Conception et réalisation des capteurs hybrides photovoltaïque-thermiques sous vide ou avec lame d’air confinée

Cette étude fait l’analyse des performances thermiques et électriques de deux types de capteurs solaires hybrides photovoltaïque-thermiques à air intégrables en toitures des bâtiments. Pour ces capteurs hybrides, les cellules PV sont isolées soit avec une lame d’air confinée ou soit avec un gap vide. La modélisation des transferts de chaleur dans les systèmes est effectuée en 2D et en régime transitoire, suivant l’approche nodale. Le code numérique développé a été validé et a permis d’analyser les comportements thermiques ainsi que les efficacités thermique et électrique des capteurs. L’optimisation des paramètres fonctionnels est ensuite effectuée et présentée.Mots-clés: énergie solaire, cellules photovoltaïques, capteurs solaires hybrides (PV/T), transferts thermiques. Conception and realization of hybrid photovoltaic thermal collectors with empty gap or with enclosed air cavityThe present work reports thermal and electrical efficiencies for two solar hybrid photovoltaic-thermal air collectors integrated into the roof of the buildings. In these hybrid collectors, the PV cells are insulated with the enclosed air film or with the empty gap cavity. The unsteady and two-dimensional heat transfer equations are proposed and these equations are discretized using nodal method. The numerical model developed is validated. Then thermal and electrical efficiencies are analyzed for the collectors. The optimization of the characteristics parameters is studied in detail.Keywords: solar energy, photovoltaic cells, hybrid solar collector, heat transfer, nodal method

Ordre local dans les oxynitrures de silicium étudié par spectroscopie de photoélectrons XPS

X-ray photoelectron spectroscopy has been used to study core level and valence band spectra of reference compounds SiO$_2$, Si$_2$N$_2$O, Si$_3$N$_4$, and thin oxinitride films SiO$_x$N$_y$ obtained by nitridation of SiO$_2$ films in an ammonia plasma. The results obtained for the reference compounds are discussed with respect to their crystallographic properties. These data are used for discussing local order and chemical composition of oxinitride films.La spectroscopie XPS a été utilisée pour mesurer les spectres des niveaux de cœur et des bandes de valence des composés définis SiO$_2$, Si$_2$N$_2$O et Si$_3$N$_4$ et de films minces d'oxynitrures SiO$_x$N$_y$ formés par nitruration de films de SiO$_2$ dans un plasma d'ammoniac. Les résultats obtenus sur les composés définis sont discutés sur la base de leurs propriétés cristallographiques. Ces données ont été ensuite mises à profit pour discuter l'ordre local et la composition chimique de couches d'oxynitrures

A New Thermally Assisted, Plasma Based, Ionic Implantation System of Treatment and Deposition

Plasma based ionic implantation (PBII) is a new alternative to conventional ion implantation to produce near-surface treatments, layer growth or semiconductor doping, with the advantage of being non-directional. Furthermore, it can be used for improving the corrosion, friction and wear resisting properties of materials. This paper describes the development of a thermally assisted plasma immersion implantation reactor (TAPIIR). The system aimed at treating samples in the 0.5-60 keV range, with temperature regulation up to 1000°C. Thermochemical treatments, like the nitriding of steels or aluminium, are studied with a separate implantation and diffusion parameter control

High Temperature Plasma Based Ionic Implantation of Titanium Alloys and Silicon

Plasma based ionic implantation (PBII) of refractory materials is an alternative technique to conventional beam line implantation which appears to be very promising in the field of aeronautics, biomaterials and semiconductor electronics. In order to monitor sample temperature independently of the plasma discharge and of the pulsed high voltage conditions, we have developed a new thermally assisted PBII set-up. The thermally assisted plasma immersion implantation reactor (TAPIIR) which enables plasma implantation in the 0.5-60 keV range at controlled temperature between 200 and 1000 °C. Thermochemical treatments like nitriding of titanium and silicon were studied with a separated control of implantation and diffusion parameters. This paper describes implantations made in TAPIIR at elevated temperatures (500-900 °C) on titanium. The new results are presented and discussed by considering transport mechanisms during implantation at high temperature

