Study on micromagnets induced local wavy mixing in a microfluidic channel

The phenomenon of ferrofluid-water mixing is investigated using a double-layer magnetic micromixer, in which a layer of micromagnet bars is placed immediately below the fluid layer. A wavy pattern of the ferrofluid-water interface is surprisingly observed at each micromagnet responsible for improved mixing. The mechanism causing the wavy mixing is discovered and analyzed through experimental measurements and numerical simulations, and the mixing efficiency under different flow conditions is discussed. For flows with Re << 1, the resultant steep gradient of opposing magnetic forces by micromagnets in the ferrofluid region gives rise to a local pressure source that induces a transverse/spanwise pressure gradient and activates momentum transfer between fluids. The current finding enables effective localized mixing of ferrofluids with a small footprint and, thus, has great potential to achieve fast mixing for high-throughput flows with an integrated parallel system of multiple microfluidic channels and micromagnets.