Strategies for Dispersion Control by Pulsed Injection: Particle Dispersion by Jet in Crossflow

Abstract

The dispersion produced by a jet injecting microparticles in a cross stream is controlled by the interaction between dispersed species and large scale time-dependent flow structures populating the transverse jet. These structures span over a wide range of spatial and temporal scales and are not equally effective in advecting and dispersing species. In many environmental and industrial applications, the species advected by the jet stream are expected to undergo rapid and homogeneous dilution away from the injection point. Preferential accumulation of particles into specific flow regions is to be avoided since this may have consequences on the overall industrial process. For instance, non uniform distribution of droplets of ammonia solution can severely downgrade the efficiency of post-combustion control devices. In a previous work (Campolo et al., 2005), we addressed the problem of identifying which of the flow structures in a jet in crossflow control the dispersion mechanisms of inertial particles, focusing specifically on the issue of their preferential distribution. Based on these results, in this work we try to identify a strategy for particle pulsed injection which can be used to optimize their dispersion. The flow field produced by the transverse jet is calculated using a finite volume solver of Navier-Stokes equations; the dispersion of injected particles is computed using a Lagrangian approach. Particle dispersion and segregation are evaluated considering the effect of the synchronicity between the particle injection time and the evolution dynamics of the mixing structures. Numerical results show that (i) transport of species is dominated by specific flow structures, (ii) particle dispersion is not uniform and (iii) the synchronicity between species injection and evolution dynamics of flow structures influences the dispersion process. These results indicate that pulsed injection may be used to control effectively particle dispersion.