Multicellular structures in thin free liquid films induced by thermocapillary effect

Hypothesis:: Multicellular convective structures that are induced in a fluid exposed to temperature differ-ence are commonly observed in nature and in daily life. Different types of basic flow patterns are induced in a free liquid film by thermocapillary effect, whereas the formation of such multicellular structures has not been hitherto unravelled. Experiments:: A thin film of high-Prandtl-number liquid is prepared in a rectangular aperture of the order of 0.1 mm in thickness sustained by its surface tension. A designated temperature difference is imposed between the end surfaces of the aperture to generate a thermocapillary-driven convection in the free liq-uid film. We monitor the induced thermal flow patterns to evaluate the cell numbers and their wave-length by experimental and numerical approaches.Findings:: The multicellular structure is established by the thermocapillary effect in the free liquid films. The cell number increases in a stepwise manner as the liquid-film width increases. When the cell number increases, another pair of the cells always newly emerges. We determine the wavelength in a non -dimensional manner, and present the variation of the wavelength against the aspect ratio corresponding to the liquid-film width. The results are compared to those of convectional Marangoni-Benard convection.(c) 2023 Elsevier Inc. All rights reserved.

Automated summary

The formation mechanism of multicellular structures in a thin liquid film driven by thermocapillary effect is investigated through experiments and numerical simulations. It is found that the number of cells increases stepwise as the liquid film width increases, with new cell pairs emerging each time. The wavelength of the multicellular structure is determined and compared to that of conventional Marangoni-Benard convection.