Particles in a turbulent gas: Diffusion, bias, modulation and collisions

Turbulence is an effective way to spread particles and drops in a fluid, which is critical for many energy systems, ranging from carbon-based power-production to spray cooling for renewable energy storage. Combining the intricacies of turbulence with the complexities of particle motion has led to numerous advances, especially in the last two decades in terms of turbulent bias, and turbulence modulations, as well as experimental confirmation of previous theories regarding turbulent diffusion and turbulent particle collisions. In this review, the fundamental features of turbulence are related to key Stokes numbers that describe one-way coupling (influence of turbulence on particle motion). This includes turbulent diffusivity for a range of inertias and drift parameters, as well as new work that describes the kinetic energy of particle velocity and of particle relative velocity. Turbulent biases are then reviewed including non-linear drag bias, preferential bias, clustering bias, diffusiophoresis and turbophoresis. Next, recent progress in turbulence modulation and particle collision frequency are discussed. Finally, a generalized flow regimes is presented to summarize the interactions as a function of particle size and particle concentration.