Pilot-Scale Laboratory Instruction for ChE: the specific case of the Pilot-unit leading group

This paper presents an original approach for Chemical Engineering laboratory teaching that is currently applied at INP-ENSIACET (France). This approach, referred to as "pilot-unit leading group" is based on a partial management of the laboratories by the students themselves who become temporarily in charge of one specific laboratory. In addition to meeting the classical pedagogic requirements of the laboratories, this teaching method allows the students to actively experience technical project management

Growth limiting conditions and denitrification govern extent and frequency of volume detachment of biofilms

This study aims at evaluating the mechanisms of biofilm detachment with regard of the physical properties of the biofilm. Biofilms were developed in Couette–Taylor reactor under controlled hydrodynamic conditions and under different environmental growth conditions. Five different conditions were tested and lead to the formation of two aerobic heterotrophic biofilms (aeHB1 and aeHB2), a mixed autotrophic and heterotrophic biofilm (MAHB) and two anoxic heterotrophic biofilms (anHB1 and anHB2). Biofilm detachment was evaluated by monitoring the size of the detached particles (using light-scattering) as well as the biofilm physical properties (using CCD camera and image analysis). Results indicate that volume erosion of large biofilm particles with size ranging from 50 to 500 lm dominated the biomass loss for all biofilms. Surface erosion of small particles with size lower than 20 lm dominates biofilm detachment in number. The extent of the volume detachment events was governed by the size of the biofilm surface heterogeneities (i.e., the absolute biofilm roughness) but never impacted more than 80% of the mean biofilm thickness due to the highly cohesive basal layer. Anoxic biofilms were smoother and thinner than aerobic biofilms and thus associated with the detachment of smaller particles. Our results contradict the simplifying assumption of surface detachment that is considered in many biofilm models and suggest that discrete volume events should be considered

Multifluid Eulerian modeling of dense gas–solids fluidized bed hydrodynamics: Influence of the dissipation parameters

Computational fluid dynamic (CFD) models must be thoroughly validated before they can be used with confidence for designing fluidized bed reactors. In this study, validation data were collected from a fluidized bed of (Geldart's group B) alumina particles operated at different gas velocities involving two fluidization hydrodynamic regimes (bubbling and slugging). The bed expansion, height of bed fluctuations and frequency of fluctuations were measured from videos of the fluidized bed. The Eulerian–Eulerian two fluid model MFIX was used to simulate the experiments. Two different models for the particle stresses—Schaeffer [Syamlal, M., Rogers, W., O’Brien, T.J., 1993. MFIX documentation: theory guide. Technical Report DOE/METC-94/1004 (DE9400087), Morgantown Energy Technology Centre, Morgantown, West Virginia (can be downloaded from Multiphase Flow with Interphase eXchanges (MFIX) website left angle brackethttp://www.mfix.orgright-pointing angle bracket); Schaeffer, D.G., 1987. Instability in the evolution equations describing incompressible granular flow. Journal of Differential Equations 66, 61–74.] and Princeton [Srivastava, A., Sundaresan, S., 2003. Analysis of a frictional–kinetic model for gas–particle flow. Powder Technology 129(1–3), 72–85.] models—and different values of the restitution coefficient and internal angle of friction were evaluated. 3-D simulations are required for getting quantitative and qualitative agreement with experimental data. The results from the Princeton model are in better agreement with data than that from the Schaeffer model. Both free slip and Johnson–Jackson boundary conditions give nearly identical results. An increase in coefficient of restitution (e) from 0.8 to 1 leads to larger bed expansions and lower heights of fluctuations in the bubbling regime, whereas it leads to unchanged bed expansion and to a massive reduction in the height of fluctuations in the slugging regime. The angle of internal friction (φ) in the range 10–40ring operator does not affect the bed expansion, but its reduction significantly reduces the height of fluctuations

Silicon CVD on powders in fluidized bed: Experimental and multifluid Eulerian modelling study

The Computational Fluid Dynamics code MFIX was used for transient simulations of silicon Fluidized Bed Chemical Vapor Deposition (FBCVD) from silane (SiH4) on coarse alumina powders. FBCVD experiments were first performed to obtain a reference database for modelling. Experimental thermal profiles existing along the bed were considered in the model. 3D simulations provide better results than 2D ones and predict silane conversion rate with a mean deviation of 9% compared to experimental values. The model can predict the temporal and spatial evolutions of local void fractions, gas and particle velocities, species gas fractions and silicon deposition rate. We aim at mid term to model FBCVD treatments of submicronic powders in a vibrated reactor since we have performed experiments proving the efficacy of the process to treat submicronic particles

Dynamics of aggregate size and shape properties under sequenced flocculation in a turbulent Taylor-Couette reactor

This paper concerns experimental investigation of the sequenced flocculation of latex particles in a Taylor-Couette reactor. The aim of this work was to investigate the evolution of both the size and the shape of aggregates under sequenced hydrodynamics. A number of studies have focused on the evolution of the aggregate size or size distribution during steps of growth-breakage-regrowth, but aggregates generally experience steps of breakage-regrowth on repeated occasions in real operating conditions (passages near the impeller or during the transfer processes, for example). The experiments conducted in this work consisted thus of an alternation of six steps with alternately low and high shear rates under turbulent conditions. The particle size distributions were monitored throughout the sequencing, and the circularity and convexity (shape parameters) distributions were measured, enabling a more precise description of the entire floc population, rather than a fractal dimension. While the aggregate size distribution was clearly controlled by hydrodynamics, the shape distributions continuously evolved during the sequencing. The main new finding of our work notes the independence between the aggregate shape and hydrodynamics. Indeed, after multiples steps of breakage-regrowth, regardless of the aggregate size distribution and hydrodynamics, the aggregate shape seemed to reach a unique steady-state morphological distribution

