Method For Measurement Of Thermal Diffusivity Research Articles

Fast Fourier transform Ångström method for fast thermal measurements of microfibers.

The Ångström method is a promising thermal diffusivity measurement method for microfibers. Based on the heat-loss Ångström method and micro-Ångström method, the FFT (Fast Fourier Transform) Ångström method can be used to shorten the testing time and enhance the testing robustness of thermal conductivity. The FFT Ångström uses multi-frequency superimposed input signals and then uses the FFT for frequency division analysis. Since different frequencies are input at the same time, the measuring time is greatly reduced. Moreover, because different frequencies are input in the same environment, the random and environmental perturbations of the frequencies are the same, enhancing the fitting robustness. In contrast, the single feeding strategy is relatively time-consuming, and its measurement homogeneity for different frequencies cannot be guaranteed. By comparing the measurement results from a multi-frequency input and separated single-frequency input, the FFT shows good feasibility and robustness. It may also have great potential in other types of thermal wave measurements.

Development for High Spatial Resolution Thermal Effusivity Measurement Method and High Functional Thermal Diffusivity Measurement Method

Development for High Spatial Resolution Thermal Effusivity Measurement Method and High Functional Thermal Diffusivity Measurement Method

Examination of Thermal Diffusivity Measurement Method of Sample in Contact with Transparent Plate by Flash Method Considering Thermal Radiation

Examination of Thermal Diffusivity Measurement Method of Sample in Contact with Transparent Plate by Flash Method Considering Thermal Radiation

Analytical Solution of a Generalized Two-Dimensional Model for Laser-Flash Thermal Diffusivity Measurements

This paper presents a two-dimensional model that generalizes the use of the laser flash method for thermal diffusivity measurements of homogeneous, opaque, and two-dimensional (2-D) anisotropic solid materials in the form of thin disk-shaped samples. The model employs partial central or annular pulse heating of the front sample side and a temperature detection over a generally decentralized circular surface on the rear or front sample side. A general analytical solution of related 2-D heat conduction problem with boundary and initial conditions that may exist in reality (such as radiation heat transfer between specimen surfaces and the environment, nonuniform pulse heating, finite pulse duration, and laser pulse penetration) is presented in a partial integral form. The solution for the transient temperature over the decentralized detection surface is transformed from a double integral to a single integral, which reduces the processing time in numerical computation. A simplified solution is given for the partial uniform pulse heating, rectangular pulse duration, and negligible laser pulse penetration depth. Following the simplified solution, four different applications of the presented model for the case of the rear-side temperature detection are described, together with an example of a related sensitivity analysis for the selected set of parametric values. The influence of the size and position of the detection surface on the transient temperature response is separately analyzed, and the results are presented in the last section of the paper.

Thermal Diffusivity Measurement Method of Transparent Material sandwiched between opaque plates by Flash Method

Thermal Diffusivity Measurement Method of Transparent Material sandwiched between opaque plates by Flash Method

Proposal of novel measurement method for thermal diffusivity from infrared thermal movie

A brand new thermal diffusivity measurement method was developed. In this new noncontact and absolute measurement method, thermal diffusivity was measured from infrared movie data. The model of one-dimensional thermal conduction was constructed by taking into account the thermal flow other than one-dimensional thermal conduction in the sample. On the basis of this thermal conduction model, the analytical equation for calculating thermal diffusivity was derived. A single-crystal sapphire plate was used as a test specimen for the new method. The test specimen was arranged to cause one-dimensional heat conduction. Infrared movies were taken by using an infrared camera at room temperature. Then, thermal diffusivity was numerically calculated from the acquired movie data using the analytical equation. It was experimentally demonstrated that thermal diffusivity was measured with an accuracy of around 10% error, from an infrared movie of a single-crystal sapphire sample.

Theory and verification of a method for parameter-free laser-flash diffusivity measurement of a single-side object

A new single-side flash method for thermal diffusivity determination is presented. The method is based on a laser-flash pulse excitation and infrared thermography non-contact temperature measurement of a thermal response of a studied object. Using this method, the both excitation and measurement at one side (front side) of the studied object are provided. An exact knowledge of the thickness, absorbed energy, emissivity or other material parameters of the object as well as temperature measurement on the opposite side (back side) of the object are not required. Thus, the method can be described as an object parameter-free single-side thermal diffusivity measurement method. The thermal diffusivity measurement procedure and data processing using an approximation algorithm are described in the paper. Simulation and experimental verification of the method is presented for several materials.

A method for thermal diffusivity measurement in fluids

A technique is proposed for thermal diffusivity measurement in fluids. It is based on the Angstrom method, but with excitation of thermal waves by electromagnetic energy absorption and pyroelectric detection. The good agreement between measured thermal diffusivity of air and some test liquids with literature values shows the validity of the method. It is free of some limitations of conventional photopyroelectric technique with length scanning because it is free of moving parts inside the sample and because it avoids problems associated with the non-parallelism between thermal wave generator surface and sensor. It does not require any data normalization procedure or special sample preparation.

