3-Dimensional analysis of the effect of semi cylindirical blocks in flow channels on PEM fuel cell performance

This thesis covers the analysis of a single-cell proton exchange membrane fuel cell (PEMFC) with different sized semi-cylindrical blocks in both anode and cathode gas flow channels by using ANSYS FLUENT PEMFC module. The results of the analysis are compared and a good agreement has been obtained with similar studies in the literature.PEMFC is made up of two sides, one anode and one cathode, each of which include four layers. Each side consists of a current collector, gas channel, gas diffusion layer and catalyst layer. There exists a membrane between the anode and cathode sides. These anode and cathode gas diffusion layers, the two catalyst layers, and the membrane compose the Membrane Electrode Assembly (MEA).Physical model consists of semi-cylindrical blocks with different radii (r=0,40 - 0,49 mm) and in various numbers that are located inside the anode and cathode gas channels. The radius and the number of blocks are selected such that the total cross sectional area of blocks is constant. For this purpose, basic principles such as conservation of mass, momentum, energy, species, and phase potential are considered. In ANSYS FLUENT PEMFC module, electrochemical equations depending on hydrogen oxidation and oxygen reduction rates are solved. MEAs are implemented in the PEMFC models and analyzed for two different thickness values. The PEMFC model is examined for the geometry of straight gas flow channel and the effects of operating pressure on current density are investigated for these two MEAs (MEA-1 and MEA-2). For all analyzed cases, the temperature condition is assumed to be constant at the anode and cathode gas channel inlet-outlet, as well as the upper and lower external surfaces of the fuel cell.The result of velocity, temperature, hydrogen and oxygen mass fraction distributions are presented along the gas flow main direction. Furthermore, hydrogen mass fraction distributions are analyzed at the cross sections (inlet, mid-way, outlet) perpendicular to the main flow direction. Polarization curves are obtained for each case and the effects of blocks on the variation of these curves are examined.According to the results of blocked channel geometries, improvements can be achieved in the values of maximum current density up to 14,5% when the number of blocks is increased for the same total cross sectional area of blocks.Key Words : PEM fuel cell, PEMFC, baffle block, polarization curves, numerical analysis.