Génie mécanique

Nombre total de résultats : 194
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Droplet Breakup Regime in a Cross-Junction Device with Lateral Obstacles

Tawfiq Chekifi  (2019)

Numerical simulation using Ansys Fluent code is performed, to investigate droplet generation in cross-junction based VOF method. Droplets of water are generated by the shear stress applied by continuous phase (oil), two configurations of cross-junction are suggested; the first is a simple model no modification is performed at the outer channel, while the second model is characterized by a lateral obstacle. we study the effect of velocity ratio, viscous parameter, interfacial tension, flow condition on droplet size and frequency, the effect of lateral obstacles on droplets generation is also focused and analysed. The numerical simulations showed that the velocity ratio and interfacial tension play a significant role in determining the droplet breakup and non-breakup. On the other side, the increase of flow rate ratio can be effectively used to decrease the droplet size. In addition, droplets produced in cross-junction with lateral obstacles are generally found to be larger than that produced with the first model. Moreover, the frequency of droplet production was increasing by increasing of flow rate ratio. The numerical results show very good agreements with previous numerical and experimental works for the growth of droplet breakup, size and frequency. Voir les détails

Mots clés : Water droplet, cross-junction, CFD, VOF, microchannel.

Effect of heat treatment on surface hardness and tribologicalbehavior of XC38 steel—approach by the experiments plans

Bourebia Mounira (2019)
Thèse de doctorat

This work aims at predicting the micro-hardness of XC38steel using the experiments plans as well asstudy of tribological behavior of thissteel. The heat treatments were considered by adopting thefactorial plans 22 methodology at two factors (temperature ‘T’ and holding time ‘t’), each at two levels(-1, +1). The results obtained allowed lead to a mathematical model predicting the micro-hardness‘Hv’ in every point of the study field. Moreover, the curves of the responses surfaces clearly show theinfluence of two factors studied (T, t) on ‘Hv’. Mechanical characterization of treated samples showedasignificant increase in the micro-hardness, which achieve to 76% for the treated sample at 850 °Cduring 2 h compared to untreated state. An investigation of wear tracks morphology shows thatfriction under a load of 10 N results in predominant adhesive wear, while a load of 2 N favorabrasive wear. Voir les détails

Mots clés : heat treatment, factorial plans, prediction, superficial hardness, tribological behavior

Thermo-physico-chemical and statistical mechanical properties of Washingtonian filifera new lignocellulosic fiber. Engineering Solid Mechanics

Djamel Edinne Gaagaiaa, Mustapha Bouakba, Abdelheq Layachi  (2019)

In this work, novel cellulosic fibers are extracted from Washingtonia Filifera (WF) plant using an environment-friendly technique. Morphological, Physico-chemical, thermal and mechanical properties are reported in this paper. Micro graphical SEM shows the presence of cells in the fiber.FTIR and XRD experimental analyzes show a cristinality index of 48.88%, and the WF fibers are found to be thermally stable until 201°C by using TGA and DTG thermographic analyzes with an appropriate activation energy of 72.46 kJ/mol, where Young modulus and tensile strength of strain were determined using tensile tests of single fiber at 2.17 GPa, 134 MPa and 26.55%, respectively. Mechanical properties are analyzed using a statistical method. Voir les détails

Mots clés : WF fibers, mechanical properties, FTIR, XRD, TGA, Statistical methods

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

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 presentpaper, a numerical study of power-law fluid flow through concentric (E = 0.0) and eccentric annulus (E = 0.3, E = 0.6 andE = 0.9) was performed for both laminar and turbulent flow regimes utilizing a finite volume method. The effects of innerpipe rotation, flow behavior index and diameter ratio on the pressure drop were studied; furthermore, the appearance anddevelopment of secondary flow as well as its impact on the pressure drop gradient were evaluated. Results indicated thatthe increment of the inner pipe rotation from 0 to 400 rpm is found to decrease pressure drop gradient for laminar flow inconcentric annulus while a negligible effect is observed for turbulent flow. The beginning of secondary flow formation in thewide region part of the eccentric annulus (E = 0.6) induces an increase of 9% and a slight increase in pressure drop gradientfor laminar and turbulent flow, respectively. On the other hand, the variation of the flow behavior index and diameter ratiofrom 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 flowbehavior 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

Microdrops in Microfluidic: Estimation of Geometrical Form

T. CHEKIFI, B. dennai, R. Khelfaoui  (2015)

Manipulation of small-sized liquid quantities is one of the key issues in technology, biology, chemistry and medicine.Where the increased surface-to-volume ratio making surface effects more dominant [42], which allows toreduce time of reaction and economies the costs of manufacturing products. The microdrop is a typical example of asmall-sized liquid quantity; that can be considered as samples, reagents and supplementary indicator to approach us inthe direction of reaction and the state of microdrop. The creation of reproducible in stable geometrical form ofmicrodrop makes a critical step during the manufacturing of microdrop. Pressure based manufacturing of microdropnowadays a common way to create reproducible and stable small-sized drops. Many geometrical form of microdropcan be generated in different techniques. Proofed that microdevices based on pressure based manufacturing ofmicrodrops has already been successfully implemented. This paper serves as a review of the most importantcontributions, in the development of the creation of reproducible and stable microdrops in the past decades. Besidesserving as a reverence for researchers in this area, this paper is also a resource for everybody who wants to identify theeasiest way to precise microdrops geometrical form for a particular application by simple analysis. Voir les détails

Mots clés : form, microdrop, description and theoretical analysis.

