The effects of oxygen groups' functionalization on the electrochemical activity of MWCNTs buckypaper electrodes toward the positive halfcell redox couples of a Vanadium Redox Flow Battery (VRFB) were investigated. The heat treatment method employed was successful in introducing carboxyl groups onto the buckypaper electrodes as proven by the FTIR analysis. Although SEM results showed no adverse effects on morphology, Raman spectroscopy showed that the treatments did induce defects into the structure of the MWCNTs. Furthermore, electrochemical results suggested that although attainable peak currents decreased as a function of the heat treatments, the overall reversibility of the electrode improved.
This paper focuses to improve wind turbine systems efficiency, in other words, to maximise the output power delivered by the wind turbine. To do this it is necessary to have a good controller. In this study, we use a nonlinear synergetic controller. Synergetic control theory is applied to reach the maximum power point tracking (MPPT) of a variable speed energy conversion system. A comparison with the robust sliding mode control allowed us to see the effectiveness of the proposed controller. These controllers are tested in a Simulink/Matlab environment. Simulation results present good performance compared to the classical sliding mode controller.
Watersplitting composite consisting of three thin films (SiO2, Al2O3 and TiO2) with embedded distribution of (Au) structures on top were fabricated and characterized. The effect of thermal annealing on the evolution of the microstructure, optical and physical properties of the watersplitting composite was studied for temperatures ranging from 450oC1100oC under atmospheric conditions. The crystal structure, chemical composition and wettability alteration were determined using Xray Diffractometer, Scanning and Transmission Electron Microscope. The influence of thermal annealing on extending the optical absorption spectrum to the visible region was evaluated by UVVis spectrophotometer. Our findings revealed that thermal annealing leads to the transformation of amorphous TiO2 to its more stable phase anatase. This transformation enhances significantly the optical properties and increases the hydrophilicity of the material surface making it suitable for watersplitting activity. More importantly, the presence of plasmonic nanostructures allows the material to extend its photoactivity to full solar spectrum.
Hydrogenation is a promising technique for TiO2 thin films to extend their visible light absorption ability in photocatalytic applications. However, fundamental insight of the TiO2 hydrogenation dynamics, which distinguish the optical effects of various processing conditions, is still missing. In order to clarify the physics of hydrogenated TiO2, thin film samples were analyzed over fabrication time. The flow rate, temperature, and surface area of the films affect the gassolid kinetics, because the hydrogenation is a complex process which cannot be modelled as simple diffusion. Moreover, as hydrogenation continues over time, the intensity of the Raman spectroscopic and FTIR signals changes. This study links the Raman and FTIR signal changes to the structural changes, which can be predicted by density functional theory as a function of the diffusion of hydrogen into the film. This will in turn explain the differences in observed photocatalytic properties from different fabrication conditions.
Ultrahigh molecular weight polyethylene (UHMWPE) nanocomposites with 0.05, 0.1, 0.3, 0.5 and 1.0 wt% CNT were fabricated by mechanical mixing followed by compression molding. The highest degree of crystallinity is obtained for 0.1 wt% CNT and beyond 0.5 wt% CNT, the values were lower than the pure UHMWPE. The nonisothermal decomposition showed that increase in CNT content, increases the degradation temperature leading to better thermal stability. For 1.0 wt% CNT, there was approximately 3% of ash residue left from the decomposition which affects its decomposition temperature but still has a better result than pure UHMWPE. Mechanical properties of the composites were improved where the elastic modulus was increased by 11.4% with the addition of 1.0 wt% CNT.
A new analytical model is proposed for the estimation of interlaminar shear stress in bonded metal laminates consisting of an arbitrary number of layers. The interface shear stress in the laminates is related to the difference in average axial strain and elongation between adjoining layers through a newly proposed interlaminar shear stress function (ILSSF). The parameters of the ILSSF are determined from finite element simulations using a data fitting procedure. The accuracy of the model is investigated by comparing experimental measurements of average elongation in threelayer aluminum laminates to values obtained using the model. Good agreement with the experimental results is achieved for several types of adhesives and for different ratios of adhesivetolayer thicknesses.
This study is focused on experimental characterization of liquidgas twophase flows across a sudden expanded diameter in a transparent horizontal pipe with the area ratio of 0.36. Experimental tests depend on two key parameters, liquid and gas flow rates. Behavior of slug flows near the expanded region of the pipe is studied. Bubble velocity, Bubble blast phenomenon, and the horizontal water jet characteristics were investigated using High Speed Photography. Through image processing, using MATLAB, it is found that bubble blast velocity is independent on the water or gas flow rates, while bubble moving velocity and water jet length can be quantified as a function of the watergas flow rates. The experiments in this study provide fundamental insights into the influence of the sudden expansion on waterair behaviors.
The paper presents the identification procedure for a 3D macroscopic constitutive model for ironbased shape memory alloys (FeSMAs) that takes into account the variation of elastic stiffness during phase transformation and the influence of plastic slip on the transformation process. The constitutive equations are derived from an expression of the free energy potential. The loading conditions for phase transformation and plastic deformation are obtained by requiring that the governing thermodynamic forces derive from an appropriate dissipation potential and the corresponding evolution of the internal variables is described by means of associated flow rules.
Lightweight materials with complex structures such as cellular solids have proven to possess desirable properties, while the density is reduced. However, in common foam structures stress concentrations might occur at the point of junction and is subjected to multiaxial stresses and progressive failures. Therefore, this paper will investigate the mechanical behavior of a novel type of foams (Gyroid skeletal cellular structure) where stress concentrations are minimized.
in this work, a cocontinuous composite with a mathematically generated reinforcement topology is presented and mechanically tested. The cocontinuous composite is made of a soft matrix phase reinforced with a solid phase. The solid phase has an architecture based on the triply periodic minimal surfaces. This approach in designing composite materials benefits from the architecturetopology relationship. Results show great potential in employing this approach to design and tailor the properties of cocontinuous composites.
