Aerosol size spectrum analysis using relaxation time measurement

Abstract

An experimental method has been developed to measure the dynamic relaxation times of aerosol particles. The particle relaxation time (τp) is determined from the ratio of the velocity amplitude of an aerosol particle (vp) to the velocity amplitude of the medium (ug) while the aerosol is subjected to acoustic excitation of a known frequency. A differential laser Doppler velocimeter is used to measure vp, while a microphone is used to measure ug. From the value of τp, the aerodynamic diameter of the particle can be determined if the particle density is known. The method can be applied to real−time in situ measurement of size distribution of an aerosol containing both solid particles and liquid droplets in the range of 0.1−10.0−μm diameters.