Ultrasonic atomization is a method to produce very fine droplets from bulk liquid with irradiating ultrasound of MHz frequency[1, 2]. The droplet size distribution has two peaks, the one is in the range of micrometers and the other one is sub micrometers. Even for the peak in the micrometer range, the width is much narrower than that for the droplets produced by conventional spraying with two-fluid. Thus, ultrasonic atomization produces well-tailored fine droplets including nanodroplets. These droplets potentially accommodate solutes or solid nanoparticles of specific size, and bring them to gas phase. Such a selective transfer of solutes or particles will achieve separation.
Our past study on separating submicron particles in aqueous suspensions by ultrasonic atomization proved the silica particles of 100 nm was brought into the fog from the mixture of silica of 100 and 300 nm[3]. Improvement of the fog recovery unit allowed recovering more than 90 % fog. Furthermore, 100 nm silica particles were enriched in the recovered liquid. The present study aims to enhance the understanding of this enrichment of a specific particle with ultrasonic atomization. Under various operating parameters, enrichment behavior was examined with silica as well as polystyrene particles.
No effect was found of the type of particles on the enrichment, but the degassing of sample suspension had a strong influence, which is a loss of enrichment. The result indicates the close relation with cavitation on the enrichment effect.
