A noncontact method for measuring thermal conductivity and thermal diffusivity of anisotropic materials

A noncontact method for measuring the thermal conductivity and thermal diffusivity of anisotropic materials is proposed. This method is based on the fact that the surface temperature variation with time depends on the thermal properties of the material when its surface is heated locally. The three-dimensional transient heat conduction equation in the material is solved numerically. The dimensionless average surface temperature variations are obtained along each principal axis: that is, thex andy axes. The relation between the dimensionless temperature and the Fourier number is expressed by a polynomial equation and used as a master plot, which is a basic relation to be compared with measured temperature variation. In the experiments, the material surface is heated with a laser beam and the surface temperature profiles are measured by an infrared thermometer. The measured temperature variations with time are compared with the master plots to yield the thermal conductivity λ _x and thermal diffusivityx _v in thex direction and the thermal conductivity ratioE _xy (=λ _y λ _x ) simultaneously. To confirm the applicability and the accuracy of the present method, measurements were performed on multilayered kent-paper, vinyl chloride, and polyethylene resin film, whose thermal properties are known. From numerical simulations, it is found that the present method can measure the thermophysical properties λ _x , α _x andE _xy within errors of ±6, ±22, and ±5%, respectively, when the measuring errors of the peak heat flux, the heating radius, and the surface temperature rise are assumed to be within ±2, ±3%, and ±0.2 K, respectively. This method could be applied to the measurement of thermophysical properties of biological materials.     

Thermal diffusivity imaging with the thermal lens microscope

A coaxial thermal lens microscope was used to generate images based on both the absorbance and thermal diffusivity of histological samples. A pump beam was modulated at frequencies ranging from 50 kHz to 5 MHz using an acousto-optic modulator. The pump and a CW probe beam were combined with a dichroic mirror, directed into an inverted microscope, and focused onto the specimen. The change in the transmitted probe beam's center intensity was detected with a photodiode. The photodiode's signal and a reference signal from the modulator were sent to a high-speed lock-in amplifier. The in-phase and quadrature signals were recorded as a sample was translated through the focused beams and used to generate images based on the amplitude and phase of the lock-in amplifier's signal. The amplitude is related to the absorbance and the phase is related to the thermal diffusivity of the sample. Thin sections of stained liver and bone tissues were imaged; the contrast and signal-to-noise ratio of the phase image was highest at frequencies from 0.1-1 MHz and dropped at higher frequencies. The spatial resolution was 2.5 μm for both amplitude and phase images, limited by the pump beam spot size.     

Pulse method of measuring the thermal diffusivity of spherical samples

Consideration is given to a version of the pulse method of measurement of the thermal diffusivity of spherical samples with the use of laser heating. The method is based on solution of the heat-conduction equation in a spherical coordinate system. The computerized experimental setup used is described. Measurement results for the thermal diffusivity of Zr, Ni, Fe, Al are reported. The measurement error is no more than 5%.     

An apparatus for measuring the thermal conductivity and diffusivity of solid materials

An apparatus is described for measuring the thermal conductivity and diffusivity on small specimens of solid materials; also the results are shown which have been obtained for refractive high-alumina concrete by such measurements.Notation thermal conductivity at the mean temperature of specimens, W/m· °C - Q power of the central heater, W - F cross section area of a specimen, m² - t_1,2 temperature drop across the specimens, °C - ₁, ₂ difference in heights between the thermocouple beads, center-to-center, in the first and in the second specimen respectively, m - t temperature, °C - time coordinate, min - d₁= (d_1u+d_1l )/2 mean distance between specimen contact plane and nearest thermocouple beads, for the upper and lower specimen, m - d₂= (d_2u+d_2l )/2 mean distance between specimen contact plane and farthest thermocouple beads, for the upper and lower specimen, m - dt(d₁,)/d rate of temperature rise at section d₁ of the specimen at time, °C/h - t=t₁+t₂ sum of temperature drops in the specimens at time, °C - m heating rate, h^–1 - a thermal diffusivity of specimens, referred to their mean temperature, m²/h - =m/a, m^–1 b=¦(t_u–t_l)/t_u¦ heating nonuniformity factor Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1049–1054, June, 1972.     

Automated apparatus for measuring the thermal diffusivity of metals by the thermal-wave method

Automated equipment for measuring the thermal diffusivity of metals by the thermal-wave method is described. The Seebeck effect is used to record the thermal waves. The thermal diffusivity of a number of metal samples 0.01–0.05 cm thick is measured with an error not greater than 10%. Translated from Izmeritel'naya Tekhnika, No. 4, pp. 48–51, April, 1996.     

陶瓷热障涂层的热导率和热扩散率测量

提出了应用3ω法进行等离子喷涂热障涂层材料的热导率和热扩散率测量的方法。测试了室温下2种典型的热障涂层材料Y2SiO5和La2Zr2O7的热导率和热扩散率,测试结果与文献中的结果吻合良好。实验中对不同孔隙率的样品的热导率在室温附近的温度区间内进行测试,结果表明,孔隙率的变化对热导率有明显的影响。另外,孔隙率对热扩散率有双向的影响,即存在某一孔隙率值使得涂层样品的热扩散率最大。     

Experimental apparatus for measuring the thermal diffusivity of pure fluids at high temperatures

