共查询到20条相似文献,搜索用时 31 毫秒
1.
K. H. Kang H. S. Moon K. C. Song M. S. Yang S. H. Lee S. W. Kim 《International Journal of Thermophysics》2007,28(5):1595-1606
The thermal diffusivity of a simulated fuel with fission products forming a solid solution was measured using the laser-flash
method in the temperature range from room temperature to 1673 K. The density and the grain size of the simulated fuel with
the solid solutions used in the measurement were 10.49 g · cm−3 (96.9% of theoretical density) at room temperature and 9.5 μm, respectively. The diameter and thickness of the specimens were 10 and 1 mm, respectively. The thermal diffusivity decreased
from 2.108 m2 · s−1 at room temperature to 0.626 m2 · s−1 at 1673 K. The thermal conductivity was calculated by combining the thermal diffusivity with the specific heat and density.
The thermal conductivity of the simulated fuel with the dissolved fission products decreased from 4.973 W · m−1 · K−1 at 300 K to 2.02 W · m−1 · K−1 at 1673 K. The thermal conductivity of the simulated fuel was lower than that of UO2 by 34.36% at 300 K and by 15.05% at 1673 K. The difference in the thermal conductivity between the simulated fuel and UO2 was large at room temperature, and decreased with an increase in temperature.
Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak
Republic. 相似文献
2.
M. Wiener G. Reichenauer F. Hemberger H. -P. Ebert 《International Journal of Thermophysics》2006,27(6):1826-1843
Amorphous carbon samples with a total porosity of about 85% were synthesized via pyrolysis of sol–gel derived resin precursors. Since the pores in the samples investigated have dimensions of a few tens of nanometers only, the gaseous contribution to the thermal conductivity is largely suppressed at ambient pressure. Values for the total thermal conductivity as low as 0.054 W·m−1·K−1 at 300°C are detected. However, the pyrolysis temperature has a great impact on the contribution of the solid backbone to the total thermal conductivity. From the same precursor a series of samples was prepared via pyrolysis at temperatures ranging from 800 to 2500°C. The thermal conductivity of this series of carbons at 300°cC under vacuum increases by a factor of about 8 if the pyrolysis temperature is shifted from 800 to 2500°C. To elucidate the reason for this strong increase, the infrared radiative properties, the electrical conductivity, the macroscopic density, the microcrystallite size, the sound velocity, and the inner surface of the samples were determined. Evaluation of the experimental data yields only a negligible contribution from radiative heat transfer and electronic transport to the total thermal conductivity. The main part of the increasing thermal conductivity therefore has to be attributed to an increasing phonon mean free path in the carbons prepared at higher pyrolysis temperatures. However, the phonon mean free path does not match directly the in-plane microcrystallite size of the amorphous carbon. Rather, the in-plane microcrystallite size represents an upper limit for the phonon mean free path. Hence, the limiting factor for the heat transport via phonons has to be defects swithin the carbon microcrystallites which are partially cured at higher temperatures.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic. 相似文献
3.
L. Miettinen P. Kekäläinen J. Merikoski J. Timonen 《International Journal of Thermophysics》2009,30(6):1902-1917
The transient fin model introduced recently for determination of the in-plane thermal diffusivity of planar samples with the
help of infrared thermography was modified so as to be applicable to poor heat conductors. The new model now includes a temperature-dependent
heat loss by convective heat transfer, suitable for an experimental setup in which the sample is aligned parallel to a weak,
forced air flow stabilizing otherwise the convective heat transfer. The temperature field in the sample was measured with
an infrared camera while the sample was heated at one edge. The symmetric temperature field created was averaged over the
central fifth of the sample to obtain one-dimensional temperature profiles, both transient and stationary, which were fitted
by a numerical solution of the fin model. One of the fitting parameters was the thermal diffusivity, and with a known density
and specific heat capacity, the thermal conductivity was thus determined. The test measurements with tantalum samples gave
the result (57.5 ± 0.2) W · m−1 · K−1 in excellent agreement with the known value. The other fitting parameter was a temperature-dependent heat loss coefficient
from which the lower limit for the temperature-dependent convection coefficient was determined. For the stationary state the
result was (1.0 ± 0.2) W · m−2 · K−1 at the temperature of the flowing air, and its temperature dependence was found to be (0.22 ± 0.01) W ·m−2 · K−2. 相似文献
4.
