UBC Theses and Dissertations
Comprehensive numerical study of microfluidic fuel cells Ebrahimi Khabbazi, Ali
The microfluidic fuel cell or laminar flow-based fuel cell is a membraneless fuel cell which typically consists of two electrodes mounted within a T- or Y-shaped microchannel. Aqueous fuel and oxidant are introduced from the two inlets of the channel and flow together side-by-side toward the end of the channel. The Reynolds number in the microchannel is low, and hence viscous forces are dominant over the inertial forces. This causes the anolyte and catholyte form a co-laminar flow inside the microchannel which is required to maintain the separation of the fuel and oxidant and limit the reactions to the appropriate electrodes. In this work, a comprehensive numerical model of the microfluidic fuel cell is developed using COMSOL Multiphysics. This model accounts for the mass and momentum transport phenomena inside the device as well as the electrochemical reaction kinetics which are described by the Butler-Volmer equations. Potential equations are used to model both the ionic conduction in the electrolyte and the electrical conduction in the solid electrodes. The validity of the developed model is first checked by verifying it against the numerical and experimental results previously reported in the literature. The model is then used to assess the effect of different modifications, which have been applied on the microfluidic fuel cell since its advent, by calculating the polarization curves associated with each modification. In this thesis, a novel design of microfluidic fuel cell with a tapered channel is also proposed. Using the numerical model, it is shown that the tapered geometry improves the fuel utilization by up to four times in addition to a substantial improvement in the power density. A similar numerical model is developed to study the performance of a microfluidic fuel cell with flow-through porous electrodes. Using this model, the effect of porosity on the net power output of the fuel cell is investigated and an optimum value for porosity is calculated. The model presented is a valuable tool, as it can be used to study the effect of any modifications on the cell performance before fabricating and testing the new design in an extensive experimental study.
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