Volume 1 Issue 1

Title Page
1

Clean and Green Energy Technologies: Sustainable Development and Environment

Abdeen Omer
[Abstract]

Key words: Renewable energy resources, technologies, sustainable development, environment.

Abstract: The move towards a de-carbonised world, driven partly by climate science and partly by the business opportunities it offers, will need the promotion of environmentally friendly alternatives, if an acceptable stabilisation level of atmospheric carbon dioxide is to be achieved. This requires the harnessing and use of natural resources that produce no air pollution or greenhouse gases and provides comfortable coexistence of human, livestock, and plants. This article presents a comprehensive review of energy sources, and the development of sustainable technologies to explore these energy sources. It also includes potential renewable energy technologies, efficient energy systems, energy savings techniques and other mitigation measures necessary to reduce climate changes. The article concludes with the technical status of the ground source heat pumps (GSHP) technologies.

1-46
2

Optimal Sizing of Photovoltaic Wind Hybrid Systems

Wissem Zghal, Gueorgui Kantchev, Hédi Kchaou
[Abstract]

Key words: hybrid system, modeling, optimal sizing, simulation algorithm.

Abstract: This paper presents an optimal sizing method of an autonomous hybrid wind photovoltaic system. The main objective of this study is to determine the optimal characteristics of a system able to cover the energy demands of a consumer for a given specific location. This method is essentially based on two main phases. The modeling of the autonomous hybrid system is considered the first phase in the process of optimal sizing. The second phase is to optimize the dimensioning of the system based on the lack of energy to generate probability (LEGP), percentage of the surplus of energy produced (PSEP) and the cost of the kilowatt-hour produced (CkWh). From these two phases, a simulation code has been developed as a working tool able to perform the analysis and optimization of a hybrid system for given load and location. Therefore, a case study that uses this code was presented to determine the optimal configuration of a system that meets the energy requirements (5kWh/jour) of a house located in Sfax, Tunisia.

47-53
3

Modelling and simulation study of regeneration and dehumidification stages used in solar air conditioning unit

Zied Guidara, Wissem Zghal, Habib Ben Bacha
[Abstract]

The aim of this paper is a presentation of a new solar air conditioning unit for office spaces at Tunisia and a simulation study of the behaviour of two stages. The first one is the dehumidification stage which is mainly composed of desiccant wheel. The second one is the regeneration stage which is mainly composed of flat plate solar collector, storage tank and heat exchanger. Thus, mathematical models for each of those components are developed which are based mainly on thermal and mass balances. A finite differences method is applied to the partial differential equations. The simulation study shows that minimizing the value of the distributed hot water mass flow for the storage tank is very interesting. This can be beneficial as it reduces thermal losses and makes the heating of the inlet cold water entering the storage tank effective. In addition, increasing the value of the hot water temperature produced by flat plate solar collector is interesting because it ensures an efficient heating of the water contained in the storage tank. Finally, the studied regeneration stage can successfully ensure the regeneration of the hygroscopic wheel used in the corresponding solar air conditioning unit.

54-64
4

Numerical investigation of flow over wind turbine airfoil NACA 23015

Mohamed Mehdi OUESLATI, Anouar Wajdi DAHMOUNI, Mohieddine BEN SALAH, Faouzi ASKRI, Sassi BEN NASRALLAH
[Abstract]

Key words: Streamfunction-vorticity formulation, Control volume based on finite element method, NACA 23015, POD analysis.

Abstract: To study the flow dynamic behavior of the NACA 23015 airfoil, used in many commercialized wind turbine, a computational fluid dynamic solving the streamfunction-vorticity formulation of Navier-Stokes equations using the Control Volume Method based on Finite Element (CVMFE) have been made to simulate the flow over the NACA 23015 at high angle of attack equal to 14° for Reynolds number equal to 1000. The Proper Orthogonal Decomposition (POD) method is adopted to analyze and extract the coherent motion structures in the flow behind the airfoil and the first two modes are used to determine the phase of the vortex shedding.

65-73
5

aIncidence angle effect on the aerodynamic structure of a Savonius wind rotor

Makram MAALOUL, Zied DRISS, Mohamed Salah ABID
[Abstract]

Key words: Savonius rotor, wind tunnel, incidence angle, aerodynamic structure.

Abstract: The study of the incidence angle effect around a Savonius wind rotor on the numerical results was obtained using "SolidWorks Flow Simulation" softaware. The objective of this study is to observe the effect of the incidence angle on the aerodynamic structure characteristics. These results are presented in different transverse and longitudinal planes of the considered control volume. To validate the numerical results, we have developed an experimental approach to measure the flow velocity in
different positions of the test vein of our wind tunnel.

73-85

Volume 1 Issue 2

Title Page
6

Entropy Generation in Double Diffusive Convection through a Rectangular Porous Cavity

Ali Mchirgui, Nejib Hidouri, Mourad Magherbi, Ammar Ben Brahim
[Abstract]

Key words: Numerical method, cavity, porous medium, heat and mass transfer, entropy generation, double diffusive convection.

Abstract: Entropy generation in double diffusive convection through a rectangular porous cavity saturated by a binary perfect gas mixture is numerically studied using Darcy – Brinkman formulation. The set of equation describing the phenomenon is solved by using a modified version of the Control Volume Finite-Element Method. Effect of the enclosure geometry on entropy generation was investigated. The results are numerically presented through graphs and maps to observe the effects of aspect ratio of the cavity on entropy generation for the two cases of opposite and cooperatives buoyancy forces.


84-89
7

Natural convection in a square cavity heated by an isothermal solid block

Basma SOUAYEH, Nader BEN CHEIKH, Brahim BEN BEYA, Taieb LILI
[Abstract]

Key words: natural convection, heat source, Rayleigh number, heat transfer, boundary conditions.

Abstract: The present work deals with the prediction of a natural convection flow in a square cavity, partially heated by an obstacle placed at the bottom wall. The two transverse walls and the top wall of the cavity are supposed to be cold. The main parameter of numerical investigations is the Rayleigh number (engine convection) ranging from 103 to 105. Different configurations relative to cooling obstacle are presented and analyzed in the current study. The simulations were conducted using a numerical approach based on the finite volume method and the projection method, which are implemented in a computer code in order to solve the Navier-Stokes equations.

90-97
8

Effect of Rayleigh number on the turbulent structures with boundary layer in a differentially heated

Abdelhadi BEGHIDJA, Djedid TALOUB
[Abstract]

Abstract: The heat transfer by convection is so far a basic principle in many industrial applications. This study led to the analysis of turbulent convection. Ra> 109 in a three-dimensional parallelepiped cavity filled with air, the two opposite vertical walls are differentially heated at a constant temperature, the other walls are hot wall except ceiling. The finite volume method has been used to discredited the equations of flow in turbulent convection turbulence model used is (κ-ε). The results are relevant because they show that for a number of Pr = 0.71 the Rayleigh number, thus generating a great influence on heat transfer within the study area, and the onset of instability due to the interaction of turbulent structures with the boundary layer.

Key words: Natural convection, finite volume, parallelepiped.

98-103
9

A theoretical study of a thermal radiation inverse problem for the estimation of the optical thickness by means of an optimization technique

Ali FGUIRI, Naouel DAOUAS, Naceur BORJINI, Habib BEN AISSIA
[Abstract]

Key words: inverse problem, Levenberg-Marquardt, optical thickness, sensitivity analysis.

Abstract: An inverse radiation problem was considered to estimate the optical thickness for a one-dimensional cylindrical model of a semi-transparent, gray and isotropically scattering medium. The radiative transfer equation is solved using the finite volume method and the temperature is determined according to the dimension of the semi-transparent medium. In order to find the points which give us more information about the optical thickness using the measured temperatures, we carried out a sensitivity analysis. The solution of the inverse problem is obtained with the Levenberg-Marquardt method. The identification results were analyzed with respect to the number of measurements and the initial estimate of the unknown radiative property. The effect of the parameter of the LM method on the stability of the solution, in particular in the vicinity of the initial estimate, was also investigated.

104-109
10

Mixed convection flow in three dimensional lid-driven square cavity with vertical temperature gradient

Noura BEN MANSOUR, Nader BEN-CHEIKH, Brahim BEN-BEYA and Taieb LILI
[Abstract]

Keywords: Mixed convection, Richardson number, lid-driven cavity, temperature gradients.

Abstract: In this study, the mixed convective heat transfer in a lid driven cubic cavity at is investigated numerically. Two cases are negotiated, the top moving lid and the bottom walls are at constant uniform temperatures (case 1: Ttop > Tb, case 2: Ttop < Tb) while the vertical walls are thermally insulated. The Reynolds number is fixed at Re=100, while the Richardson number is varied from 0.001 to 10. The effect of temperature gradient orientation on the fluid flow and heat transfer has been performed. It is shown that the downward temperature gradient yields a better heat transfer rate than the upward temperature gradients (case 1). Multiple correlations in terms of the heat transfer rate and Richardson number has been established.

