Numerical analysis of dynamic electro-osmotic flows of non-Newtonian fluids in rectangular microchannels

TL;DR

This paper numerically investigates the transient electro-osmotic flow of non-Newtonian power-law fluids in rectangular microchannels under DC and AC electric fields, revealing flow behavior and velocity profiles relevant for microfluidic device design.

Contribution

It introduces a finite element simulation framework for non-Newtonian electro-osmotic flows, validating the generalized Smoluchowski slip velocity for power-law fluids.

Findings

Flow becomes more plug-like with decreasing flow behavior index under DC fields.

Generalized Smoluchowski slip velocity accurately describes electrokinetic flow of non-Newtonian fluids.

Oscillating velocity amplitude increases with the fluid behavior index under AC fields.

Abstract

Numerical analyses of transient electro-osmosis of a typical non-Newtonian liquid induced by DC and AC electric fields in a rectangular microchannel are conducted in the framework of continuum fluid mechanics. The famous power-law constitutive model is used to express the fluid dynamic viscosity in terms of the velocity gradient. Transient start-up characteristics of electro-osmotic power-law liquid flow in rectangular microchannels are simulated by using finite element method. Under a DC electric field, it is found out and the fluid is more inert to the external electric field and the steady-state velocity profile becomes more plug-like with decrease of the flow behavior index of the power-law liquids. The numerical calculations also confirm the validity of the generalized Smoluchowski slip velocity which can serve as the counterpart for the classic Smoluchowski slip velocity when dealing with electrokinetic flow of non-Newtonian power-law fluids. Under AC electric fields, the fluid is more obviously accelerated during oscillations and the amplitude of the oscillating velocity is closer to the magnitude of the generalized Smoluchowski velocity as the fluid behavior index increases. These dynamic predictions are of practical significance for the design of microfluidic devices that manipulate non-Newtonian fluids such as biofluids, polymer solutions and colloidal suspensions.