小时,适于低温实验室推广使用. 另一个口径为φ120mm,内胆容积为10升,用喷铝涤纶薄膜和两个铜屏作多层绝热结构的液氦实验杜瓦瓶已使用六年,液氦蒸发率小于200毫升/小时.在该杜瓦瓶夹层中放有八个铜-康铜热偶温度计,提供了有关屏温分布的参考数据. 相似文献
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谢柳辉朱华强蔡延彬张夏 《低温与超导》2022,(6):97-102
蒸发率是低温气瓶绝热性能的一项重要指标,本文将气瓶做一维传热过程分析,采用二维轴对称的VOF(Volume of Fluent)模型,数值模拟研究了压力和充满率对低温绝热气瓶蒸发状态的影响。结果显示,当气瓶工作压力数倍于大气压力时,压力越高,气瓶出口蒸发质量流量越高。在蒸发过程中,气瓶内液相区温度基本保持不变,而气相区温度则出现明显的分层现象。当充满率降低时,由于液体减少,蒸发质量流量随之降低,但仍随着工作压力的升高而增大。 相似文献
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根据低温推进剂长时间在轨贮存的要求,设计并搭建了绝热系统地面验证测试装置,对绝热系统的热力学性能进行测试。针对55L贮箱,采用了泡沫绝热(spray on foam insulation,SOFI)和多层绝热(multilayer insulation,MLI)结合的复合绝热系统,分别在高真空(5×10^-3Pa以上)和大气压条件下进行了验证实验(液氮作为替代工质)。贮箱外绝热系统为15m m厚泡沫绝热层和45组多层绝热时,高真空条件下液氮日蒸发率为0.77%,多层绝热层表观热导率为1.29×10^-4W/(m·K),据此折算为液氧时日蒸发率为0.55%。将高真空和大气压条件下的实验结果比较发现,泡沫绝热层所占热阻分别为总热阻的0.19%和45.14%。 相似文献
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Quantitative measurements on field evaporation of Si(111) surfaces in hydrogen imaging gas have been carried out by field ion microscopy. The field evaporation rate is found to increase exponentially with increase of the reciprocal of tip temperature in the range 80–103 K. The evaporation field strength increases with increase of tip temperature in the investigated range, 80–300 K. Within the applied pressure range, 5× 10?6 to 2 × 10?4 Torr of hydrogen gas, the evaporation rate linearly increases with the gas pressure. Similar effects of temperature and gas pressure on field evaporation of Si(111) surfaces have been observed also in silane imaging gas. A model, based on a field-induced formation of surface hydrides as a rate-determining step, is proposed, which accounts for all the experimental results of the field evaporation process. 相似文献
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We have measured the oxidation rate of tungsten and the evaporation rate of tungsten oxide in the temperature range from 900 to 1200 K at an oxygen pressure from 5 × 10?4 to 5 × 10?3 Torr. The oxidation rate increases steadily with coverage in the whole range studied. The evaporation rate decreases at high pressure and is strongly dependent on the initial conditions of the experiments. These kinetic measurements support a qualitative model of oxidation. The surface is composed of oxide islands surrounded by oxide-free regions covered only by chemisorbed oxygen atoms. On the bare regions beside the chemisorbed oxygen atoms we suppose the existence of a dilute chemisorbed oxide layer which can either enter the condensed oxide phase or evaporate. The number of the growing islands is set up at the beginning of the reaction and does not increase further. This model, consistent with kinetic results during oxidation, has been proposed first to explain results obtained by Auger electron spectroscopy and thermal desorption spectroscopy under vacuum. Faceting is particularly important in the early stages of the experiment because it can hinder the nucleation of the oxide which is a necessary step for growth. In a narrow range of temperature and oxygen pressure this inhibited nucleation leads to an enhanced evaporation rate so that the growth rate is lower. Recording this growth rate allows us to follow faceting. The parameters studied are the oxygen coverage and the temperature, experimental results are in agreement with LEED and RHEED results. Reconstruction and faceting are discussed and are believed to be caused by a smoothing of the surface during the chemisorption step. 相似文献
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湿分分层土壤中热湿迁移与水分蒸发的实验研究 总被引:2,自引:0,他引:2
在自然环境下,对土壤中温度和湿分分布以及水分蒸发的动态特性进行了实验研究,分析了干饱和层对土壤热湿迁移及水分蒸发的影响。结果表明: (1)在周期性变化的大气环境条件下,土壤温度、湿分含量和水分蒸发强度在一天内变化;随着土壤温度的降低,土壤水分含量在晚上会出现略有增加的情况。(2)形成干饱和层后,水分蒸发锋面由土壤表面下移至非饱和层与干饱和层界面处,水分蒸发强度明显减弱,干饱和层的厚度增长缓慢。(3)随着干饱和层不断向深处发展,土壤温度的日变化幅度增大,且随着土壤深度的增加,土壤温度变化呈现出明显的滞后性。 相似文献
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冷却物冷藏间冷风机的空气除霜实验研究 总被引:1,自引:0,他引:1
冷却物冷藏间以贮藏果蔬为主,当贮藏品种产于热带地区,贮藏温度高于0℃。由于贮藏温度距水的冰点不远,制冷系统的蒸发温度会低于冰点,在工作过程中蒸发器表面必然结霜。文中对冷间温度高于冰点,蒸发温度低于冰点的冷库制冷系统,进行了空气除霜和"依次除霜法"实验,通过冷风机回风区空气温度、冷风机蒸发管组翅片温度的测量,结合肉眼观察认为,库温为5℃的情况下,依靠制冷压缩机停机阶段,冷风机风扇常开,能够基本除掉上次制冷过程产生的结霜,当制冷系统规律工作8小时,前期制冷过程积累的结冰可以通过"依次除霜法"依次关闭除霜冷风机的供液电磁阀15分钟,在保证库房降温的前提下,能够彻底除掉蒸发器表面的结霜。 相似文献
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We describe a variable temperature cryogenic scanning tunneling microscope designed for imaging and research in cryogenic liquids. It has an external Dewar type large scale cooling system with a temperature control range of roughly 85-110 K using pressure controlled liquid nitrogen cooling. The liquid nitrogen is kept in a closed chamber surrounding the STM and maintained at a pressure to suit the chosen temperature. Several gases have triple points in this temperature range and can therefore be liquified, such as argon, methane, silane and germane. The STM is based on a beetle type design built into a small cube vacuum chamber to fit into the cooling dewar. The system has been used for atomic resolution of highly oriented graphite submerged in a methane liquid at a temperature of 100 K. 相似文献