Abstract
The effect on the entrance efficiency of a filter holder caused by variations in the following parameters—air speed, Slow rate, angle between the air flow and the filter holder, and particle size—was studied in a wind tunnel. Efficiencies for particles 0.68, 6, and 20 microns in diameter were determined at wind speeds of 100, 200, 400, and 700 cm/sec and filter flow rates of 6.4, 12.7, and 25.4 liters/min over a range of angles from 60 to 120 degrees from the horizontal. The entrance efficiency varied with all parameters from less than 1% at the highest wind speed and lowest flow rate to over 100% at forward angles where impaction aided suction. Efficiency was generally lowest with the filter holder entrance at right angles to the airstream, increased as the entrance was tilted forward toward the wind, and also increased, but more slowly, as it was tilted backward away from the wind. An empirical equation was developed to model the pertinent parameters; it gave values in reasonable agreement with those found experimentally.