Geometrical and positional isomerization of alkenyl acetates produced by hydrogenation of alkynyl acetates over palladium metal catalysts

Alkenyl acetates containing both geometrical isomers can be produced by a single controlled catalytic hydrogenation of the corresponding alkynyl acetate. The hydrogenation is capable of yielding formulations containing up to 60% trans isomer; the reduction is attended by positional isomerization in both geometrical isomers.NRCC No. 16834.     

A comparison of different geometrical elements to model fluid wicking in paper-based microfluidic devices

Recently, microfluidic paper-based analytical devices (μPADs) have outstripped polymeric microfluidic devices in the ease of fabrication and simplicity. Surface tension-based fluid motion in the paper's porous structure has made the paper a suitable substrate for multiple biological assays by directing fluid into multiple assay zones. The widespread assumption in most works for modeling wicking in a paper is that the paper is a combination of capillaries with the same diameter equal to the effective pore diameter. Although assuming paper as a bundle of capillaries gives a good insight into pressure force that drives the fluid inside the paper, there are some difficulties using the effective pore radius. The effective pore radius is totally different from the average geometrical pore radius which makes it impossible to predict wicking in μPADs based on geometrical parameters. In this article, we introduce different analytical and numerical models to investigate the possibility of determining the permeability of the paper, based on geometrical parameters rather than effective parameters. The lattice Boltzmann method is used for numerical simulations. The permeability of each of the proposed models was compared with the experimental permeability. Results indicated that assuming paper as a combination of capillaries and annuluses leads to accurate results that totally depend on average geometrical values rather than effective values. This paves the way for prediction of the fluid wicking only by considering average geometrical pore and fiber diameters.     

Capillary study on geometrical dependence of shear viscosity of polymer melts

Geometrical dependence of viscosity of polymethylmethacrylate (PMMA) and high density polyethylene (HDPE) are studied by means of a twin‐bore capillary rheometer based on power‐law model. Contrary geometrical dependences of shear viscosity are observed for PMMA between 210 and 255°C, but similar geometrical dependences are revealed for HDPE between 190 and 260°C. The fact that wall slip can not successfully explain the irregular geometrical dependence of PMMA viscosity is found in this work. Then, pressure effect and dependence of fraction of free volume (FFV) on both pressure and temperature are proposed to be responsible for the geometrical dependence of capillary viscosity of polymers. The dependence of shear viscosity on applied pressure is first investigated based on the Barus equation. By introducing a shift factor, shear viscosity curves of PMMA measured under different pressures can be shifted onto a set of parallel plots by correcting the pressure effect and the less shear‐thinning then disappears, especially at high pressure. Meanwhile, the FFV and combining strength among molecular chains are evaluated for both samples based on molecular dynamics simulation, which implies that the irregular geometrical dependence of PMMA viscosity can not be attributed to the wall slip behavior. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 39982.     

Evaluation of the parameters of titanium surface micro-pits on the titanium-PEEK joint fracture toughness

The present work is to investigate fracture toughness of titanium-PEEK by linking the interface fracture toughness to surface parameters of micro-pit on titanium panels during delamination. The relationship between geometrical parameters and failure mechanisms is also explained. The regular micro-pits were fabricated on pure titanium panels by Lithography. The effects of micro-pattern on fracture toughness were systematically evaluated by changing geometrical parameters of surface topography. The results showed that by changing the parameters of surface pattern, the fracture toughness can be manipulated through plastic deformation and molecular bond breaking of PEEK. The optimized wetting angle and surface free energy, having influenced on the real contact area and the stress regions, were obtained by adjusting the geometrical parameters. Finally, it was found that the failure mechanism transition from interface to cohesive was because of the attributed optimal parameters, showing more energy dissipation.     

Three-dimensional microstructure analysis of numerically simulated cementitious materials

In order to predict the transport properties of porous media, such as permeability and electrical conductivity of cementitious materials, a better understanding of the microstructural characteristics, including the geometrical and topological properties, is required. In this contribution, the microstructure of cementitious materials is simulated by using the cement hydration model HYMOSTRUC. In this computer-based numerical model, the hydrating cement grains are modeled as gradually growing spheres, which become in contact while growing. The simulated porous medium can be described as a series of sections taken from three orthogonal directions, in which each unit (pixel) is filled either with a solid or a fluid phase (pores). Various algorithms based on a random walk process are utilized to determine the local geometrical information, such as gravity center's coordinate, perimeter and area of each individual pore. The percolating path of the fluid in three dimensions is traced by using an overlap algorithm. Both three-dimensional (3D) geometrical information and topological space characterization including branch node network and genus of the pores are derived. Calculation results of these algorithms are compared with results obtained by other microstructural models at various degree of hydration.     

