Characterization of microbubble generation in a confined turbulent jet

Microbubble populations generated via expansion of supersaturated water through an orifice into an expansion tube, in a socalled mini-tube type device, are characterized using shadowgraphy measurements. The effect of geometric scale is investigated by testing geometrically similar devices with the orifice diameters of 0.25 and 0.5 mm. To allow the detection of all bubbles passing through the imaged field-of-view, bubbly plume was discharged into a 0.5 mm thick Hele-Shaw cell, thus eliminating the need for depth-of-field correction. Saturation water was supplied at pressures between 200 and 1600 kPa. Both devices generated a poly-disperse bubble population, with dominant bubble size of about 10 µm. Halving the orifice diameter resulted with approximately an order of magnitude lower bubble production rate for the same supersaturated water supply pressure.