Polymer Flow Through Porous Media: Numerical Prediction of the Contribution of Slip to the Apparent Viscosity.

The flow of polymer solutions in porous media is often described using Darcy’s law with an apparent viscosity capturing the observed thinning or thickening effects. While the macroscale form is well accepted, the fundamentals of the pore-scale mechanisms, their link with the apparent viscosity, and their relative influence are still a matter of debate. Besides the complex effects associated with the rheology of the bulk fluid, the flow is also deeply influenced by the mechanisms occurring close to the solid/liquid interface, where polymer molecules can arrange and interact in a complex manner. In this paper, we focus on a repulsive mechanism, where polymer molecules are pushed away from the interface, yielding a so-called depletion layer in the vicinity of the wall. This depletion layer acts as a lubricating film that may be represented by an effective slip boundary condition. Here, our goal is to provide a simple mean to evaluate the contribution of this slip effect to the apparent viscosity. To do so, we solve the pore-scale flow numerically in idealized porous media with a slip length evaluated analytically in a tube. Besides its simplicity, the advantage of our approach is also that it captures relatively well the apparent viscosity obtained from core-flood experiments, using only a limited number of inputs. Therefore, it may be useful in many applications to rapidly estimate the influence of the depletion layer effect over the macroscale flow and its relative contribution compared to other phenomena, such as non-Newtonian effects

Quantitative imaging of concentrated suspensions under flow

We review recent advances in imaging the flow of concentrated suspensions, focussing on the use of confocal microscopy to obtain time-resolved information on the single-particle level in these systems. After motivating the need for quantitative (confocal) imaging in suspension rheology, we briefly describe the particles, sample environments, microscopy tools and analysis algorithms needed to perform this kind of experiments. The second part of the review focusses on microscopic aspects of the flow of concentrated model hard-sphere-like suspensions, and the relation to non-linear rheological phenomena such as yielding, shear localization, wall slip and shear-induced ordering. Both Brownian and non-Brownian systems will be described. We show how quantitative imaging can improve our understanding of the connection between microscopic dynamics and bulk flow.Comment: Review on imaging hard-sphere suspensions, incl summary of methodology. Submitted for special volume 'High Solid Dispersions' ed. M. Cloitre, Vol. xx of 'Advances and Polymer Science' (Springer, Berlin, 2009); 22 pages, 16 fig

Investigation of the Effect of Different Heat Treatments on Wear Behavior of AA7075 Alloy

In this study, wear behavior of AA7075 alloy applied different ageing heat treatments is examined. During each ageing heat treatment, the relevant samples are processed with solid solution at 485°C for 2 h. After the quenching process, ageing processes were performed. The T6 heat treatment is applied at 120°C for 24 h. Along the re-ageing heat treatment process, samples undergone the T6 process is taken into the solid solution at 120°C once more and aged at the given temperature for 24 h. In the high temperature heat treatment process, the samples are pre-precipitated at 445°C for 30 min and then taken to ageing process at 120°C for 24 h. Wear tests are carried out at 1 m/s constant sliding speed and under 20 N load along four different sliding distances (300-1200 m). The amount of precipitation observed from the structure exhibits difference at the second phase with respect to applied ageing heat treatment. Finest precipitation particle is observed with T6 heat treatment and the coarse precipitation is with the high temperature heat treatment. Furthermore, a relationship is determined between dimension of the second phase precipitation and hardness values

3D Finite Element Simulation of Processing of Generalized Newtonian Fluids in Counter-rotating and Tangential TSE and Die Combination

Abstract A full three-dimensional finite element analysis of the nonisothermal flow of generalized non-Newtonian fluids in counter-rotating tangential twin screw extruder is presented. Previous studies of the simulation of processing in tangential twin screw extruders have focused solely on the twin screw extruder, whereas here the coupled flow and heat transfer occurring in the integrated geometry of the extruder, connected to a die are considered. The FEM based numerical simulation of the coupled momentum-mass-energy conservation equations allowed the determination of the effects of some of the important system parameters, including the power law index and the staggering angle of the screws, on the pumping and pressurization capability of the extruder and the associated degree of fill in the extruder.</jats:p

Degree of Mixing Analyses of Concentrated Suspensions by Electron Probe and X-Ray Diffraction

Abstract Two x-ray based techniques involving energy-dispersive analysis and diffractometry were introduced to the analyses of the degree of mixedness, i.e. the “goodness of mixing” of concentrated suspensions. A hydroxyl terminated polybutadene matrix was mixed with aluminum and ammonium sulfate. In the analysis, the ratio of the relative volume fractions of the two solid components was used as the basis of the analytical evaluation. Both characterization techniques are capable of determining the relative volume fraction of the two solid components as a representative measurement of the distributive mixing efficiency and both are sensitive to the scale of examination. The introduced techniques should be useful in the better definition of the degree of mixedness as well as in resolving differences in mixing efficiencies of various mixers used in processing of concentrated suspensions.</jats:p

Simulation of Co-Rotating Twin Screw Extrusion Process Subject to Pressure-Dependent Wall Slip at Barrel and Screw Surfaces: 3D FEM Analysis for Combinations of Forward- and Reverse-Conveying Screw Elements

Abstract Mathematical modeling and simulation of the coupled flow, deformation, heat and mass transfer, and rate of reactions occurring in the twin screw extruder allow the optimization of process parameters and the screw and barrel geometries. In mathematical modeling of the twin screw extrusion process the conventional flow boundary condition at the screw and barrel walls is the no-slip condition. However, most complex fluids, including polymers, polymeric suspensions and blends, exhibit wall slip, with the slip behavior depending on the intrinsic properties of the materials being processed, the operating conditions, the geometries of the barrel, screw and the die, and the properties of the solid surfaces. Typically, the slip velocity is specified to be a function of temperature, stress condition at the wall and the materials of construction. However, recent investigations have further revealed that the wall slip behavior can also be significantly affected by pressure. With an objective of considering the effects of wall slip on the dynamics of twin screw extrusion, fully-intermeshing co-rotating twin screw extrusion of a concentrated suspension is analyzed using three-dimensional finite element method, FEM, subject to the wall slip boundary condition. The wall slip boundary condition is first applied systematically to barrel and screw surfaces individually followed by the application of wall slip to both surfaces simultaneously. In an integrated fashion both the forward-conveying (pressure-generating) and reverse-conveying (pressure-losing) screw sections are considered. The effects of pressure on wall slip are also analyzed and elucidated.</jats:p