Micro computed tomography and CFD simulation of drop deposition on gas diffusion layers

M Guilizzoni,S Fest-Santini,M Lorenzi,V Knisel,M Santini

doi:10.1088/1742-6596/547/1/012028

Abstract

Fuel cells are electrochemical power generation system which may achieve high energy efficiencies with environmentally friendly emissions. Among the different types, Proton Exchange Membrane fuel cells (PEMFC) seem at present one of the most promising choices. A very important component of a PEMFC is the gas diffusion layer (GDL), which has the primary role of managing water in the cell, allowing reactant gases transport to the catalyst layer while keeping the membrane correctly hydrated and preventing electrode flooding. Therefore, GDLs have to be porous and very hydrophobic. Carbon clothes or carbon papers coated with a hydrophobizing agent – typically a fluoropolymer – are used. Given the complex chemistry and morphology of the GDLs, wettability analyses on them present some critical issues when using the conventional contact angle measurement techniques. In this paper, the deposition of a drop on a GDL (produced using polytetrafluoroethylene-co-perfluoroalcoxy vinyl ether as the fluorinated polymer) was investigated by means of micro computed tomography (microCT) and numerical simulation. The microCT facility operational at the University of Bergamo was used to acquire a 3D tomography of a water drop deposed on a sample GDL. The reconstructed drop dataset allows thorough understanding of the real drop shape, of its contact area and contact line. The GDL dataset was used to create a realistic mesh for the numerical simulation of the drop deposition, which was performed using the OpenFOAM® interFOAM solver.

Highlights

Fuel cells are electrochemical power generation systems where chemical energy is directly converted into electrical energy, without passing through combustion [1,2]
Vertical slices of the simulated volume (Fig. 11, right part) show that on the more hydrophobic surface the drop is in a Cassie-Baxter wetting state, with air pockets entrapped between the drop and the gas diffusion layer (GDL)
A sessile drop deposed on the GDL-PFA surface was acquired by the micro computed tomography (microCT) and information about the real contact area, contact line and contact angle could be obtained from the tomographic volume

Summary

Introduction

Fuel cells are electrochemical power generation systems where chemical energy is directly converted into electrical energy, without passing through combustion [1,2]. In this work the use of micro computed tomography (microCT) is proposed to acquire a real threedimensional representation of a sessile drop on a GDL surface, with the aim of extracting from the tomographic volume both direct experimental information about the drop shape and the surface wettability, and a realistic mesh for the numerical simulation of a drop deposition onto such surfaces.

Results

Conclusion