Coupling of Lattice Boltzmann and Volume of Fluid Approaches to Study the Droplet Behavior at the Gas Diffusion Layer/Gas Channel Interface

Abstract

With the increased concern about energy security, global warming, and air pollution, the possibility of using polymer electrolyte fuel cells (PEFCs) in approaching renewable and sustainable energy systems has reached significant momentum [1,2]. A typical PEFC flow field consists of a series of micro/minichannels. The continuous removal of liquid water from the cathode channels is a critical issue, as water droplets forming in the channels can block the transport of gaseous oxygen to the active sites. This phenomenon gives not only an uneven current distribution, substantial loss of performance, but also, unstable operation and increased degradation rates [1]. Water generated by the electrochemical reactions often condenses into liquid form, potentially flooding the GC (gas channel), the GDL (gas diffusion layer), the micro porous layer (MPL) and the catalyst layer. Insight into the fundamental processes of liquid water transport and evolution is still not complete, preventing further FC development [1]. Computational fluid dynamics (CFD) models make it possible to reduce the number of experiments needed for cell design and development [1,3]. The aim of this work is to obtain an increased understanding of the droplet behavior at the GDL/GC interface by coupling of Lattice Boltzmann and Volume of Fluid (VOF) approaches, for gas channels relevant for PEFCs. The VOF model is an interface-resolving method and has become a widespread methodology for solving two-phase flow phenomena inside PEFCs. The volume fraction of liquid water at the computational cell volume schemes, are used to track the interface between the phases [1,3]. Input parameters in the VOF model are extracted from our in-house Lattice Boltzmann calculations [4], i.e., establishing a multiscale environment. It is clear that the contact angle as well as the size of the liquid droplet vary with positions at the interface, depending on the stochastic GDL geometry. A model describing one straight channel with one gas inlet, one liquid inlet (at the GDL surface) and one two-phase outlet is developed. The operating parameters belong to the laminar flow regime. Notice that a developing flow region covers the entire channel. The uniqueness of this work includes a calculation of contact angles at the GDL interface as well as the size of the liquid inlet, by the authors, with Lattice Boltzmann calculations (3D nineteen-velocity (D3Q19) pseudopotential multiphase multicomponent isothermal LBM) [4].