Acoustical method for determining thermal diffusivity and relative difference in molar heat capacities of tantalum and vanadium

An acoustical technique is proposed for determining the thermal diffusivity in solids and the relative difference between the molar heat capacities at constant pressure and at constant volume. The method, which consists essentially of measuring the damping of freely vibrating bars, allows determination of the thermal diffusivity with an accuracy better than ±5% and has the advantage of not requiring a heat source. It also largely eliminates the complications of precise temperature measurements and insulation of specimen holders. Results are given for tantalum and vanadium over the temperature range 60–300 K.     

Thermal diffusivity and Biot number: A new experimental method

A new simple method is presented for measuring thermal diffusivity and Biot number in cylindrical samples made of relatively highly conducting materials, subjected to laminar air flow. The basic idea is a heat source in the middle section of the sample, acting also as a thermocouple; only one additional temperature sensor at the cylinder basis is required to give all information, without requiring any hypothesis about the effective time dependence of the heat source.     

Technique of studying thermal diffusivity of metallics in different directions in a field of centrifugal accelerations and forces

Study of the thermal diffusivity of metallics in a field of centrifugal accelerations and forces is essential for aerospace engineering. Characteristics of thermal diffusivity of materials are used in calculations of thermal state of blades and disks of turbine rotors. An original technique and a device on semiconductors have been developed for determination of thermophysical characteristics of materials on an acceleration bench using a vacuum chamber, under centrifugal forces and accelerations. Presented are results on nonstationary heating of heat conductors in the radial and circumferential directions in a field of centrifugal forces and accelerations. Analysis of experimental results shows that the thermal diffusivity of heat conductors grows with rotational speed as compared with a static state without rotation. The thermal diffusivity phenomenon of concern has two components: from centrifugal acceleration and from centrifugal tensile load. From experimental data on the effect of tensile forces it follows that the second component is small. Thus, said thermal diffusivity growth is strongly associated with increase in the velocity of electron drift in ametal under centrifugal acceleration forces.     

Estimation of inaccuracies of thermocouple measurements of the temperature profile in pyrolyzed solid substances

Thermal interaction of a thermocouple embedded into a solid substance pyrolyzed by an external heat source with the thermal wave propagating inward the substance from the pyrolysis surface is considered. Numerical simulations show that a heat sink through thermocouple wires inward the substance occurs because of a significant difference in thermal conductivities of the solid substance and thermocouple material, which leads to substantial changes in thermojunction, thus, distorting thermocouple data.     

Estimation of the thermal diffusivity of solids based on ‘instantaneous velocimetry’ using an interferometer

A conceptually new approach is proposed to estimate the thermal diffusivity of optically transparent solids at ambient temperature based on the ‘position-dependent instantaneous velocity’ of isothermal surfaces using a self-reference interferometer. A new analytical model is proposed using the exact solution to relate the instantaneous velocity of isothermal surfaces with the thermal diffusivity of solids. The experiment involves setting up a one-dimensional non-stationary heat flow inside the solid via step-temperature excitation to launch a spectrum of dissimilar ‘moving isothermal surfaces’ at the origin. Moving isothermal surfaces exhibit macroscale ‘rectilinear translatory motion’; the instantaneous velocity of any isothermal surface at any location in the heat-affected region is unique and governed by the thermal diffusivity of the solids. The intensity pattern produced by the self-reference interferometer encodes the moving isothermal surfaces into the corresponding moving intensity points. The instantaneous velocities of the intensity points are measured. For a given thermo-optic coefficient, the corresponding values of the isothermal surfaces are predicted to estimate the thermal diffusivity of the solids using BK7 glass as an example. Another improved method is proposed in which thermal diffusivity is estimated without measuring thermo-optic coefficient and quartz glass is utilized as a specimen. The results obtained using the proposed approaches closely match with the literature value.     

