Wrapped multilayer insulation design and testing

New vehicles need improved cryogenic propellant storage and transfer capabilities for long duration missions. Multilayer insulation (MLI) for cryogenic propellant feedlines is much less effective than MLI tank insulation, with heat leak into spiral wrapped MLI on pipes 3–10 times higher than conventional tank MLI. Better insulation for cryogenic feed lines is an important enabling technology that could help NASA reach cryogenic propellant storage and transfer requirements. Improved insulation for Ground Support Equipment could reduce cryogen losses during launch vehicle loading. Wrapped-MLI (WMLI) is a high performance multilayer insulation using innovative discrete spacer technology specifically designed for cryogenic transfer lines and Vacuum Jacketed Pipe (VJP) to reduce heat flux.The poor performance of traditional MLI wrapped on feed lines is due in part to compression of the MLI layers, with increased interlayer contact and heat conduction. WMLI uses discrete spacers that maintain precise layer spacing, with a unique design to reduce heat leak. A Triple Orthogonal Disk spacer was engineered to minimize contact area/length ratio and reduce solid heat conduction for use in concentric MLI configurations.A new insulation, WMLI, was developed and tested. Novel polymer spacers were designed, analyzed and fabricated; different installation techniques were examined; and rapid prototype nested shell components to speed installation on real world piping were designed and tested. Prototypes were installed on tubing set test fixtures and heat flux measured via calorimetry. WMLI offered superior performance to traditional MLI installed on cryogenic pipe, with 2.2 W/m² heat flux compared to 26.6 W/m² for traditional spiral wrapped MLI (5 layers, 77–295 K). WMLI as inner insulation in VJP can offer heat leaks as low as 0.09 W/m, compared to industry standard products with 0.31 W/m. WMLI could enable improved spacecraft cryogenic feedlines and industrial hot/cold transfer lines.     

10m~3高真空多层绝热低温液体运输车的研制

10m3高真空多层绝热低温液体运输车用于运输液态氧、氮和氩等低温液体产品。详细介绍了10m3高真空多层绝热低温液体运输车的主要设计参数、结构和工艺流程,阐述了制造过程中需重点控制的环节,分析了设计制造过程中需重点考虑的方面。     

The thermal conductivity of cryogenic insulation materials and its temperature dependence

For the presentation of the thermal conductivity of cryogenic insulation materials and their integral mean values an empirical function is suggested, with which experimentally found values can be extrapolated to other temperature levels.The selection of materials includes granulated and fibrous insulations under atmospheric pressure as well as under vacuum and a multilayer insulation for most high performances.It is shown theoretically, how the constants in the empirical function can be determined. Their calculation is demonstrated practically by using real measurements.For a multilayer insulation a theory is developed, with which a measured value can be extrapolated to other temperatures, gas pressures and numbers of layers. Its application to a real insulation system is demonstrated too.The results are listed in a tabular summary.     

Interlaminar shear properties of composite insulation systems for fusion magnets at cryogenic temperatures

This paper reports the cryogenic interlaminar shear properties of composite insulation systems for the superconducting magnet coils in the International Thermonuclear Experimental Reactor (ITER). Short beam shear tests were performed at room temperature, liquid nitrogen temperature (77 K) and liquid helium temperature (4 K) on three insulation systems consisting of woven glass fiber reinforced plastic (GFRP) composites with different polymer resins and polyimide films, and the dependence of their apparent interlaminar shear strength on the temperature and the polymer resins was discussed. A detailed observation of failed specimens was made to verify the failure mechanisms. Insulation systems subjected to gamma irradiation at room temperature were also considered, and the effect of irradiation on the cryogenic interlaminar shear properties was examined.     

Thermal performance of multilayer insulation around a horizontal cylinder

Thermal performance of multiplayer insulation (MLI) is affected by contact pressure between adjacent layers. In order to evaluate the thermal performance of the MLI fabricated in the horizontal cryostats of superconducting magnets, it is important to investigate the contact pressure in the MLI. In case of a horizontal cryostat, the MLI is wound around horizontal cylindrical surface and is compressed at the upper part of the cylinder due to the MLI self-weight. At first, a single thin film wound around the horizontal cylinder was analyzed to evaluate the contact pressure acting on the cylinder. The analysis has been extended to the multiply wound film around horizontal cylinder, in order to investigate the distribution of contact pressure between adjacent layers. By using experimental data obtained with a flat panel calorimeter, the results of this analysis have been applied to evaluate the thermal performance of MLI around a horizontal cylinder. And the non-dimensional contact pressure parameter P^* has been introduced as a useful parameter to evaluate and compare the thermal performance among different kinds of MLI.     

