Impact of Geometry in PEMFC Water Management
- Type: Conference Presentation
- Conference Type: AIChE Spring Meeting and Global Congress on Process Safety
- Presentation Date: August 19, 2020
- Duration: 20 minutes
- Skill Level: Intermediate
- PDHs: 0.40
Understanding such phenomena via experimental test cases is extremely expensive. Neutron radiography is one of the most used methods to understand liquid production within the fuel cell layers whilst gas chromatography is used to understand water saturation. CFD techniques might help to provide further insights on such phenomena. In this work, three different configurations are simulated with Simcenter STAR-CCM+. A 3D single layer cell is modelled. The equations of flow, momentum and energy are solved for the anode and cathode channels with a no-slip condition at the walls to calculate the pressure drop. The channels are directly interfaced with the gas diffusion layers (GDL) calculated as a high porosity porous media. Hydrogen and oxygen diffusion from the channels through the GDL is calculated via a Darcyâs law. Bipolar plates are represented as a solid able to conduct current and can produce ohmic heating. Bipolar plates are directly interfaced with a liquid water coolant to dissipate heat. Finally, the membrane is simulated as a solid including electro-osmotic drag, able to transport the positive ions produced from the reactions. Reactions occur at the infinitely thin layer between the GDL and the membrane. Two main reactions are considered. The first at the anode side, accounts for H2 splitting into one electron and a positive ion. The second one occurs at the cathode side and accounts for the reassociation of the positive hydrogen ion, one electron and oxygen, which leads to water as product. Water sorption reactions are also considered. The energy balance of the configurations simulated considers several energy sources. In particular, the model calculates the activation, ohmic and concentration losses to reconstruct the polarization curve. The polarization curves are shown for the three configurations and analysis of the several losses is provided.
The three configurations represent a single layer cell, with wavy channels. They differ with each other with respect to the entry area and the angle of the channel waves. Three main aspects will be described in this work. The impact of the geometry on hydrogen consumption and diffusion in the anode layers is analyzed. The works tries to understand how the GDL can smooth H2 gradients at the catalytic layer to improve temperature gradients. The second aspect studied in this work deals with the current production. Current gradients are stronger at the triple-phase-boundary (TPB) and might damage the bipolar plates on the long period. Considerations to reduce such gradients by modifying the geometry are reported. Finally, further investigation on liquid water production are shown. Liquid water is produced at low voltage-high current densities. Such work provides insights to understand where water accumulates in order to improve reactants feeding to the membrane. The variations applied to the geometries offer the possibility to understand how different design solutions can significantly improve durability and fuel cells efficiency.
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