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ملخص: This work is a contribution to study the irreversibilities by using a numerical resolution of the conservative equations of continuity, momentum and energy to see the influence of a magnetic field on flow structure and entropy generation for the case of a fluid confined in a square cavity in natural convection. Study is carried on in steady–unsteady states. It was shown the important role of the magnetic field on velocity and temperature fields, heat transfer and entropy generation. As a consequence, magnetic field can play the role of control mechanism of the flows in industrial processes. In the stationary state study, it could be noticed that the heat transfer and the entropy generation depend considerably on Grashof and Hartmann numbers, the inclination angle of the magnetic field and the irreversibility coefficient. The fluid movement is intensively removed and the total entropy generation is largely decrease by the presence of a high magnetic field, which finally induces an evolution of the system towards a conductive state...

الكُتّاب المؤلفون: Atef

التاريخ: 28/9/2017

النوع: thesis

ملخص: Solar distiller

الكُتّاب المؤلفون: AMMER, Atef, EL OUEDERNI

التاريخ: 15/5/2017

النوع: patent

ملخص: 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.

الكُتّاب المؤلفون: Atef

التاريخ: 28/9/2017

النوع: article

ملخص: Irreversibility of MHD fluids in natural convection through a square cavity is numerically investigated. The cavity is heated and cooled along the active walls whereas the two other walls are adiabatic. Entropy generation due to heat transfer, fluid friction and an imposed horizontal magnetic field has been determined for a laminar flow, by solving numerically the conservation equations of continuity, momentum and energy, using the Control Volume Finite-Element Method. The structure of the studied flows depends on three dimensionless parameters which are: the Prandtl number, the thermal Grashof number and the Hartmann number. Results show that the magnetic field parameter (Hartmann number) suppresses the flow and this leads to a decrease of entropy generation. Temperature decreases with the increase of the magnetic field parameter. The average Nusselt number increases with the Prandtl number and, in particular, its effect is more evident for higher values of Hartmann number.

الكُتّاب المؤلفون: Mounir, Nejib, Mourad, Atef

التاريخ: 28/9/2017

النوع: article

ملخص: 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.

الكُتّاب المؤلفون: Atef, Amel, Mourad, Ammar

التاريخ: 26/10/2017

النوع: article

ملخص: The paper reports a numerical investigation of the entropy generation analysis due to mixed convection in laminar
flow through a channel filled with porous media. The second law of thermodynamics is applied to investigate the entropy
generation rate. The Darcy-Brinkman Model is employed. The entropy generation due to heat transfer and friction dissipations
has been determined in mixed convection by solving numerically the continuity, momentum and energy equations, using a
control volume finite element method. The effects of Darcy number, modified Brinkman number and the Rayleigh number on
averaged entropy generation and averaged Nusselt number are investigated. The Rayleigh number varied between 103 ≤ Ra ≤
105 and the modified Brinkman number ranges between 10-5 ≤ Br≤ 10-1 with fixed values of porosity and Reynolds number at
0.5 and 10 respectively. The Darcy number varied between 10-6 ≤ Da ≤10.

الكُتّاب المؤلفون: Amel, Atef, Mourad

التاريخ: 26/10/2017

النوع: article

ملخص: This paper numerically investigates the effect of an externally evanescent magnetic
field on flow patterns and heat transfer of fluid in a square cavity. The horizontal walls of the
enclosure are assumed to be insulated while the vertical walls are kept isothermal. A control
volume finite element method is used to solve the conservation equations. The effect of constant
Hartmann number on Nusselt number was studied. Validation tests with existing data demonstrate
the aptitude of the present method to produce accurate results. The effects of inclination magnetic
field angle from 0° to 90° on streamlines distributions are shown for different value of Hartmann
number. For Grashof number equal to 105, the values of relaxation time of the magnetic field are
chosen, so that the Lorentz force acts only during the startup transient of the natural convection
flow. The Nusselt number was calculated for different values of the inverse relaxation time
varying from 0 to +∞. The magnitude and the number of oscillations of the Nusselt number were
observed. It has been found that no oscillation was seen at relaxation time equal to 20. Stream
lines maps are plotted for different values of dimensionless time. The effect of relaxation time on
the transition from single-cell to double-cell configuration was observed.

