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Full-Text Articles in Engineering
On Velocity-Conditioned Scalar Mixing In Homogeneous Turbulence, Rodney O. Fox
On Velocity-Conditioned Scalar Mixing In Homogeneous Turbulence, Rodney O. Fox
Rodney O. Fox
Scalar mixing models are required to modelturbulent molecular mixing in full probability density function (pdf) simulations of turbulent reacting flows. Despite the existence of direct numerical simulation (DNS) data suggesting the contrary, most scalar mixing models assume that molecular mixing is independent of the instantaneous velocity, i.e., 〈D∇2φ|V,ψ〉=〈D∇2φ|ψ〉. Since in a joint velocity, composition pdf calculation the velocity is known, this assumption is unnecessary and leads to a lack of local isotropy in the scalar field. Moreover, since velocity conditioning offers a numerically tractable approach for including the effects of local anisotropy and mean velocity gradients on scalar mixing, it …
Oscillatory Dynamics In A Heterogeneous Surface Reaction: Breakdown Of The Mean-Field Approximation, R. Dennis Vigil, Frank T. Willmore
Oscillatory Dynamics In A Heterogeneous Surface Reaction: Breakdown Of The Mean-Field Approximation, R. Dennis Vigil, Frank T. Willmore
R. Dennis Vigil
Hierarchical mean-field rate equations and lattice-gas simulations were developed to elucidate the effects of the breakdown of the mean-field approximation for a model heterogeneous chemical oscillator that represents a simple extension of the well-known monomer-dimer surface reaction model. The bifurcation structure of the reaction kinetics depends sensitively on the details of surface transport processes, and the oscillatory behavior exhibited by the site approximation rate equations is not generally robust with respect to spatial correlations.
On The Importance Of Chain Reptation In Models Of Dissolution Of Glassy Polymers, Balaji Narasimhan, Nikolaos A. Peppas
On The Importance Of Chain Reptation In Models Of Dissolution Of Glassy Polymers, Balaji Narasimhan, Nikolaos A. Peppas
Balaji Narasimhan
Polymer dissolution was described by chain reptation incorporated into penetrant transport. The penetrant concentration field was divided into three regimes which delineate three different transport processes. Solvent penetration through the polymer was modeled to occur as a consequence of a diffusional flux and an osmotic pressure contribution. Species momentum balances were written that coupled the polymer viscoelastic behavior with the transport mechanism. Transport in the second penetrant concentration regime was modeled to occur in a diffusion boundary layer adjacent to the rubbery-solvent interface, where a Smoluchowski type diffusion equation was obtained. The disentanglement rate of the polymer is given by …