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Importnce of boundary conditions in CFD simulation of workroom concentrations.

Feigley-C; Do-T; Khan-J; Lee-E; Schnaufer-N; Salzberg-D
American Industrial Hygiene Conference and Exposition, May 31 - June 5, 2008, Minneapolis, Minnesota. Fairfax, VA: American Industrial Hygiene Association, 2008 May; :51
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 realistic boundary conditions is often not fully appreciated. In a manufacturing workroom, full-shift samples for isoamyl actetate (IAA) were collected for three days at 17 locations, and velocities were measured at supply grills, at various points near the source, and in the exhaust duct. Then, velocity and concentration fields were simulated by 3-D, steady-state CFD using: 120584 tetrahedral cells, the k-e turbulence model, standard wall function, and convergence criterions of 10-6 for all scalars. Here, we demonstrate the boundary condition treatments (for emission rates, source characteristics, supply and exhaust velocities, and flowrates) necessary to obtain good agreement between observations and CFD results. Exhaust flowrates were calculated from the solution of seven simultaneous, nonlinear equations. Emission rates for each day were determined from a two-zone model with six concentrations measured in the near-field and one upwind. With estimated emission assumed to be pure IAA, the CFD concentrations differed greatly from the measured concentrations. This assumption was unrealistic because IAA slowly diffuses out of a coating layer on many small capacitors. Thus, in subsequent simulations using the same IAA emission rate, the source was represented by emission of a dilute mixture of IAA and air. This yielded good agreement with measured values. Particular attention was paid to the region near the source, where the highest concentrations were found. Comparison between observations and CFD were made at seven locations within 1.3 m of the source center. The CFD air speeds and concentrations at these points were not significantly different from the observed values (P=0.92 and P=0.10, respectively). Thus, careful consideration of boundary conditions greatly improved agreement with measured values.
Air-contamination; Exposure-levels; Sampling; Exhaust-ventilation; Cell-biology; Cell-function; Cellular-function; Models; Emission-sources; Air-flow; Exposure-assessment
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American Industrial Hygiene Conference and Exposition, May 31 - June 5, 2008, Minneapolis, Minnesota
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University of South Carolina at Columbia, Columbia, South Carolina