Phenomenological transport

A Generalized Phenomenological Transport Model and Simple Consequences... 

Divisek et al. presented a similar two-phase, two-dimensional model of DMFC. Two-phase flow and capillary effects in backing layers were considered using a quantitatively different but qualitatively similar function of capillary pressure vs liquid saturation. In practice, this capillary pressure function must be experimentally obtained for realistic DMFC backing materials in a methanol solution. Note that methanol in the anode solution significantly alters the interfacial tension characteristics. In addition, Divisek et al. developed detailed, multistep reaction models for both ORR and methanol oxidation as well as used the Stefan—Maxwell formulation for gas diffusion. Murgia et al. described a one-dimensional, two-phase, multicomponent steady-state model based on phenomenological transport equations for the catalyst layer, diffusion layer, and polymer membrane for a liquid-feed DMFC. 

In order to investigate the relation between the phenomenological transport coefficients Ljj and Z) we formulate for the isotope (tracer) diffusion of A in A... 

B. Interpretation of L-t plot and D from Phenomenological Transport Model... 

To conclude this section, it may be interesting to mention what was concluded recently in (17) on the future of the free-volume diffusion models . .. However, phenomenological transport models based on free-volume concepts are likely to become obsolete during the coming decade, due to the development of computational techniques of simulating polymer microstructures . The development of such techniques and their results are discussed in Section 5.2. 

Phenomenological transport relationships can be developed even in the absence of any knowledge of the mechanisms of transport through the membrane or any information about the membrane structure.10 The basis of irreversible thermodynamics assumes that if the system is divided into small enough subsystems in which local equilibrium exists, thermodynamic equations can be written for the subsystems. 

A primary aim of theoretical work in this field is to obtain the phenomenological transport coefficients in terms of molecular scale processes and in terms of molecular parameters such as the intermolecular pair potential energy. Most of the work prior to 1946 rested on rather crude pictures of the liquid state, and various arbitrary assumptions were made as to the nature of the molecular scale transport processes taking place. Born and Green 3 20 21 and... 

Since the phenomenological transport coefficients can be represented in 2 x 2 matrix form for binary systems. 

This inequality in (26-11) stems from the fact that the determinant of the 2 x 2 matrix of phenomenological transport coefficients [, y] mnst be positive to ensure a positive-definite quadratic form for sq- The contribution from thermal Soret diffusion in the final expression for Ja (see equations 25-76 and 25-77) provides a definition of P in terms of the thermal diffusion coefficient kr and the temperature dependence of cpA-... 

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