Centrifugal Pumps as Extractors

The generation of dispersions with defined droplet size distributions is important for liquid-liquid extraction. In this respect, the capability of a centrifugal pump to generate dispersions was investigated for different operating points. For the analysis of the mixing process, a centrifugal pump was designed translucent. High-speed images reveal the mechanism of particle breakup. Optical measurement technology and image processing with neural networks were used to determine droplet size distributions. The influence of flow rate, rotational frequency and holdup are discussed for a paraffin oil-water system.     

The effect of catalyst formulation and Rh dispersion on the performance of a CPO fuel processor investigated by operando sampling technique and predictive modelling analysis

The catalytic partial oxidation (CPO) of methane and iso-octane on Rh-coated monoliths is studied in an adiabatic reactor where axial temperature and concentration profiles are collected by a spatially resolved sampling technique. In CH₄-CPO, the Rh/MgAl₂O₄ outperforms the Rh/α-Al₂O₃ formulation, due to a significant improvement of Rh dispersion. In iso-octane CPO, the beneficial effect of the improved Rh surface is less important due to the intrinsic lower sensitivity of the system. However, a non-negligible impact of Rh dispersion on the extent of hydrocarbon side-products is observed. This factor, together with the lower acidity of the spinel support, contributes to limit the C build-up. Reactor model and kinetic schemes allow to rationalize the measurements and explore the more general effect of Rh specific surface on the key performance indicators of the CPO reformer, that is syngas productivity and hot-spot temperature. Gas-solid diffusion rate makes such indicators strictly fuel-specific.     

薄壁金属气囊抛撒性能流固耦合分析

为研究机载布撒器囊式抛撒系统中气囊的抛撒性能,以初始为扁平结构的薄壁金属(304不锈钢)气囊为研究对象,采用流固耦合的方法对其膨胀抛弹过程展开数值仿真分析,得到囊内的流场特性和囊壁的应力响应,计算结果与试验吻合较好.分析了入口边界条件及气囊结构对抛撒结果的影响,计算结果表明:气囊入口直径和入口边界条件是影响子弹分离速度和过载的关键因素,装药量、入口直径越大,子弹过载越大;一定装药量下,气囊入口直径不同时,子弹存在极限分离速度;气囊初始面积对子弹分离速度影响很小(仅4%),主要影响囊内的燃气压力,初始面积越大囊压越小,有利于降低囊壁的应力值.计算结果可为气囊结构的优化设计与工程实际应用提供重要参考.     

Classification and identification of gas–liquid dispersion states in a jet bubbling reactor

Three gas–liquid dispersion states including flooding, loading, and complete dispersion are observed sequentially in a jet bubbling reactor with an increase of the liquid jet velocity at the nozzle outlet (u_j). The gas–liquid dispersion states are identified through the slope (k) of the curve of fluctuation distribution index (FI) versus u_j as follows: (a) under the flooding, k = 0; (b) under the loading, k > 0; (c) under the complete dispersion, k < 0. In particular, the u_j at the transition points from flooding to loading and from loading to complete dispersion are referred to flooding jet velocity (u_jf, the transition point between k = 0 and k > 0) and complete dispersion jet velocity (u_jcd, the transition point from k > 0 to k < 0), respectively. The average relative deviations of the u_j at the transition points obtained through the acoustic emission measurement and visual observation are less than 5%.     

Development of blown film linear low-density polyethylene–clay nanocomposites: Part A: Manufacturing process and morphology

In this study, linear low-density polyethylene (LLDPE)/clay nanocomposites with different clay contents were prepared by melt intercalation using two different compatibilizers: maleic anhydride grafted styrene–ethylene–butylene–styrene and maleic anhydride grafted polyethylene (PE-g-MA). Melt intercalation was achieved by twin extrusion and nanocomposite films were produced by blown film extrusion. Effects of clay and compatibilizer fractions and type of compatibilizer on the structure, permeability, and the barrier properties of the nanocomposite films were investigated. PE-g-MA was shown to notably improve the dispersion of clay layers in the polyethylene matrix, and this was examined by atomic force microscopy and X-ray diffraction. The latter tests have also highlighted the importance of the screw configuration: the presence of mixing elements favors the dispersion and distribution of nanoclay. Moreover, differential scanning calorimetry results have shown no significant effect of the clay on the crystallinity of the composite while thermogravimetric analysis tests have demonstrated a decrease of onset and peak of decomposition temperatures. Finally, barrier properties toward water vapor transmission were measured. It was proven that not also clay, but the compatibilizer participated in decreasing the permeability of the film. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48589.     

