Thermal Diffusivity by The Laser Flash Technique

Abstract

Thermal diffusivity is an important material thermophysical property. The most widely used method for measuring thermal diffusivity is the laser flash technique. In this technique, a sample is placed within a controlled atmosphere furnace and subjected to a finite impulse of radiant energy on its front surface, through the use of a laser. The transport of heat through the sample, as a result of the laser impulse, causes a transient temperature rise on the rear surface of the specimen. This temperature rise is measured by an IR detector placed above the rear sample surface. The net result is a “thermogram” which is a plot of the rear‐face temperature versus time. Assuming a proper set‐up and careful experimentation, the transfer of heat under these conditions approximates one‐dimensional heat flow. Comparing the experimental data with one‐dimensional heat flow theoretical predictions, allows an estimation of thermal diffusivity. There are several methods available to determine thermal diffusivity based on experimental and theoretical comparisons. The simplest method is to determine the “half‐rise time,” t 0.5, which is the time at which the experimentally measured rear‐face temperature reaches half of its maximum value. More accurate methods use sophisticated analysis algorithms to model and fit the entire experimental thermogram curve to an ideal theoretical curve by means of a nonlinear least‐squares procedure. These approaches can include corrections that account for the fact that the experimental measurements only approximate one‐dimensional heat flow conditions. Using the thermogram curve fitting techniques, the measurement of thermal diffusivity of a range of material types including solid thermal insulators and conductors is possible. It is also possible to measure the apparent diffusivity of inhomogeneous samples such as composites and porous materials. Using two‐ and three‐layer analysis methods allows the measurement of thermal diffusivity of liquids. The layer methods can be extended to a determination of the thermal contact resistance of interfaces encountered in coated or bonded materials.

Thermal conductivity enhancement of alumina/polyamide composites via interfacial modification

“…where K is the thermal conductivity, α is the thermal diffusivity, ρ is the bulk density and C p is the specific heat capacity [18]. The thermal diffusivity of the composites was measured by the laser flash method (TC-7000H, ULVAC, Inc., Japan).…”

Dependence of Heat Transport in Solids on Length-Scale, Pressure, and Temperature: Implications for Mechanisms and Thermodynamics

“…Because length and time, not heat input nor absolute temperature, are quantified, accuracy (±2%) is a factor of two better than in other techniques [ 17 ]. The many publications on LFA and continued developments, including the removal of spurious radiative transfer, demonstrate utility and versatility, e.g., [ 26 , 27 ].…”

Solving viscoelastic problems with a Laplace transform approach supplanted by ARX models, suggesting a way to upgrade Finite Element or spectral codes

“…Using a metaphorical expression from biology, the transfer function characterizes the łfull DNAž of the system (material) in terms of frequency information. It corresponds to the response of the system to the impulse (Dirac Delta) function H (𝑝) = σ𝛿 (𝑝) and is obviously never realized experimentally in mechanics due to an impossibility related to inertial effectsÐhowever, it is a quasi-systematic approach for thermal systems excited with laser pulses for example, as exemplified in (Corbin and Turriff 2012). When such a transfer function is known from the engineer, then it allows computing the response of the system to any input excitation.…”