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1.
This study proposes an analytical method in conjunction with existing experimental temperature to estimate the unknown relaxation time and thermal diffusivity of processed meat based on the hyperbolic heat conduction model. This analytical method is a combination of the Laplace transform and least squares methods. The thermal contact resistance at the interface between adjacent samples at different temperatures is assumed to be negligible. The relaxation time is estimated from the temperature jump at a specific measurement location. The thermal diffusivity is determined from the definition of the dimensionless spatial coordinate and the resulting relaxation time. The results show that the relaxation time and thermal diffusivity obtained are in good agreement with the existing results. The obtained dimensionless temperature history at a specific measurement location is close to the experimental temperature data. This means that the Cattaneo–Vernottee (CV) model can be suitable for this study. The proposed analytical inverse method can be applied to determine a more accurate estimate of such problems. A comparison of the estimate obtained from CV and dual phase lag models is made.  相似文献   

2.
A method for the simultaneous measurement of thermal diffusivity and specific heat by a single rectangular heating pulse on a finite cylindrical specimen is described. The method takes into account radiation losses from all the surfaces of the specimen. The theoretical principle of the technique was studied by solving the transient heat conduction equation for a finite disk heated on the front surface by a single rectangular radiant energy pulse. An apparatus was constructed to comply with the theoretical conditions and was connected to a personal computer. Thermal diffusivity and specific heat were determined from the data obtained on the temperature response of the back surface of the specimen and from the theoretical results. This method can be applied to materials having a wide range of thermal conductivity values and has a good accuracy at high temperatures. Examples of the measurements are presented.Invited paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.  相似文献   

3.
Experimental data on thermal conductivity and thermal diffusivity of a semitransparent material generally include an error due to the radiation heat transfer. This error varies in accordance with the experimental conditions such as the temperature level of the sample and the measuring method. In this paper, research on the influence of radiation heat transfer on thermal diffusivity are reviewed, and as an example, the method to correct the radiation component in the apparent thermal diffusivity measured by the stepwise heating technique is presented. The transient heat transfer by simultaneous thermal conduction and radiation in a semitransparent material is analyzed when the front surface is subjected to stepwise heating. The apparent thermal diffusivity, which includes the radiation component, is calculated for various parameters.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.  相似文献   

4.
This paper presents a new way to reduce data in the laser flash method of measuring thermal diffusivity. Experimental temperature vs time data are first transformed by using the Laplace transformation, and then they are fitted with an appropriate theoretical formula. The data reduction procedure is more efficient and enables the use of more realistic models of heat conduction in the sample, because the theoretical formulae for transformed temperatures have a simpler form than those for nontransformed ones. Some examples of the theoretical formulae of transformed temperatures are included here for one- and two-dimensional heat transfer, respectively. The models described take into account a finite pulse time and heat losses from the sample. Two fitting algorithms are proposed. Experimentally, the data reduction procedure has been tested for a correction of the finite pulse time effect in the flash method. The results show that the accuracy of our procedure is comparable with other data reduction methods. Provided that the shape and duration of the pulse are known, this procedure allows elimination of the finite pulse time effect on calculation of the thermal diffusivity for any transformable heat pulse time function, even in cases where the other specialized data reduction procedures have failed.  相似文献   

5.
In order to simulate thermal strains,thermal stresses,residual stresses and microstructure of the steel during gas quenching by means of the numerical method,it is necessary to obtain an accurate boundary condition of temperature field.The surface heat transfer coefficient is a key parameter.The explicit finite difference method,nonlinear estimation method and the experimental relation between temperature and time during gas quenching have been used to solve the inverse problem of heat conduction.The relationship between surface temperature and surface heat transfer coefficient of a cylinder has been given.The nonlinear surface heat transfer coefficients include the coupled effects between martensitic phase transformation and temperature.  相似文献   

6.
A study is made of the propagation of plane electro-magneto-thermo-visco-elastic harmonic waves in an unbounded isotropic conducting visco-elastic medium of Kelvin–Voigt type permeated by a primary uniform magnetic field when the entire medium rotates with a uniform angular velocity. The thermal relaxation time of heat conduction, the electric displacement current, the coupling between heat flow density and current density, and that between the temperature gradient and the electric current are included in the analysis. A more general dispersion relation is obtained to determine the effects of rotation, thermal relaxation time, visco-elastic parameters, and the external magnetic field on the phase velocity of the waves. Perturbation techniques are used to study the influence of small magneto-elastic and thermo-elastic couplings on the phase velocity of the waves. Cases of low and high frequencies are also analyzed to determine the effect of rotation, visco-elastic parameters, thermo elastic and magneto-elastic coupling, as well as thermal relaxation time of heat conduction on the waves.  相似文献   

7.
The numerical solution of the nonlinear heat conduction equation is used to analyze nonlinear effects in the laser flash method, when the thermophysical parameters of the sample depend on the temperature. A parameter estimation technique is proposed to determine the temperature dependence of the thermal diffusivity from a response curve. Computer generated data, as well as real experimental data, were used to demonstrate the reliability of the technique.  相似文献   

