Capillary length
In fluid mechanics, capillary length is a characteristic length scale for fluid subject to a body force from gravity and a surface force due to surface tension.
The capillary length is defined as[1]: \[\lambda_{c} = \sqrt{\frac{\gamma}{\rho g}}\],
where \(g\) is the acceleration due to gravity and \(\rho\) is the density of the fluid, and \(\gamma\) is the surface tension of the fluid-fluid interface.
For clean water at standard temperature and pressure, the capillary length is ~2mm.
A capillary surface that has a characteristic length smaller than the capillary length can be considered a low Bond number surface. A sessile drop whose largest dimension is smaller than the capillary length, for example, will take the shape of spherical cap, which is the solution to the Young-Laplace equation with gravity completely absent.
See also
References
- ↑ G.K. Batchelor, 'An Introduction To Fluid Dynamics', Cambridge University Press (1967)
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