Dynamic light scattering represents a suitable method for measuring the thermal diffusivity of optically transparent fluids. The classic application of the method is the immediate vicinity around the critical point due to its dependence upon the intensity of scattered light and its high sensitivity to undesired light scattering. By means of subsequent modifications of the experimental setup, we have been able to expand this region of applicability over the last 12 years and could systematically investigate numerous substances and their binary mixtures within a temperature range of 280 K<T<350 K. Our planned investigation of fluids suitable for ORC-HP-technology necessitates performing measurements at higher temperatures and pressures. The experimental apparatus newly designed for this purpose is capable of sustaining a relatively high temperature constance at temperatures up to 700 K. Factors restricting the measurable range of state and their influence on the design of the sample cell are discussed.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

瞬态热栅法测量La0.6Sr0.4MnO3薄膜的热扩散率

1引言 La1-xSrxMnO3是一种典型的钙钛矿巨磁阻材料,已引起广泛的关注.同时,La1-xSrxMnO3也是一种热电材料,研究该材料热学性质是探索其物理性质的一种有效方法1.我们利用瞬态热栅法检测了La0.6Sr0.4MnO3薄膜的热扩散率,并与体材料进行了比对.     

Thermal diffusivity of inhomogeneous systems. II. Experimental determination of thermal diffusivity

We investigated the methodical error in the measurement of the effective thermal diffusivity of inhomogeneous systems. We give the recommendation for the choice of the dimensions of the inhomogeneous specimen.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 5, pp. 859–861, November, 1980.     

Thermal diffusivity measurements of thin films and multilayered composites

This review discusses the following methods for measuring thermal diffusivity of thin materials: ac calorimetric method, flash method, mirage-effect method, picosecond time-resolved thermoreflectance method, photoacoustic method, etc. The measurements are classified into the following three cases: (a) that yield thermal diffusivity parallel to the surface of a thin material, (b) that yield thermal diffusivity perpendicular to the surface, and (c) that yield thermal diffusivity perpendicular to the surface of a thin material but deposited on a solid substrate. The contribution of inhomogeneity in the spatial distribution of the imparted thermal energy and obscureness at the edge of the restricted region, to which uniform thermal energy is imparted, is considered in each case. The contribution of temporal distortion of the temperature pulse, waves, etc., is considered in each measurement. The proper thickness of samples required for the measurements is discussed. In some of the measurements, the applicable materials are restricted, for instance, thermoreflectance measurements are applicable to metallic samples only.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.     

Measurement of the thermal diffusivity by the thermal wave method using low-power heat sources

The errors in measuring the thermal diffusivity by the plane thermal wave method are considered as a function of the thermal flux power density. The minimum values of the thermal flux power density required for measurements with a specified error and the optimum parameters of the samples and of the heat source are determined. __________ Translated from Izmeritel’naya Tekhnika, No. 8, pp. 44–46, August, 2007.     

Thermal conductivity and thermal diffusivity of plasma-sprayed stainless steel

Results are shown of an experimental study concerning the thermal conductivity (over the temperature range 50–400°C) and the thermal diffusivity (over the temperature range 500–1100°C) of plasma-sprayed stainless steel.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 1, pp. 112–114, January, 1973.     

Thermal diffusivity and thermal conductivity of steam in the crossover region

In this paper, we present a comparison of the thermal diffusivity and thermal conductivity data of steam in the temperature range 0.02 K<T-T _c< 140 K with a recent formulation of crossover from singular to regular behavior of the transport properties of fluids. We have used two sets of experimental data previously obtained by the authors. The agreement between experimental and calculated data is good.     

High-sensitivity capacitance method for measuring thermal diffusivity and thermal expansion: Results on aluminum and copper

Thermal diffusivity and thermal expansion in high-conducting solids can be measured by means of a capacitance method, which turns out to be simple, reliable, and accurate and yields the first property with an accuracy of 1% and the second one with an accuracy of 2%. Preliminary results, which are consistent with the literature, have been obtained on pure aluminum (99.999%) and on commercial copper, both at near room temperature.     

Use of the Laplace transformation for data reduction in the flash method of measuring thermal diffusivity

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.     

Non-destructive examination of paint coatings using the thermal wave interferometry technique

Thermal wave interferometry technique is used as a means of assessing paint coatings on metal and non-metal substrates. The non-contact technique employs a modulated laser and infrared detection of thermal waves. The experimental results presented include measurements showing the suitability of the technique for non-destructive examination of paint coatings on mild steel and fibre-reinforced composite substrates.     

Measurement of the thermal diffusivity of thin films by an AC joule-heating method

A new thermal analysis named TWA (Temperature Wave Analysis) is proposed. This technique is based on the AC joule-heating method developed in our laboratory, and makes it possible to obtain thermal diffusivity precisely as a function of temperature at a constant frequency. The theoretical background and the calculation procedure for this technique are reported. This technique was applied to the study of the first order transition of high density polyethylene and the glass transition of glycerin. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Determination of the thermal conductivity and diffusivity of thin fibres by the composite method

It is suggested that the thermal conductivity of very fine fibres can be evaluated indirectly with the aid of composite theory using the experimental data for the heat transport properties of an appropriate composite which contains the fibres. The feasibility of this approach was investigated by determining the thermal conductivity and diffusivity of fibres of amorphous silicon carbide from 25° C to 1000° C contained within a lithium aluminosilicate glass-ceramic using the laser-flash technique for measurement of the thermal diffusivity of the composite. Due to the amorphous nature of the fibres, values for their thermal conductivity and diffusivity were found to be far less than the corresponding data for crystalline silicon carbide. The positive temperature dependence of the thermal conductivity, coupled with the independent observation of an increase in thermal conductivity with specimen thickness, suggests that radiative heat transfer makes a significant contribution to the total heat transferred. A number of advantages and limitations of the composite method for the evaluation of thermal transport properties of fibres are discussed.