Flow through an experimental model of a U-shaped fuel cell channel is used to investigate the hydrodynamic phenomena that occur within serpentine reactant transport channels of fuel cells. Achieving effective mixing within these channels can significantly improve the performance of the fuel cell and proper understanding and characterization of the underlying fluid dynamics is required. Classes of vortex formation within a U-shaped channels of square cross-section are characterized using high-image-density particle imaging velocimetry (PIV). A range of Reynolds numbers, 109≤Re≤872, corresponding to flow rates encountered in a fuel cell operating at low to medium current densities is investigated. The flow fields are characterized in terms of the instantaneous and time-averaged representations of the velocity, streamline topology, and vorticity contours. The critical Reynolds number necessary for the onset of the instability is determined. Generally speaking, the flow undergoes a transition to a different regime when two recirculation zones, which originally develop in the U-bend region, merge into one separation region.

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