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

N Ibrahim-Rassoul,N Djilali,E.-K Si-Ahmed,J Legrand,A Serir,A Kessi

doi:10.3390/en12112061

Abstract

This paper presents a quantitative visualization study and a theoretical analysis of two-phase flow relevant to polymer electrolyte membrane fuel cells (PEMFCs) in which liquid water management is critical to performance. Experiments were conducted in an air-flow microchannel with a hydrophobic surface and a side pore through which water was injected to mimic the cathode of a PEMFC. Four distinct flow patterns were identified: liquid bridge (plug), slug/plug, film flow, and water droplet flow under small Weber number conditions. Liquid bridges first evolve with quasi-static properties while remaining pinned; after reaching a critical volume, bridges depart from axisymmetry, block the flow channel, and exhibit lateral oscillations. A model that accounts for capillarity at low Bond number is proposed and shown to successfully predict the morphology, critical liquid volume and evolution of the liquid bridge, including deformation and complete blockage under specific conditions. The generality of the model is also illustrated for flow conditions encountered in the manipulation of polymeric materials and formation of liquid bridges between patterned surfaces. The experiments provide a database for validation of theoretical and computational methods.

Highlights

Multiphase flows and heat transfer in micro channels are found in an increasing number of applications [1,2,3,4,5,6] and allow innovations not realizable with conventional channels
Fuel cells operate under a wide range of reactant flow rates and liquid water generation rates
Proper water management, which is critical to performance, requires good understanding and quantification of the flow conditions that favour particular two-phase flow regimes

Summary

Introduction

Multiphase flows and heat transfer in micro channels are found in an increasing number of applications [1,2,3,4,5,6] and allow innovations not realizable with conventional channels. A number of studies have focused on two-phase flows in micro-channels related to fuel cells [1,10], where water generated as a by-product of electrochemical reactions can often condense. Excess accumulation of water (“flooding”) reduces reactant transport and limits performance [11,12], but can impact durability and operation under sub-zero temperatures [13,14]. Hydrophobic surfaces that promote water transport are commonly

Methods

Results

Conclusion