Unite de Recherche Materiaux

Gafsa, Tunisia

Unite de Recherche Materiaux

Gafsa, Tunisia
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Braham A.,Unite de recherche Materiaux | Braham A.,Tunisian National Institute of Applied Sciences and Technology | Lachiri Z.,SiRF | Lachiri Z.,Tunisian National Institute of Applied Sciences and Technology
International Review of Electrical Engineering | Year: 2010

In induction machines, motor current signature analysis has been tested in many industrial cases with good results. However, this method does not always achieve successfully results to detect broken-rotor-bar under variable load torque. Recent advances on signal processing techniques have provided more powerful tools for faults diagnosis. This paper proposes a novel approach based on Power Spectrum Density estimation (PSD) to diagnose and detect broken-rotor-bar faults in induction motor under different levels of load. This paper also analyses three different spectral decomposition methods applied to induction machine stator current, namely Welch, Burg and Multiple Signal Classification (MUSIC). Based on different power spectral estimation concepts, the frequency resolution, variance and detection capability are different from each other according to the set of parameters used. The proposed methodology aims to determine which spectral estimate method best suited for implementation in an automated system for fault detection. Also, the PSD estimate is used for feature extraction and aims at identifying the descriptors that show high variability between different classes and thus would help distinguishing between them. Various scenarios are examined using data sets of stator current signals from experiments under different load, and the results are compared to obtain the best performance for automated process. © 2010 Praise Worthy Prize S.r.l. - All rights reserved.


Mejri I.,Unite de Recherche Materiaux | Mahmoudi A.,Unite de Recherche Materiaux
Chemical Engineering Research and Design | Year: 2015

This paper examines the natural convection in an open cavity with a sinusoidal thermal boundary condition. The cavity is filled with a water-Al2O3 nanofluid and subjected to a magnetic field. Lattice Boltzmann method (LBM) is applied to solve the coupled equations of flow and temperature fields. This study has been carried out for the pertinent parameters in the following ranges: Rayleigh number of the base fluid, Ra=103 to 106, Hartmann number varied from Ha=0 to 60, the phase deviation (γ=0, π/4, π/2, 3π/4 and π) and the solid volume fraction of nanoparticles between ϕ=0 and 6%. Results show that the heat transfer rate decreases with the increase of Hartmann number and increases with the rise of Rayleigh number. At Ha=30 and Ra=103 to 105, for all phase deviations the addition of nanoparticles increases heat transfer rate. Also, at low Rayleigh number (Ra≤104) the highest heat transfer rate is obtained for γ=π/2. © 2015 The Institution of Chemical Engineers.


Mabrouki J.,Unite de Recherche Materiaux | Abbassi M.A.,Unite de Recherche Materiaux | Guedri K.,University of Umm Al - Qura | Omri A.,Unite de Recherche Materiaux | Jeguirim M.,CNRS Mulhouse Institute of Materials Science
Fuel | Year: 2015

Abstract The main purpose of this present work is to optimize the biofuel production from the fast pyrolysis of three palm oil residues, namely palm shell (PS), empty fruit bunch (EFB) and mesocarp fiber (MF). Hence, a biofuel process is simulated using SuperPro Designer (SPD) software. The simulation includes pretreatment, fast pyrolysis, product collection, and upgrading sections. The developed SPD model was validated firstly with published data of the fast pyrolysis of wood oak in fluidized bed reactor. Secondly, the influence of the operating conditions such as pyrolysis reactor temperature and residence time on the fast pyrolysis of the different residues was examined. The obtained results indicate that temperature at 550 C is suitable for obtaining a maximum liquid yield. Moreover, it was found that 0.5 s is the optimized residence time to maximize this liquid yield. Above the optimum residence time, an increase in the gas fraction and a decrease of the bio-oil and char fractions are observed. Comparison of the different residues indicates that the higher yield of liquid fraction was obtained from the EFB and MF while pyrolysis of the PS produced a higher yield of char. These product yields were strongly correlated to the biomass polymer components. The obtained correlation was in agreement with the products yields found in literature for various biomass sources. The developed model provides very useful information about different conditions of pyrolysis for oil palm residues and product yields. Moreover, the model can be generalized and help to assist in the optimization of the fast pyrolysis process of different biomass without performing heavy experimental investigations. Such model will contribute strongly to the intensification and the improvement of the biomass fast pyrolysis. © 2015 Elsevier Ltd.


