Capillary pressure

In fluid statics, capillary pressure is the difference in pressure across the interface between two immiscible fluids, and thus defined as:$p\_c=p\_\{\; ext\{non-wetting\; phase-p\_\{\; ext\{wetting\; phase$.In oil-water systems, water is typically the wetting phase, while for gas-oil systems, oil is typically the wetting phase.

The Young–Laplace equation states that this pressure difference is proportional to the surface tension, $gamma$, and inversely proportional to the effective radius, $r$, of the interface, it also depends on the wetting angle, $heta$, of the liquid on the surface of the capillary.:$p\_c=frac\{2gamma\; cos\; heta\}\{r\}$

The equation for capillary pressure is only valid under capillary equilibrium, which means that there can not be any flowing phases.

ee also

* Capillary action
* Capillary number
* Leverett J-function
* Young–Laplace equation

References

* Kim Kinoshita, Electrochemical Oxygen Technology p139, John Wiley & Sons, Inc. 1992.
* [http://www.articleworld.org/index.php/Capillary_pressure Capillary pressure equations]