共查询到20条相似文献,搜索用时 10 毫秒
1.
P. L. Woodfield J. Fukai M. Fujii Y. Takata K. Shinzato 《International Journal of Thermophysics》2008,29(4):1278-1298
Unlike the conventional transient hot-wire method for measuring thermal conductivity, the transient short-hot-wire method
uses only one short thermal-conductivity cell. Until now, this method has depended on numerical solutions of the two-dimensional
unsteady heat conduction equation to account for end effects. In order to provide an alternative and to confirm the validity
of the numerical solutions, a two-dimensional analytical solution for unsteady-state heat conduction is derived using Laplace
and finite Fourier transforms. An isothermal boundary condition is assumed for the end of the cell, where the hot wire connects
to the supporting leads. The radial temperature gradient in the wire is neglected. A high-resolution finite-volume numerical
solution is found to be in excellent agreement with the present analytical solution. 相似文献
2.
P. L. Woodfield J. Fukai M. Fujii Y. Takata K. Shinzato 《International Journal of Thermophysics》2008,29(4):1299-1320
The transient short-hot-wire method for measuring thermal conductivity and thermal diffusivity makes use of only one thermal-conductivity
cell, and end effects are taken into account by numerical simulation. A search algorithm based on the Gauss–Newton nonlinear
least-squares method is proposed to make the method applicable to high-diffusivity (i.e., low-density) gases. The procedure
is tested using computer-generated data for hydrogen at atmospheric pressure and published experimental data for low-density
argon gas. Convergence is excellent even for cases where the temperature rise versus the logarithm of time is far from linear.
The determined values for thermal conductivity from experimental data are in good agreement with published values for argon,
while the thermal diffusivity is about 10 % lower than the reference data. For the computer-generated data, the search algorithm
can return both thermal conductivity and thermal diffusivity to within 0.02 % of the exact values. A one-dimensional version
of the method may be used for analysis of low-density gas data produced by conventional transient hot-wire instruments. 相似文献
3.
4.
5.
M. J. Assael K. D. Antoniadis K. E. Kakosimos I. N. Metaxa 《International Journal of Thermophysics》2008,29(2):445-456
This article describes the final refinements of a novel application of the transient hot-wire technique developed for the
absolute, accurate measurements of the thermal conductivity of solids. Although the technique was originally developed five
years ago, these new refinements allow a full understanding of the method and hence the performance of measurements with an
absolute uncertainty of less than 1 %. New measurements of Pyroceram 9606 up to 420 K are reported. The maximum deviation
of the present measurements is 0.54 %, while their standard deviation at the 95 % confidence level is 0.25 %. Since May 2007,
Pyroceram 9606 is a European Commission certified thermal-conductivity reference material, designated as BCR-724, with an
uncertainty of ±6.5 % at the 95 % confidence level. 相似文献
6.
Numerical Analysis of Convective Instabilities in a Transient Short-Hot-Wire Setup for Measurement of Liquid Thermal Conductivity 总被引:1,自引:0,他引:1
Roberto Rusconi Wesley C. Williams Jacopo Buongiorno Roberto Piazza Lin-Wen Hu 《International Journal of Thermophysics》2007,28(4):1131-1146
Numerical simulation has been used to investigate the effects of natural convection on measurements of the thermal conductivity
of fluids by transient hot-wire methods. Comparison of the numerical data with the experimental results obtained with a custom-built
setup exploiting a short-wire geometry allows fixing an operationally useful time scale, where convective effects can be safely
neglected. 相似文献
7.
E. Yusibani P. L. Woodfield M. Kohno K. Shinzato Y. Takata M. Fujii 《International Journal of Thermophysics》2009,30(3):833-850
A two-dimensional analytical solution is derived for the three-omega method for measurement of thermal conductivity of materials
with a fine wire. The analytical solution includes the wire heat capacity and the effect of heat losses from the ends of the
wire. To derive the solution, finite Fourier transforms are applied in the direction parallel to the wire axis. The solution
is compared with a one-dimensional solution and experimental data. It is found that heat losses from the wire ends have a
significant effect on the 3ω components at low frequency and tend to be less important at high frequency. Moreover, it is shown that two-dimensional effects
will be severe for nano-scale wires, even if the wire length-to-diameter ratio is very large. 相似文献
8.
