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As an example, wine may exhibit a visible effect called "tears", as shown in the photograph. The effect is a consequence of the fact that alcohol has a lower surface tension than water. If alcohol is mixed with water inhomogeneously, a region with a lower concentration of alcohol (greater surface tension) will pull on the surrounding fluid more strongly than a region with a higher alcohol concentration (lower surface tension). The result is that the liquid tends to flow away from regions with higher alcohol concentrationalong the tension gradient. This can also be easily demonstrated by spreading a thin film of water on a smooth surface and then allowing a drop of alcohol to fall on the center of the film. The liquid will rush out of the region where the drop of alcohol fell.
The Marangoni number, a dimensionless value, can be used to characterize the relative effects of surface tension and viscous forces.
A very detailed mathematical treatment of this from the point of view of the Navier-Stokes equations and the equations of thermodynamics can be found in the first third of Subrahmanyan Chandrasekhar's Hydrodynamic and Hydromagnetic Stability, originally published in 1961 by Oxford, and republished by Dover in 1981.
Under earth conditions, the effect of gravity causing density-driven convection in a system with a temperature gradient along a fluid/fluid interface is usually much stronger than the Marangoni effect. Many experiments (ESA MASER 1-3) have been conducted under microgravity conditions aboard sounding rockets to observe the Marangoni effect without the influence of gravity.
The effect of the Marangoni effect on heat transfer in the presence of gas bubbles on the heating surface (e.g., in subcooled nucleate boiling) has long been ignored, but it is currently a topic of ongoing research interest because of its potential fundamental importance to the understanding of heat transfer in boiling.
One important application of the Marangoni effect is the use for drying silicon wafers after a wet processing step during the manufacture of integrated circuits. Liquid spots left on the wafer surface can cause oxidation that damages components on the wafer. To avoid spotting, an alcohol vapor (IPA) or other organic compound in gas, vapor, or aerosol form is blown through a nozzle over the wet wafer surface (or at the meniscus formed between the cleaning liquid and wafer as the wafer is lifted from an immersion bath), and the subsequent Marangoni effect causes a surface-tension gradient in the liquid allowing gravity to more-easily pull the liquid completely off the wafer surface, effectively leaving a dry wafer surface.
The Marangoni effect is also important to the fields of welding, crystal growth and electron beam melting of metals.
Category:Fluid mechanics Category:Convection Category:Physical phenomena
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