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Abstract
The currently recommended EPA screening procedure for calculating maximum concentrations in the downwind recirculation cavity is contained in the SCREEN model. This procedure has not been previously compared with observed data. Because of the potential widespread application of the SCREEN cavity downwash model, this paper presents the results of an evaluation of both the SCREEN procedure and a proposed alternative screening model.
The SCREEN cavity downwash model was found to have significant deficiencies that could lead to unrealistically high or low concentrations in different circumstances. These were caused by the inappropriate application of a recirculation cavity height formula, and the lack of fractional capture of the plume by the cavity for reattached flow.
The proposed model avoided these deficiencies and showed much better agreement with a limited comparison to wind tunnel observations, and more reasonable behavior for applications to full-scale electric generating facilities. The inclusion of plume buoyancy was found to be a significant effect for high buoyancy flux emissions.