The Effects of Small Contaminants on the Formation of Structures during Rayleigh–Bénard–Marangoni Convection in a Planar Liquid Layer

Abstract

It is shown that convective structures that form upon heating a planar liquid layer from below are determined not only by standard similarity parameters, such as the Prandtl, Rayleigh, and Marangoni numbers, but also by the presence or absence of an elastic film on the surface of the liquid, which occurs because of impurities and stabilizes the surface. The level of impurities contained in distilled water is enough to prevent Marangoni convection, and only additional purification (deionization) of water allows one to induce the thermocapillary effect. Using the method of infrared surface thermography, the mean size of thermal structures that emerge on the surface in different liquids at different temperatures and layer thicknesses is determined. A convection theory that takes the impurities in the linear and nonlinear approximations into account is examined and good compliance of the theoretical calculations with the experimental data obtained in the present work is demonstrated.