热流传感器传热特性电弧风洞实验及数值模拟

高超声速飞行器面临剧烈的气动加热环境, 电弧风洞是飞行器防热材料地面考核筛选的主力设备。热流密度是电弧风洞重要的模拟参数之一, 需要进行准确有效的测量。针对电弧风洞气流环境特点, 开展传统塞式量热计和新型同轴热电偶的对比测热试验, 并采用数值模拟对两种热流传感器的传热特性进行了分析。在电弧风洞平板自由射流试验热流密度分布在0~1 100 kW/m2范围内, 同轴热电偶的热流密度测试试验结果相对塞式量热计偏低10%~15%。数值模拟结果表明, 塞式量热计本身结构热物性参数不匹配会导致热流密度测量数值偏高至少10%, 而同轴热电偶测量数值偏高最大仅为2.19%, 相对塞式量热计具备更高的测量精度。同时, 电弧风洞中不同材质热流密度测试模型使用同轴热电偶进行测热试验时, 需要在同轴热电偶同模型之间增加适当厚度的不锈钢套以满足传感器周围环境的热匹配。      

非线性拟合方法用于透射式脉冲红外技术测试碳/碳复合材料的热扩散系数

为了测试碳/碳复合材料的热扩散系数,本文提出了非线性拟合用于透射式脉冲红外检测的数据处理方法.非线性拟合通过循环迭代的方法持续调整拟合参数,让理论值不断逼近实验值,直至获得最佳结果.传统的透射式脉冲红外成像技术利用半高时间法测试材料的热扩散系数,但通常会受到采集时间不足和信噪比差的限制.本文提出的非线性拟合方法可以有效消除或减弱这两种影响.在使用该方法之前,首先选用常见的304不锈钢评估了该方法的测量精度及拟合长度对测试结果的影响.结果显示304不锈钢的测量精度达到0.3%,且当拟合长度不小于半高时间法采集时间的1/5时,拟合长度对非线性拟合结果影响很小.随后使用该拟合方法测试了不同厚度的碳/碳复合材料试件,并通过热扩散系数测量结果分析了试件之间的热参数差异性和材料自身的均匀性.     

Thermal conductivity and thermal diffusivity of tantalum in the temperature range from 293 to 1800 K

Thermal diffusivity of polycrystalline tantalum at the temperature range from 293 to 1800 K has been measured by the laser flash method with the error of 2–4 %. Thermal conductivity has been calculated with the use of reference data on density and heat capacity. Approximating equations and tables of reference data for the temperature dependence of heat transfer coefficients have been obtained; comparison with the published data has been carried out. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 07-08-00071).     

Photothermal deflection studies on heat transport in intrinsic and extrinsic InP

Laser induced transverse photothermal deflection technique has been employed to determine the thermal parameters of InP doped with Sn, S and Fe as well as intrinsic InP. The thermal diffusivity values of these various samples are evaluated from the slope of the curve plotted between the phase of photothermal deflection signal and pump-probe offset. Analysis of the data shows that heat transport and hence the thermal diffusivity value, is greatly affected by the introduction of dopant. It is also seen that the direction of heat flow with respect to the plane of cleavage of semiconductor wafers influences the thermal diffusivity value. The results are explained in terms of dominating phonon assisted heat transfer mechanism in semiconductors . PACS 78.20.Nv; 66.30.Xj; 61.72.Vv     

The thermal characteristics of “Se-As”-glasses in the neighbourhood of the transformation point

In this work the dependence of specific heat per unit volume, thermal conductivity and of thermal diffusivity on the temperature in amorphous specimen of selenium containing from 1 to 20 atomic percent of arsenic is studied. It has been found out that the admixture of arsenic considerably moves the transformation point-Tg-to higher values. It is shown that for definition of Tg it is advantageous to employ the extremes of the thermal diffusivity curve which is simply measured and has immediate connection with the microprocesses (with the mean free path of phonons). The changes of the specific heat per unit volume and of the thermal diffusivity in the point Tg are first growing, with increasing content of As, they reach a maximum in the neighbourhood of about 5 atomic percent of arsenic, and afterwards they are again decreasing. The measured curves are explained by the appearance of the additional thermal modes in the neighbourhood of the transformation point.Dúbravská cesta, Bratislava, Czechoslovakia.I thank Dr. J. Krempaský, C.Sc., for his valuable advices and remarks.     

