Experimental study on the removal of submicron droplets by fibrous filter media in a sound field

The acoustic agglomeration technology is proposed as pretreatment to effectively reduce the concentration of particles produced in the industrial process, thus to improve the filtration efficiency of subsequent filter devices. However, the removal of submicron droplets by sound waves has not yet received attention. In this paper, a new method is proposed for high-efficient filtration of submicron droplets based on sound waves. According to the entrainment mechanism of sound waves on the submicron droplets, a sound field is introduced in the filtration system to enhance the collision probability between the droplets and the fibers in filter materials. The effects of sound pressure level (SPL) and sound frequency on the droplet removal were experimentally investigated at different filtration gas velocities. The results show that there is no shift for the upstream particle size distribution, however, the downstream droplet concentration decreases when the sound field is introduced. The effect of the sound field on filtration performance is determined by the vibration amplitude and the vibration period of the droplets. In the SPL range of 130-145 dB, the improvement of the filtration performance is better with the increase of the SPL for a fixed sound frequency. In the frequency range of 500-900 Hz, the optimal filtration performance of the filter material is obtained at 700 Hz. When the filtration gas velocity is between 0.2 and 0.4 m/s, the improvement of the filtration performance gradually weakens as the filtration velocity increases. Furthermore, the reduction of the downstream droplet concentration is more significant for low-efficient filters or those with fewer layers under the same condition in the sound field.