The effect of probe bluntness on sampling particulates from calm air

The size-selective characteristics of circular inlets as a function of bluntness was examined using polydisperse spherical glass beads. Four levels of bluntness (0.5, 1, 5, and 50) and three sampling velocities (4, 20, and 40 cm/sec) were studied. Particle count and weight percent distributions were determined using a 15-channel electronic counter. At a sampling velocity of 40 cm/sec the weight percent distributions shifted toward particles of larger diameters with increasing bluntness. Little or no effect was discerned at sampling velocities of 20 and 4 cm/sec. As the velocity increased from 4 to 40 cm/sec at constant bluntness, the weight percent distributions shifted away from larger diameter particles. The results suggest that at some sampling conditions probe bluntness may be a variable which deserves consideration in particulate sampling.