Influence of pressure on microbubble production rate in a confined turbulent jet

The size spectra and production frequency of microbubbles generated within a confined turbulent jet from the expansion of supersaturated water are characterized by optical measurement. The generated microbubble plume is homogeneously dispersed into a uniform dilution flow before being discharged from a radial diffuser. Shadowgraphy measurements are made with a near range microscope on a 1 mm deep test volume at the outer radius of the diffuser eliminating depth of field limitations and allowing all detectable passing bubbles within the field of view to be imaged . The supersaturated water is expanded through a 0.5 mm diameter × 0.3 mm thick orifice plate into a 1.2 mm diameter expansion tube. The effect of tube geometry is investigated on two devices of 100 mm and 200 mm in length. Saturation water pressures ranging from 400 kPa up to 1200 kPa were tested. For all operating conditions the dominant size bubble was found to be between 10 to 15 µm while total production frequencies varied from 800 kHz up to 1183 kHz.