真空多层绝热性能测试装置及初步实验验证

建立了一套低温用真空多层绝热材料性能测试装置,用于研究变密度多层绝热材料的特性规律。以内密外疏的层密度分布方式为例,在测试装置充注液氮之后,通过稳态量热法实验研究了真空条件下该布置方式绝热层内不同层位置的温度瞬态和稳态分布规律、单点的降温规律、以及单位面积漏热率情况。考察了稳态温度分布以及单位面积热流随热边界温度的变化特性,并将理论温度分布曲线与实验曲线进行了对比,从而验证层与层模型的准确性。     

Equipment for long-term creep testing at cryogenic temperatures

Equipment and procedures for long-term cryogenic creep testing are presented in detail. Particular attention was given to the maintaining of constant cryogenic test temperature and with respect to the stability and sensitivity of strain measurements. Typical long-term cryogenic creep testing results on oxygen free high conductivity (OFHC) copper are presented.     

Experimental study of the influences of degraded vacuum on multilayer insulation blankets

The paper presented experimental investigation on the heat transfer of MLI with different rarefied gases at different pressures. The investigations were carried out using an innovative static liquid nitrogen boil-off rate measurement system in the case of the small temperature perturbations of cold and warm boundaries. The heat fluxes for a number of inert and some polyatomic gases have been analyzed at different heat transfer conditions ranging from molecular to continuum regime, apparent thermal conductivities of the multilayer insulation were measured over a wide range of temperature (77 K–300 K) and pressure (10⁻³–10⁵ Pa) using the apparatus. The experimental results indicated that under degraded vacuum condition, the influences of rarefied gas on the MLI thermal performance very depend on the gas rarefaction degree which impacted by the MLI vacuum degree. Under the condition of molecular regime heat transfer, the MLI thermal performance was greatly influenced by gas energy accommodation coefficients (EAC), when under the continuum regime, the performances depend on the thermal conductivity of rarefied gas itself. Compared to the results of N₂, Ar, CO₂, Air and He as interstitial gases in the MLI, Ar was the better selection as space gas because of its low EAC and thermal conductivity characteristics on the different vacuum condition ranging from high pressure to vacuum. So different residual gases can be utilized according to the vacuum level and gas energy accommodation coefficient, in order to improve the insulation performance of low vacuum MLI.     

Review of tape materials for cable insulation at liquid nitrogen temperatures

This Paper reviews the electrical breakdown, partial discharge and loss angle characteristics of taped cable insulation impregnated with liquid nitrogen. Also life expectancy and the effects of semiconducting screens are surveyed. With the recent announcement of a superconductor at liquid nitrogen temperatures a review of cable insulation impregnated with liquid nitrogen is felt to be appropriate.     

Effect of substrate temperature and annealing treatment on the electrical and optical properties of silver-based multilayer coating electrodes

Multilayer coatings consisting of thin silver layers sandwiched between layers of transparent conducting metal oxides are investigated from the view point of low-resistance electrodes for use in flat panel displays, solar cells, etc. ZnO/Ag/ZnO multilayer films were prepared on glass substrates by simultaneous RF magnetron sputtering of ZnO and dc magnetron sputtering of Ag. Optimization of the deposition conditions of both ZnO layers and metallic layers were performed for better electrical and optical properties. The structural, electrical and optical properties of the films (deposited at room temperature, different substrate temperature and annealed at different conditions) were characterized with various techniques. We could not produce high-quality transparent conductive electrodes simply by annealing at various temperatures. However, improved electrical properties and a considerable shift in the transmittance curves was observed after heat treatment. The experimental results show that the electrical resistivity of as-grown films can be decreased to 10^− 5 Ω cm level with post-annealing at 400 °C for 2 h in vacuum atmosphere. After heat treatment, the sheet resistance was reduced as much as 20% which was due to the increased grain size of Ag film. The samples heat treated at 200-400 °C under vacuum or nitrogen atmosphere showed the best electrical properties. The key to the superior electrical and optical properties of the multilayer is the optimization of growth conditions of the silver layer by careful control of the oxide properties and the use of appropriate annealing temperature and atmosphere.     

Thermal convection in sections of multilayer cryogenic heat insulation

An experimental investigation has been made of heat transfer during natural convection in multilayer heat insulating structures consisting of anisotropic permeable porous materials.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 61, No. 2, pp. 239–243, August, 1991.     

On standards for mechanical testing of materials at cryogenic temperatures

The basic principles of the ASTM, ISO, and GOST standards specifying the procedure for tensile testing of metals at liquid helium temperatures are considered and analyzed. The main factors that influence the parameters of the strain- and stress-controlled loading, as well as the dimensions of specimens in tests of metals and alloys under the above temperatures are determined. Recommendations on extending and revising the provisions of standards are provided.     

A calorimeter for multilayer insulation (MLI) performance measurements at variable temperature

Here we describe a concentric cylindrical calorimeter with radiation guards developed to measure the thermal performance of multilayer insulation (MLI) for low temperature applications. One unique feature of this calorimeter is its ability to independently control the boundary temperatures between room temperature and about 15 K using two single-stage Gifford–McMahon cryocoolers. Also, unlike the existing calorimeters that use the evaporation rate of a liquid cryogen to measure the heat load, in the present system the total heat transfer through the MLI is measured by recording the temperature difference across a calibrated heat load support rod that connects the cold inner cylinder to the lower temperature cryocooler. This design allows the continuous mapping of MLI performance over a much wider temperature range with independently controlled boundary conditions. The calorimeter is also suitable for performing a variety of radiation heat transfer experiments including the determination of the temperature dependence of the total emissivity.     