Mejri I.,Unite de Recherche Materiaux | Mahmoudi A.,Unite de Recherche Materiaux
Fluid Dynamics and Materials Processing | Year: 2015

This paper examines natural convection in an open cavity with a sinusoidal thermal boundary condition. The cavity is filled with a water-Al2O3 nanofluid and subjected to a magnetic field. The Lattice Boltzmann method (LBM) is applied to solve the coupled equations of flow and temperature. The study has been carried out considering parameters in the following ranges: Rayleigh number of the base fluid, Ra = 103 to 106, Hartmann number varied from Ha = 0 to 60, phase deviation (γ = 0,π=4,π=2, 3π=4 and π) and solid volume fraction of nanoparticles between ø= 0 and 6%. Results show that the heat transfer rate decreases with the Hartmann number and increases with Rayleigh number. At Ha = 30 and Ra = 103-105, for all phase deviations the addition of nanoparticles increases the heat transfer rate. Also, at low Rayleigh number (Ra≤ 104) the highest heat transfer rate is obtained for γ = π=2. © 2015 Tech Science Press.


Mahmoudi A.,Unite de Recherche Materiaux | Mejri I.,Unite de Recherche Materiaux
International Journal of Heat and Technology | Year: 2015

In this paper, the lattice Boltzmann method (LBM) is proposed as a potential solver for one-dimensional heat and mass transfer for isothermal carbonization of wood particles. To check the validity of this method, the LBM results are compared with the published résults and a good agreement is obtained. The LBM model is also tested for different operating conditions (reactor temperature and particle size) and for different types of wood particle to study the evolution of the local temperature and mass loss inside the wood particle.


Mejri I.,Unite de Recherche Materiaux | Mahmoudi A.,Unite de Recherche Materiaux | Abbassi M.A.,Unite de Recherche Materiaux | Omri A.,Unite de Recherche Materiaux
Alexandria Engineering Journal | Year: 2016

This paper presents a numerical study of natural convection in a triangular cavity filled with water. The horizontal wall is hot, the vertical wall is cold and the inclined wall is insulated. Lattice Boltzmann method (LBM) is applied to solve the coupled equations of flow and temperature fields. This study has been carried out for the pertinent parameters in the following ranges: Rayleigh number varied from Ra =103 to 106 and the inclination angle between Φ=0° and 315°. The effects of Rayleigh numbers and inclination angle on the streamlines, isotherms, Nusselt number are investigated. Results show that the heat transfer rate increases with the increase of Rayleigh number. In addition it is observed that the lower heat transfer rate is obtained for Φ=135°; however, the highest heat transfer is achieved at Φ=0°. The inclination angle greatly influences the heat transfer rate depending on the Rayleigh number. © 2016 Faculty of Engineering, Alexandria University.


Mahmoudi A.,Unite de Recherche Materiaux | Mejri I.,Unite de Recherche Materiaux | Omri A.,Unite de Recherche Materiaux
International Journal of Heat and Technology | Year: 2016

This paper presents a numerical study of natural convection cooling of water-Al2O3 nanofluid by two heat sinks vertically attached to the horizontal walls of a cavity subjected to a magnetic field. The left wall is hot, the right and the horizontal walls are insulated. Lattice Boltzmann method (LBM) is applied to solve the coupled equations of flow and temperature fields. This study has been carried out for the pertinent parameters in the following ranges: Rayleigh number of the base fluid, Ra = 103 to 105, Hartmann number varied from Ha = 0 to 60 and the solid volume fraction of nanoparticles between φ = 0 and 6%. In order to investigate the effect of heat sinks location, three different configurations of heat sinks are considered. Results show that the heat sinks positions greatly influence the heat transfer rate depending on the Hartmann number, Rayleigh number and solid volume fraction of nanoparticles.