The role of pore structure in the catalytic behavior of “unaged” and “aged” silica-alumina catalysts

This is a review of research concerning the role played by the porous structure of silica-alumina catalysts on the evolution of organic catalytic processes. A strong effect of the geometrical shape of the pores on catalytic activity and selectivity has been evidenced. The experimental results have also been interpreted by means of a simplified mathematical model, able to relate selectivity for a reaction of the type A → B → C to the geometrical features of macro-microporous catalyst pellets, or granules. The theoretical results are in qualitatively satisfactory agreement with the experimental data.     

Determination of Geometrical Length of Airborne Carbon Nanotubes by Electron Microscopy,Model Calculation,and Filtration Method

The geometrical length of carbon nanotubes (CNTs) is of significant importance and this study aims at its fast determination. We evaluated a method to determine the geometrical length of CNTs by electrical mobility classification and developed a filtration based method. The measurement was carried out in air and the suitable generation method for airborne CNTs from liquid suspensions was investigated, followed by a proper control of the CNT dispersion degree by changing the CNT concentration in the liquid suspension. Airborne CNTs were generated by an atomizer, classified by a differential mobility analyzer and characterized by electron microscopy. The CNT geometrical lengths measured by electron microscopy served as the basis for comparison with other methods. Two theoretical models (Lall and Friedlander 2006; Li et al. 2012) for elongated particles were investigated and the comparison showed good agreement. This demonstrated the validity of the approach to determine the CNT length by the combination of mobility measurement and model calculation. The newly developed method, which employed a filtration model with uniform screens, showed comparable results with the CNT lengths as obtained from the electron microscopy.

Copyright 2013 American Association for Aerosol Research     

Computer-built polyethylene spherulites for mesoscopic Monte Carlo simulation of penetrant diffusion: Influence of crystal widening and thickening

An algorithm able to mimic crystal lengthening, branching, widening and thickening was developed in order to build spherulites similar to those observed in polyethylene. The ranges of volume crystallinity and crystal width-to-thickness ratio attainable were ≤40% and 8-35, respectively. An on-lattice Monte Carlo-based algorithm was used to generate penetrant trajectories in the built spherulites. Diffusivity was assessed from the mean-square displacement of the penetrant molecules, normalized with respect to the mean-square displacement of the penetrant molecules in a crystal-free system, and compared with the geometrical impedance factor calculated from the Fricke theory using morphological data samples in the simulated spherulites. The crystal blocking effect was greater in the tangential plane than along the spherulite radius. All data, except that for the highest crystallinity system (40%), conformed to a linear relationship between the geometrical impedance factor obtained from the diffusivity data and the geometrical impedance factor calculated from morphological data; the latter being calculated according to the Fricke model using averages based on the squares of the crystal width-to-thickness ratio data. This finding suggests that wide crystals had a more pronounced effect on the geometrical impedance factor than was indicated by their number fraction weight. The system with the highest volume crystallinity (40%) showed a markedly higher geometrical impedance factor than predicted by the Fricke theory using the two aforementioned modifications.     

Electromagnetic determination of clay water content: role of the microporosity

The electromagnetic determination of clay water content requires a good understanding of the main factors that affect the relationship between the clay relative permittivity κ and the water content θ. The first part of this paper proposes a review of the different factors affecting it: (a) a significantly high imaginary part of the relative permittivity; (b) a frequency-dependent response; (c) a high content of bound water with a relative permittivity value lower than that of free water; (d) a geometrical effect associated with “platy” units that characterize the clay texture. The next sections focus on the c and d factors related to the microporosity of clayey geomaterials; both factors are studied with two theoretical tools: the Moment Method (MoM) and the Differential Effective Medium (DEM) theory.The calculations indicate that bound water effect and geometrical effect act as competing processes: when water is added in a dry clayey material, the geometrical effect contributes to increase the clay relative permittivity compared to media with isotropic particles; a significant amount of bound water generates a decrease in the clay bulk permittivity. Consequently, the results allow to identify two types of behaviour: (1) low surface area systems, typically kaolinite geomaterials, for which the geometrical effect is predominant, and (2) high surface area systems, typically smectite clays, for which a balance between the geometrical effect and the bound water effect is expected.Moreover, the MoM simulations suggest that the derivative ∂κ/∂θ is affected by the bound water content, but slightly depends on clay content. These numerical observations that may contribute to improve in situ water content monitoring should be validated by experimental investigations.     

