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High-efficiency magnetophoretic separation based on synergy of magnetic force field and flow field in microchannels

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Abstract

Magnetophoresis is one of the most important separation methods in biological and chemical engineering. In this paper, a novel impact parameter on separation efficiency, i.e., the angle between the vectors of magnetic force and fluid velocity, was derived from the basic equation describing the motion of magnetic beads in microchannels. It is proposed that one of the most important approaches for separation efficiency enhancement is to improve the coordination of magnetic force field and fluid flow field. A T-shaped microchannel magnetophoretic separator was designed based on the angle. And then a two-dimensional dynamic model of magnetic beads moving in microchannels was established to study the separation efficiency of T-shaped microseparator by combined use of finite element method and Runge-Kutta method. The results show that the capture efficiency of T-shaped microseparator is much higher than that of the straight microseparator at the same conditions. For small magnetic beads at high fluid velocities, the designed T-shaped microseparator could still keep high separation efficiency whereas the conventional straight microseparator fails to separate the magnetic beads. Further analysis shows that the mechanism of separation efficiency enhancement lies in the synergy of magnetic force field and flow field, which directly leads to large deflected velocity of the magnetic beads from the main stream, and thus increasing the separation efficiency. It is anticipated that the results in this paper are theoretically helpful for the optimum design of highly efficient magnetophoretic separators.

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Abbreviations

B :

total magnetic flux density, T

B 0 :

external magnetic flux density, T

B 1 :

magnetic flux density generated by soft magnets, T

d p :

diameter of the magnetic bead, μm

e R :

relative error

f D :

wall drag multiplier

F d :

drag force, N

F m :

magnetic force, N

h 1 :

width of main channel, μm

h 2 :

width of bifurcates, μm

h 3 :

length of each soft magnet, μm

H :

total magnetic field intensity, A m−1

H 1 :

magnetic field intensity generated by soft magnets, A m−1

L 1 :

length of computation domain, mm

L 2 :

width of computation domain, mm

L e :

width of each soft magnet, μm

L s :

space between two neighboring soft magnets, μm

M es :

saturated magnetization of the soft magnet, A m−1

M ps :

saturated magnetization of the magnetic bead, A m−1

P f :

pressure, Pa

R p :

radius of the magnetic bead, μm

R :

vector position of the magnetic bead, m

s :

distance between the magnetic bead and the microchannel wall, m

SE :

separation efficiency

t :

time, s

t 0 :

residential time, s

U :

average fluid velocity in the microchannel, m s−1

u f :

fluid velocity vector, m s−1

u p :

velocity vector of the magnetic bead, m s−1

u py :

y-component of the magnetic bead velocity, m s−1

V p :

volume of the magnetic bead, m3

Δy :

deflection, m

η f :

dynamic viscosity, Pa s

θ :

synergy angle

μ 0 :

permeability of vacuum, N A−2

ρ f :

fluid density, kg m−3

ϕ 1 :

magnetic potential, A

χ eff :

effective magnetic susceptibility of the magnetic bead

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Authors and Affiliations

  1. School of Mechanical and Power Engineering, Shanghai Jiao Tong University, Shanghai, 200240, China

    XinYu Wu, HuiYing Wu & DingHua Hu

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  1. XinYu Wu
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  2. HuiYing Wu
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Correspondence to HuiYing Wu.

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Wu, X., Wu, H. & Hu, D. High-efficiency magnetophoretic separation based on synergy of magnetic force field and flow field in microchannels. Sci. China Technol. Sci. 54, 3311–3319 (2011). https://doi.org/10.1007/s11431-011-4593-8

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  • DOI: https://doi.org/10.1007/s11431-011-4593-8

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