Theoretical Analysis and Experimental Evidence of Non-Fourier Heat Conduction Behavior

This paper consists of two parts. (1) For a hollow sphere with sudden temperature changes on its inner and outer surfaces, the hyperbolic heat conduction equation is employed to describe this extreme thermal case and an analytical expression of its temperature distribution is obtained. According to the expression, the non-Fourier heat conduction behavior that will appear in the hollow sphere is studied and some qualitative conditions that will result in distinct non-Fourier behavior in the medium is ultimately attained. (2) A novel experiment to observe non-Fourier heat conduction behavior in porous material (mainly ordinary duplicating paper) heated by a microsecond laser pulse is presented. The conditions for observing distinct non-Fourier heat conduction behavior in the experimental sample agree well with the theoretical results qualitatively.

Model of Fractional Heat Conduction in a Thermoelastic Thin Slim Strip under Thermal Shock and Temperature-Dependent Thermal Conductivity

The present paper paper,we estimate the theory of thermoelasticity a thin slim strip under the variable thermal conductivity in the fractional-order form is solved.Thermal stress theory considering the equation of heat conduction based on the time-fractional derivative of Caputo of order
is applied to obtain a solution.We assumed that the strip surface is to be free from traction and impacted by a thermal shock.The transform of Laplace(LT)and numerical inversion techniques of Laplace were considered for solving the governing basic equations.The inverse of the LT was applied in a numerical manner considering the Fourier expansion technique.The numerical results for the physical variables were calculated numerically and displayed via graphs.The parameter of fractional order effect and variation of thermal conductivity on the displacement,stress,and temperature were investigated and compared with the results of previous studies.The results indicated the strong effect of the external parameters,especially the timefractional derivative parameter on a thermoelastic thin slim strip phenomenon.

Time fractional dual-phase-lag heat conduction equation

We build a fractional dual-phase-lag model and the corresponding bioheat transfer equation, which we use to interpret the experiment results for processed meat that have been explained by applying the hyperbolic conduction. Analytical solutions expressed by H-functions are obtained by using the Laplace and Fourier transforms method. The inverse fractional dual-phase-lag heat conduction problem for the simultaneous estimation of two relaxation times and orders of fractionality is solved by applying the nonlinear least-square method. The estimated model parameters are given. Finally, the measured and the calculated temperatures versus time are compared and discussed. Some numerical examples are also given and discussed.

Study on thermal wave based on the thermal mass theory

The conservation equations for heat conduction are established based on the concept of thermal mass.We obtain a general heat conduction law which takes into account the spatial and temporal inertia of thermal mass.The general law introduces a damped thermal wave equation.It reduces to the well-known CV model when the spatial inertia of heat flux and temperature and the temporal inertia of temperature are neglected,which indicates that the CV model only considers the temporal inertia of heat flux.Numerical simulations on the propagation and superposition of thermal waves show that for small thermal perturbation the CV model agrees with the thermal wave equation based on the thermal mass theory.For larger thermal perturbation,however,the physically impossible phenomenon pre-dicted by CV model,i.e.the negative temperature induced by the thermal wave superposition,is eliminated by the general heat conduction law,which demonstrates that the present heat conduction law based on the thermal mass theory is more reasonable.

Roles of rare earth oxide additives in millimeter-wave sintering of AlN

Roles of rare earth oxide （RE2O3） additives in millimeter-wave（MM） sintering of AIN were investigated from the standpoints of phase diagram, heating characteristics of rare earth oxides, and morphology of intergranular oxide phase. In the millimeter-wave sintering of AIN, densification temperature decreased with the decrease of the ionic radius of rare earth ion and was closely related with the eutectic temperature in the RE2Oa-Al2O3 binary system. The lowest densification temperature in the millimeter-wave sintering of AIN with Yb2O3 additive was attributed to the largest heating rate of Yb2O3-Al2O3 binary oxide under millimeter-wave radiation. Furthermore, the lowest densification temperature could be attained while selecting the Yb2O3 content so as to form the intergranular phase with the eutectic composition in the Yb2O3-Al2O3 binary system. The result showed good agreement with the above mentioned during the sintering of Si3N4 with Yb2O3-Al2O3 additive. From TEM observation, it was verified that film-like intergranular oxide phase formed under millimeter-wave radiation was favorable for attaining high thermal conductivity in the Yb2O3 added AINs.