基于目标函数瞬时值的反应器网络综合方法

反应器网络综合是化工过程集成的关键问题之一,但求解过程十分复杂。提出了目标函数瞬时值的概念,并研究了利用目标函数瞬时值曲线所对应的面积进行反应器网络综合的方法。以两个复杂反应为例说明了该方法的应用并和国内外文献进行了对比。从案例研究可以看出,本方法能够得到最优反应器网络,也避免了求解大规模的非线形最优化问题,也克服了可得区法维数的限制,具有几何直观的特点。     

一种计算泡沫金属等效热导率的新模型

提出一种针对泡沫金属等效热导率预测的新模型,该模型基于泡沫金属Kelvin十四面体元胞结构建模,以凹面三棱柱近似金属韧带,并考虑韧带交汇处的结点特点,通过热阻分析得到计算等效热导率的表达式。研究表明：该模型对充填不同介质的不同材质泡沫金属等效热导率均有较高的预测精度（平均偏差均小于10%）,与文献其他半经验模型相比能更好兼顾预测精确性和通用性。     

The determination of the addition variation and geometrical isomerism of a polybutadiene as a function of molecular weight by preparative gel permeation chromatography and infrared analysis

The addition variation, 1,2 and 1,4 units, and the geometrical isomerism, 1,4-cis and 1,4-trans units, of a fractionated polybutadiene were determined as a function of molecular weight using preparative gel permeation chromatography followed by infrared analysis of the fractions. Both the addition variation and geometrical isomerism remained essentially constant across the molecular weight distribution.     

Carbonization of pitches in geometrically restricted spaces. Application to granular carbon–carbon composites

During granular carbon–carbon composites manufacturing, the binder (a pitch) is carbonized while surrounded by solid filler particles. This geometrical limitation imposed on the carbonization medium results in constraints responsible for textural modifications of the pitch-based coke. We studied the consequences of geometrical limitation on pitch carbonization, and also the influence of the as-formed composites multiscale organization on their mechanical properties and carboxyreactivity behavior. The micrometer scale is relevant to understand composite reactivity while the submillimeter scale enables a better comprehension of the mechanical properties.     

Preparation of geometrical isomers of linolenic acid

Two methods were developed to prepare important quantities of 18:3Δ9,12,15 geometrical isomers. The first method was based on the isolation of 18:3Δ9c,12c,15c from a linseed oil by a combination of urea inclusion and preparative high performance liquid chromatography (HPLC). The isolated 18:3 was isomerized using nitrous acid. The second method was based on the isolation of 18:3Δ9,12,15 geometrical isomers which usually are formed during the heat treatment of vegetable oils. For that purpose a linseed oil was heated at 275 C for 12 hr under nitrogen. The geometrical isomers were isolated using a combination of column chromatography on silicic acid, urea inclusion and preparative HPLC.     

聚合物水下切粒模板温度场的数值模拟研究

建立了7种不同模孔和3种不同加热油流道水下切粒模板的三维传热模型,并对各个模型进行了数值求解,获得了各个模板模型内部的温度场;并且计算了在不同温度的冷却水、不同的加热油的对流换热系数、不同模板材料下的模板的温度场。计算结果表明,由于受到冷却水的冷却作用,各模板切粒带表层处温度比较低;沿着厚度方向,由于受到加热油和聚合物的加热作用,切粒带深层的温度逐渐升高;在加热油加热和冷却水冷却共同作用下,在0≤z≤10mm处,切粒面浅层的温度梯度较大。通过分析,模孔尺寸对模板的温度场基本没有影响;加热油流道形式、冷却水的温度、加热油的对流换热系数和模板的材料对模板的温度场有一定的影响,这为模板的结构设计、边界条件的确定和模板材料的选择提供了可靠的理论依据。     

