Bubbles are widely used for various purposes, such as product cleaning, medical treatments, food processing, and fishery operations. There are several ways to produce smaller bubbles, such as using venturi tube cavitation, pressure discharge, ultrasonic waves, and swirl flows.?? In a number of recent patents, micro/nano-bubbles generated by a swirl flow have been used in several applications because this method involves low cost and simple design and provides high performance as well as the ability to generate very small bubbles. In recent years, the controllable bubble size generator, which enables the bubble size to be changed according to the sequence of operations, has been devised, and this swirl-type generator can be used to vary the bubble size and production rate. The swirl-type generator, which is operated using air and water as fluids, makes bubbles that are divided into smaller bubbles by means of the shear stress produced by the swirl flow. In the present paper, micro/nano-bubble applications and technology mentioned in recent patents are reviewed, and the applicability of the swirl-type generator was discussed. Various applications in six fields, i.e., industry, fishery, medicine, agriculture, home amenity, and miscellanea, were surveyed and introduced for the novel inventions, methods, techniques and design centered on the recent patents using the fine bubble characteristic properties such as electrical charges, suspended floating particles, and large surface area volume ratio. The present article analyzes and compares recent patents involving the use of micro/nano-bubbles and gives the extension/vector of the micro/nano-bubble utilization in profitable business prospects.
bubble generator, micro-bubble, nano-bubble, swirl flows, ultrasonic waves, industry, fishery, medicine, home amenities, agriculture
Department of Intelligent Systems Engineering, the Ichinoseki National College of Technology, Hagisyo, Ichinoseki City, Iwate 012-0902, Japan.