Computational Evaluation of an Enhanced Serpentine Flow Field Design for PEM Fuel Cells

Abstract

Fuel cell is a electro-chemical energy conversion system, which converts the chemical energy of fuel, directly into electrical energy. The ever increase in energy demand, non-polluting energy generation, and other environmental issues have persuaded many researchers to look for new efficient energy conversion technologies. Proton exchange membrane (PEM) fuel cells have many unique features compared with other types of fuel cell, such as relatively low operating temperature (around 80?C), high power density, quick start, rapid response, and high modularity which makes them as the most promising system in the applications such as automotive, distributed power generation and portable electronic devices. In this work, a new compound serpentine flow field is introduced and conducted simulations to study its performance. A 3-D PEM fuel cell model of size 49 cm2 and 84 cm2 active area is developed. A conventional serpentine flow field is modified and the same is considered for the supply of reactants. Computational fluid dynamics (CFD) based simulations were conducted to analyse the pressure drop, distribution of reactants (H2 and O2), liquid water activity, current flux density and water content in the membrane.

Introduction

I. INTRODUCTION

Fuel cell (FC) is an electro-chemical energy conversion device, which converts chemical energy of fuel directly into electrical energy. The ever increase in energy demand, pollution free energy generation, and other ecological issues have persuaded many researchers to look for new efficient energy conversion technologies [1]. Within such perception FC systems may consider as promising alternative due to practical advantages such as high-energy density, less harm to the environment, good dynamic response, and lightweight. Depending on type of electrolyte material used FCs are categorized as polymer membrane, alkaline, phosphoric acid, molten carbonate, and solid oxide fuel cells [2]. Proton exchange membrane (PEM) fuel cell has unique features such as relatively low operating temperature (around 80oC), high power density, quick start, rapid response, and high modularity make them as the most promising system for power generation in the applications such as automotive, distributed power generation and portable electronic devices [3,4].

In the early 1960s, PEM fuel cell (PEMFC) was first used in the Gemini space program, that FC was developed by General Electric based on the work of Grubb and Niedrach. Following the Gemini Program the FC was also used in the Apollo program, to produce electricity for life support and communications. These FCs were made by Pratt and Whitney based on the Bacon's patents. Due to their high cost, use of FC systems were limited in space applications and in some special applications. In 1990, Ballard Power systems started development of PEMFC systems. The strategy of Ballard was to reduce the cost of the fuel cell by using low cost materials and fabrication techniques, that FC turn out to be a real option for many applications. In 1993, Ballard Power Systems manifested fuel cell powered buses. Figure 1.1 illustrates the schematic of a PEMFC. Hydrogen (H2) comes into the anode flow channel and disperses into the anode gas diffusion layer (GDL) whereas oxygen (O2) enters into the cathode flow channel and disperses into the cathode gas diffusion layer (GDL). The membrane comprises catalyst usually platinum, on both sides and it is made from a material that only permits the hydrogen ions and offer resistance to the flow of electrons. When hydrogen and oxygen reaches the catalyst layers (CLs) through GDLs on the PEM, the following reaction takes place.

Being enthralled with Grove’s invention, Bacon began working on FCs in 1939 and successfully constructed a FC stack of 6 kW output power 1959. Later FCs have been used in the U.S. Space Program for the first time. Furthermore, the FCs were used in the Apollo Space Program to produce power for life support and communications. Based on Bacon’s patents, Pratt and Whitney made the fuel cells. General Motors made trials with a FC operated van by the mid-1960s, in the meantime the U.S. Space Program has continued to effectively make use of FCs up to today. In the 1960s many industries recognised that the FCs can be used in different applications, but because of their high manufacturing cost and technical difficulties, FCs were not have the capacity to monetarily focused with other energy conversion devices. In the 1980s, the Canadian Government sponsored the preliminary development work of FCs which was supported by Ballard Power Systems. Later in 1989, the company decided to concentrate on FC systems for transportation and stationary applications.

II. METHODOLOGY

Computational evaluation of PEM fuel cell performance includes three major steps. The first step is modeling the geometry of the PEMFC by means of computer-aided design software. The geometrical model forms the basis for creating a computational mesh.

The second step involves generating the mesh from the geometry. In order to solve the numerous of equations associated with a fuel cell simulation, the entire cell is split into a finite number of discrete volume elements or computational cells. The relevant equations are then solved in each individual cell and integrated over the computational domain to give a solution for the entire domain. Generating a good mesh is one of the challenging steps. It needs a careful balance of generating adequate computational cells to capture the geometry without exceeding the available memory of the meshing computer. Many other factors must also be considered in order to create a computational mesh which delivers archetypal results when simulated.

The third and final step involves inputting the various physical and operating parameters of the simulation. Some of these include thermal and electrical properties of the various materials, operating temperatures and pressures, inlet gas flow rates, open circuit voltage, porosity, and humidification among many others. The flow chart of the computational methodology can be seen in Figure 2.1.

A. Modeling Assumptions

The developed models were assumed as 3-D, steady and isothermal. The reactants at inlet to the channel assumed as perfect gases, the flow is laminar, incompressible and the porous layers assumed as isotropic and the thermo-physical properties assumed as constant.

B. Governing Equations

Fundamental conservation equations such as conservation of mass, momentum and charge were used to develop a mathematical model for PEMFC. Conservation of energy equation was not considered as the model was assumed as isothermal. The PEMFC was examined in four parts: flow channels, GDLs, CLs and the membrane.

