EXPERIMENTAL STUDY OF MARANGONI-BENARD CONVECTION IN A LIQUID LAYER INDUCED BY EVAPORATION

Marangoni-Benard instability and convection in evaporating liquid layers have been studied experimentally through flow visualization and temperature profile measurement. Benard cells have been observed in an evaporating thin liquid layer whether it is heated, adiabatic, or cooled from below. This experimental study has revealed a different mechanism from the traditional Rayleigh-Benard and Marangoni-Benard instabilities and convections, which require a negative temperature gradient in the thin liquid layer. Evaporation rate and enthalpy of evaporation have been found to be important parameters of instability and convection in an evaporating liquid layer. A modified form of Marangoni number, Ma*, is proposed and its critical values, Ma* c, for alcohol and Freon-113 evaporating layers are determined experimentally. A quantitative comparison between Ma* and the traditional Marangoni number, Ma, shows that Ma* is an adequate indicator of the stability status in evaporating liquid layers.