Evolution Mechanisms of T91 Steel in Subcritical Conditions and Role of an Internal Oxidation Zone

Corrosion of a T91 steel tube, used in subcritical conditions in an oil power plant for 157,000 h, was characterized mainly through SEM, TEM, EDX and DRX analyses. Severe oxidation and carburization took place in both the outer (boiler) and inner (steam) wall sides. The nature and morphology of the oxide scale multilayer structure (hematite, magnetite and spinel) depended on the environment exposure. Specific attention was given to the internal oxidation zone at the oxide/metal interface. Diffusion of chromium during the oxidation process was determined and was proposed to be responsible for the continuous advancement of oxidation to the core of material, which eventually gave rise to the spinel. Finally, in the bulk material, coarsening of the secondary carbides (M\(_{23}\)C\(_{6}\)) was the main form of microstructural evolution.     

Pinch and exergy based thermosolar integration in a dairy process

Solar thermal is a promising renewable energy supplying technology that is being introduced slowly in industrial activities. Integration of solar thermal energy in a complex process, in combination with other energy provision devices, must be evaluated carefully, in order to obtain its maximum capacity and performance. This study tackles the integration of the thermosolar technology in a dairy process, sited in a climatic zone where diffuse irradiation is the meaningful one, based on two well developed thermodynamic tools: pinch and exergy analysis. Both tools have been utilized in the context of a low and middle temperature for the production of hot water for the steps of the dairy process. A combined implementation of both methodologies, helped by economical estimation, provides a powerful tool that allows finding the best integration of thermosolar and, by this, taking substantial design decisions.     

Integration of a solar thermal system in a dairy process

Any analysis of the current energy world scenario draws on the combination of energy efficiency improvement and the use of renewable-type energies. The industrial use of renewable energies is not still well established as they present several problems that generate insecurity in this sector. Some of the renewable energy resources work intermittently (like the sun or wind) and the energy they provide is, often, of low intensity. Solar thermal technology has been successfully introduced in domestic applications and buildings. Many industrial processes work in temperature intervals where solar thermal technology would be able to supply an important amount of the total energy input at an acceptable price. Based on mathematical modeling, this work evaluates the viability of integrating a solar thermal system to the conventional energy structure of a dairy plant in the Atlantic side of Spain. Pinch methodology has been used to develop the integration of the solar subsystem in the energy installation of the plant. In order to determine the potential of the solar thermal energy, several hypotheses and scenarios were analyzed, based on real cases of the productive process. As a result, it could be stated that the solar thermal energy potential for the studied industrial process, operating at low and middle temperatures, was considerable, and must be taken into account as an energy option.     

Simulation of immiscible liquid–liquid flows in complex microchannel geometries using a front-tracking scheme

The three-dimensional two-phase flow dynamics inside a microfluidic device of complex geometry is simulated using a parallel, hybrid front-tracking/level-set solver. The numerical framework employed circumvents numerous meshing issues normally associated with constructing complex geometries within typical computational fluid dynamics packages. The device considered in the present work is constructed via a module that defines solid objects by means of a static distance function. The construction combines primitive objects, such as a cylinder, a plane, and a torus, for instance, using simple geometrical operations. The numerical solutions predicted encompass dripping and jetting, and transitions in flow patterns are observed featuring the formation of drops, ‘pancakes’, plugs, and jets, over a wide range of flow rate ratios. We demonstrate the fact that vortex formation accompanies the development of certain flow patterns, and elucidate its role in their underlying mechanisms. Experimental visualisation with a high-speed imaging are also carried out. The numerical predictions are in excellent agreement with the experimental data.     

Lead removal from aqueous solutions by a Tunisian smectitic clay

The adsorption of Pb(2+) ions onto Tunisian smectite-rich clay in aqueous solution was studied in a batch system. Four samples of clay (AYD, AYDh, AYDs, AYDc) were used. The raw AYD clay was sampled in the Coniacian-Early Campanian of Jebel A?doudi in El Hamma area (South of Tunisia). AYDh and AYDs corresponds to AYD activated by 2.5 mol/l hydrochloric acid and 2.5 mol/l sulphuric acid, respectively. AYDc corresponds to AYD calcined at different temperatures (100, 200, 300, 400, 500 and 600 degrees C). The raw AYD clay was characterized by X-ray diffraction, chemical analysis, infrared spectroscopy and coupled DTA-TGA. Specific surface area of all the clay samples was determined from nitrogen adsorption isotherms. Preliminary adsorption tests showed that sulphuric acid and hydrochloric acid activation of raw AYD clay enhanced its adsorption capacity for Pb(2+) ions. However, the uptake of Pb(2+) by AYDs was very high compared to that by AYDh. This fact was attributed to the greater solubility of clay minerals in sulphuric acid compared to hydrochloric acid. Thermic activation of AYD clay reduced the Pb(2+) uptake as soon as calcination temperature reaches 200 degrees C. All these preliminary results were well correlated to the variation of the specific surface area of the clay samples. The ability of AYDs sample to remove Pb(2+) from aqueous solutions has been studied at different operating conditions: contact time, adsorbent amount, metal ion concentration and pH. Kinetic experiments showed that the sorption of lead ions on AYDs was very fast and the equilibrium was practically reached after only 20 min. The results revealed also that the adsorption of lead increases with an increase in the solution pH from 1 to 4.5 and then decreases, slightly between pH 4.5 and 6, and rapidly at pH 6.5 due to the precipitation of some Pb(2+) ions. The equilibrium data were analysed using Langmuir isotherm model. The maximum adsorption capacity (Q(0)) increased from 25 to 25.44 mg/g with increasing temperature from 25 to 40 degrees C. Comparative study between sulphuric acid activated clay (AYDs) and powder activated carbon (PAC) for the adsorption of lead was also conducted. The results showed that sulphuric acid activated clay is more efficient than PAC.     

