Increasing unsaturated dissolved oxygen concentration in water by fine bubbles induced by ultrasonic vibrations

Abstract

In the past, much research has centered on dispersing liquids into gases, and dispersing solids and liquids into liquids. However, there has been almost no research on dissolving gases into liquids by dispersion, possibly because of concerns about the effect of deaeration due to cavitation of a liquid by ultrasound. Here, we consider a method using ultrasound to finely disperse and dissolve a supplied gas. The method entails placing the gas supply outlet close to the tip of an ultrasonic longitudinal vibration source and dissolving the gas into the liquid by finely dispersing the gas by means of the vibrations. In this method, the occurrence of cavitation is reduced as much as possible and deaeration effects are reduced. Here, air is used as the gas to be dissolved and water is used as the solvent. The unsaturated dissolved oxygen concentration in water is used as an indicator for evaluating the proportion of dissolved air. The results show that ultrasonic vibration increases the concentration of oxygen dissolved in the liquid and that almost no deaeration by cavitation occurs.