查看更多>>摘要：This work presents a stress model and a process model for dispersing processes in laminar shear flow, which are performed in devices such as kneaders, extruders and three roller mills. Based on deep investigations of two kneaders (lab-and pilot-scale) a methodology is presented, which allows modelling the dispersing process by applying a stress model along with a population balance model to the given task. Stress models describe how often particles are stressed during the process and which energy is transferred to the particles. For dispersing in laminar shear flow, it is crucial to distinguish between dispersing-effective and ineffective stress events based on whether the stress intensity is high enough to overcome the particle strength. Results suggest, that the effective specific energy input determines the dispersing progress independent of the process scale. A process model in form of a population balance was required to obtain otherwise unknown parameters for the stress model. The applied population balance model accounts for the acting working principles during dispersing. For such a mechanistic depiction of the dispersing progress, the trilateral dependency between particle size, resulting viscosity, particle stressing and fragmentation must be modelled. It was found that based on the models, the process behaviour on both scales can be depicted, which offers the perspective of a knowledge-based scale-up of machines and processes, process control and process design based on these results.
查看更多>>摘要：A great issue in the development of an all-solid-state lithium-ion battery (ASSLIB) is the fabrication of a composite electrode with good contact between active materials (AMs) and solid electrolytes (SEs). To overcome this challenge, it is important to develop a powder processing technology that produces composite particles of AMs and SEs. In this study, we investigated a dry impact blending process for producing graphite composite particles (typical anode AM) and sulfide SEs. First, by controlling the rotating speed of the rotor in the dry impact blending process, two types of composite particles, namely surface-coated (SC) composite particles with no graphite breakage and matrix-type (MT) composite particles with graphite breakage, were produced. The SC composite particles showed higher electrochemical performance than the MT composite particles due to less change in the graphite crystallinity. Second, the longer the processing times for the preparation of SC composite particles, the higher the SE coating on graphite, resulting in higher electrochemical performance. Third, we demonstrated that the SC composite particles exhibited higher electrochemical performance than those prepared using a conventional lab-scale mixing technique. We demonstrated the effectiveness of the dry impact blending process for the preparation of an anode composite electrode for ASSLIBs.
查看更多>>摘要：Understanding the movement law and orientation control mechanism of non-spherical particles are significant for industrial applications. In this work, the flow characteristics of rectangular particles, in the uniform and wedge viscous fluid domain, are simulated by the immersed smoothed finite element method (IS-FEM). The influences of mesh resolution and time-step on particle velocity are analyzed, and the numerical procedure is validated by the published model and sedimentation experiments. The operating parameters that affect the particle flow are systematically studied, including Reynolds number, initial angle, channel offset distance, and aspect ratio. Moreover, the particle angles are adjusted by the velocity gradient of fluid domains. The result indicates that the velocities, angle, and drag of rectangular particles are closely related to the working conditions. The long axis of rectangular particles is consistent with the flow direction in shrinking fluid domains and is perpendicular to the flow direction in expanding fluid domains. The angle distribution law of rectangular particles in moving wedge fluid domains is determined. These findings provide a theoretical foundation for particle sedimentation and suspension flow, which is helpful for the further separation and orientation control of mixed particles.
Akbar ArsalanlooMajid AbbasalizadehMorteza Khalilian
16页
查看更多>>摘要：Targeted drug delivery is an advanced method discussed in the literature for optimized treatment of diseases. However, the data for a precise understanding of pharmaceutical aerosol transport to the desired positions in the airways is not sufficient in the literature. Hence, in this work the transport and deposition of particles have been studied numerically in a realistic model of the respiratory system. The model was reconstructed based on CT-scan images of a healthy 28-year-old male and the commercial code ANSYS Fluent was used for analysis. After validation, distribution and deposition patterns of particles have been presented along with analysis of flow field dynamics. It was found that majority of particles enter the right lung while deposition is higher in the left lung and that the left lower lobe, left upper lobe and right lower lobe have the highest rate of lobar deposition. It was also observed that inertial impaction plays the dominant role in deposition of larger diameter particles at higher flow rates at the upper airways. The present findings improve our insight toward regional distribution and deposition of particles and assists in more accurate prediction of particle transport for drug delivery.
Moritz BuchholzJohannes HausSwantje Pietsch-Braune
14页
查看更多>>摘要：Due to the widespread application of spray dryers, the model-based optimization and control of the process are of great interest. Therefore, a reduced order model based on a population balance approach for the spray drying process is developed to accurately capture the shrinkage and drying mechanisms. The population balances describe the two-dimensional distribution of the moisture content and the granule size. The model is validated by experiments in a pilot scale spray dryer. Information from CFD simulations and previous single droplet experiments are used to determine suitable model parameters. The results show a good agreement of the model with experimental findings and promote the suitability of the population balance approach. Furthermore, a novel method of extracting information on the trajectories from detailed CFD simulations and inserting them into the reduced order model is presented. This increases the accuracy of the model without changing the computational complexity.