Mahmoudi A.,Unite de Recherche Materiaux | Mejri I.,Unite de Recherche Materiaux | Omri A.,Unite de Recherche Materiaux
Physica A: Statistical Mechanics and its Applications | Year: 2016

This paper presents a numerical study of natural convection cooling of water-Al2 O3 nanofluid by two heat sinks vertically attached to the horizontal walls of a cavity subjected to a magnetic field. The left wall is hot, the right wall is cold, while the horizontal walls are insulated. Lattice Boltzmann method (LBM) is applied to solve the coupled equations of flow and temperature fields. This study has been carried out for the pertinent parameters in the following ranges: Rayleigh number of the base fluid, Ra=103 to 105, Hartmann number varied from Ha=0 to 60 and the solid volume fraction of nanoparticles between Pdbl=0 and 6%. In order to investigate the effect of heat sinks location, three different configurations of heat sinks are considered. The effects of Rayleigh numbers, Hartmann number and heat sinks location on the streamlines, isotherms, Nusselt number are investigated. Results show that the heat transfer rate decreases with the increase of Hartmann number and increases with the rise of Rayleigh number. In addition it is observed that the average Nusselt number increases linearly with the increase of the nanoparticles solid volume fraction. Also, results show that the heat sinks positions greatly influence the heat transfer rate depending on the Hartmann number, Rayleigh number and nanoparticle solid volume fraction. © 2016 Elsevier B.V. All rights reserved.


Ait-Djafer A.Z.,Equipe Plasma and Applications | Saoula N.,Equipe Plasma and Applications | Aknouche H.,Unite de Recherche Materiaux | Guedouar B.,Equipe Plasma and Applications | Madaoui N.,Equipe Plasma and Applications
Applied Surface Science | Year: 2015

The aim of this study is to investigate the influence of plasma deposition parameters (the pressure and the substrate bias voltage Vs) on structure, surface morphology, hardness and electrochemical behavior (studied by potentiodynamic polarization and optical microscope (OM) in aggressive environment NaCl 3.5 wt%) of TiAlN coatings. The coatings were deposited by reactive RF magnetron sputtering (13.56 MHz). They were carried out during 60 min and their thickness was approximately 1 μm. Structural analysis shown that TiAlN coating crystallized in cubic (fcc) and hexagonal (hcp) structure with orientations in (1 0 0), (1 1 1), (2 0 0), (1 1 0), (2 2 0) and (3 1 1) planes. The deposited coatings present maximum hardness (H = 25.75 GPa) and Young's modulus (E = 479.82 GPa) at low pressure (20 mTorr) and -60 V of negative substrate bias. Also, mechanical properties (H&E) were strongly influenced by coatings density and grain size. Electrochemical tests revealed that XC48 steel substrate covered with TiAlN coating exhibits excellent corrosion resistance. © 2015 Elsevier B.V. All rights reserved.


Aich W.,Unite de Recherche Materiaux | Hajri I.,University of Monastir | Omri A.,Unite de Recherche Materiaux
Thermal Science | Year: 2011

Natural convection heat transfer and fluid flow have been examined numerically using the control-volume finite-element method in an isosceles prismatic cavity, submitted to a uniform heat flux from below. Inclined sides are maintained isothermal and vertical walls are assumed to be perfect thermal insulators, without symmetry assumptions for the flow structure. The aim of the study is to examine a pitchfork bifurcation occurrence. Governing parameters on heat transfer and flow fields are the Rayleigh number and the aspect ratio of the enclosure. It has been found that the heated wall is not isothermal and the flow structure is sensitive to the aspect ratio. It is also found that heat transfer increases with increasing of Rayleigh number and decreases with increasing aspect ratio. The effects of aspect ratio become significant especially for higher values of Rayleigh number. Eventually the obtained results show that a pitchfork bifurcation occurs at a critical Rayleigh number, above which the symmetric solutions becomes unstable and asymmetric solutions are instead obtained.

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