Pulsing to improve bubble column performance: 1. Low gas rates

The liquid phase of a batch bubble column was subjected to low-amplitude pulsations at modest frequencies (range 0-30 Hz). At low gas rates (up to 5 mL/s) using a single-injector tube we found that substantial bubble breakage occurred at firequencies < 30 Hz. At the low flow rates examined, enhanced bubble breakup occurred mainly as a result of two-phase flow developing within the injector tube. External sinusoidal pulsation caused high-velocity water ingestion (suck-back) and expulsion from the injector. This suck-back action caused intense fragmentation of gas slugs within the injector, often into many very small bubbles, as high-speed imaging showed. Mass transfer coefficients were measured as a function of pulsation frequency and driver amplitudes at several air flow rates, demonstrating the benefits of this type of pulsed bubble column. A simple dynamic mechanical model of the pulsed liquid column predicted resonance, which depended on membrane thickness of the driving piston. (c) 2005 American Institute of Chemical Engineers.