Mini Bénard-Marangoni cells floating over thermocapillary flow in evaporative thin liquid layers

Abstract

The Marangoni convection instability patterns were experimentally investigated in evaporating thin rectangular liquid layers and a kind of mini cells were found in the layers. Although the geometrical size of the mini cells is quite smaller than the classical Bénard-Marangoni (BM) cell, they actually belong to a kind of BM cells according to their behaviors and characteristics. They floated on the upper portion of the layer but did not penetrate the entire thickness of layer. The mini cells were generated in a basically flow layer, i.e., the horizontal thermocapillary flow caused by evaporation. They moved along the basic thermocapillary flow from endwalls to the central area of liquid layers. The stagnant points of the mini cells deflected the opposite direction of cells motion. The wavelength, penetration depth, and the movement speed of the mini cells were measured. The critical horizontal Marangoni number for the incipience of the mini cells were determined and the mechanisms were analyzed carefully.