DESIGN OF A SHROUDED PROBE FOR AIRBORNE AEROSOL SAMPLING IN A HIGH-VELOCITY AIRSTREAM

In this paper, we present our design of a shrouded probe for high velo city airborne aerosol sampling of particles in the size range 0.1-15 p m diameter. We address many of the problems associated with traditiona l samplers and discuss the use of a shrouded sampling probe, designed with the aid of computational fluid dynamics, to solve these problems. Techniques for solving the equations governing the fluid motion and i ndividual particle motions are discussed, and the aspiration efficienc y of the sampler is calculated. We verify our computational procedures by calculating the airflow and aspiration efficiency of the shrouded probe recently used by McFarland et al. (1989, Environ. Sci. Technol. 23, 1487-1492). The final design includes an evaluation of different i nlet tip contours and shroud diameters and their effects on the flow c haracteristics near the probe inlet, as well as the results of placing a second shroud around the probe to further reduce the velocity of th e airflow near the probe inlet. We conclude by presenting a calibratio n curve for our sampler which can be used to reconstruct freestream pa rticle concentrations and size distributions based on measurements wit h the sampler.