Aerosol sampling by annular aspiration slots

Abstract

Annular aspiration slots were studied in laboratory conditions in order to investigate their performance in sampling airborne particles. The sampling efficiency was measured in a wind tunnel as a function of particle aerodynamic diameter in various conditions of external wind speed. The geometric parameters of the annular slot and the aerodynamic conditions of sampling were optimised in order to improve the sampling efficiency. Optimal selection of these parameters led to the sampling efficiency decreasing very slightly with increasing particle size. Two semi-empirical models of sampling efficiency—in moving and calm air conditions—were derived and experimentally checked. Omnidirectional annular sampling heads are less sensitive to the external wind and their inner particle losses can be minimised. A prototype of a personal aerosol sampler for exposure assessment in occupational safety and health was designed on the basis of these models. It broadly meets the conventional efficiency for inhalable aerosol sampling.