Fluid drag reduction by magnetic confinement

TL;DR

This paper demonstrates a method to significantly reduce fluid drag in microchannels using magnetic confinement of a ferrofluid, achieving 60-99% reduction without continuous lubricant flow, which could revolutionize microfluidic device efficiency.

Contribution

The study introduces a novel magnetic confinement technique with a modified Reynolds number model to optimize drag reduction in liquid-liquid flows.

Findings

Achieved 60-99% drag reduction in microchannels.

Developed a laminar flow model with a new Reynolds number.

Identified key design parameters for maximizing drag reduction.

Abstract

The frictional forces of a viscous liquid flow are a major energy loss issue and severely limit microfluidics practical use. Reducing this drag by more than a few tens of percent remain illusive. Here, we show how cylindrical liquid-in-liquid flow leads to drag reduction of 60-99% for sub mm and mm sized channels, irrespective of whether the viscosity of the transported liquid is larger or smaller than that of the encapsulating one. In contrast to lubrication or sheath flow, we do not require the continuous flow of the encapsulating lubricant, here made up of a ferrofluid held in place by magnetic forces. In a laminar flow model with appropriate boundary conditions, we introduce a modified Reynolds number with a scaling that depends on geometrical factors and viscosity ratio of the two liquids. It explains our whole range of data and reveal the key design parameters for optimizing the drag reduction values. Our results therefore open the route to microfluidics designs with pressure gradients possibly reduced by orders of magnitudes.