Amawal n yimuddiren n teẓgi n Rric n tγiwant n Tubiret (tasleḍt tasnamkant)

Amawal n yimuddiren n teẓgi n Rric n tγiwant n Tubiret (tasleḍt tasnamkant)Amawal n yimuddiren n teẓgi n Rric n tγiwant n Tubiret (tasleḍt tasnamkant

Etude du vieillissement de silices pyrogéniques à taux d’humidité relative variables

Pyrogenic silicas , produced by combustion of SiCl4 into a mixture hydrogene/air, are widely used as filler for polysiloxanes, but also as one of the main components of super-thermal insulating. However, the nanoscale of these silicas and surface chemistry (silanol groups) is also responsible for their ability to adsorb water vapour, which alters their insulation and reinforcement properties, especially when stored in uncontrolled conditions. Initially the surface of pyrogenic silicas is partially hydroxylated, silanol groups, but presents also strained siloxane bridges, which can react with adsorbed water, leading to a change in their surface properties when exposed to the atmospheric moisture. Despite its industrial importance, this phenomenon has been rarely studied in the literature, except a single study, which was rather limited.Our study was focused on a set of six pyrogenic silicas, having specific surface areas comprised between 150 to 400 m2 / g. They were aged at constant temperature 22.5 ± 0.1 ° C in a closed chamber under controlled relative humidity (RH): 62, 75, 84, 92 and 100%.The water adsorption was followed gravimetrically. The mass of water adsorbed per unit area increases with both HR and the specific surface area. This increase, which can reach nearly 60% of the initial mass at 100% RH, is induced by the increase of their surface hydrophilicity due to the formation of new silanol groups. But, the study of the influence of the variation in RH, indicates that a threshold exists around HR50%, below which these silicas are stable.Finally, fitting the gravimetric curves, it was evidenced that the water sorption follows a first order kinetics and that the kinetic constant goes through a maximum for an HR equal to 84%. This increase of silanol density was testified by chemical titration. It increases by about 50%, from 2.4 to 3.6 SiOH/nm2 for ageing under 100% RH, but is dependent of the specific surface area and surface roughness. IR spectroscopy clearly indicates a net decrease of isolated silanol band correlated with an increase of H-bounded silanol. Proton and silicon NMR spectroscopies confirm the increase of the local density silanol groups on the aged silca surface.Finally, the evolution of the surface properties of these silica samples, aged during about 1000 h, was followed by inverse gas chromatography in infinite dilution (IGC-ID) and at finite concentration (CGI-FC) conditions.The CGI-ID was performed using linear and cyclic alkane probes. It shows that the ageing process affects only very slightly both the dispersive component of surface energy and the nano-roughness at the molecular level of all studied, indicating that the surface morphology is quite unchanged. Then; the variation of their surface heterogeneities with ageing time, in terms of the distribution functions of the probe adsorption energies, was assessed by CGI-CF, using isopropanol as probe.The aging process leads, as expected, to an increase of the high energy component related to the appearance of new silanol groups by nucleophilic opening of siloxane bridges by water confirming the reactivity of fumed silicas toward water when exposed to a high RH. All our observations, existence of a threshold, maximum for the kinetic constant and decrease of the chemisorbed of water amount with both specific surface area and surface roughness is supported by a model for the ageing process. [...]Les silices pyrogéniques sont très utilisées comme charge pour les polysiloxanes mais elles sont l’un des principaux constituants des superisolants thermiques. Cependant, l’échelle nanométrique de ces silices et leur chimie de surface (groupes silanol) est également responsable de leur aptitude à adsorber la vapeur d’eau, ce qui a pour conséquence d’altérer leurs propriétés d’isolant thermique au cours du temps, notamment lors de leur stockage dans des conditions non contrôlées. Malgré son importance industrielle ce phénomène n’a fait l’objet dans la littérature que d’une seule étude assez limitée.En effet, initialement la surface de ces silices ne sont que partiellement hydroxylées et la présence de ponts siloxanes tendus, susceptibles de réagir avec l’eau va mener à une évolution de leurs propriétés de surface en présence d’humidité.Une première étude a porté sur les silices N20, T30 et T40 (Wacker Chemie AG) sont obtenues par combustion de SiCl4 dans un mélange air/H2, de surfaces spécifiques égales respectivement à 200, 300 et 400 m2/g. Elles ont été vieillies à température constante 22,5 ± 0,1 °C, dans une enceinte fermée, sous humidité relative (HR) contrôlée : 62, 75, 84, 92 et 100%.L'adsorption d'eau a été suivie par gravimétrie. La masse d’eau adsorbée, par unité de surface augmente à la fois avec HR et la surface spécifique. Cette augmentation qui peut atteindre près de 60% de la masse initiale pour une HR de 100%, est liée à l’augmentation de l’hydrophilie de la surface de la silice liée à la formation de nouveaux groupes silanol. Nous avons démontré que cette augmentation suit une cinétique du 1er ordre et que la constante cinétique passe par un maximum pour une RH égale à 84%.L’augmentation du nombre de silanol superficiels a été confirmée par leur dosage chimique. Leur densité superficielle augmente d’environ 50%, passant de 2,4 SiOH/nm2 à 3,6 SiOH/nm2 pour l’HR égale à 100%.La spectroscopie IR atteste clairement d’une diminution nette des silanol isolés au profit de silanol fortement liés par pont hydrogène. Les spectroscopies RMN du proton et du silicium confirment l’augmentation de la densité locale en groupes silanols.L’évolution des propriétés superficielles des silices vieillies environ 1000 h a été suivie par chromatographie inverse à dilution infinie (CGI-DI) et concentration finie (CGI-CF).La CGI-DI pratiquée avec des sondes alcanes linéaires et cycliques démontre que le vieillissement n’affecte que très faiblement tant la composante dispersive de l’énergie de surface que leur rugosité à l’échelle moléculaire, autrement dit qu’il ne modifie pas la morphologie de la surface. Notamment la rugosité superficielle des silices T30 et T40 n’est pas affectée.La variation de l’hétérogénéité superficielle avec le vieillissement a été déterminée, en termes de fonctions de distribution des énergies d’adsorption de l’isopropanol, par CGI-CF.Le processus de vieillissement conduit, comme attendu, à une augmentation de la composante de haute énergie liée à l'apparition de nouveaux groupes silanol par ouverture nucléophile des ponts siloxane. Le glissement du maximum de cette composante vers les hautes énergies montre la formation d’un nouveau type de silanol plus interactif par liaison hydrogène.Ces résultats confirment la réactivité des silices de combustion vis-à-vis de l'eau lorsqu’elles sont exposées à une humidité relative élevée. L'eau est chimisorbée sur la surface de la silice par une réaction d'ouverture des ponts siloxane. L'étude de l'influence de la variation de l'humidité relative, montre qu’il existe un seuil (HR50%) au-dessous duquel ces silices restent stables par rapport à la vapeur d'eau. [...

