Marangoni effect

About: Marangoni effect is a research topic. Over the lifetime, 5336 publications have been published within this topic receiving 98562 citations. The topic is also known as: Gibbs–Marangoni effect.

Microgravity experiments and analysis of oscillatory thermocapillary flows in cylindrical containers

Abstract: Results are reported of thermocapillary flow experiments performed aboard the Spacelab. Oscillatory thermocapillary flows were investigated in open cylindrical containers filled with 2 cS kinematic viscosity (Prandtl number = 27 at 25 °C) silicone oil. The fluid was heated by a cylindrical cartridge heater placed at the symmetry axis of the container while the container sidewall was maintained at a lower temperature. Test containers with three different diameters of 1.2, 2.0 and 3.0 cm were used. The ratio of heater to test container diameter was fixed at 0.1. The liquid free-surface shape was either flat or concave. The flow and temperature fields were investigated for steady and oscillatory flows. Free-surface deformation was observed during oscillations. The conditions for the onset of oscillatory flow were determined. It is shown that the Marangoni number alone does not correlate the onset conditions. A new parameter, which represents free surface deformation, is derived for flat free surfaces and is shown to correlate the onset conditions well. Infrared images of free surface and oscillation frequencies are also presented.

The initial coalescence of miscible drops

Abstract: When two drops of different miscible liquids are brought into contact, their coalescence speed is governed by the liquid having the weaker surface tension. Marangoni waves propagate along the drop with the stronger surface tension. We present surface profiles and propagation speeds of these waves, from experiments with a pendent water drop coalescing with a flat ethanol surface or with a sessile drop of ethanol. We find in the former case that the capillary-Marangoni waves along the water drop show self-similar character when measured in terms of arc length along the original surface. The coalescence of two liquids of different viscosities is also studied. For large viscosity difference, mobility is confined to the lower viscosity fluid and a sharp corner forms where the two liquids meet along the free surface. The coalescence speed of a water drop with a much more viscous liquid is nearly independent of the strength of the viscosity difference.

Thickening Factor in Marangoni Coating

Abstract: We have recently shown that a wire, and more generally a solid, drawn out of a solution containing surfactants entrains a thicker film than one drawn out of a pure liquid (Marangoni coating). The thickening factor, generally of order 2, was found to be independent of the capillary number (for surfactant concentration of the order of the cmc) but depends on the wire radius: the thinner the wire, the larger the thickening. After summarizing these results, we propose a model for understanding this effect, which is shown to result from a balance between convection and adsorption. Finally, a scaling form is proposed for the thickening factor.

The effects of surfactant on the multiscale structure of bubbly flows.

Abstract: It is well known that a bubble in contaminated water rises much slower than one in purified water, and the rising velocity in a contaminated system can be less than half that in a purified system. This phenomenon is explained by the so-called Marangoni effect caused by surfactant adsorption on the bubble surface. In other words, while a bubble is rising, there exists a surface concentration distribution of surfactant along the bubble surface because the adsorbed surfactant is swept off from the front part and accumulates in the rear part by advection. Owing to this surfactant accumulation in the rear part, a variation of surface tension appears along the surface and this causes a tangential shear stress on the bubble surface. This shear stress results in the decrease in the rising velocity of the bubble in contaminated liquid. More interestingly, this Marangoni effect influences not only the bubble’s rising velocity but also its lateral migration in the presence of mean shear. Together, these influences cause a drastic change of the whole bubbly flow structures. In this paper, we discuss some experimental results related to this drastic change in bubbly flow structure. We show that bubble clustering phenomena are observed in an upward bubbly channel flow under certain conditions of surfactant concentrations. This cluster disappears with an increase in the concentration. We explain this phenomenon by reference to the lift force acting on a bubble in aqueous surfactant solutions. It is shown that the shear-induced lift force acting on a contaminated bubble of 1 mm size can be much smaller than that on a clean bubble.