In-situ measurement of particulate in turbulent duct flows

Experiments were conducted using straight sampling probes to determine the errors in measuring the concentration of particulate in a flowing gas stream using non-isokinetic aspiration rates. The experiments were done in a 100 mm (4-in.) I.D. round pipe using a dual probe arrangement to obtain simultaneous measurements of the concentration under isokinetic and non-isokinetic conditions. Monodisperse aerosols were generated using glass beads in size ranges characterized by mass mean diameters of 3.0, 5.3, and 7.4 microns. Corresponding Stokes numbers varied in the range 0.02 to 0.24 for probes having internal diameters of 10.9 and 6.1 mm. The trends in the experimental data are in general agreement with the data for higher Stokes numbers reported previously in the literature and the results of a numerical analysis of aspiration flow into a thin-walled tube. Negligible differences were observed in the sampling accuracy when the probes were moved from the 0.50 to the 0.75 dimensionless radial location off the centerline of the test section. Effects due to the thickness of the sampling probes were observed for all tests with the general result that the concentration measurement was lower in value as the thickness of the probe was increased.