110-116

Volume 1 Issue 3

Title Page
11

Effects of inclination angle on natural convection in enclosure partially heated and filled with cu-water nano-fluid

Jmai Ridha, Brahim BEN-BEYA, Taieb LILI
[Abstract]

Key words: Nanofluid, Natural convection, Partially active walls, Inclination angle.

Abstract: Effects of inclination angle on natural convection heat transfer and fluid flow in an enclosure with partially heated side walls filled with cu-water nanofluid has been analyzed numerically. A two heat sources maintained at a constant heat flux q’’ are embedded in the right and the left wall. The enclosure was cooled from the top and bottom walls. The remaining boundary parts are kept insulated. The angle of inclination is used as a control parameter for improve flow and heat transfer enhancement depicted in our recently work. Using a home developed code a parametric study is conducted and a set of graphical results is presented and discussed to illustrate the effects of inclination angle on the flow and heat transfer characteristics. The inclination angle was varied from 0 to 90° and two mainly case are considered, namely Middle-Middle (MM) and Down-Top (DT) depending of the two vertical sources location along the two side walls. It is found that optimal heat transfer enhancement can be improved. A percentage of heat transfer enhancement using 10% of Cu- nanoparticles is obtained for an inclination angle of 15° at higher Rayleigh number (Ra=105).

117-122
12

Entropy Generation in Double Diffusive Convection with Soret Effect through a Square Porous Cavity

Nejib HIDOURI, Ali MCHIRGUI, Mourad MAGHERBI, Ammar BEN BRAHIM
[Abstract]

Key words: Numerical method, Soret effect, entropy generation, porous medium, cavity, double diffusive convection.

Abstract: This paper consists of a numerical investigation about the influence of Soret effect on entropy generation in double diffusive convection. It consists of a square porous Darcy – Brinkman cavity saturated by a binary perfect gas mixture and submitted to horizontal thermal and concentration gradients. The Control Volume Finite-Element Method was employed in order to solve the set of equations describing the studied phenomena. Influence of the Soret effect on the different irreversibilities was carried out by the variation of the thermal diffusion ratio and the Darcy number. Taking into consideration the Soret effect induces an increase of heat transfer and viscous irreversibilities. The diffusive entropy generation presents different behaviours.

123-130
13

Influence of wall boundary conditions on the 3Ddouble diffusive convectionand on the entropy generation

Kaouther GHACHEM, Chamseddine MAATKI, Lioua KOLSI, Mohamed Naceur BORJINI, Habib BEN AISSI
[Abstract]

Keywords: 3D cavity, entropy generation, natural convection, double diffusive

Abstract:In this paper we study numerically the 3D double-diffusive natural convection in a cubic cavity. The main purpose of this paper is to study the effect of the modification of the boundary condition of the upper and down sides of a cubical cavity, on the flow and heat transfer in the one side and on the entropy generated on the other side. The flow is considered laminar and caused by the interaction of thermal energy and the chemical species diffusions. The governing equations of the problem, concentration, energy and momentum, are formulated using vector potential-vorticity formalism in its three-dimensional form, then solved by the finite volumes method. The Rayleigh number is fixed at Ra=105 and the effects of the buoyancy ratio is studied for opposed temperature and concentration gradients. The particular interest is focalized on the three-dimensional aspects and entropy generation.

131-138
14

Effects of magnetic field on Rayleigh-Bénard convection inside enclosures at different aspect ratios

Awatef NAFFOUTI, Brahim BEN-BEYA, Taieb LILI
[Abstract]

Key words: Rayleigh-Bénard; Magnetoconvection; Entropy; Hartmann number.

Abstract: The present paper focuses, in particular, on aspect ratio (AR) effects on Rayleigh-Bénard convection within enclosure under a uniform magnetic field. Results are presented and analyzed for different values of Hartmann number (60≤ Ha ≤ 80) and for a range of aspect ratios (0.75≤AR≤1) at various Rayleigh numbers (Ra). It is found that both enclosure aspect ratio and magnetic field intensity play a significant role in controlling the onset of the Rayleigh-Bénard convection flow. The entropy generation analysis demonstrates that irreversibility phenomena increase for lower aspect ratio values and moderate Hartmann numbers.

139-144
15

Numerical investigation of three-dimensional thermosolutal convection in a cubic enclosure under magnetic field

Chamseddine MAATKI, Kaouther GHACHEM, Lioua KOLSI, Mohamed Naceur BORJINI, Habib BEN AIISSIA
[Abstract]

Keywords: Convection, thermosolutal, hydromagnetic, three-dimensional.

Abstract: In the present study, thermosolutal convection of fluid in a cubic enclosure filled with a binary mixture is numerically investigated in a strong magnetic field. The physical model is heated from left-hand side vertical wall and cooled from opposing wall. Above this enclosure an electric coil is set to generate a magnetic field. The numerical method in the present work is the formalism vector potential vorticity in a three-dimensional configuration using the finite volume method. The influence of the intensity of magnetic field on the three-dimensional flow, the distributions of temperature and concentration and the characteristics of heat and mass transfer are revealed. The results show that the magnetic force has significant effect on the three-dimensional flow structure and heat and mass transfer.

145-156

Volume 1 Issue 4

Title Page
16

Evaluation of the models of the pressure-strain correlation in the turbulent compressible flow

Aicha HANAFI, Hachmi KHLIFI, Taieb LILI
[Abstract]

Key words: Compressible turbulence, Pressure-strain correlation, Homogeneous shear flow .

Abstract: Several DNS results show that compressibility has an important effect on the pressure-strain correlation, the termrecognized as the principal responsible for the change in the magnitude of Reynolds-stress anisotropies. Thus, the pressure-strainincompressible models do not correctly predict compressible turbulence at high-speed shear flow. A method of includingcompressibility effects in the pressure strain correlation is the subject of the present study. The LRR model developed byLaunder-Reece and Rodi has shown a great success in the simulating a variety of incompressible complex turbulent flows. On theother hand this model has not predicted correctly the compressible turbulence at high speed shear flow. Thus, a compressiblecorrection for this model is the major aim of this study. In the present work, five recent compressible models for the pressure-straincorrelation have been used to modify the LRR model. This correction concerns essentially the C1, C2, C3 and C4 coefficients which became in a compressible situation a function of the turbulent Mach number.

157-163
17

Water hammer wave for leak detection in elastic and viscoelastic pipes

Lazhar AYED, Lamjed HADJ-TAIEB, Ezzeddine HADJ-TAIEB
[Abstract]

Key words: Water Hammer, Leak detection, Elastic pipe, viscoelastic pipe, Transient pressure.

Abstract: This paper further investigates leaks detection in elastic and viscoelastic pipes based on the analysis of water hammer wave. Leak as an internal exciter and a discontinuity that occurs in a hydraulic system may affect the waveform. Its effects on the pressure wave at the end section of a reservoir-pipe-valve system can be used as a tool for its location and sizing. The leak modeled as an orifice is located in the studied system either with elastic or viscoelastic behavior. Its location is given by analyzing the head pressure at the valve either in the time or the frequency domain. The effect of the pipe-wall elasticity (instantaneous elastic response) and viscoelasticity (retarded –viscoelastic response) on the leak detection are investigated either in time or frequency domain. Finally a comparison between the two analyses for leak detection is drawn.

164-171
18

Numerical modeling of microfluidic flow through a channel with sensitive membrane

Marwa SELMI, F. ECHOUCHENE, H. MEJRI, and H. BELMABROUK
[Abstract]

Key words: Binding reaction, microfluidic systems, biosensors, finite element method, biological analytes, simulation.

Abstract: The binding reaction is a significant characteristic which is adopted in the design of biosensors. This aim of the present work is to investigate the binding reaction kinetics through a microchannel. The  diffusion boundary layer on the reaction surface of a biosensor operating in fluid environment, presents restraining effects. Therefore, it is useful to optimize several critical parameters, which affect the binding reaction such as, the length of the reaction surface, the inlet flow velocity, and the initial biological analyte concentration (e.g. molecule, protein, toxin, peptide, vitamin, sugar, metal ion…) in order to reduce the thickness of the diffusion
boundary layer. The study is performed using 2D finite element method. Then, the space-time evolution of analyte concentration (such as C-reactive protein or IgG) is simulated. The results prove that the reaction kinetic is strongly affected and hence the diffusion boundary layer is assigned by the physical and geometrical parameters of the microfluidic biosensor.

172-176
19

Lattice-Boltzmann code for a multiphase fluid flow through reconstructed porous media

Atia ABDELMALEK, Mohammedi KAMAL
[Abstract]

Keywords: Lattice Boltzmann method, multiphase flow simulation, Darcy law, porous media, kinematic viscosity.

Abstract: In this paper, we present a Lattice Boltzmann simulation of multiphase flow in a homogeneous two-dimensional porous media. For this study, we develop a program based on lattice Boltzmann equation. The underlying theoretical model makes it possible to couple the state equation of a non-ideal fluid with the pressure tensor at the interface and uses the excess free-energy density formalism. The fluid properties can be  prescribed in a thermodynamically consistent manner, which remains accurate at states close to the critical point. We have simulated some known two-phase flow configurations, like displacement of vapor by its liquid in homogeneous two-dimensional porous media reconstructed by image treatment under the action of an external flow field. We present also results for the averaged velocity as a function of time iteration and the permeability of two dimensional porous media as a function of kinematic viscosity and mesh resolution. Our results confirm that the LBM scheme reproduces Darcy’s law through the analysis of the dependency of the permeability on the kinematic viscosity.

