Electrochimica Acta 54 (2009) 1166–1176 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Pore-network analysis of two-phase water transport in gas diffusion layers of polymer electrolyte membrane fuel cells Kyu-Jin Lee a , Jin Hyun Nam b,∗ , Charn-Jung Kim a a School of Mechanical and Aerospace Engineering, Seoul National University, Seoul 151-742, Republic of Korea b School of Mechanical and Automotive Engineering, Kookmin University, 861-1 Jeongneung-dong, Seongbuk-gu, Seoul 136-702, Republic of Korea article info Article history: Received 19 March 2008 Received in revised form 27 August 2008 Accepted 29 August 2008 Available online 9 September 2008 Keywords: Polymer electrolyte membrane fuel cell Gas diffusion layer Pore-network model Water transport Two-phase flow Invasion percolation abstract A pore-network model was developed to study the water transport in hydrophobic gas diffusion layers (GDLs) of polymer electrolyte membrane fuel cells (PEMFCs). The pore structure of GDL materials was modeled as a regular cubic network of pores connected by throats. The governing equations for the two- phase flow in the pore-network were obtained by considering the capillary pressure in the pores, and the entry pressure and viscous pressure drop through the throats. Numerical results showed that the saturation distribution in GDLs maintained a concave shape, indicating the water transport in GDLs was strongly influenced by capillary processes. Parametric studies were also conducted to examine the effects of several geometrical and capillary properties of GDLs on the water transport behavior and the saturation distribution. The proper inlet boundary condition for the liquid water entering GDLs was discussed along with its effects on the saturation distribution. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction Liquid water is one of the crucial factors that limit the power and efficiency of polymer electrolyte membrane fuel cells (PEMFCs) [1]. Water is continuously produced by electrochemical reactions dur- ing the operation of PEMFCs. If the product water is not properly removed from PEMFCs, it condenses in electrodes and subsequently floods the pores in gas diffusion layers (GDLs) or blocks the reac- tant flow in gas channels (GCs). The liquid water present in PEMFCs hinders effective diffusion of fuel and oxidant gases towards cata- lyst layers (CLs), resulting in a reduced catalyst effectiveness or a slow dynamic response. Moreover, the volume expansion of liquid water upon freezing may lead to a mechanical failure when PEM- FCs are exposed to sub-zero temperature conditions. Therefore, the transport of liquid water in PEMFCs has been an important topic of recent researches. Conventionally, studies on the water transport through polymer electrolyte membranes (PEMs) by electro-osmosis, back-diffusion and hydraulic permeation processes have been conducted in the context of the water management in PEMFCs. Currently, efforts are being directed to develop more efficient PEMFCs which can operate at higher power densities with higher water production rates. This ∗ Corresponding author. Tel.: +82 2 9104858; fax: +82 2 9104839. E-mail address: akko2@kookmin.ac.kr (J.H. Nam). requires more knowledge about the water transport and flooding behaviors in GCs and GDLs. Accordingly, many works have been reported concerning the water transport in GCs, including experi- mental observations of the transport behavior of water droplets in GCs of transparent PEMFCs [2–6] as well as numerical simulations of the behavior based on volume of fluid (VOF) methods utilizing computational fluid dynamics (CFD) tools [7–9]. The transparent PEMFCs provided a straightforward way to observe an important characteristic of GDLs, i.e., the breakthrough of liquid water from a GDL to a GC. However, it is still difficult to observe the transport behavior of liquid water and to measure its saturation distribution inside very thin GDLs. Thus, only few exper- imental studies have so far been reported on the transport behavior and the saturation distribution in GDLs. Nam and Kaviany [10] reported the microscale behavior of vapor condensation and liquid water transport in a hydrophobic GDL observed by an environmen- tal scanning electron microscope (ESEM). The ESEM technique was also used to observe the microscale behavior of water droplets in hydrophobic CL [11,12]. Recently, Litster et al. [13] and Djilali [14] conducted microscopic observations of the transient water trans- port behavior inside a GDL using a fluorescein dye solution. Several researchers reported the water saturation levels in GDLs which were indirectly evaluated by measuring the pressure drop or the concentration loss in PEMFCs [15–17]. Although the data are dependent on the liquid water content in PEMFCs, the transfor- mation of them into the saturation levels produces uncertainty. 0013-4686/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2008.08.068