Production of monodisperse microbubbles avoiding microfluidics

Here we report the production of monodisperse microbubbles with typical diameters of the order of ten microns at frequencies of the order of 10 MHz by taking advantage of the large values of both the pressure gradients and of the local velocities existing at the leading edge of airfoils in relative motion with a liquid. The relative velocity field is imposed either submerging a static wing composed by symmetrical airfoils within a flowing hydraulic channel or by rotating closed wings within a reservoir containing an otherwise quiescent liquid. It is shown here that the scaling laws for the bubbling frequencies and the bubble diameters are identical to those found in microfluidics. Therefore, the metre-sized geometries presented here are feasible candidates to circumvent the inherent problems of using micron-sized geometries in real applications – namely, wettability, the low productivity and the clogging of the microchannels by particles or other impurities.