新型耐高温多层隔热结构研究

为了改善传统应用的多层隔热材料的耐温及隔热效果等性能,以耐高温硅酸铝纤维纸和石英纤维网为基体材料,疏水性SiO2气凝胶颗粒为隔热填料,采用粘结工艺制备了新型耐高温多层隔热结构.采用石英灯阵列光电加热装置测试该结构冷面温度随时间的变化情况,采用PBD-02P平板导热仪测试各个指定温度下的导热系数,采用扫描电镜表征胶层的微观形貌.研究改变疏水性SiO2气凝胶颗粒添加量对导热系数的影响,结果表明,当疏水性SiO2气凝胶颗粒与耐高温胶粘剂质量比为2∶40时制备出的试样具有最低导热系数.这种新型耐高温多层隔热结构最高使用温度可达1000℃,平均密度小于0.25g/cm3,热面温度为1000℃时最佳配比试样的导热系数仅为0.080W/(m·K).该结构优异的综合性能能够很好地应用于航空航天隔热领域.     

两种绝热型式低温液体槽车的分析比较

文章从绝热性能、外形尺寸与重量、有效载液容积、制造工艺难度及槽车价格五个方面对真空粉末绝热与高真空多层绝热低温液体槽车进行了比较 ,分析了各自在使用上的优势与不足 ,并对具体运用时槽车的选择提出一些建议     

Thermoelastic analysis of cracked woven GFRP laminates at cryogenic temperatures

We deal with the thermal-mechanical response of multi-layered G-11 woven glass/epoxy laminates with cracks and temperature-dependent properties under tension at liquid helium temperature (4 K). The composite material is assumed to be in generalized plane strain. Cracks are located in the fill fiber bundles and are assumed to span the width of the fill fiber bundles. Finite element model is used to study the influence of residual thermal stresses on the mechanical behavior of multi-layered woven laminates with cracks. Numerical calculations are carried out, and the Young's modulus and stress distributions near the crack tip are shown graphically.     

High quality transparent conductive ZnO/Ag/ZnO multilayer films deposited at room temperature

We have fabricated, by simultaneous DC and RF magnetron sputtering, multilayer transparent electrodes having much lower electrical resistance than the widely used transparent conductive oxide electrodes. The multilayer structure consists of three layers (ZnO/Ag/ZnO). Ag films with different film thickness were used as metallic layers. Optimum thicknesses of Ag and ZnO films were determined for high optical transmittance and good electrical conductivity. Several analytical tools such as spectrophotometer, atomic force microscopy, scanning electron microscopy and four-point probe were used to explore the possible changes in electrical and optical properties. A high quality transparent electrode, having resistance as low as 3 Ω/sq and high optical transmittance of 90% was obtained at room temperature and could be reproduced by controlling the preparation process parameters. The electrical and optical properties of ZnO/Ag/ZnO multilayers were determined mainly by the Ag film properties. The performance of the multilayers as transparent conducting materials was also compared using a figure of merit.     

An apparatus for infrared transmittance and reflectance measurements at cryogenic temperatures

A facility for measuring the optical properties of solid materials at cryogenic temperatures is being developed at the National Institute of Standards and Technology. A cryostat that houses four ur bolometric detectors and a six-position sample holder was designed and built. The bolometers operate near 5 K, and the sample temperature can he varied from 6 to 100 K. The beam from a Fourier transform spectrometer is directed to the cryostat by reflective optical components. The measurable wavelengths extend from 1m to 1 mm, with appropriate sources and beamsplitters in the spectrometer as well as windows and detectors in the cryostat. The angle of incidence on the sample ranges from 7.5 to 60. The mechanical electrical, and optical designs are described in this paper. Initial measurement results at wavelengths from 2 to 30m and a sample temperature of 10 K are presented.     

变密度多层绝热的理论分析

讨论了一种新型的多层绝热结构,针对径向内外侧不同层间辐射阻断的强弱比例特征、材料重量、以及结构强度,对多层材料的布置进行了优化设计.主要分析多层绝热的绝热性能随层密度分布的变化规律,寻找特定条件下最优化层密度的分布方式,并研究了最优化层密度分布方式与绝热系统各参数之间的关系.     

Copper-TFE friction at cryogenic temperatures

Interfaces between metals and polytetrafluoroethylene (TFE) are common in cryogenic systems. In this paper we present results from measurements of the temperature dependence of the dynamic coefficient of friction between commercially pure copper and TFE. The effect of the copper surface finish was also determined. The effects of load and speed were evaluated over a small range, but nearly all data were taken at a surface speed of 5.4 cm s^?1 with a load of 1.63 N cm^?2. These values are typical of those encountered by the moving parts of some cryogenic machinery.