Numerical and Experimental Study of Natural Convection Air Flow in a Solar Tower Dryer

This work focuses on the study of the flow of air in natural convection in a solar tower of small size. The behavior of air in the tower, considered as a solar dryer, provides information on the amount of heat absorbed by the air upon entry into the collector. A theoretical approach allows us to theoretically simulate the flow by using a mathematical model characterizing the physical parameters of the system during a daily sunshine. An analysis of this phenomenon is made and results are obtained

Dirichlet’s problem on a cracked trapezium

This paper deals with solving Poisson’s equation with conditions on Dirichlet’s limits in an isosceles trapezium with two cracks. The large singular finite elements method used gives satisfactory results in all the domain of study. Numerical values obtained are very accurate for the constraint function and its first derivatives except at the ends of cracks where major changes were registered.Keywords: Large elements, finite elements, singularities, crack

Caractérisation expérimentale de l’émission d’oxydes d’azote dans l’incinération des déchets ménagers en four à grilles

International audienceIn front of a deposit of waste in constant evolution, the incineration became a very interesting alternative within the fields of management of waste. Nevertheless the combustion is generative of polluting, notably gas among whom nitrogen oxides. The study of the mechanisms of formation of these species shows a very strong dependence of their yield face to face of the local level in oxygen. So, our study was led to determine the influence of the excess air on the formation of NOx during the incineration of municipal solid wastes. This study allows to note the importance of the distribution of the airs between the primary and secondary injections.Face à un gisement de déchets en constante évolution, l’incinération est devenue une alternative très intéressante au sein des filières de gestion des déchets. Néanmoins la combustion est génératrice de polluants, notamment gazeux parmi lesquels les oxydes d’azote. L’étude des mécanismes de formation de ces espèces montre une très forte dépendance de leur rendement de formation vis à vis de la richesse locale en oxygène. Ainsi, notre étude a été menée afin d’étudier l’influence des débits d’air comburant sur la formation des NOx lors de l’incinération des déchets ménagers en four à grille. Cette étude permet de noter l’importance de la répartition des airs entre les injections primaires et secondaires

Structural and elastic properties of perovskite HoMnO3 crystal structures from ab-initio calculations

International audienceThe structural and elastic properties of the oxide perovskite HoMnO3 have been investigated by density-functional theory (DFT) implemented on the Quantum ESPRESSO code for the hexagonal, orthorhombic, rhombohedral and cubic crystal structures in the non-magnetic (NM), ferromagnetic (FM) and antiferromagnetic (AFM) configurations. The results show that all these compounds are thermodynamically stable, the hexagonal and the orthorhombic being the most stables in agreement with experimental results. The calculated bulk modulus, B, is about 168.5 ± 1.0 GPa and 178.9 ± 1.0 GPa for hexagonal structure in FM and configurations, respectively, and 188.7 ± 0.6 GPa and 175.6 ± 2.1GPa for orthorhombic structure in FM and AFM configurations, respectively. These values and those of the elastic constants Cij in the present work are comparable to values recently obtained with DFT calculations and experimentally for other perovskites RMnO3 (R = Eu, Gd, Tb and Dy). The calculated Poisson’s ratio is about 0.19; 0.27; 0.23 and 0.3 for hexagonal, orthorhombic, rhombohedral and cubic structure, respectively. The calculated Pugh’s ratio is about 1.30; 1.77–1.98; 1.54–1.60 and 2.11, respectively. These results show that the perovskite HoMnO3 tends to be brittle in hexagonal phase and ductile in cubic phase. In the orthorhombic or rhombohedral phase, it is near brittle-ductile boarder line