Single pore model evaluation

In terms of both quantitative and qualitative modeling, PEMs have been modeled within two extremes, the macroscopic and the microscopic, as discussed in various chapters in this book and in recent review articles [1, 9, 10]. The microscopic models provide the fundamental understanding of processes like diffusion and conduction in the membrane on a single-pore level. They allow for the evaluation of how small perturbations like heterogeneity of pores and electric fields affect transport, as well as the incorporation of small-scale effects. 

The density functional approach has also been used to study capillary condensation in slit-like pores [148,149]. As in the previous section, a simple model of the Lennard-Jones associating fluid with a single associative site is considered. All the parameters of the interparticle potentials are chosen the same as in the previous section. Our attention has been focused on the influence of association on capillary condensation and the evaluation of the phase diagram [42]. 

Taking these effects into account, internal pore diffusion was modeled on the basis of a wax-filled cylindrical single catalyst pore by using experimental data. The modeling was accomplished by a three-dimensional finite element method as well as by a respective differential-algebraic system. Since the Fischer-Tropsch synthesis is a rather complex reaction, an evaluation of pore diffusion limitations... 

This paper seeks to contribute to a clarification of the overall perspective. The influence of a single layer of clay in a sandstone sequence on the basic mechanics of fault development and associated seal formation are examined by numerical comparisons with shear band and fault development in a homogeneous sandstone. The potential sealing capacity of shear bands, formed in the absence of clay layers, is re-evaluated by reference to pore physics models relating permeability and capillary pressure, supported by field data. By this means it is hoped to expedite resolution of apparently ongoing industry misconceptions of the potential sealing capacity of such structures. 

In the absence of experimental data it is necessary to estimate from the physical properties of the catalyst. In this case the first step is to evaluate the diffusivity for a single cylindrical pore, that is, to evaluate D from Eq. (11-4). Then a geometric model of the pore system is used to convert D to for the porous pellet. A model is necessary because of the complexity of the geometry of the void spaces. The optimum model is a realistic representation of the geometry of the voids, with tractable mathematics, that can be described in terms of easily measurable physical properties of the catalyst pellet. As noted in Chap. 8, these properties are the surface area and pore volume per gram, the density of the solid phase, and the distribution of void volume according to pore size. 

Systematic and reliable experimental data of single adsorbates and binary and ternary mixtures on samples of activated carbon with various pore structures and surface chemistry are badly needed for the critical evaluation of models of multi-component adsorption equilibria. 

The dynamics of sulphur uptake in a prereformer is like a fixed-bed absorption as seen in a zinc-oxide bed (refer to Chapter 1). However, in a tubular reformer the pore diffusion restrictions in the sulphur adsorption in a single pellet has a complex influence on the transient sulphur profiles in the reactor and a mathematical model [112] [387] [389] is required to evaluate more exactly the time for fiill saturation and the breakthrough curves of sulphur. 

A model of the ORR in a single water-filled pore with charged walls of Pt will be presented. It affords the definition of an effectiveness factor, by which the performance of any nanoporous CL material could be evaluated. Furthermore, a remarkable conclusion is drawn in view of the coupling of ORR kinetics and metal corrosive dissolution. 

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