CONTINUOUS AEROSOL-SIZE SPECTROMETRY WITH A VARIABLE-ORIFICE IMPACTOR

An aerosol size spectrometer based on a round-jet impactor of continuo usly variable geometry is tested using an iris diaphragm as the nozzle . The impactor is run by fixing the nozzle-to-plate distance L, the ae rosol mass flow rate m', and the volumetric pumping capacity Q, which results in a nearly fixed downstream pressure at variable nozzle diame ter d(n). Tests are carried near 30 torr, with oil drops 0.078-0.49 mu m in diameter, which get captured at nozzle apertures at or below 1.3 and 2.5 mm. The size spectrometer has an excellent resolution when th e jet Reynolds number and nozzle-to-plate distance are kept within the ranges 175 less than or equal to Re less than or equal to 700; 0.75 l ess than or equal to L/d(m) less than or equal to 3.33. The instrument may also be run at atmospheric pressure, with an estimated lower size range of 1.7 mu m. Copyright (C) 1996 Elsevier Science Ltd