177-183
20

Numerical investigation of natural convection of water-CuO nanofluid

Mefteh BOUHALLEB, Hassan ABBASSI
[Abstract]

Key words: Nanofluid, Natural convection, Heat transfer, Solid volume fraction.

Abstract: This paper analyzes heat transfer and fluid flow of natural convection in an inclined cavity filled with CuO/water nanofluid that operates under differentially heated walls. The transport equations for the flow are solved numerically by the finite volume element method using the SIMPLER algorithm. Simulations are performed for various aspect ratios. The inclination angle is varied between 0 and 90°, and the Rayleigh number is in the range of 103 and 105. Temperature distribution and heat transfer rates are analyzed and discussed. It is found that the addition of solid nanoparticles in working fluid lead to a considerable enhancement of heat transfer. Effects of aspect ratio, inclination angle, and Rayleigh number on heat transfer are analyzed.

184-191

Volume 2 Issue 1

Title Page
1

Effect of thermal rayleigh number and buoyancy ratio on the fluid flow, heat and mass transfer in a salt–gradient pond

Ridha Boudhiaf, Mounir Baccar
[Abstract]

Key words: Stratified fluid layers; Salt–gradient pond; Hydrodynamic, heat and mass transfer; Numerical simulation; Finite–volume method; Transient regime.

Abstract: In this paper, we studied numerically the effect of thermal Rayleigh number and the buoyancy ratio on the transient fluid flow, heat and mass transfer in a salt–gradient pond (SGP) wherein the layers of fluid are stratified. The objective of this numerical work is to give a fine knowledge of the hydrodynamic, thermal and solute characteristics during the storage of thermal energy in a SGP. The pond is filled with a mixture of salt and water to constitute three zones with different salinities: Upper Convective Zone (UCZ), Non–Convective Zone (NCZ) and Lower Convective Zone (LCZ). Water is heated by a heat serpentine covered the bottom of the pond. The transport equations for continuity, momentum, thermal energy and mass transfer are solved by a finite–volume method to provide
the fields of temperature, concentration and velocities in a SGP in transient regime. Simulations are performed for several values of both the thermal Rayleigh number in the range between 104 and 107, and the buoyancy ratio in the range between 0 and 10, whose influence on the temporal evolution of velocities, temperature and concentration distributions in a SGP are analyzed and discussed. The flow structure shows the generation of convective cells in the lower and upper zones of the pond, and permits to explain the slight increase of temperature in the UCZ and the important rise of temperature in the LCZ. In addition, this work shows the importance of the buoyancy ratio to preserve the high temperature in the bottom of the pond and to reduce the phenomena of heat and mass transfer across the NCZ.

1-13
2

Thermal characterization of fluids using the coaxial cylinders method

Ali Adili, Mohamed Lachheb, Sassi Ben Nasrallah
[Abstract]

Key words: Thermal conductivity, liquids, coaxial cylinders method.

Abstract: Thermal conductivity is an important thermophysical property; its value is required in all heat transfer calculations. This study deals with the elaboration of theoretical principles of measurement and with the  realization of an apparatus based on the coaxial cylinders method allowing us to obtain, simply, the thermal conductivity of liquids. In this work, we have measured the variation of thermal conductivity versus temperature of some liquids like ethanol and ethylene glycol. Thermal conductivities of some other liquids are measured at 25°C. The obtained results have been compared with literature data and they present a good agreement with them.

14-19
3

Numerical study of the airflow induced by a heat source in a room

Ons Tlili, Hatem Mhiri, Philippe Bournot
[Abstract]

Key words: CFD modeling, fire source, smoke.

Abstract: In this study, the spread of fire smoke in a room that contains a heat source is simulated numerically using the CFD code Fluent. We’re studying essentially the heat transfer between two fluids of different densities, typically hot and cold air in a space containing a heat source. A simple geometry is adopted, consisting of a room with a door that plays the role of inlet-outlet for the fluid. A volumetric heat source was placed at the centre of the room. As the flow is turbulent and buoyant we used the standard k-e model together with the Boussinesq approximation. The results of the mathematical model are validated with available  experimental data. These results give a detailed description of the flow studied; the distribution of velocity and temperature are reasonably predicted. Following this conclusion, the mathematical model adopted can provide a knowledge base for the evaluation of thermal and dynamic parameters in the case of a fire in the studied configuration, and can be extended to a more complex geometry. It is concluded that this work illustrates the ability of the CFD approach in the study of heat transfer between tow fluids of different densities, however it would be extended and improved by studying the effect of various geometric parameters and thermal diffusion of the heat in a confined environment.

20-26
4

Entropy generation in mixed convection through a horizontal porous channel

Atef El Jery, Amel Tayari, Mourad Magherbi, Ammar Ben Brahim
[Abstract]

Key words: Numerical method, Entropy generation, porous media, mixed convection.

Abstract: The numerical analysis of two-dimensional laminar mixed convection flow through a channel filled with saturated porous media under thermal gradient is investigated. The Darcy-Brinkman model is employed. The conservation equations are solved using a Control Volume Finite Element Method. Total entropy generation is investigated at global and local levels by varying the porosity from 1 to 0.2 at fixed values of Ra= 104, Re =10, Br*=10-3. Results show the existence of dissipative structures.

27-34
5

Finite element model for sound transmission analysis through a double panel inserted in an infinite baffle

Walid Larbi, Rawad Assaf
[Abstract]

Key words: Fluid-structure, finite element, modal reduction, double panel, sound transmission.

Abstract: This paper presents a finite element model for sound transmission analysis through a double panel inserted in an infinite baffle. The proposed model is derived from a multi-field variational principle involving structural displacement and acoustic pressure inside the fluid cavity. To solve the vibro-acoustic problem, the plate displacements are expanded as a modal summation of the plate's eigenfunctions in vacuo. Similarly, the cavity pressure is expanded as a summation of the modes of the cavity with rigid boundaries. Then, an appropriate reduced-order model is introduced. The structure is excited by a plane wave at the source side. The radiated sound power is calculated by means of a discrete solution of the Rayleigh Integral. Fluid loading is neglected. An example of the normal
sound transmission loss of a double aluminum panel is shown. This example illustrates the accuracy and the versatility of the proposed reduced order model, especially in terms of prediction of sound transmission.

35-44

Volume 2 Issue 2

Title Page
6

Simulation of a solar driven ammonia-water absorption refrigeration system

Yasmina Boukhchana, Ali Fellah, Ammar Ben Brahim
[Abstract]

Key words: Solar energy, Absorption refrigeration, Ammonia-water, Simulation, COP.

Abstract: A steady state computer simulation model has been developed to predict the performance of an absorption refrigeration system using NH3-H2O as a working pair and driven by solar energy. It satisfies the air-conditioning supplies of a classroom. The absorption system includes an absorber, a generator, a condenser, an evaporator and a liquid heat exchanger. It uses a solar collector to achieve the thermal necessities of the vapor generator. The model is based on detailed mass and energy balances and heat and mass transfer relationships. The effects of the coefficient of performance and effectiveness of heat exchangers on the key operational parameters are investigated. To eliminate the numerical errors, thermodynamic properties of the working pair are taken from the EES software. The results show that the COP of the system can reach a value greater than 0.4. The effectiveness increase leads to an increase in COP of about 55%.

45-54
7

Coupled study hydrodynamic and thermal behaviour of a ventilated disc brake

Mohamed Kaffel, Hédi Kchaou, Mounir Baccar
[Abstract]

Key words: hydrodynamic, thermal, disc brake.

Abstract: Optimization ventilated disc brake requires a thorough knowledge of the hydrodynamics of the air flow through the ventilation ducts of the disk to determine the design to facilitate the evacuation of heat by friction pads engaging the disc. In this work we present the results of numerical simulation giving behaviors coupled hydrodynamic and thermal cooling air on the one hand, and the thermal behavior of unsteady ventilated disc, on the other hand.

55-58
8

Numerical Investigation of Electrothermal flow Instability in Microchannel

Marwa Selmi, Fraj Echouchene, Hafedh Belmabrouk
[Abstract]

Key words: Modeling, microchannel, fluid flow, heat transfer, ac electric field.

Abstract: In the last decade, microfluidics has flourished for their required in several sectors. The applications areas involved are huge, from the world of transport to the nuclear engineering, aerospace, engineering wind, and from biomechanics to the micro-electronics (e.g. cooling integrated circuits). In this paper, we present a numerical investigation of electrothermal fluid flow through a microchannel. The main purpose of this study is to investigate the flow instability induced by the electrothermal forces. The mathematical model includes the Navier-Stokes equation coupled with Maxwell and the balance energy equations. The equation system obtained is solved using the finite element method (FEM). The model provides insight and understanding of many physical and dynamic properties of flow. The numerical results show that the flow becomes highly unstable when the potential difference is great inducing the appearance of large swirls localized at the electrodes. Specifically, numerical calculations of voltage influence on the temperature and velocity of fluid flow fields are presented. Numerical suggest that 40 V applied to electrodes can increase maximum velocity by a factor of 600 compared to the inlet velocity. A slight increase in temperature (300 to 318 for Vrms = 40 V) was achieved.

