SOME STUDIES ON THE GEOMETRIC PARAMETERS OF THE STRAIGHT PARALLEL FLOW FIELD DESIGN OF PROTON EXCHANGE MEMBRANE FUEL CELL

Abstract

In an era where environmental concerns have reached a critical point, the quest for clean and efficient energy sources has become paramount. Proton exchange membrane fuel cells (PEMFCs) offer a glimmer of hope, with their ability to directly convert the chemical energy of fuels into useful work, leaving a negligible environmental impact. However, maximizing the performance of PEMFCs requires innovative design approaches, particularly in the realm of flow field Designs (FFDs) of the bipolar plates (BPs). The study presents a comprehensive analysis of the performance and local species transport phenomena of PEMFCs, focusing on the impact of geometric designs and FFDs. An enhanced FFD provides more homogeneous reactant diffusion in the cell, lowers the pressure drop, and provides higher electrical performance. The FFDs can be improved by adding baffles in the flow channel, developing completely new and innovative FFDs, or adopting nature/bio-inspired designs. However, a detailed analysis of various aspects of FFDs like cell performance, cost, and manufacturing difficulties has to be done Therefore, a simple and novel tapered-trapezoidal FFD is proposed considering the varying dimensions of the parallel sides at the inlet, denoted as "a" and "b", aiming to enhance the performance of PEMFCs compared to conventional straight parallel FFD and tapered FFD. For this purpose, a three-dimensional non-isothermal, single-phase, steady state, model for a single PEMFC is developed. The equations governing the transfer of v mass and momentum are carefully solved by the ANSYS program using the computational fluid dynamics (CFD) technique, taking into account the relevant source terms arising from electrochemical reactions occurring in various zones of the fuel cell. The study revealed that the geometrical dimensions of the FFDs had a substantial impact on the electrochemical reactions and electrical characteristics of the cell. Compared with the conventional straight parallel FFD and tapered FFD, the proposed novel tapered trapezoidal FFD enhances the temperature distributions, reactants distributions, water removal, and cell performance. According to the results, the limiting current density and maximum power density of the proposed novel tapered-trapezoidal FFD with case C4 have 13.8 % and 8.1 % with respect to the conventional straight parallel FFD respectively, and 7.9 % and 4.3 % with respect to the tapered FFD at 0.5 V. Moreover, an increase in the maximum temperature of the novel FFDs compared to C1 and C2 results in improved heat transfer efficiency of the PEMFC. The average oxygen mass fraction at the interface between the channel and GDL on the cathode side for case C4 is 19.8 % more than C1. In addition, the water removal capability has also improved for the novel tapered trapezoidal FFDs. Therefore, the employment of the proposed design can be strongly recommended for high current-density operating conditions. The present study discusses in detail the reasoning for the mentioned observations.