https://www.eng.buffalo.edu/Courses/ce435/MasaroZhu99.pdf

Physical models of diffusion for polymer solutions, gels and solids

Transport phenomena through polymeric systems

Concentration of polychlorinated biphenyls (PCBs) in beached resin pellets: Variability among individual particles and regional differences

http://www.geo.brown.edu/geocourses/geo292/papers/old/Coussot-and-Meunier1996debrisflows.pdf

Recognition, classification and mechanical description of debris flows

Most concentrated colloidal suspensions such as cement, drilling fluids, paints, muds, etc., have been considered until now thixotropic fluids with a flow curve of an ideal yield stress fluid. We start by showing from inclined plane tests, intended to determine the yield stress, that these systems in fact exhibit peculiar properties. Unlike ideal yield stress fluids, they stop flowing abruptly below a critical stress, and start flowing at a high velocity beyond a critical stress, which in addition increases with the time of preliminary rest. In order to clarify these features we carried out a complete set of rheometrical tests with a model fluid, a bentonite suspension. Our results show that under controlled stress, in some cases after significant flow, there is bifurcation of the behavior towards either stoppage or rapid shear, depending on the relative values of the imposed and critical stresses. As an immediate consequence, we find that no (homogeneous) steady state flows at a shear rate below a critical value can be obtained. These results can be qualitatively predicted by a simple theoretical model that assumes that the viscosity of the material results from the competition between aging and shear rejuvenation, associated to, respectively, the organization or disorganization of the network of particle interactions. This shows that the flow curve in the steady state of concentrated colloidal suspensions and, more generally, of structured fluids, is strongly affected by their thixotropy.

/pdf/viscosity-bifurcation-in-thixotropic-yielding-fluids-8kwttfun10.pdf

Viscosity bifurcation in thixotropic, yielding fluids

Extensive experimental results on the free fall of a range of non-spherical particles such as square bars, cylinders, spheres and crushed rock chips in Newtonian, inelastic, viscoelastic and Boger fluids are presented. It is demonstrated that the use of a volume equivalent sphere diameter in addition to a shape factor provides an adequate approximation for the non-sphericity of particles used in this study. The applicability of two rheological models, namely, the power-law and the Carreau viscosity model has been examined in representing the drag coefficient results. Appropriate predictive expressions of the drag coefficient as a function of the particle Reynolds number and the Deborah number, encompassing wide ranges of rheological and kinematic conditions, are presented.



On presente une grande quantite de resultats experimentaux sur la chute libre de particules non spheriques telles que des barres, des cylindres, des spheres et des debris de pierre dans des fluides de Boger, newtoniens, non elastiques et viscoelastiques. On demontre que le fait d'utiliser un diametre de sphere equivalent au volume en plus d'un facteur de forme donne une approximation convenable de la non-sphericite des particules utilisees dans cette etude. L'applicabilite de deux modeles rheologiques, soit le modele de loi de puissance et le modele de Carreau, a ete examinee pour la representation des resultats de coefficient de trainee. On presente des expressions de prediction adequates pour le coefficient de trainee en fonction du nombre de Reynolds et du nombre de Deborah des particules, et ce pour une vaste gamme de conditions rheologiques et cinematiques.

Drag on non-spherical particles in non-newtonian fluids

Within the general category of so called generalized Newtonian fluids, there exists a class of materials which do not deform until the applied shear stress exceeds a critical value called yield stress Conversely, such a material behaves like a solid as long as the shear stress is less than the yield stress This class of materials is called viscoplastic fluids The question whether the true yield stress exists or not is indeed far from settled (1), but the notion of a yield stress has proved to be quite useful in practice in describing the steady shear rheological behaviour of a range of materials especially of particulate suspensions Consequently, yield stress appears as a parameter in all constitutive relations (which purport to describe the steady shear behaviour of viscoplastic materials), and its evaluation is important before an engineering flow problem can be solved Conversely, there are some simple hydrodynamic situations which allow the value of the yield stress to be extracted from macroscopi

Flow of viscoplastic fluids on an inclined plane: evaluation of yield stress

This communication reports (photographically) on the shapes of bubbles of different gases in several Newtonian and polymer solutions, encompassing a wide range of rheological behavior. Effects of a surface active agent are mentioned and bubble coalescence in viscoelastic solutions is visualized.

A photographic study of shapes of bubbles and coalescence in non-Newtonian polymer solutions

The effect of penetrant diffusion on the barrier properties of PVC geomembranes have been determined for the following organic environmental contaminants: benzene, dichloromethane, and trichloroethylene. The membranes experienced swelling to a degree which depends on the type of penetrant used. Some dissolution may occur, and in general we are dealing with Case II transport. The experimental work was performed with an ASTM-cell, a Cahn balance, and an in-house built gravity (G-) cell. Those instruments generated comparable data on breakthrough times. The obtained diffusion coefficients as well as the breakthrough times obeyed an Arrhenius-type relation over the temperature range studied. Liquid sorption of the various penetrants modified the geomembrane structure. Membrane surface pretreatment with different contaminants influences the subsequent transport of organic penetrants through PVC geomembranes. That is to say: the induced swelling, as result of membrane contact with one penetrant, is likely to alter the system free volume, allowing for a different rate of mass transport for subsequent penetrants.

Sorption and permeation of organic environmental contaminants through PVC geomembranes

A recent technique, developed to measure yield stress has here also been used to determine the elastic modulus of a suspension. Temperature effects have been measured.

D. De Kee

Papers

Drag on non-spherical particles in non-newtonian fluids

Flow of viscoplastic fluids on an inclined plane: evaluation of yield stress

A photographic study of shapes of bubbles and coalescence in non-Newtonian polymer solutions

Sorption and permeation of organic environmental contaminants through PVC geomembranes

Elastic modulus and yield stress of suspensions