Transitional pressure drop in a cavitied microchannel

Microchannels have become prevalent as an integrated part of microfluidic devices in biochemistry and electronics applications. In such devices, the small scale results in a characteristically low Reynolds number laminar flow. The small scale also results in an associated high flow resistance. A design concept has been developed that reduced the flow resistance by featuring geometrically modified microchannels with cavities. Compared to an unmodified microchannel, the modification reduces flow resistance at low Reynolds numbers but conversely leads to higher flow resistance at high Reynolds numbers: i.e., a reversal of flow resistance occurred. Thus far, plausible fluidic mechanisms underlying such reversal have remained largely unstipulated. Based upon detailed pressure and flow field measurements, we stipulate that flow progression from laminar flow slippage to rotational vortices in cavitied microchannels is the main mechanism causing the reversal. We further clarify that the earlier transition of initial laminar flow to turbulent flow is triggered by instabilities generated along shear layers, formed between the mainstream flow and rotational vortices in each cavity.