超导电缆波纹管内过冷液氮流动阻力特性研究

基于Fluent软件,采用30 m高温超导电缆模型,分析了波纹管几何结构对恒温器内液氮压力损失的影响,也与光滑管的流阻特性进行了对比分析.结果表明:压力损失与液氮流量的平方成正比,在相同体积流量下,过冷液氮在波纹管内的压力损失随着波纹管波距的增大而减小,随着波纹管波高的增大而增大.     

液氮罐内低温氮气的温度场研究

对装有少量液氮的液氮罐内的温度分布进行了系统研究,提出了相应的温度分布模型.研究表明,在10 L容积的液氮罐内注入少量液氮时,罐内温度可保持低于-130℃持续约25天,适用于多种场合的超低温保存.通过调节距离液氮面的高度,可选择保存样品的温度范围并控制样品的升降温速度.理论计算的温度分布与测量的结果符合较好,证实了所建立模型的合理性和有效性.     

Contact thermal resistance of some graphites

Experimental data on the contact thermal resistance of VPP, ARV, and MPG-6 graphites in relation to the compression and finish of the contact surfaces are given.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 33, No. 3, pp. 455–459, September, 1977.     

Contact resistance in air-cooled plate fin-tube air-conditioning condensers

Test equipment and procedures have been developed to measure the heat transfer performance of an industry-standard wavy plate fin-tube condenser, and to compare it with alternative designs. Two test rigs were employed: one used direct electric heating, and the other used an R22 thermosyphon. Analysis revealed that the standard production heat exchanger suffered from excessive fin-tube resistance. This was confirmed by sectioning and microscopic examination. Seven different designs were compared at the same Reynolds number. The results were analysed to isolate the air-side heat transfer coefficient.     

PVT gauging with liquid nitrogen

Experimental results are presented for pressure–volume–temperature (PVT) liquid quantity gauging of a 0.17 m³ liquid nitrogen tank pressured with ambient temperature helium in the normal gravity environment. A previously reported PVT measurement procedure has been improved to include helium solubility in liquid nitrogen. Gauging data was collected at nominal tank fill levels of 80%, 50% and 20% and at nominal tank pressures of 0.3, 1.0, and 1.7 MPa. The test tank was equipped with a liquid pump and spray manifold to circulate and mix the fluid contents and therefore create near-isothermal conditions throughout the tank. Silicon diode sensors were distributed throughout the tank to monitor temperatures. Close-spaced arrays of silicon diode point sensors were utilized to precisely detect the liquid level at the nominal 80%, 50%, and 20% fill levels. The tests simulated the cryogenic tank-side conditions only; helium mass added to the tank was measured by gas flowmeters rather than using pressure and temperature measurements from a dedicated helium supply bottle. Equilibrium data for cryogenic nitrogen and helium mixtures from numerous sources was correlated to predict soluble helium mole fractions. Results show that solubility should be accounted for in the PVT gauging calculations. Mole fractions predicted by Dalton’s Law were found to be in good agreement with the compiled equilibrium data within the temperature–pressure range of interest. Therefore, Dalton’s Law was deemed suitable for calculating ullage composition. Gauging results from the PVT method agreed with the reference liquid level measurements to within 3%.     

Sliding performance of polymer composites in liquid hydrogen and liquid nitrogen

Outstanding features favour the application of polymers and polymer composites in low-temperature technology. The booming hydrogen technology is a challenge for these materials, which are considered as seals and bearings in cryogenic pumps. In the present study, three types of thermoplastics, i.e., polyetheretherketone (PEEK), polyetherimide (PEI) and polyamide 6,6 (PA6,6), and one epoxy were considered as matrix materials. Micron-sized fillers, i.e., short carbon fibres, graphite flakes, and PTFE powders, were incorporated into these polymers together with nano-sized TiO₂ particles. Optimised compositions of each matrix were selected from our previous works at room temperature in order to be studied at very low temperature conditions. In particular, frictional tests were carried out with polymer composite pins against polished steel surfaces under constant load over a certain distance in liquid hydrogen and liquid nitrogen. Afterwards, worn surfaces were analysed by using scanning electron microscopy (SEM). It was found out that the tribological properties in liquid hydrogen are dominated by the matrix materials, in particular thermoplastics perform generally slightly better than thermosetting resins.     

