Measurement of in-plane thermal diffusivity of solids moving at constant velocity using laser spot infrared thermography

Abstract

In this work, an infrared thermography setup is proposed to measure the in-plane thermal diffusivity of (an)isotropic samples that are moving at constant velocity, as it is the case of in-line production or in-line quality control processes in factories. The experiment consists in heating the moving sample with a focused laser spot, which remains at rest, and recording the surface temperature by an infrared camera. An analytical expression for the surface temperature of the moving sample has been obtained. By analyzing the surface temperature in logarithmic scale, three simple linear relations are obtained, whose slopes give the thermal diffusivity in the direction of the sample movement and in the perpendicular direction. These three linear methods, which are not disturbed by heat losses by convection and radiation, are valid for both opaque and semitransparent samples. Measurements performed on calibrated samples confirm the validity of the methods, which are also valid when the sample is at rest and the laser spot scans its surface at constant velocity, the so-called ‘‘flying spot” technique.