Influence of through-flow on linear pattern formation properties in binary mixture convection

We investigate how a horizontal plane Poiseuille shear flow changes linear convection properties in binary fluid layers heated from below. The full linear field equations are solved with a shooting method for realistic top and bottom boundary conditions. Through-flow induced changes of the bifurcation thresholds (stability boundaries) for different types of convective solutions are deter- mined in the control parameter space spanned by Rayleigh number, Soret coupling (positive as well as negative), and through-flow Reynolds number. We elucidate the through-flow induced lifting of the Hopf symmetry degeneracy of left and right traveling waves in mixtures with negative Soret coupling. Finally we determine with a saddle point analysis of the complex dispersion relation of the field equations over the complex wave number plane the borders between absolute and convective instabilities for different types of perturbations in comparison with the appropriate Ginzburg-Landau amplitude equation approximation. PACS:47.20.-k,47.20.Bp, 47.15.-x,47.54.+rComment: 19 pages, 15 Postscript figure

Influence of the Dufour effect on convection in binary gas mixtures

Linear and nonlinear properties of convection in binary fluid layers heated from below are investigated, in particular for gas parameters. A Galerkin approximation for realistic boundary conditions that describes stationary and oscillatory convection in the form of straight parallel rolls is used to determine the influence of the Dufour effect on the bifurcation behaviour of convective flow intensity, vertical heat current, and concentration mixing. The Dufour--induced changes in the bifurcation topology and the existence regimes of stationary and traveling wave convection are elucidated. To check the validity of the Galerkin results we compare with finite--difference numerical simulations of the full hydrodynamical field equations. Furthermore, we report on the scaling behaviour of linear properties of the stationary instability.Comment: 14 pages and 10 figures as uuencoded Postscript file (using uufiles

Influence of the Soret effect on convection of binary fluids

Convection in horizontal layers of binary fluids heated from below and in particular the influence of the Soret effect on the bifurcation properties of extended stationary and traveling patterns that occur for negative Soret coupling is investigated theoretically. The fixed points corresponding to these two convection structures are determined for realistic boundary conditions with a many mode Galerkin scheme for temperature and concentration and an accurate one mode truncation of the velocity field. This solution procedure yields the stable and unstable solutions for all stationary and traveling patterns so that complete phase diagrams for the different convection types in typical binary liquid mixtures can easily be computed. Also the transition from weakly to strongly nonlinear states can be analyzed in detail. An investigation of the concentration current and of the relevance of its constituents shows the way for a simplification of the mode representation of temperature and concentration field as well as for an analytically manageable few mode description.Comment: 30 pages, 12 figure

Onset of convection in binary liquid mixtures: improved Galerkin approximations

Two approximate mode truncations (one for nonzero and one for zero Lewis number) are presented in order to describe the onset of convention of a binary mixture between realistic no slip impermeable horizontal boundaries. Stability thresholds as well as the Hopf frequency are determined analytically. The outcomes are compared with earlier approximations and the exact result obtained numerically.Deux modèles approchés (l'un valable lorsque le nombre de Lewis L est différent de zéro, l'autre lorsque $L=0$) sont présentés en vue de décrire les conditions d'apparition de la convection dans un mélange binaire lorsque les bords horizontaux sont rigides et imperméables. Les seuils de stabilité ainsi que la fréquence de Hopf sont déterminés analytiquement. Les deux modèles sont comparés avec les approximations précédentes et avec la solution exacte obtenue numériquement

A model for the prediction of the morphology of immiscible blends of polymers

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Predicting the Young's modulus and the impact strength of immiscible polyolefin blends

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Enhanced electromagnetic interference shielding effectiveness of polypropylene/hybrid metallic fillers composite materials by coalescence-driven guided electrical percolation

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