Thermal conductivity of liquid hydrogen filled foam

The effective thermal conductivities of silica aerogel foam [0.1(10)⁻³ kg m⁻³ nominal density] filled with liquid n-H₂, liquid n-D₂ and an equimolar mixture of liquid H₂D₂ were measured near 19.6 K. Our measured value of 97 mW m⁻¹ K⁻¹ for hydrogen filled foam is essentially the same as for the liquid alone. This result agrees with predictions for the thermal conductivity of porous systems which give a 2% enhancement in the effective thermal conductivity for this system relative to the liquid alone.     

Spray-on foam insulations for launch vehicle cryogenic tanks

Spray-on foam insulation (SOFI) has been developed for use on the cryogenic tanks of space launch vehicles beginning in the 1960s with the Apollo program. The use of SOFI was further developed for the Space Shuttle program. The External Tank (ET) of the Space Shuttle, consisting of a forward liquid oxygen tank in line with an aft liquid hydrogen tank, requires thermal insulation over its outer surface to prevent ice formation and avoid in-flight damage to the ceramic tile thermal protection system on the adjacent Orbiter. The insulation also provides system control and stability throughout the lengthy process of cooldown, loading, and replenishing the tank. There are two main types of SOFI used on the ET: acreage (with the rind) and closeout (machined surface). The thermal performance of the seemingly simple SOFI system is a complex array of many variables starting with the large temperature difference of 200–260 K through the typical 25-mm thickness. Environmental factors include air temperature and humidity, wind speed, solar exposure, and aging or weathering history. Additional factors include manufacturing details, launch processing operations, and number of cryogenic thermal cycles. The study of the cryogenic thermal performance of SOFI under large temperature differentials is the subject of this article. The amount of moisture taken into the foam during the cold soak phase, termed Cryogenic Moisture Uptake, must also be considered. The heat leakage rates through these foams were measured under representative conditions using laboratory standard liquid nitrogen boiloff apparatus. Test articles included baseline, aged, and weathered specimens. Testing was performed over the entire pressure range from high vacuum to ambient pressure. Values for apparent thermal conductivity and heat flux were calculated and compared with prior data. As the prior data of record was obtained for small temperature differentials on non-weathered foams, analysis of the different methods is provided. Recent advancements and applications of SOFI systems on future launch vehicles and spacecraft are also addressed.     

Unguarded cryostat for thermal conductivity measurements of multilayer insulations

A cryostat for measurements of the effective thermal conductivity of multilayer insulations in conditions similar to those in normal cryogenic liquid containers has been constructed. Results for two multilayer insulations are presented.     

Integrated design approach for advanced aerospace vehicles

Advanced aerospace vehicle design requires special design features that should meet the mission requirements of high payload to weight ratio in the case of space launchers and low radar cross-section for specific missiles/aircraft. The conventional design packages used are discussed in relation to their constraints. An interactive integrated design approach to eliminate the constraints imposed by individual design modules through interface design modules is discussed. Typical examples of such interface design modules are given. Also, a computer network necessary for an interactive integrated design approach interfacing the mainframe with a computer-aided design and drafting system and parallel processing is presented. This note has been prepared based on detailed discussions with designers in various areas of technology.     

Thermal conductivity and Kapitza resistance of cyanate ester epoxy mix and tri-functional epoxy electrical insulations at superfluid helium temperature

In the framework of the European Union FP7 project EuCARD, two composite insulation systems made of cyanate ester epoxy mix and tri-functional epoxy (TGPAP-DETDA) with S-glass fiber have been thermally tested as possible candidates to be the electrical insulation of 13 T Nb₃Sn high field magnets under development for this program. Since it is expected to be operated in pressurized superfluid helium at 1.9 K and 1 atm, the thermal conductivity and the Kapitza resistance are the most important input parameters for the thermal design of this type of magnet and have been determined in this study. For determining these thermal properties, three sheets of each material with different thicknesses varying from 245 to 598 μm have been tested in steady-state condition in the temperature range of 1.6–2.0 K. The thermal conductivity for the tri-functional epoxy (TGPAP-DETDA) epoxy resin insulation is found to be k = [(34.2 ± 5.5)?T ? (16.4 ± 8.2)] × 10^?3 Wm^?1 K^?1 and for the cyanate ester epoxy k = [(26.8 ± 4.8)?T ? (9.6 ± 5.2)] × 10^?3 Wm^?1 K^?1. For the Kapitza resistance, R_k, the best curve fitting the experimental data is described by R_k = (3057 ± 593) × 10^?6?T (?1.79 ± 0.34) m² KW^?1 for the TGPAP-DETDA insulation and R_k = (4114 ± 971) × 10^?6?T (?1.73 ± 0.41) m² KW^?1 for the cyanate ester epoxy insulation. Our results are compared with other epoxy based composite electrical insulation found in the literature.     

