Stochastic modelling of the effects of liquid droplet collisions in impinging streams absorbers and combustors

Abstract

A stochastic model based on the Boltzmann kinetic equation and employing the comprehensive treatment of the dynamics of binary droplet collisions is suggested to describe the droplet size and spatial distribution in dense spray. The model is valid for highly non-equilibrium impinging sprays in which the inertia of the droplets is very high and dynamic coupling with the gas is low. A Monte Carlo simulation procedure is developed for the solution of the kinetic equation. A model is used to analyse the absorption of a gas in a liquid spray in an impinging streams absorber. It is demonstrated that droplet collisions result mainly in coalescence, and reduce the overall droplet concentration and the interphase area in the reactor. The results of the analysis of the vaporization of a pentane spray in an impinging streams combustor are presented. It is shown that while droplet collisions reduce the vaporization rate by deflecting droplets out of the reactor and by coalescence, collision-induced fragmentation strongly affects the droplet size distribution and increases the fuel vaporization rate. The obtained results indicate that in the high velocity combustion of light fuels the collision-induced fragmentation of fuel droplets has a profound effect on the droplet size and spatial distribution.