Factors affecting push/pull ventilation were investigated. Air was blown across a heated tank containing an ethanol/water mixture toward an exhaust hood. Generation rates, escape rates, and capture efficiency were determined for tank widths of 1.2 to 1.8 meters (m); 30 and 50 degrees-C bath temperature; and 0.38m/second cross draft. Escape quantity only was measured for the same tanks at temperatures of 30, 50, and 60 degrees, and with cross drafts of 0, 0.38, and and escape increased. At 30 degrees, ethanol escape rate was maintained below 0.02 gram/second/square meter (g/second/m2) even at the lowest push flow; however, at both temperatures of 50 and 60 degrees, respective push flow rates of 0.02 and 0.06 cubic meter (m3/second/m) were required to reduce ethanol emissions below flow, for example, was 0.38m3/second/m2, then as push flow changed from 0.054 to 0.070m3/second/m, escape was reduced by 20 percent. For this same change in push flow, however, the efficiency improvement was only 2 percent due to the increase in evaporation rate as push flow increased. As push flow increased, bath evaporation rate increased. For push flows greater than the bath width increased, the quantity escaping increased. With no cross draft, very little push flow was required to achieve optimum control of bath emissions. With a moderate cross draft of cross draft. The authors conclude that push/pull ventilation can provide effective emission control while significantly reducing exhaust requirements.
David J. Huebener, NIOSH, Robert A. Taft Laboratories, Cincinnati, Ohio 45226