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Sustainable magnet-responsive nanomaterials for the removal of arsenic from contaminated water
No full textIn this study, chitosan and bio-based substances (BBS) obtained from composted biowaste were used as stabilizers for the synthesis of magnet-sensitive nanoparticles (NPs) via coprecipitation method. A pyrolysis treatment was carried out on both biopolymers at 550 °C, and their consequent conversion into a carbon matrix was followed by means of different physicochemical characterization techniques (mainly FTIR spectroscopy and XRD), whereas magnetic properties were evaluated by magnetization curves. The prepared materials were tested in water remediation processes from arsenic (As) species (both inorganic and organic forms). These tests, explained by means of the most common adsorption models, evidenced that the best performances were reached by both materials obtained after pyrolysis treatments, pointing out the promising application of such magnet-sensitive materials as easy-recoverable tools for water purification treatments
Electromechanical actuators affected by multiple failures: Prognostic method based on spectral analysis techniques
No full textThe proposal of prognostic algorithms able to identify precursors of incipient failures of primary flight command electromechanical actuators (EMA) is beneficial for the anticipation of the incoming failure: an early and correct interpretation of the failure degradation pattern, in fact, can trig an early alert of the maintenance crew, who can properly schedule the servomechanism replacement. An innovative prognostic model-based approach, able to recognize the EMA progressive degradations before his anomalous behaviors become critical, is proposed: the Fault Detection and Identification (FDI) of the considered incipient failures is performed analyzing proper system operational parameters, able to put in evidence the corresponding degradation path, by means of a numerical algorithm based on spectral analysis techniques. Subsequently, these operational parameters will be correlated with the actual EMA health condition by means of failure maps created by a reference monitoring model-based algorithm. In this work, the proposed method has been tested in case of EMA affected by combined progressive failures: in particular, partial stator single phase turn to turn short-circuit and rotor static eccentricity are considered. In order to evaluate the prognostic method, a numerical test-bench has been conceived. Results show that the method exhibit adequate robustness and a high degree of confidence in the ability to early identify an eventual malfunctioning, minimizing the risk of fake alarms or unannounced failures. © 2017 Author(s)
Capacitive sensor for tagless remote human identification using body frequency absorption signatures
No full textComparison results for inactivity times of k-out-of-n and general coherent systems with dependent components
No full textConsider a coherent system with possibly dependent components having lifetime T, and assume we know that it failed before a given time t > 0. Its inactivity time t-T can be evaluated under different conditional events. In fact, one might just know that the system has failed and then consider the inactivity time (t-T | T < t), or one may also know which ones of the components have failed before time t, and then consider the corresponding system's inactivity time under this condition. For all these cases we obtain a representation of the reliability function of system inactivity time based on distortion functions, which, in turn, includes a description of the structure of depen-ence between components through the copula of the vector of components' lifetimes. Making use of these representations, new stochastic comparison results for inactivity times under the different conditional events are provided, as well as comparison results for inactivity times of systems having different structure functions. These results also apply to order statistics, being the order statistics particular cases of coherent systems (k-out-of-n systems)
Thermoeconomic cost assessment in future district heating networks
No full textThis paper aims at showing the capabilities of thermoeconomic analysis for solving cost assessments in district heating systems both at user and producer sides. In the near future it is expected that multiple producers are allowed to supply heat to the same district heating network, similarly to what happens in the case of the electric grid. Not only the amount of heat they may produce should be properly accounted, but also its quality, and also the pumping power that is requested to supply a unity of thermal energy to the endusers. Moreover, buildings equipped with low temperature heating system allow better use of the thermal energy vector, thus allowing larger efficiency of thermal plants. In the present work, the use of thermoeconomics for the analysis of these aspects is proposed. The approach allows one performing cost assessment in district heating, taking into account the effects of investment and operating costs and thermodynamic irreversibilities in the cost formation of heat from its production in the plants to its use in the buildings. Simple examples are analyzed in order to provide a quantitative evaluation of the various cost terms, depending on the operating conditions, topology and characteristics of the users/producers
