Evaluation of Flow Field Performance of Industrial Local Exhaust Hood by Means of a Simplified Tracer Gas Technique

A simplified tracer gas technique which enables the performance evaluation of a local exhaust suction hood is proposed by detecting the high-concentration region of tracer gas (CO2) flowing from a point source placed in the suction field. In this technique, the high-concentration region of the gas can be easily distinguished from the background field because of the nondiffusible property of CO2. When the velocity of gas from a nondirectional point source is lower than that of the suction flow field, streamlines of the flow field can be traced as a narrow high-concentration region. With faster tracer gas flowing from the directional point source, the performance of various hood types can be evaluated by introducing some parameters indicating the shape characteristics of the high-concentration region. In the industrial practice, the suitability of the hood for a certain kind of pollutant is easily checked by monitoring the gas concentration at the points on the side plane of the hood opening. By testing three different hood performances using this technique, the "dominant region" of each hood that was proposed by authors was confirmed.