共查询到20条相似文献,搜索用时 0 毫秒
1.
A. J. Slifka B. J. Filla J. M. Phelps 《Journal of research of the National Institute of Standards and Technology》1998,103(4):357-363
The thermal conductivity of polycrystalline magnesium oxide has been measured over the temperature range from 400 K to 1300 K using a modified guarded-hot-plate design. Three different thicknesses of specimens having 93 % of theoretical density were tested to verify the operation, accuracy, and reproducibility of our apparatus. The measured thermal conductivity ranges from 30 W · m−1 · K−1 down to 8 W · m−1 · K−1 and has an inverse-temperature functionality. The results agree well with literature values for this material. 相似文献
2.
Robert R. Zarr 《Journal of research of the National Institute of Standards and Technology》2010,115(1):23-59
An assessment of uncertainties for the National Institute of Standards and Technology (NIST) 1016 mm Guarded-Hot-Plate apparatus is presented. The uncertainties are reported in a format consistent with current NIST policy on the expression of measurement uncertainty. The report describes a procedure for determination of component uncertainties for thermal conductivity and thermal resistance for the apparatus under operation in either the double-sided or single-sided mode of operation. An extensive example for computation of uncertainties for the single-sided mode of operation is provided for a low-density fibrous-glass blanket thermal insulation. For this material, the relative expanded uncertainty for thermal resistance increases from 1 % for a thickness of 25.4 mm to 3 % for a thickness of 228.6 mm. Although these uncertainties have been developed for a particular insulation material, the procedure and, to a lesser extent, the results are applicable to other insulation materials measured at a mean temperature close to 297 K (23.9 °C, 75 °F). The analysis identifies dominant components of uncertainty and, thus, potential areas for future improvement in the measurement process. For the NIST 1016 mm Guarded-Hot-Plate apparatus, considerable improvement, especially at higher values of thermal resistance, may be realized by developing better control strategies for guarding that include better measurement techniques for the guard gap thermopile voltage and the temperature sensors. 相似文献
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U. Hammerschmidt 《International Journal of Thermophysics》2002,23(6):1551-1570
In civil engineering, the thermal conductivity is the most important quantity for thermal insulations and, as such, is in most cases determined with the guarded hot plate instrument in accordance with the applicable standards. These standards are to assure that uniform and reliable measurements will lead to comparable results. In addition, the quality of a measurement result essentially depends on its measurement uncertainty which, for reasons of acceptance, should also be determined according to a uniform guideline. For some time now, such a standard has been available: The ISO Guide to the Expression of Uncertainty in Measurement, often abbreviated to GUM. Its application will be demonstrated comprehensively, and in detail, by the example of a guarded hot plate instrument which can be used at working temperatures from –70 to 200°C. The terms and definitions of the GUM required for this purpose will be extended by the instrument-and-sample-specific corrections and used as a basis for establishing the uncertainty budget. As far as possible, both alternatives offered by the GUM—type A and type B methods—are used in parallel. The combination of the sensitivity coefficients and variances of the budget yields the expanded standard uncertainty of the specific guarded hot plate instrument examined. In this case, it is 1.9% at 20°C. 相似文献
5.
热障陶瓷涂层的最新发展 总被引:9,自引:2,他引:9
综述了现代航空发动机用热障陶瓷涂层的最新发展,着重介绍了双陶瓷层,电子束物理气相沉积(EB-PVD)和溶液等离子喷涂(SPS)纳米热障陶瓷涂层的性能和特点。 相似文献
6.
