The Experts below are selected from a list of 222 Experts worldwide ranked by ideXlab platform
Renata V. Tonon - One of the best experts on this subject based on the ideXlab platform.
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Characterization of spray-dried nanofibrillated cellulose and effect of different homogenization methods on the stability and rheological properties of the reconstituted suspension
Cellulose, 2020Co-Authors: Maraysa R. Furtado, Virgínia M. Matta, Carlos W. P. Carvalho, Washington L. E. Magalhães, André L. Rossi, Renata V. TononAbstract:In the present study, a suspension of nanofibrillated cellulose from eucalyptus was spray-dried in order to obtain a Powdered Material that could be easily transported and stored. The original suspension and the dried Material were characterized for their physical, morphological and thermal properties. An increase in crystallinity and reduction in thermal stability were observed after drying. In addition, the fibrils size passed from nano to micro scale The powder obtained was rehydrated and homogenized by two methods: rotor-stator homogenization (5000, 10,000 and 15,000 rpm) and ultrasound (10, 30 and 50% maximum amplitude), during 3 and 5 min, in order to verify the possibility of obtaining a stable reconstituted suspension comparable to the original one. Higher treatment intensities resulted in suspensions with higher viscosity and stability. The suspension homogenized by ultrasound at 50% amplitude for 5 minutes was the most stable one and restored the nano dimensions of the original suspension. Both the original and the reconstituted suspensions showed a shear thinning and “gel-like” behavior. Higher Ultra-Turrax speed and ultrasound amplitude resulted in higher viscoelastic modulus (G′ and G″), although these values were lower than those found in the initial nanocellulose suspension. Graphic abstract
N W Page - One of the best experts on this subject based on the ideXlab platform.
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Particle morphology and packing effects on the shock loading of powders
Shock Waves, 1994Co-Authors: N W PageAbstract:A physically based model for the shock Hugoniot of a Powdered Material is described which allows separate identification of the cold and thermal contributions to pressure and specific internal energy. Special features of this model are provision for the effects of porosity on the stress state and an empirically determined cold loading contribution to pressure. The model was tested against published Hugoniot data for iron and gave excellent agreement for shock pressures ranging from low to high values. This shock Hugoniot was used to explore the shocked state of 4 samples of iron powder derived from commercially available Material. The purpose of this study was to investigate the effect of powder particle characteristics and initial starting densities on the shocked state. The powder samples investigated had a range of morphologies and sizes. Powders with either a large shape factor or high internal friction, as determined in shear cell experiments, exhibited a higher stiffness in the cold loading curve. In the shocked state, this translated into a higher cold component of pressure and energy than found in the other powders. The effect of initial powder density was studied by applying the Hugoniot model to two impact initiated shock loadings, one for a stainless steel flyer impacting at 0.5 km/s and one at the higher velocity of 2.0 km/s. Both were applied to iron powder targets preloaded to a range of initial densities. For a given impact event, the proportion of shock energy in the thermal mode was found to decrease with increasing initial density. This decrease was more pronounced at higher shock strengths. As a result of the decreasing component of thermal energy with higher initial density, there was a reduction in the continuum temperature behind the shock. However, the corresponding increase in the component of cold energy with the falling relative contribution from the thermal energy lead to increasing density behind the shock suggesting that there is a trade off in terms of temperature and density achievable with a given impact event.
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an equation of state for shock loaded powders
Journal of Applied Physics, 1991Co-Authors: M W Petrie, N W PageAbstract:A simple analytical model is developed for the shock Hugoniot of a Powdered Material. Previous models have exhibited decreasing accuracy when applied to powders and porous Materials of high initial porosity. This deficiency has been avoided in the present model. A special feature of this model is provision for a cold pressure loading relation which covers the full range of consolidation mechanics including relative particle movement, elastic and plastic deformation,fracture and bulk compression. This empirical cold loading relation is incorporated into a Mie–Gruneisen treatment of the shock process. This ensures that the model correctly describes behavior for all starting porosities and shock strengths and as such is suitable for use with all Powdered and porous Materials. A limiting density ratio is prediced at high shock strengths. The accuracy of the model is demonstrated by comparison with previously published shock compaction data.
Fabien Sixdenier - One of the best experts on this subject based on the ideXlab platform.
