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 (τ_p) is determined from the ratio of the velocity amplitude of an aerosol particle (v_p) to the velocity amplitude of the medium (u_g) while the aerosol is subjected to acoustic excitation of a known frequency. A differential laser Doppler velocimeter is used to measure v_p, while a microphone is used to measure u_g. From the value of τ_p, 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.