Spheres in the vicinity of a bifurcation: elucidating the Zweifach-Fung effect

TL;DR

This study investigates the Zweifach-Fung effect in bifurcating channels, demonstrating through experiments and simulations that particle enrichment in the high flow rate branch results from initial distribution, not attraction.

Contribution

The paper clarifies the mechanism behind particle distribution in bifurcations, refuting the idea of attraction towards high flow branches and emphasizing initial conditions.

Findings

Particles are attracted to the low flow rate branch, not the high flow rate branch.

Enrichment in the high flow rate branch is due to initial distribution effects.

Misleading interpretations in literature are addressed and corrected.

Abstract

The problem of the splitting of a suspension in bifurcating channels dividing into two branches of non equal flow rates is addressed. As observed for long, in particular in blood flow studies, the volume fraction of particles generally increases in the high flow rate branch and decreases in the other one. In the literature, this phenomenon is sometimes interpreted as the result of some attraction of the particles towards this high flow rate branch. In this paper, we focus on the existence of such an attraction through microfluidic experiments and two-dimensional simulations and show clearly that such an attraction does not occur but is, on the contrary, directed towards the low flow rate branch. Arguments for this attraction are given and a discussion on the sometimes misleading arguments found in the literature is proposed. Finally, the enrichment in particles in the high flow rate branch is shown to be mainly a consequence of the initial distribution in the inlet branch, which shows necessarily some depletion near the walls.