Simultaneous measurement of thermal diffusivity and effusivity of solids using the flash technique in the front-face configuration

Abstract

Both thermal diffusivity and effusivity (or conductivity) are necessary to characterize the thermal transport properties of a material. The flash method is the most recognized procedure to measure the thermal diffusivity of free-standing opaque plates. However, it fails to simultaneously obtain the thermal effusivity (or conductivity). This is due to the difficulty of knowing the total energy absorbed by the sample surface after the light pulse. In this work, we propose using the flash method in the front-face configuration on a two-layer system made of the unknown plate and a fluid of known thermal properties. We demonstrate that the surface temperature is sensitive to the thermal mismatch between the plate and the fluid, which is governed by their thermal effusivity ratio. In order to verify the validity of the method and to establish its application limits we have performed flash measurements, using a pulsed laser and an infrared camera, on a set of calibrated materials (metals, alloys, ceramics and polymers) covering a wide range of thermal transport properties. These results confirm the ability of the flash method to simultaneously retrieve thermal diffusivity and effusivity in a fast manner in samples whose effusivities are lower than three times the effusivity of the liquid used as backing fluid.

Percolation Threshold of the Thermal, Electrical and Optical Properties of Carbonyl-Iron Microcomposites

“…The backing fluid was ethyleneglycol with a thermal effusivity of 858 Ws 1∕2 m −2 K −1 [32]. For times smaller than the diffusion one ( t < 0 = L 2 ∕( ) ), the logarithmic plot of the surface temperature evolution exhibits a slope m ≈ −0.5 , in agreement with previous reported works [29,39]. For long times ( t > 0 = L 2 ∕( ) ), on the other hand, the temperature behavior becomes sensitive to the interface between the sample and backing, and therefore its slope is driven by the ratio of their thermal effusivities.…”

“…The use of the fluid allows to have a proper contrast between the thermal effusivities of the samples and their backing fluid, for low vf. As thermal effusivity of the polyester resin matrix (550 Ws 1∕2 m −2 K −1 [28]) increases along with the CIP concentration, it is expected a contrast reduction for high concentrations, which will not allow the simultaneous determination of the thermal diffusivity and thermal effusivity of our samples, as shown by Pech-May et al [29]. This is why both thermal properties were measured separately.…”

“…In both cases, the composite of thickness L is subjected to a short pulse of light with intensity Q, at z = 0 , whose temperature evolution in time is recorded. The factor h represents the heat losses by convection conduction in the sample is along the z axis mainly, and the Laplace transform of the temperature at z = 0 is given by [29] where b 21 = e f ∕e s and h is the heat transfer coefficient by convection from the illuminated surface to air. Considering that is a known parameter, the values of the other three unknown ones, Q∕e s , b 21 and h p in Eq.…”

Photoacoustic thermal characterization of low thermal diffusivity thin films

“…In an optimized measurement system, thermal diffusivity and effusivity can both be determined. Hence, sensitivity to both variables is essential to derive the thermal conductivity correctly by [19] , [21] : …”

Comment on “Photothermal radiometry parametric identifiability theory for reliable and unique nondestructive coating thickness and thermophysical measurements” [J. Appl. Phys. 121, 095101 (2017)]

“…A significant number of papers have already addressed the problem of identifiability regarding the parameters of a coating in the course of a photothermal measurement, with periodic excitation [2][3][4][5] , pulsed excitation [6][7][8][9][10][11][12] or both 13 . Of benefit are also some works on the thermal characterization of a given layer in a multilayer stacking [14][15][16] .…”