The influence of residual gas pressure on the thermal conductivity of microsphere insulations

Experimental results of investigations of the heat exchange by residual gas in microsphere insulations are presented. The results of measurements of microsphere effective thermal conductivity versus residual gas (N₂) pressure in the pressure range of 10^–3–10⁵ Pa are also given. A sample of self-pumping microsphere insulation was prepared and its thermal parameters were tested. In comparison to the standard microsphere insulation, the self-pumping insulation yielded lower thermal conductivity results over the entire pressure range. The stability of its thermal parameters as a result of considerable gas input into the insulation volume is discussed. Measurements of temperature and pressure distributions inside the microsphere layer were performed. Plots of temperature and pressure gradients inside the layer of the microsphere insulation are presented.Nomenclature d _m Mean value of the microsphere diameter - k Apparent thermal conductivity coefficient - ¯k Average thermal conductivity coefficient - k _c Component of the heat transfer by conduction - k _g Modified gas thermal conductivity under atmospheric pressure - k _r Component of the heat transfer by radiation - k _s Thermal conductivity of the sphere material - k _gc Component of the heat conduction by gas - k _go Gas thermal conductivity under atmospheric pressure - k _gr Sphere effective conductivity - k _ss Component of the heat conduction by the solid state - K 1–(k _g/k _gr) - Kn Knudsen number - ¯L Mean free path of gas molecules - m 1–_s; porosity - m Empty volume of a single sphere - p Residual gas pressure - ¯p Average pressure - p _g Pressure measured by gauge - p ₀ Residual gas pressure above the insulation bed - r Radial coordinate - T Temperature - T _c Temperature of the cold calorimeter wall - T _g Temperature of the pressure gauge - T _H Temperature of the hot calorimeter wall - T _i Gas temperature inside the bed - T _y Constant dependent on the sort of gas - v Volume - Accommodation coefficient - Density - _a Local distance between surfaces - _s Solid fraction - Constant dependent on the sort of gas - Time measured from the initiation of insulation cooling     

航天复合材料热导率测量的实验研究

通过实验研究了复合材料中玻璃纤维和碳纤维的不同配比对热导率影响。采用瞬态平面热源法,使用Hotdisk热常数分析仪获得了不同配比下玻璃纤维-碳纤维复合材料热导率与温度变化曲线。实验结果表明:随着温度降低,复合材料热导率减小;复合材料的热导率都随着碳纤维布含量的增加而升高。     

Thermal performance indicators for refrigerated road vehicles

An experimental evaluation of insulation effectiveness, pull-down times and effectiveness of a mechanical refrigeration unit was performed on five refrigerated panel vans. Additionally, a mapping of temperature variability in the cargo space was carried out during a simulated journey encompassing several door openings. The temperature variability measured in the vans was neither correlated to the effectiveness of the insulation nor the time required to achieve complete cooling of the cargo space. These criteria are common thermal performance indicators used to evaluate refrigerated vehicles in international standards. The efficiency of insulation was correlated to the pull-down times, presenting the possibility of calculating the former as a function of the latter. The temperature variability was correlated with the time required for the unit to recover temperature control after a door opening and the difference between the maximum and minimum temperatures reached during a door opening cycle.     

Fracture toughness tests of a rigid polyurethane foam

The results of some exploratory tests for determining the fracture toughness of a rigid polyurethane foam are presented. The specimen geometries used included centre- and double-edge-cracked plates, the single-edge-cracked tensile specimen and the double cantilever beam specimen. The validity of applying the concepts of linear elastic fracture mechanics to the fracture of this foam is discussed. Some unique features of the fracture of foam are discussed.     

Experimental investigations in embedded sensing of composite components in aerospace vehicles

This paper summarizes the experimental investigations for smart embedded sensing in rotorcraft composite components. The overall objective of this effort was to develop smart embedded sensor technologies for condition based maintenance (CBM) for composite components in army rotorcraft. This paper presents the results of experimental investigations related to development and maturation of different types of embedded sensing solutions for structural health monitoring of composite components including Fiber Bragg Grating (FBG) sensors, phased and discrete piezoelectric sensor arrays. A discussion is provided relative to embedment of optical fibers into composites, and the results from embedded FBG sensors in a rotorcraft flexbeam subcomponent test specimen with seeded delamination subjected to dynamic loading. Likewise, results are analyzed of surface mounted phased array and embedded smart piezoelectric sensors in the flexbeam subcomponent test specimen with embedded delamination, subjected to fatigue cyclic loading. The paper also summarizes the lessons learned from efforts to nucleate and propagate delamination within composite components under dynamic cyclic loading.     

