Pattern formation without heating in an evaporative con - vection experiment

– We present an evaporation experiment in a single fluid layer reproducing conditions of volatile fluids in nature. When latent heat associated to the evaporation is large enough, the heat flow through the free surface of the layer generates temperature gradients that can destabilize the conductive motionless state giving rise to convective cellular structures without any external heating. Convective cells can be then observed in the transient range of evaporation from an initial depth value to a minimum threshold depth, after which a conductive motionless state appears until de evaporation finish with a unwetting sequence. The sequence of convective patterns obtained here without heating, is similar to that obtained in Bénard-Marangoni convection. This work present the sequence of spatial bifurcations as a function of the layer depth. The transition between square to hexagonal pattern, known from non-evaporative experiments, is obtained here with a similar change in wavelength. Introduction. – Pattern formation in different areas of knowledge had received great attention in the last decade [1, 2]. Interest in this kind of research arises from the general interest in nature understanding and also from requirements of industrial processes like painting , film drying or crystal growth, where pattern formation knowledge plays a fundamental role. Pattern formation during evaporation is a common phenomena that can be frequently observed in nature. Natural convection self-generated by the evaporation of a thin layer of water, normally left the brand of its individual convective cells in the bottom clay. Since the first rigorous work devoted to study pattern formation in fluids [3] the existence of cellular structures was recognized be linked to surface tension and buoyancy. Experimental and theoretical studies where movements are generated mostly by interfacial forces [4, 5] have been increased in the last years [6, 7]. Generally convective movements originated in surface tension gradients are associated with the names Marangoni or Bénard-Marangoni convection (BM). In evaporative convection there are two main physical mechanisms of instability relating surface tension gradients, one with a change in the composition or concentration, so called thermosolutal convection and the other with the local dependence of surface tension with temperature or thermocapillary convection.