Visualizing heat-convection using laser spot step heating thermography

This paper introduces a novel application of laser spot step heating thermography, namely the visualization of a convective phenomenon. A fluid confined in a measurement cell is in intimate contact with the inner face of a thin vertical metallic sheet, on whose external surface a laser beam is tightly focused generating heat that diffuses to the closest part of the fluid layer adjacent to the sample decreasing its density locally. This induces a density gradient that generates internal motion of the fluid affecting thermograms recorded on the external side of the sheet, which are visualized after a given time has elapsed since the laser is switched on. The results of these measurements agree with those obtained using the finite-element analysis simulation software COMSOL Multiphysics®. A simple model for free convection explains why the effect is only observed for some fluids. [Display omitted] •Laser spot step heating thermography is used to visualize convective flow.•Fluid is in contact with a metallic sheet with a superficial punctual heat source.•The induced motion of the fluid affects thermograms recorded on the sheet's surface.•Thermograms are recorded after a time has elapsed since the laser is switched on.•Asymmetries in vertical temperature profiles show the effects of convection.