Acoustic agglomeration with addition of sprayed liquid droplets: Three-dimensional discrete element modeling and experimental verification

Abstract

Acoustic agglomeration is an aerosol preconditioning technology in which intense sound field is applied to promote relative motions and rapid agglomeration among particles. In order to improve the acoustic agglomeration efficiency and reduce its energy consumption, the method of adding liquid droplets into the aerosol was proposed and demonstrated to be effective. However, modeling and theoretical prediction of this process has been still lacking until now. In this paper, a three-dimensional discrete element modeling of aerosol acoustic agglomeration with addition of sprayed liquid droplets is established, which includes the agglomeration mechanisms of orthokinetic interaction, acoustic wake effect, gravity force and Brownian random force. In particular, the immersion mechanism is employed to describe the microscopic formation of aggregates. In addition, the multiple-time-step algorithm and the contact detection method based on a search grid are employed to speed up the simulation. Meanwhile, the corresponding experiments using coal-fired fly ash particles were performed to validate the simulation. It is found that the results of the discrete element modeling simulation are in reasonable good agreement with the experimental results, for both cases with and without the addition of water droplets. However, when the agglomeration efficiency exceeds 80% at the later stage of the process, some discrepancy is observed due to the breakage of large aggregates which is not taken into consideration in the modeling.