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Dive into the research topics where Ammar Ben Brahim is active.

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Featured researches published by Ammar Ben Brahim.


Entropy | 2006

SECOND LAW ANALYSIS IN CONVECTIVE HEAT AND MASS TRANSFER

Mourad Magherbi; H. Abbassi; Nejib Hidouri; Ammar Ben Brahim

This paper reports the numerical determination of the entropy generation due to heat transfer, mass transfer and fluid friction in steady state for laminar double diffusive convection, in an inclined enclosure with heat and mass diffusive walls, by solving numerically the mass, momentum, species conservation and energy balance equations, using a Control Volume Finite-Element Method. The influences of the inclination angle, the thermal Grashof number and the buoyancy ratio on total entropy generation were investigated. The irreversibilities localization due to heat transfer, mass transfer and fluid friction is discussed for three inclination angles at a fixed thermal Grashof number.


Entropy | 2010

Effect of an External Oriented Magnetic Field on Entropy Generation in Natural Convection

Atef El Jery; Nejib Hidouri; Mourad Magherbi; Ammar Ben Brahim

The influence of an external oriented magnetic field on entropy generation in natural convection for air and liquid gallium is numerically studied in steady-unsteady states by solving the mass, the momentum and the energy conservation equations. Entropy generation depends on five parameters which are: the Prandtl number, the irreversibility coefficients, the inclination angle of the magnetic field, the thermal Grashof and the Hartmann numbers. Effects of these parameters on total and local irreversibilities as well as on heat transfer and fluid flow are studied. It was found that the magnetic field tends to decrease the convection currents, the heat transfer and entropy generation inside the enclosure. Influence of inclination angle of the magnetic field on local irreversibility is then studied.


International Journal of Thermal Sciences | 2003

Entropy generation in Poiseuille–Benard channel flow

H. Abbassi; Mourad Magherbi; Ammar Ben Brahim

The issue of entropy generation in Poiseuille–Benard channel flow is analyzed by solving numerically the mass, momentum and energy equations with the use of the classic Boussinesq incompressible approximation. The numerical scheme is based on Control Volume Finite Element Method with the SIMPLER algorithm for pressure–velocity coupling. Results are obtained for Rayleigh numbers Ra and irreversibility φ ranging from 103 to 5×104 and from 10−4 to 10 respectively. Variations of entropy generation and the Bejan number as a function of Ra and φ are studied. The limit value φl for which entropy generation due to heat transfer is equal to entropy due to fluid friction is evaluated. It has been found that φl is a decreasing function of the Rayleigh number Ra. φl varies from 0.0015 to 0.096 when Ra decrease from 5×104 to 103. Stream lines and entropy generation maps are plotted at six times over one period at Ra =104 and φ=10−3. It has been found that the maximum entropy generation is localized at areas where heat exchanged between the walls and the flow is maximum. No significant entropy production is seen in the main flow.


Entropy | 2011

Entropy Generation at Natural Convection in an Inclined Rectangular Cavity

Mounir Bouabid; Mourad Magherbi; Nejib Hidouri; Ammar Ben Brahim

Natural convection in an inclined rectangular cavity filled with air is numerically investigated. The cavity is heated and cooled along the active walls whereas the two other walls of the cavity are adiabatic. Entropy generation due to heat transfer and fluid friction has been determined in transient state for laminar natural convection by solving numerically: the continuity, momentum and energy equations, using a Control Volume Finite Element Method. The structure of the studied flows depends on four dimensionless parameters which are: the thermal Grashof number, the inclination angle, the irreversibility distribution ratio and the aspect ratio of the cavity. The obtained results show that entropy generation tends towards asymptotic values for lower thermal Grashof number values, whereas it takes an oscillative behavior for higher values of thermal Grashof number. Transient entropy generation increases towards a maximum value, then decreases asymptotically to a constant value that depends on aspect ratio of the enclosure. Entropy generation increases with the increase of thermal Grashof number, irreversibility distribution ratio and aspect ratio of the cavity. Bejan number is used to measure the predominance of either thermal or viscous irreversibility. At local level, irreversibility charts show that entropy generation is mainly localized on bottom corner of the left heated wall and upper corner of the right cooled wall.


Transport in Porous Media | 2012

Entropy Generation in Double-Diffusive Convection in a Square Porous Cavity using Darcy–Brinkman Formulation

Ali Mchirgui; Nejib Hidouri; Mourad Magherbi; Ammar Ben Brahim

The article reports a numerical study of entropy generation in double-diffusive convection through a square porous cavity saturated with a binary perfect gas mixture and submitted to horizontal thermal and concentration gradients. The analysis is performed using Darcy–Brinkman formulation with the Boussinesq approximation. The set of coupled equations of mass, momentum, energy and species conservation are solved using the control volume finite-element method. Effects of the Darcy number, the porosity and the thermal porous Rayleigh number on entropy generation are studied. It was found that entropy generation considerably depends on the Darcy number. Porosity induces the increase of entropy generation, especially at higher values of thermal porous Rayleigh number.


