Weber number
Weber number is a dimensionless quantity that is often useful in analysing fluid flows where there is an interface between two different fluids, especially for multiphase flows with strongly curved surfaces. It can be thought of as an index of the inertial force to the surface tension force acting on a fluid element. The quantity is useful in analyzing thin film flows and the formation of droplets and bubbles. It may be written as:
where ρ is the density of the fluid, v is its velocity, l is its characteristic length and σ is the surface tension.