A GENERAL EQUATION FOR AEROSOL ASPIRATION BY THIN-WALLED SAMPLING PROBES IN CALM AND MOVING AIR

When measuring coarse aerosols, particle aspiration from the atmosphere to the inlet face has a significant effect on the overall sampling efficiency of the inlet. In applying predictive equations to calculate the aspiration efficiency, past practice has required that the user decide between sampling from a calm air environment or one where there is significant air motion in a given direction. Many occupational and environmental air environments, however, are weakly disturbed with air motions that do not fall into either category. To bridge this gap, a universal equation has been developed for sharp-edged tubular inlets. The new model considers the inertial and gravitational effects in calm air and low-velocity flows at various inlet orientations. At high wind velocities, the inertial effect becomes dominant. Sample calculations with the new model compare well with experimental data.