A rapid magnetic particle driven micromixer

Abstract

Performances of a magnetic particle driven micromixer are predicted numerically. This micromixer takes advantages of mixing enhancements induced by alternating actuation of magnetic particles suspended in the fluid. Effects of magnetic actuation force, switching frequency and channel's lateral dimension have been investigated. Numerical results show that the magnetic particle actuation at an appropriate frequency causes effective mixing and the optimum switching frequency depends on the channel's lateral dimension and the applied magnetic force. The maximum efficiency is obtained at a relatively high operating frequency for large magnetic actuation forces and narrow microchannels. If the magnetic particles are actuated with a much higher or lower frequency than the optimum switching frequency, they tend to add limited agitation to the fluid flow and do not enhance the mixing significantly. The optimum switching frequency obtained from the present numerical prediction is in good agreement with the theoretical analysis. The proposed mixing scheme not only provides an excellent mixing, even in simple microchannel, but also can be easily applied to lab-on-a-chip applications with a pair of external electromagnets. Keywords Magnetic particles Á Micromixing Á Microfluidic Á Magnetic actuationList of symbols A cross-section area of the microchannel (m 2 ) A p cross-section area of the particle (m 2 ) B magnetic flux density (Tesla)force (N) f switching frequency (Hz) f cr critical switching frequency (Hz) H channel height (m) H e magnetic field strength (A/m) H M electromagnet thickness (m) I current (A) L streamwise dimension or length (m) m particle mass (kg) M magnetization of the particle (A/m) P pressure (N/m 2 ) Pe peclet number (ReSc) r particle radius (m) Re Reynolds number (UWq f /g) Sc Schmidt number (g/q f D) St Strouhal number (Wf/U) S distance between two parallel electromagnets (m) t time (s) T period, 1/f (s) U relative velocity between the fluid and particle along y direction (m/s) V volume (m 3 ) V fluid's velocity vector v particles' velocity vector W lateral dimension or width (m)

Effects of Magnetic Particles Entrance Arrangements on Mixing Efficiency of a Magnetic Bead Micromixer

“…Passive mixers have no moving parts and don't consume energy. In this kind of micromixers, mixing is achieved by virtue of their structure or topology alone [5]. Most passive mixers reported only show relatively high mixing efficiency at low flow rate [5].…”

“…In this kind of micromixers, mixing is achieved by virtue of their structure or topology alone [5]. Most passive mixers reported only show relatively high mixing efficiency at low flow rate [5]. T-type micromixer, cross-shaped micromixer, 3D serpentine microchannel and microchannel with obstacles or patterned grooves are some examples of passive micromixers [2].…”

“…T-type micromixer, cross-shaped micromixer, 3D serpentine microchannel and microchannel with obstacles or patterned grooves are some examples of passive micromixers [2]. Active micromixers use external energy sources and can produce excellent mixing in the flow [5]. Ultrasound, acoustically induced vibrations, electrokinetic instabilities, small impellers, magnetohydrodynamic action and magnetic field are some examples for external energy sources which are used in active micromixers [5,6].…”

“…Active micromixers use external energy sources and can produce excellent mixing in the flow [5]. Ultrasound, acoustically induced vibrations, electrokinetic instabilities, small impellers, magnetohydrodynamic action and magnetic field are some examples for external energy sources which are used in active micromixers [5,6]. Magnetic field has many advantages which make it as a promising energy source to use in active micromixers.…”

“…The other group is designed for mixing two or more fluids [5,7,9,10,13]. The main idea in this kind of micromixer is to use momentum transfer between magnetic beads and fluid flow to induce some disturbances in the flow field and as a result mixing occurs.…”