The onset of convection in liquid with the free surface cooled from above: Influence of the surface behavior on the size and formation time of critical perturbations

• Published in: Physics of fluids (1994) 2021-11, Vol.33 (11)
• Main Authors: Pushtaev, A. V., Vinnichenko, N. A., Plaksina, Yu. Yu, Uvarov, A. V.
• Format: Article
• Language: English
• Subjects: Boundary conditions; Contaminants; Convection cooling; Deep water; Distilled water; Evaporative cooling; Fluid dynamics; Free surfaces; Heat flux; Infrared imaging; Perturbation; Physics; Thermography; Wavelengths
• ISSN: 1070-6631; 1089-7666
• DOI: 10.1063/5.0070595

The onset of convection in an initially homogeneous liquid layer cooled from above is investigated by means of a non-normal approach. This method is based on the analysis of the temporal evolution of small perturbations. The most amplified perturbation and the moment, when convection can be observed, are determined. Experimental measurements are performed for a layer of distilled water cooled by evaporation. Instantaneous surface temperature fields are obtained using infrared thermography. The effect of the surface mobility on the size and onset time of convective cells is examined. The comparison of experimental results with numerical simulations for different boundary conditions reveals the presence of a film of adsorbed contaminants on the surface of distilled water, which corresponds to the no-slip condition. In the presence of the film, boundary conditions for cooling from above and heating from below become the same, and the obtained results agree with the experimental data available for a liquid layer with a heated bottom. As the layer depth increases, the onset time and the average horizontal wavenumber of convective cells become independent from the layer depth. The condition for the transition to a deep water approximation is determined by the surface heat flux and thermophysical parameters of the liquid.