Papers by Rebei Bel Fdhila
... reference ». Author: Sandberg, Jan (Mälardalen University, Department of Public Technology). ... more ... reference ». Author: Sandberg, Jan (Mälardalen University, Department of Public Technology). Sand, Ulf. Bel Fdhila, Rebei. Title: Numerical simulation of fouling on super-heater tube walls. Department: Mälardalen University, Department of Public Technology. Publication type: ...
Iron Steel Technology, 2009
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A two step reaction model for the pyrolysis process of a dry cylindrical pine wood particle, expo... more A two step reaction model for the pyrolysis process of a dry cylindrical pine wood particle, exposed to a hot gas flow field, has been developed adding user defined subroutines to the commercial computational fluid dynamics code CFX 4.4. The wood ...
Renewable and Sustainable Energy Reviews, 2014
ABSTRACT Mixing in an anaerobic digester keeps the solids in suspension and homogenizes the incom... more ABSTRACT Mixing in an anaerobic digester keeps the solids in suspension and homogenizes the incoming feed with the active microbial community of the digester content. Experimental investigations have shown that the mixing mode and mixing intensity have direct effects on the biogas yield even though there are conflicting views on mixing design. This review analyzes and presents different methods to evaluate the mixing in a digester (chemical and radioactive tracers and laboratory analysis), tools for digester design (computational fluid dynamics and kinetic modeling) and current research on the effects of mixing on the anaerobic digestion process. Empirical data on experiments comparing different mixing regimes have been reviewed from both a technical and microbial standpoint with a focus both on full scale digesters and in lab-scale evaluations. Lower mixing intensity or uneven mixing in the anaerobic digestion process can be beneficial during the startup phase to allow for methanogenic biomass growth and alleviate process instability problems. Intermittent mixing has been shown to be able to yield a similar gas production as continuous mixing but with the possibility to reduce the maintenance and energy demands of the process. Problems often experienced with experimental design include the effect of mixing on the solids retention time, and measurement of steady state gas production because of startup instabilities. Further research should be aimed at studying the effects of mixing on a chemical and microbial level and on the different stages of anaerobic digestion (hydrolysis, acidogenesis, acetogenesis and methanogenesis). The focus should be on the effects of mixing on a multiple stage digestion process and also finding new methods to evaluate the effects of mixing in the one stage digestion process rather than evaluating a wider range of mixing modes, intensities and substrates.
Proceedings of International Symposium on Convective Heat and Mass Transfer in Sustainable Energy, 2009
Energy Procedia, 2014
Heatsinks have long been used for cooling of electronic components to maintain them under the max... more Heatsinks have long been used for cooling of electronic components to maintain them under the maximum allowed operational temperature. Forced air cooling with heatsink is suitable and enough efficient for low power applications cooling. Varieties of heatsinks are proposed by specialized industries to cool different kinds of electronic components. However, in most cases we need the appropriate heatsink to each specific case and particularly under transient heat generation that can be caused by many electronic or power electronic devices. The heat transport and evacuation process is tightly related to the heatsink performance. This paper examines the cooling characteristics of a heatsink used in a specific industrial application. The investigation is performed using Computational Fluid Dynamics (CFD) and the heat transfer performance of the heatsink is mainly determined by the Nusselt number which can be calculated from the numerical results. Analysis and discussion of the numerical results and especially the level of Nusselt number obtained at the contact surface of the heatsink with the surrounding cooling air allow optimization of the industrial heatsink shape to meet the requested cooling performance. Comparison of cooling performance before and after heatsink design optimization showed noticeable improvement.
Physics of Fluids, 1996
. In English. Experiments and numerical simulations of rising spherical bubbles in quiescent surf... more . In English. Experiments and numerical simulations of rising spherical bubbles in quiescent surfactant solutions are presented. The rise velocities versus the concentration in the bulk are measured using three surfactants, Triton X 1oo , Brij3o and SDS for different bubble sizes, between 0.4 and 1 mm equivalent radius. We also present a brief description of the finite-difference numerical method developed to solve the full Navier-Stokes equations around the contaminated bubble for Reynolds numbers ranging from 50 to 200. The distributions of the tangential velocity, the vorticity, the pressure and the surfactant concentration on the bubble surface are calculated. The numerical technique described here is similar to the one used by Ryskin and Lea1 for a clean surface but does not take into account the deformation. However, we consider the influence of a gradient of surface tension due to the presence of a surfactant. Coupled with the surfactant transport equations this procedure provides all the flow quantities at the interface. The bubble rise velocity versus the bulk concentration is calculated by incorporating this numerical procedure in an iterative process accounting for the changes in the bulk concentration. The computed results are compared with our measurements. (after Authors)
International Journal of Green Energy, 2006
This paper describes a mathematical model for the pyrolysis of a small dry pine wood cylinder. Th... more This paper describes a mathematical model for the pyrolysis of a small dry pine wood cylinder. The computational domain is axisymmetric and involves the heating chamber, with the wood cylinder vertically situated in the centre of the chamber. The model simulates the ...
International journal of …, 2006
The present investigation involves measurements and theories on the mechanisms of the forming of ... more The present investigation involves measurements and theories on the mechanisms of the forming of deposit layers on super-heater tubes in a biomass-fired CFD boiler. The deposit layer thickness and the sootblowing frequency effect on the super-heaters heat transfer are the main subject of the study that has been conducted over a 3-year period. The measurements show a deposit growth rate on the super-heaters of approximately 4 g m À2 h À1 . The distribution of the deposit material varies significantly between the windward and the leeward side of the tubes, with the thickest layers on the windward side. Further down stream of the first super-heater, the fouling problem on the super-heater and re-heater tubes are not so severe. A theoretical model shows that a deposit layer of 20 mm will decrease the heat transfer rate of the first super-heater by nearly 40%. The soot-blowing system shows a strong positive effect on the heat transfer rate of the super-heater a few hours after a soot-blowing sequence has been completed. However in the long run, the varied soot-blowing frequency does not have a significant influence on the deposit layer growth rate.
Chemical Engineering Communications, 1996
This paper in memory of Pr Dukler summarizes a set of experiments on bubbly shear flows carried o... more This paper in memory of Pr Dukler summarizes a set of experiments on bubbly shear flows carried out by two groups, in Toulouse and in Lyon. Homogeneous shear flows, plane mixing layer, boundary layer on a flat plate and sudden area expansion have been investigated, for low and moderate void fraction. Measurements of mean liquid velocity show that the main
International Journal of Green Energy, 2006
The present investigation involves theories, simulations and experiments on deposit layers on sup... more The present investigation involves theories, simulations and experiments on deposit layers on super-heater tubes in a circulating fluidised bed in Västerås in Sweden. Simulation of particle trajectories in the vicinity of two super-heater tubes is conducted in a Eulerian-Lagrangian mode for the flue gas and the ash particles from the combustion process. Particle impingements on the tubes are investigated for
La Houille …, 1996
Le régime d'écoulement diphasique à bulles se rencontre dans de nombreuses applications indu... more Le régime d'écoulement diphasique à bulles se rencontre dans de nombreuses applications industrielles et a été étudié intensivement durant ces dernières années, Cepen-dant, la compréhension des phénomènes physiques impli-qués dans ce régime est encore trop limitée pour ...
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Papers by Rebei Bel Fdhila