Aerodynamic particle size measurement by laser-Doppler velocimetry

Abstract- A method of measuring the aerodynamic diameter of aerosol particles is presented. Particles are accelerated in a converging nozzle and their velocity is measured near the exit with a laser-Doppler velocimeter. Nozzle parameters and flow conditions are chosen so that the particle velocity depends primarily on aerodynamic diameter, Experimental studies utilizing a test nozzle are reported. Particles of a known diameter in the range from 0.5 to 11.3/~m were accelerated under various flow conditions. Particle velocities were measured near the nozzle exit. The measurements demonstrated the feasibility of determining particle size from particle velocity. Theoretical studies of the test nozzle showed that it was possible to accurately calculate the particle velocities. Additional theoretical investigations showed that aerodynamic diameter can be de-termined from particle velocity if the particle motion is not too ultra-Stokesian, A nozzle configuration and flow rate are proposed for the measurement of the aerodynamic diameter of atmospheric aerosol in the range from 0.5 to 10 #m. NOMENCLATURE a radius of the nozzle at the exit C slip correction Co drag coefficient d distance from nozzle exit to point of measurement d s fringe spacing Da aerodynamic diameter Dj, particle diameter ADp diameter interval corresponding to ag, fo Doppler frequency Fb body force acting on a particle Fd drag force acting on a particle g gravitational cceleration m particle mass AP pressure drop across the nozzle r radius of trajectory of particle executing curved motion R radius of nozzle at position