MOLECULAR-DIFFUSION EFFECTS ON ENTRAINMENT IN WIND-TUNNEL STUDIES OF DENSE GAS DISPERSION

Wind tunnel experiments were performed to study the vertical dispersio n (mixing) of a denser-than-air gas plume continuously released from a floor-level line source in a smooth-wall turbulent boundary layer. Ve rtical entrainment rates were inferred from concentration measurements . The Richardson number was varied over a wide range; at larger Richar dson numbers, turbulence within the dispersing plume was significantly damped. Analytical solutions of the diffusion equation were examined to fix the theoretical passive limit for air entrainment and to study the relative importance of molecular and turbulent diffusion in experi mental measurements. Hot-wire and cross-wire anemometry measurements i n the approach flow and the plume are also reported. Based on comparis on with analytical solutions, turbulence measurements and flow visuali zation experiments, molecular diffusion processes clearly dominated tu rbulent diffusion processes in the gas plume for some conditions teste d.