Periodic projection of a random spatial pattern for the assessment of the in-plane thermal diffusivity

Abstract

This work deals with the characterization of biochar deposited on a thin metallic sheet, used to enhance the evaporation in heat exchangers. The effectiveness of such deposit is done by means of the heated thin foil thermographic technique. The thermal diffusivity of the foil is the main objective of this study. In the proposed method, a pulse of 2 ms duration is produced by a laser, and periodically projected on the surface of an opaque sample of which the thermal parameters have been determined by classical measurements. The spatial distribution of the laser light pattern is random, after passing through a mask like a QR code. Several masks with different spatial features and distribution were prepared by sputtering thin layer (100 nm) of gold on a piece of glass covered by a pattern. Using the masks, samples were photothermally excited by impulsive laser light patterns. The resulting dynamic temperature field evolution at the sample surface was observed by a fast IR camera in the LW, and the thermal diffusion process was recorded by a sequence of IR images. In this contribution, a theoretical model is described and utilized to analyze the spatiotemporal dependence of the temperature field.