1 / 8

Example: Maxwell-Stefan Diffusion in a Proton Exchange Membrane Fuel Cell

Example: Maxwell-Stefan Diffusion in a Proton Exchange Membrane Fuel Cell. Maxwell-Stefan diffusion in a fuel cell - Geometry.

shaeleigh-newman
Download Presentation

Example: Maxwell-Stefan Diffusion in a Proton Exchange Membrane Fuel Cell

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Example:Maxwell-Stefan Diffusion in a Proton Exchange Membrane Fuel Cell

  2. Maxwell-Stefan diffusion in a fuel cell - Geometry This example models the cross-section of a proton exchange membranefuel cell cathode. The cross-section includes equal parts of the current collector and the channel in the bipolar plate as upper boundary.The active layer defines the lower boundary.

  3. Maxwell-Stefan diffusion in a fuel cell - Equation Equation: • Mass balance; divergence of the mass flux through diffusion • M - total molar mass of the mixture • Mj - molar mass of species j • wj - mass fraction of species j

  4. Maxwell-Stefan diffusion in a fuel cell - Equation • The symmetric diffusivities are strongly dependent on the composition and are given by the following expressions: • xj is the molar fraction of species j • Dij is the Maxwell-Stefan diffusivity for the pair ij • Subsequent entries can be obtained by permutation of the indices

  5. Maxwell-Stefan diffusion in a fuel cell - Diffusivities • The Maxwell-Stefan diffusivities can be described with asemi-empirical equation based on kinetic gas theory: • Resulting diffusivities, in m2 s-1, at T=353 K and p=101 kPa are: DO2N2 = DN2O2 = 9.7e-6 DO2H2O= DH2OO2= 1.20e-5 DH2ON2= DN2H2O= 1.24e-5

  6. Maxwell-Stefan diffusion in a fuel cell - BC’s • At the reactive boundary, oxygen is consumed according to the following expression • Subscript 0 in the mass fraction for oxygen represents the reference state, and kis the reaction rate given by the Tafel expression: • Combining all constants, the flux can be written as: -0.0442*wO2

  7. Maxwell-Stefan diffusion in a fuel cell - Results Results – mass fraction of oxygen, wO2. • Oxygen transport limits the rate of the reaction. • The concentration of oxygen in the active layer is less than 50% of the concentration at the position of the channel.

  8. Maxwell-Stefan diffusion in a fuel cell - Results Results – concentration dependent diffusion coeficcients • Large variations in concentration have a direct influence on the value of the diffusion coefficients. • DD11, reflects the interaction between oxygen molecules.

More Related