الكُتّاب المؤلفون: Atef, Nejib, Mourad, Ammar

التاريخ: 14/5/2017

النوع: article

ملخص: 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.

الكُتّاب المؤلفون: Atef, Nejib, Mourad, Ammar

التاريخ: 26/10/2017

النوع: article

ملخص: This paper numerically investigates the effect of an externally evanescent
magnetic field on total entropy generation in a fluid enclosed in a square cavity
by using a volume finite element method to solve the conservation equations at
Prandtl number of 0·71. The values of relaxation time of the magnetic field are
chosen, so that the Lorentz force acts only in the transient state of entropy generation
in natural convection. The total entropy generation was calculated for, fixed
value of irreversibility distribution ratio, different relaxation time varying from 0
to 1/5 and Grashof number varying from 104 to 105. The effects of the Hartman
number and the magnetic field inclination angle on the evolution of total entropy
generation throughout the transient regime were investigated. Results show that the
application of evanescent magnetic field not only suppresses the fluctuation of the
total entropy generation in the transient state, but also reduces the gap for magnetic
field relaxation time less than 1/10.

الكُتّاب المؤلفون: Mourad, Atef, Nejib, Ammar

التاريخ: 22/10/2017

النوع: article

ملخص: This paper investigates the effect of an imposed magnetic field on the flow patterns, and the entropy generation in a square cavity. A control volume finite element method is used to solve the conservation equations at Prandtl number of 0.71. The effects of Grashof number, Hartmann number and inclination angle of the magnetic field are investigated. The study covers the range of the Hartmann number from 0 to 50, the magnetic field inclination angle from 0° to 90° with Grashof number ranging between 10^3 and 10^5. The effects of Hartmann number and the magnetic field inclination angle are presented graphically in terms of isotherm and streamline plots. The effect of the magnetic field is found to suppress the convection currents and heat transfer inside the cavity. This effect is significant for high Grashof numbers. Results show that the Nusselt number is clearly affected by the magnetic field. The effect of the Hartmann number on entropy generation was investigated in steady-unsteady state of natural convection. It was found that entropy generation in the steady state decreases when Hartmann number increases. Additionally, the oscillatory behaviour of the entropy generation at the onset of natural convection can be suppressed at critical Hartmann number.

الكُتّاب المؤلفون: Mourad, Atef, Ammar

التاريخ: 22/10/2017

النوع: article

ملخص: Following to a main work done on various collector systems and solar models, we proceeded to choose a model to predict global solar irradiance to Gabes city (Tunisia). Once EUFRAT model was chosen, the optimal tilt angle had been determined for a good captation of the solar energy in this city. These optimal tilt angles have been translated by a relation joining them to the quantum of the year. Finally it has been defined the function gain of energy that has been joined to the quantum of the year and the optimal tilt angle.

الكُتّاب المؤلفون: Ridha Fethi, Atef, Ammar

التاريخ: 22/10/2017

النوع: article

ملخص: This work is dedicated to the study of the plant Oudneya africana, the endemic plant, from the family of Brassicaceae. This plant is notably found in the Sahara area. The extraction, the antimicrobial and the antioxidant activities were realized for stems, leaves, and flowers. Hydrodistillation techniques used for the extraction of essential oil. Flowers contain the highest yield 5.75 %. The determination of the humidity showed that the leaves of Oudneya africana contain approximately half of their weight of water. The chemical analysis of essential oil by GC-MS shows that stems contain 28 compounds, leaves contain 43 compounds and flowers contain 12 compounds. The flavonoids and phenolics contents are ranged from 148 ± 29.44 (for stems) to 77.03 ± 24.5 μg/ml (for flowers) and from 238.8 ± 23.71 (for leaves) to 33.03 ± 13.79 mg/ml (for stems). For the DPPH (1,1diphenyl-2-picrylhydrazyl) assay, the oils of the three parts showed various antioxidant activities. The most active part was the leaves, with an IC50 value of 51.25 μg/l, followed by flowers (IC50 = 40.37 μg/l). The essential oils showed significant antibacterial activities against Gram-positive and Gram-negative bacteria, but with various activity levels.

الكُتّاب المؤلفون: Atef, Faten, MD Mamoon

التاريخ: 13/11/2018

النوع: article