59-62
9

An Element-Free Galerkin Analysis of Elasto-Plastic Fracture Problems

El Hassan Boudaia, Mourad Kaddiri, Lahbib Bousshine
[Abstract]

Key words: Elasto-plasticity, numerical analysis, EFGM, MLS, transformation method.

Abstract: In this paper, we present a theoretical and numerical analysis of elasto-plastic problems based on the element-free Galerkin method (EFGM) and the numerical analysis. The study has been examined in planar stress analysis around the tip of a crack and in its opening mode of loading. In the EFGM, the implementation of the Moving Least Squares (MLS) approximation is used to obtain the approximation function and the transformation method is proposed to impose the essential boundary conditions. The discritized variational formulation for elasto-plastic materials obeying to the von Mises criterion is presented. To examine the validity of this technique, stress fields in a plate with a crack have been calculated.

63-67
10

Solar unit for air conditioning and desalination: theoretical and experimental investigation of the desiccant wheel

Zied Guidara, Alexander Morgenstern, Peter Schossig, Habib Ben Bacha
[Abstract]

Key words: Air conditioning; desalination; design; desiccant wheel; modelling; simulation; experimental investigation.

Abstract: In this research, a presentation of a new solar unit for air conditioning and desalination is presented firstly. Secondly, a dynamic modelling study of the desiccant wheel is developed. After that, a simulation study and an experimental investigation of the behaviour of desiccant wheel are developed. Concerning the modelling study, mathematical equations are based mainly on thermal and mass balances. Concerning the simulation study, a finite differences method is applied to the partial differential equations. The experimental investigation is done in the chamber of commerce in Freiburg-Germany. Indeed, the variations of calculated and measured temperatures and specific humidity of dehumidified and rejected air are presented. Finally, this study shows that good agreement is found when comparing the model predictions with experimental data under the considered range of operating conditions.

68-74

Volume 2 Issue 3

Title Page
11

Response of a Plane Free Jet Subjected to Sinusoidal Excitations

Response of a Plane Free Jet Subjected to Sinusoidal Excitations
[Abstract]

Key words: jet, vortex, instability, excitation, frequency, mode.

Abstract: A numerical study of the instabilities is realized for 2D incompressible, isothermal and plane jet. The eulerian numerical finite volume method is used. Numerical parameters and boundary conditions are optimized for the studied configuration. This study was operated for moderate Reynolds numbers. The flow is perturbated at the entry of the nozzle. The excitation frequency is a harmonic or sub-harmonic of the natural instability. The instability amplification depends on the excitation frequency. A response mode inherent to the shear flows was detected. The vortex energy is amplified allowing to know their sinuous or varicose behavior. The vortex dissociation and pairing phenomena are highlighted.

75-82
12

Bifurcation to unsteady natural convection in square enclosure containing an obstacle at Rayleigh number of 107

Basma Souayeh, Nader Ben Cheikh, Brahim Ben Beya, Taieb Lili
[Abstract]

Key words: Natural convection, heating obstacle, Rayleigh number, unsteady state, heat transfer.

Abstract: The present work deals with the prediction of a natural convection flow in a square cavity, partially heated by an obstacle placed at the bottom wall. The two transverse walls and the top wall of the cavity are supposed to be cold, the remaining walls are kept insulated. The main parameter of numerical investigations is the Rayleigh number (engine convection) varying from 103 to 105. When Ra is fixed at 107, the flow and thermal fields bifurcate and undergoes an unsteady behavior at critical positions.
Flow patterns corresponding to the unsteady state are presented and analyzed in the current study. The simulations were conducted using a numerical approach based on the finite volume method and the projection method, which are implemented in a computer code in order to solve the Navier-Stokes equations.

82-86
13

Finite Element Analysis of ECAE Deformation of Polycarbonate

F. Bouaksa, C.M. Ovalle-Rodas, F. Zaïri, M. Naït-Abdelaziz, T. Tamine
[Abstract]

Key words: FEM, ECAE , molecular orientation

Abstract: The behavior of molecularly orientated polycarbonate (PC) sheets was investigated numerically. In the present contribution finite element simulations, using a physically-based viscohyperelastic-viscoplastic constitutive model, were carried out in order to evaluate the degree and distribution of molecular chain anisotropy in polycarbonate and the effect of strain rate on distribution of plastic deformation when it is extruded by the ECAE process at 135°.

87-95
14

Temperature-dependent viscosity effect on free convection in a square cavity filled with a shear-thinning and subjected to cross thermal gradients

Mourad Kaddiri, Mohamed Naimi, Abdelghani Raji, Mohammed Hassnaoui
[Abstract]

Key words: Heat transfer; Natural convection; Non-Newtonian fluids; Numerical study; Square cavity.

Abstract: Study of buoyancy driven convection of thermo-dependent a shear-thinning power-law fluid confined in a square cavity, submitted to cross uniform heat fluxes is conducted numerically using a finite difference method. The combined effects of the ratio between the cross heat fluxes and the thermo-dependency parameter on the flow and thermal fields, and the resulting heat transfer are examined and discussed.

96-101
15

Effect of the heat flow on the turbulent macrostructure with boundary layer in a cavity differentially heated

Djedid Taloub, Abdelhadi Beghidja
[Abstract]

Key words: Natural convection, finite volume, parallelepiped, k-epsilon.

Abstract: The heat transfer by convection is, so far, a basic principle of many industrial applications. This study led to the analysis of turbulent convection. Ra > 109 in a rectangular three-dimensional cavity filled with air, the two opposite vertical walls are differentially heated a constant temperature at cold wall and the heat flux at the hot wall, the other walls are hot wall except ceiling wall is cold according to fig. 2. The finite volume method has been used to discretize the equations of flow in turbulent convection. The model of turbulence used is κ-ε. The results obtained are suitable, because they show that for a number of Pr = 0.71 and while varying the heat flow, generating consequently a great influence on the transfer of heat inside the field of study, the numerical results of the heat flux at the hot wall are over predicted. The strong influence of the undulation of the cavity and its orientation is well shown, and the release of the instability due to the interactions of the swirling structures with the boundary layer.

102-107

Volume 2 Issue 4

Title Page
16

CFD simulations on CO production in a longitudinally ventilated tunnel fires for different aspect ratio

Soufien Gannouni , Rejeb Ben Maad
[Abstract]

Key words: Tunnel fire, CO concentration, aspect ratio, CFD.

Abstract: In a tunnel fire, the production of smoke and toxic gases remains the principal factors prejudicial to users. More than 80 % of deaths are in direct relation to the toxicity and the opacity of smoke. In this paper, the smoke propagation and CO production in a longitudinally ventilated tunnel fires for different aspect ratio is analyzed numerically with large eddy simulation (LES) by Fire dynamic simulator (FDS). The evolution of the CO concentration longitudinally along the tunnel will be studied in this work. The tunnel slope’s effect on the CO concentration will also be studied. The FDS Numerical results are firstly verified by comparison with the experimental measurements of Li et al. [15-16], in terms of the critical velocity and the maximum smoke temperature under the ceiling. A relatively good agreement has been obtained. Results show that the CO concentration increases with the aspect ratio while this latter remains lower than 1 and then decreases as the aspect ratio increases for an aspect ratio greater than 1.

108-116
17

Determination of Turbidity Parameters over Ghardaia Site Using MODIS Data

Zaiani Mohamed, Djafer Djelloul
[Abstract]

Key words: Aerosols, Optical Thickness, MODIS, turbidity parameters.

Abstract: In this work, three basic parameters for aerosol characterization, Aerosol Optical Thickness, Angstrom Exponent and Angstrom Coefficient are used for aerosol analysis. Their monthly average values are obtained from MODIS data for Ghardaia site. We have found that the transmission of solar radiation can reach 95 % and the 94% of the Angstrom exponent values lie between 1.2 and 1.27 and 70% of Angstrom coefficient lie between 0.019 and 0.062.

117-121
18

Cutting Forces Prediction in Turning by Technique of ANNs

Makhfi Souâd, K. Haddouche, M. Habak, R. Velasco, A. Bourdim
[Abstract]

Key words: Artificial neural network, cutting force components, hard turning, machining process.

Abstract: In this study, we develop a robust ANN technique to predict cutting force components during hard turning of an AISI 52100 steel using CBN cutting tool. The training network is performed on 20 pairs of input-output experimental dataset where cutting parameters and workpiece hardness are taken as the input dataset. Back-propagation training is performed by using Bayesian Regularization in combination with Levenberg-Marquardt algorithm. The optimal network architecture is determined after several simulations by MATLAB Neural Networks Toolbox and it is consisting of 8 neurons in hidden layer. The developed model was verified with other experimental test data not used in training; for this purpose, the maximum average MAPE value of 11.79 % was obtained for the cutting forces prediction.

