Numerical Investigation of Baffle-Plate Effect on Hood-Capture Flow

Abstract

To protect laborers in a working environment containing toxic vapor, particles and contaminants, an efficient ventilation facility is essential. A well-designed industrial ventilation facility should capture most of the pollutants. An exterior hood is one of the basic tools for local industrial ventilation. The aspiration of an exterior hood is able to extract pollutants into a certain space. A bell-like volume below an exterior hood is usually used to characterize its capture zone. Pollutants within this bell-like zone can be collected and released into the atmosphere. However, a cross draft may exist in the working site where an exterior hood operates due to, for example, flow induced by an air conditioner. Even a very slow cross draft at several centimeters per second could have a negative influence on the capture zone. As a result, a cross draft does not only change the shape of the capture zone, but also its capture efficiency. The bell-like capture volume becomes a Rankine body-of-revolution and the volume is contracted because of a cross draft. Avoidance of the detrimental influence of a cross draft on the capture zone becomes an important topic for the design and operation of an exterior hood. This study is to propose a passive control method which uses a flange and a baffle plate to overcome the negative effect and to enhance the capture efficiency. Numerical results are shown to investigate the effect of the proposed approaches and compared with available experimental data provided by Huang et al. (1-3). Acceptable agreements are found between numerical and experimental results.