基于微段组合的干气密封端面型槽结构模型及其参数影响

为解决现有干气密封端面型槽型线方程表征能力不强和结构参数定义体系不统一的问题,提出了一种基于径向微段组合以表征任意形状型线的广义对数螺旋槽结构模型。给出了广义对数螺旋槽结构参数定义体系,对比了不同压力和速度条件下广义螺旋槽与经典螺旋槽干气密封的开启力、气膜刚度和泄漏率等稳态性能,重点研究了广义螺旋角分布和型线周向偏转两个特征量对干气密封性能的影响,基于不同目标函数获得了广义螺旋槽的最优形状。结果表明：型槽上游侧壁型线形状对各项稳态性能参数均有显著影响,而下游侧壁型线形状仅对泄漏率和气膜刚度影响显著;经典对数螺旋槽是一种流体动静压效应很强的端面结构,单纯依靠型线优化难以使气膜承载力显著提高,不过在低压高速条件下优化广义螺旋角分布,在高压低速条件下合适设置型线周向偏转有望提高干气密封的气膜刚度和刚漏比。     

Experimental study on performance of steam-water injector with central water nozzle arrangement

The steam-water injector (SI) is a simple mechanical device that has been widely used in industry. We did an experimental study to find the influence of physical and geometrical parameters on performance of the SI. The physical parameters studied were steam inlet pressure, water inlet pressure and water inlet temperature. Whereas, the geometrical parameters studied were steam nozzle area ratio, area ratio of steam nozzle to water nozzle and the mixing section converging angle. Pump head was introduced to evaluate the lifting-pressure performance of the SI under different operating and geometrical conditions. Optimal values of steam nozzle area ratio and mixing section converging angle were 1.3 and 11.6° respectively, for the present work, and optimal value of area ratio of steam nozzle to water nozzle increased with increasing water inlet pressure. Two head-capacity curves were introduced to highlight the effect of various physical and geometrical parameters on the performance of SI.     

基于质量守恒边界条件的下游泵送螺旋槽液膜密封空化分析

液膜中空化的产生会影响密封润滑性能。基于质量守恒的JFO空化边界条件,建立螺旋槽液膜密封数学模型,采用流线迎风有限元法求解Reynolds控制方程,获得端面空化分布,并通过可视化试验进行了验证。以空化临界转速和临界压力为表征,分析了螺旋槽结构参数对空化特性的影响。结果表明：螺旋槽内空化区域呈机翼截面型,且随着转速的增加而变大,随着内径压力的增加而减小,空化周向最大长度位于近槽根处;空化临界转速随着槽数、槽深的增加而增加,随着螺旋角、槽长坝长比、槽台宽比的增加而减小;空化临界压力随各结构参数的变化趋势与空化临界转速相反。通过对各结构参数的合理选择,可实现对空化的有效控制。     

Towards prediction of local corrosion on alumina refractories driven by Marangoni convection

Refractory materials are used in the high-temperature melting of iron and steel, which are the basic materials in various metallurgical processes and other high-temperature industrial production and technology development methods. The Marangoni effect is a key factor in the direct premature destruction of refractory materials in use and exerts a significant impact on low-cost, high-quality steel production. In this study, the area of refractory/air/slag interface was expressed and observed. Based on the previous studies, the geometrical model of corrosion groove is modified by considering the erosion and dissolution of refractory oxides. The model is used to analyze the corrosion evolution caused by the Marangoni effect. The difference between the calculated results and the experimental results is compared, and the reliability of the geometrical and corrosion models is verified for predicting the Marangoni convection influence on the service life of refractory materials.     

Fabrication of ceramic micro-scale hollow components by micro-powder injection moulding

Rapid developments in microsystem technologies demand ceramic microcomponents of increasing geometrical complexity. State-of-the-art microfabrication routes of ceramics are either limited in geometrical complexity and/or high volume capabilities. This paper presents a process route by which ceramic microcomponents with relatively complex three-dimensional architectures could be realised by a high-volume technique. The proposed strategy, in which yttria-stabilised zirconia was implemented, combines the capabilities of insert-micromoulding, powder micro-overmoulding, catalytic debinding and sintering. The produced architectures demonstrate the capability of the technique to combine the high performance of ceramic materials with the dimensional accuracy and mass manufacturability of powder micromoulding.