Numerical Investigation of Turbulent Diffusion in Push–Pull and Exhaust Fume Cupboards

Abstract

The aim of this study is to investigate airflow motions and associated pollutant distributions in fume hoods. Currently, most exhaust fume hoods are designed to use an airflow induced by a fan at the top to remove pollutants. Ambient fluids are drawn, flowing toward the opening and subsequently turning to the outlet at the roof. Pollutants are supposedly captured by the airflow and brought out from the cupboard. The present numerical study based on the finite-volume method and the standard k-epsilon turbulence model simulates flow patterns and pollutant distributions in an exhaust fume hood with and without a manikin present. Subsequently, a push-pull air curtain technique is applied to a fume cupboard. To investigate the capturing performance of a push-pull fume cupboard, numerical approaches are used to simulate flow and concentration variations. Numerical results reveal that four characteristic flow modes exist for a variety of speed ratios of push-pull flows and openings. A concave curtain mode which has a fast pull flow and a weak push flow is suggested for the operation of a push-pull fume cupboard. According to ANSI-ASHRAE Standard 110-1995, the local concentration at the specified point is <0.1 parts per million (p.p.m.). Meanwhile, we also examine concentration variations at 12 selected points in front of the sash, and all where the concentration is <0.1 p.p.m. A manikin is put in front of the sash to observe its effect. As a result, the flow and the concentration contours in a push-pull fume cupboard are not affected by a manikin. In terms of those predicted results, it turns out that a push-pull fume cupboard successfully captures pollutants and prevents an operator from breathing pollutants.