Sampling submicrometer particles suspended in near sonic and supersonic free jets of air

Graduation date: 1991This experiment is concerned with sampling submicrometer\ud particles in near sonic and supersonic flows.\ud The study employed a high volume condensation aerosol\ud generator to produce stearic acid particles having a\ud geometric mean diameter of 0.8 μm and a geometric\ud standard deviation of 1.28. The aerosol was diluted\ud with dry air and accelerated to Mach 0.6, 0.8, 1.26, or\ud 1.47 through a flow nozzle. Aerosol mass concentrations\ud were determined using a small bore probe in the\ud jet and by a large bore probe sampling isokinetically\ud upstream of the jet nozzle. The results of both\ud samples were compared to compute the sampling error\ud associated with the high speed jet sample. The mass of\ud stearic acid collected on polycarbonate membrane\ud filters was determined by gravimetric and chromatographic\ud methods. Studies at Mach 0.8 with four\ud sampling probes having inlet wall to bore area ratios\ud ranging from 3.8 to 0.28 demonstrated that probe wall\ud thickness effects are not significant when the sample\ud is extracted isokinetically. Subisokinetic experiments\ud using a knife edged probe showed relative errors of\ud 124 ± 12% when sampling at 20% of the isokinetic\ud condition. The subisokinetic results are compared\ud favorably with the extended empirical results of other\ud authors. For the supersonic cases it is shown that the\ud subsonic velocity downstream of the sampling probe bow\ud shock can be used in estimating the sampling error