Contribution à l’étude des émissions polluantes dans un moteur diesel par modélisation numérique 2D

Le travail présenté est une contribution à l’étude des émissions polluantes dans un moteur diesel par modélisation numérique 2D, ce moteur est de type diesel LISTER PETTER à aspiration naturelle, monocylindrique, à injection directe sous le code CFD ANSYS-Fluent 16, pour sept richesses différentes à une vitesse de 1500 [tr/min]. La première partie est consacrée à l’étude bibliographique des moteurs à combustion interne, la deuxième partie est consacrée à la modélisation numérique des écoulements turbulents réactifs bi-phasiques et la troisième partie est consacrée aux résultats de la simulation numérique du moteur. Finalement on a présenté les performances énergétiques et environnementales

Activité antioxydante des composés phénoliques d’huile d’olive extraite par méthode traditionnelle

L'objectif de cette etude est de determiner la teneur en composes phenoliques totaux de lfhuile dfolive de la variete Chemlal obtenue par extraction artisanale et dfen tester leur pouvoir antioxydant. La teneur phenolique a ete determinee par la methode universelle Folin-Ciocalteu, alors que lfactivite antioxydante a ete evaluee par deux methodes complementaires: le test du radical libre 2,2-diphenyl-1-picrylhydrazyl et le test du β-carotene/acide linoleique. Cette huile dfolive a montre une teneur en composes phenoliques totaux de 167,29 ± 2,71mg EAG/kg et une valeur dfIC50 egale a 25, 38 ± 0,64mg/kg par le test DPPH et une activite antioxydante relative par le test β-carotene/acide linoleique de lfordre de 67,40 ± 1,02%. Le controle positif hydroxy toluene butyle (BHT) a devoile respectivement 23,86 ± 0,14mg/kg et 95,88 ± 0,85%. Ces resultats revelent une possible utilisation de cette huile dans la lutte contre les maladies lies au stress oxydant.Mot cles : Oleaeuropea, β-carotene/acide linoleique, DPPH, variete Chemlal, regime mediterraneen

GeneFarm, structural and functional annotation of Arabidopsis gene and protein families by a network of experts

Genomic projects heavily depend on genome annotations and are limited by the current deficiencies in the published predictions of gene structure and function. It follows that, improved annotation will allow better data mining of genomes, and more secure planning and design of experiments. The purpose of the GeneFarm project is to obtain homogeneous, reliable, documented and traceable annotations for Arabidopsis nuclear genes and gene products, and to enter them into an added-value database. This re-annotation project is being performed exhaustively on every member of each gene family. Performing a family-wide annotation makes the task easier and more efficient than a gene-by-gene approach since many features obtained for one gene can be extrapolated to some or all the other genes of a family. A complete annotation procedure based on the most efficient prediction tools available is being used by 16 partner laboratories, each contributing annotated families from its field of expertise. A database, named GeneFarm, and an associated user-friendly interface to query the annotations have been developed. More than 3000 genes distributed over 300 families have been annotated and are available at http://genoplante-info.infobiogen.fr/Genefarm/. Furthermore, collaboration with the Swiss Institute of Bioinformatics is underway to integrate the GeneFarm data into the protein knowledgebase Swiss-Pro