Conclusion

First, a computational fluid dynamics study on two active area PEMFCs with three types of serpentine flow fields (1-S, 2-S and 3-S) has been carried out and key parameters such as pressure drop, reactants mass fraction, liquid water activity, the membrane water content, polarization and performance of the PEMFC were presented. The following conclusions were drawn from this study. 1) Highest pressure drops were observed in single (1-S) and lowest pressure drops were observed in triple (3-S) serpentine flow fields. Therefore the 3-S flow field is considered for further investigations. 2) Oxygen mass fraction distributions were more uniform than hydrogen mass fraction distributions. 3) Liquid water activity in the cathode channels is less at inlet and increases gradually towards outlet and 3-S flow field has the better water removal capability 4) PEMFCs with triple serpentine flow field performs better than PEMFCs with single and double serpentine flow fields. 5) A thin membrane (N212) offers less ohmic resistance than thick membrane (N112 and N117) and results in improvement in the cell performance. 6) Fuel cell performance was increased with increase in platinum loading from 0.6 to 1.0 mg/cm2. Rate of increase in performance is more when the platinum loading increased from 0.6 to 0.8 mg/cm2 than 0.8 to 1.0 mg/cm2.

References

[1] A. Beicha and R. Zaamouche, “Electrochemical model for proton exchange embrane fuel cells systems,” J. Power Technol., vol. 93, no. 1, pp. 27–36, 2013. [2] J. Larminie and A. Dicks, Fuel Cell Systems Explained, 2nd ed., John Wiley & Sons Ltd, London, 2003. [3] D. D. Boettner, G. Paganelli, Y. G. Guezennec, G. Rizzoni, and M. J. Moran, “Proton Exchange Membrane Fuel Cell System Model for Automotive Vehicle Simulation and Control,” J. Energy Resour. Technol. Trans. ASME, vol. 124, no. 1, pp. 20– 27, 2002. [4] H. Zhao and A. F. Burke, “Optimization of fuel cell system operating conditions for fuel cell vehicles,” J. Power Sources, vol. 186, no. 2, pp. 408–416, 2009. [5] M. Shichun, W. Xiaoen, T. Haolin, L. Peigang, L. Ming, P. Mu, and Y. RunZhang, “A Self-Humidifying Composite Membrane with Self-Assembled Pt Nanoparticles for Polymer Electrolyte Membrane Fuel Cells,” J. Electrochem. Soc., vol. 153, no. 10, pp. A1868–A1872, 2006. [6] P. K. Das, X. Li, and Z. S. Liu, “A three-dimensional agglomerate model for the cathode catalyst layer of PEM fuel cells,” J. Power Sources, vol. 179, no. 1, pp. 186– 199, 2008. [7] C. Lim and C. Y. Wang, “Effects of hydrophobic polymer content in GDL on power performance of a PEM fuel cell,” Electrochim. Acta, vol. 49, no. 24, pp. 4149–4156, 2004. [8] P. Choopanya and A, “Computational Fluid Dynamics Modelling of a Polymer Electrolyte Membrane Fuel Cell under Transient Automotive Operations,” PhD Thesis Univ. Sussex, 2015. [9] F. B. P. Ryan O’hare, Suk-Won Cha, Whitney G. Colella, Fuel Cell Fundamentals. . [10] J. T. Pukrushpan, H. Peng, and A. G. Stefanopoulou, “Control-Oriented Modeling and Analysis for Automotive Fuel Cell Systems,” Trans. ASME, vol. 126, no. March 2004, pp.14–25, 2004. [11] F. Barbir, “PEM Fuel Cells: Theory and Practice,” Elsevier Inc, 2013. [12] V. Gurau, F. Barbir, and H. Liu, “An Analytical Solution of a Half-Cell Model forPEM Fuel Cells,” J.Electrochem. Soc., vol. 147, no. 7, p. 2468, 2000. [13] D. M. Bernardi and M. W. Verbrugge, “A Mathematical Model of the Solid-PolymerElectrolyte Fuel Cell,” J. Electrochem. Soc., vol. 139, no. 9, pp. 2477–2491, 1992. [14] A. Parthasarathy, S. Srinivasan, a. J. Appleby, and C. R. Martin, “Temperature dependence of the electrode kinetics of oxygen reduction at the platinum/Nafion interface - A microelectrode investigation,” J. Electrochem. Soc., vol. 139, no. 9, pp. 2530–2537, 1992. [15] J. C. Amphlett, R. F. Mann, B. A. Peppley, P. R. Roberge, and A Rodrigues, “A practical PEM fuel cell Model for Simulating Vehicle Power Sources,” Proceedings of the Tenth Annual Battery Conference on Applications and Advances, USA, 1995. [16] S. S. and C. E. C. Junbom Kim, Seong-Min Lee, “Modeling of Proton Exchange Membrane Fuel Cell Performance with an Empirical Equation,” J. Electrochem. Soc., vol. 142, no. 8, pp. 2670–2674, 1995. [17] A. Kazim, H. T. Liu, and P. Forges, “Modelling of performance of PEM fuel cells with conventional and interdigitated flow fields,” J. Appl. Electrochem., vol. 29, no. 12, pp. 1409–1416, 1999.

Copyright

Copyright © 2024 Gaddala Dinakar, K. Prasada Rao, S Venkateswara Rao. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.