Transient drag in sprays

Abstract

To extend the current capability for modelling gas-phase mixing and reaction processes where one of the reactants is introduced as a spray, data on the transient motion of decelerating particles have been analysed. The object of the analysis has been to establish the basis for predicting the instantaneous drag coefficients that determine the local exchanges of momentum in a given gas spray system. The equations developed by Tchen are shown to adequately explain transient particle motion in an isothermal system with negligible mass transfer. The instantaneous drag coefficients consist of: o 1) a viscous drag component, 2) a form drag component that can depend on the spray formation process, and 3) a component due to the acceleration experienced by both the particle and the ambient gas over the elapsed period of the flight. The effect of deceleration in a quiescent atmosphere is to lower the instantaneous drag coefficient by comparison with that expected from steady-state data.