Design and Calibration of an In-Stack Low-Pressure Impactor

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Abstract
A high-flow-rate, 10-stage, low-pressure impactor has been constructed for the in-stack measurement of industrial aerosols. The particle collection characteristics of the stages were determined using solid ammonium fluorescein calibration aerosols in conjunction with greased impaction substrates. Cutpoints of the stages were 10, 5.5, 2.9, 1.7, 0.95, 0.50, 0.32, 0.20, 0.11, and 0.047 (μm aerodynamic diameter. Measurement of the nonideal fluid behavior through the impaction nozzles under compressible flow conditions led to the development of empirical discharge coefficients for sharp entry nozzles. Use of these coefficients allows prediction of stage pressure drops as a function of the nozzle dimensions and the fluid properties at the nozzle inlet. Variations in the low-pressure impactor performance have been predicted as a function of temperature and pressure.

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