Design and Development of Novel Large Particle Inlet for PM Larger Than 10 μm (PM _{> 10})

Abstract

A novel Large Particle Inlet (LPI) for accurate sampling of particles larger than 10 μ m (PM _{> 10} ) over a wide range of wind velocities was designed and evaluated using computational fluid dynamics. The inlet samples air via a narrow circular slit into a funnel-shaped section that turns the sampled flow from a horizontal to vertical direction, facilitating effective post-sampling analysis. The elliptical funnel shape ensures that air drawn through the slit entrance enters omni-directionally and is transported to the vertical section with minimal recirculation. The omni-directional entrance provides a counter-flow effect that aids in turning large particles from the horizontal sample plane to the vertical exit port. The LPI efficiencies are dependent on inlet geometry, particle sizes, sample flowrate, and ambient wind speeds although they are independent of wind direction. At an average wind speed of 2 ms⁻¹, a LPI with a one cm slit entrance width results in sampling efficiencies greater than 27% for particles as large as 100 μ m. The upper cut-size and inlet efficiencies are dependent on the ratio of ambient wind speed and the sample flow velocity at the entrance slit. The aspiration and transport efficiencies as a function of inlet characteristics and ambient wind conditions were determined. This analysis enables optimal inlet design for sampling particles of desired sizes over a broad range of ambient wind conditions.

ACKNOWLEDGEMENT

This work was supported by a MRI development grant from the National Science Foundation BES-0521137, Cynthia Ekstein project officer.