An analysis of bubble formation using microporous hollow fiber membranes

A study was conducted to characterize bubble formation behavior of pressurized microporous hollow fiber membranes with water flow normal to the fiber axis. The influence of operating conditions such as water velocity (0.07 to 0.6 m/s), gas pressure (275 to 380 kPa), and gas fluxes (0.001 to 0.02 m/s) on bubble formation behavior was examined. Within these operating conditions, bubbles with a diameter smaller than a 100 μm were formed at the membrane surface. Coalescence occurred close to the membrane, which resulted in bubble diameters of 100 to 500 μm above the fiber. Bubble diameters increased with increasing gas flow rate and decreasing water velocity. These effects are expected as they both lead to increased local bubble density and rates of coalescence. Bubble formation behavior of the membrane was predicted well by an empirical equation determined for a single orifice by Ito and Hirata, (1980).