NIOSHTIC-2 Publications Search
Center-line velocity models for flanged local exhaust openings.
Appl Ind Hyg 1988 Dec; 3(12):342-347
A generalized potential flow theory based approach was presented for developing exhaust hood center line air velocity models directly for flanged openings of practical geometries. Flanged opening geometries included rectangle, square, circle, and slot. Model calculations were compared with experimental measurements of center line velocities for a flanged circular opening to validate the potential flow assumption. Theoretical models were compared with empirical models from the Industrial Ventilation Manual, except for square openings. The models agreed well for circular openings and for rectangular openings with large aspect ratios. For slots, empirically derived values for large distances from the hood were underestimated by the theoretical model. The theoretical model correctly predicted face velocity for slots while the empirical model predicted an infinite value. Face velocities were also predicted accurately by theoretical models for other geometries. Experimental data for the flanged circular opening were in excellent agreement with theoretical values. The aspect ratio at which a rectangle becomes a slot was determined by comparing theoretical models for the two geometries at various aspect ratios. Agreement was exact at a ratio of 0.01. The authors conclude that potential flow theory provides a good approximation for flow into local exhaust openings, and these models not only predict center line velocities but show a general approach to predicting air velocities produced by unobstructed openings.
NIOSH-Author; Exhaust-ventilation; Analytical-models; Ventilation-equipment; Exhaust-hoods; Exhaust-systems; Ventilation-systems; Air-flow; Mathematical-models
Issue of Publication
Applied Industrial Hygiene
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division