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Presenter: Bob Moss, Dwyer

This presentation reviews test data revealing significant errors associated with many commercial diffuser types on capture hoods as measured using a precision calibration station. Information on the effect of entrance size and elbow direction is presented on several specific diffuser types as well. Computational Fluid Dynamic models are presented for some of the diffuser types to help in understanding the origin of these errors. This study also includes a composite graph that depicts errors, in percent, by diffuser type, over the normal velocity range. This information can be used to correct capture hood readings on the job site.