共查询到20条相似文献,搜索用时 15 毫秒
1.
AbstractIn this review, we summarize the recent progress in thermal conductivity analysis of nanocellulose materials called cellulose nanopapers, and compare them with polymeric materials, including neat polymers, composites, and traditional paper. It is important to individually measure the in-plane and through-plane heat-conducting properties of two-dimensional planar materials, so steady-state and non-equilibrium methods, in particular the laser spot periodic heating radiation thermometry method, are reviewed. The structural dependency of cellulose nanopaper on thermal conduction is described in terms of the crystallite size effect, fibre orientation, and interfacial thermal resistance between fibres and small pores. The novel applications of cellulose as thermally conductive transparent materials and thermal-guiding materials are also discussed. 相似文献
2.
A. Sparavigna M. Omini A. Pasquarelli A. Strigazzi 《International Journal of Thermophysics》1992,13(2):351-360
A comparative method is presented, suitable to measure both thermal diffusivity and conductivity of low-conducting solids. The repeatibility of the measurements of thermal conductivity is 3%, whereas for diffusivity is 6%. Data for some low-conducting materials are given, consistent with those reported in the literature. 相似文献
3.
This paper reports new measurements of the thermal conductivity of sulfur hexafluoride at the nominal temperature of 27.5°C as a function of density in the range up to 200 kg · m–3. The measurements were performed in a transient, hot-wire instrument. When combined with earlier measurements of the viscosity of the gas, they allow us to calculate the rather large contribution stemming from the internal degrees of freedom. The present measurements compare well with those in the literature. All of them suggest that the excess thermal conductivity is a unique function of density in the present range of states. An empirical correlation of our measurements can serve users in the ranges 0 < t< 100°C and 0 < < 200 kg · m–3. 相似文献
4.
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
相似文献
5.
S. Nagarjuna 《Bulletin of Materials Science》2004,27(1):69-71
The thermal conductivity (TC) of peak aged Cu-4.5 wt% Ti alloy was measured at different temperatures and studied its variation
with temperature. It was found that TC increased with increasing temperature. Phonon and electronic components of thermal
conductivity were computed from the results. The alloy exhibits an electronic thermal conductivity of 46.45 W/m.K at room
temperature. The phonon thermal conductivity decreased with increasing temperature from 17.6 at 0 K to 1.75 W/m.K at 298 K,
which agrees with literature that the phonon component of thermal conductivity is insignificant at room temperature. 相似文献
6.
7.
Thermal conductivity of composites 总被引:2,自引:0,他引:2
P. G. Klemens 《International Journal of Thermophysics》1990,11(5):971-976
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. 相似文献
8.
A new expression for the thermal conductivity of anN-component polyatomic gas mixture in the dilute-gas limit has been derived, based on the Thijsse approximation. The results
are presented in terms of experimentally accessible quantities to allow for easier calculation of the thermal conductivity
and easier interpretation of the experimentally available data. The resulting expression are much simpler than other formulae
hitherto available. An additional new expression for the thermal conductivity of anN-component polyatomic gas mixture has been derived by replacing the effective cross-section by their spherical limits. These
results are cast in a form which is analogous with, and no more complicated than, the corresponding expressions for purely
monatomic mixtures.
Paper dedicated to Professor Edward A. Mason. 相似文献
9.
C. E. Hickox D. F. McVey J. B. Miller L. O. Olson A. J. Silva 《International Journal of Thermophysics》1986,7(4):755-764
Results are reported for effective thermal conductivity measurements performed in situ and in core samples of illite marine sediment. The measurements were obtained during a recent oceanographic expedition to a study site in the north central region of the Pacific Ocean. This study was undertaken in support of the U.S. Subseabed Disposal Project, the purpose of which is to investigate the scientific feasibility of using the fine-grained sediments of the sea floor as a repository for high-level nuclear waste. In situ measurements were made and 1.5-m-long hydrostatic piston cores were taken, under remote control, from a platform that was lowered to the sea floor, 5844 m below sea level. The in situ measurement of thermal conductivity was made at a nominal depth of 80 cm below the sediment surface using a specially developed, line-source, needle probe. Thermal conductivity measurements in three piston cores and one box core (obtained several kilometers from the study site) were made on shipboard using a miniature needle probe. The in situ thermal conductivity was approximately 0.91 W · m–1 · K–1. Values determined from the cores were within the range 0.81 to 0.89 W · m–1 · K–1.Paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A. 相似文献
10.
11.
12.
J. C. G. Calado J. M. N. A. Fareleira U. V. Mardolcar C. A. Nieto de Castro 《International Journal of Thermophysics》1988,9(3):351-363
The thermal conductivity of liquids has been shown in the past to be difficult to predict with a reasonable accuracy, due to the lack of accurate experimental data and reliable prediction schemes. However, data of a high accuracy, and covering wide density ranges, obtained recently in laboratories in Boulder, Lisbon, and London with the transient hot-wire technique, can be used to revise an existing correlation scheme and to develop a new universal predictive technique for the thermal conductivity of liquid normal alkanes. The proposed correlation scheme is constructed on a theoretically based treatment of the van der Waals model of a liquid, which permits the prediction of the density dependence and the thermal conductivity of liquid n-alkanes, methane to tridecane, for temperatures between 110 and 370 K and pressures up to 0.6 MPa, i.e., for 0.3T/T
c0.7 and 2.4P/P
c3.7, with an accuracy of ±1%, given a known value of the thermal conductivity of the fluid at the desired temperature. A generalization of the hard-core volumes obtained, as a function of the number of carbon atoms, showed that it was possible to predict the thermal conductivity of pentane to tetradecane±2%, without the necessity of available experimental measurements. 相似文献
13.