查看更多>>摘要：A new series of Pickering emulsions that can be photo-cured by interparticle photo-cross-linking reactions using small amounts of multifunctional acrylate (MA) monomers is proposed to rapidly manufacture complex-structured porous ceramic materials. In our new process, water in oil (w/o) Pickering emulsion was designed by vigorous mixing of water and polyethyleneimine partially complexed with oleic acid (PEI-OA)-stabilized SiO2/toluene suspension containing small amounts of MA and a photo-radical initiator. Ultraviolet light irradiation to this w/o Pickering emulsion induced the formation of interparticle photo-crosslinks, which resulted in successful photocuring by photo-radical polymerization of MA and the Michael addition reaction between the polymerized MA and PEI-OA on the particles in the oil phase. We further applied the newly designed photo-curable Pickering emulsion and demonstrated that SiO2 components with pores related to the dispersed aqueous phase and complexed outer structures could be shaped via silicone molding or a hybridized approach of photocuring and green machining. Because of the reduced amounts of MA used, the porous SiO2 green components could be heat-treated using rapid heating profiles without any structural collapse for dewaxing and partial sintering.
查看更多>>摘要：High energy mechanical milling was used to fabricate nanoparticulate Si using A12O3 grinding media. Two ratios of grinding media to charge of 5 and 10 were used with milling times, such as 7, 10, 13, 16, and 19 h. Morphology of the milled powders was investigated by scanning and transmission electron microscopy. Crystallinity of the milled powders was found to be preserved for all milling conditions without amorphization. Crystallite size of the milled powders was calculated from x-ray diffractograms by various methods. From morphology and crystallite size it was observed that 13 h of milling is the optimum time to produce well dispersed Si nanoparticulates. Further increase in milling duration clearly indicated agglomeration of the powders and cold welding of the crystallites for samples of both media-to-charge ratios. X-ray diffractograms and Raman spectrographs of the milled samples were used to calculate the strain induced in the materials, which indicated progressive increase in strain with milling duration. The results indicate that A12O3 milling media can be used with optimized process conditions for the production of large quantities of nanoparticulate Si.
查看更多>>摘要：The velocity and thermal behavior (temperature, enthalpy, solid fraction) of atomized droplets in a metal spray play the most important role in the spray forming process. These properties mainly determine the materials yield and the final product quality (e.g., porosity, microstructure) of the as-sprayed materials. Changing the gas temperature in the atomization process directly influences these droplet properties in the spray. To understand the droplet behavior in the spray at various atomization gas temperatures (i.e., room temperature RT 293 K, 573 K, 873 K), numerical simulations using computational fluid dynamics (CFD) techniques have been performed and validated by experiments. A series of atomization runs (powder production and spray-forming with AISI 52100 steel) has been conducted at different atomization gas temperatures and pressures with a close-coupled atomizer (CCA). The in-situ temperature detection of the deposit surface (pyrometer) and in the substrate (thermocouples) has been performed to observe the effect of particle properties on the deposit. The result shows that hot gas atomization provides smaller droplets with faster velocity in the spray, affecting the droplet impact and deformation time in the deposition zone. A higher solid fraction of the smaller droplets by hot gas atomization also reduces the deposit surface temperature. Increasing the substrate diameter further decreases the deposit surface temperature without compromising the deposit quality (i.e., porosity) and also refines the grain size. Pre-heating of the substrate up to 573 K results in lower porosity in the vicinity of the substrate.
查看更多>>摘要：A CFD-DEM model was developed to reproduce the packing densification process of mono-sized equiaxed cylindrical particles under air impact. The effects of operating parameters on packing density were firstly studied. Then various microscopic properties of packing structures such as coordination number (CN), contact types, particle orientations, pore features were characterized and compared. And corresponding densification mechanisms were analysed based on particle motion behaviour, local structure evolution, and forces. Results indicate that the air impact can realize the packing densification of cylindrical particles under appropriate conditions. The pore size distribution in the packing of cylindrical particles shows a tail at larger pore sizes compared with that in the packing of equal spheres. Both the size and the sphericity of the pores decrease in the final dense packing; also, more surface-surface and less surface-edge contacts between two particles therein can be formed. More cylindrical particles tend to be in parallel or perpendicular contact with each other to form more stable local structures during air impact. Most particles at higher position move down (direction of gravity/air impact) with about one particle length during the densification process and most particles exhibit translational motion to realize the local rearrangement for pore filling through air impact induced inter-particle forces.
Traian Florin MarincaAndrei loan SuleRazvan Hirian
9页
查看更多>>摘要：A new alloy, permalloy alloyed with aluminum, has been obtained by mechanical alloying using elemental powders as raw materials. The new alloy was obtained in powder form by adding an amount of 5 wt% of Al to permalloy (75% Ni and 25% Fe, wt.%) resulting Al-Permalloy with Ni71.25Fe23.75A15 composition. The alloy was obtained using different ball to powder ratio (BPR): 4:1, 8:1 and 17:1 and keeping the rest of the mechanical alloying/milling parameter constant. The BPR influences the time required for the alloy synthesis and alloy characteristics. The time required for alloy synthesis as FCC single phase varies from 4 h when using a BPR of 17:1 to 8 h when using a BPR of 4:1. A more compact cubic structure is obtained when using a BPR of 8:1. The particles are flattened for all BPRs used, but upon changing the BPRs particles shape is changing and become more or less flattened. Large particles have been obtained when using BPRs of 4:1 and 17:1 and finer particles when using a BPR of 8:1. Curie temperature of the Al-Permalloy is depending on synthesis conditions varying from 478 °C to 501 °C. The higher saturation magnetization has been found when using a BPR of 8:1. The powder characteristics evolution upon increasing the milling time for all three BPRs is discussed in the light of X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectrometry, differential scanning calorimetry, particles size analyses and magnetic investigation.
NSTL