Effective transport properties

Figure 12. Comparison between cup average conversion predicted by axisymmetric model with effective transport properties and experimentally measured values for styrene [5] and vinyl acetate [2],...

Tassopoulos, M. Relationships between particle deposition mechanism, deposit microstructure and effective transport properties . PhD Thesis, Yale University, USA (1991). 

The chapters in this volume present detailed insights into the synthesis-structure-properties relationships of nanostructured materials. In particular, the catalytic and photocatalytic properties of nanoclusters and nanostructured materials with ultrahigh surface-to-volume ratio are demonstrated. The gas absorption characteristics and surface reactivity of nanoporous and nanocrystalline materials are shown for various separation and reaction processes. In addition, the structural manipulation, quantum confinement effects, transport properties, and modeling of nanocrystals and nanowires are described. The biological functionality and bioactivity of nanostructured ceramic implants are also discussed. 

Calculation of Effective Transport Properties on Reconstructed Porous Media... 

Calculation of the effective transport properties thermal or electrical conductivity, effective diffusivity, and permeability—as a function of the... 

Experimentally determined effective transport properties of porous bodies, e.g., effective diffusivity and permeability, can be compared with the respective effective transport properties of reconstructed porous media. Such a comparison was found to be satisfactory in the case of sandstones or other materials with relatively narrow pore size distribution (Bekri et al., 1995 Liang et al., 2000b Yeong and Torquato, 1998b). Critical verification studies of effective transport properties estimated by the concept of reconstructed porous media for porous catalysts with a broad pore size distribution and similar materials are scarce (Mourzenko et al., 2001). Let us employ the sample of the porous... 

Textural Analysis and Effective Transport Properties of Sample G1... 

Salejova, G., Kosek, J., Nevoral, V., Solcova, O., and Schneider, P. Effective Transport Properties of Reconstructed Porous Catalyst Carriers. Proceedings of CHISA 2004 , 22-25 August 2004, Prague, Czech Republic (2004). 

The general approach for modelling catalyst deactivation is schematically organised in Figure 2. The central part are the mass balances of reactants, intermediates, and metal deposits. In these mass balances, coefficients are present to describe reaction kinetics (reaction rate constant), mass transfer (diffusion coefficient), and catalyst porous texture (accessible porosity and effective transport properties). The mass balances together with the initial and boundary conditions define the catalyst deactivation model. The boundary conditions are determined by the axial position in the reactor. Simulations result in metal deposition profiles in catalyst pellets and catalyst life-time predictions. 

In addition to the kinetic parameters such as rate constant and activation energy that we have become accustomed to dealing with, the analysis of this section has introduced some very important newcomers. Two of these, the effective transport properties within the porous matrix of the catalyst, and k ff, differ in substance from the transport coefficients in homogeneous phases with which we are familiar, and warrant some special discussion. 

From Meso-to-Macroscale Effective Transport Properties... 

Whereas the thermodynamic properties of heavy-fermion compounds are determined to a large degree by single-ion effects, transport properties reveal the... 

O Connell, J. P. 1994. Thermodynamics and fluctuation solution theory with some applications to systems at near or supercritical conditions. In Part 11 Eluctuations, crossover effects, transport properties. In Supercritical Fluids Fundamentals for Application, edited by E. Kiran and J. M. H. Levelt Sengers. Dordrecht, The Netherlands Kltiwer Academic... 

Kim, S.H. and Pitsch, H. (2009) Reconstruction and effective transport properties of the catalyst layer in PEM fuel cells./. Electrochem. Soc., 156 (6), B673-B681. 

Pressure control by movement of liquid may not easily, and certainly won t immediately, be effected. Transport properties (viscosity, etc.), physical properties (density, etc ), and surface properties (surface tension) are so different for liquids than vapors. 

Rosen T et al (2012) Saturation dependent effective transport properties of PEFC gas diffusion layers. J Electrochem Soc 159 F536-F544... 

Abstract The polymer electrolyte fuel cell (PEFC) consists of disparate porous media microstructures, e.g. catalyst layer, microporous layer, gas diffusion layer, as the key components for achieving the desired performance attributes. The microstmcture-transport interactions are of paramount importance to the performance and durability of the PEFC. In this chapter, a systematic description of the stochastic micro structure reconstmction techniques along with the numerical methods to estimate effective transport properties and to study the influence of the porous structures on the underlying transport behavior is presented. 

Akey performance limitation in the polymer electrolyte fuel cell (PEFC) originates from the multiple, coupled and competing, transport interactions in the constituent porous components. The suboptimal transport behavior resulting from the underlying complex and multifunctional microstmctures in the catalyst layer (CL), gas diffusion layer (GDL) and microporous layer (MPL) leads to water and thermal management issues and undesirable performance loss. Therefore, it is imperative to understand the profoimd influence of the disparate porous microstmctures on the transport characteristics. In this chapter, we highhght the stochastic microstmcture reconstmction technique and direct transport simulation in the CL, GDL and MPL porous stmctmes in order to estimate the effective transport properties and imderstand the microstmctural impact on the imderlying transport behavior in the PEFC. 

Quantitative estimation of the effective material properties and constitutive closure relations is of paramount importance for high-fidelity macroscopic, voliune-averaged computational models deployed in the PEFC performance simulations. The microstractural heterogeneity (e g. morphology, pore connectivity, pore size distribution, anisotropy) inherent in the PEFC components (CL, GDL, MPL) poses a profound impact on the effective transport properties, such as effective diffusivity in the unsaturated and partially saturated (e g. pore blockage by liquid water)... 

Percolation theory represents the most advanced and most widely used statistical framework to describe structural correlations and effective transport properties of random heterogeneous media (Sahimi, 2003 Torquato, 2002). Here, briefly described are the basic concepts of this theory (Sahimi, 2003 Stauffer and Aharony, 1994) and its application to catalyst layers in PEFCs. 

Percolation relations for effective transport properties use the lowest order of stmc-tural information for the layer, namely, its composition. In principle, more detailed structural models could be devised to incorporate higher-order structural information, that is, pore and particle shapes, and correlations in distributions of distinct components. Random network simulations, variational principles, and effective medium theory could be involved to study these relations (Milton, 2002 Torquato, 2002). 

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