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Porous materials simple geometric model

This approach to finding effective transport coefficients was first used for evaluating the permeability of a porous medium to fluid flow. For example, as described in the previous section, one of the first geometric models of a porous medium was developed by assuming a simple geometrical model for the porous material-a parallel bundle of capillaries with different diameters but constant length [8]. The determination of realistic models for flow through porous media is the subject of many reviews [5, 12, 28] and textbooks [9, 29, 30]. [Pg.180]

Such more realistic models of porous materials can also be used to rigorously test existing characterization methods. The model material is precisely characterized (we know the location of every atom in the material, hence the pore sizes, surface area and so on). By simulating adsorption of simple molecules in the model material and then inverting the isotherm, we can obtain a pore size distribution for any particular theory or method. Such a test for porous glasses is shown in Figure 8, where the exactly known (geometric) PSD is compared to that predicted by the Barrett-Joyner-Halenda (BJH) method, which is based on the modified Kelvin equation. [Pg.49]

In the industrial applications of electrochemistiy, the use of smooth surfaces is impractical and the electrodes must possess a large real surface area in order to increase the total current per unit of geometric surface area. For that reason porous electrodes are usually used, for example, in industrial electrolysis, fuel cells, batteries, and supercapacitors [400]. Porous siufaces are different from rough surfaces in the depth, /, and diameter, r, of pores for porous electrodes the ratio Hr is very important. Characterization of porous electrodes can supply information about their real surface area and electrochemical utilization. These factors are important in their design, and it makes no sense to design pores that are too long and that are impenetrable by a current. Impedance studies provide simple tools to characterize such materials. Initially, an electrode model was developed by several authors for dc response of porous electrodes [401-406]. Such solutions must be known first to be able to develop the ac response. In what follows, porous electrode response for ideally polarizable electrodes will be presented, followed by a response in the presence of redox processes. Finally, more elaborate models involving pore size distribution and continuous porous models will be presented. [Pg.203]


See other pages where Porous materials simple geometric model is mentioned: [Pg.165]    [Pg.1]    [Pg.110]    [Pg.121]    [Pg.80]    [Pg.366]    [Pg.477]    [Pg.246]    [Pg.537]    [Pg.134]    [Pg.543]    [Pg.284]   
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