09. Heat and Mass Transfer

In an oscillatory baffled reactor (OBR) for gas-liquid systems, orifice baffles are placed in a bubble column to generate vortices by providing periodic oscillatory flow. The vortices increase the gas-liquid interfacial area, but the effect of the vortex flow on the mass transfer coefficient is still unclear. Generally, a high-speed camera is used to measure bubble diameter and gas holdup, from which the gas-liquid interfacial area is obtained. In addition, using the absorption of CO2 into NaOH solution, the state of the entire OBR can be observed, and the mass transfer on the liquid side can be effectively evaluated. In this study, the effective interfacial area was precisely determined using the image analysis method and the reactive absorption method, and the mass transfer coefficient of the OBR was obtained. The experimental setup involved a baffled acrylic pipe, 400 mm in vertical pipe length and 12.7 mm in inner diameter. This was filled with 47 mL of water or NaOH solution, and air or air containing CO2 was introduced at a volumetric flow rate vvm : 0.1-1.0. The oscillatory Reynolds number, Reo, defined as the maximum velocity of the oscillatory flow, was operated at 0-2776. In Reo ≥ 2000, the gas-liquid interfacial area increased significantly at vvm = 0.60 as Reo was increased. This was due to the breakup bubbles by the vortices and the groups of small bubbles trapped by the vortices at higher oscillations. Furthermore, the liquid side mass transfer coefficient kL was calculated using the gas-liquid interfacial areas obtained by the image analysis method and the reactive absorption method, and an increase in kL was observed with the increase of Reo. It is inferred that the bubbles were exposed to an unsteady flow field by being incorporated into the vortices and that the mass transfer was enhanced.