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Power Loss Prediction and Precise Modeling of Magnetic Powder Components in DC-DC Power Converter Application
IEEE Transactions on Power Electronics, 2017Co-Authors: Alaa Hilal, Marie-Ange Raulet, Christian Martin, Fabien SixdenierAbstract:In power electronics applications, magnetic components are often subjected to nonsinusoidal waveforms, variable frequencies, and dc bias conditions. These operating conditions generate different losses in the core compared to sinusoidal losses provided by manufacturers. In the conception and design stage, lack of precise losses diagnosis has unacceptable effects on sys-tem's efficiency, reliability, and power consumption. Since virtual prototyping is used to predict and improve system's behavior before realization, losses and behavior prediction of components is possible. Circuit simulators and their compatible components models are required. This paper is summarized by proposing nonlinear dynamic model of Powdered Material magnetic core for use in circuit simulators. It includes the Material's nonlinear hysteresis behavior with accurate winding and core modeling. The magnetic component model is implemented in circuit simulation software " Simplorer " using VHDL–AMS modeling language. Waveforms and losses of a powder core inductor in a buck converter application are simulated and compared to measured ones. The model is validated for different ripple currents, different loads, and a wide frequency range. DC bias is taken into account in both continuous and discontinuous conduction modes.
Xavier Courtois - One of the best experts on this subject based on the ideXlab platform.
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Use of a µ-Scale Synthetic Gas Bench for Direct Comparison of Urea-SCR and NH3-SCR Reactions over an Oxide Based Powdered Catalyst
Catalysts, 2015Co-Authors: Mickael Seneque, Fabien Can, Daniel Duprez, Xavier CourtoisAbstract:The selective catalytic reduction (SCR) of NOx by NH3 has been extensively studied in the literature, mainly because of its high potential to remediate the pollution of diesel exhaust gases. The implementation of the NH3-SCR process into passenger cars requires the use of an ammonia precursor, provided by a urea aqueous solution in the conventional process. Although the thermal decomposition and hydrolysis mechanisms of urea are well documented in the literature, the influence of the direct use of urea on the NOx reduction over SCR catalysts may be problematic. With the aim to evaluate prototype Powdered catalysts, a specific synthetic gas bench adjusted to Powdered Material was developed, allowing the use of NH3 or urea as reductant for direct comparison. The design of the experimental setup allows vaporization of liquid urea at 200 °C under 10 bar using an HPLC pump and a micro injector of 50 μm diameter. This work presents the experimental setup of the catalytic test and some remarkable catalytic results towards further development of new catalytic formulations specifically dedicated to urea-SCR. Indeed, a possible divergence in terms of DeNOx efficiency is evidenced depending on the nature of the reductant, NH3 or urea solution. Particularly, the evaluated catalyst may not allow an optimal NOx conversion because of a lack in ammonia availability when the urea residence time is shortened. This is attributed to insufficient activity of isocyanic acid (HNCO) hydrolysis, which can be improved by addition upstream of an active solid for the hydrolysis reaction such as ZrO2. Thus, this µ-scale synthetic gas bench adjusted to Powdered Materials enables the specific behaviour of urea use for NOx reduction to be demonstrated.
Maraysa R. Furtado - One of the best experts on this subject based on the ideXlab platform.
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Characterization of spray-dried nanofibrillated cellulose and effect of different homogenization methods on the stability and rheological properties of the reconstituted suspension
Cellulose, 2020Co-Authors: Maraysa R. Furtado, Virgínia M. Matta, Carlos W. P. Carvalho, Washington L. E. Magalhães, André L. Rossi, Renata V. TononAbstract:In the present study, a suspension of nanofibrillated cellulose from eucalyptus was spray-dried in order to obtain a Powdered Material that could be easily transported and stored. The original suspension and the dried Material were characterized for their physical, morphological and thermal properties. An increase in crystallinity and reduction in thermal stability were observed after drying. In addition, the fibrils size passed from nano to micro scale The powder obtained was rehydrated and homogenized by two methods: rotor-stator homogenization (5000, 10,000 and 15,000 rpm) and ultrasound (10, 30 and 50% maximum amplitude), during 3 and 5 min, in order to verify the possibility of obtaining a stable reconstituted suspension comparable to the original one. Higher treatment intensities resulted in suspensions with higher viscosity and stability. The suspension homogenized by ultrasound at 50% amplitude for 5 minutes was the most stable one and restored the nano dimensions of the original suspension. Both the original and the reconstituted suspensions showed a shear thinning and “gel-like” behavior. Higher Ultra-Turrax speed and ultrasound amplitude resulted in higher viscoelastic modulus (G′ and G″), although these values were lower than those found in the initial nanocellulose suspension. Graphic abstract