Numerical simulation and error analysis for thermal diffusivity measurements using laser-induced thermal grating technique

Abstract

The laser-induced thermal grating technique has been used to determine the thermal diffusivity of liquids and liquid mixtures. But the dynamic behaviour of the transient thermal grating has not yet been thoroughly investigated, and the systematic errors, which result from the departures from one-dimensional heat conduction, have scarcely been studied quantitatively. In this paper. a three-dimensional numerical simulation and results of the transient thermal grating technique are presented, which enable a good understanding of the dynamic behaviour of the transient thermal grating. The results of this simulation are important for the proper design of the experimental setup to keep the systematic errors for the diffusivity measurement small. Based on the simulation method, the systematic errors were analyzed quantitatively. Here, the following effects were studied: (I) sample thickness, (2) intersection angle, (3) absorption, (4) Gaussian beam intensity distribution and focusing of heating laser beam, and (5) heating pulse duration and laser power. This error analysis makes it possible to specify the criteria for optimum measuring conditions, to correct the measured thermal-diffusivity values for systematic errors, and to estimate the accuracy of the measurements.