Augmentation of fuel cell performance at high current densities is essential to improve the overall power density and to reduce the cost of proton exchange membrane fuel cell (PEMFC) systems. Primarily, the fundamental non-linearity of the equations governing PEMFC performance on a three-dimensional model necessitates iterative solution approaches. As of now, mass transport over-potential is the major barrier to achieving high performance at a high current density. Condensed water, specifically in the gas diffusion layer, decreases oxygen transport to the oxygen reduction reaction area. Experimental investigations of oxygen transport are limited by an inability to resolve the water saturation-dependent properties.
The alternative approach to comprehend and overcome transport resistances, predominantly inside the gas diffusion layer, is to use advanced mathematical modeling. The Lattice Boltzmann method (LBM) is an alternative advanced modeling technique that has been implemented to model the transports inside the structure of microscale geometries, such as: a gas diffusion layer and micro porous layer. Better still, LBM is one class of computational fluid dynamics that solves Boltzmann equations to simulate the fluid with collision models.
In a recent publication, University of South Carolina researchers Professor Sirivatch Shimpalee, Pongsarun Satjaritanun and Professor John Weidner from the Department of Chemical Engineering in collaboration with Professor Nakorn Tippayawong at Chiang Mai University and Mr. Shinichi Hirano at the Research and Innovation Center for Ford Motor Company presented a study where their goal was to couple the conventional computational fluid dynamics (CFD) model in the macroscale geometry and LBM in the microscale geometry, using the technique called co-simulation. Their demonstrated the successful development of a multi-scale calculation technique with co-simulation approach that incorporates a detailed structure of each scale dimension for every component of a fuel cell. Their research work is currently published in Journal of The Electrochemical Society.
In brief, the aforementioned coupling (of the conventional CFD model and LBM) was implemented in a bid to achieve boundary conditions that were dynamic. By employing this approach, the solutions of each iteration from conventional CFD and LBM were required to simultaneously exchange for the next iteration until all solutions converge. Generally, their approach entailed the calculation of flow-field bipolar plates and membrane electrode assembly models using traditional CFD method with existing PEMFC model; whereas the detail structured gas diffusion layers were numerically predicted by LBM technique.
The research team reported that the calculation from multiscale PEMFC was able to descriptively predict the transports inside the gas diffusion layer microstructure when compared with the predictions from macroscale PEMFC. In fact, the effects of operating conditions on the performance and liquid transport were effectively exhibited. The figure shown here demonstrates how multiscale with co-simulation can realistically predict behavior inside PEMFC. With a lot of certainty, the researchers highlighted that the outcomes from the multiscale model could definitely enhance understanding of the transport behavior inside PEMFC, particularly the liquid saturation and temperature inside the gas diffusion layer.
In summary, a multiscale model using co-simulation approach was successfully demonstrated to predict the transports and electrochemical behaviors inside a PEMFC. The approach incorporates a detailed structure of gas diffusion layers and a micro porous layer into the microscale model. Overall, the modeling approach shown by Professor Sirivatch Shimpalee and his colleagues could enhance the potential capability of a model-based investigation of mass and heat transports to find solution of designs and operational conditions in the PEMFC.
S. Shimpalee, P. Satjaritanun, S. Hirano, N. Tippayawong, J. W. Weidner. Multiscale Modeling of PEMFC Using Co-Simulation Approach. Journal of The Electrochemical Society, volume 166 (8) page F534-F543 (2019).Go To Journal of The Electrochemical Society