In fluid dynamics, the ****Morton number (Mo) is a dimensionless number used together with the Eötvös number or Bond number to characterize the shape of bubbles or drops moving in a surrounding fluid or continuous phase, c. It is named after Rose Morton, who described it with W. L. Haberman in 1953.

Definition

The Morton number is defined as where g is the acceleration of gravity, \mu_c is the viscosity of the surrounding fluid, \rho_c the density of the surrounding fluid, \Delta \rho the difference in density of the phases, and \sigma is the surface tension coefficient. For the case of a bubble with a negligible inner density the Morton number can be simplified to

Relation to other parameters

The Morton number can also be expressed by using a combination of the Weber number, Froude number and Reynolds number, The Froude number in the above expression is defined as where V is a reference velocity and d is the equivalent diameter of the drop or bubble.