Modeling deposition of particles in vertical square ventilation duct flows

Abstract

The presence, flow, and distribution of particle in heating, ventilation, and air-conditioning (HVAC) ducts influence the quality of air in buildings and hence the health of building occupants. To shed a better light on the flow of particles in HVAC ducts this a paper has considered the effects of drag, lift force, gravity, Brownian diffusion, and turbulent diffusion on the dimensionless deposition velocity of particles in smooth vertical ventilation ducts using fully developed and developing velocity profiles. Based on the Reynolds stress transport model (RSM) at two different air velocities, 3.0 m/s and 7.0 m/s, the aforementioned effects were predicted using Reynolds-averaged Navier–Stokes (RANS)–Lagrangian simulation on square shaped ducts under vertical flows. Preliminary results suggest that the gravity of particles does not directly change the dimensionless deposition velocity in vertical flows. Nevertheless, the gravity of particles contributes to changing the Saffman lift force. It is thus the Saffman lift force that directly changes the dimensionless deposition velocity of particles in vertical flows. In addition, the difference in the dimensionless deposition velocities between fully developed and developing flows is owing to the turbulent diffusion, turbulent intensity, and needless to say, the Saffman lift force under different dimensionless particle relaxation time.