Liste des publications

Nombre total de résultats : 541
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Computational study of droplet breakup in a trapped channel configurationusing volume of fluid method

T. CHEKIFI  (2018)

Computational Fluid Dynamics is performed to numerically investigate the droplet breakup of water in oil intrapped channel configuration. The volume-of-fluid (VOF) method based the commercial code FLUENT isadopted to track the interface. Two designs are suggested to study the effect of flow conditions parameters andouter channel size on the droplet breakup mode, droplet generation frequency and size. As a function of thevelocity ratio, droplets are formed in two modes, dripping mode: droplets were generated closed to the nozzle, itwas identified at low capillary number (Ca<0.005) and jetting mode: droplets were produced after a long jet,where the capillary number Ca varies from 0.01 to 0.025. The numerical results indicated the collection channeldiameter plays potential role in the determination of droplet size and droplet generation frequency, the shearforces excreted by the continuous phase on the dispersed thread are reduced in the wider model leading to havedroplets much bigger than the narrow model, the latter produced small droplets due the high shear stressgenerated in the confinement region. Furthermore, the droplet frequency and size are found to be stronglydependent on the capillary velocity ratio. However, increasing the flow velocity ratio in both models leadsdroplets to be generated in high frequency, while the droplet length was decreasing. This work also demonstratesthat the VOF method is an effective way to simulate the droplets breakup in trapped channel geometry. Voir les détails

Mots clés : T. Chekifi

Computational Investigation of Droplets Behaviour inside Passive Microfluidic Oscillator

T. CHEKIFI, B. dennai, R. Khelfaoui  (2017)

Recently, modeling immiscible fluids such as oil and water have been a classical research topic. Droplet-based microfluidics presents a unique platform for mixing, reaction, separation, dispersion of drops and many other functions. In this paper, we suggest a numerical CFD study of microfluidic oscillator with two different lengths of feedback loop. In order to produce simultaneous droplets of gasoil on water, a typical geometry that includes double T-junction is connected to the fluidic oscillator. Droplets production is computed by volume-of-fluid method (VOF). Flow oscillations of droplets were triggered by the Coanda effect of jet flow. The aim of work is to get a high oscillation frequency in the output of this passive device, the influence of hydrodynamics and physics parameters on the droplets frequency in the output of our microsystem is also investigated, the computational results show that, the length of feedback loop, operating pressure and interfacial tension have a significant effect on the droplets dynamic inside microfluidic oscillator. Across the range of low Reynold number, the droplets generation and its dynamics have been accurately controlled by adjusting applying pressure ratio of two phases. Voir les détails

Mots clés : Droplet, microfluidics, fluidic oscillator, CFD and VOF (volume of fluid method).

Enhancement of photoelectrochemical and optical characteristics using a TiO2 nanoparticles interlayer in MEH-PPV heterojunction devices

F Habelhames, M Girtan, A Manole, L LAMIRI, W Zerguine, B Nessark  (2012)

In this work, MEH-PPV+TiO 2 composite material was prepared by incorporation of titanium oxide nonoparticles (TiO 2) into poly[2-methoxy-5-(2′-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) polymer matrix and deposited by spin coating on glass and indium thin oxide (ITO) substrates. The absorbance of various MEH-PPV composites incorporating different concentrations of TiO 2 nanoparticles shows that addition of TiO 2 improves absorption of the composites. TiO 2 and the conjugated polymer have absorption in the UV and visible regions, respectively. As a result, the composite has slightly broader absorption. In addition, absorption of the composite shows that the polymer induces a certain structuring, as evidenced by the presence of fine structures. The effect of inserting a TiO 2 nanoparticles interlayer in the MEH-PPV polymer heterojunction device on the photoelectrochemical and optical characteristics of the device has been studied. The modified device (MEH-PPV+TiO 2) shows improved photocurrent density characteristics, and increased with TiO 2 concentration. The study showed that the presence of inorganic semiconductor nonoparticles (TiO 2) in polymer film improves the optical and the photovoltaic properties of MEH-PPV, and was designed to explore new approaches to improve light-collection efficiency in polymer photovoltaic. Voir les détails

