Pierpaolo Polverino

Abstract: Water management is one of the most important topics for Proton Exchange Membrane Fuel Cells (PEMFCs) since it affects the achievement of high/peak power performance. This research work deals with the main water dynamics from the viewpoint of the fuel cellcontrol and diagnosis to improve on-field operation. Therefore, attention has been given to the achievement of synthetic but comprehensive models, which can be easily applied for both control and diagnosis strategies design and on-board applications. The paper focuses on the effects of water transport mechanism through the components of the cell on PEMFC�s performance. For this purpose, it is assumed that evaporation and capillarity are the predominant processes in the water flow through the gas diffusion layer (GDL). These mechanisms are simulated through accurate, computationally fast and low order models (mean value models - MVM). Fast simulation time is achieved by lumping the space dependence of the main variables. The novelty of the work lies in the fusion of a comprehensive PEMFC stack model with a map-based simulation model, which reproduces the water transport through the GDL and at the interface between GDL and gas flow channel (GFC). This approach can lead to the exploration of advanced control strategies to enhance stack performance, improve fault diagnosis and increase system durability.

Abstract: Proton Exchange Membrane Fuel Cell performance significantly depends on electrode water content. Indeed, an excess of liquid water in the pores of the gas diffusion layer (GDL) and in the gas flow channel (GFC) can drastically bring down the output power. Depending on the operating conditions, liquid water emerging from the GDL micro-channels can form droplets, films or slugs in the GFC. In the regime of droplets formation, the interaction with the gas crossing-flow leads to an oscillating mechanisms that is fundamental to studying the detachment from the GDL surface, as the authors have shown in a previous publication. In this work, a numerical model of a droplet growing on the GDL surface is developed to describe the interaction between droplet cross-flowing gas stream. The droplet shape and its deformation are reconstructed assuming a known geometry. Therefore, a lumped force balance is enforced to determine the center of mass motion law. Oscillation frequencies during growth and at detachment are found as a function of droplet size. The model is also exploited to find the relationship between droplet critical detachment size and gas velocity. The numerical results are compared with the droplet frequency-size and detachment size-gas velocity experimental results previously presented by the authors. The matching between the numerical and experimental data is very good and is a mean of validation for the model. The low computational burden and the conciseness of the results make the model suitable for applications such as control and optimization strategies development to enhance PEMFC performance. Additionally, the model can be exploited to implement monitoring and diagnostic algorithm.

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