Optimizing Nanobubble Production in Ceramic Membranes: Effects of Pore Size, Surface Hydrophobicity, and Flow Conditions on Bubble Characteristics and Oxygenation

Precise control of nanobubble size is essential for optimizing the efficiency and performance of nanobubble applications across diverse fields, such as agriculture, water treatment, and medicine. Producing fine bubbles, including nanobubbles, is commonly achieved by purging gas through porous media, such as ceramic or polymer membranes. Many operational factors and membrane properties can significantly influence nanobubble production and characteristics. This study examines how membrane pore size, surface hydrophobicity, and gas/water flow conditions affect nanobubble size and concentration. Findings reveal that reducing the ceramic membrane pore size from 200 to 10 nm slightly decreased the mean nanobubble diameter from 115 to 89 nm. Furthermore, membranes with a hydrophilic outer surface and hydrophobic pore surface generated smaller nanobubbles with higher concentrations in water. Additionally, a high water cross-flow rate (e.g., >1 L·min^-1) increased the nanobubble concentration, though bubble size remained unaffected. In contrast, the gas flow rate had a more pronounced effect. Increasing the gas flow rate from 0.5 to 12 L·min^-1 significantly raised the nanobubble concentration from 3.09 × 10⁸ to 1.24 × 10⁹ bubbles·mL^-1 while reducing the mean bubble diameter from 100 to 79 nm. An interfacial force model was applied to analyze bubble detachment at the membrane pore outlet, considering factors such as gas flow/pressure, surface tension, and shear forces from the water flow. These findings offer valuable insights into the mechanisms governing nanobubble generation via gas injection through porous membranes.