Flow in Porous Electrodes

The mass continuity and momentum equations for the bulk fluid flow in a chaimel are significantly altered in a porous media owing to the presence of complex flow geometries. A detailed description of fluid in a gas diffusion layer electrode is given in Chapter 6. 

Most general fluid flow equations in porous media are given by the modified Navier-Stokes equation given by Equation 6.22 as 

The mass continuity equation for flow in a porous media is given as 

In order to determine the reactant gas transport rates in the electrode/gas diffusion layers and the consumption rates at electrode-membrane interfaces. 

S represents the reactant gas consumption rates in the active layer for hydrogen and oxygen and the mass source term for the water transport. For the GDL with no volume reaction zone, the source term is dropped and included as a boundary condition at the electrode-membrane interfaces. 

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Notice that Brinkman s equation includes both the pressure force and the viscous force terms. The effective viscosity for the slower-moving fluid in the porous media is selected such that continuity in shear stress is maintained at the interface between the faster-moving gas flow in the channel and the slower-moving gas flow in porous electrode. The continuity in shear stress at the interface is given as... 

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