Capillary number

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Entry by Haifei Zhang, AP 225, Fall 2009

In fluid dynamics, the capillary number represents the relative effect of viscous forces versus surface tension acting across an interface between a liquid and a gas, or between two immiscible liquids. It is defined as

<math>\text{Ca} \ \stackrel{\mathrm{def}}{=}\ \frac{\mu V}{\gamma} </math>

where <math>\mu</math> is the viscosity of the liquid, <math>V</math> is a characteristic velocity and <math>\gamma</math> is the surface or interfacial tension between the two fluid phases. For low capillary numbers (a rule of thumb says less than <math>10^{-5}</math>), flow in porous media is dominated by capillary forces.

References

[1] http://en.wikipedia.org/wiki/Capillary_number

[2] http://www.cfd-online.com/Wiki/Capillary_number


Keyword in references:

Absolute Instability of a Liquid Jet in a Coflowing Stream