Pressure-driven flow of a micro-polar fluid: measurement of the velocity profile

TL;DR

This study investigates the flow behavior of a polarized suspension of spinning particles in a channel under electric fields, revealing deviations from classical flow profiles due to particle rotation and altered viscosity.

Contribution

It introduces an acoustic measurement method for velocity profiles in a micro-polar fluid suspension influenced by Quincke rotation effects.

Findings

Velocity profiles deviate from Poiseuille flow due to particle rotation.

Effective viscosity decreases with electric field strength.

Measured profiles agree with rheological law-based computations.

Abstract

The pressure-driven flow of a suspension of spinning particles in a rectangular channel is studied using an acoustic method. The suspension is made of insulating particles (PMMA) dispersed in a slightly conducting oil (Ugilec + Dielec) and is subjected to a DC electric field. In such a case, the particles are polarized in the direction opposite to that of the electric field and begin to rotate in order to flip their dipoles in the field direction. Such a rotation of the particles is known as Quincke rotation and is responsible for an important decrease of the effective viscosity of the suspension. Indeed, due to the electric torque exerted on the particles, the stress tensor in the suspension is not symmetric anymore and a driving effect arises from the anti-symmetric part. When such a suspension flows through a rectangular channel, the velocity profile is expected to deviate from the usual Poiseuille flow. In this paper, the velocity profiles are measured using Pulsed Ultrasound Doppler Velocimetry technique. They compare well with those that are computed from the otherwise measured rheological law.