ON THE SHAPE OF IMPACTOR EFFICIENCY CURVES

The effect of impactor stage geometry on impactor collection efficienc y curves is explored numerically. It is found that the geometry of the impaction stage where the gas is accelerated does not affect the 50% cut size but has a strong effect on the sharpness and shape of the eff iciency curve. This phenomenon is explained from the aerodynamic focus ing effect of the particles in the nozzle (gas acceleration) section. The flat-plate orifice configuration, commonly used in cascade impacto rs, tends to focus particles closer to the centerline than the angled nozzle. When the real nozzle configuration is used, the prediction sho ws a characteristic S shape, in good agreement with the experimental r esults in the literature.