222-227
19

Analysis and Experimental Validation of a Partially Shaded PV Array with different configurations

Abd Essalam Badoud , Mabrouk Khemliche
[Abstract]

Key words: Photovoltaic, Partial Shading, Maximum Power Point Tracking, Configuration

Abstract: Partial shading of photovoltaic (PV) modules can affect a wide variety of plants ranging from utility-sized solar trackers to residential building-integrated PV, resulting in lower energy production yields. This paper presents background and experimental results from a PV system, operated under a variety of shading conditions. A procedure of simulation and modeling solar cells and PV modules, working partially shadowed in symbols environment, is presented. Simulation results have been contrasted with real measured data from a commercial PV module of Photowatt PW1650. Some cases of study are presented as application examples of this simulation methodology, showing its potential on the design of bypass diodes configuration to include in a PV module and also on the study of PV generators working in partial shading conditions.

236-243
20

Bond Graph Modeling, Design and Safety of the Hydrodynamics Variable Speed

Abd Essalam Badoud, Mabrouk Khemliche
[Abstract]

Key words: Variable Speed Hydrodynamics; Bond Graph; Modeling; Fault Detection and Isolation; Simulation

Abstract: Hydrodynamic couplers are often assigned to a group of their own research in the classification of couplings. This is justified by the particular operating principle of hydrodynamic power transmission. The transformation between the form of mechanical energy and hydropower offers various possibilities to vary the transmission power according to precise laws. The main idea to understand and study the dynamics of real systems is the modeling. The models are simplified and abstract constructs used to predict the real behavior. We proposed to use not the bond graph approach like the single tool responsible for modeling, as that is classically proposed in the literature, but like a mechanism complementary to enrichment. With this work, we helped to develop a platform for modeling of a hydrodynamic variable speed transmission able to model its bodies and to simulate and analyze its total behavior thereafter. This paper describes the application of our qualitative fault detection and isolation FDI approach to a hydrodynamics variable speed. We developa pseudo bond graph model of the system and demonstrate the FDI effectiveness. We introduce the problem analysis involved in the faults localization in this process. A number of new and interesting issues have been dealt with in this paper.

228-235

Volume 3 Issue 1

Title Page
1

Half-metallic ferromagnetism in the Mn2CoAs Heusler compound

Miloud Ibrir, Said Lakel, Safia Alleg, Rachid Bensalem
[Abstract]

Key words: Heusler compounds; FP-LAPW; DFT+U; Spintronics.

Abstract: First-principles calculations for the structural, electronic, and magnetic properties of Mn2CoAs Heusler compound, have been performed for using full-potential linearized augmented plane wave (FP-LAPW) scheme within the (GGA-WC) and GGA+U. Features such as the lattice constant, bulk modulus, and its pressure derivative are reported, in addition to the results of the band structure and the density of states. The electronic structure in the ferromagnetic configuration for Mn2CoAs Heusler compound shows that the spin-up electrons are metallic, but the spin-down bands have a gap of 0.48 and 0.77 eV for GGA-WC and GGA+U, respectivly. The Mn2CoAs Heusler is ferrimagnetic and maintains the half-metallic character having 100 % polarization for lattice parametres in 5.5 and 5.82 Å.

1-7
2

Wear resistance characterization of coated Nano-scale structure surfaces

Said LAKEL, K. ALMI, M. IBRIR, Y. BERRICHE
[Abstract]

Key words: Mechanics, energy, wear resistance, wear, Calowear, Tribology.

Abstract: One of the most commonly used tribological thin-film coatings is Chromium Nitride (CrN), typically deposited by Physical Vapor Deposition (PVD) process. Examples of current applications of this coating include cutting and forming tools: ICE piston ring, hydrodynamic pumps, etc. In selecting coating for tribological applications, one of the critical parameter is the specific wear rate κ c of the coating. Micro-scale abrasion testing has been used to evaluate the specific wear rate κ c of chromium-nitride (CrNx) with nanoscale structure coatings on identical a DIN 1.4301 steel substrates. Two different abrasives, SiC and diamond were used. The hardness of the films was found to be in the range of 8-38 GPa. The aim of this paper is to evaluate the abrasion resistance of hard coatings, and high abrasive wear resistance Ωc = (1/κ c ) of these coatings are compared. The results were compared to those of a chromium nitride reference coating. The results obtained show an excellent correlation between coating hardness and abrasion resistance. The micro-abrasion testing employed offers a simple and inexpensive method for pre-selecting and ranking of coating materials for tribological applications.

8-12
3

A semi-implicit scheme for the stabilized finite element method for the incompressible Navier-Stokes equations

Bart Janssens,Tamás Bányai, Karim Limam, Walter Bosschaerts
[Abstract]

Keywords: Finite element method, Incompressible flow, Predictor–corrector scheme

Abstract: We apply a predictor-multicorrector scheme to thePressure Stabilized and Streamline Upwind Petrov-Galerkin (PSPG and SUPG) stabilized incompressible Navier-Stokes equations, solving separate systems for the velocity and pressure. The advective terms are treatedexplicitly. The algorithm is tested against the analytical solution for the Taylor-Green vortices case and shown to be of second order accuracy. We analyze the performance and compare with a fully coupled, implicit solution technique. The semi-implicit predictor-multicorrector scheme proves to be advantageous when small time steps are required due to the flow physics.

13-24
4

Entropy Generation Study of Mixed Convection in Porous Channel for Different Prandtl Numbers

Amel Tayari, Atef Eljery, Mourad Magherbi and Ammar Ben Brahim
[Abstract]

Key words: Numerical method, Entropy generation, porous media, mixed convection, Darcy, Brinkman.

Abstract: This work deals with the numerical study of mixed convection in a saturated porous medium which is enclosed in horizontal channel. A laminar flow model for mixed convection with porous media is the focus of this work. The porous media is modeled through the Brinkman-extended Darcy’s equation. The Boussinnesq-Oberbek approximation is used to simulate the effects of mixed convection. The Control Volume Finite Element Method is used to elaborate the computational code. Then, Implicit Alternates Directions method is used for solving the governing equations. The coupled pressure-velocity is treated by using the SIMPLER algorithm. The effect of the Prandtl, the modified Brinkman, the Darcy and the Raleigh numbers on the total entropy generation as well as on averaged Nusselt number are studied.

25-32
5

Transient modeling and simulation of an ammonia-water absorption solar refrigerator

Yasmina Boukhchana, Ali Fellah, Ammar Ben Brahim
[Abstract]

Key words: Solar Energy, Absorption refrigerator, Modeling, Simulation, Dynamic regime, Ammonia/Water.

Abstract: The performance analysis of a solar absorption refrigerator operating in an autonomous way is investigated. The Ammonia/water machine satisfies the air-conditioning needs along the day. The refrigerator performances were simulated regarding a dynamic model. For the solar driven absorption machines, two applications could be distinguished. The sun provides the thermal part of the useful energy. In this case, it is necessary to use additional energy as the electric one to activate the pumps, the fans and the control system. On the other hand, the sun provides all the necessary energy. Here, both photovoltaic cells and thermal concentrators should be used. The simulation in dynamic regime of the cycle requires the knowledge of the geometric characteristics of every component as the exchange areas and the internal volumes. Real characteristics of a refrigerator available at the applied thermodynamic research unit (ATRU) at the engineers' national school of Gabes are notified. The development of the thermal and matter balances in every component of the cycle has permitted to simulate in dynamic regime the performances of a solar absorption refrigerator operating with the Ammonia/Water couple for air-conditioning needs. The developed model could be used to perform intermittent refrigeration cycle autonomously driven.

33-42

Volume 3 Issue 2

Title Page
6

The effect of Richardson number on thermal and mass behavior of laminar boundary layer flow

Maroua Nefzi, Mohamed Ali Knani
[Abstract]

Key words: Boundary layer, laminar flow, heat transfer, Richardson number, diffusion, friction coefficient.

Abstract: The laminar boundary layer is frequently found in nature and in industry. For example: aerodynamic, hydrodynamic, in meteorology and in oceanography. Such as: it causes many problems in aerodynamic such as a jet engine. A numerical study of the boundary layer developing along a horizontal plate is carried out . The aim of this work is to study the effect of Richardson number on thermal and mass behavior of laminar boundary layer, when the flow is subjected to thermal and solutal diffusions.

 

43-48
7

Effects of internal heat generation/absorption on heat transfer in a porous enclosure

Najib Hdhiri, Brahim Ben-Beya, Taieb Lili
[Abstract]

Key words: Porous medium, heat generation/absorption.

Abstract: The present investigation deals with study of laminar natural convection flow with internal heat generation or absorption in porous enclosure. The numerical simulations were conducted using a numerical approach based on the finite volume method implemented in the code "Nasim". It is interesting to see that the internal heat generation numbers (RaI), Darcy number (Da) and porosity number (?), have a significant role in the heat transfer rate. For all values of the considered Da, the stream function maximum (?max) is found to increase as Da increases. On other hand, at higher value of (?=1), the transfer rate of the heat is so strong which causes a deviation of the heat source maximum temperature corresponding to the absorption case. 

