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
where is the viscosity of the liquid, is a characteristic velocity and is the surface or interfacial tension between the two fluid phases.
For low capillary numbers (a rule of thumb says less than ), flow in porous media is dominated by capillary forces.
Famous quotes containing the word number:
“How often should a woman be pregnant? Continually, or hardly ever? Or must there be a certain number of pregnancy anniversaries established by fashion? What do you, at the age of forty-three, have to say on the subject? Is it a fact that the laws of nature, or of the country, or of propriety, have ordained this time of life for sterility?”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)