Feasibility Study of a Wind-Diesel Hybrid System in a Remote Site on Southern of Algeria

In this study, we present an autonomous solution for a village located north of Timimoun in Algeria, with around thirty households. As the region has good wind potential with an average annual speed of around 5m/s, this resource is used to develop a hybrid wind/diesel/battery system. A technical-economic analysis is carried out using the HOMER optimization tool to determine the optimal solution. We considered a range of load sizes, from 0.9 kWh/d to 3.6 kWh/day, and a range of wind speeds, from 3.99 m/s to 5.42 m/s at 10 m from the ground. Several wind turbines with powers ranging from 1 kW to 10 kW have been tested.The best combination is given by the wind/diesel/battery system operating with the WES 5 Tulipo turbine with a rated power of 2.6 kW, with a diesel price equal to 0.22 $/kWh. This solution reduces the COE to 0.569$/kWh and renewable fraction is maximum (86%). In addition, the emissions of CO2, CO and SO2 decrease to less than 70% of the emissions of Diesel power system. The sensitivity study shows that the wind/diesel/battery system is optimal for any wind speed greater than 3.5 m/s whatever the price of diesel

AHP Optimization Method for Windy Site in Costal Annaba Region

The majority of countries worldwide rely on fossil fuels as a source of energy. Nevertheless, the utilization of this source of energy is associated with significant environmental problems. To reduce their impact, innovative clean energy solutions are needed. Wind power is currently the most cost-effective and competitive renewable energy source. The identification of an optimal location for a wind farm is a crucial aspect of the decision-making process. This involves considering numerous factors, including wind speed, terrain quality, distance to the power grid, road network, housing, agricultural land, and environmental concerns. The use of Multi-Criteria Decision Method (MCDM) and Geographic Information System (GIS), along with other techniques, facilitates the selection of sites that meet the desired criteria. This study employed GIS and MCDM-AHP methods in order to identify suitable sites for wind farm installation in an eastern Algerian coastal area. In the context of MCDM analysis, it is important to note that not all criteria are of equal importance. Consequently, each criterion is assigned a specific weight to reflect its importance. The weights assigned in this study were calculated using the Analytic Hierarchy Process (AHP). The result was a wind speed suitability map that combined all criteria into two site categories in fact, 20% of the land area is highly suitable and 10% is found to be most suitable

New Actuator Disk Model for the Analysis of Wind Turbines Wake Interaction with the Ground

Wake models based on Actuator Disk theory are usually applied to optimize the wind farm layouts and improve their overall efficiency and expected AEP. Despite the effectiveness of the existing models, most Actuator Disk approaches are based on the flow axisymmetric assumption, without considering the ground effect on the wake behavior. However, it has been shown that the mast’s height, or distance from the wind turbine to the ground, has an influence on the wake expansion on both hub’s side and at downstream of the wind turbine. Therefore, in this study, a hybrid CFD-BEM-Actuator Disk approach is developed to address the lack of the existing models. In the proposed model, the 3D wind rotor is modeled by a set of blade elements. Then, the local lift and drag forces acting on each blade element are calculated using BEM theory and incorporated into the momentum equation. This BEM-AD model is implemented in a User Defined Function (UDF) that is loaded into the CFD software. Thereby, ground effects are considered to be a wall boundary and defining a wind boundary layer profile at the inlet boundary, which describes the Atmospheric Boundary Layer (ABL). For the validation of this new Actuator Disk model, an enhanced experimental study is conducted at the Dynfluid Laboratory wind tunnel (ENSAM School Paris Tech). The Particle Image Velocimetry (PIV) measurements are used for the experimental wake explorations applied to a miniature two-bladed wind turbine. The wake developments are analyzed at two different hub heights ratio, h/D = 0.7 and 1.0 (where h is the hub height, and D is the wind rotor diameter). The analysis of the outcomes showed that the numerical simulations are in good correlation with the experimental measurements of the ENSAM wind tunnel. The numerical results show that for h/D=0.7, the upper half of the rotor operates within the boundary layer whereas the lower tip vortices are mainly developed in the horizontal direction with lower intensity compared to the upper tip vortices. This effect was not observed for the case h/D=1.0 where the rotor operates outside of the boundary layer; however, the wake centerline is upward deflected at about 0.3D. The main conclusion is that a distance above 7D must be observed between wind turbines to optimize the wind farm performance and over 1D hub height be required to limit the influence of the ground boundary layer effect