Mechanical and Electrostatic Dispersion of a Polydisperse Cluster of Drops for Soot Control

A model is presented for the behavior of a polydisperse cluster of spherical evaporating drops in a cylindrical, axisymmetric inviscid vortex. The formulation accounts for drop interactions and for complete dynamic and thermodynamic coupling between drops and gas. The drops may or may not be electrostatically charged. When the drops are charged, the resulting electrostatic force is included in the drops momentum equations. Calculations are made for drops having benzene properties. For charged drops, the calculations are stopped at the Rayleigh limit. The results show that electrostatic dispersion is superior to drop-induced dispersion in decreasing the mass fraction of the evaporated compound and the gas density. This is because the electrostatic force maintains a large drop velocity angle at the outer edge of the cluster thus dispersing the drops more effectively while maintaining a finite slip velocity between drops and gas and promoting engulfment of hot air, both of which enhance evaporation. The relationship between these findings and soot control is discussed.