Perturbation theories behind thermal mode spectroscopy for high-accuracy measurement of thermal diffusivity of solids

Thermal mode spectroscopy (TMS) has been recently proposed for accurately measuring thermal diffusivity of solids from a temperature decay rate of a specific thermal mode selected by three-dimensional (anti)nodal information [Phys. Rev. Lett., 117, 195901 (2016)]. In this paper, we find out the following advantages of TMS by use of perturbation analyses. First, TMS is applicable to the measurement of high-thermal diffusivity with a small-size specimen. Second, it is less affected by thermally resistive films on a specimen in the sense that the resistance at the interface does not affect the first-order correction of thermal diffusivity. Third, it can perform doubly accurate measurement of the thermal diffusivity specified at a thermal equilibrium state even if the diffusivity depends on temperature in the sense that the measurement can be performed within tiny temperature difference from the given state and that the decay rate of the slowest decaying mode is not affected by the dependence.     

Modèle correctif de la mesure de la température d'un gaz par couple thermoélectrique. Application à une zone à fort gradient thermique

Corrective model of the gas temperature thermocouple measure. Application to an important thermal gradient zone. The gas temperature measurement with a thermocouple in important thermal gradient zones requires a corrective model. For example, such zones exist for thermal boundary layers near active walls. We have calculated these thermocouple thermal exchanges where connection wires are considered as fins with a variable ambient gas temperature. The heat exchanges by convection and radiation on the thermocouple head are analytically calculated, then a numerical method is used for fins where the space increment is the same as for the experimental measure. The corrective model in steady state is semi-analytical. Its validation is made with experimental results from studies of flows along a non-isothermal vertical wall in a cavity filled with wet air. Several applications are offered for many thermal curves, for more important gradient zones corrections are larger than 1.5 K for a K type thermocouple of 0.08 mm wire diameter.     

Thermoelectricity without absorbing energy from the heat sources

We analyze the power output of a quantum dot machine coupled to two electronic reservoirs via thermoelectric contacts, and to two thermal reservoirs – one hot and one cold. This machine is a nanoscale analogue of a conventional thermocouple heat-engine, in which the active region being heated is unavoidably also exchanging heat with its cold environment. Heat exchange between the dot and the thermal reservoirs is treated as a capacitive coupling to electronic fluctuations in localized levels, modeled as two additional quantum dots. The resulting multiple-dot setup is described using a master equation approach. We observe an “exotic” power generation, which remains finite even when the heat absorbed from the thermal reservoirs is zero (in other words the heat coming from the hot reservoir all escapes into the cold environment). This effect can be understood in terms of a non-local effect in which the heat flow from heat source to the cold environment generates power via a mechanism which we refer to as Coulomb heat drag. It relies on the fact that there is no relaxation in the quantum dot system, so electrons within it have a non-thermal energy distribution. More poetically, one can say that we find a spatial separation of the first-law of thermodynamics (heat to work conversion) from the second-law of thermodynamics (generation of entropy). We present circumstances in which this non-thermal system can generate more power than any conventional macroscopic thermocouple (with local thermalization), even when the latter works with Carnot efficiency.     

Reprint of : Thermoelectricity without absorbing energy from the heat sources

We analyze the power output of a quantum dot machine coupled to two electronic reservoirs via thermoelectric contacts, and to two thermal reservoirs – one hot and one cold. This machine is a nanoscale analogue of a conventional thermocouple heat-engine, in which the active region being heated is unavoidably also exchanging heat with its cold environment. Heat exchange between the dot and the thermal reservoirs is treated as a capacitive coupling to electronic fluctuations in localized levels, modeled as two additional quantum dots. The resulting multiple-dot setup is described using a master equation approach. We observe an “exotic” power generation, which remains finite even when the heat absorbed from the thermal reservoirs is zero (in other words the heat coming from the hot reservoir all escapes into the cold environment). This effect can be understood in terms of a non-local effect in which the heat flow from heat source to the cold environment generates power via a mechanism which we refer to as Coulomb heat drag. It relies on the fact that there is no relaxation in the quantum dot system, so electrons within it have a non-thermal energy distribution. More poetically, one can say that we find a spatial separation of the first-law of thermodynamics (heat to work conversion) from the second-law of thermodynamics (generation of entropy). We present circumstances in which this non-thermal system can generate more power than any conventional macroscopic thermocouple (with local thermalization), even when the latter works with Carnot efficiency.     