Mots clés : Hybrid composite materials, MEH-PPV, morphology, photocurrent

Growth and characterization of electrodeposited Cu2O thin films

S. Laidoudi, A.Y. Bioud, A. Azizi, G. Schmerber, J. Bartringer, S. Barre, A. Dinia  (2013)

This work demonstrates the electrodeposition of cuprous oxide (Cu2O) thin films onto a fluorine-doped tin oxide (FTO)-coated conducting glass substrates from Cu(II) sulfate solution with C6H8O7 chelating agent. During cyclic voltammetry experiences, the potential interval where the electrodeposition of Cu2O is carried out was established. The thin films were obtained potentiostatically and were characterized through different techniques. From the Mott–Schottky measurements, the flat-band potential and the acceptor density for the Cu2O thin films are determined. All the films showed a p-type semiconductor character with a carrier density varying between 2.41 × 1018 cm−3 and 5.38 × 1018 cm−3. This little difference is attributed to the increase of the stoichiometric defects in the films with the deposition potential. Atomic force microscopy analysis showed that the Cu2O thin films obtained at high potential are more homogenous in appearance and present lower crystallites size. X-ray Voir les détails

Mots clés : Cu2O, electrodeposition, Mott–Schottky, optical properties, Thin films, XRD

Electrochemical and spectroscopic characterization of poly (bithiophene + 2-methylfuran) copolymer.

Leila LAMIRI, Belkacem Nessark, Farid Habelhames, Lakhdar Sibous  (2017)

In this work, Poly(bithiophene + 2-methylfuran) copolymer is successfully achieved by an electrochemical polymerization of two monomers, bithiophene and 2-methylfuran in acetonitrile containing lithium perchlorate. The resultant copolymer was characterized via cyclic voltammetry, impedance spectroscopy, UV-visible, scanning electron microscope, conductivity and photocurrent measurements. The cyclic voltammetry study showed two redox couples characteristic of Poly (bithiophene + 2-methylfuran) copolymer. The impedance spectroscopy study revealed that the resistance of the copolymer ?lm increases with the addition of 2-methylfuran. The photocurrent measurement showed good photoelectrochemical properties, making this copolymer an ideal candidate for photovoltaic cell applications. Voir les détails

Mots clés : Electrochemical polymerization, copolymer, polybithiophene, poly2-methylfuran, morphology, photo-electrochemical properties.

Electrochemical behavior, characterization and corrosion protection properties of poly(bithiophene + 2-methylfuran) copolymer coatings on A304 stainless steel

Leila LAMIRI, Belkacem  (2018)

Polybithiophene (PBTh), poly(2-methylfuran) (PMeFu) and poly(bithiophene + 2-methylfuran) noted poly(BTh + MeFu) copolymer films were synthesized by electrochemical deposition on 304-stainless steel, from an acetonitrile (ACN) solution containing 10−2 m bithiophene, 10−2 m 2-methylfuran and 10−1 m lithium perchlorate (LiClO4), by cyclic voltammetry (CV) between 0 V and 2 V vs. SCE, with a scan rate of 50 mV · s−1. The copolymers coated were studied in a corrosive sulfuric acid medium (H2SO4 1 N) using the potensiodynamique polarization method and the electrochemical impedance spectroscopy (EIS). Copolymers coated characterization was performed using scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The polarization curves show that the copolymer film formed on A304, shifts the corrosion potential towards more positive potentials. The presence of the poly(BTh + MeFu) improves the corrosion resistance of the metal in a corrosive medium, H2SO4. This protection against corrosion is caused by the barrier effect of the layer of copolymer, which covers the surface of the A304 stainless steel against the aggressive ions of the corrosive medium. Voir les détails

Mots clés : 2-methylfuran, bithiophene, copolymers, protection against corrosion, stainless steel.

Metallic Coating for Carbon Fiber Reinforced Polymer Matrix Composite Substrate

Amine REZZOUG, Said ABDI, Nadjet BOUHELAL, Ismail DAOUD  (2016)

This paper investigates the application of metallic coatings on high fiber volume fraction polymer matrix composites. For the grip of the metallic layer, a method of modifying the surface of the composite by introducing a mixture of copper and steel powder filler powders which can reduce the impact of thermal spray particles. The powder was introduced to the surface at the time of the forming. Arc spray was used to project the zinc coating layer.The substrate was grit blasted to avoid poor adherence. The porosity, microstructure, and morphology of layers are characterized by optical microscopy, SEM and image analysis. The samples were studied also in terms of hardness and erosion resistance. This investigation did not reveal any visible evidence damage to the substrates. The hardness of zinc layer was about 25.94 MPa and the porosity was around 6.70 percent. The erosion test showed that the zinc coating improves the resistance to erosion. Based on the results obtained, we can conclude that thermal spraying allows the production of protective coating on PMC. Zinc coating has been identified as acompatible material with the substrate. The filler powders layer protects the substrate from the impact of hot particles and allows avoiding the rupture of brittle carbon fibers. Voir les détails

