Numerical study on mass transfer in a falling film on structured plates with micro-baffles

Falling film microreactors are applied to fast gas-liquid reactions to utilize a high interface area per liquid volume. The reaction rate in such reactors is still mass transfer-limited because the flow is laminar, and mass transfer occurs only by diffusion. Therefore, it is desirable to induce convective mixing in thin liquid films. In this study, multiple baffles with a predetermined height of 0.1-0.2 mm were constructed at equal intervals of 1-3 mm on a flat plate to induce a swirling flow, that is, convective mixing, in the liquid. Two types of microstructured plates with horizontal and alternately inclined baffles (IBs) with predetermined angles of 30-60 degrees were designed, and CO2 absorption into water was numerically investigated for the mass transfer coefficient on the liquid side (kL) at Reynolds numbers ranging from 28 to 111. The IB plates outperformed the standard plate without baffles because of the IB-induced swirling flow in a ~0.2-mm-thick liquid film. kL was increased by 61%, as compared to the standard plate, by adopting a baffle height of 0.2 mm, angle of 45 degrees, and interval of 2 mm, achieving process intensification.