Diffuse interface method for fluid flow and heat transfer in cellular solids

This work presents a contribution on the numerical modelling capabilities for the simulation of fluid flow and heat transfer in cellular solids – in particular we focus on open cell aluminium foams. Rather than applying one of the classical academical or commercial numerical finite volume (FV), finite difference (FD) or finite element (FE) interface tracking methods, we base our models on an interface capturing phase field method (Nestler, 2005). A coupled diffuse interface lattice Boltzmann fluid flow solver (Ettrich, 2014) and a diffuse interface heat transfer approach (Ettrich et al., 2014) are combined in view of dealing with even more convoluted geometries, incorporating the dynamics of interfaces and complex multiphysics applications. Numerical results for the combined fluid flow and heat transfer simulations in open cell metal foams are in very good agreement with experimental data (Ettrich and Martens, 2012; Ettrich et al., 2012).     

0Cr17Ni4Cu4Nb零件端面黑点原因分析

通过宏观观察、光学显微分析、电镜扫描等分析手段对0Cr17Ni4Cu4Nb零件端面黑点进行分析。结果表明:黑点缺陷的显微组织存在异常,与基体组织存在轻微的过渡层,缺陷周围不存在氧化及脱碳现象,导致零件产生黑点的原因为电渣重熔过程中产生了异金属夹杂。     

Thermodynamic performance of the 3-stage ADR for the Astro-H Soft-X-ray Spectrometer instrument

The Soft X-ray Spectrometer (SXS) instrument (Mitsuda et al., 2010) [1] on Astro-H (Takahashi et al., 2010) [2] will use a 3-stage ADR (Shirron et al., 2012) to cool the microcalorimeter array to 50 mK. In the primary operating mode, two stages of the ADR cool the detectors using superfluid helium at ⩽1.20 K as the heat sink (Fujimoto et al., 2010). In the secondary mode, which is activated when the liquid helium is depleted, the ADR uses a 4.5 K Joule–Thomson cooler as its heat sink. In this mode, all three stages operate together to continuously cool the (empty) helium tank and single-shot cool the detectors. The flight instrument – dewar, ADR, detectors and electronics – were integrated in 2014 and have since undergone extensive performance testing. This paper presents a thermodynamic analysis of the ADR’s operation, including cooling capacity, heat rejection to the heat sinks, and various measures of efficiency.     

Wide-band,passively Q-switched Yb- and Tm-doped fibre laser using WSSe saturable absorber

A wide-band, passively Q-switched fibre lasers based on ytterbium- and thulium-doped fibre gain medium are proposed and demonstrated. The lasers employ a transition metal dichalcogenide, tungsten sulphoselenide as a saturable absorber (SA) which is prepared by mechanical exfoliation technique. By integrating the SA in the laser cavities, self-starting Q-switched at 1038 and 1982?nm are obtained. The generated pulses exhibit a microsecond pulse duration with few kilohertz repetition rate. The proposed SA has high potential as a new material to cater to the needs of various scientific, industrial and biomedical applications.     

Synthesis and characterization of monomeric and polymeric pyridinylimine‐based Ni(II) complexes and their catalytic activities in ethylene oligomerization

A new polymeric ligand was synthesized through the reaction of 4‐(pyridinylimine)phenol and formaldehyde in a basic medium, and its corresponding polymer–nickel complexes were formed in a 1:1 molar ratio. The synthesized compounds were characterized using elemental and spectral analyses. The monomeric and polymeric Ni(II) complexes (C₁ and C₂, respectively) were evaluated as catalyst precursors for ethylene oligomerization, using methylaluminoxane as an activator at two different ethylene pressures. C₂ was found to be a more effective pre‐catalyst than C₁, with the co‐catalyst having a similar effect in both cases. C₂ exhibited an activity of 1.282 × 10⁶ g (mol Ni)^?1 h^?1 bar^?1, with an Al:Ni ratio of 2000:1 at room temperature and 1 atm ethylene pressure. Meanwhile C₁ exhibited an activity of 1.126 × 10⁶ g (mol Ni)^?1 h^?1 bar^?1 under similar experimental conditions. At 5 atm ethylene pressure, C₁ favoured the formation of high‐density polyethylene, whereas C₂ favoured the formation of branched low‐density polyethylene. Copyright © 2012 Society of Chemical Industry     