利用导体的电阻温度关系,讨论了精确测定导体的电阻,实现瞬态测定材料传热性能的理论和方法。利用这种方法,可以精确测量从金属到热的不良导体等众多固体材料的传热性能。 相似文献
9.
H. Fukuyama T. Yoshimura H. Yasuda H. Ohta 《International Journal of Thermophysics》2006,27(6):1760-1777
The transient hot-wire method, incorporating a static magnetic field, has been developed to measure thermal conductivities of liquid mercury and gallium. Prior to the measurements, the effect of an alumina-coated hot wire on the measurements has been evaluated. Natural convection in the liquid metals has been effectively suppressed by the Lorentz force acting on the liquid metals in a static magnetic field. The thermal conductivities of liquid mercury and gallium have been determined to be 7.9 W.m
−1.K
−1 at 291 K and 24 W.m
−1.K
−1 at 302.9 K, respectively.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic. 相似文献
10.
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
11.
Contact transient methods, some of which are available as commercial forms, are now widely used worldwide for thermal properties
measurements on broad ranges of materials used in physical, chemical, and medical applications. However, in many cases the
claimed measurement uncertainty has not been substantiated while in others – especially for the multiproperty techniques –
internal inconsistencies in measured and/or derived values are clearly apparent. Following recommendations of participants
of two workshops held on the subject in Würzburg (1999) and Cambridge, Massachussetts (2001), NPL agreed to coordinate a task
to develop a standard test-method for these techniques. This involved using inputs provided by a small group of individuals
from organizations in several European countries and also taking note of comments from other interested parties via the internet
during the course of the development. Details are provided on the resulting document, which takes the form of a generic standard
containing appropriate details and related information common to all techniques. These sections include the scope, theory,
summaries of method, basic apparatus and experiment, the influencing factors, specimen requirements, procedure, and recommended
approach for analysis of the experiment and calculation of the results. In addition, there are six annexes, each of which
contains additional information that applies to a specific technique. Finally, the document proposes a recommended approach
for verification of a technique together with a list of appropriate reference materials having known values for one or more
properties. The status of intercomparison studies will also be reported.
Paper presented as the Fifteenth Symposium on Thermophysical Properties, June 22–27, 2003, Boulder. 相似文献
12.
LiviuMarin 《计算机、材料和连续体(英文)》2009,12(1):71-100
In this paper, the alternating iterative algorithm originally proposed by Kozlov, Maz'ya and Fomin (1991) is numerically implemented for the Cauchy problem in anisotropic heat conduction using a meshless method. Every iteration of the numerical procedure consists of two mixed, well-posed and direct problems which are solved using the method of fundamental solutions (MFS), in conjunction with the Tikhonov regularization method. For each direct problem considered, the optimal value of the regularization parameter is chosen according to the generalized cross-validation (GCV) criterion. An efficient regularizing stopping criterion which ceases the iterative procedure at the point where the accumulation of noise becomes dominant and the errors in predicting the exact solutions increase, is also presented. The iterative MFS algorithm is tested for Cauchy problems related to heat conduction in two-dimensional anisotropic solids to confirm the numerical convergence, stability and accuracy of the method. 相似文献
13.
A heat conduction analysis of the functionally graded material (FGM) plates has been investigated based on the hybrid numerical method (HNM). HNM combines the layer element method with the method of Fourier transforms and proves to be efficient and reliable. The FGM plates are infinite large and the material properties vary continuously through thickness. The heat source continually acted one the FGM plates. The temperature distribution of the FGM plates is obtained in different time and different position. Some useful results for heat conduction problems are shown in figures. This article applies HNM to heat conduction firstly and provides us a new way for studying the heat conduction problems. 相似文献
14.
A damped heat wave (DHW) algorithm is applied for the temperature distribution calculation in a solution of a linear inverse heat conduction problem (IHCP). A nonlinear least squares algorithm is used for calculation of the unknown boundary heat flux history in a one-dimensional medium. The solution is based on the assumption that the temperature measurements are available, at least, at one point of the medium over the whole time domain. Sample calculations, for a comparison between exact heat sources and estimated ones, are made to confirm the validity of the proposed method. The close agreement between the exact and estimated values calculated for both exact and noisy data shows the potential of the proposed method for finding a relatively accurate heat source distribution in a one-dimensional homogeneous finite medium. The proposed method of solving inverse heat conduction problems is very simple and easy to implement.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic.M. L?ffler: Deceased 相似文献
15.
