Proceedings of the 4 th International Conference of Fluid Flow, Heat and Mass Transfer (FFHMT'17) Toronto, Canada – August 21 – 23, 2017 Paper No. 133 DOI: 10.11159/ffhmt17.133 133-1 Interaction between Liquid Droplet Growth and Two-Phase Pressure Drop in PEM Fuel Cell Flow Channels Mehdi Mortazavi 1 , Kazuya Tajiri 2 1 Multiscale Thermal Fluids Laboratory, Western New England University 1215 Wilbraham Road, Springfield, MA 01119, USA mehdi.mortazavi@wne.edu 2 Multiscale Transport Process Laboratory, Michigan Technological University 1400 Townsend Drive, Houghton, MI 49931, USA ktajiri@mtu.edu Abstract - In this paper, liquid-gas two-phase flow pressure drop in proton exchange membrane (PEM) fuel cell is studied in an ex- situ experimental setup. The two-phase flow pressure drop is measured during liquid water droplet emergence and growth on the surface of the gas diffusion layer (GDL). The two-phase flow pressure measurement is synchronized with a high speed camera that records droplet emergence and growth. Simultaneous study of droplet size and liquid-gas two-phase flow pressure drop reveals useful information which can be utilized in analyzing existing two-phase flow pressure drop models. Keywords: PEM fuel cell, two-phase flow, pressure drop, droplet 1. Introduction Proton exchange membrane (PEM) fuel cells are an efficient and pollutant free type of energy system that can provide power for different applications [1,2]. As the electrochemical reactions occur within the cell, hydrogen and oxygen are utilized to generate electricity. Such reactions have water and heat as their byproducts. The gas diffusion layer (GDL) is a porous layer inserted between flow channels and catalyst layer. GDL has different roles including distributing reactant gases over catalyst layers and transporting produced water in catalyst layer to the flow channels. The water produced in an operating PEM fuel cell can fill the open pores of the GDL which eventually blocks the transport of reactant gases to the catalyst layer. This phenomenon is referred to as GDL flooding and has been reported to significantly lower the performance of the cell [3,4,5]. A reliable fuel cell performance requires an uniform and continuous supply of reactants to the electrodes. This can be achieved by acquiring an accurate knowledge about the liquid water interaction with gas species within the gas channel and porous layers. During the operation of a PEM fuel cell, liquid water may emerge from the surface of the GDL at some preferential locations [6] and enter the gas channel. This causes liquid-gas two-phase flow within the gas channel. When water removal rate is less than water production rate, liquid water accumulates in gas channel and eventually causes channel flooding. Similar to GDL flooding, channel flooding has been reported to lower the performance of the cell [7,8]. Liquid-gas two-phase flow in PEM fuel cell flow channels can be studied by direct and indirect techniques. Direct techniques include procedures that directly study liquid-gas two-phase flow in flow channels. Methods such as visualizing a transparent cell [9,10,11], neutron imaging [12,13], X-ray microtomography [14,15], or gas chromatography [16,17] fall into this category. The indirect study of the liquid-gas two-phase flow in PEM fuel cell flow channels, on the other hand, can be achieved by studying the properties that are the immediate consequence of the liquid water accumulation within flow channels. The two-phase flow pressure drop along the gas channel, for instance, is a property that can describe the amount of liquid water within the flow channels. This property can be considered as an in-situ diagnostic tool that reveals useful information about the amount of liquid water within the gas channel.