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Aerodynamics of multiple orifice hoods.

Esmen-NA; Weyel-DA
Ventilation '85, Proceedings of the 1st International Symposium on Ventilation for Contaminant Control, Toronto, Canada, October 1-3, 1985 1986:735-741
The aerodynamic characteristics of exhaust hoods were discussed. The general assumptions used in designing industrial ventilation systems were considered. These typically involve balancing the ability of the system to control contaminant concentrations against the costs of achieving this control. During this process, the performance of the exhaust hoods may be neglected. Hoods are usually chosen on the basis of reading a handbook or guide and the required flow rates are calculated on the basis of centerline velocities. This approach was considered to be unsatisfactory because the selected hood is usually overdesigned with respect to its ability to control air contaminants and more costly to operate than necessary. This situation can be avoided by simulating the flow field in front of an exhaust opening (hood) for any flow rate as an arrangement of three dimensional velocity contours and varying the design of the hood face until the minimum face velocity that generates the required velocity at all points on that surface has been found. This design will be the most efficient, both technically and economically. This also means that several hood opening configurations can be compared until the one that provides optimal operational and economic efficiency is determined. This approach was illustrated by applying it to a hood design problem in which a control velocity of 150 feet (ft) per minute over a 1 by 2ft plane located 1ft in front of a plane flanged hood was desired. The optimum design was found to be one in which the hood face consisted of 18 small square orifices (openings) arranged in a three by six array. This required an air flow rate of 1,081 cubic feet/minute (cfm), which was around 20% lower than the 1,350cfm required by a conventional hood with a single large opening. The authors conclude that approaching hood design problems by computing three dimensional velocity fields and considering multiple openings can produce a design that is both operationally and economically efficient.
NIOSH-Grant; Control-technology; Exhaust-hoods; Air-flow; Industrial-ventilation; Industrial-hygiene; Equipment-design; Mathematical-models; Simulation-methods
Industrial Environ Health Scis University of Pittsburgh 130 Desoto Street Pittsburgh, PA 15261
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Ventilation '85, Proceedings of the 1st International Symposium on Ventilation for Contaminant Control, Toronto, Canada, October 1-3, 1985
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University of Pittsburgh at Pittsburgh, Pittsburgh, Pennsylvania