Boiling from metal surfaces immersed in liquid nitrogen and liquid hydrogen

A study of bubble nucleation in liquid nitrogen and liquid hydrogen has been made in a 120 mm bubble chamber using a high speed cine camera.The initiation and growth of bubbles from artificially prepared cavities was studied. These cavities, produced in both copper and brass surfaces, had mouth radii ranging from 50 μm to 190 μm with depths varying from 110 μm to 500 μm. The liquids were superheated by either heating the surface containing the cavities or by reducing the pressure of the liquid, or by combining both of these methods.The heat fluxes required for initiation of boiling were greater than those required to sustain nucleation from a given site. The growth rate of the bubbles at constant liquid pressure was dependent on a number of factors. It changes as a bubble grew out of the thermal or superheated layer above the metal surface. After an initial period of more rapid growth the vapour volume increased linearly with time. The growth rate was dependent on the liquid used; being slower in liquid hydrogen than in liquid nitrogen. Formulae were obtained which predicted the observed variations in growth rate and departure volume.No nucleation was observed from the test surfaces for a pressure drop alone; the surfaces had to be heated before nucleation would occur. It is thought that this was due to the existence of a zero contact angle for cryogenic liquids on solid surfaces.     

Contact resistance characteristics with AlSi alloy metallization

Contact resistance characteristics of n⁺ Si shallow junctions metallized by sputtering an AlSi 2% alloy were investigated for different contact window sizes varying from 2 to 8 μm. The increase in the contact resistance with reducing contact area is measured employing Kelvin test structure. The effect of AlSi microstructure, silicon precipitation and annealing cycle on the contact resistance is discussed.     

Contact thermal resistance of machined metal surfaces in vacuo

The paper presents the results of an experimental investigation of contact thermal resistances of stainless steel and molybdenum samples for the range of compressive loads between 1.5 and 58 · 10^–5 N/m² and for an absolute pressure of the surrounding medium of 10^–4 mm Hg. An equation describing the dependence of the contact heat exchange in vacuo for small compressive loads was derived based on experimental data published in the literature.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 18, No. 2, pp. 259–269, February, 1970.     

钢板夹钢管组合板抗接触爆炸性能研究

鉴于钢管良好的变形能力、吸能特性和夹层结构在强度、刚度上的优势,提出了分层结构为钢板-钢管芯层-钢板的三明治型抗爆组合板。对芯层钢管数量为5根、4根、3根的组合板进行了TNT装药量为1kg的接触爆炸试验,考察了各板在承受接触爆炸冲击荷载时的变形及破坏情况,并对变形破坏过程进行了理论分析和数值模拟。研究表明,钢板夹钢管组合板承受接触爆炸冲击荷载时,主要发生局部压缩变形。钢管变形是组合板耗散能量的主要途径。增加钢管数量,增大钢板厚度,增大钢管管壁厚度,均可减小组合板在接触爆炸条件下的变形破坏,提高抗接触爆炸性能。     

The temperature of liquid nitrogen in cryostat dewars

Measurements of the temperature distribution of liquid nitrogen contained in 15 and 7.5 cm diameter dewars show that the bulk of the liquid is at an approximately constant temperature .15 to .3 K above the surface temperature. About half the liquid in the dewar is in a superheated state and this state, allthough easily disturbed from equilibrium by thermal and mechanical perturbations, occurs in an unclean vessel and with liquid nitrogen likely to contain impurities. The usefulness of this phenomenon is demonstrated by showing that an immersed copper waveguide was within a volume (50 cm long by 15 cm diameter) of liquid nitrogen that was isothermal to ±10 mK.     

Equation of state for liquid nitrogen

An equation of state has been found for nitrogen that satisfies the p, v, T data in the temperature interval 63.15–140° K at reduced densities=1.8–3 (and pressures up to 700 bar).     

The solubility of solidified toluene in liquid nitrogen

A method of determining the solubility of some heavier hydrocarbons, which are slightly soluble in liquid nitrogen, is described. The investigations were carried out by a combination of the filtration method and an analytical technique for ultra-microtraces determination (enrichment and gas chromatography with mass spectrometry). The solubility of solidified toluene in liquid nitrogen was determined at 77.4 K. The experimental result, 4.45 × 10^?8 mol fraction, was compared with the solubility calculated by the Preston-Prausnitz method.     

An automatic liquid nitrogen filling system

Spectroscopic measurements at low temperature require liquid nitrogen in some type of research dewar. Often the research dewar must be refilled from a reservoir dewar several times during the course of an experiment. A system is described which automatically refills a research dewar from a reservoir dewar. Two sensors are used for detecting the liquid nitrogen level in the research dewar, and an external nitrogen gas supply is used to provide the pressure to effect the transfer of liquid nitrogen.