Investigating changes in geometric dimensions of vortex zones at the inlet of an exhaust hood set over a plane

Abstract

Local exhaust ventilation systems are the most effective – yet power-consuming – method of capturing contaminants. Shaping of the ventilation ductwork elements is an approach that is actively pursued now as a means of reducing energy losses. Past research concerned with determining vortex zone outlines at inlet of circular exhaust hoods and shaping the hood along these outlines has shown shaping to be highly efficient as a means of reducing pressure losses at the inlet of the exhaust hood. The goal of this study is to determine the vortex zone outline in a setting where a flanged hood is placed over an impermeable plane, and to determine the distance at which shaping will retain its effectiveness. Using the discrete vortices method, we examined variations in characteristic vortex zones of exhaust hoods with tilt angles α = 0°, 30°, 60°, 90° and lengths of 0.5, 1.5, 2.5, 5.0 times gauge (gauge defined as the air duct radius). We determined distances away from the plane at which the vortex zone dimensions cease to show any difference from the case of an exhaust hood in unlimited space. It follows from natural experiment performed by us that pressure losses at the inlet of a shaped exhaust hood remain the same when the hood is set at a distance up to one gauge away from the plane. The discovered vortex zone outlines can be used for shaping a circular exhaust hoods above an impermeable plane. This will reduce its local resistance factor, eliminate vortex zones.