The thermal conductivities, thermal diffusivity, thermal anisotropy ratio, and thermal boundary resistance for the multilayered
microstructure of a carbon nanotube (CNT) array are reconstructed experimentally using the 3ω method with two different width
metal heaters. The thermal impedance in the frequency domain and sensitivity coefficients are introduced to simultaneously
determine the multiple thermal parameters. The thermal conductivity at 295 K is 38 W · m−1 · K−1 along the nanotube growth direction, and two orders of magnitude lower in the direction perpendicular to the tubes with the
anisotropy ratio as large as 86. Separation of the contact and CNT array resistances is realized through circuit modeling.
The measured thermal boundary resistances of the CNT array/Si substrate and insulating diamond film interfaces are 3.1 m2 · K · MW−1 and 18.4 m2 · K · MW−1, respectively. The measured thermal boundary resistance between the heater and diamond film is 0.085 m2 · K · MW−1 using a reference sample without a CNT array. The thermal conductivity for a CNT array already exceeds those of phase-changing
thermal interface materials used in microelectronics. 相似文献
5.
M. Wiener G. Reichenauer S. Braxmeier F. Hemberger H.-P. Ebert 《International Journal of Thermophysics》2009,30(4):1372-1385
Carbon aerogels, monolithic porous carbons derived via pyrolysis of porous organic precursors synthesized via the sol–gel
route, are excellent materials for high-temperature thermal insulation applications both in vacuum and inert gas atmospheres.
Measurements at 1773K reveal for the aerogels investigated thermal conductivities of 0.09W · m−1 · K−1 in vacuum and 0.12W · m−1 · K−1 in 0.1MPa argon atmosphere. Analysis of the different contributions to the overall thermal transport in the carbon aerogels
shows that the heat transfer via the solid phase dominates the thermal conductivity even at high temperatures. This is due
to the fact that the radiative heat transfer is strongly suppressed as a consequence of a high infrared extinction coefficient
and the gaseous contribution is reduced since the average pore diameter of about 600nm is limiting the mean free path of the
gas molecules in the pores at high temperatures. Based on the thermal conductivity data detected up to 1773K as well as specific
extinction coefficients determined via infrared-optical measurements, the thermal conductivity can be extrapolated to 2773K
yielding a value of only 0.14W· m−1 · K−1 in vacuum. 相似文献
6.
This paper reports the d.c. conductivity behaviour of milled carbon fibre reinforced polysulphide modified epoxy gradient
composites. Milled carbon fibre reinforced composites having 3 vol. % of milled carbon fibre and poly sulphide modified epoxy
resin have been developed. D.C. conductivity measurements are conducted on the graded composites by using an Electrometer
in the temperature range from 26°C to 150°C. D.C. conductivity increases with the increase of distance in the direction of
centrifugal force, which shows the formation of graded structure with the composites. D.C. conductivity increases on increase
of milled carbon fibre content from 0·45 to 1·66 vol.%. At 50°C, d.c. conductivity values were 1·85 × 10−11, 1·08 × 10−11 and 2·16 × 10−12 for samples 1, 2 and 3, respectively. The activation energy values for different composite samples 1, 2 and 3 are 0·489,
0·565 and 0·654 eV, respectively which shows decrease in activation energy with increase of fibre content. 相似文献
7.
Sayyadul Arafin Ram N. Singh Abraham K. George 《International Journal of Thermophysics》2011,32(10):2139-2147
The thermal diffusivity, D, and its temperature dependence of Oman harzburgite rock and its major mineral olivine have been evaluated from the basic
properties such as seismic velocities, density, and Debye temperature. The Arrhenius-type temperature dependence of the diffusivity
was utilized to evaluate the heat of formation, ΔH
D. The diffusivity values, 1.80mm2 · s−1 and 2.1mm2 · s−1 obtained at room temperature for harzburgite and olivine, respectively, are consistent with available data. The diffusivity
values for Oman harzburgite are overestimated by an amount of 0.27mm2 · s−1 relative to those of PNG harzburgite. The ΔH
D value (−2.40 kJ · mol−1) for harzburgite rock of the Oman ophiolite suite is comparable with that (−2.90 kJ · mol−1) of the harzburgite rock of Papua New Guinea. The disagreements in the thermal diffusivity and heat of formation values may
be partly due to ignoring the effect of pyroxene in Oman harzburgite. 相似文献
8.