P. L. Woodfield J. Fukai M. Fujii Y. Takata 《International Journal of Thermophysics》2009,30(3):796-809
A fast and accurate procedure is proposed for solution of the two-dimensional unsteady heat conduction equation used in the
transient short-hot-wire method for measuring thermal conductivity. Finite Fourier transforms are applied analytically in
the wire-axis direction to produce a set of one-dimensional ordinary differential equations. After discretization by the finite-volume
method in the radial direction, each one-dimensional algebraic equation is solved directly using the tri-diagonal matrix algorithm
prior to application of the inverse Fourier transform. The numerical procedure is shown to be very accurate through comparison
with an analytical solution, and it is found to be an order of magnitude faster than the usual numerical solution. 相似文献
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在一维稳态热传导模型的基础上,设计了一套用于测量聚合物薄膜纵向热导系数的实验装置,并利用Comsol软件对该测量装置进行数值模拟并优化设计。同时利用本文设计的实验装置,测量得到了不同温度下聚酰亚胺(PI)膜、聚四氟乙烯(PTFE)膜以及混合纤维素酯(MCE)膜的热导系数。在35℃~60℃的温度范围内热导系数测量值分别维持在0.21 W/(m.K),0.26 W/(m.K),0.13 W/(m.K)左右,标准不确定度在9.5%以下。测量结果与参考值相符,验证了实验装置的测试精度。 相似文献
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Zhuolei Zhang Namhoon Lee Ketan Patel Mitchell Young Jingming Zhang Simona Percec Shenqiang Ren 《Advanced Engineering Materials》2018,20(9)
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介绍了作者单位研制的低温大平板热导装置的特点,关键技术,装置的构成及对一些问题的探讨,利用这套装置做一些材料的测试分析工作。 相似文献
12.
含TiB2陶瓷相热喷涂涂层的研究进展 总被引:1,自引:1,他引:0
TiB2具有高耐磨、高耐腐蚀、耐高温、抗氧化等优异性能,但由于高脆性和材料制备的困难性,使其用作结构材料还很难.通过各种工艺制备含有TiB2陶瓷相的涂层既可充分发挥材料的优异特性,满足工件所需的耐磨耐高温耐腐蚀等性能,又节省了材料节约了成本.本研究介绍了先进陶瓷材料TiB2的主要结构性能以及目前制备TiB2涂层的主要方法,着重介绍了有关国内外热喷涂法制备含TiB2陶瓷相涂层的研究进展和成果,并对不同热喷涂工艺的特点与发展趋势做了分析和讨论,最后阐述了TiB2涂层的成功应用情况及其广阔的发展前景. 相似文献
13.
D. R. Smith 《International Journal of Thermophysics》1997,18(6):1557-1573
In the early 1980s, an international round-robin was held in which the apparent thermal conductivity of specimens of fibrous
glass insulation board was measured by users of guarded hot plates (GHPs) and heat-flow meters (HFMs). The round-robin was
performed over a period of several years by laboratories in Europe, North America, Australia, and the Far East. Participants
in this round-robin were organized into 12 “loops.” 8 for participants with GHPs and 4 for those with HFMs. Each loop included
laboratories located in the same region of the world and sharing the same set of specimens. In an attempt to obtain insight
into the accuracy of the measurements, participants were also asked to measure the thermal conductivity of a layer of air.
The data submitted in this round-robin are exhibited and analyzed. The overall agreement of individual measurements with a
least-squares fitted curve, as measured by one standard deviation σ, was σ=2.4% for GHPs and σ=2.7% for HFMs. Suggestions
are made for conducting future round-robins of this type 相似文献
14.
