A study of MHD-based chaotic advection to enhance mixing in microfluidics using transient three dimensional CFD simulations

Abstract

Building on our previous work on transient, two dimensional simulations of the Navier-Stokes equations to investigate mixing enhancement by introducing the Lorentz force in MHD as a control parameter to create turbulentlike chaotic advection, this paper describes transient, three-dimensional simulations. Our approach differs from many previous analytical investigations by other workers based on potential flow and linearized stokes flow. A shallow disk-ring cylindrical microfluidic cell with gold electrodes deposited on the floor serves as a representative lab-on-a-chip. By applying a voltage across specific disk electrodes and a ring counter electrode, a current is established in the weak conductive solution. The current interacts with an externally applied magnetic field generating a Lorentz force that causes fluid motion. Velocity vectors, electric potential distributions and ionic current lines are presented. By switching on and off a pair of disk electrodes with a certain period T, a "blinking vortex" that induces chaotic advection is produced. Various particle trajectory-based analyses using extensive postprocessing of the simulation results show that the period T plays an important role in generating chaotic advection. Large periods provide efficient stirring which improves mixing performance. Taking a step further, we show that by having two pairs of disk electrodes that were subjected to a different on/off switching scheme, more complex chaotic motion can be generated, and the mixing region can be extended to almost the entire fluid domain. This study establishes CFD simulation of MHD at the microscale as a robust tool to develop efficient strategies for mixing by chaotic advection. The techniques developed in the present work are also applicable in MHD-based flow control in microfluidics for other applications such as pumping and steering fluid to target locations.

Design of a Novel μ-Mixer

“…As it has been reported [1,[7][8][9] in the micro-scale, mixing can be improved by "chaotic advection", which involves breaking, stretching, and folding of liquid streams leading to an increase of the interfacial contact area of the fluids. In our laboratory, the mixing efficiency of several types of passive μ-mixers was investigated both experimentally and numerically [5][6][7]10].…”

“…Several comprehensive reviews of µ-mixing devices and their principles can be found in the relevant literature [1][2][3][4][5][6]. As it has been reported [1,[7][8][9] in the micro-scale, mixing can be improved by "chaotic comprehensive reviews of μ-mixing devices and their principles can be found in the relevant literature [1][2][3][4][5][6]. As it has been reported [1,[7][8][9] in the micro-scale, mixing can be improved by "chaotic advection", which involves breaking, stretching, and folding of liquid streams leading to an increase of the interfacial contact area of the fluids.…”

Effect of External Magnetic Field on Dynamics of Two-dimensional Isotropic Conducting Flow

“…In many studies, mixing process is investigated experimentally or by numerical of some passive scalars, while less numerical research has been done on analysis of mixing characteristics in MHD flows. [14][15][16] In this article the effect of uniform and constant external magnetic field in mixing properties of isotropic MHD flow is investigated by analyzing large and small scale eddies dynamics; In order to explore mutual interaction of velocity and magnetic field, MHD flow with moderate magnetic Reynolds number is considered and solved by use of DNS. The results of this research can be useful in phenomenology and also prediction of mixing behavior of some industrial equipment as well as natural phenomena.…”

Electrolyte Magnetohydrondyamics Flow Sensing in an Open Annular Channel—A Vision System for Validation of the Mathematical Model

“…Its principle of operation is based on the Lorentz force acting in an electrical conductive solution, in the presence of magnetic and electric fields, resulting in a motion flow. The most used solutions in the beginnings of MHD research were liquid metals and ionized gases, though in the more recent scientific literature electrolyte solutions have made an incursion [ 2 ]. This is because the flow in a MHD stirrer depends on the solution electrical conductivity.…”