Assessment of velocity fields in the vicinity of rectangular exhaust hood openings

In this paper new empirical formulas for the prediction of the air velocity in front of rectangular (slot) openings (both plain and flanged) are presented. The new equations here introduced are inferred from an exhaustive experimental study carried out by the authors on one of the most common and widespread shape of local exhaust opening (slot). The new empirical formulas presented here describe the three-dimensional velocity field near a rectangular exhaust hood, providing the velocity gradients (decays) along suitable directions, parallel to the slot axis. These formulas have been tested and show an accurate fitting of the experimental data. The suggested equations are simple and can be friendly used by the designer, in order to predict the air velocity in front of a suction opening, and therefore to dimension correctly a local exhaust ventilation system.