Entropy | 2011

Analysis of the Magnetic Field Effect on Entropy Generation at Thermosolutal Convection in a Square Cavity

Mounir Bouabid; Nejib Hidouri; Mourad Magherbi; Ammar Ben Brahim

Thermosolutal convection in a square cavity filled with air and submitted to an inclined magnetic field is investigated numerically. The cavity is heated and cooled along the active walls with a mass gradient whereas the two other walls of the cavity are adiabatic and insulated. Entropy generation due to heat and mass transfer, fluid friction and magnetic effect has been determined in transient state for laminar flow by solving numerically the continuity, momentum energy and mass balance equations, using a Control Volume Finite—Element Method. The structure of the studied flows depends on four dimensionless parameters which are the Grashof number, the buoyancy ratio, the Hartman number and the inclination angle. The results show that the magnetic field parameter has a retarding effect on the flow in the cavity and this lead to a decrease of entropy generation, Temperature and concentration decrease with increasing value of the magnetic field parameter.


International Journal of Exergy | 2011

Conceptual and functional study of a solar absorption refrigeration cycle

Emna Berrich; Ali Fellah; Ammar Ben Brahim; Michel Feidt

The paper presents an optimised conceptual design approach. It deals with the analysis of the solar absorption refrigerators performances. Hierarchical decomposition and endoreversibility principles of technical and energetic systems are used. Optimisation is carried out according to the Lagrange multipliers method. The general optimal performances of the cycle are coupled into a derived set of equations. The functional and conceptual characteristics are studied and the effects of the external sources temperatures on both the performances and the functional and conceptual characteristics are highlighted. This approach could be useful all time when we have to handle with a great number of variables.


Journal of Thermodynamics | 2013

Second Law Analysis of a Gas-Liquid Absorption Film

Nejib Hidouri; Imen Chermiti; Ammar Ben Brahim

This paper reports an analytical study of the second law in the case of gas absorption into a laminar falling viscous incompressible liquid film. Velocity, temperature, and concentration profiles are determined and used for the entropy generation calculation. Irreversibilities due to heat transfer, fluid friction, and coupling effects between heat and mass transfer are derived. The obtained results show that entropy generation is mainly due to coupling effects between heat and mass transfer near the gas-liquid interface. Total irreversibility is minimum at the diffusion film thickness. On approaching the liquid film thickness, entropy generation is mainly due to viscous irreversibility.


international renewable energy congress | 2016

Study of the performance of a single solar still for a typical day in Gabès region

Nejib Hidouri; Yemna Sarray; Ali Mchirgui; Ammar Ben Brahim

The performance of a single solar still is numerically studied by solving the energy balance equations, concerning Gabès region. Effects of the glass cover thickness and the saline water depth on water-to-inner glass cover temperature difference and on daily yield for June 21st are determined and graphically presented. It was found that optimum values of glass cover thickness and water depth giving highest productivity are 3 mm, and 1.5 cm, respectively.


Entropy | 2016

Hierarchical Decomposition Thermodynamic Approach for the Study of Solar Absorption Refrigerator Performance

Emma Berrich Betouche; Ali Fellah; Ammar Ben Brahim; Fethi Aloui; Michel Feidt

A thermodynamic approach based on the hierarchical decomposition which is usually used in mechanical structure engineering is proposed. The methodology is applied to an absorption refrigeration cycle. Thus, a thermodynamic analysis of the performances on solar absorption refrigerators is presented. Under the hypothesis of an endoreversible model, the effects of the generator, the solar concentrator and the solar converter temperatures, on the coefficient of performance (COP), are presented and discussed. In fact, the coefficient of performance variations, according to the ratio of the heat transfer areas of the high temperature part (the thermal engine 2) Ah and the heat transfer areas of the low temperature part (the thermal receptor) Ar variations, are studied in this paper. For low values of the heat-transfer areas of the high temperature part and relatively important values of heat-transfer areas of the low temperature part as for example Ah equal to 30% of Ar, the coefficient of performance is relatively important (approximately equal to 65%). For an equal-area distribution corresponding to an area ratio Ah/Ar of 50%, the COP is approximately equal to 35%. The originality of this deduction is that it allows a conceptual study of the solar absorption cycle.

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Michel Feidt

University of Valenciennes and Hainaut-Cambresis

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Fethi Aloui

École des mines de Nantes

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H. Abbassi

École Normale Supérieure

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