Nanobubbles generation in a high-rate hydrodynamic cavitation tube

Abstract

Gas dispersion parameters (air holdup-ɛg, superficial air velocity-Jg and bubble surface area flux-Sb) and especially the concentration of formed nanobubbles in a hydrodynamic cavitation tube were measured. Best results were obtained at 30% air/liquid volume ratio; 49 mN m−1 air/liquid interfacial tension resulting in an air holdup of 16%, a Jg of 0.87 cm s−1, a Sb of 85 s−1 and a nanobubbles (230–280 nm) concentration of 6.4 × 108 NBs mL−1. The lower the air/liquid interfacial tension, the higher the air holdup; this proceed by assisting cavitation and formation of micro and nano-sized bubbles. Data obtained are discussed in terms of solution, hydrodynamics and interfacial phenomena. Main mechanisms involving the role of the nanobubbles and their interactions with solids and bigger bubbles were envisaged. It is believed that these findings are important because of the need for techniques and devices producing nanobubbles at low cost and high rate. This work shows that the cavitation tube studied has a high potential, due to the wide size of bubbles formed, high bubble surface flux obtained and especially the generation of a high concentration of nanobubbles. These bubbles are very important in modern flotation of mineral fines and in pollutant separation in wastewater treatment and some examples are shown and discussed.