Maragoni Index 1

[Rodin]

Does anybody have any idea what the Maragoni index is and what its units (if any) are. I suspect it is something to do with foaming in distillation columns, but am looking for a more precise definition than that.

 

[25362]

Marangoni effects are associated with variations in surface tension.

The Marangoni number (Ma) is a dimensionless number that is meant to explain flow of liquid films (for example, on foams, or on drops) due to gradients in surface tension. These temporary non-equilibrium gradients may be caused by temperature variations, or, more generally, by concentration differences, surfactants, etc.

Ma = (delta sigma)(h)/[(density)(kinematic viscosity)(thermal diffusivity)

delta sigma: the surface tension span in the film, N/m = kg/s²
h: film thickness, m
density of liquid: kg/m³
kin visc.: of liquid, m²/s
thermal diffusivity: m²/s

Perry VI, section 18, discusses the Marangoni effect on foams' stability.

As finely divided solids that are poorly wetted by a liquid can stabilize a foam, so can electric double layers and surface tension effects.

Marangoni flows are those that oppose foam's drainage and act as a stabilizing factor to restore the thickness of the film layer (lamella) by the motion of the liquid surface from regions of lower to those of higher surface tension.

Marangoni (mass transfer) effects are defined as those caused by a disturbance in the interfacial tension at liquid-liquid interfaces in extraction columns.

I hope I've answered your query to your satisfaction.

 

[Rodin]

An excellent and comprehensive answer thanks very much!