Cell single-phase flow

From a purely electrokinetic point of view (i.e. for single-phase flow), the calculated cell voltage equal to 0.732 V is mainly attributed to S02 oxidation kinetics which is responsible for the anodic overvoltage (fig. 3). 

Figure 3 Cell potential distribution for single-phase flow (x = 0.02, z =...

The focus of this review has been on mass transfer in laminar, single-phase flows. Significant work is necessary for the rigorous analysis of current distribution in turbulent flows. Progress is also required for the analysis of current distribution in multiphase flows, especially in porous media relevant to fuel cell or battery applications. 

Jiang, Y., Khadilkar, M. R., Al-Dahhan, M. H., Dudukovic, M. P., Single phase flow modeling in packed beds Discrete cell approach revisited. Chemical Engineering Science, 2000, 55,10, 1829-1844... 

The aim of this section is to understand the features of single-phase flow in the cathode channel of a PEFC or DMFC. The model below takes into account mass and momentum transfer through the channel/GDL interface. The model gives exact solutions and helps in clarifying how the electrochemical reactions and electro-osmotic effect affect the flow in the fuel cell channels (Kulikovsky, 2001). 

The present chapter focuses on single-phase flow, but extensions to multi-phase flow or monitoring other variables, such as the coke content and / or activity level of catalyst pellets, concentrations within coalescing droplets, changing pore sizes in a reacting solid, biochemical properties of growing cells, sizes of growing crystals, are possible. Some of these extensions are dealt with in Chapters 13 and 14. 

Rodatz et al.10 studied a large PEM fuel cell stack used in automotive applications at different operating conditions. One of the main parameters that were studied was the pressure drop within the stack and its relationship with the flow field (bends in the channels) and single- and two-phase flows. It was observed that once the current in the fuel cell stack was reduced (i.e., applying dry conditions) the pressure drop decreased slowly until it reached a new value. This was attributed to the fact that the reduction of current reduces the flux of product water in the flow channels, and thus, it reduces the total mass flow in the flow channels. 

The first equation represents the equilibrium between hydrated Ag+ ions and Ag atoms in a single-crystal configuration. Alternatively, we may say that there is a heterogeneous thermodynamic equilibrium between Ag+ ions in the solid phase (where they are stabilized by the gas of free electrons) and Ag+ ions in the liquid phase (stabilized by interaction with water molecules). The forward reaction step corresponds to the anodic dissolution of a silver crystal. On an atomic level, one may say that a Ag" " core ion is transferred from the metallic phase to the liquid water phase. In an electrochemical cell, an electron flows from the Ag electrode (the working electrode) to the counter electrode each time that one Ag+ ion is transferred from the solid to the liquid phase across the electrochemical double layer. Although the electron flow is measured in the external circuit between the working... 

The snapshot approach for gas-liquid flows was implemented using a commercial CFD code, FLUENT (Fluent Inc., USA). User-defined subroutines were used for this purpose. Half of the vessel was considered as a solution domain. The solution domain and details of the finite volume grid used was similar to those used for singlephase flows discussed earlier (however, the number of cells in the 6 direction were half of that used in single-phase simulations). A QUICK discretization scheme with SUPERBEE limiter function was used to integrate all the equations (Fluent User Guide, 1997). Simulations were carried out for three values of dimensionless gas flow rates (Qc/ND ), 0.01, 0.02 and 0.03. 

Further develop the 3-D single-phase model improve on reformate feed and for different flow fields. Improve the fuel cell stack model. 

The geometry of a single fuel cell is shown in Figure 1. The PEM fuel cell is divided into 9 regions according to the material properties and flow characteristics. In FY 2000, this project started with 2-D single-phase models that included 2 sub-models... 

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