The dispersion of effluent from a stack was measured in an atmospheric wind tunnel whose boundary layer was representative of a slightly unstable atmosphere. Wind-tunnel tests consisted of releasing an ethane tracer gas from the stack in the tunnel and measuring horizontal and vertical concentration profiles as well as ground-level concentration profiles to "full-scale distances" of about 1,000 ft (600 m) downwind of the stack. Results of the concentration measurements show values that agree favourably with those predicted by Gaussian dispersion models in most cases, however, where complex surface conditions existed, wind-tunnel results differed from Gaussian model results. The wind-tunnel results are thought to be more representative of the full-scale situation, since the tunnel is site specific and automatically accounts for unique and complex boundary conditions. The wind-tunnel results also were favourably compared to a full-scale case for which ground-level concentration data were available.

KEYWORDS: wind tunnels, exhaust gases, flues, measuring, testing, tracers, content, stack effect, horizontal, vertical, comparing, pipe stacks, laboratories