Capillarity and the Young-Laplace Equation

Capillarity describes the phenomenon of the rising or depression of a liquid into a capillary, a thin tube with inner diameter less than 1 mm in the case of water. Usually, the pressure drop across a curved liquid-gas interface is given by the Young-Laplace equation  

Ap pressure drop across the curved interface in Pa y surface tension of the liquid in mN.m  

The Young-Laplace equation is very useful for calculating the pressure drop across curved liquid-gas interfaces in various practical cases (see Table 20.7). 

Geometry Capillary Single plane Two walls Ring 

The pressure drop can be calculated by the Young-Laplace equation Ap = 2y/R = AycosOID 

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