Electroosmotic-peristaltic flow of a couple stress fluid: a hybrid analytical-numerical analysis of critical reflux and flow reversal

Abstract

Purpose Electroosmotic and peristaltic mechanisms play an important role in controlling fluid transport in microfluidic and physiological systems. The combined effects of arbitrary Reynolds number, electrokinetic forcing and couple-stress rheology strongly influence microscale transport behavior. This study aims to examine their influence on velocity characteristics, critical-reflux and flow reversal in a symmetric microchannel using a hybrid analytical-numerical framework. Design/methodology/approach The problem is formulated using the conservation laws of mass and momentum together with the Poisson–Boltzmann equation. A finite difference scheme is adopted to obtain numerical solutions of the linear ODEs derived from the perturbation method applied to the governing nonlinear PDEs. MATLAB (R2025b) is used to illustrate the graphical results. Findings The results reveal that electroosmotic force enhances flow when aligned with peristalsis and opposes it when reversed. A thicker electrical double layer (EDL) opposes flow in the direction of the electric field more than a thinner EDL. Increasing Reynolds number enhances forward flow under a favorable pressure gradient but promotes reflux under an adverse pressure gradient. The fluid with a larger couple-stress viscosity opposes the flow in both forward and reflux flow regimes. Practical implications The results aid in optimizing electroosmotic microfluidic and lab-on-a-chip devices by enabling controlled flow and suppressing reflux through parameter tuning. Originality/value This study uniquely examines electroosmotic peristaltic transport of a couple-stress fluid in a microchannel for arbitrary Reynolds numbers using a combined perturbation and finite difference approach, with emphasis on time-averaged axial velocity, critical reflux and reflux flow.