The nonlinear response of Cattaneo-type thermal loading of a laser pulse on a medium using the generalized thermoelastic model

The nonlinear thermoelastic responses of an elastic medium exposed to laser generated shortpulse heating are investigated in this article. The thermal wave propagation of generalized thermoelastic medium under the impact of thermal loading with energy dissipation is the focus of this research. To model the thermal boundary condition(in the form of thermal conduction),generalized Cattaneo model(GCM) is employed. In the reference configuration, a nonlinear coupled Lord-Shulman-type generalized thermoelasticity formulation using finite strain theory(FST) is developed and the temperature dependency of the thermal conductivity is considered to derive the equations. In order to solve the time-dependent and nonlinear equations, Newmark’s numerical time integration technique and an updated finite element algorithm is applied and to ensure achieving accurate continuity of the results, the Hermitian elements are used instead of Lagrangian’s. The numerical responses for different factors such as input heat flux and nonlinear terms are expressed graphically and their impacts on the system’s reaction are discussed in detail.The results of the study are presented for Green–Lindsay model and the findings are compared with Lord-Shulman model especially with regards to heat wave propagation. It is shown that the nature of the laser’s thermal shock and its geometry are particularly determinative in the final stage of deformation. The research also concluded that employing FST leads to achieving more accuracy in terms of elastic deformations;however, the thermally nonlinear analysis does not change the results markedly. For this reason, the nonlinear theory of deformation is required in laser related reviews, while it is reasonable to ignore the temperature changes compared to the reference temperature in deriving governing equations.

高导热吸波材料的作用机理研究

为解决材料高导热性能与吸波效能之间的矛盾,将不同组分配比的硅橡胶、预处理后的吸波剂(羰基铁粉)和导热填料(Al_(2)O_(3))进行混炼和模压硫化成型,制备出导热吸波材料,并研究了样品的介电常数与磁导率频谱的规律,以及其高导热和电磁波吸收机理。结果表明,制备出的导热吸波材料在8~16 GHz频段范围内具有较好的吸波性能,最高导热系数达到1.75 W/(m·K),较普通吸波材料导热系数提高2倍以上。为解决电子器件散热和电磁干扰问题提出了一种便于操作、行之有效的方法。

受移动热源作用的两端固定杆的广义热-弹耦合问题

基于带有一个热松弛时间的Lord-Shulman广义热弹性理论,研究了受移动热源作用的两端固定的均质各向同性杆的热-弹动态响应。该文给出了杆的广义热-弹耦合的控制方程,借助拉普拉斯积分变换及其数值反变换对控制方程进行了求解。计算得到了杆内温度、应力及位移的分布规律,从其分布图上可以看出,温度、应力及位移随移动热源速度的增大而减小。

热波理论的应用——良导热体热导率的动态法测量

介绍了根据热波理论用动态法测量导体热导率的实验.其特点是当热量在样品中传播时,样品中各点的温度不像稳态法那样必须保持恒定.只要给定适当边界条件,样品上各点温度均可随时间作简谐变化,利用这种变化可计算出样品材料的热导率.

关于晶体材料表面导热性质的研究

目的研究晶体材料表面层中的导热问题。方法从偏离理想边界条件将导致格波之间发生能量交换,进而限制声子平均自由程这个方向出发,利用德拜固体比热理论,对理想边界条件下的固体内部导热系数进行剖析。结果理论推导出与实验事实相符的晶体表面导热系数随温度的变化规律。结论理论模型比较成功,为晶体材料表面层中的导热问题提供了有力的理论依据。

功能梯度材料亚表面缺陷的热波多重散射问题

基于热传导波动模型,采用波函数展开法,研究了半无限功能梯度材料亚表面球形缺陷的热波多重散射。给出了热波散射的一般解。温度波由调制光束在材料表面激发,球形缺陷表面的边界条件为绝热,非均匀参数为指数函数变化。分析了结构几何参数和物理参数对温度分布的影响,并给出了温度变化的数值结果。本研究可为功能梯度材料的分析研究、物理反问题和红外热波成像等提供理论基础和参考数据。

半无限板条中任意形亚表面缺陷的热波散射

基于非傅里叶热传导方程,采用复变函数与保角映射方法,研究了半无限板条结构中任意形亚表面缺陷的热波的多重散射问题,给出了热波散射问题的一般解.温度波由调制光束在材料表面激发,缺陷表面的边界条件为绝热.分析了结构几何和物理参数对热波散射与温度分布的影响,并给出了温度变化的数值结果.分析方法和数值结果可为工程材料结构的热传导分析、热波成像、物理反问题和材料内部缺陷评估等提供理论基础和参考数据.

