Flow velocity oscillations in a PEM fuel cell cathode channel induced by harmonic pressure perturbations

To measure electrochemical pressure impedance spectra, oscillating pressure gradient is applied at the PEM fuel cell channel inlet or outlet. A model for air flow velocity oscillations induced by the AC pressure gradient is developed. The Nyquist spectrum of velocity oscillations has a form of a parallel RC-circuit electric impedance. Due to viscous forces, the amplitude of oscillations decays with the frequency. Analytical solution allows one to estimate this amplitude and the characteristic frequency of damping. A dominating effect of velocity oscillations on the pressure impedance at low air flow stoichiometries is demonstrated.