Challenges in Computational Modeling of Two-Phase Transport in Polymer Electrolyte Fuel Cells Flow Channels: A Review

Abstract

Excess of liquid water in gas channels of polymer electrolyte fuel cells is responsible for malfunctioning of these devices. Not only it decreases their efficiency via partial blockage of reactants and pressure drop, but it can also lead to the irreversible damage due to oxygen starvation in case of complete channel flooding or full coverage of the gas diffusion layer with a liquid film. Liquid water evacuation is carried out via airflow in gas channels. Several experimental and computational techniques have been applied to date for the analysis of the coupled airflow-water behavior in order to understand the impact of fuel cell design and operation regimes upon the liquid water accumulation. Considerable progress has been achieved with the development of sophisticated computational fluid dynamics (CFD) tools. Nevertheless, the complexity of the problem under consideration leaves several issues unresolved. In this paper, analysis techniques applied to liquid water-airflow transport in fuel cells gas channels are reviewed and most important results are summarized. Computationally efficient, yet strongly simplified analytical models are discussed. Afterwards, CFD approaches including the conventional fixed grid (Eulerian) and the novel embedded Eulerian-Lagrangian models are described. Critical comparative assessment of the existing methods is provided at the end of the paper and the unresolved issues are highlighted.

An implicit surface tension model for the analysis of droplet dynamics

“…The interface, defined by the zero value of the scalar function, cuts the fixed grid elements at arbitrary positions. Piecewise linear interface calculation (PLIC) techniques [8,9] are most commonly used for reconstructing the interface with the VOF method and have been included in commercial codes [10]. In order to represent the discontinuity in the flow variables across the cut elements, shape function enrichment must be introduced [11].…”

Investigation of Two-Phase Flow in a Hydrophobic Fuel-Cell Micro-Channel

“…A key aspect of the process is the highly dynamic nature of the contact line and the significant departure of both advancing and receding angles from the static value. This is a particularly challenging aspect of two-phase flow simulations [11,23]; for instance the recent simulations in [15] Energies 2019, 12, 2061 13 of 32 exhibit a maximum hysteresis of~5 • between advancing and receding values compared to up to over 100 • experimentally.…”

“…The experimental flow maps obtained from quantitative flow visualization show significant differences between hydrophilic [18,21,22] and hydrophobic channels [12]. Fundamental challenges on both theoretical [11,23] and experimental [24] fronts remain in understanding of the flow regimes in such systems, including the impact of geometrical and surface parameters. This study is particularly concerned with bridging phenomena, which can play an important role in micro-channels as well as in PEMFCs.…”

“…Fundamental aspects of water transport in PEMFC flow channels have been investigated computationally [46] and experimentally [1,12], highlighting some key interactions of dynamics with capillary forces and wetting properties. Some of the particularly challenging issues to resolve are the characterization and modeling of the dynamic contact angle [11,23] and the prescription of complex boundary conditions such as sliding on hydrophobic surfaces [47]. Better understanding of fundamental processes can open the door to novel water management such as the use of passive capillary transport explored by Tobias et al [48] who designed channel geometries that exploit specific modes of droplet shapes.…”

An Investigation of Direct Hydrocarbon (Propane) Fuel Cell Performance Using Mathematical Modeling

“…An extremely large body of literature describing fuel cell models now exists. Some recent reviews are those by Jarauta and Ryzhakov [23], Salomov et al [24], and Zhang and Jiao [25].…”