Flow-field characteristics and ventilation performance of the high-temperature buoyant jet controlled by spray-local exhaust ventilation

Abstract

High-temperature buoyant jets are common pollutants in hot-rolling plants. Owing to the constraints of the process equipment, local exhaust hoods cannot be set near the buoyant jet source, resulting in low ventilation efficiency and high energy consumption. To efficiently control the high-temperature buoyant jet, spray-local exhaust ventilation (SLEV) is used in this study. The aspects discussed the flow-field characteristics, ventilation performance and recommended optimization parameter order for initial spray droplet diameter, spray angle, and exhaust velocity. The results showed that when the initial droplet diameter was 50 μm ≤ D < 100 μm, the spray gained significant entrainment and cooling effect on the buoyant jet, and when it increased to 150 μm, the spray gained almost no effect. Besides, when the spray angle was 20°<α ≤ 80°, the control ability of the spray on buoyant jet was enhanced; when α ≤ 20°, it was difficult to control buoyant jet owing to the small coverage of the droplets. In addition, the spray helps the escaped buoyant jet to be captured by the exhaust hood. The capture efficiency of the SLEV was higher than that of the local exhaust ventilation (LEV) at the same exhaust velocity. Finally, the exhaust hood and spray parameters must be matched for efficient buoyant jet control since they are interactive. The interaction between the exhaust velocity and initial spray droplet diameter can exert a greater impact on the capture efficiency than the interaction between the exhaust velocity and spray angle. The research results provide guidance for the application of SLEV and reduce ventilation energy consumption.