Enhanced performance of Ni catalysts supported on ZrO2 nanosheets for CO2 methanation: Effects of support morphology and chelating ligands

A series of Ni/ZrO₂ catalysts was prepared by the impregnation method with modification of the morphology of ZrO₂ support as well as the impregnation procedure and tested for CO₂ methanation. The catalysts supported on the ZrO₂ nanosheets displayed superior catalytic performance as compared with that on ZrO₂ nanoparticles, which could be mainly attributed to the abundant oxygen vacancies promoting the adsorption and dissociation of CO₂ molecules as well as the high dispersion of Ni species. With the introduction of ethylenediamine (En) in the impregnation procedure, the resulting Ni-15En/ZrO₂-1.5 catalyst showed the optimal activity with CO₂ conversion of 86% significantly higher than Ni/ZrO₂-0 of 44% and Ni/ZrO₂-1.5 of 79% at 0.5 MPa and 300 °C. The excellent performance was attributed to increased moderately basic sites for CO₂ adsorption in ZrO₂ nanosheets, as well as the enhanced dispersion of nickel caused by the complexation of Ni ions with En, which inhibited the aggregation of nickel particles in the subsequent thermal treatments. In conclusion, the synergistic effects of the morphology of ZrO₂ nanosheets as well as the chelating behavior of En contributed to the enhanced performance of Ni-15En/ZrO₂-1.5 in the CO₂ methanation reaction. The strategy shows good prospects for controlling the size of active metals, especially those that were dispersed on the surface of the two-dimensional (2D) metal oxide materials.     

On the CFD modelling of hydrogen dispersion at low-Reynolds number release in closed facility

Hydrogen release inside closed facilities could cause explosions with harmful consequences. Safety assessment should be performed, in order to design prevention and mitigation measures in case of such an accident. A numerical study for helium (as hydrogen surrogate) accumulation inside a closed facility representative of a real-scale garage at low release rate is conducted. Due to the nature of the examined flow several turbulence modelling approaches (RANS and LES type) and the laminar approach are examined with the aim to evaluate their predictive capabilities in flows resulting from low-Reynolds number leaks. Best practice guidelines are followed in the simulations, several sensitivity studies are performed and different grid types are examined. The comparison of computational results with experimental data shows that RANS and LES approaches reproduce well the gas distribution inside the facility, while laminar approach predicts more enhanced stratification at the release phase. Statistical Performance Measures are used to evaluate the models and narrower acceptable ranges are suggested for releases in indoor configurations compared to open environments.     

Stabilizing effect of the cyclodextrins additive to spray-dried particles of curcumin/polyvinylpyrrolidone on the supersaturated state of curcumin

Although curcumin is considered to have various therapeutic effects, its use as a functional food or supplement is restricted owing to its low water solubility and bioavailability. To increase the solubility of curcumin in water, the use of polyvinylpyrrolidone (PVP) and vinylpyrrolidone-vinyl acetate copolymers with a pyrrolidone skeleton was noted to be promising. In particular, the bi-component formulations of curcumin/PVP prepared through spray drying exhibited an amorphous state in powder X-ray diffraction observations and temporally increased the apparent solubility of curcumin to over 5000 times that of untreated curcumin; nevertheless, after 24 h, the solubility decreased owing to the unstable supersaturated state of curcumin. The addition of α-cyclodextrin (α-CyD) in the bi-component curcumin/PVP formulation helped maintain the supersaturated state of curcumin, whereas the addition of β- and γ-CyD led to the collapse of the supersaturated state. The addition of α-CyD can likely help inhibit the nucleation and crystal growth of curcumin, through the interaction among the solubilized units of curcumin/PVP and α-CyD.     

Diffusion Magnetic Resonance Imaging-Based Biomarkers for Neurodegenerative Diseases

There has been an increasing prevalence of neurodegenerative diseases with the rapid increase in aging societies worldwide. Biomarkers that can be used to detect pathological changes before the development of severe neuronal loss and consequently facilitate early intervention with disease-modifying therapeutic modalities are therefore urgently needed. Diffusion magnetic resonance imaging (MRI) is a promising tool that can be used to infer microstructural characteristics of the brain, such as microstructural integrity and complexity, as well as axonal density, order, and myelination, through the utilization of water molecules that are diffused within the tissue, with displacement at the micron scale. Diffusion tensor imaging is the most commonly used diffusion MRI technique to assess the pathophysiology of neurodegenerative diseases. However, diffusion tensor imaging has several limitations, and new technologies, including neurite orientation dispersion and density imaging, diffusion kurtosis imaging, and free-water imaging, have been recently developed as approaches to overcome these constraints. This review provides an overview of these technologies and their potential as biomarkers for the early diagnosis and disease progression of major neurodegenerative diseases.