49-54
8

Numerical investigation on pressure drop through rectangular microchannels

Ines Hamidi, Abdelmottaleb Ouederni
[Abstract]

Key words: Rectangular microchannels, pressure drop, friction factor, single-phase flow.

Abstract: This paper focuses on investigating, numerically, the laminar single-phase flow through rectangular microchannels with hydraulic diameters varying from 150μm to 550μm, with aspect ratio changing from 0.3 to 0.97. The numerical model employs the three dimensional Navier-Stokes equations to simulate the flow behavior in microchannels. The numerical solution is obtained by discretizing the governing equations using the finite-element method (FEM). The numerical simulations are done on a range of the Reynolds number (Re) varied from 1 to 400. For the isotherm and laminar single-phase flow model, the liquid water is used as the testing fluid. The viscous dissipation, the pressure work and the gravity are neglected. In this study pressure drop shows an agreement with the theoretical results for rectangular channels. However, for Reynolds number range ≤ 100, the friction factor data were found less than the predicted theoretical data presented by Shah and London in rectangular channels.

55-60
9

Nanofluid Effects On Heat Transfer By Natural Convection

Rihab Ben Fradj, Brahim Ben Beya
[Abstract]

Key words: Natural convection, nanoparticles, Nusselt number, Rayleigh number.

Abstract: This work deals with a numerical study on natural convection problem in a rectangular cavity, two-dimensional, differentially heated: the left vertical wall is heated to a constant temperature TH, while the right vertical wall is kept at a cold temperature TC such as (TH ? TC) filled with nanoparticles at different concentrations φ. The fluid is considered incompressible, Newtonian and obeys the Boussinesq approximation. The influence of nanofluid, on the structure of the flow and heat transfer in the cavity was examined for a Rayleigh number Ra varies between 103 ≤ Ra ≤ 106 and concentration of nanoparticles ranging from 0% ≤ φ ≤ 4% in order to examine the best average heat transfer rate through the cavity. The results show, in particular, that the increase of the volume fraction of the nanoparticles (φ) increases the average heat transfer rate. 

61-66
10

Evaluating the performance of two eddy-viscosity turbulence models to predict airflow and Local Mean Age of air

Guilherme Anrain Lindner, Karim Limam, Lelia POPESCU, Brahim BENHAMOU c
[Abstract]

Key words: Computational Fluid Dynamics, indoor airflow, standard k-ε, SST k-ω, local mean age.

Abstract: The goal of this work is to investigate the performance of two eddy-viscosity turbulence models, standard k-ε and SST k-ω, in predicting the two-dimensional airflow in a rectangular room and the local mean age of air using an open-source simulation tool, OpenFOAM. Two geometries were analyzed: the room used in the first case (Bartak, 2001), which consists of a lateral air entrance and an outlet on the top of the opposite side, and the experimental room from the second case (Annex 20 room by Nielsen, 1990), which represents a large rectangular room where the air is supplied horizontally on the upper left and is exhausted through the opening on the lower right of the opposite side. The velocity profiles and local mean age of air were analyzed in both cases.

67-76

Volume 3 Issue 3

Title Page
11

Modeling and fault diagnosis of Engine Ignition Systems using bond graph approach

Abd Essalam Badoud
[Abstract]

Abstract: This paper discusses the fundamentals of an engine ignition system modeling using bond graph approach and its mathematical interpretation and physics for the different stages of motor operation. Other topics covered in this paper show that fault detection and localization of the defects in the engine ignition system with lighting presented by its bond graph model. One of the original points is that this work treated the utilization of fault detection and isolation method (FDI). A new method is proposed to avoid the exploration of all the combinations for its application to the diagnostic of this system operation and to determine the gravity of a detected failure. The causal paths help us in this procedure in order to generating the analytical redundancy relations ARR at each step from constitutive and structural junction relations. This is shown through an algorithm for monitoring the system by sensors placements on the corresponding bond graph model. The diagnosis performances are controlled by a sensitivity analysis of these residues, making it possible to define indices of sensitivity, and detectability indices of the defects.

Key words: Modeling, Bond Graph, Engine ignition system, Sensors Placement, Detection, Localization.

77-83
12

Evaluation of the performance of two turbulence models in the prediction of swirling turbulent flow

Djemoui Lalmi, Redjem Hadef
[Abstract]

Abstract: The performance of two different turbulence closure models in the prediction of turbulent swirling flow is presented .The models evaluated are the Reynolds stress transport model (RSM_SSG) and the Kw_SST model . This study is a direct comparison between numerical simulation and measurements of the overall flow variables mean and kinetic turbulent of a swirled turbulent flow with different sections. The comparison of the calculation results with measurements confirmed the inadequacy of two models. This handicap is related to the complexity of the structure of the flow (unsteady, three-dimensional, various turbulence scales...)

Key words: Swirl, Turbulence, Simulation.

84-89
13

Forced convection of slip-flow in porous micro-duct under Local Thermal Non-Equilibrium conditions

Raja Rabhi, Bayssain Amami, Hacen Dhahri and Abdallah Mhimid
[Abstract]

Abstract: Forced convection heat transfer inside a porous micro duct is performed to investigate the effects of porous material on the heat transfer rate. The flow in the porous material is described by the Darcy- Brinkman- Forchheimer model. The assumption of local thermal non equilibrium (LTNE) condition is adopted for heat transfer and viscous dissipation effects are included in the energy equation of the fluid phase. The obtained governing equations are solved using the Lattice Boltzmann Method (LBM). Knudsen, Eckert and Darcy numbers are selected as the influence parameters. The computational simulations are done for different Knudsen numbers (Kn ), Darcy number ( Da) and Eckert number ( Ec). It is found that both fluid and solid temperatures increases as the Kn decreases, Da decreases and Ec increases. However, the augmentation in Da is related to the important fluid friction effects which decrease the temperature gradient.

Key words: Porous media, Local thermal non-equilibrium, Lattice Boltzmann Method, micro duct.

90-95

Volume 4 Issue 1

Title Page
1

Effects of inclination angle on natural convection in enclosures filled with a shear thinning Thermo-dependent fluids

Mourad Kaddiri, Mohamed Lamsaadi,Hassan Elharf, Mohamed Naimi, Abdelghani Raji, Mohammed Hassnaoui
[Abstract]

Abstract:Natural convection heat transfer in inclined square cavity filled with thermo-dependent power-law fluids has been investigated numerically. The enclosure considered here is heated and cooled with uniform fluxes from the horizontal walls, while the verticals ones are adiabatic. The effects of the governing parameters, which are the thermo-dependence number (0 £ m£10) , the flow behavior index (n = 0.6) , the Rayleigh number (Ra =104 ) and the angle of inclination (0° £f £ 120°) , on flow structure and heat transfer characteristics have been examined. Results are presented in the form of treamline and isotherm plots as well as the variation of the Nusselt number under different conditions.

Keywords:Heattransfer; Natural convection; Non-Newtonianfluids; Tilted square cavity; Thermo-dependentBehavior.

1-7
2

The combined effects of the ratio between the cross heat fluxes and the thermo-dependency parameter on free convection in a square cavity filled with a shear thinning

Mourad Kaddiri, Mohamed Naimi, Abdelghani Raji, Mohammed Hassnaoui
[Abstract]

Abstract: Two-dimensional steady-state buoyancy driven flows of thermo-dependent shear-thinning power-law fluid confined in a square cavity, submitted to cross uniform heat fluxes, has been conducted numerically using a finite difference technique. The
parameters governing the problem are the thermo-dependence number (0 £ m £ 10) and the ratio between the heat flux imposed on the vertical walls and that imposed on the horizontal ones represented by a (0 £ a £1) , while the flow behavior index n is fixed at
(n = 0.6) and the Rayleigh number at (Ra = 5. 103) . The effects of these parameters on the flow structure and heat transfer characteristics have been analyzed.

Key words: Heat transfer; Natural convection; Non-Newtonian fluids; Numerical study; Square cavity.

8-13
3

Air humidification by forced convection and gas radiation in a cylindrical annular duct

Abir Sakly, Akram Mazgar, Faycal Ben Nejma
[Abstract]

Abstract: A numerical study is described for combined forced convection and radiative heat transfer. The humid air supposed to be a perfect gas in a boundary layer approached laminar flow is confined between two coaxial cylinders. The inner cylinder, covered by a thin water film, is assumed to be adiabatic, while the outer is thermally insulated and dry. The numerical model, based on the finite volume technique is used to solve the one dimensional Navier-Stokes and energy equations. The radiative part of this study was solved using the “Ray Tracing” method, associated with the “Statistical Narrow Band Correlated–k” (SNBCK) model. This study has been made of the effect of gas radiation and the influence of dry surface emissivity are presented. Results showed that the gas radiation remains non negligible and acts as an influent factor in the humidification process. Also, increasing the dry surface emissivity results in a rising of the humid surface temperature and the evaporated flow rate.

