Some Entry Efficiencies of Disklike Samplers Facing the Wind

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Abstract
Measurements have been made of entry efficiencies of airborne particle samplers, of simple disk shape, facing the wind. Experiments were conducted in a wind tunnel in velocity ranges from 0.5 to 4.5 m/s using monodisperse DOP aerosols (3–13μm diameter). The sampler intake velocity was always less than the wind speed. Efficiencies were in general greater than one, and were shown to increase as Stokes number (defined from disk diameter) increased, and as orifice diameter increased and intake velocity decreased. An 80-mm-diameter disk with a 5-mm orifice aspirated at 2 1/min shows little variation of efficiency in the range measured, and is insensitive to changes in flow rate and disk diameter, and would therefore be a useful substitute for isokinetic sampling for this particle size and wind velocity range. Best-fit values were determined for the parameters of Vincent and Mark's theory.