Capillary number

The capillary number (symbol: ) is a dimensionless parameter, it is again the ratio of viscous forces to surface tension at the phase boundaries ( interfaces) of liquids and gas or immiscible liquids.

The capillary is defined as:

Where:

  • : Dynamic viscosity of the liquid ( in SI units: Pa · s )
  • : Kinematic viscosity of the liquid ( in SI units: m2 s -1)
  • : Characteristic velocity ( in SI units: m / s)
  • : Surface tension ( in SI units: N / m)

Alternatively, the capillary can be calculated as the ratio of the Weber number () of the Reynolds number ():

The capillary number can also be interpreted as the ratio of the velocity to the characteristic relaxation rate of a liquid.

The relaxation is induced by the surface tension of endeavor to assume a small surface area as possible. This drive is inhibited by the viscosity. The capillary is much smaller than one, the relaxation rate is higher than the external force applied to for example a drop of the speed and increases in each moment, a static ideal form of very small surface area to. If the Kapillargeschwindigkeit much greater than one, then the relaxation of the drop of the external speed does not follow and the drop is deformed without being able to accept a form of very small surface.

  • Code ( Fluid Mechanics )
464098
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