## 3 Results  
Figure 2 shows the measured gas velocity in Designs 1 and 2. A very slow flow velocity appeared at the square corners when the flow changed direction abruptly (Figure 3A). Therefore, water could accumulate here, which would lead to uneven gas and current distributions. A very slow flow-velocity region was not observed when the flow direction changed gradually in Design 2. Figure 3B-D presents the electrical current distributions in both designs at high cathode overpotential (0.8 V). The porous media mitigated the effect of the slow flow-velocity regions, and the distributions of the current  
Figure 2: (**A**) Design 1 consisted of serpentine channels with abrupt changes in flow direction. (**B**) Design 2 consisted of serpentine channel with a more gradual change in flow direction; (**C**) Design 3 (serpentine) consisted of curvilinear bends; (**D**) Design 4 consisted of a crisscross pattern; and (**E**) Design 5 was made with straight and parallel channels. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Parameter** & **Design 1** & **Design 2** & **Design 3** & **Design 4** & **Design 5** \\ \hline Channel width & 1 mm & 1 mm & 1 mm & 1 mm & 1 mm \\ Channel depth & 1 mm & 1 mm & 1 mm & 1 mm & 1 mm \\ Rib width & 1 mm & 1 mm & 1 mm & \(1\times 8\times 1\) mm & 1 mm \\ Diffusion layer geometric area & 12.32 cm\({}^{2}\) & 12.32 cm\({}^{2}\) & 31.8 cm\({}^{2}\) & 31.8 cm\({}^{2}\) & 31.8 cm\({}^{2}\) \\ Diffusion layer thickness & 0.2 mm & 0.2 mm & 0.2 mm & 0.2 mm & 0.2 mm \\ Geometric area for fluid flow & 6.16 cm\({}^{2}\) & 5.97 cm\({}^{2}\) & 15.19 cm\({}^{2}\) & 16.27 cm\({}^{2}\) & 15.9 cm\({}^{2}\) \\ Channel length & \multicolumn{3}{c}{—————————————————————————————————————————————————  
density were similar in both geometries. From computed polarization curves, it was found that at low and medium power demands, both flow field designs gave basically the same performance. At a higher power demand, the performances differed, but only slightly. Figure 4 shows the electrical current variation in the y axis, which is perpendicular to the downstream channel direction (Table 2). The wave shape of the current variation was correlated with the lengths of both the channel and the rib [27; 28]. This figure shows that the electrical current decreased gradually along the y axis with the maximum value near the inlet. For example, when the distance was 4.4 cm, the total electrical current at 0.8 V was 27.28 mA in Design 1 and 27.69 mA in Design 2. The difference in the total electrical currents between the two designs was 1.48%. Figure 3: Flow velocity within the channels (m/s) in (**A**) Design 1 and (**B**)) Design 2. Air introduced via an intake located at the top right side (inlet). The electrical current density distribution obtained on the bottom of the porous cathode for (**C**) Design 1 and (**D**) Design 2. In this case, the air was introduced via an intake located at the top left side (inlet). Although this is a negligible difference between designs in one cell, this translates into a large difference in a stack configuration. A comparison between these designs in terms of pressure drop with increasing Reynolds number [22; 29] was made. According to some authors, the serpentine square bends (Design 1) exhibited consistently higher pressure drops compared to the curvilinear bends used in Design 2. A large pressure drop leads to inefficient fuel cell performance. Furthermore, because fuel starvation was more likely to occur in Design 1, Design 2 was selected as the superior standard. Design 2 was therefore modified to create Design 3; see Figure 2C. The oxygen mass fraction distributions for Designs 3-5 are shown in Figure 5. These appeared to be more uniform in Designs 4 or 5 than in Design 3. At a cathode overpotential of 0.66 V, the final oxygen mass fraction in the gas diffusion layer was slightly lower than 0.123 in Design 3. In contrast, in Designs 4 and 5, the final oxygen mass fractions were slightly over 0.137.