22,887 research outputs found
Modelling of large-scale dense gasâsolid bubbling fluidised beds using a novel discrete bubble model
In order to model the complex hydrodynamic phenomena prevailing in industrial scale gasâsolid bubbling fluidised bed reactors and especially the macro-scale emulsion phase circulation patterns induced by bubbleâbubble interactions and bubble coalescence, a discrete bubble model (DBM) has been developed. In the DBM, the (larger) bubbles are modelled as discrete elements and are tracked individually during their rise through the emulsion phase, which is considered as a continuum. The DBM, originally developed for the description of gasâliquid flows, has been adapted to cope with bubbles with a diameter larger than the size of an Eulerian cell, which is required in view of the large bubble size distribution at higher gas flow rates. Moreover, a new drag model for a single bubble rising in a fluidised bed derived from empirical correlations has been implemented, as well as a simple model to account for bubble coalescence and break-up. The strong advantage of the DBM compared to other models previously reported in the literature for the description of large-scale fluidised beds is that it fully accounts for the two-way coupling between the bubbles and the emulsion phase, which enables direct computation of the emulsion phase velocity profiles. Comparison of the results of simulations ignoring bubble coalescence and simulations taking bubble coalescence properly into account demonstrated the significant effect of bubble coalescence on the large-scale circulation patterns prevailing in bubbling fluidised beds. The simulation results for the lateral profiles of the visible bubble flow rate have been compared qualitatively with experimental results reported by Werther [1974. Influence of the bed diameter on the hydrodynamics of gas fluidized beds. A.I.Ch.E. Symposium Series 70(141), 53â62]. The effect of the superficial gas velocity on the velocity and porosity profiles has been studied. In general, it can be concluded that the DBM is able to capture the salient features of the hydrodynamics of bubbling fluidised beds. However, further research is required to improve the closure equations for the bubble behaviour, bubbleâbubble interactions and bubble coalescence and break-up to enable a complete quantitative description
The XDEM Multi-physics and Multi-scale Simulation Technology: Review on DEM-CFD Coupling, Methodology and Engineering Applications
The XDEM multi-physics and multi-scale simulation platform roots in the Ex-
tended Discrete Element Method (XDEM) and is being developed at the In- stitute
of Computational Engineering at the University of Luxembourg. The platform is
an advanced multi- physics simulation technology that combines flexibility and
versatility to establish the next generation of multi-physics and multi-scale
simulation tools. For this purpose the simulation framework relies on coupling
various predictive tools based on both an Eulerian and Lagrangian approach.
Eulerian approaches represent the wide field of continuum models while the
Lagrange approach is perfectly suited to characterise discrete phases. Thus,
continuum models include classical simulation tools such as Computa- tional
Fluid Dynamics (CFD) or Finite Element Analysis (FEA) while an ex- tended
configuration of the classical Discrete Element Method (DEM) addresses the
discrete e.g. particulate phase. Apart from predicting the trajectories of
individual particles, XDEM extends the application to estimating the thermo-
dynamic state of each particle by advanced and optimised algorithms. The
thermodynamic state may include temperature and species distributions due to
chemical reaction and external heat sources. Hence, coupling these extended
features with either CFD or FEA opens up a wide range of applications as
diverse as pharmaceutical industry e.g. drug production, agriculture food and
processing industry, mining, construction and agricultural machinery, metals
manufacturing, energy production and systems biology
Liquid spreading in trickle-bed reactors: Experiments and numerical simulations using Eulerian--Eulerian two-fluid approach
Liquid spreading in gas-liquid concurrent trickle-bed reactors is simulated
using an Eulerian twofluid CFD approach. In order to propose a model that
describes exhaustively all interaction forces acting on each fluid phase with
an emphasis on dispersion mechanisms, a discussion of closure laws available in
the literature is proposed. Liquid dispersion is recognized to result from two
main mechanisms: capillary and mechanical (Attou and Ferschneider, 2000;
Lappalainen et al., 2009- The proposed model is then implemented in two
trickle-bed configurations matching with two experimental set ups: In the first
configuration, simulations on a 2D axisymmetric geometry are considered and the
model is validated upon a new set of experimental data. Overall pressure drop
and liquid distribution obtained from -ray tomography are provided for
different geometrical and operating conditions. In the second configuration, a
3D simulation is considered and the model is compared to experimental liquid
flux patterns at the bed outlet. A sensitivity analysis of liquid spreading to
bed geometrical characteristics (void-fraction and particles diameter) as well
as to gas and liquid flow rates is proposed. The model is shown to achieve very
good agreement with experimental data and to predict, accurately, tendencies of
liquid spreading for various geometrical bed characteristics and/or phases
flow-rates
1-dimensional modelling and simulation of the calcium looping process
Calcium looping is an emerging technology for post-combustion carbon dioxide capture and storage in development. In this study, a 1-dimensional dynamical model for the calcium looping process was developed. The
model was tested against a laboratory scale 30 kW test rig at INCAR-CSIC, Spain. The study concentrated on steady-state simulations of the carbonator reactor. Capture efficiency and reactor temperature profile were compared against experimental data. First results showed good agreement between the experimental observations and simulations
Gas-liquid hydrodynamics in Taylor Flows with complex liquids
UniversitĂĄ di Pisa
FacoltĂĄ di Ingegneria
Dipartimento di Ingegneria Chimica, Chimica Industriale e Scienza dei Materiali
Relazione di tirocinio
in Ingegneria Chimica
Gas-liquid hydrodynamics in Taylor Flows with complex liquids
Il candidato:
Federico Alberini
Il relatore: Prof. Elisabetta Brunazzi
Controrelatore:
Prof. Ing. Roberto Mauri
Anno Accademico 2009-201
Intensification of Ester Production in a Continuous Reactor
Numerous continuous intensified reactors are now accessible on the market that offer enhanced thermal performances in a continuous reactor. Such reactors are then particularly suited to fast and highly exothermic reactions. In this paper, the ability to also manage a slow and equilibrated system, the methyl acetate esterification reaction, on condition of intensification in terms of design and operating conditions is presented. To achieve this purpose, a new kinetics model has been developed and validated from experiments carried out in a lab scale batch reactor.
Implemented in a simulation framework, this model leads to an intensified design of the reactor and the associated operating conditions. All this intensification methodology has been supported and validated by experimental studies
Simulation of the influence of hydrophones used for the characterization of pressure field distribution in low frequency, high power ultrasonic reactor vessels
This paper describes the use of a finite element (FE) modeling approach to investigate the influence of different hydrophone designs in laboratory scale reactor vessels. In addition to conventional PVDF membrane and piezoceramic hydrophone, the performance of a conceptual array hydrophone, comprising a 2D matrix of PVDF array elements, will be simulated. The FE modeling concentrates on two issues: the disturbance to the field through the introduction of each hydrophone configuration; and their suitability and response to measuring non-linear effects. To simplify the model the ultrasonic transducer is not directly represented. Here, a pressure loading function is used as the excitation technique, with a sawtooth waveform applied for the simulation of the non-linear detection capability of each hydrophone configuration. The results from the simulation programme demonstrate that the dynamics of the reactor vessel are critical to optimize the performance of the ultrasonic system. In addition, the introduction of a hydrophone alters the wave propagation, and hence the field distribution beyond a given probe location. Nevertheless, the spatial pressure distribution at the active area remains reasonably accurate if within the useable bandwidth of the device. Accordingly, the broadband nature of the membrane device is suited to operation in both the linear and non-linear regimes, with the PVDF array membrane device offering a fast, convenient measurement of the pressure field distribution for industrial applications
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