Critical factors affecting the photovoltaic characteristic and comparative study between two maximum power point tracking algorithms

This paper presents the characterization and the modeling of the electric characteristics of currentvoltage and power–voltage of the photovoltaic (PV) panels. The philosophy behind digital simulation of solar energy systems is that experiments which normally should be done on real systems under high assembling costs can be done numerically in a short time on a computer, thus saving time and investments. The electric parameters of PV cells and the optimal electric quantities of PV panels have been analyzed (voltage and power) according to the meteorological variations (Temperature, solar irradiation …). The obtained results show that the diode parameters of the PV cells depend on solar irradiation: the current saturation increases with solar irradiation. This induces a decrease of the optimal voltage with solar irradiation; when the solar irradiation varies from 600 W/m² to 1000 W/m². By taking into consideration all the modeling results, the electric behavior of the cells association in parallels or in series, as well as the aging of a PV panel have been analyzed. Moreover, a comparative study between two types of MPPT techniques that are used in photovoltaic systems to extract the maximum power have been introduced which are Perturb and Observe (P &O) and Incremental Conductance (INC).     

Three-dimensional simulations of viscous folding in diverging microchannels

Three-dimensional simulations on the viscous folding in diverging microchannels reported by Cubaud and Mason (Phys Rev Lett 96(11):114,501, 2006a) are performed using the parallel code BLUE for multiphase flows (Shin et al. in A solver for massively parallel direct numerical simulation of three-dimensional multiphase flows. arXiv:1410.8568). The more viscous liquid \(L_1\) is injected into the channel from the center inlet, and the less viscous liquid \(L_2\) from two side inlets. Liquid \(L_1\) takes the form of a thin filament due to hydrodynamic focusing in the long channel that leads to the diverging region. The thread then becomes unstable to a folding instability, due to the longitudinal compressive stress applied to it by the diverging flow of liquid \(L_2\). Given the long computation time, we were limited to a parameter study comprising five simulations in which the flow rate ratio, the viscosity ratio, the Reynolds number, and the shape of the channel were varied relative to a reference model. In our simulations, the cross section of the thread produced by focusing is elliptical rather than circular. The initial folding axis can be either parallel or perpendicular to the narrow dimension of the chamber. In the former case, the folding slowly transforms via twisting to perpendicular folding, or it may remain parallel. The direction of folding onset is determined by the velocity profile and the elliptical shape of the thread cross section in the channel that feeds the diverging part of the cell. Due to the high viscosity contrast and very low Reynolds numbers, direct numerical simulations of this two-phase flow are very challenging and to our knowledge these are the first three-dimensional direct parallel numerical simulations of viscous threads in microchannels. Our simulations provide good qualitative comparison of the early time onset of the folding instability, however, since the computational time for these simulations is quite long, especially for such viscous threads, long-time comparisons with experiments for quantities such as folding amplitude and frequency are limited.     

Medical social network content analysis for medical image retrieval purpose

Background and objective: Medical social networking platforms provide virtual spaces ensuring the interaction between different healthcare participants. As a part of the exchange, these spaces allow subscribers to upload medical images, describing different medical cases for an analysis or an interpretation proposal. Facing this expected huge amount of uploaded images generated daily, it is needed to engage new mechanisms to effectively deal with this circumstance, for enhancing the search function process of medical images, based on what is uploaded. To overcome this issue, setting up of images visual searching based on a content-based medical image retrieval scheme is the solution. More clearly, such mechanism will help and motivate medical social networking subscribers to find visually similar stored images. Methods: To ensure this task, the development of this mechanism, technically, is based mainly on a fusion of three visual features, which offers a flexible and more precision. It is reinforced by a weighted distance approach through attributing weights for feature vectors to scale up the performance. Indeed, the displayed results of this system can be updated based on user's intention by a user interactive feedback mechanism to indicate the truly relevant images. Results: We provide the theoretical performance of our scheme. Extensive experiments were conducted on a categorically classified collection containing 500 images. We conduct a practical evaluation on this dataset classes, putting returned results in a comparative study with other models results, existing in the literature. Conclusions: The proposed scheme preserves the efficiency of the search task. As theoretically and experimentally established, our scheme offers an effective image retrieval model that can support different subscribers' expectations. The relevance feedback mechanism can keep the dynamism of the system, thus offering a continuous searching result evolution. Experimentation outcomes indicate better findings compared with the other models.     

Markov Chain Mobility Model for Multi-lane Highways

Mobile Networks and Applications - Traffic congestion is one of the biggest challenges around the world, resulting in multiple harmful consequences such as air pollution, road fatalities, and...     

Numerical Modelling of the Flow of Fibre Suspensions through a Planar Contraction

This study presents results of numerical simulations of the flow of fibre suspensions in a Newtonian fluid through a 4:1 planar contraction. Two approaches are adopted to determine the fibre orientation. The first one uses orientation tensors defined as dyadic products of the orientation vector, while the second one is based on the fibre aligned assumption. An implicit time discretization scheme and a mixed finite element method based on the introduction of the rate of deformation tensor as an additional unknown are used to obtain the steady‐state flow. The numerical technique we use allows us to examine the flow of fibre suspensions in both dilute and semi‐dilute regimes at high values of the parameters controlling inertial and fibre effects. The predicted flow patterns and fibre orientation are discussed, and a systematic comparison between the predictions of the two approaches is presented.