Keywords: Film evaporation, forced convection, thermal radiation, non-grey gas, SNBCK4 model

14-23
4

Estimation of Solar Radiation on Horizontal Surfaces in Gabès located in the South east of Tunisia

Ahmed Ayadi, Zied Driss
[Abstract]

Abstract: Solar radiation data are important tools for many areas of research and applications in various engineering and scientific fields including for example climatology, agro meteorology, hydrology and solar energy converting system design. The main objective of the present study is to predict the daily solar radiation and the hourly irradiation on a horizontal surface for the city of Gabès located in the south east of Tunisia. The obtained results are used to develop a Matlab program which can be used in the estimation of the solar radiations for all the city of Tunisia.

Key words: solar radiation, solar energy, daily solar radiation, hourly solar irradiation.

24-29
5

Fluid dynamic study of a NACA2415 airfoil type wind turbine with a wedging angle equal to 30°

Tarek Chelbi, Zied Driss, Ahmed Kaffel, Mohamed Salah Abid
[Abstract]

Abstract: In this paper, numerical simulations and experimental validation were carried out to gain an insight into the complex flow field developing around a small wind rotor and to evaluate its performance. We consider the Navier-Stokes equations in conjunction with the standard k-ε turbulence model to study the aerodynamic parameters of a NACA2415 airfoil type wind turbine. These equations are solved numerically to present the local characteristics of the flow and the models tested are implemented using the software "SolidWorks Flow Simulation". Experiments have been also conducted on an open wind tunnel equipped by a small NACA2415 airfoil type wind turbine to validate the numerical results. This will help improving the aerodynamic efficiency in the design of packaged installations of the NACA2415 airfoil type wind turbine.

Key words: NACA2415 airfoil wind turbine, wind tunnel, turbulent flow, aerodynamic structure.

30-35

Volume 4 Issue 2

Title Page
6

Mixed Convection of Nanofluid Flows in a Ventilated Cavity Submitted to Varying Heating

Ismail Arroub, Ahmed Bahlaoui, Abdelghani Raji, Mohammed Hasnaoui, Mohamed Naîmi
[Abstract]

 Abstract: The phenomenon of mixed convection heat transfer through Al2O3-water nanofluid inside a horizontal ventilated enclosure is studied numerically. The obtained results demonstrate clearly the positive role of the nanoparticles addition on the improvement of the heat transfer rate and the mean temperature within the cavity. The flow structure and the temperature distribution within the cavity are seen to be very affected by the Reynolds number and the heating type. Also, it is shown that, in general, the decreasing heating mode is more favorable to the heat transfer while the cooling efficiency is found to be more pronounced by applying the increasing heating type.

Key words: Mixed convection, ventilated cavity, injection, nanofluid, varying heating.

36-43
7

Effect of viscous dissipation on thermally developing laminar forced convection for a pseudoplastic fluid

Abderrahmane Horimek, Lakhdar Bougaa, Noureddine Ait Messaoudene, Saad Abeda
[Abstract]

 Abstract: In this work,we treat thethermal development problem, for apseudoplasticfluid in asinglepipe. A fully developed flow is supposed at the pipe inlet, with an imposedtemperature at the surface inthe case of aheating andcooling. In addition, the effect ofviscous dissipationis considered. Finite difference method with an implicit scheme is used to solve the energy equation. The main objectiveof the workisto provide results, enabling to well understandthe effect of viscous dissipationassociated with that ofrheological behavior. For this, different values oftheBrinkman(Br) number characterizing theheat generation byviscousfriction, and therheological index(n)have been taken in heating situation as well as cooling. It has been found that the fluid shear-thinning (n↓) significantly reduces the dissipative effect, by reducing the friction between the fluid layers.

Keywords:Forced convection; thermaldevelopment; pseudoplasticfluid; viscous dissipation.

44-50
8

Prandtl number effect on mixed convection inside a horizontal lid-driven rectangular cavity

Mohamed Lamsaadi, Mourad Kaddiri, Mohamed Naîmi, Hassan EL Harfi, Mohammed Hasnaoui
[Abstract]

 Abstract: Mixed convection within a rectangular cavity confining a Newtonian fluid is studied analytically and numerically in thecase where the horizontal walls, whose upper one is moving, are adiabatic, whereas those vertical are submitted to uniform density offlux. Numerical calculations are carried out for values of governing parameters within the ranges, 0.1 ? Ri ? 103 , 0.1 ? Re ? 10 ,0.1 ? Pr ? 50 and A = 20, where Ri is the Richardson number, Re is the Reynolds number, Pr is the Prandtl number and A is theaspect ratio. In such a situation, the obtained results testify of a strong influence of Pr on flow and heat transfer characteristics.Key words: Heat transfer; mixed convection; lid-driven rectangular cavity.

Keywords: Heat transfer; mixed convection; lid-driven rectangular cavity.

51-56
9

Heat Exchanger Technology and Applications in Heat Exchanger Engineering

Abdeen Omer
[Abstract]

 Abstract: Over the years, all parts of a commercial refrigerator, such as the compressor, heat exchangers, refrigerant, and packaging,have been improved considerably due to the extensive research and development efforts carried out by academia and industry.However, the achieved and anticipated improvement in conventional refrigeration technology are incremental since this technology isalready nearing its fundamentals limit of energy efficiency is described is ‘magnetic refrigeration’ which is an evolving coolingtechnology. The word ‘green’ designates more than a colour. It is a way of life, one that is becoming more and more commonthroughout the world. An interesting topic on ‘sustainable technologies for a greener world’ details about what each technology isand how it achieves green goals. Recently, conventional chillers using absorption technology consume energy for hot water generatorbut absorption chillers carry no energy saving. With the aim of providing a single point solution for this dual purpose application, aproduct is launched but can provide simultaneous chilling and heating using its vapour absorption technology with 40% saving inheating energy. Using energy efficiency and managing customer energy use has become an integral and valuable exercise. Thereason for this is green technology helps to sustain life on earth. This not only applies to humans but to plants, animals and the rest ofthe ecosystem. Energy prices and consumption will always be on an upward trajectory. In fact, energy costs have steadily risen overlast decade and are expected to carry on doing so as consumption grows. Refrigerants such as hydrochloroflurocarbons (HCFCs) arepresent in the ground source heat pump (GSHP) systems and can pose a threat to the environment through being toxic, flammable orhaving a high global warming potential.

Key words: Absorption cycles, environment, heat pumps, refrigeration cycles, thermodynamic

57-63
10

Semi-Empirical Investigation of the Hydrodynamic drag force over a UUV hull form

Mohamed Zouari, Aymen Mohamed, Mohamed Salah Abid, Zied Driss
[Abstract]

 Abstract: This paper investigates the validation of an empirical method that estimates the hydrodynamic coefficients of streamlinedunderwater vehicles. These coefficients are non-dimensional parameter appearing in the equation of motion of the vehicle. Datcom(U.S, Air Force compilation code) is used to determine these coefficients in aquatic medium. The body configuration in this studyincludes axisymmetric body without wing tail or body tail. Results obtained with the Datcom are presented here and compared toexperimental results taken from a Planar Platform Mechanism mounted over a towing tank. A 6dof balance was used to extract themeasurements forces and moments acting on the derived vehicle. These measurements were carried out at typical speeds ofautonomous underwater vehicles (0.2-0.6 m / s) by varying the angles of inclination (0-15 degrees). This study was limited to theaxial forces which mean the coefficient of drag. Static hydrodynamic characteristics computed by Datcom method are shown to agreeclosely with experimental results for torpedo slender body of circular cross sectional.

Keywords: Underwater Vehicle, Hydrodynamic coefficients, Towing Tank, Datcom.

64-71

Volume 5 Issue 1

Title Page
1

Modeling and simulation of a solar cooker with box type

Zied Guidara, Mahamoud Souissi, Alexander Morgenstem, Aref Maalej
[Abstract]

Abstract: In this paper, the design of a box type solar cookeris presented first. The main components of this solar cooker are inner and outer reflectors, a double glazing, an absorber plate and a cooking box. Secondly, in order to predict the evolution of the temperatures of the main components of the solar cooker,a mathematical model was developed and implemented in a MATLAB program using finite differences method. To validate the accuracy of the calculations further numerical simulations were realized using Solidworks simulation tool. After that, simulations were developed on the solar cooker before enhancement and after enhancement with four outer reflectors. The obtained results show that the enhancement has a great influence on the maximum temperature of each component and on the availability of the solar cooker.

Key words: Design, box type solar cooker, mathematical model, numerical simulations, reflectors.

1-6
2

Static study of a double pass solar air heater support

Oumaima Eleuch, Badis Bakri, Zied Msaed, Zied Driss
[Abstract]

Abstract: This work presents the design of a double pass solar air heater fixed on the wall by a four legs design pivoting system. In the case of supplying a building with hot air, for heating purposes, or for industrial applications such as drying or preheating, this pivoting mechanism consists of two supports with two legs linked to the collector itself and the fixing is ensured by two clevises. To make a static simulation of the pivoting mechanism, we use the CAD software Solid Works. According to the obtained results, we can approve that our support can bear the load of the solar collector and resist to weather conditions.

