Modeling RedOx-based magnetohydrodynamics in three-dimensional microfluidic channels

Abstract

RedOx-based magnetohydrodynamic ͑MHD͒ flows in three-dimensional microfluidic channels are investigated theoretically with a coupled mathematical model consisting of the Nernst-Planck equations for the concentrations of ionic species, the local electroneutrality condition for the electric potential, and the Navier-Stokes equations for the flow field. A potential difference is externally applied across two planar electrodes positioned along the opposing walls of a microchannel that is filled with a dilute RedOx electrolyte solution, and a Faradaic current transmitted through the solution results. The entire device is positioned under a magnetic field which can be provided by either a permanent magnet or an electromagnet. The interaction between the current density and the magnetic field induces Lorentz forces, which can be used to pump and/or stir fluids for microfluidic applications. The induced currents and flow rates in three-dimensional ͑3D͒ planar channels obtained from the full 3D model are compared with the experimental data obtained from the literature and those obtained from our previous two-dimensional mathematical model. A closed form approximation for the average velocity ͑flow rate͒ in 3D planar microchannels is derived and validated by comparing its predictions with the results obtained from the full 3D model and the experimental data obtained from the literature. The closed form approximation can be used to optimize the dimensions of the channel and to determine the magnitudes and polarities of the prescribed currents in MHD networks so as to achieve the desired flow patterns and flow rates.

Stripping analysis of mercury(II) ionic solutions under magneto-hydrodynamic convection

“…The slope of δI P vs B curve in the presence of the supporting electrolyte is 3.36 times of that in the absence of the supporting electrolyte. The relative peak current enhancement increases almost linearly as the magnetic flux density increases since the induced MHD convection linearly increases with the applied magnetic field [31][32][33][34][35][36]. In the presence of the supporting elec- trolyte, the effects of the magnetic field on the enhancement of the stripping peak current become more significant since the total current level in the presence of the supporting electrolyte is higher than that in the absence of the supporting electrolyte as depicted in Figs.…”

“…For both in the absence and presence of the supporting electrolyte, the effects of the magnetic field on the stripping signal increase as the concentrations of the Hg 2+ ions increase. This is due to the fact that the current transmitted through the solution increases with the concentration of the mercury(II) ions [36], which leads to higher Lorentz forces and stronger fluid motion to enhance the ionic mass transport.…”

Ultrasensitive detection of mercury (II) ions using electrochemical surface plasmon resonance with magnetohydrodynamic convection

“…The induced MHD convection plays a significant role in the electrochemical system even though the dimensions of the electrochemical cell are quite small [63][64][65]71]. Since the MHD convection increases with the increase in the strength of the magnetic field [62,72], one expects that the MHD convection effects increase in importance as the strength of the magnetic field increases.…”

“…The MHD boost on the SPR angle shifts thus increases as the concentration of Hg 2+ ions increases, and seems to saturate in micromolar order. The current transmitted through the solution increases with the concentration of the mercury (II) ions [68,70], which leads to higher Lorentz force and stronger fluid motion to enhance the ionic mass transport [70,72].…”

Lattice Boltzmann simulation of thermofluidic transport phenomena in a DC magnetohydrodynamic (MHD) micropump

“…They further demonstrated the advantage of using multiple electrode pairs with dielectric gaps between adjacent electrodes instead of a single electrode pair with an equivalent length. Kabbani et al (2007) developed a three dimensional (3D) mathematical model for the RedOx based MHD flows in microchannels by coupling the Nernst-Planck equations for the concentrations of ionic species, the local electroneutrality condition for the electric potential and the Navier-Stokes equations for the flow field. Patel and Kassegne (2007) developed a generalized numerical framework for solution of the full 3D MHD equations that governs the multi-physics of MHD micropumps.…”