Rear-Face Photothermal Analysis Under Random Excitation and Parametric Analysis: Application to Thermal-Diffusivity Measurement

The aim of this article is to approach thermal-diffusivity measurement possibilities, under low energy constraints, offered by a rear-face random photothermal analysis. A theoretical study demonstrates first the method’s feasibility. It shows then that the random method allows a good estimation of thermal diffusivity with a low temperature rise in the studied sample. This constitutes an advantage for the thermophysical characterization of fragile materials (artworks, biological samples). A study, experimental, carried out around the thermophysical characterization of a glass sample validates the possibilities of the random photothermal method for thermal-diffusivity measurements.

Thermal-Diffusivity Measurement in Low Thermal-Conductivity Solids by a Transient Heating Method

A simple method for thermal-diffusivity measurement in low thermal-conductivity solids is proposed on a basis of the analytical solution of the heat diffusion equation for a solid plate with uniform continuous heating at one of its surfaces. The method involves combined measurements of the temperature evolution at both the front (illuminated) and rear surfaces of the sample in both the thermally thin and thick regimes. The principal advantage of the method is its independence on a knowledge of the convection and radiation heat loss coefficient, and hence, the non-necessity of performing measurements in blackbody similar samples under vacuum conditions. If these conditions are achieved, the thermal conductivity and specific (volume) heat capacity could also be achieved.

Measurement of the thermal diffusivity of thin materials using an infrared thermal wave imaging technique

A thermal wave imaging technique was developed for the evaluation of thermal properties. In this paper we report both theoretical and experimental studies on an infrared thermal wave imaging method for thermal diffusivity measurements of thin materials in the direction parallel to the surface. © 1999 Scripta Technica, Heat Trans Asian Res, 28(2): 89–94, 1999

New photothermal deflection method for thermal diffusivity measurement of semiconductor wafers

The photothermal deflection technique is applied in transverse configuration to measure the thermal diffusivity of semiconductor wafers. The large size of these samples inhibits the possibility to make the probe beam skim the sample at a small height which is required for a direct thermal diffusivity measurement. To overcome this problem, three new experimental schemes are proposed, each one based on a different geometry of the heat diffusion (one-, two-, or three-dimensional scheme). In particular for the 3D experimental scheme, a new mirage setup is described which uses two crystalline prisms 6 mm apart from each other to let the probe beam skim 50±3 μm high over the sample surface, with a spot size of 22 μm. The main advantages of this setup, here discussed, are the obtained low probe beam height which is, moreover, independent of the sample dimensions, and the cheap technology to produce the necessary high-quality prisms. The performances of the new schemes have been tested by comparing, for well-known semiconductor wafers (InSb, InAs, InP, GaAs, GaP, Ge, and Si), the experimentally measured thermal diffusivity with the values reported in the literature.

Method for thermal diffusivity measurements based on photothermal deflection

The thermal diffusivity measurement through pulsed photodeflection in a modified collinear configuration is presented and discussed; comparison between theory and experiment is also shown.

Development of ac Calorimetric Method for Thermal Diffusivity Measurement III. Heat Loss in the Measurement of Fine Wires

The measurement of the thermal diffusivity of a fine wire is developed, using a light-irradiation-type ac calorimetric method. It is pointed out that in the analysis, the contribution of heat loss or external relaxation time should be taken into account for the measurement of a fine wire. To examine the measurement, a wire of stainless steel with a diameter of 30 µm is used as a sample and the test is carried out in the wide frequency range of 1–25 Hz. The result obtained agrees with the value reported for the bulk material.

On the analysis of the thermal diffusivity measurement method with modulated heat input

The present paper proposes a simplified way to analyze thermal diffusivity experiments in which the phase shift is measured between the modulations of the temperatures on either face of a disk-shaped sample. The direct application of complex numbers mathematics avoids the use of the cumbersome formulae which hitherto have hampered a wider confirmation of the method and which restricted the range of the phase lag to an angle of 180°. The algorithm exposed makes it more practical to refine the analysis, which may lead to a higher accuracy and a wider use of the method. The origins of some possible errors in the calculated results are briefly reviewed.

Development of ac Calorimetric Method for Thermal Diffusivity Measurement. II. : Sample Dimension Required for the Measurement

In an ac light-irradiated method for thermal diffusivity measurements of rectangular plate-like samples partly shadowed by a mask, the required dimensions are considered. The contour length around the cross-section (given by the thickness times the width) should be so long that the sample has a proper amount of heat capacity; then, the external thermal relaxation time becomes sufficiently long so as not to dissipate ac thermal energy. The thickness, however, should be thin enough so as to obtain a uniform temperature across the sample during oscillations (as discussed in detail previously). For the sample length, the distance between the thermocouple and the sample boundary on which ac light is irradiated should be sufficiently long so that the thermal waves reflected at the boundary decay. However, there is no restriction on the other bourtdary shadowed by the mask, i.e., the thermocouple can be placed at the boundary.

A pulsed method for thermal-diffusivity measurements of polymer films with submicrometre thickness

The use of pyroelectric calorimeters for pulsed measurements of the thermal diffusivity of thin films is described. The material under study is directly coated on to a pyroelectric calorimeter. A transient heat source is generated at the surface of the sample via absorption of a laser pulse. By analysis of the transmitted heat pulse, the thermal diffusivity of the sample can be determined. The potentials of this method are demonstrated on polymer films with thicknesses in the submicrometre range.