Directional pollutant extraction—the mathematics of the two-dimensional Aaberg exhaust hood

By deflecting unpolluted air away from the exhaust inlet by means of directional air jets, the Aaberg exhaust hood can focus the extraction flow it produces directly onto a source of contaminant and, thereby, achieve directional extraction of pollutant at high concentration. While significantly outperforming conventional hoods, such ‘jet-reinforced’ flows are notoriously challenging to control in practice and if operating incorrectly disperse, rather than extract, airborne pollutants. To provide a rapid predictive capability and insight into the role of device geometry, a mathematical model for the airflow created by the Aaberg exhaust hood is developed. Modelling the induced flow as potential flow, conformal mapping techniques are used to develop analytical solutions for the stream function and airspeed, from which we identify the region of pollutant capture. Investigating these flows as the directionality of the air jets and the ratio of jet-to-suction strengths are varied, our analytical solutions offer insights into the effective deployment of jet-reinforced exhaust hoods to improve indoor air quality in industrial workplaces.