Marangoni Convection in Capillary Tubes Filled With Volatile Liquids

Abstract

The work is an experimental investigation of the evaporation process from a liquid meniscus formed in capillary tubes of various sizes (ranging from 200 to 900 μm). The results have been compared with those of a previous analytical work and show how the strong convection in the liquid phase is responsible for the discrepancy found. In the analytical prediction the evaporation process is sustained only by diffusion and in this model the meniscus position vs. time is a linear function of the tube size; instead, our experimental results show how this parameter is inversely correlated with the pore size. The surface roughness of the tubes was characterized and particular care has been devoted to the capillaries’ cleaning procedure from which wetting properties are strongly dependent. Marangoni convection prevails at tube sizes less than one millimeter in diameter as in the present case, while at larger sizes a coupling between Marangoni and Rayleigh convection is expected. The Marangoni roll of thoroidal shape in the liquid phase has been visualized and characterized using seeding particles. As pointed out clearly in the present study, Marangoni convection enhances the heat-mass transfer from a pore.