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Eloukabi H.,Laboratoire dEtudes des Systemes Thermiques et Energetiques | Sghaier N.,Laboratoire dEtudes des Systemes Thermiques et Energetiques | Prat M.,CNRS Institute of Fluid Mechanics of Toulouse | Ben Nassrallah S.,Laboratoire dEtudes des Systemes Thermiques et Energetiques
Chemical Engineering and Technology | Year: 2011

The evaporation of an aqueous NaCl solution in a hydrophobic two-dimensional model porous medium was studied experimentally. The process is characterized by the formation of efflorescence at the porous medium surface. It is shown that the onset of efflorescence formation and its growth depends on the initial solution concentration. The experiments show that the invasion patterns are little affected by the presence of salt, but that the efflorescence contributes to gradually increase of the evaporation rate as the initial concentration in salt is increased. Then, a second phase was identified where the efflorescence dries out and drying becomes very slow. Results suggest that there exists an initial concentration marking the transition between the regime with high impact of efflorescence and the regime with low impact of efflorescence. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Najjari M.,Gabes University | Khemili F.,Laboratoire dEtudes des Systemes Thermiques et Energetiques | Ben Nasrallah S.,Laboratoire dEtudes des Systemes Thermiques et Energetiques
International Journal of Hydrogen Energy | Year: 2013

The work presented in this paper includes contributions that provide insight into liquid water transport in the proton exchange membrane fuel cell (PEMFC). The purpose of the present study is to investigate the influence of gravity on the cathode flooding by accumulated liquid water at the interface between catalyst layer and gas diffusion layer (CL-GDL interface) in a PEMFC. We introduce a one-dimensional and transient model based on numerical resolution of mass transport of liquid water and oxygen in the porous GDL domain. Obtained results indicate that gravity has significant effects on the transient time and on the cell voltage at the steady regime. In this work, both opposing and aiding gravity cases, as reference to capillary actions, are considered.


Megdouli K.,Unite de Recherche Energetique et Environnent | Tashtoush B.M.,Jordan University of Science and Technology | Nahdi E.,Unite de Recherche Energetique et Environnent | Elakhdar M.,Unite de Recherche Energetique et Environnent | And 2 more authors.
International Journal of Refrigeration | Year: 2016

Waste heat from the gas cooler is a form of free energy, which can be utilized to drive an ejector cooling cycle. This paper presents a new CO2 ejector-cascade refrigeration cycle. The effects of important parameters on the thermodynamic performance of the new cycle are theoretically investigated based on energetic and exergetic analyses. Furthermore, the performance comparison of the proposed cycle and conventional cycle is carried out. The theoretical study shows that the new cycle exhibits a reasonable value of COP (coefficient of performance) and system second law efficiency. For the same cooling capacity, the improvements of the maximum COP and second law efficiency could reach 37% and 12%, respectively, over those of the conventional cascade cycle under the given operating conditions and at the optimum gas cooler pressure. © 2016 Elsevier Ltd and IIR


Khemili F.,Laboratoire dEtudes des Systemes Thermiques et Energetiques | Najjari M.,Laboratoire dEtudes des Systemes Thermiques et Energetiques | Nasrallah S.B.,Laboratoire dEtudes des Systemes Thermiques et Energetiques
Journal of Porous Media | Year: 2011

By using a separate phase-flow method, we have studied numerically the effects of the temperature on two-phase transport phenomena in the porous cathode of a proton exchange membrane fuel cell (PEMFC). The startup of the two-phase regime is controlled by a threshold current density which indicates the emergence of the liquid phase. The mass conservation equations are solved using the control volume finite element (CVFE) method. Electrochemical responses of the PEMF cell have been analyzed and discussed. Profiles of oxygen concentration, liquid water saturation, and cathode overpotential are presented for different values of the temperature of the PEMFC. © 2011 by Begell House, Inc.

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