Simulations and comparisons of flows in conventional and push-pull fume hoods

• Main Authors: Wei-Ying Cheng, 鄭暐縈
• Other Authors: Ming-Jyh Chern
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/2sfdn2

碩士 === 國立臺灣科技大學 === 機械工程系 === 94 === A fume hood is a device which prevents pollutants leaking at a laboratory. The function of a fume hood is to use a fluid flow to bring out pollutants from the exhaust.In this study, we simulate a three-dimension air flow captured by conventional and push-pull fume hoods using the commercial software STAR-CD TM. The finite volume method and standard k-ε turbulence model are employed to describe structures and characteristics of lows.Moreover, the turbulent mass transfer equation is adopted to predict the distribution of concentration. Therefore we can obtain the flow patterns and pollutant distribution inside the hood. There are different flow patterns, when various sash openings of the conventional fume hood are considered. Four characteristic vortices are found in flows, i.e. vortices behind the sash, vortices in the vicinity of the doorsill and the gatepost, and a vortex pair between the manikin and sash. Those vortices transport pollutants and, as a result, they connot be removed out the hood. According to numerical results, the concentration of pollutant at the measuring point is higher than the standard of ASHRAE[19] The predicted results of a push-pull fume hood reveal that all the flow fields can be concluded in four dominant modes: concave curtain, straight curtain, under-suction, and over-blow. The ratio of push and pull flow speeds should be adjusted into a concave curtain mode to ensure that all pollutants do not leak out. Furthermore, we find the relationship between the critical values of pull flow speed and sash opening. It can be fitted to empirical formulae which are useful for design and operation of a push-pull fume hood.