ONSET OF CONVECTION IN NEAR-SURFACE LAYER OF THE LIQUID
Onset of convective motion in near-surface layers of water and ethanol due to heating of the liquid surface part with IR heater or due to exposing part of the surface to evaporative cooling is studied using Particle Image Velocimetry (PIV). In case of partial heating of the upper liquid layer the boundary conditions at the surface are shown to be important. In ethanol, dynamics of which is well described using Pearson boundary conditions, non-uniform heating is accompanied with rapid motion of the surface, associated with Marangoni effect. In water, due to presence of«elastic film» at the surface, Rayleigh convection is dominant. Maximal velocity in ethanol, heated by IR radiation, is observed at the surface, whereas in water velocity maximum is located in the lower part. In case of heating from above vortices are located near the surface, which differs from the cooling case, where convective vortices occupy the whole volume. Also, Marangoni convection during cooling of ethanol results in fast decrease of horizontal gradients of temperature near the surface. However, at later stages Rayleigh convection is developed.