Supercritical and Subcritical Modes in Mixing in Rotating Microchannel

The flow and mixing in a rotating radial microchannel is investigated by both numerical simulations and experiments. Mixing is by crossflow due to Coriolis acting on the throughflow in the channel. For a given mixing quality from the two liquids in the channel, from the numerical simulation we found that there are two operating modes depending on the channel width-to-height (W/H) ratio. A smaller W/H corresponds to a subcritical mode for which the flow is dominated by viscous friction and mixing can be inhibited. On the other hand, a larger W/H ratio corresponds to operating under supercritical mode for which the time for liquid to flow from one side to the opposite side of the channel may become too long limiting the mixing. These two modes have been confirmed by experiments. We found that the supercritical has the advantage that a higher throughflow can be accommodated.