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排序方式: 共有10000条查询结果,搜索用时 265 毫秒
981.
982.
983.
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985.
G. C. Bussolino J. Spišiak F. Righini A. Rosso P. C. Cresto R. B. Roberts 《International Journal of Thermophysics》1993,14(3):525-539
A new dynamic technique for the measurement of thermal conductivity is being developed at IMGC. The experiment consists in bringing the specimen to high temperatures with a current pulse and in measuring the temperature profiles during the free cooling period. Different techniques can be used to extract the information on thermal conductivity from the profiles. The numerical computation of thermal conductivity from the experimental temperature profiles in absolute space is possible, but it is difficult and cumbersome because one must know and take into the account the exact position of the infinitesimal elements of the specimen in different profiles. Computations in tube-space (a fictitious space where no thermal expansion occurs) are simpler and lead to less complex numerical computations. Complementary techniques to evaluate thermal conductivity as a function of temperature or at constant temperature are presented with a discussion of advantages and disadvantages of each method. Computer simulations have tested the precision of the complex software. Numerically generated temperature profiles from known thermophysical properties have been obtained and thermal conductivity has been recomputed from the profiles. The relative difference using different computational approaches and different fitting functions is always less than 0.1%.Paper presented at the Third Workshop on Subsecond Thermophysics, September 17–18, 1992, Graz, Austria. 相似文献
986.
H. M. Roder 《International Journal of Thermophysics》1984,5(4):323-350
The paper presents new experimental measurements of the thermal conductivity of hydrogen. The ortho-para compositions covered are normal, near normal, para, and para-rich. The measurements were made with a transient hot wire apparatus. The temperatures covered the range from 78 to 310 K with pressures to 70 MPa and densities from 0 to a maximum of 40 mol · L–1. For compositions normal and near normal, the isotherms cover the entire range of pressure, and the temperatures are 78, 100, 125, 150, 175, 200, 225, 250, 275, 294, 300, and 310K. The para measurements include eight isotherms at temperatures from 100 to 275 K with intervals of 25 K, pressures to 12 MPa, and densities from 0 to 12 mol · L–1. Three additional isotherms at 150, 250, and 275 K cover para-rich compositions with para percentages varying from 85 to 72%. For these three isotherms the pressures reach 70 MPa and the density a maximum of 30 mol · L–1. The data for all compositions are represented by a single thermal conductivity surface. The data are compared with the experimental measurements of others through the new correlation. The precision (2) of the hydrogen measurements is between 0.5 and 0.8% for wire temperature transients of 4 to 5 K, while the accuracy is estimated to be 1.5%. 相似文献
987.
The paper presents thermal conductivity measurements of ethane over the temperature range of 290–600 K at pressures to 700 bar including the critical region with maximum uncertainty of 0.7 to 3% obtained with a transient line source instrument. A correlation of the data is presented and used to prepare tables of recommended values that are accurate to within 2.5% in the experimental range except near saturation, and in the critical region, where the anomalous thermal conductivity values are predicted to within 5%.Nomenclature
a
k
, b
ij
, b
k
, c
i
Parameters of the regression model, k=0 to n, i=0 to m, j=0 to n
-
P
Pressure, (MPa or bar)
-
Q
l
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 K
-
T
*
Reduced temperature difference (T–T
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
Thermal conductivity anomaly, 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 相似文献
988.
Study of Nano-Porous Silicon with Low Thermal Conductivity as Thermal Insulating Material 总被引:1,自引:0,他引:1
V. Lysenko Ph. Roussel B. Remaki G. Delhomme A. Dittmar D. Barbier V. Strikha C. Martelet 《Journal of Porous Materials》2000,7(1-3):177-182
Recently discovered phenomenon of extremely low thermal conductivity of nano-porous silicon (nano-PS) is discussed in detail. A theoretical model describing specific mechanisms of heat transport in as-prepared and oxidized nano-PS layers is described. The theoretical estimations are in a good agreement with experimental data obtained earlier. The low thermal conductivity values allow to use this promising material as thermal insulator in microsensors and microsystems. To ensure an efficient thermal isolation, a nano-PS layer has to be as thick as possible and mechanically stable. We describe here the procedures to form thick (up to 200 m) and stable nano-PS layers. Distribution of Si oxidized fraction along the layer thickness after thermal oxidation in dry O2 atmosphere at 300°C during 1 h is studied. 相似文献
989.
990.
The function of vinylene carbonate as a thermal additive to electrolyte in lithium batteries 总被引:1,自引:0,他引:1
Hsiang-Hwan?Lee Yung-Yun?Wang Chi-Chao?WanEmail author Mo-Hua?Yang Hung-Chun?Wu Deng-Tswen?Shieh 《Journal of Applied Electrochemistry》2005,35(6):615-623
The role of vinylene carbonate (VC) as a thermal additive to electrolytes in lithium ion batteries is studied in two aspects: the protection of liquid electrolyte species and the thermal stability of the solid electrolyte interphase (SEI) formed from VC on graphite electrodes at elevated temperatures. The nuclear magnetic resonance (NMR) spectra indicate that VC can not protect LiPF6 salt from thermal decomposition. However, the function of VC on SEI can be observed via impedance and electron spectroscopy for chemical analysis (ESCA). These results clearly show VC-induced SEI comprises polymeric species and is sufficiently stable to resist thermal damage. It has been confirmed that VC can suppress the formation of resistive LiF, and thus reduce the interfacial resistance. 相似文献