چكيده به لاتين
In the first part of this thesis, the first goal is achieved by the utilization of the aluminum porous media in the gas flow channel of these fuel cells. By this action, the convective heat transfer can be improved considerably due to increasing the surface of the heat transfer. It is noteworthy to mention that enhancement in heat transfer is a result of improving the velocity and temperature profiles. Totally, increasing the heat transfer can be achieved due to two main reasons; first, modification in the geometry of the porous ribs in the gas flow channel, second, finding an optimum value of the porous media’s parameters such as permeability and porosity. In order to obtain a comprehensive study on this field, both methods have been studied well in this thesis. The results indicate that the wave-like porous ribs (Nu=15.4) have positive effects on the convective heat transfer in comparison to the trapezoidal and flat (Nu=4.2) likes ribs. Performing the simulations, it was concluded that increasing the permeability and decreasing the porosity can also enhance the convective heat transfer. It should be noted that in this analysis a microporous layer (MPL) is also used to improve the water management. Along with the gas diffusion layer (GDL), results indicated that increasing the thickness of this layer can simply enhance the heat transfer. As Nu number is not the only affecting parameter in the convective heat transfer, in this thesis friction factor is considered as well to attain a comprehensive study. Additionally, a parameter called performance evaluation criterion (PEC) is utilized to complete the analysis as Nu number should be increased while friction factor is needed to be reduced as much as possible. Therefore, the optimization can be easily obtained by the application of this parameter. In the last section of first goal, as the number of effecting parameters on the convective heat transfer is a lot and the problem needs optimization, artificial neural networks (ANN) is utilized. These networks can simply model the system and produce large data for optimization and sensitivity analysis. By the output result of sensitivity analysis, one can easily perceive the share of each input parameter on the output results. Results indicate the considerable effect (96%) of the porous layer thickness in addition to the 46% effect of the base width of the trapezoid ribs on the output Nu.
The main goal of the current thesis is to model and simulate Proton Exchange Membrane’s fuel cells. This goal is achieved by the numerical analysis of the convective heat transfer in the PEM fuel cells by the application of the porous media. In the first step, this porous media was assumed to be a simple flat layer in the gas diffustion layer and after approving its positive effects, the trapezoid and wave-like geometries were used to evaluate the performance of the system.
