Role of wettability and water droplet size during water removal from a PEMFC GDL by lattice Boltzmann method

• Role of GDL wettability and water droplet size is investigated simultaneously.
• The inertial ejection and evaporation mechanisms act better for smaller droplets.
• Increasing hydrophobicity will improve inertial ejection and worsen evaporation.
• Inertial ejection mechanism may face with structural barriers for larger droplets.
• The results help understand complicated process of droplet removal more deeply.

To mitigate water flooding in PEMFCs electrodes, fundamental understanding of water droplet dynamic behavior in a PEMFC electrode is necessary. If a water droplet forms inside a PEMFC gas diffusion layer (GDL), two mechanisms of inertial ejection and evaporation can be considered for its removal. Inertial ejection mechanism (ejection of droplet to the channel by the inertial force of gas flow) is influenced by several parameters such as inertial, interfacial, viscous and gravitational forces and also GDL microstructure. On the other hand, evaporation mechanism is influenced by several parameters such as GDL thermal condition and wettability and also droplet size. All this said, water droplet removal from a PEMFC GDL is a complicated process which needs more fundamental research to be deeply understood.In the present study, the role of two effective parameters, GDL wettability (affecting both removal mechanism) and water droplet size (affecting evaporation mechanism), is investigated simultaneously by several 3D LB simulations. The results show that the inertial ejection mechanism may face with difficulties when GDL is not hydrophobic enough or the droplet size is not small enough.