Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE

Kairouan, Tunisia

Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE

Kairouan, Tunisia

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Wjihi S.,University of Monastir | Sellaoui L.,University of Monastir | Bouzid M.,University of Monastir | Dhaou H.,Qassim University | And 5 more authors.
International Journal of Hydrogen Energy | Year: 2016

In the present work, experimental absorption isotherms of hydrogen in LaNi5 at three temperatures have been fitted using a monolayer model treated by statistical physics by means of the grand canonical ensemble. Six parameters of the model are fitted, namely two numbers of absorbed atoms per, site n1 and n2, two receptor site densities, N1M and N1M and two energetic parameters, P1 and P2. The behaviors of these parameters are discussed in relationship with absorption process. Starting from the monolayer model, we determined the absorption energies which are typically ranged between 85 and 101 kJ/mol comparable to usual chemical bond energies. Calculated thermodynamic potentials such as internal energy (Eint) and Gibbs free energy (G) suggested that the absorption processes was exothermic and spontaneous. © 2016 Hydrogen Energy Publications LLC.


Lachheb M.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE | Albouchi F.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE | Mzali F.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE | Ben Nasrallah S.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE
Applied Thermal Engineering | Year: 2016

This paper addresses the development and the thermal investigation of new composite materials with improved thermo-physical properties destined for solar thermal energy storage at high temperature. The thermo-physical properties of composites are characterized by using several techniques based on the temperature measurement and the obtained results are compared to the theoretical values calculated by different analytical models. The results of these experiments revealed a clear improvement in the different thermal properties when integrating graphite particles in the composite. In the other hand, a good agreement between experimental and theoretical values was obtained. © 2016 Elsevier Ltd. All rights reserved.


Wjihi S.,University of Monastir | Bouzid M.,University of Monastir | Sellaoui L.,University of Monastir | Knani S.,University of Monastir | And 4 more authors.
Fluid Phase Equilibria | Year: 2016

Analytical expression for the modeling of hydrogen sorption isotherms on LaNi4.75Fe0.25 alloy at three temperatures (293 K, 303 K and 313 K) is developed using statistical mechanics formalism. Our objective in this modeling is to select the adequate model that presents a high correlation with the experimental curves in order to obtain new physicochemical interpretations at a molecular level. The parameters involved in the model, such as the number of sorbed hydrogen atom per site, n, the receptor sites' density, NM, and the energetic parameters, P1 and P2, were determined directly from the experimental sorption isotherms by numerical simulation. The results of fitting are interpreted. A dynamic study of the α and β phases of sorption was carried out by focusing on the formation of one of these phases in relation to the other, depending on the pressure and the evolution of the adjustment parameters. Then, the model is further applied to calculate thermodynamic functions which govern the sorption mechanisms such as entropy, free enthalpy of Gibbs and internal energy. © 2016 Elsevier B.V.


Adili A.,A-D Technologies | Hasni N.,Institute National des science Appliquees et des Technologies INSAT | Kerkeni C.,A-D Technologies | Ben Nasrallah S.,Laboratoire des Etudes des systemes Thermiques et Energetiques LESTE
International Journal of Thermal Sciences | Year: 2010

In the past few decades, the study on how to apply genetic algorithms to problems in the industrial engineering world has aroused a great deal of curiosity of many researchers in the area of management science, industrial operations and engineering systems. This paper shows an experimental process of thermophysical properties estimation of fouling deposited on internal surface of a heat exchanger tube using genetic algorithms. In brief, the deposits on heat exchanger tubes are caused by the presence of inorganic salts, of small quantities of organic materials and products of corrosion in the water. From thermophysical point of view, the deposited fouling has harmful effects on the heat exchanger efficiency. For these reasons the determination of its thermophysical properties became very important. The experimental bench using a photothermal method with a finite width pulse heat excitation is used. The genetic algorithm is used to minimize an objective function containing a calculated and a measured temperature. This last is measured on the rear face of a bi-layer system composed of a section of a heat exchanger and the fouling deposited on during and after a finite width pulse heat excitation on its front face. The calculated temperature, that is a function of the unknown thermophysical properties of the bi-layer system, is calculated by the resolution of the one-dimensional linear inverse conduction problem, and by the use of the thermal quadrupoles formalism. The motivation in using genetic algorithms was their potential to overcome the restriction to the estimation of non-correlated parameters of gradient-based methods, and their powerful ability to work well for many complex problems which are very difficult to solve by conventional techniques. The results of the estimation procedure show on the one hand the efficiency and the stability of the developed genetic algorithm to estimate the thermophysical properties of fouling and the high accuracy of the obtained results on the other hand. © 2010 Elsevier Masson SAS. All rights reserved.


