On the mechanisms of secondary flows in a gas vortex unit

The hydrodynamics of secondary flow phenomena in a disc‐shaped gas vortex unit (GVU) is investigated using experimentally validated numerical simulations. The simulation using ANSYS FLUENT^® v.14a reveals the development of a backflow region along the core of the central gas exhaust, and of a counterflow multivortex region in the bulk of the disc part of the unit. Under the tested conditions, the GVU flow is found to be highly spiraling in nature. Secondary flow phenomena develop as swirl becomes stronger. The backflow region develops first via the swirl‐decay mechanism in the exhaust line. Near‐wall jet formation in the boundary layers near the GVU end‐walls eventually results in flow reversal in the bulk of the unit. When the jets grow stronger the counterflow becomes multivortex. The simulation results are validated with experimental data obtained from Stereoscopic Particle Image Velocimetry and surface oil visualization measurements. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 64: 1859–1873, 2018     

Oxidative catabolism of α-tocopherol in rat liver microsomes

The goal of this study was to clarify the mechanism responsible for the catabolism of α-tocopherol. The vitamin, bound to albumin, was incubated with rat liver microsomes and appeared to be broken down. Optimal production of the metabolite was obtained when 1 mg of microsomal protein was incubated with 36 μM of α-tocopherol in the presence of 1.5 mM of NADPH. Chromatographic and mass spectrometric analyses of the metabolite led to the conclusion that it consists of an ω-acid with an opened chroman ring, although we could not perform nuclear magnetic resonance analysis to confirm this. Our data show that α-tocopherol is ω-oxidized to a carboxylic acid and that this process can occur in rat liver microsomes in the presence of NADPH and O₂. The oxidation to the quinone structure appears to be a subsequent event that may be artifactual and/or catalyzed by a microsomal enzyme(s).     

Model of a polymer chain twisted inside a statistical segment. Poly(3‐hexylthiophene) in chloroform solutions

A set of hydrodynamic methods in extremely dilute solutions (determination of intrinsic viscosity [η ], translational diffusion D and flotation in a centrifugal field s ) was used in the studies of conformational properties, dimensions and equilibrium rigidity of individual molecules of a series of samples of poly(3‐hexylthiophene). Absolute molecular masses M _sD were determined. The Mark–Kuhn–Houwink equations for the range of M _sD from 2240 to 15 300 g mol^?1 are given. For the first time, an analysis of conformational properties and equilibrium flexibility of poly(3‐hexylthiophene) molecules was carried out using the model of a statistical segment containing a twisted polymer chain. © 2017 Society of Chemical Industry     

Periodic reactive flow simulation: Proof of concept for steam cracking coils

Streamwise periodic boundary conditions (SPBCs) have been successful in reducing the computational cost of simulating high aspect ratio processes. Extending beyond the classic assumptions of constant property flows, a novel approach incorporating non‐equilibrium kinetics was developed and implemented for the simulation of an industrial propane steam cracker. Comparison with non‐periodic benchmarks provided validation as relative errors on the main product yields were consistently below 1% for different reactor configurations. A further order‐of‐magnitude reduction of the radial errors on product concentrations was obtained via an intuitive correction method based on the concept of local fluid age. The computational speedup achieved through application of SPBCs was a factor 16–250 compared to the non‐periodic simulations. The presented methodology thus serves as a quick screening tool for the development of novel reactor designs and unlocks the potential for using more elaborate kinetic models or a more fundamental approach toward turbulence modeling. © 2016 American Institute of Chemical Engineers AIChE J, 63: 1715–1726, 2017     

Direct Measurement of Energy Barriers on Rough and Heterogeneous Solid Surfaces

The “three-liquid” contact angle approach to the surface free energy components of solids was applied to poly (vinyl fluoride), rough and flattened, with and without flame treatment. Lifshitz-van der Waals (LW), γ ^LW _SL , and acid-base (AB), γ ^LW _SL , components were determined and used to calculate ?δG _SL (W ^adhesion _SL ) for the formation of interfaces of five liquids with polymer. The automated goniometer allowed the determination of the energy barriers, ?δ G? _SL as the advancing liquid moved from pinned configuration to a metastable one. The acid-base component of the barriers was much greater than the LW, and the magnitude of the barriers was only slightly reduced by flattening.     

Plasma-Assisted Diesel Oxidation Catalyst on Bench Scale: Focus on Light-off Temperature and NOx Behavior

The effect of a non-thermal plasma reactor over a commercial Diesel oxidation catalyst (DOC) was investigated. Studies have been focused on the gas treatment efficiency together with lowering light-off temperature when a DOC catalyst was connected downstream to plasma reactor in test bench scale. Experiments have been conducted using multi-DBDs (dielectric barrier discharge) reactor in planar configuration driven by a HV AC generator (11 kV–15 kHz). The specific input energy was set to 57 and 85 J/L. Experiments were performed in gas composition simulating Diesel exhaust. Commercial DOC, monolith-supported Pt–Pd/Al₂O₃, was used at gas hourly space velocities of about 55,000 and 82,000 h^?1. CO and hydrocarbons light-off curves were determined for DOC, plasma, and plasma-DOC systems by temperature programmed surface reaction from 80 to 400 °C. Particular attention has been paid to the gas temperature between the plasma reactor and the DOC. Results show that the plasma-catalyst system provides the lowest light-off temperatures for CO and HCs. Under conditions of this study, light-off temperature improvement by about 57 °C was obtained and the plasma reactor totally oxidized NO to NO₂ at low temperature.     

髋关节整体替代陶瓷材料

许多材料在医学领域应用广泛,例如,整体替换硬组织或软组织的元件(如骨盆、骨头、关节、植牙等)、修补、诊断或矫正仪器(如起搏器、心脏阀等)。这些材料不仅要有好的力学性能,还要保持长期稳定,不能与人体相排斥。由于陶瓷材料在生理环境中具有强度高、生物相容性强和稳定性好的优点,人们研究用陶瓷材料替换骨骼。从20 世纪70 年代起,欧洲人用陶瓷组件置换整个髋关节。这些组件主要由氧化铝和氧化锆单体制成。然而,在有水环境中,氧化锆会发生低温降解。目前人们的研究重点在于提高陶瓷组件的强度和耐磨性,同时缩小其尺寸并延长其使用寿命。研究中使用的材料是氧化锆增韧的氧化铝复合陶瓷和其它氧化铝复合陶瓷,不再是单体陶瓷。另外,还可以使用氧化铝和氧化锆功能梯度复合材料。该梯度材料可以利用电泳沉积法(EPD)制得,其表面为纯氧化铝,中心部分为均匀的氧化铝、氧化锆复合材料,中间过渡部分是呈连续梯度渐变的氧化铝、氧化锆复合材料,烧成后会产生剩余热应力。设计这样的梯度结构是为了使复合材料具有最大表面压应力和最小内部张应力,与纯氧化铝组件相比,提高了强度和耐磨性。     

Modélisation Mathématique de la Décantation de la Boue Rouge

A good performance of the solid‐liquid unit operation is required for the economical exploitation of the Bayer process. A computational fluid dynamics (CFD) model simulating the operation of the last washing stage mud thickener of a large Canadian alumina plant is presented. The parametric study of the impact of changes in four parameters shows that the diameter of flocculated red mud particles, the feed flow rate and the radius of the feed well are critical parameters for the operation of the thickener.