Liangfa Hu Chang-An Wang Zijun Hu Sheng Lu Chencheng Sun Yong Huang 《Journal of Materials Science》2011,46(3):623-628
This study describes the experimental results of thermal diffusivity, specific heat at constant pressure, and thermal conductivity
of porous 8 mol% yttria-stabilized zirconia (YSZ) ceramics in a temperature range from room temperature to 1,400 °C. It is
a follow-up study of the earlier report titled by “Porous YSZ ceramics with ultra-low thermal conductivity”, which focused
on the room-temperature thermal conductivity. The thermal diffusivity of porous YSZ ceramics decreased with the increase of
the measurement temperature up to 600–1,000 °C, followed by an increasing trend with increasing temperature. The specific
heat did not exhibit any significant dependence on sintering temperature and agreed with literature data. The thermal conductivity
of the porous YSZ ceramics showed an insensitive tendency of change with measurement temperature. The thermal conductivity
fell in groups by the sintering temperature level. This investigation also discussed an appropriate sintering temperature
of porous YSZ ceramics, which had both low thermal conductivity and high strength required by the practical service. 相似文献
9.
Influence of cryogenic thermal cycling treatment (from ?120 °C to 120 °C at 1.3 × 10?3 Pa) on the thermophysical properties including thermal conductivity (TC), thermal diffusivity (TD), specific heat (SH) and coefficient of thermal expansion (CTE) ranging from room temperature to 1900 °C of carbon/carbon (C/C) composites in x-y and z directions were studied. Test results showed that fiber/matrix interfacial debonding, fiber pull-out and microcracks occurred after the cryogenic thermal treatment and they increased significantly with the cycle number increasing, while cycled more than 30 times, the space of microdefects reduced obviously due to the accumulation of cyclic thermal stress. TC, TD, SH and CTE of the cryogenic thermal cycling treated C/C composites were first decreased and then increased in both directions (x-y and z directions) with the increase of thermal cycles. A model regarding the heat conduction in cryogenic thermal cycling treated C/C composites was proposed. 相似文献
10.
S. W. Kim S. H. Lee J. S. Kang K. H. Kang 《International Journal of Thermophysics》2006,27(6):1873-1881
With restrictions for environmental protection being strengthened, thermoplastics reinforced with natural fibers such as jute, kenaf, flax, etc., have replaced automotive interior materials such as chemical plastics. In this study, the thermal conductivity of several kinds of thermoplastic composites in the form of board composed of 48.5 mass% polypropylene (PP) and 48.5 mass% natural fiber (NF), and reinforced with 3.0 mass% maleated polypropylene (MAPP) and 0.3 mass% silane as the coupling agents, were measured at temperatures of −10, 10, and 30°C, using a heat flow meter apparatus. The results show that the thermal conductivity is in the range of 0.05–0.07 W · m−1 · K−1, and the thermal conductivity increased about 10–15% by adding MAPP and about 10–25% by soaking in a silane aqueous solution. The tensile strength was also measured, and the result shows similar trends as the thermal conductivity.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic. 相似文献
11.
The extended dynamic plane source (EDPS) method is one of the transient methods for measurements of the thermal conductivity
and thermal diffusivity in solids. This technique uses a transient plane source (TPS) sensor, which serves as the heat source
and thermometer. Its calibration consists of measuring the temperature dependence of the TPS sensor resistance and computing
the temperature coefficient of resistance (TCR) using least-squares (LS) estimation. The goal of this study is to calibrate
the TPS sensor directly in the apparatus for the EDPS method. The article presents an uncertainty assessment of the TCR measurement.
The main sources of uncertainty stem from resistance measurements of the constant resistor and platinum thermometer calibration.
The LS estimate of the TCR in a nickel TPS sensor is 4.83 × 10−3 K−1 at 20 °C and 4.57 × 10−3 K−1 at 45 °C with a combined standard uncertainty better than 0.04 × 10−3 K−1, which is 0.7 %. 相似文献
12.
