Multiphase Modeling of a Flowing Electrolyte-Direct Methanol Fuel Cell

Direct methanol fuel cells (DMFCs) are considered one of the leading contenders for low power applications due to their energy dense, liquid fuel and their low greenhouse gas emissions. However, DMFCs have lower than predicted performance due to methanol crossover. One proposed solution is to allow a liquid electrolyte, such as diluted sulfuric acid, to flow between the anode and cathode, thereby removing any methanol that attempts to crossover to the cathode. This fuel cell is named the flowing electrolyte - direct methanol fuel cell, or FE-DMFC. So far few researchers have examined the effectiveness of this fuel cell and none have explored the multiphase flow within the membrane electrode assembly (MEA) of this fuel cell. In this study, the well-known Multiphase Mixture Model (MMM) was improved with a new single domain approach which was used to model the flow behaviour and performance of the FE-DMFC. Unlike the existing methods, the proposed model only requires the mixture variables, thereby removing the requirement for information about the gaseous state, when attempting to couple the porous and electrolyte layers together. Furthermore, the model's formulation gives the capability to resolve liquid saturation jumps in a single domain manner. The proposed approach is sufficiently flexible that it could be applied to other modeling methods, such as the Multi-Fluid Model (MFM). The corresponding derivation for the MFM is provided. The fidelity of the improved MMM is examined through 3 test cases, which include a comparison to: the analytical liquid saturation jump solution, the analytical single phase solution for the FE-DMFC, and to in-house FE-DMFC experimental data. The numerical model was shown to be capable of accurately reproducing all three test cases. To understand the FE-DMFC's underlying physics, the numerical model was applied under baseline operating conditions, and a series of parametric studies were conducted to understand the effect that: the anode and cathode membrane (AM and CM, respectively) thicknesses and the flowing electrolyte channel's (FEC) porosity and thickness each have on the fuel cell's performance. The findings of the parametric study were used to provide recommendations on conditions which yield maximum power density and minimal