https://doi.org/10.1351/goldbook.S06029
Sometimes referred to as the inertial parameter; it is an index of the impactability of an @[email protected] particle. It is defined by the equation: \(St = 2\ \tau \ (V_{\text{t}}- \nu_{\text{t}})\ D_{\text{p}}\) where \(D_{\text{p}}\) is the diameter of a small drop, \(V_{\text{t}}- \nu_{\text{t}}\) is the difference in fall velocities of the drop and @[email protected] particles and \(\tau \) is the characteristic @[email protected] of a particle.