Recirculating induction (RCI) effect of interfacial species transfer for stratified wavy flow in superconfined microchannels

Direct numerical simulation, combining linear stability analysis, is employed to investigate the effect of wall corrugations on liquid-side species transfer across the stratified wavy liquid film driven by pressure difference in superconfined microchannels (with height H ~ ≤ 0.2 mm). For the plate wall reference, the recirculating area within solitary-like waves would be severely shrunk due to the suppressing effect, causing the high-concentration species accumulation at wave humps. A semi-circle bump (with radius r ) is imposed on the liquid-side wall to disturb the liquid flow structure. When r is relatively small, the wave hump will slide over the bump and show little transfer enhancement compared to the plate wall. When increasing r , a nascent wave hump would be generated at the downstream side of the wall bump, inducing a recirculating flow to convectively transfer the species plume into the nascent wave hump. The original species accumulated at the old hump would be left at the trailing substrate of the new hump and altogether move along the flow direction. By arranging bump arrays, the recirculating induction (RCI) effect could be activated intermittently on different liquid lumps attributed to different positions of nascent and old wave humps, yielding a jump rise of bulk liquid concentration when wave humps alternate near wall bumps. Synthesized assessments of transfer enhancement and pressure drop indicate that an optimal match of size and separation of wall bumps could make the transfer enhancement rate overwhelm the increase rate of pressure drop along the transport distance.