Thermal conductivity of composites

A general expression for the effective thermal conductivity of inhomogeneous media in terms of the Fourier components of the spatial variation of the conductivity is applied to composites consisting of inclusions in a continuous matrix. It is reformulated in terms of the mean square fluctuations of the conductivity. Specific cases treated are spherical inclusions and long cylinders, both random and with preferred directions. The results hold provided the difference in thermal conductivities is small or provided the concentration of inclusions is not too large. The theory fails if the thermal conductivity of the matrix is much smaller than that of the inclusions. The same considerations also apply to electrical conductivity.     

Thermal conductivity of methane

This paper reports thermal conductivity data for methane measured in the temperature range 120–400 K and pressure range 25–700 bar with a maximum uncertainty of ± 1%. A simple correlation of these data accurate to within about 3% is obtained and used to prepare a table of recommended values.Nomenclature a _k ,b _ij ,b _k Parameters of the regression model, k= 0 to n; i =0 to m; j =0 to n - P Pressure (MPa or bar) - Q _kl Heat flux per unit length (mW · m^–1) - t time (s) - T Temperature (K) - T _cr Critical temperature (K) - T _r reduced temperature (= T/T _cr) - T _w Temperature rise of wire between times t ₁ and t ₂ (deg K) - T ^* Reduced temperature difference (TT _cr)/T _cr - Thermal conductivity (mW · m^–1 · K^–1) - ₁ Thermal conductivity at 1 bar (mW · m^–1 · K^–1) - _bg Background thermal conductivity (mW · m^–1 · K^–1) - _cr Anomalous thermal conductivity (mW · m^–1 · K^–1) - _e Excess thermal conductivity (mW · m^–1 · K^–1) - Density (g · cm^–3) - _cr Critical density (g · cm^–3) - _r Reduced density (= / _cr) - ^* Reduced density difference (– _cr )/ _cr      

Thermal conductivity of solutions

The results of an experimental and theoretical study of the thermal conductivity of binary, ternary, and multicomponent solutions are presented. A probable mechanism of heat conduction in solutions is proposed and calculation formulas are obtained.     

Determination of the thermal conductivity of foam aluminum

We present calculations and experimental data on determination of the thermal conductivity of porous foam aluminum materials. We analyze the possibility of their use for thermal insulation.     

全水发泡聚氨酯泡沫塑料在花盆中的应用

将全水发泡聚氨酯泡沫塑料用于制成花盆,介绍了全水发泡聚氨酯泡沫塑料的原料、配方、加工设备及花盆的生产工艺和测试方法.     

Development of rigid bio-based polyurethane foam reinforced with nanoclay

Integration of organic nanoclay into bio-based polyurethane (PU) foam is a promising alternative to enhance the foam’s properties via green technology. In this paper, modified diaminopropane montmorillonite (DAP-MMT) nanoclay was introduced into palm oil-based PU foam at different weight loadings, namely, 0, 2, 4, 6, 8, and 10 wt.%, in order to investigate the effects on the mechanical and thermal properties of the foam. Several tests and characterizations were carried out to study the surface morphology, density, compressive strength and thermal stability of the foam. It was found that foam exhibited an exfoliated or intercalated microstructure based on the DAP-MMT contents. The X-ray diffraction analysis showed that below 4 wt.%, the foams displayed exfoliated structures while beyond the value, the foams exhibited the intercalated morphologies. Closed cells with different cell sizes were observed when the DAP-MMT contents were varied. Meanwhile, thermal stability and compressive strength of foams increased with increasing DAP-MMT contents up to 4 wt.%, as shown by thermogravimetry analysis and compression test, respectively.     

Thermal conductivity of ternary mixtures for concrete pavements

This study used a standard procedure to measure the thermal conductivity of ternary concrete mixtures and investigated several factors influencing thermal conductivity. Three different coarse aggregates (Kentucky limestone, Mexican limestone, and river gravel) were used for the concrete mixtures. The measured thermal conductivity of concrete is significantly affected by the type and percentage of coarse aggregate, and moisture content. This finding was confirmed statistically by an Analysis of Variance (ANOVA) method. To understand the effect of supplementary cementitious materials (SCMs), the thermal conductivity of the control and ternary mixtures were measured and provided for use in Portland cement concrete (PCC) pavement design. The thermal conductivity of ternary mixtures increased by 7-10% due to an increase of 1% in moisture. The study developed a model equation that predicts the thermal conductivity of concrete as a function of moisture content and coarse aggregate percentage.     

Thermal conductivity of consolidated systems

A structural model and method for calculating the effective thermal conductivity of consolidated granular materials are proposed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 27, No. 1, pp. 55–62, July, 1974.