Improved aerodynamic performance of the exhaust hood with triple-faced flange

Abstract

For a local exhaust ventilation system to trap contaminants effectively, it is highly important to minimize its energy consumption without forgoing efficiency. Energy savings can be achieved by reducing the aerodynamic drag of non-straight elements of local ventilation systems. Goal of the study is to minimize the drag of an exhaust with a triple-faced flange by varying shelves lengths and tilt angles by the method of coordinated descent. Study conducted numerically and experimentally. For the first time a pattern of changes in LDC value depending on the size of the shelves was revealed. The minimum value of LDC is reached when the length of the first shelf adjacent to the exhaust channel is 0.5l (l -half width of the slot or radius of round exhaust hood), the angle of its inclination is 30°; the length of the second shelf is 0.7l with an angle of inclination of 90°; the length of the third shelf is 0.2l with an angle of inclination of 120°. The found velocity distribution shows the effectiveness of the exhaust hood capture. The reduction of the LDC, when compared with the typical exhaust hood with the flange inclined on 90° was 76%, and compared with a real industrial exhaust hood from the welding table – 65.7%. The outline of vortex zones at the entrance to the exhaust hood was determined by different methods. The findings can be used for the design and development of energy-saving slotted and round exhaust hoods.