Computational Modelling of Mesophase Pitches’ Shear Rheology

ABSTRACTFlow modelling of mesophase pitches is performed using a previously formulated mesoscopic viscoelastic rheological theory [1] that takes into account flow-induced texture transformations. A complete extra stress tensor equation is developed from first principles for liquid crystal materials under non-homogeneous arbitrary flow. Predictions for a given simple shear flow, under non-homogeneous conditions, for the apparent shear viscosity and first normal stress differences are presented. The rheological functions are explained using macroscopic orientation effects, which predominate at low shear rates. The predicted normal stress differences and apparent shear viscosity are in agreement with experimental measurements.</jats:p

Defect Nucleation and Annihilation in Sheared Polymeric Liquid Crystals

ABSTRACTShear–induced nucleation and annihilation of topological defects due to hydrodynamic instability in nematic liquid crystals is a phenomenon of both scientific interest and practical importance. We use a complete generalized non-linear second order tensor Landau-de Gennes model that takes into account short range order elasticity, long-range elasticity and viscous effects, to simulate the nucleation and annihilation of twist inversion walls in flow-aligning nematic polymers subjected to shear flow. Shearing a homogeneous nematic sample perpendicular to the director results in an linear instability that maybe symmetric at low shear rates, and antisymmetric at higher shear rates. At even higher shear rates the onset of nonlinearities results in the nucleation of a parallel array of twist inversion walls, such that asymmetry prevails. By increasing the shear rate the following director symmetry transition cascade is observed: symmetric → antisymmetric → asymmetric → symmetric. The nucleation of the parallel array of twist inversion walls in the asymmetric mode is due to the degeneracy in reorientation towards the shear plane. The annihilation of twist walls is mediated by twist waves along the velocity gradient direction. Twist walls annihilate by three mechanisms: wall-wall annihilations, wall-wall coalescence, and wall-bounding surface coalescence. The annihilation rate increases with increasing shear rate and at sufficiently high rates the layered structure is replaced by a homogeneously aligned system. The role of short range and long range elasticity on defect nucleation and annihilation is characterized in terms of the Deborah and Ericksen numbers. Close form solutions to approximated equations are used to explain the numerical results of the full Landau-de Gennes equations of nematodynamics.</jats:p

Population balance modeling for the growth of agglomerates via primary and secondary agglomeration in gas-fluidized beds

A population balance model is developed for the growth of pre-formed agglomerates in a fluidized bed with several agglomeration mechanisms considered. Primary agglomeration takes place when dry particles collide with the wet surface of the original agglomerate. Secondary agglomeration occurs either by wet particles colliding with the dry surface of agglomerates, or by liquid migration to the top layer of an agglomerate and subsequent collisions with dry particles. The properties of the liquid binder determine the dominant mechanism. The new agglomeration model for high-and low-viscosity liquid binders is implemented in ANSYS FLUENT commercial software. Model predictions agree reasonably well with available experimental results without altering the previously published parameters of the sub-models employed. It is found that the viscosity of the liquid binder and surface asperities play notable roles in the agglomeration. Surface asperities are especially important when asperity heights are of the same order as the thickness of the liquid film. (C) 2017 Published by Elsevier B.V

Morphological changes of the liver parenchyma after embolization of the right branch of the portal vein

To determine the morphological changes of the parenchyma of the right and the left lobe of the liver after embolization of the right branch of the portal vein. Material and Methods: Embolization of the right branch of the portal vein was performed in 15 patients. All patients by CT of the abdomen future liver remnant (FLR) sizes were less than 30% (from 17 to 27%) in average - 19,78%. Before and after the procedure was performed a biopsy of the right and the left lobe of the liver, followed by assessment of morphological changes of the parenchyma. Results: The volume of the liver after portoembolizatsii on average increased by 12,5%, the volume of the left lobe of the liver increased by an average of 41,7%. Expected hypertrophy of the left lobe of the liver is not obtained in one patient (6,66%). In the remaining 14 patients (93,3%) the size of the left lobe of the liver, and increased by more than 30%. Radical surgical treatment performed 9 (60%) patients. Study of histological changes after hepatic parenchyma portoembolization showed that hypertrophy of the contralateral lobe of the liver, occurs due to hypertrophy of the existing and the emergence of new, functionally active hepatocytes. The use of embolization of the right branch of the portal vein in most cases allows for vicarious hypertrophy of the left lobe of the liver due to hypertrophy of the existing and the emergence of new, functionally active hepatocytes.</jats:p