Self-Structuring of Granular material under Capillary Bulldozing

An experimental observation of the structuring of a granular suspension under the progress of a gas/liquid meniscus in a narrow tube is reported here. The granular material is moved and compactifies as a growing accumulation front. The frictional interaction with the confining walls increases until the pore capillary entry pressure is reached. The gas then penetrates the clogged granular packing and a further accumulation front is formed at the far side of the plug. This cyclic process continues until the gas/liquid interface reaches the tube’s outlet, leaving a trail of plugs in the tube. Such 1D pattern formation belongs to a larger family of patterning dynamics observed in 2D Hele-Shaw geometry. The cylindrical geometry considered here provides an ideal case for a theoretical modelling for forced granular matter oscillating between a long frictional phase and a sudden viscous fluidization

X-ray micro-tomography and pore network modeling of single-phase fixed-bed reactors.

A three-dimensional (3D) irregular and unstructured pore network was built using local topological and geometrical properties of an isometric bead pack imaged by means of a high-resolution X-ray computed micro-tomography technique. A pore network model was developed to analyze the 3D laminar/inertial(non-Darcy) flows at the mesoscopic (pore level) and macroscopic (after ensemble-averaging) levels. The non-linear laminar flow signatures were captured at the mesoscale on the basis of analogies with contraction and expansion friction losses. The model provided remarkably good predictions of macroscopic frictional loss gradient in Darcy and non-Darcy regimes with clear-cut demarcation using channel-based Reynolds number statistics. It was also able to differentiate contributions due to pore and channel linear losses, and contraction/expansion quadratic losses. Macroscopic mechanical dispersion was analyzed in terms of retroflow channels, and transverse and longitudinal Péclet numbers. The model qualitatively retrieved the Péclet-Reynolds scaling law expected for heterogeneous networks with predominance of mechanical dispersion. Advocated in watermark is the potential of pore network modeling to build a posteriori constitutive relations for the closures of the more conventional macroscopic Euler approaches to capture more realistically single-phase flow phenomena in fixed-bed reactor applications in chemical engineering

Modeling and simulation of drying operations in PVC powder production line: Experimental and theoretical study of drying kinetics on particle scale

An experimental method to determine drying kinetic at a particle scale and a pneumatic dryer model are presented. The particle scale kinetics were obtained by immersion of a fixed mass of wet PVC particles (cake) in a batch dense fluidized bed containing inert hot particles (glass bead). It appears clearly that the PVC drying is controlled by a competition between internal and external transfers. The drying kinetic was described by a shrinking core type model and integrated in a one-dimensional steady-state model simulating a pneumatic dryer. A two-phase continuum model was used to describe the steady-state flow of a diluted dispersed phase (wet PVC powder) and a continuous phase (humid air) through dryer. Themodel takes into account the convective heat,mass and momentumtransfers. The numerical results are compared with industrial experimental data. The results show that the inlet temperature is the most important parameter in the operation