We have investigated the thermal conductivity tensor of strongly sheared atomic and molecular liquids by computer sinudation methods. According to linear nonequilibrium thermodynamics. licat and transverse momentum transport are uncoupled in the linear reginx. We also expect the thermal conductivity to he independent of the zero-wavevector strain rate in the linear regime. Away from the linear regime. the Situation is dillcrent. Although even a large zero-wavevector strain rate cannot induce a heat flux. the thermal conductivity can become strain-rate dependent. Furthermore, the thermal conductivity becomes a lensor because a strong velocity prolile can destroy the isotropy of a fluid. These effects are only apparent at extremely high strain rates for atomic liquids, but are experimentally observable for polymeric liquids.Paper presented at the Twelfth Symposium on Thermophysical Properties. June 19-24. 1994, Boulder, Colorado. U.S.A. 相似文献
14.
P Balaya H S Jayanna Hemant Joshi G Sumana V G Narasimha Murthy V Prasad S V Subramanyam 《Bulletin of Materials Science》1995,18(8):1007-1011
We describe briefly the experimental facilities developed for the measurement of thermal conductivity of solids in the temperature
range 10K–300K. Different techniques have been used for the determination of thermal conductivity, depending on the relaxation
time of the system under investigation. Measurements on stainless steel 304, using steady state and non-steady state methods
are presented. Values of thermal conductivity obtained by both these methods agree to each other and are consistent with those
reported earlier.
Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995 相似文献
15.
Thermal conductivity and diffusivity of biomaterials measured with self-heated thermistors 总被引:4,自引:0,他引:4
This paper presents an experimental method to measure the thermal conductivity and thermal diffusivity of biomaterials. Self-heated thermistor probes, inserted into the tissue of interest, are used to deliver heat as well as to monitor the rate of heat removal. An empirical calibration procedure allows accurate thermal-property measurements over a wide range of tissue temperatures. Operation of the instrument in three media with known thermal properties shows the uncertainty of measurements to be about 2%. The reproducibility is 0.5% for the thermal-conductivity measurements and 2% for the thermal-diffusivity measurements. Thermal properties were measured in dog, pig, rabbit, and human tissues. The tissues included kidney, spleen, liver, brain, heart, lung, pancreas, colon cancer, and breast cancer. Thermal properties were measured for 65 separate tissue samples at 3, 10, 17, 23, 30, 37, and 45°C. The results show that the temperature coefficient of biomaterials approximates that of water. 相似文献
16.
J. C. G. Calado J. M. N. A. Fareleira C. A. Nieto de Castro W. A. Wakeham 《International Journal of Thermophysics》1983,4(3):193-208
The paper presents the results of new, absolute measurements of the thermal conductivity of five alkanes as a function of temperature at their saturation vapor pressure. The alkanes studied include the four normal alkanes n-octane, n-nonane, n-undecane, and n-tetradecane as well as the branched alkane, iso-octane. The results, which extend over the temperature range 282–373 K, have an estimated uncertainty limit of 1.5% deriving mainly from a correction for the effects of radiation absorption in the measurement process. The results are employed to generate effective core volumes for the fluids studied which may be employed to predict the density dependence of the thermal conductivity by means of an existing correlation. 相似文献
17.
In this paper, we present a comparison of the thermal diffusivity and thermal conductivity data of steam in the temperature range 0.02 K<T-T
c< 140 K with a recent formulation of crossover from singular to regular behavior of the transport properties of fluids. We have used two sets of experimental data previously obtained by the authors. The agreement between experimental and calculated data is good. 相似文献
18.
热线法测量保温材料的导热系数 总被引:3,自引:0,他引:3
本文在分析热线法测量导热系数原理的基础上,应用热线法测定了几种保温材料不同温度下的导热系数。并通过Origin 7.0对测量结果进行了数据线性拟合,可快捷、精确的获得测量结果。 相似文献
19.
超高分子量聚乙烯基纳米复合材料的导热性能研究 总被引:1,自引:1,他引:0
通过添加导热系数较高的纳米AIN、C纤维来制备超高分子量聚乙烯复合材料,采用Hot Disk导热系数仪测试了其导热系数,同时分析了不同添加物及其含量对导热系数的影响.结果表明,制备的超高分子量聚乙烯复合材料的导热性能有明显提高.在本实验条件下,当纤维的添加量达到20%时,复合材料的热导率为0.8969 W·m-1·K-1,比纯超高分子量聚乙烯提高了150%. 相似文献
20.
A coaxial cylinder method was used to measure the thermal conductivity of ethane in the pressure range from 10 up to 280 bar and in the temperature range from 308 up to 365 K. 相似文献