This study was conducted to evaluate ventilation efficiency of 4-stage slot hood by variation of slot width, flow rate, hood size and baffle size. The slot velocity, control velocity and plenum velocity were related to slot width and the distance between source of contamination and hood. The results obtained from laboratory experiment for local exhaust ventilation systems were as follows ;
1. When slot widths were constant(equally changed) and the velocity was 6-10 m/s, the slot velocity from 1st slot to 4th slot gradually decreased. As the slot width-to-slot length ratio(WLR) decreased, the slot velocity of each stage increased. But if WLR value was less than 0.04, the slot velocity decreased.
2. When slot velocity exceeded 10 m/s wish constant slot widths. the slot velocity of each stage was uniform.
3. When the slot velocity was uniform within 10 m/s and the first slot width was 14-20 ㎜, the slot width ratio between 1st slot and each of three other slots were 1, 1.25, 1.5 and 3.0, respectively.
4. The slot and plenum velocity were uniform when exhaust flow rate changed from 14 to 19 ㎥/min and there were no hood splitter vanes.
5. When the slot velocity at each stage was uniform, the control velocity at site 30 ㎝ away from hood No. 2 increased from 0.15-0.30 to 0.25-0.45 m/s and the control distance from 20 to 30 ㎝(about 1.5 times).
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