Z. L. Wang D. W. Tang S. Liu X. H. Zheng N. Araki 《International Journal of Thermophysics》2007,28(4):1255-1268
A 3ω technique is developed for simultaneous determination of the thermal conductivity and thermal diffusivity of nanofluids.
The 3ω measuring system is established, in which a conductive wire is used as both heater and sensor. At first, the system is calibrated
using water with known thermophysical properties. Then, the thermal conductivity and thermal diffusivity of TiO2/distilled water nanofluids at different temperatures and volume fractions and the thermal conductivity of SiO2 nanofluids with different carrier fluids (water, ethanol, and EG) are determined. The results show that the working temperature
and the carrier fluid play important roles in the enhancement of thermal transport in nanofluids. These results agree with
the predictions for the temperature dependence effect by the Brownian motion model and the micro-convection model. For SiO2 nanofluids, the thermal-conductance enhancement becomes strong with a decrease in the heat capacity of the carrier fluids.
Finally, according to our results and mechanism analysis, a corrected term is introduced to the Brownian motion model for
providing better prediction of heat transport performance in nanofluids. 相似文献
16.
The paper reports an assessment of the repeatability of a method for the measurement of the thermal conductivity of high temperature melts. The main goal is to demonstrate that a novel approach to the transient hot-wire technique can yield highly accurate results that are consistent with previous, independent measurements. The paper summarizes the modified transient hot-wire method, presents improvements in the finite-element analysis of its operation, and briefly discusses deviations from available analytical equations. The transient hot-wire instrument and experimental configuration are also described. Results from measurements on molten metals, in particular, tin and indium, in the temperature range from their melting points up to 750 K are presented. A comparison with previously measured values is given, and the accuracy and repeatability of the method are discussed.Paper presented at the Seventeenth European Conference on Thermophysical Properties, September 5–8, 2005, Bratislava, Slovak Republic. 相似文献
17.
J. P. Garnier J. P. Maye J. Saillard G. Thévenot A. Kadjo S. Martemianov 《International Journal of Thermophysics》2008,29(2):468-482
The transient hot-wire technique is widely used for measurements of the thermal conductivity of most fluids. However, for
some particular liquids such as concentrated nitric acid solutions or similar nitric mixtures, for which the thermal properties
are important for industrial or security applications, this technique can be difficult to use, which is essentially due to
incompatibility between measurement probe materials and highly electrically conducting and corrosive liquids. Moreover, the
possible highly energetic (explosive) character of these liquids requires minimum volume liquid samples, and safety measurement
devices and processes. It is the purpose of this paper to report on a new patented instrument, based on tantalum short-hot-wire
probe technology, which responds to the above requirements and allows safe automated thermal-conductivity measurements of
concentrated acid nitric solutions and similar nitric mixtures for liquid samples less than 2 cm3, with uncertainties better than 5%. 相似文献
18.
19.
拓展导热逆问题原理测算物体导热系数方法的最优化问题再探讨 总被引:1,自引:1,他引:0
对拓展导热逆问题原理测算物体导热系数方法的最优化问题进行了更广泛、深入的研究,提示了敏感度系数X^+k、X^+h的变化规律,得到了最优化判别式和判据。实验测算中,探讨并确定了实测环境与条件、参数优选及最优化测算程序。对于导热系数k值数量级为10^-2-10W/(m.℃)的三种不同试材测量与计算结果表明,本方法所测算的k值与传统方法所测值相比,相对误差在1.59%-4.00%之内:而本方法简单、可靠 相似文献
20.
Evaluation of the radiative and conductive heat loss from a molten metal sample to the cell has been made in order to obtain accurate thermal diffusivities of molten metals at high temperature with a laser flash method. The results suggest that thermal diffusivity values of molten nickel can be determined in the temperature range from 1728 to 1928 K with an uncertainty of ±3% in comparison with case considering only the effect of radiative heat loss. The usefulness of a cell for a laser flash method has been confirmed by applying simulated results to evaluate the heat leakage in the thermal diffusivity measurement of molten metals. 相似文献