In this paper, a new method for microbubble generation independent of porous media has been introduced. The approach used in the microbubble generator is based on high turbulent intensity rotational flow. At first, a simple cylindrical model is investigated experimentally. In the model, water enters the device via six diagonal nozzles and mixes with air coming from six holes at the bottom of the device. Passing a rotational trace around central motionless rod, air particles are broken up to tiny bubbles. Size of bubbles is measured and bubbles smaller than 1mm in diameter were found. Finally, improved microbubble generator with the similar mechanism has been introduced. Internal flow passes longer trajectory around the central rotating hub because of its design characteristic that let it rotate by inlet water excitation. Bubbles with diameters less than 300 microns are generated by this method. Size of bubbles is measured experimentally in different void fractions for different outlet gap size. Outlet flow gap changes from 20mm to 8mm and 3mm in three experiments. The best result is observed in the third experiment at which microbubbles smaller than 100 micron are observed. The desirable bubbles’ size is achieved at void fraction of 15% that could be increased up to 60%.

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In present research, improvement of a microbubble generator's performance via reliance on fluid dynamics characteristics is studied numerically, and then some experiments are executed. In an elementary cylindrical microbubble generator, water flow enters the device via six diagonal nozzles, and passes a rotational path around a central motionless hub. This flow breaks the big bubbles entering the device by gas injection from air nozzles. The high-intensity turbulence and shear flow in this device is the cause of the air bubble breaking process. These small bubbles can be used to reduce frictional drag on the contact surface of moving solid bodies in water flow. To improve the operation of the apparatus, some suggested geometrical shapes were investigated numerically and were optimized based on the bubbles' effective breaking-up parameters. The experimental results illustrated good performance of the recent apparatus for generating smaller bubbles.