Reacting porous medium

The experiment reported by Hecht et al. [64] treats the anode of a SOFC as the reacting porous medium. A 750 pm thick anode is sandwiched between two flow channels of 6.25 mm cross sectional area. The flow channels are 5 cm long. One flow channel carries the species that typically are present in the fuel channel of a real fuel cell, while the other channel carries mainly reforming gas (CO2 and H2O) and fuel. A schematic representation of the flow configuration is shown in Fig. 5.1. Three cases are described in the report, (i) dry reforming, (ii) steam-reforming, and (iii) combination of both. In order to follow up the work of Hecht et al., the same naming conventions used by the authors are adopted here. One of the flow channels is referred as fuel channel, while the other is referred as electrol)4e channel. 

Reactive transport equations In the formulation proposed by Guimaraes (2002), several dissolved chemical species (solutes) are transported in the water phase through the porous medium and, simultaneously, they react among themselves (homogeneous reactions) and, also, with species present in the solid phase (heterogeneous reactions). The homogeneous reactions include aqueous complex formation, acid/base and oxidation/reduction. The relevant heterogeneous reaction for the case presented in this paper refers to dissolution and precipitation of minerals. 

Facilitated transport has been briefly described in Chapter 1. In facilitated transport, the selective transport medium is a liquid or molten salt contained or immobilized in a porous support. The liquid membrane is held tightly in the support pores by capillary forces. The liquid or molten salt selectively reacts with a gas or vapor species and the reacting species diffuses across the liquid or salt and desorbed on the other side of the facilitated transport membrane. The major advantage of the facilitated transpoa is that diffusion is generally several orders of magnitude faster than diffusion through solid membranes. The support is, therefore, not a membrane by definition. Comprehensive... 

The mechanism of electrochemical etching to produce porous silicon has been studied by a number of researchers [11-13]. Although it is certain that several different reactions are occurring simultaneously, anodic etching of crystalline silicon ultimately leads to oxidation and dissolution of the surface to silicon hexafluoride (Scheme 16.1). Under these conditions, Si-Si bonds are electrochemically activated and react with fluoride ions to form soluble, molecular perfluoro species solvation of these silicon fluorides by the etching medium yields a physically irregular, high area porous silicon matrix. Visual indicators for the anodization are the appearance... 

A mixture of linear polymer and good solvent as an inert medium can be used to obtain copolymers with a porous structure in more advantageous conditions than with the use of a single component as an inert medium. The presence of a solvent in addition to a polymer will contribnte to a more nniform distribution of the inert polymer medium in the network, thus increasing the copolymer dispersion degree. The mixture can affect the size and distribution of pores because it acts as a unit of inert medium—the two components are inseparable and nnable to react independently of one another. 

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