by Naillon et al., Physical Review Fluids, 2019, 4, 053301
Particles migrate in the transverse direction of the flow due to the existence of normal stress anisotropy in weakly viscoelastic liquids. We test the ability of theoretical predictions to predict the transverse velocity migration of particles in a confined Poiseuille flow according to the viscoelastic constitutive parameters of dilute polymer solutions. First, we carefully characterize the viscoelastic properties of two families of dilute polymer solutions at various concentrations using shear rheometry and capillary breakup experiments. Second, we develop a specific three-dimensional particle tracking velocimetry method to measure with a high accuracy the dynamics of particles focusing in flow for Weissenberg numbers Wi ranging from10-2 and 10-1, and particle confinement β of 0.1 and 0.2. The results show unambiguously that the migration velocity scales as Wiβ2, as expected theoretically for weakly elastic flows of an Oldroyd-B liquid. We conclude that classic constitutive viscoelastic laws are relevant to predict particle migration in dilute polymer solutions whereas detailed analysis of our results reveals that theoretical models overestimate by a few tenths the efficiency of particle focusing.Learn more
Thursday 4th of April 2019 from 2 pm to 3pm, salle de conférences (RDC) du bâtiment NANOBIO DCM, 570 rue de la chimie, 38610 GIERES
Verifiable modelling of physical processing in the various compartments of the gut
Summary - I discuss the rheological and physiological difficulties in predicting mixing and propulsion of digesta within the intestinal lumen. I also describe the use of spatiotemporal mapping to quantify movements in ex vivo segments of the intestinal wall in real time, the use of this data in computational fluid dynamic models to predict flow and mixing, and the concurrent use of dye marker excretion profiles to validate the models. Further I give an example of how discrepancies between the two can highlight previously unknown sources of mixing. Finally I discuss recent work of the stomach.
Flows and interfaces at micro scales : the gut and the microcapsule, Clément de Loubens.