8.
薛齐文  杨海天 《工程力学》2007,24(12):43-46,52
基于一种时域正演精细算法,引入Bregman距离函数作为Tikhonov函数的正则项,建立了求解多宗量一维瞬态非线性热传导反问题的数学模型,可对非线性内热源强度、导温系数和边界条件等多个热学参数进行组合识别。对信息测量误差作了初步探讨,数值验证给出令人满意的结果。  相似文献   

9.
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   

10.
The thermophysical properties (thermal diffusivity, effusivity) of a film coated on a substrate have been measured by a pulsed transient analysis. The experimental approach is to utilize the film surface temperature decay following a heating pulse from a Q-switched Nd:glass laser. The temperature decay was measured using a HgCdTe infrared detector. Following the collection of data, a nonlinear least-squares regression was performed to estimate the optimal values of three separate thermal parameters by fitting the data to the semiinfinite substrate model solution. The model was checked systematically by analysis of the sensitivity and correlation of the three parameters, and the thermal diffusivity and effusivity ratio of the film and substrate were obtained from the optimal values of the estimated parameters.  相似文献   

11.
Due to lack of reliable thermal diffusivity data of sintered steels in literature, experimental investigations were conducted on samples made of different powder types (based on prealloyed, or diffusion-bonded, or admixed powders) and under different process conditions. So the influence of pressing pressure and sintering temperature on thermal diffusivity was established. Thermal diffusivity was measured using the “flash method”: a sample in the shape of a slab is irradiated with a light pulse on one of the two surfaces, and temperature of the other surface is detected by an ambient temperature pyrometer. The value of the thermal diffusivity is obtained by a least squares regression on the entire trend of the temperature vs. time using the analytical solution of the heat conduction as regression model. Results show the increase of the thermal diffusivity with increasing density. This outcome can be explained from the mutual effect of thermal conductivity and density on thermal diffusivity in porous media. The experimental results have also permitted to verify the influence of the composition of the sintered materials and carbon contents on thermal diffusivity.  相似文献   

12.
Non-Fourier hyperbolic heat conduction in a heterogeneous sphere is investigated in this article. Except for the thermal relaxation time, which is assumed to be constant, all other material properties vary continuously within the sphere in the radial direction following a power law. Boundary conditions of the sphere are assumed to be spherically symmetric, leading to a one-dimensional heat conduction problem. The problem is solved analytically in the Laplace domain, and the final results in the time domain are obtained using numerical inversion of the Laplace transform. The transient responses of temperature and heat flux are investigated for different non-homogeneity parameters and normalized thermal relaxation constants. The current results for the specific case of a homogeneous sphere are validated by results available in the literature.  相似文献   

13.
The numerical method of design optimization for structural thermally induced vibration is originally studied in this paper and implemented in the software JIFEX. The direct and adjoint methods of sensitivity analysis for thermal‐induced vibration coupled with both linear and non‐linear transient heat conduction is firstly proposed. Based on the finite element method, the linear structural dynamics is treated simultaneously with linear and non‐linear transient heat conduction. In the heat conduction, the non‐linear factors include the radiation and temperature‐dependent materials. The sensitivity analysis of transient linear and non‐linear heat conduction is performed with the precise time integration method; and then, the sensitivity analysis of structural transient responses is performed by the Newmark method. Both the direct method and the adjoint method are employed to derive the sensitivity equations of thermal vibration. In the adjoint method, two adjoint vectors of structure and of heat conduction are used to derive the adjoint equations. The coupling effect of heat conduction on thermal vibration in the sensitivity analysis is particularly investigated. With the coupling sensitivity analysis, the optimization model is constructed and solved by the sequential linear programming or sequential quadratic programming algorithm. Numerical examples are given to validate the proposed methods and to demonstrate the importance of the coupled design optimization. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

14.
基于区间有限元和矩阵摄动理论, 引入同伦技术, 建立了瞬态热传导不确定性区间参数反演识别的数值求解模式。利用测量信息和计算信息的区间残差构造同伦函数, 将反演识别问题转化为一个优化问题进行求解。时间域上, 引入时域精细算法进行离散, 空间上, 采用八节点等参元技术进行离散, 并结合区间有限元法, 建立了便于敏度分析的不确定性正反演数值模型。该模型不仅考虑了非均质和参数分布的影响, 而且也便于正演和反演问题的敏度分析, 可对导热系数和热边界条件等宗量的区间范围进行有效的单一和组合识别, 并给出了相关的数值算例。数值结果表明了所建数值模型的有效性和可行性, 并具有较高的计算精度。  相似文献   

15.
An ac calorimetric method for measuring the thermal diffusivity of thin-film materials has been widely applied. In the application of this method, the systematic errors caused by the heat loss effect, the edge reflection effect, etc., have been analyzed and corresponding correction methods have been developed. But when measuring films with low thermal diffusivity or with thickness comparable to the thermal diffusion length, a two-dimensional effect which will also result in a systematic error of the measurement is present. In this paper, the mechanism of two-dimensional heat conduction within a thin sample which is supplied a periodic heat flux by a chopped light beam is analyzed. A numerical analysis method is developed to study the effect of the two-dimensional heat conduction on the measured thermal diffusivity values. The relations between the measured thermal diffusivity and independent parameters such as frequency, thickness of sample, width of light spot, etc., are demonstrated to indicate the two-dimensional effect. The experimental precondition for minimizing the systematic error caused by the two-dimensional effect is determined. In addition, the analysis method presented in this paper should be useful for more difficult problems such as error estimation of the thermal diffusivity measurement of coatings or composite films.  相似文献   

