Student Research: William T. Geer
Conventional indoor air quality modeling has used variations on the mass balance box model to describe contaminant concentration and ventilation characteristics. An alternative model based on turbulent diffuson predicts that concentration from a point source would fall with increasing distance from the source. The description of this behavior would be a function of a parameter D, eddy diffusivity, which would be a proxy for turbulent mixing, molecular diffusino and other mmixing processes. Analysis of this concentration gradient prediction may be more valuable in certain industrial situations where the box model assumptions of complete and instantaneous mixing are violated. This experiment has measured the distribution of readings from one to three meters from a jet and a diffuse point source. The turbulent diffusion model was used to determine the apparent eddy diffusivity from the fifteen minute mean concentrations recorded. Many of the concentrations from the jet source were greater than could be predicted for any diffusivity using this model given the sourcce emission rate. The apparent diffusivities that could be calculated varied widely and do not appear to be a useful parameter. The observed data demonstrates that the assumption of uniform diffusivity is an oversimplification of the complex dispersion mechanism in this experiment.