Influence of exhaust hood geometry on the capture efficiency of lateral exhaust and push–pull ventilation systems in surface treatment tanks

In a local exhaust ventilation system, where the pollutant or the emitted flows are captured near the generated source, the knowledge of the capture efficiency is necessary to evaluate performance. This article reports a study of the influence of the exhaust hood slot height on the capture efficiency. For this study, the emission of gases and vapors from open surface tanks used in industrial treatments has been simulated in an installation fitted with two ventilation systems: lateral exhaust and push–pull. Several configurations were possible by varying the geometrical and operational conditions. Both qualitative and quantitative evaluations have been performed, the former through observations of the flows using smoke and the latter by using sulfur hexafluoride as tracer gas. The results obtained on capture efficiency for both ventilation systems tested with several exhaust slot height and as a function of the operating flows rates, are presented. It was found that varying the exhaust slot height between 15 and 45 cm had no effect on capture efficiency. The results show that there are no significant differences between the exhaust slots heights tested, although, in the case of 60 cm for lateral exhaust ventilation, the efficiency was slightly lower.