Mechi N.,University of Monastir | Sellaoui L.,University of Monastir | Ben Khemis I.,University of Monastir | Dhaou H.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE | And 3 more authors.
Fluid Phase Equilibria | Year: 2016

Modeling of absorption and desorption isotherms of hydrogen on LaNi4.85Al0.15 alloy at 298 K, 303 K and 313 K has been achieved through the use of grand canonical ensemble in statistical physics. In fact, a monolayer model with two levels of energy has been adopted to better fit the experimental data. Besides, six physicochemical parameters have been used to better describe the absorption and desorption processes from the point of view of α and β phases. These parameters are divided into two types. The first type of parameters contains four main parameters, namely the number of atoms per site, nα and nβ, and the densities of hydrogen receptor sites Nmα as well as Nmβ. The second type of parameters are mainly the two energetic parameters Pα and Pβ which respectively refer to the pressures at half saturations for the α phase and the β phase. Thanks to these steric and energetic parameters, we could compare the absorption and desorption processes to highlight the evolution of these parameters during hysteresis encountered in the desorption isotherms. © 2016 Elsevier B.V.


Mechi N.,University of Monastir | Ben Khemis I.,University of Monastir | Dhaou H.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE | Knani S.,University of Monastir | And 2 more authors.
Fluid Phase Equilibria | Year: 2016

Using the grand canonical ensemble in statistical physics, a hydrogen absorption and desorption isotherms on LaNi4.85 Al0.15 alloy have been modeled by a monolayer model with two level of energy. The model has six physicochemical parameters which are deduced from the fitting of the isotherms at three temperatures T = 298 K, T = 303 K and T = 313 K. These parameters were used to better understand and compare between the absorption and desorption phenomena. A macroscopic study is achieved through thermodynamic functions as the internal energy, the entropy, the free enthalpy, the chemical potential, the enthalpy, and the free energy. We proved the coexistence of the α and β phases during absorption process. © 2016


Ben Yahia M.,University of Monastir | Knani S.,University of Monastir | Dhaou H.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE | Hachicha M.A.,University of Monastir | And 2 more authors.
International Journal of Hydrogen Energy | Year: 2013

Three theoretical expressions for the adsorption isotherms of hydrogen on LaNi4.75Fe0.25 alloy at 303 K and 313 K have been established. Our objective in this modeling is to select the adequate model that presents a high correlation with the experimental curves. The establishment of these new expressions is based on statistical physics formalism. This method has allowed the estimation of physicochemical parameters in the theoretical model. The parameters intervening in the adsorption process have been deduced directly from experimental adsorption isotherms by numerical simulation. We will mainly introduce four parameters affecting the adsorption process, namely; the density of hydrogen receptor sites NM, the number of molecules per site and the hydrogen adsorption energy. Then we apply the model to calculate thermodynamics functions which govern the adsorption mechanism such as entropy, free enthalpy and internal energy. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.


Lachheb M.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE | Albouchi F.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE | Mzali F.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE | Nasrallah S.B.,Laboratoire des Etudes des Systemes Thermiques et Energetiques LESTE | Benameur T.,Laboratoire Of Genie Mecanique
International Journal of Heat and Technology | Year: 2013

This paper deals with the analysis of a LiNO3/ graphite composite for thermal storage at high temperature. In such a composite, the salt (LiNO3) serves as a latent heat storage material and the graphite has been used to enhance the thermal conductivity of the salts. The elaboration method consists of a cold uni-axial compression of a physical mixing of salts powder and graphite particles. The thermal conductivity of the LiNO3/ graphite composites with different mass fraction of graphite was measured using transient hot wire technique. Also, the influence of the moisture content on the measurement was studied.

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