Characterization of small aerosol sampling cyclones

Abstract

A laser Doppler velocimeter was used to measure three components of velocity in the body of an 88.9 mm diameter, multiport, reverse flow sampling cyclone with a flat bottom. This velocity data was then nondimensionalized and used in conjunction with a computer program which solves the equations for particle trajectory to predict the collection efficiency for the cyclone. Results for the prediction of cutpoint at the same Reynolds number as that for which the velocities were measured, both for this cyclone and another geometrically similar at on half the scale, are excellent. The model predicts cutpoints of 10 μm and 5.1 μm for the large and small cyclone respectively, while the actual cutpoints determined from aerosol tests were 9.9 μm and 5.2 μm. The efficiency curve generated by the model was steeper (geometric a standard deviation of 1.1) than the efficiency curve determined through aerosol testing (geometric standard deviation of 1.4). A simplification of the Dirgo and Leith equation fitting Barth's design curve is suggested which provides a significantly better fit of the aerosol data (geometric standard deviation of 1.3). At 1.5N[RQ], where N[RQ] = (4pQ)/(πμDc), the error in predication of the cutpoint in the large cyclones is less than eight percent while at 0.4N[RQ] the error is less than two percent. Although results are good over a limited range of Reynolds numbers, the model is strictly applicable only for flows which are dynamically similar to those studied here.