Magnetic resonance velocimetry shows detailed flow patterns in open microchannels

Open microchannels facilitate gas–liquid contact. This unit operation has many uses in industrial and medical processing, generally requiring gravity-driven falling liquid films. Modulation of the microchannel geometry, either through smooth cross-sectional waviness or using herringbone structures, can achieve optimal surface-to-volume ratios, increase gas–liquid contact, and provoke chaotic mixing. Using non-intrusive magnetic resonance velocimetry, we reveal the internal three-dimensional flow profiles and confirm vortex-driven mixing patterns. The wavy channels affected the shape of the gas/liquid interface, especially at lower flow rates for which slight improvement in the surface-to-volume ratio was observed. The open-channel micromixers were most effective for higher groove depth to film thickness ratios. The deeper the grooves, the more prominent the mixing vortices were, which is also the case for closed-channel micromixers.