Flow and mixing in rotating zigzag microchannel

摘要

The flow and mixing in rotating zigzag microchannel was investigated experimentally and numerically with objective of improving mixing, which is largely due to recirculating crossflow in the cross-sectional plane of the channel and the bend connecting tilted channel segments. Unlike the conventional rotating radial channel, crossflow in the zigzag channel is highly intensified from a combination of : (a) centrifugal acceleration component in the cross-sectional plane due to the inclined channel segments, (b) centrifugal acceleration generating Gortler vortices at "channel bends", and (c) Coriolis acceleration. When the channel segment in the zigzag channel is inclined towards rotation direction (prograde), all three accelerations are aligned intensifying the crossflow; however, when it is inclined opposite to rotation (retrograde), Coriolis acceleration competes with the other two accelerations producing complex flow. Unlike a stationary zigzag channel, flow in a rotating prograde bend with outlet in the direction of rotation further induces Coriolis acceleration which adds onto the centrifugal acceleration producing enhanced crossflow and mixing, vice versa for a retrograde bend. A numerical model has been developed accurately accounting for the interactions of throughflow, crossflow and material dispersion by diffusion and convection in a rotational platform. An experimental microfluidic platform with rotating zigzag microchannel has also been developed. Experimental results on mixing quality carried out at two rotation speeds compared well with prediction from the numerical model. The overall mixing quality of a rotating zigzag channel is much improved compared with that of a stationary zigzag channel and of a rotating radial channel, due to the intensified crossflow driven by the additional acceleration components. A study on different bend angle on mixing quality in zigzag channel revealed that there is no optimal bend angle to achieve superior mixing enhancement, as a result of the complex flow pattern generated by the three competing accelerations.