Silicon nitride-silicon carbide (Si3N4-SiC) composites were prepared by varying the percentage of silicon nitride at temperatures of 1350 to 1450°C. The mechanical
and thermal properties of these composites were determined. The modulus of rupture of the composites increases with increase
of temperature whereas the thermal expansion decreases. Composites with 10% and 50% Si3N4 have modulus of rupture of 49 and 86 MPa at 1400°C and thermal expansion coefficients (25°–1000°C) of 4·4 × 10−6 and 3·2 × 10−6°C−1 respectively. 相似文献
13.
A high sensitivity thermoelectric sensor to measure all relevant thermal transport properties has been developed. This so-called transient hot bridge (THB) decidedly improves the state of the art for transient measurements of the thermal conductivity, thermal diffusivity, and volumetric specific heat. The new sensor is realized as a printed circuit foil of nickel between two polyimide sheets. Its layout consists of four identical strips arranged in parallel and connected for an equal-ratio Wheatstone bridge. At uniform temperature, the bridge is inherently balanced, i.e., no nulling is required prior to a run. An electric current makes the unequally spaced strips establish an inhomogeneous temperature profile that turns the bridge into an unbalanced condition. From then on, the THB produces an offset-free output signal of high sensitivity as a measure of the properties mentioned of the surrounding specimen. The signal is virtually free of thermal emf’s because no external bridge resistors are needed. Each single strip is meander-shaped to give it a higher resistivity and, additionally, segmented into a long and short part to compensate for the end effect. The THB closely meets the specific requirements of industry and research institutes for an easy to handle and accurate low cost sensor. As the key component of an instrument, it allows rapid thermal-conductivity measurements on solid and fluid specimens from 0.02 to 100 W· m−1·K−1 at temperatures up to 250°C. Measurements on some reference materials and thermal insulations are presented. These verify the preliminary estimated uncertainty of 2% in thermal conductivity. 相似文献
14.
Sanghyun Lee Hye Jeong Ham Su Yong Kwon Sok Won Kim Chang Min Suh 《International Journal of Thermophysics》2013,34(12):2343-2350
Magnesium alloys have been widely used in recent years as lightweight structural materials in the manufacturing of automobiles, airplanes, and portable computers. Magnesium alloys have extremely low density (as low as 1738 kg · m?3) and high rigidity, which makes them suitable for such applications. In this study, the thermal conductivity of two different magnesium alloys made by twin-roll casting was investigated using the laser-flash technique and differential scanning calorimetry for thermal diffusivity and specific heat capacity measurements, respectively. The thermal diffusivity of the magnesium alloys, AZ31 and AZ61, was measured over the temperature range from ?125 °C to 400 °C. The alloys AZ31 and AZ61 are composed of magnesium, aluminum, and zinc. The thermal conductivity gradually increased with temperature. The densities of AZ31 and AZ61 were 1754 kg · m?3 and 1777 kg · m?3, respectively. The thermal conductivity of AZ31 was about 25 % higher than that of AZ61, and this is attributed to the amount of precipitation. 相似文献
15.
J. Blumm A. Lindemann M. Meyer C. Strasser 《International Journal of Thermophysics》2010,31(10):1919-1927
Polytetrafluoroethylene (PTFE) is a synthetic fluoropolymer used in numerous industrial applications. It is often referred
to by its trademark name, Teflon. Thermal characterization of a PTFE material was carried out using various thermal analysis
and thermophysical properties test techniques. The transformation energetics and specific heat were measured employing differential
scanning calorimetry. The thermal expansion and the density changes were determined employing pushrod dilatometry. The viscoelastic
properties (storage and loss modulus) were analyzed using dynamic mechanical analysis. The thermal diffusivity was measured
using the laser flash technique. Combining thermal diffusivity data with specific heat and density allows calculation of the
thermal conductivity of the polymer. Measurements were carried out from − 125 °C up to 150 °C. Additionally, measurements
of the mechanical properties were carried out down to − 170 °C. The specific heat tests were conducted into the fully molten
regions up to 370 °C. 相似文献
16.
M. Geisler J. Wachtel F. Hemberger T. Schultz S. Vidi H.-P. Ebert 《International Journal of Thermophysics》2008,29(4):1385-1394
Recent measurements have shown a record-breaking low thermal conductivity λtotal of less than 0.25 × 10−3 W·m−1·K−1 at temperatures of 120 K for an evacuated sample consisting of polyimide fibers with a trilobal fiber cross section. Existing
models for the heat transport in fiber insulations cannot sufficiently describe fiber insulations consisting of fibers with
non-cylindrical cross sections. In this article, a modification for the model for cylindrical fibers will be presented. The
modifications for the trilobal cross section of the fiber will be explained and compared to the original cylindrical model.
