Visualization of airflows in push-pull ventilation systems applied to surface treatment tanks

A pilot installation was designed that simulates a surface treatment tank fitted with a push-pull ventilation system. The installation contained elements for measuring and controlling the operational variables (flow rate and tank temperature) and smoke generating equipment for injecting smoke through the holes of the push unit and from the tank surface. Visual observation and video recording of the flows involved meant it was possible to follow the qualitative behavior of the push flow rate along the tank surface and to identify any emissions not captured by the exhaust system. It was possible to differentiate the initial semifree push curtain, its impact with the tank surface, the wall jet that moved toward the exhaust, and its entrance into the exhaust. The methodology proposed is complemented by a quantitative technique for measuring the efficiency, using sulfur hexafluoride as tracer, which permits the causes and location of losses in the ventilation system to be determined.