ETUDE PAR ELLIPSOMETRIE EN TEMPS REEL D'ANODISATIONS PLASMA DE SILICIUM MONOCRISTALLIN

Un ellipsomètre monochromatique (632.8 nm.) à analyseur tournant a été utilisé pour suivre en temps réel l'oxydation anodique du silicium dans un plasma d oxygène (13.56 MHz, 600 W, 4 Pa). Un modèle comportant une seule couche transparente homogène sur du silicium monocristallin avec une interface abrupte n'est pas suffisant pour expliquer les résultats expérimentaux ; la présence d'une couche interfaciale entre le silicium et la silice est examinée.A monochromatic (632.8 nm) rotating analyzer ellipsometer has been developed for real time analysis of the anodic oxidation of silicon in an oxygen plasma (13.56 MHz, 600 W, 4 Pa). A single transparent layer on crystalline silicon with an abrupt interface cannot explain the experimental results ; the presence of a silicon-silicon dioxide interfacial layer is discussed

Improved nitridation efficiency and mechanical property of stainless steel surface after N2-H2 plasma nitridation at low temperature

In the thermochemical process of stainless steel nitridation, the improvement of mechanical properties is governed by the way the nitrogen diffusion profiles extend into the material. The efficiency of conventional thermal or ionic nitridation is substantially reduced at temperatures lower than 550 °C because of low nitrogen diffusivity. The present study shows that improved nitrogen transport can be obtained after nitridation in N 2 -H 2 plasma at floating potential, that is without cathodic bias on the samples. Such cold conditions allow for the iron matrix to be nitrided in a depth range of 10 μm at a temperature as low as 430 °C. Under these conditions, the top surface hardness was increased by a factor of three. Using the nanoindentation technique on cross-sections prepared on plasma nitrided samples, we could determine the profiles of hardness and Young modulus. Unexpectedly, the Young modulus was shown to be almost unaffected by the treatment. Furthermore, hardness profiles correlated very well with the nitrogen chemical profile and the results showed that the interface between the treated layer and the untreated part of the sample was very abrupt. The high level of surface strengthening and the increased nitridation efficiency at low temperature are thought to be a consequence of an activation of surface transport and diffusion using plasma (cold) conditions at floating potential

Improved nitrogen transport in Fe-C alloys during NH₃ plasma nitridation

In the thermochemical process of Fe-C alloy nitridation, improvements of mechanical properties are governed by the way the nitrogen diffusion profiles extend into the material. Up to now, thermal or ionic nitridation cannot be achieved at temperature lower than 550°C because of the strong lowering of nitrogen diffusivity. The present study shows that improved nitrogen transport can be obtained after nitridation in NH 3 plasma without cathodic bias on the samples. Such cold conditions allow the iron matrix to be nitrided in a depth range of 100-400 μm at a temperature as low as 350°C. The top surface hardness was shown to be improved by a factor of 3. This surface strengthening, markedly superior to that obtained with the classical treatments, is a well-known consequence of the temperature lowering that avoids coarsening of nitride microprecipitates. In addition, using this particular process, no growth of compound layer was observed at the surface. This absence of diffusion barrier is clearly beneficial to the improvement of the nitrogen transport. The high nitridation efficiency obtained at low temperature may be explained by an enhanced grain boundary diffusion due to defects generated by hydrogenous radicals produced in the plasma

Correlation between compacity distributions in compressed Si powders and in Si sintered pellets

Resistivity measurements have been performed on silicon powder beds with different thicknesses which were submitted to uniaxial pressure (0–640 MPa). For the smallest thicknesses of the Si pellets, the pressure dependence of conductivity may be described using models based on effective medium theory or strongest stresses network. For largest Si thicknesses, it exists an inhomogeneous distribution of pressure in the granular medium as a consequence of arching effects. It is shown that the conductivity variation with Si powder thickness may be understood using a distribution of conductivity induced by the distribution of pressure. Finally, it is shown that the conductivity of the sintered Si pellets is correlated with the uniaxial compression step