Purpose

The characteristics of fluid motions in micro-channel are strong fluid-wall surface interactions, high surface to volume ratio, extremely low Reynolds number laminar flow, surface roughness and wall surface or zeta potential. Due to zeta potential, an electrical double layer (EDL) is formed in the vicinity of the wall surface, namely, the stern layer (layer of immobile ions) and diffuse layer (layer of mobile ions). Hence, its competent designs demand more efficient micro-scale mixing mechanisms. This paper aims to therefore carry out numerical investigations of electro osmotic flow and mixing in a constricted microchannel by modifying the existing immersed boundary method.

Design/methodology/approach

The numerical solution of electro-osmotic flow is obtained by linking Navier–Stokes equation with Poisson and Nernst–Planck equation for electric field and transportation of ion, respectively. Fluids with different concentrations enter the microchannel and its mixing along its way is simulated by solving the governing equation specified for the concentration field. Both the electro-osmotic effects and channel constriction constitute a hybrid mixing technique, a combination of passive and active methods. In microchannels, the chief factors affecting the mixing efficiency were studied efficiently from results obtained numerically.

Findings

The results indicate that the mixing efficiency is influenced with a change in zeta potential (ζ), number of triangular obstacles, EDL thickness (λ). Mixing efficiency decreases with an increment in external electric field strength (Ex), Peclet number (Pe) and Reynolds number (Re). Mixing efficiency is increased from 28.2 to 50.2% with an increase in the number of triangular obstacles from 1 to 5. As the value of Re and Pe is decreased, the overall percentage increase in the mixing efficiency is 56.4% for the case of a mixing micro-channel constricted with five triangular obstacles. It is also vivid that as the EDL overlaps in the micro-channel, the mixing efficiency is 52.7% for the given zeta potential, Re and Pe values. The findings of this study may be useful in biomedical, biotechnological, drug delivery applications, cooling of microchips and deoxyribonucleic acid hybridization.

Originality/value

The process of mixing in microchannels is widely studied due to its application in various microfluidic devices like micro electromechanical systems and lab-on-a-chip devices. Hence, its competent designs demand more efficient micro-scale mixing mechanisms. The present study carries out numerical investigations by modifying the existing immersed boundary method, on pressure-driven electro osmotic flow and mixing in a constricted microchannel using the varied number of triangular obstacles by using a modified immersed boundary method. In microchannels, the theory of EDL combined with pressure-driven flow elucidates the electro-osmotic flow.

中文翻译：

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三角障碍物在狭窄微通道内压力驱动电渗流与混合的数值研究

目的

微通道中流体运动的特征是强的流体-壁表面相互作用，高的表面体积比，极低的雷诺数层流，表面粗糙度和壁表面或ζ电势。由于ζ电势，在壁表面附近形成了双电层（EDL），即，船尾层（不可移动的离子层）和扩散层（可移动的离子层）。因此，其胜任的设计需要更有效的微型混合机制。因此，本文旨在通过修改现有的浸入边界方法，对狭窄的微通道中的电渗流和混合进行数值研究。

设计/方法/方法

通过将Navier–Stokes方程与Poisson和Nernst–Planck方程分别关联用于电场和离子传输，可以得到电渗流的数值解。具有不同浓度的流体进入微通道，并通过求解为浓度场指定的控制方程来模拟沿其混合过程。电渗效应和通道收缩都构成了一种混合混合技术，是被动方法和主动方法的结合。在微通道中，从数值结果中有效地研究了影响混合效率的主要因素。

发现

结果表明，混合效率受zeta电位（ζ），三角形障碍物数量，EDL厚度（λ）的变化影响。）。混合效率随着外部电场强度（Ex），Peclet数（Pe）和雷诺数（Re）的增加而降低。随着三角形障碍物的数量从1增加到5，混合效率从28.2增加到50.2％。随着Re和Pe的值减小，对于混合情况，混合效率的总体百分比增加为56.4％微通道收缩成五个三角形障碍物。同样生动的是，随着EDL在微通道中重叠，对于给定的zeta电位，Re和Pe值，混合效率为52.7％。这项研究的发现可能在生物医学，生物技术，药物输送应用，微芯片冷却和脱氧核糖核酸杂交中有用。

创意/价值

由于其在各种微流体设备（如微机电系统和芯片实验室设备）中的应用，因此对微通道中的混合过程进行了广泛的研究。因此，其胜任的设计需要更有效的微型混合机制。本研究通过修改现有的沉浸边界方法，对压力驱动的电渗流进行了数值研究，并通过使用变型的浸入边界方法，利用变化数量的三角形障碍物在狭窄的微通道中混合。在微通道中，EDL理论与压力驱动流相结合阐明了电渗流。