Heat diffusivity and heat conductivity of Ni near the Curie point

The heat diffusivity of Ni near the Curie point was measured by an a.c. oscillating method. The period of self-oscillation is related to the heat diffusivity. The principle and some technical details of the experimental method is given. The critical behavior of heat diffusivity near the Curie temperature is analysed. Using known specific heat data the heat conductivity for Ni can be calculated. A conclusion is made that the Wiedemann-Franz law is not valid near the ferromagnetic phase transition.     

Simultaneous measurement of thethermal diffusivity and specific heat near phase transitions

A technique for measuring the absolute thermal diffusivity along with the relative specific heat is introduced which is readily adaptable to a wide variety of applications. The thermal diffusivity and specific heat of CoO, near the antiferromagnetic transition; of SrTiO₃, near the structural phase transition; of Cr, near the first-order SDW-paramagnetic transition; and of EuO, near the ferromagnetic Curie point were measured. Except for SrTiO₃, the thermal diffusivities are found to mirror the specific heats, with no evidence for anomalies in the thermal conductivities, contrary to some earlier reports. A step increase in the thermal conductivity is observed on passing through the structural transition of SrTiO₃ from below which is of the same relative size as the step decrease of specific heat at T_c.     

SiNx薄膜热物性参数实验测量与分析研究

采用一种新的实验测量方案，将金属加热单元与温度探测单元合二为一，间接获得了在半导体和微电子学MEMS领域内有重要用途的SiN_x薄膜的导热系数、发射率、比热容和热扩散系数，并对实验结果进行了不确定度分析，为微电子电路设计和掩模成型工艺等提供了可靠的热物性数据. 实验结果表明，薄膜的导热系数、发射率、热扩散系数远比相应体材质低，而且还与温度、厚度有关，尺寸效应显著，而比热容则与体材质相差不大. 关键词： 微尺度传热 热物性参数 x薄膜')" href="#">SiN_x薄膜 测量技术     

Mesure de la diffusivité longitudinale de matériaux anisotropes

Measurement of in-plane diffusivity of anisotropic solid samples. Survey of the techniques developed at LEMTA. Three techniques for the measurement of in-plane diffusivity of anisotropic solid samples have been developed at the Laboratory and are presented here :

• •the two directional heat pulse (flash) method with local contact measurement of two temperatures;
• •the fin method with local contact or contactless measurement of two temperatures;
• •the two directional heat pulse method with measurement of the temperature field by an infrared camera and data processing through integral transformations.

     

MHD swirling flow and heat transfer in Maxwell fluid driven by two coaxially rotating disks with variable thermal conductivity

We develop a mathematical modeling for an electrically conducting non-Newtonian Maxwell fluid flow occurring between two coaxially parallel stretchable rotating disks at constant distant apart. The pressure and heat transfer analysis is carried out subject to the effects of axial magnetic field and temperature dependent thermal conductivity. The stretching and rotating rates of both disks are assumed different from each other. The two diverse phenomena, such as, when both disks are rotating with different angular velocities in the same as well as in the opposite directions are discussed. The similarity procedure adopted by von Kármán is utilized to reduce the governing momentum and energy equations into nonlinear ordinary differential equations. The solution of the governing problem is obtained numerically using bvp4c scheme in Matlab. The effects of active parameters including stretching rates, Deborah number, magnetic number, Prandtl number, thermal conductivity parameter and Reynolds number are examined for same as well as opposite rotation direction for radial, azimuthal, and axial flows, pressure and temperature fields. The classical flow pattern happening between the disks is significantly altered by the stretching action which is a main physical significances of this study. The azimuthal flow is observed higher for the same direction of disks rotation as compared to opposite disks rotation. The pressure field drops near the lower disk with increasing values of Reynolds number. The role of thermal conductivity parameter is quite useful to enhance the fluid temperature.