Fractal Flow Patterns in Hydrophobic Microfluidic Pore Networks: Experimental Modeling of Two-Phase Flow in Porous Electrodes

Experimental two-phase invasion percolation flow patterns were observed in hydrophobic microporous networks designed to model the operational conditions encountered in the porous electrodes of polymer electrolyte membrane fuel cells. The microporous networks were fabricated mimicking the small thickness of porous electrodes and their pore distributions. The inlet channels were invaded homogeneously with flow rates corresponding to fuel cell current densities of 1.0-0.1 A/cm(2) (Ca 10(-7)-10(-8)). A variety of fractal breakthrough patterns were observed and analyzed to quantify flooding density and geometrical diversity in terms of the total saturation, S(t), local saturations, s, and fractal dimension, D. S(t) increased monotonically during the invasion process until the breakthrough point was reached, and s profiles indicated 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 (IPT). Fractal dimensions of different IPT flow patterns spanned an interval of 1.6-1.8 depending on the flow rate of invasion. In this work, we proposed to correlate the fractal dimension to the total saturation and use this map as a parameter for modeling liquid water transport in porous electrodes.