Transport and wall surface deposition of airborne particles in enclosed, buoyancy-driven turbulent flows using fully-resolved numerical simulations

Abstract

Airborne particle transport and deposition on solid surfaces play a key role in aerosol deposition, infectious diseases transmission and surface soiling. Moving fluids disperse particles by the action of several forces including drag, lift, thermophoresis, buoyancy and Brownian effects. The relative importance of each contribution depends on the phases density ratio and the particle size. These two parameters, along with the characteristics of the boundary layers, control the local wall deposition rate. Experiments and analytical solutions have provided partial information on deposition velocity for several particle sizes and turbulent intensities in air filled cavities. While experimental data is restricted to few selected wall locations, boundary layer models results only provide wall-average values. Using Direct Numerical Simulations to solve the flow hydrodynamics and Exponential-Lagrangian Tracking Schemes for the disperse phase, deposition rates on each surface of a cubical cavity with oppositely heated walls have been determined. Numerical results at Ra = 5.4 × 108 are in very good agreement with experiments for 0.1 and 0.5 μm particle diameters. Deposition rate on adiabatic walls is found to be spatially inhomogeneous with particles accumulating near the corners where hot and cold walls meet. These preferential spots are explained by intensified wall-normal turbulent transport in these particular regions.