Fractal flow patterns in hydrophobic microfluidic pore networks: experimental modeling of two-phase flow in porous electrodes

TL;DR

This study experimentally investigates two-phase flow patterns in hydrophobic micro-porous networks that model fuel cell electrodes, revealing fractal invasion patterns and proposing a correlation between fractal dimension and water transport modeling.

Contribution

It introduces experimental modeling of flow patterns in micro-porous networks with fractal analysis, linking fractal dimension to water transport in fuel cell electrodes.

Findings

Fractal invasion patterns observed in micro-porous networks.

Fractal dimension correlates with total saturation during invasion.

Flow regime confirmed as invasion percolation with trapping.

Abstract

Experimental two-phase invasion percolation flow patterns were observed in hydrophobic micro-porous networks designed to model fuel cell specific porous media. In order to mimic the operational conditions encountered in the porous electrodes of polymer electrolyte membrane fuel cells (PEMFCs), micro-porous networks were fabricated with corresponding microchannel size distributions. The inlet channels were invaded homogeneously with flow rates corresponding to fuel cell current densities of 1.0 to 0.1 A/cm2 (Ca 10e-7-10e-8). A variety of fractal breakthrough patterns were observed and analyzed to quantify flooding density and geometrical diversity in terms of the total saturation, St, local saturations, s, and fractal dimension, D. It was found that St increases monotonically during the invasion process until the breakthrough point is reached, and s profiles indicate the dynamic distribution of the liquid phase during the process. Fractal analysis confirmed that the experiments fall within the flow regime of invasion percolation with trapping. In this work, we propose to correlate the fractal dimension, D, to the total saturation and use this map as a parameter for modeling liquid water transport in the GDL.