On the Sampling Efficiency of a Large Downward Inlet Aerosol Sampler

The purpose of aerosol sampling is to determine the concentration and the mass of size distribution of particles suspended in a given volume of air at a given time. A fundamental parameter required by researcher is the sampling efficiency, defined as the fraction of particles of a given size and density that will be collected by a sampling system. Sampling efficiency changes from one sampling system configuration to another. Calculations usually deal with the sampler orientation and air flow rate. This report involves a computer simulation of the interaction of particles undergoing sedimentation on a large-aperture inverted filter holder having a large entrance aperture. Flow-field calculations have been done by solving the Laplace equation for a flat disk with uniform air velocity over its surface. Initial positions from which particles reach an equilibrium position at which the sedimentation speed equals the air suction speed of the sampler are obtained by iterative solution of the equations of motion. These distances are time-dependent and are called critical distances. The time-dependent sampling efficiency is obtained by combining critical distances with the sampler interactions distance for a given sample volume of air. The effect on sampling efficiency of various parameters such as the sampling flow rate, sampling period, height of the aerosol above the filter, and rim size is evaluated.
in French.