NIOSHTIC-2 Publications Search

Computation of the initially unknown boundaries of flow fields generated by local exhaust hoods.

Anastas MY
Am Ind Hyg Assoc J 1991 Sep; 52(9):379-386
This paper addressed the problem of solving for the air velocities generated by a suction device drawing air from a quiescsent medium. A general approach for computing airflow fields generated by exhaust hoods is proposed and governing differential equation and boundary conditions, solution of the boundary/value problem, computation of the normal derivative at the boundary, and adjustment of the locations of boundary points are discussed. The feasibility of approximating the equal air velocity contours for any local exhaust hood was explored by assuming that these contours are also equipotential contours. The accuracy of the assumption was evaluated using a slot configuration. Using a good approximation for the 15% velocity contour as a starting point, three other boundaries were generated. Generating boundaries after the initial one involved solution of Laplace's equation, assuming constant potential along the boundary and adjustment of boundary location on the basis of differences between the calculated value of the normal derivative of the velocity potential at a point on the boundary and the specified value (15%). An oscillation in the values of the normal derivative, which was detrimental to the desired solution, was observed with the next to last boundary generated by this procedure. Possible causes for this oscillation and possible refinements in the procedure were discussed.
NIOSH-Author; Ventilation-systems; Exhaust-ventilation; Ventilation-hoods; Ventilation-equipment; Air-flow; Mathematical-models
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American Industrial Hygiene Association Journal
Page last reviewed: September 22, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division