A numerical method for the efficient design of free opening hoods in industrial and domestic applications

•A review of empirical formula for velocity assessment in front of free hoods.•The assessment of the limit of validity of empirical formula for hood design.•The detection and investigation of the viscous effects affecting hood performance.•The formulation of a new equation for hood design which includes viscous and geometrical dependence.

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.