(186b) Pulsing to Improve Bubble Column Performance - Low Gas Rates

Abstract 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/sec) using a single injector tube we found that substantial bubble breakage occurred at frequencies below 30Hz. At the low flow rates examined, enhanced bubble breakup occurred mainly because 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. The extension of external pulsation to improve the performance of monolith based microreactor systems will also be demonstrated.