The results of the theoretical calculations will be discussed in comparison to experimental results of measurements performed
with a guarded hot-plate apparatus at temperatures in the range from 120 K to 420 K. 相似文献
17.
Koji Takahashi Norsyazwan Hilmi Yohei Ito Tatsuya Ikuta Xing Zhang 《International Journal of Thermophysics》2009,30(6):1864-1874
The small size of nanomaterials deposited by either focused ions or electron beams has prevented the determination of reliable
thermal property data by existing methods. A new method is described that uses a suspended platinum hot film to measure the
thermal conductivity of a nanoscale deposition. The cross section of the Pt film needs to be as small as 50 nm × 500 nm to
have sufficient sensitivity to detect the effect of the beam-induced nanodeposition. A direct current heating method is used
before and after the deposition, and the change in the average temperature increase of the Pt hot film gives the thermal conductivity
of the additional deposited material. In order to estimate the error introduced by the one-dimensional analytical model employed,
a two-dimensional numerical simulation was conducted. It confirmed the reliability of this method for situations where the
deposit extends onto the terminals by (1 μm or more. Measurements of amorphous carbon (a-C) films fabricated by electron beam
induced deposition (EBID) produced thermal conductivities of 0.61 W · m−1 · K−1 to 0.73 W · m−1 · K−1 at 100 K to 340 K, values in good agreement with those of a-C thin films reported in the past. 相似文献
18.
Joko Sulistyo Toshimitsu Hata Hiroyuki Kitagawa Paul Bronsveld Masashi Fujisawa Kozo Hashimoto Yuji Imamura 《Journal of Materials Science》2010,45(4):1107-1116
Porous SiC/SiO2/C composites exhibiting a wide range of high thermal and electrical conductivities were developed from carbonized wood infiltrated
with SiO2. As a pre-treatment, the samples were either heated at 100 °C or kept at room temperature followed by sintering in the temperature
range 1200–1800 °C. The microstructure, the morphology, and the electrical and thermal conductivities of the composites were
investigated. Pre-treatment at room temperature followed by sintering up to 1800 °C produced composites exhibiting a greater
size of carbon crystallites, a higher ordering of the microstructure of carbon and β-SiC and a smaller amount of SiO2, resulting in electrical and thermal conductivities of 1.17 × 104 Ω−1 m−1 and 25 W/mK, respectively. The thermal conductivity could be further improved to 101 W/mK by increasing the density of the
composite to 1.82 g/cm3. In contrast, the pre-treatment at 100 °C produced composites possessing a lower thermal conductivity of 2 W/mK. 相似文献
19.
Measurements of the thermophysical properties of Gioia marble in the temperature range from −20 to 60°C are presented. Thermophysical
properties, namely, thermal diffusivity, thermal conductivity, and specific heat, were measured by the pulse transient technique.
The data were compared for dry and water-saturated states. Despite the very low porosity of marble of about 0.6 vol%, an increase
of the transport property parameters (thermal diffusivity and thermal conductivity) up to 20% after water saturation was found.
To verify the differences in the transport parameters, the ultrasonic pulse velocity method was employed. A detailed analysis
of thermophysical property data during the freeze/thaw process for dry and water-saturated marble was carried out in the temperature
range from −8 to 1°C, where an anomaly in the water freezing process was observed. In order to study artificial aging of Gioia
marble, up to 60 freeze/thaw cycles were performed. No significant changes in the thermophysical properties of Gioia marble
were observed during the artificial aging process.
Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak
Republic. 相似文献
20.
C. Glorieux J. De Groote J. Fivez W. Lauriks J. Thoen 《International Journal of Thermophysics》1993,14(6):1201-1214
Heat conduction in a free-standing chemical vapor-deposited polycristalline diamond film has been investigated by means of
combined front and rear photoacoustic signal detection techniques and also by means of a “mirage” photothermal beam deflection
technique. The results obtained with the different techniques are consistent with a value of α=(5.5±0.4)×10−4 m2 · s−1 for thermal diffusivity, resulting in a value ofκ=(9.8±0.7)×102 W·m−1·K−1 for thermal conductivity when literature values for the density and heat capacity for natural diamond are used. 相似文献