Micro-bubble generation techniques are proposed in former investigations. In the present study one of the effective technique by using converging-diverging nozzle (venturi tube) is introduced. Rapid pressure recovery in the diverging nozzle induced bubble fission. The purpose of this study is to develop the new micro bubble generator, clarify the mechanism of the bubble fission in the venturi tube and elucidate the relation between the flow structure in the tube and the generated bubbles’ diameter. The developed micro generator has an advantage on the usage of wide range of void fraction. The observation by a high speed camera suggests that the bubble fission is caused by the strong shock-type pressure recovery in venturi tube. Finally in order to verify the applicability of micro-bubbles that generated by venturi tube to water purification system, floatation experiment was conducted. Bubble diameter in each condition is estimated by image processing technique respectively.

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