Deriving Realistic Source Boundary Conditions for a CFD Simulation of Concentrations in Workroom Air

Computational fluid dynamics (CFD) is used increasingly to simulate the distribution of airborne contaminants in enclosed spaces for exposure assessment and control, but the importance of re-alistic boundary conditions is often not fully appreciated. In a workroom for manufacturing ca-pacitors, full-shift samples for isoamyl acetate (IAA) were collected for 3 days at 16 locations, and velocities were measured at supply grills and at various points near the source. Then, velocity and concentration fields were simulated by 3-dimensional steady-state CFD using 295K tetrahe-dral cells, the k-e turbulence model, standard wall function, and convergence criteria of 1026 for all scalars. Here, we demonstrate the need to represent boundary conditions accurately, espe-cially emission characteristics at the contaminant source, and to obtain good agreement between observations and CFD results. Emission rates for each day were determined from six concentra-tions measured in the near field and one upwind using an IAA mass balance. The emission was initially represented as undiluted IAA vapor, but the concentrations estimated using CFD dif-fered greatly from the measured concentrations. A second set of simulations was performed us-ing the same IAA emission rates but a more realistic representation of the source. This yielded good agreement with measured values. Paying particular attention to the region with highes