Diffusion-limited agglomeration

Belite agglomerations (a) Sharply outlined olusters (b) Diffuse limited olusters (o) Streaks (d) Spots Classification of belite agglomerations (Flofmanner, 1973)... 

Fiarticle morphology porosity, relative length scale of polymer and pore phases, particle shape, distribution of phases in high-impact polypropylene Interphase heat and mass transfer phenomena Intraphase heat and mass transfer phenomena Observed kinetics, rate limiting steps Phase equilibrium, monomer sorption and desorption in polymer phase, diffusion Fbrticle agglomeration Micromixi ng... 

Diffusion-limited aggregation of particles also yields fractal agglomerates that have scale symmetry within wide cutoff limits. 

Electrode Kinetic and Mass Transfer for Fuel Cell Reactions For the reaction occurring inside a porous three-dimensional catalyst layer, a thin-film flooded agglomerate model has been developed [149, 150] to describe the potential-current behavior as a function of reaction kinetics and reactant diffusion. For simplicity, if the kinetic parameters, such as flie exchange current density and diffusion limiting current density, can be defined as apparent parameters, the corresponding Butler-Volmer and mass diffusion relationships can be obtained [134]. For an H2/air (O2) fuel cell, considering bofli the electrode kinetic and the mass transfer, the i-rj relationships of the fuel cell electrode reactions within flie catalyst layer can be expressed as Equations 1.130 and 1.131, respectively, based on Equation 1.122. The i-rj relationship of the catalyzed cathode reaction wifliin the catalyst layer is... 

For negligible oxygen diffusion limitations, an integral expression for flie effectiveness factor of ideal spherical agglomerates was found,... 

Fluid-Bed Processes. For the very exothermic and pore diffusion-limited synthesis reaction, a fluid-bed mode of operation would seem ideal on account of the feasibility of high heat transfer coefficients and small catalyst particles. However, the presence of relatively heavy compounds in the product spectrum may cause deposition of these compounds on the catalyst, leading to agglomeration of particles and fluidization problems. 

Factors Effi and Eff2 are correction factors for pure kinetic current density owing to diffusion limitation in the agglomerate and in the electrolyte layers. These factors are expressed as... 

The equations used in these models are primarily those described above. Mainly, the diffusion equation with reaction is used (e.g., eq 56). For the flooded-agglomerate models, diffusion across the electrolyte film is included, along with the use of equilibrium for the dissolved gas concentration in the electrolyte. These models were able to match the experimental findings such as the doubling of the Tafel slope due to mass-transport limitations. The equations are amenable to analytic solution mainly because of the assumption of first-order reaction with Tafel kinetics, which means that eq 13 and not eq 15 must be used for the kinetic expression. The different equations and limiting cases are described in the literature models as well as elsewhere. 

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