Fuel cells, and direct methanol fuel cells in particular, are a technology with intriguing potential. However, methanol crossover is a significant concern in direct methanol fuel cells that reduces power and efficiency. The flowing electrolyte -direct methanol fuel cell is a concept intended to combat this issue by using a sulphuric acid flowing electrolyte layer to remove crossed-over methanol before it can reach the cathode.Hydrodynamic modelling of the flowing electrolyte channel was conducted in order to investigate the flow characteristics in this porous channel and analyze its response to various parameters. It was concluded that pressure drop decreases with temperature, is proportional to volume flux but unaffected by channel thickness, and can be reduced by increasing permeability, which can be achieved with higher porosities and pore diameters. Experimental studies noted improved cell performance at higher temperatures, but limited improvements at higher volume fluxes, likely due to leakage associated with higher pressure drops. Experimentally estimated permeability values had some discrepancy with theoretical values, highlighting the sensitivity of permeability values to imprecise parameters.It was recommended that the flowing electrolyte channel should be very thin with a higher sphere diameter and lower porosity with a flow rate high enough to effectively negate methanol crossover. However, a possible alternative may be to use a higher porosity, but increase the flow rate to achieve the same performance; this may result in a lower pressure drop. iii Acknowledgements I would like to thank a number of individuals for their roles in making this work possible. First of all, I would like to thank my supervisors, Dr. Edgar Matida and Dr. Cynthia Cruickshank. Their advice, guidance, and feedback have always been helpful and insightful, and I am truly grateful to have had such excellent supervisors. Secondly, I would like to thank my colleagues David Ouellette and Yashar Kablou for sharing their expertise and experience on fuel cell modelling and experimentation with me.
The performance of a direct methanol fuel cell (DMFC) can be significantly reduced by methanol crossover. One method to reduce methanol crossover is to utilize a flowing electrolyte channel. This is known as a flowing electrolyte–direct methanol fuel cell (FE–DMFC). In this study, recommendations for the improvement of the flowing electrolyte channel design and operating conditions are made using previous modeling studies on the fluid dynamics in the porous domain of the flowing electrolyte channel and on the performance of a 1D isothermal FE-DMFC incorporating multiphase flow, in addition to modeling of the nonisothermal effects on the fluid dynamics of the FE-DMFC flowing electrolyte channel. The results of this study indicate that temperature difference between flowing electrolyte inflow and the fuel cell have negligible hydrodynamic implications, except that higher fuel-cell temperatures reduce pressure drop. Reducing porosity and increasing permeability is recommended, with a porosity of around 0.4 and a porous-material microstructure typical dimension around 60–70 μm being potentially suitable values for achieving these goals.
The performance of a direct methanol fuel cell (DMFC) can be significantly reduced by methanol crossover. One method to reduce methanol crossover is to utilize a flowing electrolyte channel. This is known as a flowing electrolyte-direct methanol fuel cell (FE-DMFC). In this study, recommendations for the improvement of the flowing electrolyte channel design and operating conditions are made using previous modelling studies on the fluid dynamics in the porous domain of the flowing electrolyte channel, and on the performance of a 1D isothermal FE-DMFC incorporating multiphase flow, in addition to modelling of the non-isothermal effects on the fluid dynamics of the FE-DMFC flowing electrolyte channel. The results of this study indicate that temperature difference between flowing electrolyte inflow and the fuel cell have negligible hydrodynamic implications, except that higher fuel cell temperatures reduce pressure drop. Reducing porosity and increasing permeability is recommended, with a porosity of around 0.4 and a porous material microstructure typical dimension around 60–70 μm being potentially suitable values for achieving these goals.
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