Pressure-Driven Electro-Osmotic Flow and Mass Transport in Constricted Mixing Micro-Channels

Abstract

Both micro electro mechanical systems (MEMS) based and lab-on-a chip (LoC) devices demand efficient micro-scale mixing mechanisms for its effective control which necessitates the quality research towards more efficient designs. A new venture is investigated in those direction with mixing micro-channel constricted with rectangular block under pressure-driven electro-osmotic flow and is numerically simulated by a modified immersed boundary method (IBM), an alternative technique in computational fluid dynamics (CFD). The electro-osmotic flow elucidated by electrical double layer theory when simultaneously considered with pressure driven flow in micro channels can be effectively figured out by the solution of Navier-Stokes equations linked with Nernst-Planck and Poisson equations for transportation of ion and electric field respectively. In this study, the effect of varying the height of rectangular block on the flow and mixing performance are analyzed. A hybrid method, which is a combination of active and passive techniques, is introduced simultaneously in the microchannel by the electro-osmotic effects and channel constriction. The approach is on the basis of finite volume methodology on a staggered mesh. The governing equations are solved by a time-integration technique based on a fractional step method. The velocity fields are corrected by a pseudo-pressure term to ensure the continuity in each computational time step. The extent of mixing in every cross section of the micro channel is assessed by a suitable mixing efficiency parameter. This study has shed light on the most predominant factors that influence mixing efficiency in a micro-channel, such as geometry of the block, non-dimensional numbers (Reynolds number, Re and Peclet number, Pe), zeta potential, external electric field strength and electrical double layer (EDL) thickness. The maximum efficiency in this micro mixer design is found to be 51.3% for Reynolds number of 0.05 and Peclet number of 450 with the rectangular block height of 0.75. It is clear that both electro osmotic effects and flow perturbations due to channel constriction caused a remarkable improvement in mixing efficiency. The outcomes of this investigation are widely applicable in cooling of microchips, heat sinks of MEMS based devices, drug delivery applications and Deoxyribonucleic acid (DNA) hybridization. The present IBM model is validated by experimental and numerical results from the literature.

Numerical investigation on pressure-driven electro osmatic flow and mixing in a constricted micro channel by triangular obstacle

“…Usually, the mixing in macro HFF 31,3 channels can be enhanced by turbulent flow but not possible in micro-channels as it is subjugated by diffusion effect due to amazingly feeble inertia forces. As liquid flow and mixing in microchannels have extensive applications in industry, such as cooling of microchips, heat sinks of micro electro-mechanical systems (MEMS), estrangement of biological components within microfluidic chips used in drug delivery applications, DNA hybridization and so on, any method to improve the mixing efficiency is highly appreciated by the microfluidics scientific community (Li, 2004;Mampallil and van den Ende, 2013;Chen and Cho, 2007;Babaie et al, 2011;Bayraktar and Pidugu, 2006;Ahamed et al, 2020). The general sketch of the present problem is shown in Figure 1.…”

Nanoconfined Fluids: What Can We Expect from Them?

“…Electro-osmotic flow is easier to understand and more widely studied − than diffusio-osmotic flow. In salinity solutions, an electrostatic double layer (EDL) usually exists near the charged solid surfaces.…”