Numerical analysis of transient processes in molten carbonate fuel cells via impedance perturbations

In this paper, the dynamic response of a molten carbonate fuel cell is studied by means of computational fluid dynamics. First, a rigorous three-dimensional, transient and non-isothermal model is developed through a comprehensive inclusion of various transport phenomena. Next, a sinusoidal impedance approach is used to examine the dynamic response of the unit cell to inlet perturbations at impedance frequencies of 1, 0.1, 0.01 and 0.001 Hz. This analysis is further used to determine the phase shifts and time scales of the major dynamic processes within the fuel cell. The load-following capability of the unit cell is studied by examining the dynamic responses of the average current density, electrochemical reactions rates, heat and mass transfer, mass fractions and temperature. The results show that the electrochemical reactions and the charge transport process adjust within a millisecond. The mass transport process shows a comparatively larger time scale that is about 1 s. The heat transport process is the slowest process in the cell and takes about an hour to reach its steady-state. The developed model along with the dynamic analysis results can be used to design process control strategies.

► A rigorous three-dimensional, transient and non-isothermal model is developed.
► A sinusoidal impedance approach is used to examine the dynamic response of the cell.
► The phase shifts and time scales of the major dynamic processes are determined.