Analysis of Ru/La-Al2O3 catalyst loading on alumina monoliths and controlling regimes in methane steam reforming
No full textIn this work Ru (1.5 wt%)/La (3 wt%)-modified-Al2O3 coated α-alumina monoliths of different geometries (100 cpsi square channel, 170 cpsi hexagonal channel, diameter 9 mm, length 30 mm) were prepared by in-situ catalyst washcoating technique with catalyst loadings in the range 100 - 250 mg. The powder and structured catalysts were characterized by various physio-chemical characterization techniques: particle size distribution, zeta potential, slurry viscosity, N2 physisorption, H2 chemisorption, X-ray diffraction, washcoat adherence, optic and scanning electron microscopy. The influence of catalyst loading was investigated on geometric, hydraulic and catalytic performance towards methane steam reforming (SMR) reaction by varying temperature (600 - 900°C), weight hourly space velocity (WHSV = 27 - 368 NL h-1 gcat-1) at fixed molar steam to carbon ratio (S/C = 3.0). Well adhered and uniform catalyst layers were achieved with stable catalytic performance towards methane steam reforming. Characteristic time analysis and dimensionless numbers were utilized to identify the controlling regime in catalytic monoliths. The values of optimum washcoat thickness for 100 cpsi and 170 cpsi monoliths are found to be 58.5 μm and 78.9 μm respectively. SMR is reaction controlled for 100 -150 mg catalyst loaded monoliths. No external diffusion control regime is observed. At higher catalyst loadings (> 200 mg) SMR is influenced by washcoat diffusion limitation and availability of less contact time for the reaction, suggesting the use of higher cell density monoliths with smaller hydraulic diameter, and higher geometric surface area
Hygrothermal analysis of multilayered composite plates by variable kinematic finite elements
No full textAdvanced plate models with variable kinematics for steady state hygrothermal analysis of composite laminates are proposed. The refined models discussed include both layer-wise (LW) and equivalent single layer (ESL) models, and the Carrera Unified Formulation (CUF) is used. The mixed interpolation of tensorial component (MITC) method is applied to a nine-node element to contrast the shear locking phenomena. The governing equations are derived from the principle of virtual displacement (PVD) taking into account elastic mechanical, thermal and hygroscopic effects. Through-the-thickness variations of temperature and moisture concentration are calculated by solving the Fourier equation and the Fick law, respectively. Cross-ply plates with symmetrical lamination and simply supported edges subjected to bisinusoidal thermal/hygroscopic loads are analyzed considering various thickness ratios. Results obtained with assumed linear and calculated temperature/hygroscopic profiles are compared. Variable kinematics with a variety of thickness functions are compared regarding both accuracy and computational costs. The results show that all the kinematics proposed can approximate the transverse shear stress distribution through the thickness with satisfactory accuracy when sufficient expansion terms are adopted. In some cases, miscellaneous expansions can lead to significant reductions in computational costs. The results presented here can be used as benchmark solutions for future works
Variable kinematic shell elements for composite laminates accounting for hygrothermal effects
No full textThis article presents advanced shell models for the steady-state hygrothermal analysis of composite laminates. The Carrera Unified Formulation is used to derive refined models that include both layer-wise and equivalent single layer models. The governing equations are derived from the principle of virtual displacement taking into account thermal and hygroscopic effects. The geometrical relations for the exact cylindrical geometry are here considered. Through-the-thickness variations of temperature and moisture concentration are calculated by solving the Fourier equation and the Fick law, respectively. The mixed interpolation of tensorial component method is applied to a nine-node shell element to contrast the membrane and shear locking phenomena. Simply supported cross-ply cylindrical shells with antisymmetrical lamination subjected to bisinusoidal thermal/hygroscopic loads are analyzed considering various thickness/curvature ratios. Results obtained with assumed linear and calculated temperature/hygroscopic profiles are presented. Variable kinematics are compared regarding both accuracy and computational costs. The results show that all the kinematics can approximate the transverse shear stress distribution through the thickness with satisfactory accuracy when sufficient expansion terms are adopted. In some cases, miscellaneous expansions can lead to significant reductions in computational costs. The results presented here can be used as benchmark solutions for future works