16.
The critical energy characteristics of cooled composite superconductors is analytically predicted based on the one-dimensional hyperbolic heat conduction model. The temperature dependence of the Ohmic heat generation, the finite speed of heat transfer, and the finite duration and finite length of the thermal disturbances are taken into account in the present model. The critical energies are calculated using a model based on the analytical solution of the hyperbolic heat conduction equation by the Laplace transformation method. The computational model results show that the critical energy depends on the relaxation time and disturbance duration. It is found that the hyperbolic conduction model predicts a lower-critical energy as compared to the predictions of the parabolic heat conduction model.  相似文献   

17.
This paper presents the measurements and the results on thermal and electrical transport properties of three nuclear reactor cladding materials: Zircalloy 2, Zircalloy 4, and Inconel 625. Study of these materials constituted a part of the IAEA coordinated research program aimed at the generation and establishment of a reliable and complete database of the thermal properties of reactor materials. Measured properties include thermal diffusivity, specific heat, and electrical resistivity. Thermal diffusivity was measured by the laser pulse technique. Specific heat and electrical resistivity were measured using a millisecond-resolution direct electrical pulse heating technique. Thermal conductivity was computed from the experimentally determined thermal difusivity and specific heat functions and the room temperature density values. Measurements were performed in the 20 to 1500°C temperature range, depending on the material and property concerned.  相似文献   

18.
《Composites Part B》2007,38(2):201-215
Nonlinear thermal bending analysis is presented for a simply supported, shear deformable functionally graded plate without or with piezoelectric actuators subjected to the combined action of thermal and electrical loads. Heat conduction and temperature-dependent material properties are both taken into account. The temperature field considered is assumed to be a uniform distribution over the plate surface and varied in the thickness direction and the electric field considered only has non-zero-valued component EZ. The material properties of functionally graded materials (FGMs) are assumed to be graded in the thickness direction according to a simple power law distribution in terms of the volume fractions of the constituents, and the material properties of both FGM and piezoelectric layers are assumed to be temperature-dependent. The governing equations of an FGM plate are based on a higher order shear deformation plate theory that includes thermo-piezoelectric effects. A two step perturbation technique is employed to determine the thermal load–deflection and thermal load–bending moment curves. The numerical illustrations concern nonlinear bending response of FGM plates without or with surface bonded piezoelectric actuators due to heat conduction and under different sets of electric loading conditions. The results reveal that for the case of heat conduction the nonlinear thermal bending responses are quite different to those of FGM plates subjected to transverse mechanical loads, and the temperature-dependency of FGMs could not be neglected in the thermal bending analysis.  相似文献   

19.
The laser pulse method can be successfully applied to the measurement of thermal diffusivity of isotropic materials subject to some assumptions. For anisotropic materials, this method is applicable to the measurement of principal thermal diffusivity only on the condition that there is no difference in direction between the principal axis and that of the temperature gradient. After analyzing the heat conduction process in an anisotropic solid, it has been shown that large errors in the measurement of thermal diffusivity would exist if the direction of the principal axis deviates inconspicuously from that of the temperature gradient. The experimental results of thermal diffusivity of highly oriented pyrolytic graphite (HOPG) samples with various deviation angles have been compared with the analytical results. The laser pulse method is not applicable to measurements on semitransparent pyrolytic boron nitride (PBN). We adopted a two-layer composite sample to measure the thermal diffusivity of PBN in the c direction and a particular graphite-PBN composite sample has been prepared which has a very low thermal resistance at the interface. The thermal diffusivity and thermal conductivity of PG (below 2300°C) and PBN (below 1000°C) are given.Invited paper presented at the Ninth Symposium on Thermophysical Properties, June 24–27, 1985, Boulder, Colorado, U.S.A.  相似文献   

20.
The paper presents an analysis of the experimental parameters involved in application of the dual-probe heat pulse technique, followed by a critical review of methods for processing thermal response data (e.g., maximum detection and nonlinear least square regression) and the consequent obtainable uncertainty. Glycerol was selected as testing liquid, and its thermal diffusivity was evaluated over the temperature range from ??20 °C to 60 °C. In addition, Monte Carlo simulation was used to assess the uncertainty propagation for maximum detection. It was concluded that maximum detection approach to process thermal response data gives the closest results to the reference data inasmuch nonlinear regression results are affected by major uncertainties due to partial correlation between the evaluated parameters. Besides, the interpolation of temperature data with a polynomial to find the maximum leads to a systematic difference between measured and reference data, as put into evidence by the Monte Carlo simulations; through its correction, this systematic error can be reduced to a negligible value, about 0.8 %.  相似文献   

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