考虑非傅里叶效应的亚表面球形异质缺陷的热波散射

以往对材料内缺陷热波散射问题的研究,多假定孔洞缺陷内无异质且边界条件为绝热的。异质体孔洞缺陷是工程中更为常见的情况。基于非Fourier热传导方程,采用波函数展开法,对含异质球形缺陷的半无限体内部的热波散射与温度分布进行了研究。给出了问题的解析解和数值计算结果。分析了缺陷物理参数和几何参数以及入射波波数等对材料表面温度分布的影响。结果表明:异质体的物理参数和几何参数等对材料表面温度的影响是显著的,主要影响因素包括无量纲导热系数,无量纲热扩散长度,无量纲埋藏深度等。

室外气候作用下建筑外墙含湿量对热工性能的影响

根据多孔介质热湿传递机理,分析了室外气候荷载作用下含湿量变化对建筑墙体的温度波衰减系数、温度波延时时间等热工性能参数的影响.结果显示,随着含湿量的增加,墙体的有效导热系数和容积比热均增大,然而含湿量增大可减小温度波通过墙体时的衰减系数,同时增大了温度波达到墙内表面的延时时间.这些特性有利于减少温度波对室内环境舒适性的影响,尤其是对非空调的通风房间舒适性的影响.

含圆柱夹杂功能梯度板条中的热波散射问题

采用复变函数法和镜像法,研究了功能梯度板条结构中含圆柱亚表面夹杂的热波散射问题.基于双曲型热传导方程,求解了含圆柱亚表面夹杂板条中热波散射与温度场,并给出了温度场的一般解.温度波由调制光束在材料表面激发,板条上下表面的热边界条件为表面温度等于环境温度.分析了夹杂的几何参数和热物性参数对板条左表面温度的影响,如板条的宽度和非均匀参数对板条表面温度的影响.可望为功能梯度材料的红外热波无损检测提供计算方法和参考数据.

双相滞热传导的振动现象

本文用解析的方法研究了双相滞热传导的振动现象,给出了热传导振动发生的条件。发现传热介质的尺寸越小,热扩散系数越大,易引发温度场的振动现象。

基于热质理论的热波传递现象研究

基于热质的概念应用牛顿力学原理建立了热质输运的控制方程,推导得到了普适的导热定律。在惯性力可以忽略时它即退化为傅立叶导热定律,反映出非傅立叶导热现象的本质是热质的惯性引起的。当热流和温度对空间的惯性以及温度对时间的惯性可以忽略时,所得到的导热定律可以退化为CV模型。对热波传递的数值分析表明:当热扰动和热流都比较小时,热流在空间加速的惯性可以忽略,基于热质理论的热波方程和CV模型符合得很好;但是,在描述较大的热扰动时,由于热流的空间加速惯性不能够被忽略,CV模型的结果在两个温度波峰叠加时会出现负温度的非物理现象,而基于热质理论的普适导热定律的结果则克服了这一缺陷。

亚表面双球孔洞的热波散射与温度分布

基于非Fourier热传导方程,采用波函数展开法,对含双球形孔洞缺陷的半无限体材料内部的热波散射与温度分布进行了研究,给出了材料内部任一点温度的解析解和表面温度分布的数值计算结果。分析了孔洞的几何参数和物理参数对金属材料表面温度分布的影响。结果表明:相对热扩散长度、入射波波数和埋藏深度对表面温度分布的影响比较大,当孔洞间距较大时,可以忽略孔洞之间的热波散射。

考虑气温年变化的地面传热计算方法

现有的稳态分地带计算方法没有考虑土壤层强大的蓄热性能及导热系数的不同,地面传热量计算结果偏大。在该方法的基础上,将室外气温近似为其年平均值和一列1年周期正弦波相加,用三维动态有限差分法建立了地面传热计算模型,与稳态分地带方法的计算结果进行了比较。给出了土壤层不同导热系数和热扩散率下各地带的稳态传热系数及热流振幅和相位。

功能梯度材料中亚表面圆柱缺陷的热波散射问题研究

基于非傅里叶导热定律,采用镜像法和波函数展开法,研究了半无限功能梯度材料中亚表面圆柱缺陷的热波散射问题。根据热波模型,分析了几何结构参数和物理参数对物体表面温度分布的影响。温度波由调制超短激光脉冲在非透明功能梯度材料表面激发,圆柱缺陷表面的边界条件为绝热。计算结果可望在功能梯度材料的红外热波无损检测中得到应用和为导热反问题提供基础和参考数据。