Microbubbles are very small bubbles with a diameter of 50 mu m or less. The important characteristics of microbubbles are their large specific area and small buoyancy, and therefore effective dissolution of gas phase and high adsorption rate are expected. The utilization of microbubbles is useful in improving water environments. Research efforts at a number of institutions have been devoted to the development of microbubble generators. However, in previous microbubble generation devices, complex mechanisms and a high power supply have been required. In this study, a compact and low-power microbubble generator has been developed. Microbubbles were generated by inducing local shear stress in the flow of water through a pipe with slits. Three types of model (slit angle theta = 30 degrees, 60 degrees, and 90 degrees) were used in order to investigate the effect of slit angle on the purification technique. The proposed microbubble generator with the slit angle theta = 60 degrees showed superior performance for the water purification technique in comparison with the other two models. It was confirmed that microbubble generation was affected by slit angle. Also, in this study, we investigated the electrical property of the gas-water interface, and the zeta-potential of microbubbles was measured by electrophoresis. The results of the floatation experiments were affected by the zeta-potential of the microbubbles. (c) 2008 The Japan Society of Fluid Mechanics and Elsevier B.V. All rights reserved.
