In the palette of new solutions for improving the sustainability of energy systems, the concepts of renewable energy source, distributed energy generation and sustainable mobility represent some of the most important topics for innovative research&development strategies. In this field Fuel Cells (FCs) represent the most promising devices as they are characterized by high efficiency and the capability to work with different feedstocks locally available provided that a gasification (and desulphuration) of the fuel is possible. In particular, Direct Methanol Fuel Cells (DMFCs) represent the most suitable technology for mobile applications due to the possibility to easily store and transport the fuel. On the other hand, this technology still has to overcome some issues in order to become market competitive. Main unsolved technological questions are: 1) the methanol cross‐over that causes lowering of power density and global efficiency due to the leakage of fuel from anode to the cathode causing cathode polarization; 2) the presence of CO2 bubbles flow in the anode channel increasing the liquid methanol solution velocity and causing lowering of fuel Utilization Factor (UF). We analyzed the first phenomenon in a previous paper. This paper represents the first step of a comprehensive analysis of the influence of CO2 in the DMFC channels. The flow is treated as gaseous (and not as liquid‐gaseous mixture) to separately assess the importance of several parameters, such as methanol concentration, mass flow, current density. In the model mass transport of the different species and the electric field inside the fuel cell are considered. The 3D computational model with multicomponent flow is solved using COMSOL Multiphysics software. The set of governing equations is composed by: a) Maxwell‐Stefan equation for species transport; b) Brinkman equation to calculate momentum in porous media; c) Butler‐Volmer equation to calculate the current density over the catalyst layers allowing the achievement of the quantity of generated/consumed species. The equations system is validated against available experimental data. The V/I characteristic of the cell, species distributions, velocity fields and current density distributions will be discussed. The generation and the dispersion of CO2 in the anode channel is also analyzed.
|Titolo:||SIMULATION OF FLUID DYNAMIC AND ELECTRIC FIELD IN A DIRECT METHANOL FUEL CELL|
|Data di pubblicazione:||2013|
|Appare nelle tipologie:||4.1 Contributo in Atti di convegno|