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Zhang L.Y.,University of Oxford | He L.,University of Oxford | Stuer H.,Ad Energy
Proceedings of the ASME Turbo Expo | Year: 2012

The rotating instability phenomenon in a last stage of steam turbines at low mass flow conditions has been previously identified experimentally. Recently, the rotating instability has also been numerically studied in a whole annulus domain on 2D blade sections. In the present work, 3D simulations of unsteady flows are carried out on two model steam turbines over a range of mass flow conditions. The pressure-ratio volume-flow characteristics in rotor row tip region under different flow conditions are well captured in the computations in comparison with the experiment. The effect of blade scaling is examined to identify the influence of changing blade counts for a circumferential domain reduction, showing relatively small effects on the overall performance characteristics. The present 3D unsteady solutions on a reduced multi-passage domain have been able to predict a rotating instability in the rotor blade tip region, in accord with the corresponding experiment. Further Fourier analysis is carried out to examine the frequency pattern and spatial modal features. The 3D flow behavior is highlighted by comparison between the 3D and 2D calculations. The present results seem to suggest that the rotating instability onset in the rotor tip region is largely independent of the large scale flow separation in the downstream diffusor. Copyright © 2012 by ASME. Source

Lara-Cueva R.,Ad Energy | Benitez D.,San Francisco de Quito University | Fernandez C.,Ad Energy | Morales C.,Ad Energy
Proceedings - 2015 Asia-Pacific Conference on Computer-Aided System Engineering, APCASE 2015 | Year: 2015

Usage of wireless networks is rising in popularity. In this setting different kinds of networks for indoor environments, such as Ad-Hoc, IEEE 802.11b (Wi-Fi) and Wireless Distribution System (WDS) has been developed. In this paper, an analysis of Quality of Service (QoS) has been made for each network in order to verify the values of bit rate, delay, jitter and packet loss. For performance comparison of these networks, injection of UDP traffic was accomplished by means of the Distributed Internet Traffic Generator (D-ITG). Distance and number of obstacles were varied in several deployed network scenarios. In each scenario, QoS parameters were measured and efficiency was estimated. According to results, WDS networks have better performance which has 30% more efficiency in long distance communication than Ad-Hoc and 802.11 networks. © 2015 IEEE. Source

Ltaief O.O.,Ad Energy | Siffert S.,ULCO | Fourmentin S.,ULCO | Benzina M.,Ad Energy
Comptes Rendus Chimie | Year: 2015

In this study, a faujasite type zeolite synthesized from cheap local Tunisian illitic clay and having a hierarchical porosity was used for adsorption of heavy metals. The adsorption behavior of the FAU with respect to Cu (II), Cr (III) and Co (II) has been investigated using batch experiments. The removal efficiency was determined at different contact times, initial metal concentrations, temperatures, pHs, and adsorbent amounts. Both Langmuir and Freundlich isotherms fit well with the equilibrium data. Kinetic studies showed that the adsorption followed a pseudo-second-order model. The observed selectivity was determined as follow: Cu (II). >. Co (II). >. Cr (III). Une zéolite de type faujasite ayant une porosité hiérarchisée a été synthétisée à partir d'une argile tunisienne. Les capacités d'adsorption de cette zéolite ont été évaluées vis-à-vis de la rétention de métaux lourds: Cu (II), Cr (III) et Co (II). L'influence de divers paramètres tels que le temps, la concentration, la température, le pH et la quantité d'adsorbant a été étudiée. Les résultats obtenus ont montré que les modèles de Langmuir et Freundlich décrivaient bien l'adsorption des métaux étudiés et que l'adsorption suivait un modèle cinétique du deuxième ordre. La sélectivité observée suit l'ordre: Cu (II). >. Co (II). >. Cr (III). © 2015 Académie des sciences. Source

Ltaief O.O.,Ad Energy | Siffert S.,ULCO | Poupin C.,ULCO | Fourmentin S.,ULCO | Benzina M.,Ad Energy
European Journal of Inorganic Chemistry | Year: 2015

Raw clay, which is an interstratified illite-kaolinite, has been used as a raw material to prepare Faujasite-type zeolites. The synthesis was based on the alkaline fusion method followed by hydrothermal treatment without the addition of any extra silica or alumina sources. The effects of various factors on the synthesis process, such as NaOH/clay ratio, crystallization time and temperature, were investigated. The results obtained underlined that these parameters determined whether or not Faujasite-type zeolites were formed. The optimum synthesis conditions for the synthesis of a single Faujasite zeolite phase were a weight ratio of NaOH/clay of 1.2 fused at 500 °C for 2 h and crystallized at 60 °C for 24 h after homogenization for 12 h. The compounds obtained were characterized by X-ray diffraction, FTIR spectroscopy, and scanning electron microscopy. Their textural properties were investigated by N2 adsorption/desorption measurements. The BET surface area of the product synthesized with the optimum conditions was 360 m2/g with a relatively high total pore volume of 0.33 m3/g. Toluene adsorption on the synthesized trimodal Faujasite zeolite was four times higher than on commercial zeolite. This synthesis is therefore a good way to obtain a cheap and efficient adsorbent for environmental applications. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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