# Tag Info

When to use

This tag should be used for fluid dynamics and statics, if surface tension will play a significant role in the physical process of interest. This significance can be roughly determined by looking at the following two dimensionless numbers:

The Weber number: $We=\frac{\rho u^2 L}{\gamma}$ which signals the relative importance with respect to inertial forces

The Capillary number: $Ca=\frac{\\mu u}{\gamma}$ which signals the relative importance with respect to viscous forces

When both numbers are small, surface tension will be dominant in the system.

Translated this means that the tag should be used for: fluid-fluid systems at small scales ($\mu$m to cm) and small velocities (typically $<1$ cm/s). Also flows with large surface tension gradients such as weld pools should wear this tag.