Numerical Simulation of Droplet Breakup, Splitting andSorting in a Microfluidic Device

T. CHEKIFI, B. dennai, R. Khelfaoui  (2015)

Droplet generation, splitting and sorting are investigated numericallyin the framework of a VOF technique for interface tracking and a finite-volumenumerical method using the commercial code FLUENT. Droplets of water-in-oilare produced by a flow focusing technique relying on the use of a microchannellequipped with an obstacle to split the droplets. The influence of several parameterspotentially affecting this process is investigated parametrically towards the endof identifying "optimal" conditions for droplet breakup. Such parameters includesurface tension, the capillary number and the main channel width. We show thatthe capillary number plays a crucial role in determining droplet properties and theefficiency of the related generation process. An obstacle configuration can be effectivelyused to split a droplet, with the droplets being naturally sorted at the endof the main channel. Larger values of the capillary number generally lead to anincrease in the droplet frequency and a decrease in its typical size. Voir les détails

Mots clés : Water droplet, flow focusing, splitting, sorting, CFD, VOF, microchannel

Numerical Investigation of Flow Dynamic in Mini- Channel: Case of a Mini Diode Tesla

B. dennai, M. belboukhari, T. CHEKIFI, R. Khelfaoui  (2016)

Microfluidic systems are used and exploited in various fields, as they are highly specific and developed in their use. The micro devices are used in various analyzes of medical disciplines, chemical and other fields. Our research team "MAAt" within ENERGARID laboratory is in the process of triggered several lines of research in this area, the micro-mixing, separation of micro particles, droplet production. For that, we need tools and micro devices to study the phenomena.. In this work, we present a theoretical study and numerical simulation of micro device (micro diode Tesla). A Diode Tesla is similar to a heart valve conduit profile is shown in the following figure: In this simulation work, we will focuse the variation of geometrical parameters, the inside length lw (lw1> lw2> lw3), this study aims to optimize this setting to get a better efficiency. Then we will investigate the effect of the pressure variation on the volume flow. Voir les détails

Mots clés : Mini channel, diode Tesla, Efficiency, gas flow, microsystem.

Numerical and Experimental Investigation of FluidicMicrodrops Manipulation by Fluidic Mono-Stable Oscillator

T. CHEKIFI, B. dennai, R. Khelfaoui, A. Maazouzi  (2016)

A numerical and experimental study of passive microdrops manipulation hasbeen presented. This paper focuses on the modeling of micro-oscillators systemswhich are composed by passive amplifier without moving part. The characteristicsize of the channels is generally about 35 ¹mof depth. The numerical results indicatethat the production and manipulation of microdrops are possible with passivedevice within a typical oscillators chamber of 2:25 mm diameter and 0:20 mmlength when the Reynolds number is Re = 490. The novel microdrops methodthat is presented in this study provides a simple solution about the production ofmicrodrops problems in micro system. We undertake an experimental step. Thefirst part is based on realization of sample oscillator; the second part is consistedof visualization of the microdrops production and its manipulation. Voir les détails

Mots clés : microdrop, fluidic oscillator, CFD

MicroFluidic Oscillator: A Technical Solutionfor MicroMixture

B. dennai, A. BENTALEB, T. CHEKIFI, R. Khelfaoui, A. Abenbi  (2015)

The diffusion flux given by the Fick’s law characterizethe mixing rate. A passive mixingstrategy is proposed to enhance mixing of two fluids through perturbed jet low. A numerical studyof passive mixers has been presented. This paper is focused on the modeling of a micro-injectionsystems composed of passive amplifier without mechanical part. The micro-system modeling isbased on geometrical oscillators form. An asymmetric micro-oscillator design based on amonostable fluidic amplifier is proposed [2,7]. The characteristic size of the channels is generallyabout a few hundred of microns. The numerical results indicate that the mixing performance can beas high as 99 % within a typical mixing chamber of0.20 mm diameter inlet and 2.0 mm distance ofnozzle - spliter. In addition, the results confirm that self-rotation in the circular mixer significantlyenhances the mixing performance. The novel micro mixing method presented in this study providesa simple solution to mixing problems in microsystem. Voir les détails

Mots clés : Micro oscillator, modeling, Micro mixture, diffusion, Size effect.

Effect of Geometrical Parameters on Vortex Fluidic Oscillators Operating with Gases and Liquids

T. CHEKIFI, B. dennai, R. Khelfaoui  (2018)

The fluidic oscillator is an interesting device developed for passive flow measurement. These microsystems can produce a high oscillating jet frequency with high flow velocity. The main advantages of fluidic oscillators are that no moving parts is included in the device. Commercial CFD code FLUENT was used to perform analysis of flows in fluidic oscillator. Numerical simulations were carried out for different flow conditions, where water and air were used as working fluids. The oscillation frequencies were identified by the discrete fast Fourier transform method (FFT). Furthermore a low-pressure vortex of fluid flow in the oscillating chamber was observed. The effect of the operating pressure and the oscillating chamber shape on the fluidic oscillator performance is investigated. Moreover the velocity fluctuations of the feedback flows through both feedback channels and the output were determined quantitatively. In addition, the behaviour of the low-pressure vortex in both models is analysed. Also, numerical result revealed small vortices are developed at the end of nozzle while oscillation, which maintains the deflection of jet flow between attachments wall. Comparison of our numerical simulations with available results showed reasonably and good agreement. Voir les détails

Mots clés : fluidic oscillator, CFD, oscillating chamber, vortex, size effect, Coanda effect.