Comparison of ultrasonic attenuation models for small droplets measurement based on numerical simulation and experiment

Abstract

Ultrasonic method has developed rapidly in particle measurement. Suitable ultrasonic attenuation theoretical models are very important for measuring different kinds of particles. In this paper, the ultrasonic measurement technique for small droplets in air is studied based on simulation and experiment, and the applicability of some theoretical models is discussed. In simulation method, both pressure acoustic module and thermoviscous acoustic module are compared, and a method of randomly placing small droplets is proposed. Based on the thermoviscous acoustic module, four ultrasonic attenuation theoretical models including ECAH model, McClements model, Hemar model and Qian model are compared. The mechanism of ultrasonic attenuation under different ultrasonic frequency, droplet radius and concentration is analyzed. And the results show that ECAH model and McClements model are closer to the simulation results, but ECAH model is the most consistent with the simulation data. Furthermore, the flowing experiment is carried out to measure the ultrasonic attenuation coefficient of small droplets in air. The experimental results are inverted using above four theoretical models and hybrid particle swarm optimization algorithm to obtain the droplet radius and concentration. Compared with the results of optical photographing method, the error of ECAH model and McClements model is the smallest within ± 10%. Based on the simulation results and experimental results, ECAH model is the most suitable theoretical model for ultrasonic attenuation method to inverse droplet radius and concentration for small droplets in air measurement at low concentrations, and McClements model has a very close performance to ECAH model.