Numerical and experimental study of droplet-air flow interaction on the GDL surface of PEMFC for water management monitoring, control and diagnostics

The proper operation of a Proton Exchange Membrane Fuel Cell (PEMFC) is guaranteed only if proper water management is achieved. Performance depends on water transport mechanisms within a single cell. In particular, the liquid water transport is strongly affected by the air flow--water (vapor or liquid droplets) interaction at the interface between the porous electrode and the gas flow channel. On the other hand, the water management is only practically achievable through indirect control of the inlet flows properties, i.e. flow rate, humidity, pressure and temperature.;In this work, an accurate and computationally fast model that captures the main water transport mechanisms through the components of a PEM Fuel Cell is developed. Fast simulation time is achieved by lumping the space-dependence of the relevant variables. However, the novelty of the model is not only to simulate the water transport inside the membrane and porous electrode with relative simplicity but also to simulate the water transport at the interface between gas diffusion layer and gas flow channel. This model links the water flow inside the GDL to the water-air interaction in the cathode channel.;In parallel to the modeling, an experimental activity is presented. Experiments are necessary to further understand the nature of the interaction between air flow and water droplets. The experimental apparatus employs a straight channel to reproduce a PEMFC gas flow channel. Its walls are transparent to allow for imaging with Charge-Coupled Device (CCD) Image Photometry, while the water production by the electrochemical reaction is mimicked with feeding from underneath the GDL. The water formation and movement on the GDL surface is observed and recorded. Images analysis allows the definition of quantitative correlations amongst operating conditions and water removal processes. The experimental data are used to develop models of the droplet detachment and velocity due to the interaction with air cross-flow. These data are also elaborated to provide an interpretation of the droplet unsteady behavior when exposed to an air stream. A dimensionless analysis is performed to characterize the droplet oscillation frequency at detachment. Additionally, a lumped approach is developed to simulate the droplet geometry and its deformation under the action of the air drag. The droplet shape and its deformation is reconstructed assuming a known geometry. Therefore, a lumped force balance is enforced to determine the center of mass motion. Oscillation frequencies during growth and at detachment as a function of droplet size are predicted. The results are validated with the experimental data.;The knowledge gained with the experimental and modeling activity is exploited to engineer a simple and cheap technique to enhance water removal and new control strategies to improve the water management in PEMFCs.;The reduced computational time and good accuracy make the model suitable for control strategy, monitoring and diagnostic algorithms development to ensure PEM fuel cells operation within optimal electrode water content. Furthermore, the model is useful for optimization analysis oriented to both PEMFC design and balance of plant.