Abstract
The empirically derived equation for the centerline velocity gradient of a flanged circular inlet, obtained by DallaValle in the 1930s, is still used today as a basis for local exhaust design. This paper presents a theoretical solution for the three-dimensional velocity field into a flanged circular hood, and compares the results with velocity contours obtained by DallaValle. A simple and easily-used equation is derived for computing the velocity at any point under the influence of the hood.