Statistical approach for free-rising bubbles in quiescent water under single bubbling regimes*

Free-rising bubbles in quiescent water are frequently observed in daily living and industrial applications. Occurrences can go from simple boiling phenomena, liquid metal stirring in metallurgy, or bubble leakage under subsea conditions. The measurements of free-rising air bubble sizes issuing from a Borda hole in quiescent water are investigated in this work by means of a robust statistical description. Single bubbling flows are considered in the range of gaseous Reynolds numbers from 0 to 120. Optical diagnostics for bubble characterization are based on diffused backlight illumination technics. Experimental measurements are held for detached bubbles and attached bubbles to the injector, under noncorrelated (fps<10) and correlated (fps>100) image acquisition, respectively. The good agreement between the volumes of the detached bubble and the maximum bubble attached to the injector validates the statistical approach. The results based on a pdf of bubble diameters show that, depending on the flow rate, mainly three types of bubbles are observed: flow formation, fragmentation, and coalescence.