Abstract
An air curtain generated by a jet is used to enhance an exhaust hood’s capture ability in many research studies on local ventilation systems. This paper focuses on experimental methods to investigate the flow characteristics formed by an exhaust hood associated with a jet. The basic flow characteristics of this kind of exhaust hood are obtained by smoke visualization as a jet forms an air curtain, and the flow field is a combination of three parts: the jet flow region, the exhaust flow region and the vortex flow region. The conditions for forming an air curtain are determined. The air curtain generated by a jet can decrease the decay of the exhaust centreline velocity Vx, therefore enhancing the efficient capture distance. Increasing the exhaust flow rate has higher efficiency than increasing the supply air velocity to enhance the control effect. A regression formula to determine the required supply velocity is obtained if the capture distance and the capture velocity for different contaminants are known. Furthermore, it is found that installing vertical guard-plates between the inlet and the outlet can effectively enhance the capture ability of the hood.
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