Settling velocity ($W$)

The settling velocity is a particle's vertical velocity relative to a stated frame. With height increasing upward, a sedimenting particle has $W<0$.

The Stokes settling velocity is the terminal relative velocity obtained by balancing gravity, buoyancy, and the Stokes drag law for a dilute isolated sphere.

Hindered settling is the reduction or modification of particle settling by the displaced carrier-fluid backflow and by interactions with other particles. A simple dilute mixture model gives every species the same volume-averaged backflow.