Key words: Double pass solar air heater, four legs design pivoting system, static simulation, Solidworks.

 

7-12
3

Investigations CFD numerical of the combustion of methane or propane: aero-thermo-chemical study

Mohammed El Hadi Attia, Zied Driss, Fethi Bouras and Abderrahmane Khechekhouche
[Abstract]

Abstract: In this paper, we simulated numerically the non-premixed combustion provided by two coaxial methane-propane/air jets in a cylindrical combustion chamber. Using CFD Fluent commercial calculation software. In order to find the aero-thermo-chemical characteristics in the burner: temperature, axial velocity and mass fraction of carbon monoxide CO. To study this kind of phenomenon, we used a special treatment of the mathematical model and we chose two models of computation large eddy simulation (LES) and the probability density function (PDF). The objective of this work is to reduce the emission of carbon monoxide CO, and what is considered a gas toxic to the environment. The results obtained give the fuel of methane reduces the carbon monoxide in the products of combustion.

Key words: Models LES and PDF; Combustion Chamber; Methane; Propane; Numerical Simulation CFD.

13-19
4

Modeling and numerical simulation of turbulent premixed flames impinging onto a wall

Ahmed Neche, Zineddine Youbi, Rachid Renane
[Abstract]

Abstract: This paper will present an algebraic model closure of the turbulent fluxes as the sum of two contributions acting in opposite directions, one induced by turbulent motions and the other by thermal expansion. The turbulent transport is analyzed that for a sufficiently high turbulence level, the flame is unable to impose its own dynamics to the flow field, and the turbulent transport is of the gradient transport type for the reacting scalar c and when the turbulence level remains low, the thermal expansion due to heat release dominates the process of turbulent scalar transport and the turbulent transport is of a counter gradient turbulent transport. The combustion will occur in a variable equivalence ratio and as partially premixed combustion is highlighted as one of the most relevant and important modeling challenges in the field of turbulent premixed combustion, we will use the LW-P model of combustion for this situation. The resulting model is combined with the second order model of turbulence Rij, ? has evidenced the pressure drop across the flame due to counter gradient diffusion turbulent fluxes which has well predicted the jump of the axial velocity across the flame brush. A numerical simulation which corresponds to the experimental conditions of the experiment of Escudié and Haddar is presented in order to validate the model. The comparison of the results with the measurements were showing remarkable consistency and indicates that the model is a valid approach for predicting partially turbulent premixed flames stabilized in a stagnation flow.

Key words: Partially premixed combustion, Stagnating flow, Libby-Williams-Poitiers model, Numerical combustion simulation, Counter gradient diffusion turbulent fluxes

20-34
5

Analysis of stability and control of the longitudinal flight under the influence of longitudinal modes of flight, frequencies and damping coefficients

A.Chegrani, Z.Youbi, R.Renane
[Abstract]

Abstract: In this work a comparative study was conducted on the longitudinal dynamics and flight control for four types of aircraft (General aircraft, business aircraft, fighter aircraft and commercial aircraft). We have established the fundamental equations of motion for a rigid aircraft using the laws of mechanical and aerodynamic models. Therefore, an analysis of stability and control is made for every case to determine different dynamic characteristics (longitudinal modes of flight, frequencies and damping coefficients). Also, two kinds of automatic control systems have been designed for four types of aircraft. At the end, some applications are carried on real aircraft models (Cessna 172, M24Learjet, F4C and Boeing 747) and simulation results are presented for each type of aircraft.

Key words: Aircraft, Flight dynamic, Flight control, Stability, Simulation, Modes, Frequency, Damping.

35-42

Volume 6 Issue 1

Title Page
1

Simulation of transonic flow around the aerodynamic airfoils and wings (Application to UAV)

Rachid Renane, Rachid.ALLOUCHE, Nadir Bekka, Abdelkader Nour
[Abstract]

Abstract: The flight regime of modern transport aircraft, is at transonic speeds, in terms of Mach number M∞ = 0.75-0.85 and at very high Reynolds numbers. The transonic flow occurs when the two regimes of subsonic and supersonic flows occur in the same local flow field. It is characterized by the development of a supersonic pocket, delimited by the wall on the one hand and by the sonic line on the upper surface of the wing on the other hand. The appearance of a supersonic pocket on the under-surface of the wing is also possible; all depends on the incidence angle and the geometrical form of the wing. This work is devoted to the evaluation and the validation of the numerical results resulting from transonic calculation of flow around a NACA0012 aerofoil, then around a wing 3d having the same basic airfoil. All calculations are executed by using the turbulence models of two equations k-ε, k-ω and SST k-w.

Key words: Transonic flow, Numerical simulation, Aerofoil NACA0012, Mach wave, unmanned aircraft vehicle (UAV)

1-6
2

Natural convection for a Herschel-Bulkely fluid inside a differentially heated square cavity

Horimek Abderrahmane, Djouaf Salah-Eddine, Nouereddine Ait-Messaoudene
[Abstract]

Abstract: Natural convection for a Herschel-Bulkely fluid, inside a differentially heated square cavity, is studied numerically using Fluent/Ansys 15.0 code. The cavity is heated from the vertical sides and insulated from the horizontal ones. We have studied the effect of Bingham-number (Bn) at a fixed Rayleigh-number (Ra), then the effect of Rayleigh-number at fixed Bn and finally the effect of the rheological index n at fixed Bn and Ra. Prandtl-number (Pr) is taken equal 1.0 for the whole study. Results showed that an increasing Bn leads to a flow-intensity decrease, and hence its perturbation. Therefore, temperature field becomes less perturbed and the Nusselt decreases. The opposite happens if Bn decreases. Increasing Ra, leads to similar results as those known for the Newtonian-case, but with a lower intensity because of Bn effect. The decrease of n has an opposite effect of that of increasing Bn, and inversely. A rapid tendency toward the conductive problem (Ra=0.0) is registered if Bn>0 particularly when n>1.0.


Key words: Natural convection, square cavity, Bingham fluid, Herschel-Bulkely fluid.

7-15
3

Solar concentration using flat reflectors: parametric study and experimental investigation

Mahmoud Souissi, Zied Guidara, Aref Maalej
[Abstract]

Abstract: A new design of a solar collector is proposed in this paper. The introduced novelty consists on using low cost flat reflectors with adjustable inclination. A detailed description of the solar collector as well as its functioning are also provided in the paper. Moreover, a mathematical model, that takes into account the variation of the heat transfer coefficients, is proposed and validated experimentally. Several experiments were also done in order to determine the influence of the new parameters that were induced by the use of reflectors. The parameters that were considered for this study are: the use or no-use of outer reflectors, the number of reflectors equipping the solar collector, and finally the reflectors inclination. The obtained results showed that the enhancement had a great effect on the performance of the solar collector. Indeed, the operating temperature range as well as the availability of the solar collector had increased. This allows the solar collector to work even during days with low solar radiation.

Keywords: New design; solar collector; flat outer reflectors; performance; experiment.

16-24
4

Experimental analysis of Implant–cement interfacial behaviour under shear mode loading conditions

Mohamed Mokhtar Bouziane, Mokhtar Khaldi, Boualem Serier, Nourddine Benseddiq, Mokhtar Zerdali, Smaïl Benbarek, Bel Abbes Bachir Bouiadjrab
[Abstract]

Abstract: The failure of the bone cement (PMMA) is the most prominent scenario, in a cemented total hip arthroplasty and an eventual implant loosening. Among the many factors influencing the long-term stability of cemented hip prostheses, the interface between the implant and bone cement is considered to be one of the most susceptible to failure. Implant surface roughness is an important parameter affecting the fracture behavior of the implant–cement interface. This study investigated the influence of implant surface roughness on the resistance of the implant–cement interface. Mechanical fixation at the implant–cement interface was evaluated in vitro using shear loading with stainless steel rods with different surface roughness preparations. Increasing surface roughness improved the mechanical properties at the implant–cement interface. Therefore, it increases the long-term stability of the hip prostheses assembly.

Keywords: Bone cement, Hip prostheses, Roughness, Mechanical properties, Shear strength.

25-31
5

Influence of the Debit and the Orientation of a Solar Converter

Abdelkarim Bouras, Djedid Taloub, N. Bellel, Badis Bakri, Driss Zied
[Abstract]

Abstract: The work presented in this paper is the numerical study of a thermal converter. The main objective of the work is to study the effect of certain parameters on a flat solar collector. We are particularly interested in determining the influence of water flow on the operating characteristics of the solar collector and the effect of the orientation of a surface on the energy received. We have realized a mathematical model simulating the thermal behavior of collectors, to solve the mathematical model using an iterative method of Gauss-Seidel. According to the results obtained on this device, we note that: The inclination between 30 and 37 ° gives the best performances. The outlet temperature is higher for low flow. The overall efficiency increases with the flow of water.

Key words: the solar power, debit, solar converter, performance of the converter

32-36

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