Particle dispersion and mass transfer in turbulent shear flows

Abstract

DNS of condensation mass transfer in particle-laden incompressible turbulent mixing layers are performed. The flows are comprised of a particle-free condensable vapor mixing with micron-size porous particles. Simulations are performed at a single Reynolds number while varying the particle Stokes number, the mass transfer and convective time scales, and the vapor concentration at the particle surface. Convection-enhanced mass transfer and the surface concentration at the gas/particle interface are of great importance in accurately predicting gas–particle mass transfer rates. Particle slip velocities are varied by considering different particle Stokes numbers. Simulations utilizing the “perfect sink” assumption are compared with simulations in which the non-zero, steady-state surface concentration is calculated taking into account the sorption properties of porous particles. Results indicate that particle dispersion is greater at lower particle Stokes numbers. However the increased particle slip velocity in the higher particle Stokes number flows result in increased condensation. Furthermore, results show that the perfect sink assumption leads to an overprediction in the condensation mass transfer rate.