Effects of Solution Physical Properties on Separation Characteristics in Ultrasonic Atomization

When the high power ultrasound irradiates the liquid, small liquid droplets are generated from the liquid surface. This phenomenon is called as ultrasonic atomization [1]. Recently, it has been reported that ethanol is concentrated from the aqueous solution by ultrasonic atomization [2-4]. Since ultrasonic atomization scarcely accompanies the phase change, this is a great advantage comparing with the distillation operation. Therefore, the method has been applied to the concentration of ethanol in Japanese sake. Sato et al. [2] have studied the effects of initial content and temperature in bulk solution on the concentration characteristics. With decreasing temperature in bulk solution, the content in droplet increased and the droplet amount decreased. D. M. Kirpalani and F. Toll [3] investigated the ultrasonic fountain jet, which was the source of atomization. In the fountain jet, the temperature was higher and the ethanol content was lower than those in bulk solution. They considered that the formation of alcohol-rich droplet was due to the corollary effects of the surface excess on ultrasonic cavity and the alcohol vaporization during cavity collapse. However the separation mechanism in ultrasonic atomization is still unclear. The ultrasonic atomization occurs from the liquid surface. It is considered that the separation characteristics are governed by adsorption behavior of solute on liquid surface. In this study, the aqueous solutions of alcohols, amides, carboxylic acids and inorganic salts were used. The separation characteristics and droplet diameter distribution in ultrasonic atomization were measured. The separation mechanism was modeled, and the surface solute amount in droplet was estimated.