Large-scale synthesis of WO3 nanoplates by a microwave-hydrothermal method

Tungsten oxide (WO₃) nanoplates were synthesized by a 270 W microwave-hydrothermal reaction of Na₂WO₄·2H₂O and citric acid (C₆H₈O₇·H₂O) in deionized water. X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED) were used to reveal the synthesis of WO₃ complete rectangular nanoplates in the solution of 0.2 g citric acid for 180 min, with O-W-O FTIR stretching modes at 819 and 741 cm⁻¹, and two prominent O-W-O Raman stretching modes at 804 and 713 cm⁻¹. The 2.71 eV indirect energy gap, and 430-460 nm blue emission wavelength range of WO₃ complete rectangular nanoplates were determined using UV-visible and photoluminescence (PL) spectrometers. The formation mechanism was also proposed according to the experimental results.     

Performance of C18 Derivatized Silica Gels: A Structure-Performance Study

Abstract

Significant performance differences in the separation of desamido-insulin from insulin and of amitriptyline from imipramine have been found for five, macroscopically similar, preparative C18 silica materials. Structure-performance relations have been used to understand this difference. Physical measurements on the unpacked silica gels as well as chromatographic measurements have been carried out. The latter measurements comprise: hydrophobicity, metal impurity, steric selectivity and silanol activity. The performance difference could not be explained by the difference in hydrophobicity, steric selectivity or metal impurity between the materials. Instead a correlation between the silanol ion exchange activity and the selectivity could be found. The highest performance was found under conditions where the silanol groups have a moderate activity. For the separations considered in this work, the silanol groups have a beneficial effect.     

Emerging opportunities in the two-dimensional chalcogenide systems and architecture

Inspired by the triumphs - and motivated by the need to overcome the limitations - of graphene, the science and engineering community is rapidly exploring the landscape of other potential two-dimensional materials, particularly in their single - or few layer form. Dominating this landscape are the layered chalcogenides; diverse in chemistry, structure and properties, there are well over 100 primary members of this materials family. Driven by quantum confinement, single layers (or few, in some cases) of these materials exhibit electronic, optical, and transport properties that diverge dramatically from their bulk counterparts. The field has evolved considerably since the time when single or few layer flakes were “synthesized” by the scotch-tape mechanical cleavage method. New and more sophisticated methods for controlled synthesis (or thinning), deposition and chemical exfoliation have been developed that can “dial” the number of layers with large areal coverage on diverse substrates. Further, the 2D chalcogenide layers are being used as “substrates” onto which other dimensionally confined structures are being integrated in the spirit of nanoscale composites. Some composite structures exhibit synergy of multiple functionalities of the individual components, while in other cases they represent quantum coupling or unusual behavior that is contrary to nominal synergy or the proportional contribution of individual components. Last but not the least, there remain many structural and chemical combinations that are yet to be explored with deeply intriguing properties or phenomena that are waiting to be revealed. Thus, it is timely to review the status of the field; particularly in the context of synthesis, geometric architecturing and characterization of 2D layered systems.Herein we review the evolving architecture of two-dimensional chalcogenide materials. We outline classes of specific materials and the evolution of their properties as they transition from nominally three to two-dimensionality, and especially in their single (or few) layer form. A variety of vapor-phase synthetic methods for the direct growth of large area single layers and the typical techniques for their characterization are presented. Lastly, we examine the potential of these materials as the fundamental building blocks of two-dimensional heterostructures and multi-dimensional nanocomposites. However, we also emphasize the need for fundamental experimental and theoretical undertaking to probe the classical problems like basic characterization and the dynamics of nucleation and growth in these 2D systems for realizing complex architecturing and resultant technologically useful phenomena and properties.     

Infiltration mechanism and factors influencing carbon/carbon–Zr–Ti–C composites prepared by liquid metal infiltration

The effects of fibre architecture, reaction temperature and holding time on the infiltration performance of carbon/carbon (C/C)–Zr–Ti–C composites prepared by liquid metal infiltration were investigated. The results indicated that samples with a chopped-web needled preform and low initial density had a high final density. Increasing the reaction temperatures resulted in a decrease of the final density of samples. Additionally, increasing the initial holding time appeared to obviously result in a high final density, but its effectiveness was not obvious in later observations. An analysis of the infiltration kinetics and mechanisms indicated that the diffusivity of carbon in the carbide, the open-pore sizes and their distribution in C/C composites were the essential characteristics that controlled the height of infiltrating melts.