In this paper, a numerical method for the design of free opening hoods in industrial and domestic applications
is presented. The method is based on a CFD (Computational Fluid Dynamics) formulation for
the capturing velocity assessment in capturing hoods which account for geometrical and viscous effects.
Different hoods, which differ in shape (square and rectangular) and size, are created and their velocity
field determined numerically. A comparison between the obtained numerical results and results obtained
from empirical formula found in literature are presented and the discrepancy between them
highlighted. Then, starting from the numerical results, a new equation, which takes into account viscous
effects, is proposed, together with its range of applicability and its level of confidence. The suggested
equation is simple in nature and it can be user friendly for the designer, in order to predict the air velocity
in front of a capturing hood, and therefore to correctly and efficiently design the ventilation
system.