Mots clés : Arc spray, coating, composite, erosion

Thermal spray metallisation of carbon fibre reinforced polymer composites Effect of top surface modification on coating adhesion and mechanical properties


Thermal Spray TS processes are used to enhance the surface properties of Polymer Matrix Composites. However, poor adhesion and mechanical degradation are usually experienced. The main objective of this work is to investigate the effect of the modification of the top surface of Carbon Fibre Reinforced Polymer CFRP substrate on the TS deposition of metallic coatings. CFRP composite panels were manufactured with different upper layers I pure epoxy overflow layer, II pure copper powder filler layer, III mixture copper and stainless steel powder filler layer, and IV aluminium mesh layer. The top layers of the CFRP substrates were manufactured during the forming process. Arc Spray, one of the TS processes, was used to deposit zinc coating onto the manufactured CFRP panels. The substrates were sandblasted before the TS process to enhance the adhesion of the deposited zinc to the substrate. The quality of the coatings including adhesion and mechanical properties was investigated using tensile adhesion and bending test, respectively. The porosity, microstructure, morphology and surface fracture of the metallised CFRP coupons were characterized using optical and electronical microscopy techniques. The results obtained revealed that pure epoxy top layer did not resist to sandblasting prior to TS process, contrary to the substrates with fillers and mesh top layer. Moreover, the aluminium based mesh layer improved the adhesion strength by about 50 percent. Bending test results indicated that coating on CFRP composites decreased their mechanical properties. However, the use of a metallic mesh layer reduced the degradation effect of spraying. Voir les détails

Mots clés : CFRP composite, Zn coating, Arc spray, Filler layer, Adhesion strength

Experimental and numerical analysis of mode?I interlaminar fractureof composite pipes

F M L.REKBI, M.Hecini, A.KHECHAI  (2018)

A common industrial production process for composites is filament winding, widely used for the production of axially symmetriccomponents. In these composite components, delamination is a predominant failure mechanism. The current workfocuses on investigating experimentally the effect of the initial crack and fiber bridging length on the mode-I delaminationresistance curve (R-curve) behavior of various double cantilever beam (DCB) specimens. For this purpose, the magnitudesof initiation and propagation fracture toughness (GIC-init and GIC-prop) and the compliance C are calculated. DCB specimenswith a stacking sequence of [± 50]6 and various initial crack lengths of a0 = 33, 37, 59 and 70 mm are manufactured from areal composite pipe using filament winding process. In order to evaluate the critical energy release rate in mode-I, variousfracture tests are conducted on these specimens. The greatest bridging zone length dues to good penetration of two adjacentlayers of the delamination interface. Moreover, the results indicate that the fiber bridging length has a significant effect onthe GIC and the largest value of fiber bridging causes a large fracture toughness value. Finally, numerical simulations areperformed using finite element (FE) method and GIC-init measurements obtained experimentally are compared to the numericalfindings. The numerical displacements and GIC-init, calculated from the numerical displacements, are found to be in goodagreement compared to the experimental results. Voir les détails

Mots clés : Filament wound composite, Critical energy release rate, Propagation energy release rate, DCB specimen, Fiber bridging

Numerical study of parameters affecting pressure drop of power-law fluid in horizontal annulus for laminar and turbulent flows

Hicham Ferroudji, Ahmed Hadjadj, Ahmed HADDAD, Titus Ntow Ofei  (2019)

Efficient hydraulics program of oil and gas wells has a crucial role for the optimization of drilling process. In the present paper, a numerical study of power-law fluid flow through concentric (E = 0.0) and eccentric annulus (E = 0.3, E = 0.6 and E = 0.9) was performed for both laminar and turbulent flow regimes utilizing a finite volume method. The effects of inner pipe rotation, flow behavior index and diameter ratio on the pressure drop were studied; furthermore, the appearance and development of secondary flow as well as its impact on the pressure drop gradient were evaluated. Results indicated that the increment of the inner pipe rotation from 0 to 400 rpm is found to decrease pressure drop gradient for laminar flow in concentric annulus while a negligible effect is observed for turbulent flow. The beginning of secondary flow formation in the wide region part of the eccentric annulus (E = 0.6) induces an increase of 9% and a slight increase in pressure drop gradient for laminar and turbulent flow, respectively. On the other hand, the variation of the flow behavior index and diameter ratio from low to high values caused a dramatic increase in the pressure drop. Streamlines in the annulus showed that the secondary flow is mainly induced by eccentricity of the inner pipe where both high values of diameter ratio and low values of flow behavior index tend to prevent the secondary flow to appear. Voir les détails

Mots clés : Computational fluid dynamics (CFD) Power-law fluid Pressure drop Secondary flow