Interaction between monodisperse fine particles in a standing wave acoustic field

Abstract

The external acoustic field can be used to promote the interactions between fine particles suspended in the gas phase. Due to the particle interaction, collision and agglomeration between fine particles occur, causing the average particle size to increase and the particle number concentration to decrease. This offers an important technical route to controlling the emissions of fine particles. However, the interaction behaviors between the fine particles under the acoustic field are still not well understood, which severely hinders the technology from developing for fine particle emission control by using acoustic agglomeration. In order to reveal the interaction between monodisperse fine particles in a standing wave acoustic field, a particle interaction model with consideration of the drag force, gravity and acoustic wake effect is developed. The particle motion equations in the model are solved by using the classical Runge-Kutta method combined with the second-order implicit Adams interpolation method. The particle velocity due to acoustic entrainment and the interaction process between particles obtained from the numerical simulation are compared with the corresponding analytical solutions and experimental results to validate the accuracy of model prediction. Good agreement is found, which indicates that the model and the numerical method are capable of accurately predicting the interaction between fine particles in the standing wave acoustic field. On this basis, the effects of initial conditions and diameters of particles on the interaction behaviors are explored. The results show that when the initial particle centerline is closer to the acoustic wave direction or the initial particle position is closer to the wave antinode, the acoustic wake effect between the particles becomes stronger, and shorter time is required for particles to collide. It is also found that the influence of particle diameter on particle interaction depends on the initial deviation of particle centerline from the acoustic wave direction. When the deviation is small, the larger the particle diameter, the shorter the time required for particles to collide is. When the deviation is large, the collision between particles with smaller diameters occurs, while the collision between particles with larger diameters may not occur.