Review Numerical simulations of two-phase flow in proton exchange membrane fuel cells using the volume of fluid method e A review Rui B. Ferreira, D.S. Falc ~ ao, V.B. Oliveira, A.M.F.R. Pinto * Centro de Estudos de Fen omenos de Transporte, Departamento de Engenharia Química, Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal highlights  Numerical simulations on two-phase flow in proton exchange membrane fuel cells are reviewed.  Focus is given to simulations performed using the VOF method.  Researchers have focused exclusively on the cathode side.  Simulations on the two-phase flow in the anode are recommended.  Couple the VOF method with the electrochemical reactions is a major issue. article info Article history: Received 10 May 2014 Received in revised form 17 November 2014 Accepted 26 November 2014 Available online 15 December 2014 Keywords: PEM fuel cell Two-phase flow Numerical simulations Volume of fluid method abstract Water management in proton exchange membrane (PEM) fuel cells, i.e., balance between membrane drying and liquid water flooding, is a major aspect in the operation of these devices. Flooding results in gaseliquid two-phase flow that causes high pressure drops, flow maldistribution and poor cell perfor- mances. Limitations related to the experimental techniques dedicated to investigate the dynamics of liquid water in a PEM fuel cell have motivated researchers to conduct computational modeling and simulation to better understand the two-phase flow and its implications. Among different mathematical models employed, the volume of fluid (VOF) method is the most popular approach. This paper reviews the VOF numerical simulations of two-phase flow in PEM fuel cells. The focus of the study, numerical details, and main outcomes of each research work are discussed during this review. Moreover, recom- mendations for future simulations as well as challenges of applying the VOF method to PEM fuel cells are presented. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Proton exchange membrane (PEM) fuel cells are devices that produce electricity through the electrochemical reaction between hydrogen (fuel) and oxygen (oxidant). Features like high efficiency, quick/cold start-up, easy scale-up, and low to zero emissions make PEM fuel cells a viable, clean and efficient technology to generate power for various utilizations. In particular, these devices have a great potential as an alternative to the internal combustion engines for automotive applications. From several technical issues that still hamper the wide commercialization of PEM fuel cells, water management is a major aspect. The presence of water in the membrane is essential to ensure good proton conductivity. However, due to the low oper- ating temperature of a PEM fuel cell (60e80  C [1]), liquid water is unavoidable and too much of it can flood the cell. Liquid water flooding in PEM fuel cells results in gaseliquid two-phase flow that increases the transport resistance of the reactants to the active sites causing performance deterioration. Moreover, water flooding cre- ates parasitic energy losses (high pressure drops) and accelerates cell degradation. Therefore, a profound understanding of the two- phase flow phenomena in PEM fuel cells is essential in order to mitigate its negative effects. Over the past decade, experimental investigation dedicated to the two-phase flow in PEM fuel cells have been reported employing various techniques, such as optical visualization [2e7], magnetic resonance imaging (MRI) [8,9], neutron imaging [10e12] and X-ray radiography [13,14]. Experimental insights obtained to date have * Corresponding author. E-mail address: apinto@fe.up.pt (A.M.F.R. Pinto). Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour http://dx.doi.org/10.1016/j.jpowsour.2014.11.124 0378-7753/© 2014 Elsevier B.V. All rights reserved. Journal of Power Sources 277 (2015) 329e342