CHEMEPASS – Innovative Tools to promote Chemical Engineering Mobility

CHEMEPASS – Innovative Tools to promote Chemical Engineering Mobilit

Morphological properties of flocs under turbulent break-up and restructuring processes

Bentonite flocculation was performed in a Taylor–Couette reactor coupled with an in situ method of image acquisition and analysis. A hydrodynamic sequencing is imposed to perform successive cycles of flocculation and breakage. Depending on the shear rate applied during the breakage step, one or two cycles are needed after the first flocculation step to recover a full reversibility on both size and shape factors. The breakup step produces flocculi that are the building blocks for the next. The re‐flocculation steps produce smaller sizes and more regular shapes than the initial growth step. The floc size is calibrated by the turbulence as the radius of gyration is close to the Kolmogorov microscale whereas the floc structure is determined by flocculi aggregates. An analysis of the change of the flocs morphology, despite of their diversity, can also be achieved thanks to some relevant moments of the distributions

GRAPE: A Stochastic Geometrical 3D Model for Aggregates of Particles With Tunable 2D Morphological Projected Properties

The main goal of this paper is to propose a method for the 3D morphological characterization of compact aggregates using 2D image analysis. The problem at hand is the 3D morphometric characterization of latex nanoparticle aggregates. The only available information is 2D projection images of these aggregates, one projection per aggregate. In this context, a method to estimate the 3D morphological characteristics of an aggregate such as the Volume, Surface Area or Solidity from a single projection is proposed. This method is based on a stochastic geometric model called GRAPE (Geometrical Random Aggregation of Particles Emulation) and requires some strong assumptions, and in particular prior estimation of the volume. The model is based on an iterative packing of spheres of identical radii. For each iteration, a fitting function allows to reach objectives corresponding to the desired 2D properties (Area, Perimeter, Aspect Ratio, ...). In order to implement the method, an optimization process must be performed on two parameters of the model: the radius of the elementary particles r and an overlapping distance di. As a validation, this process will be applied to synthetic aggregates, themselves generated from the GRAPE model, then to a population of 104 synthetic aggregates, and finally to 3D printed aggregates whose 3D morphological properties are known thanks to an STL file, and whose projected images have been produced using a morphogranulometer. The results obtained show an excellent approximation of 2D properties by the GRAPE model, and very good results for 3D properties, with less than 5% error on average and less than 2% error in most cases

Retour d'expérience sur un dispositif de Réflexivité et de Contextualisation en formation d'ingénieur par Apprentissage : RéCAp

International audienceRéCAp est un dispositif de problématisation permettant de mettre en lien les expériences professionnelles vécues en entreprise et les savoirs académiques dispensés dans les formations par apprentissage de Toulouse INP-ENSIACET. L’objectif de ce dispositif est double : (i) pour les élèves, il s’agit de les initier à une analyse réflexive de leurs activités et de leur positionnement en entreprise et de les accompagner dans la co-construction de leurs apprentissages à partir de la mise en relation des expériences en entreprise et des enseignements à l’école, (ii) pour les enseignants, il s’agit de leur donner l’opportunité de mieux contextualiser leurs enseignements et de mieux appréhender la notion de compétences au travers de situations authentique complexes. Par ailleurs, ce dispositif est suffisamment souple pour être adapté à différents contextes et il permet de relever le défi de la coopération via sa dimension collaborative tant au niveau des élèves que des enseignants

Fractal dimensions and morphological characteristics of aggregates formed in different physico-chemical and mechanical flocculation environments

Flocculation experiments were performed in a Taylor-Couette reactor in turbulent conditions characterized by the mean shear rate. A sequenced hydrodynamic protocol was applied which consists in low and high shear rates steps allowing to promote respectively aggregation and breakage processes. The particle size distribution and the 3D fractal dimension were determined on line by laser diffraction while morphological parameters were characterized off line using an automated microscope coupled with image processing. After a first aggregation-breakage cycle, the flocs formed by charge neutralization have smaller sizes than during the first aggregation step when the main aggregation mechanism is the charge neutralization whereas coarser but more resistant aggregates can be produced by bridging mechanism. During the flocculation process, high shear rates calibrate the flocs, creating small flocs having a size close to the Kolmogorov microscale. These small flocs serve as bricks to form larger flocs when lower shear rates are applied and a full reproducibility is observed after one or two cycles of the sequence depending on the aggregation mechanism. A clear correspondence was put in evidence between the shear rate conditions and the volume base mean size or fractal dimension of flocs. The morphological fractal dimension, as well as the fractal dimension derived from laser measurements, are in good agreement with the mean trend of the morphological data but cannot represent the whole diversity of floc sizes and shapes. The 3D surface base area and perimeter distributions appear as a promising tool allowing a deeper analysis of the impact of physico-chemical and shear conditions on aggregate properties during a flocculation proces