Transmission and Deposition Behavior of Aerosols in Sampling Inlets

Abstract

Under many conditions of aerosol sampling, particle deposition inside the inlet has an equal or greater effect on the overall sampling efficiency than particle aspiration from the environment to the inlet face. This paper describes quantitatively the deposition and transmission behavior of particles inside an aerosol sampling inlet. The experimental data have been obtained in a horizontal wind tunnel in which uranine-tagged aerosols are dispersed and subsequently sampled by thin-walled, circular inlets. The inlets are aligned parallel to the wind direction and feed the transmitted aerosols into the view volume of an optical single particle counter. Through washoff and fluorescent analysis of the particle deposits combined with the particle count from the optical particle counter, the transmission efficiencies have been determined for various particle sizes, wind and inlet velocities, and inlet sizes. A model has been developed from the data, and a uniform and general expression for the transmission efficiency has been derived through the introduction of a new nondimensional inlet deposition parameter that consists of Stokes number, Reynolds number, and the conventional gravitational deposition parameter. The effects of all experimental parameters are represented very well by our new expression for transmission efficiency.