The micro bubbles have a diameter of 10 to several ten μm when just produced. That is, the micro bubbles are very small in comparison to air bubbles normally developed in water. Such air bubbles are about a few millimeters in diameter. Being so extremely small, the micro bubbles will adsorb fine contaminants and make them rise to the water surface. Thus, the micro bubbles are used in marine-product washing, water purification, etc.
As a typical micro-bubble generator, a swirling type micro-bubble generator is disclosed in the brochure of the International Publication No. 00/69550. The swirling type micro-bubble generator includes a container having a bottomed cylindrical internal space, a pressurized liquid inlet formed open in a part of the container wall tangentially of the cylindrical-space circumference, a gas inlet formed open in the bottom of the cylindrical space and a swirling gas-liquid mixture outlet formed open in the top of the cylindrical space.
Also, the Japanese Published Unexampled Patent Application No. 2003-205228 discloses a swirling type micro-bubble generator including a cone-shaped container having a conical internal space, a pressurized liquid inlet formed open in a part of the container wall tangentially of the cylindrical-space circumference, a gas inlet formed open in the bottom of the cylindrical space and a swirling gas-liquid mixture outlet formed open in the top of the cylindrical space.
Further, a swirling type micro-bubble generator is disclosed in the Japanese Published Unexampled Patent Application No. 2000-447. The micro-bubble generator includes a structure to swirl a liquid flow under pressure into a circular chamber, a structure to form a swirl-up flow at the periphery of a gradually divergent covered cylinder provided above the liquid flow introducing structure, a structure formed inside the periphery of the cylinder to form a swirl-down flow, a swirling cavity formed at the middle of the swirl-down flow generating structure to have a negative pressure under centrifugal/centripetal separation, a structure formed in the negative-pressure swirling cavity to form a down-swirling gas vortex tube by expanding and taping the flow, and a structure in which the gas vortex tube rushing into and out of a central back-flow hole is forcibly discontinued to generate micro bubbles.
However, the above conventional micro-bubble generator cannot easily be designed small or large and connected directly to an existing apparatus using the micro bubbles since the components thereof are not disposed linearly. The size of air bubbles generated depends upon the amount of the gas introduced into the liquid but cannot accurately set since the feed rate has to be adjusted intuitively.
Accordingly, it is desirable to overcome the above-mentioned drawbacks of the related art by providing a micro-bubble generator that can be designed small or large for direct connection to an existing equipment using micro bubbles, a vortex breakdown nozzle and vane swirler, suitable for use with the micro-bubble generator, a micro-bubble generating method and a micro bubbles-applied apparatus using the micro-bubble generator.
The foregoing and other problems in the related art will become apparent from the following description.