降低热障涂层面层中的低熔点杂质含量,可提高涂层的高温稳定性和延长服役寿命。SiO2、Al2O3和Fe2O3是氧化钇稳定氧化锆(Yttria-Stabilized Zirconia, YSZ)热障涂层中几种常见的低熔点氧化物杂质,均会对涂层的性能产生一定的影响。本研究采用大气等离子喷涂法,制备SiO2、Al2O3和Fe2O3的含量从小于0.01wt%增加至1.00wt%的YSZ热障涂层。采用扫描电镜(SEM)和透射电镜(TEM)研究了上述涂层的微观结构;采用激光热导仪测试了涂层的热扩散系数和抗热震次数。研究结果表明,低熔点氧化物杂质对YSZ涂层的导热性、热处理状态的孔隙率具有明显影响,且更容易引起涂层的热震失效。当杂质氧化物含量在小于0.2wt%范围内变化时,涂层的性能变化更为显著。 相似文献
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A. J. Slifka B. J. Filla 《Journal of research of the National Institute of Standards and Technology》2003,108(2):147-150
An industrial ceramic thermal-barrier coating designated PWA 266, processed by electron-beam physical-vapor deposition, was measured using a steady-state thermal conductivity technique. The thermal conductivity of the mass fraction 7 % yttria-stabilized zirconia coating was measured from 100 °C to 900 °C. Measurements on three thicknesses of coatings, 170 μm, 350 μm, and 510 μm resulted in thermal conductivity in the range from 1.5 W/(m·K) to 1.7 W/(m·K) with a combined relative standard uncertainty of 20 %. The thermal conductivity is not significantly dependent on temperature. 相似文献
17.
电流密度对MgO-ZnO陶瓷薄膜结构和热控性能的影响 总被引:1,自引:0,他引:1
在Zn(H2PO4)2电解液中, 利用微弧氧化技术在AZ31镁合金表面原位生长MgO-ZnO热控陶瓷薄膜, 研究了电流密度对薄膜结构组成、结合强度和热控性能的影响, 以及紫外辐照作用下薄膜太阳吸收率的变化规律。结果表明:薄膜主要由MgO、ZnO和非晶态物质组成, 随着电流密度增大, 微孔数量逐渐减少而粗糙度逐步增大, 其厚度、结合强度和发射率先增大后减小, 而太阳吸收率则先减小后增大。电流密度9 A/dm2时所得薄膜的结合强度达到最大12.6 MPa, 且热控性能最佳, 其发射率为0.872, 太阳吸收率为0.363; 且随着紫外辐照时间延长, 此薄膜太阳吸收率先升高而后趋于平缓。研究结果为制备良好结合强度和抗紫外辐照能力的低吸收高发射热控薄膜提供技术 支持。 相似文献
18.
H. Inaba 《International Journal of Thermophysics》1986,7(4):773-787
This paper reports new measurements of the effective thermal conductivity of agricultural materials such as grains by means of the transient heat flow method using a line heat source. The effect of a probe diameter used for the transient heat flow method on the effective thermal conductivity was studied using standard spherical particles and some grains. It was concluded that the transient heat flow method can be applied to the measurement of the effective thermal conductivity of agricultural materials such as grains provided that the ratio of the probe diameter to the diameter of the particles of the specimen is greater than unity.Nomenclature
A
Area of heating surface
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d
Diameter of particles of the specimen
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d
e
Hydrodynamic diameter of particles of the specimen
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E
Error
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H
Distance between hot and cold walls
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L
Probe length
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M
Moisture content
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N
Number of contact points of particles of the speciment to the probe surface
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Q
Net heat flux
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q
Heat flux per probe length added to probe
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R
Probe radius
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r
Radial distance
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T
Temperature
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T
h
Surface temperature of the hot wall
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T
c
Surface temperature of the cold wall
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t
Time
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a
Thermal conductivity of air
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eff
Effective thermal conductivity
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s
Thermal conductivity of a single kernel
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Thermal diffusivity
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s
Thermal diffusivity of a single kernel
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Porosity
-
Euler constant (=0.5775...)
-
Angle
Invited paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A. 相似文献
19.
M. V. Peralta-Martinez M. J. Assael M. J. Dix L. Karagiannidis W. A. Wakeham 《International Journal of Thermophysics》2006,27(2):353-375
The paper reports the design and construction of a new instrument for the measurement of the thermal conductivity of molten metals and salts. The apparatus is based on the transient hot-wire technique, and it is intended for operation over a wide range of temperatures, from ambient up to 1200 K. The present experimental technique overcomes problems of convection and thermal radiation, and it is demonstrated that it operates in accord with a theoretical model. The uncertainty of the thermal conductivity results is estimated to be ±2% which is superior to that achieved in most earlier work. 相似文献