Numerical study of pipeline restart of weakly compressible irreversibly thixotropic waxy crude oils

A 3‐D axisymmetric model is developed to predict pressure wave propagation processes during gelled waxy oil pipeline restart operations. A finite volume method is implemented on a staggered grid. An iterative predictor‐corrector algorithm provides solutions to the combined parabolic‐hyperbolic set of governing equations. A new shear‐history‐dependent thixotropic rheology model is proposed for pressure wave propagation computations. Moderate Reynolds number flows within the laminar regime are computed, demonstrating the impact of inertial effects. The results clearly illustrate the important mechanisms of pipeline restart. The nature of pressure wave propagation is governed by gel strength as well as overall fluid compressibility. Three sequential pressure wave propagation regimes are dominated by inertial, viscous, and gel degradation phenomena, respectively. The viscous and gel degradation regimes are effectively coupled by imposed deformation conditions. For initially homogenous thixotropic gels, strain tends to localize near the pipeline wall, playing a central role in assuring the pipeline restart. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2657–2671, 2015     

Application of finite-difference time domain to dye-sensitized solar cells: The effect of nanotube-array negative electrode dimensions on light absorption

We examine the light absorbing behavior of dye-sensitized solar cells (DSCs) having cathodes (negative electrodes) comprised of highly ordered TiO₂ nanotube arrays using the electromagnetic computational technique, finite-difference time domain (FDTD). The highly ordered nanotube arrays, grown using anodic oxidation of titanium foils or thin films, feature an open end with the other end fixed on a dense oxide layer (barrier layer). The numerical simulation model is comprised of nanotube arrays on a transparent conducting glass substrate under front-side illumination. In the FDTD analysis, a transverse electromagnetic (TEM) wave is incident onto a N719 dye-coated nanotube array initially passing through the barrier layer; light that emerges from the nanotubes is reflected by a perfectly conducting layer (perfect electric conductor—PEC) boundary that simulates the effect of the DSC platinum counter electrode. An observation plane placed between the electromagnetic source and DSC detects the intensity of both the incident wave and the wave returning back from the DSC structure. The absorbance and transmittance spectra are determined in the wavelength range 300–700 nm as a function of nanotube-array dimensions including length, pore size, barrier layer thickness, and surface roughness while keeping the wall thickness constant at 12 nm. The validity of the computational simulations is experimentally verified. A significant increase in the light absorption by the dye-coated nanotubes was observed for increasing nanotube length; smaller pore sizes, and increased surface roughness. Changes in the barrier layer thickness had a negligible effect on the absorbance spectrum. Our efforts demonstrate FDTD to be a broadly applicable technique capable of guiding design of an optimal DSC architecture.     

Incorporation of Monovalent Ions in ZnO and Their Influence on Varistor Degradation

An atomistic simulation technique has been used to predict the spatial arrangement of the dopant species sodium, lithium, and chlorine within the zinc oxide lattice. The alkaline oxides are preferentially incorporated via a self-compensating mode, forming interstitial cations which hinder the migration of zinc interstitials and hence slow the degradation of the varistor. The addition of chloride ions is shown to negate this effect by forming sodium and chloride substitutional defects rather than any species involving sodium interstitial ions.     

Separation and recovery of cellulose and lignin using ionic liquids: a process for recovery from paper‐based waste

BACKGROUND: The production of paper makes use of cellulose and lignin as a raw material, and almost all cellulose and lignin production comes from raw wood materials, contributing to deforestation and resulting in potential environmental harm. It is therefore beneficial to develop technologies for cellulose and lignin recovery for re‐use and sustainability of resources. RESULTS: Three imidazolium based ionic liquids (ILs), 1‐(2‐cyanoethyl)‐3‐methylimidazolium bromide (cyanoMIMBr), 1‐propyl‐3‐methylimidazolium bromide (propylMIMBr) and 1‐butyl‐3‐methylimidazolium chloride (butylMIMCl), were synthesised by microwave technology and fully characterised by mass spectrometry, thermogravimetric differential scanning calorimetry, thin layer chromatography, nuclear magnetic resonance and Fourier transform infrared spectroscopies. Cellulose and lignin were soluble in all three ILs with solubility being greatest in cyanoMIMBr. Regeneration of cellulose and lignin was achieved from saturated solutions of cellulose in IL and lignin in IL for all three ILs. The ILs propylMIMBr and butylMIMBr have been used for the first time in the separation and recovery of cellulose and lignin and regeneration of the IL from a mixture of cellulose and lignin in IL. FTIR analysis confirms successful recovery. CONCLUSIONS: This work demonstrates the ability of ILs to separate and recover cellulose and lignin from a mixed system. Copyright © 2009 Society of Chemical Industry     

Novel sintered glass-ceramics from vitrified oil well drill cuttings

An amorphous glass was obtained by melting drill cuttings from oil and gas exploration and production operations in the North Sea that have been blended with sodium and calcium oxides to minimise the melting temperature. Mixtures containing dried drill cuttings:sodium oxide:calcium oxide in the weight ratio 8:1:1 held at 1300 °C for 5 h produce an amorphous solid that can be further treated at temperatures between 750 and 800 °C to give a largely crystalline glass-ceramic. The glass-ceramics have been characterised by physical, chemical and mechanical analyses and shown to have properties of machinability, strength, wear-abrasiveness, thermal resistance, resistance to crack propagation, and stability towards leaching that make the materials suitable for tiling applications, allowing diversion of the drill cutting wastes from final disposal in landfill.     

Measurement of trust over time in hybrid inspection systems

A study was conducted to measure the effects of human trust and to determine how it develops over time in a hybrid inspection system given different types of errors (i.e., false alarms and misses). The study also looked at which of the four dimensions of trust (competence, predictability, reliability, and faith) were the best predictors of overall trust. Results from the study showed that trust is sensitive to the type of errors made by a system. There was a significant change in overall trust between the stages for the conservative and risky systems, but no significant change in the neutral system. In regards to the best predictors of trust, faith appeared as one of the predictors in all three trial blocks for the conservative and risky systems. As time progressed, predictability emerged in the second and third trial blocks for the conservative system. Competence played an important role in the development of trust for the risky system, whereas reliability played an important role for the neutral system. These results suggest that subjective ratings of trust and the properties of the system can be used to predict the allocation of functions in hybrid inspection systems. © 2005 Wiley Periodicals, Inc. Hum Factors Man 15: 177–196, 2005.     

Fabrication of metallic nanowire arrays by electrodeposition into nanoporous alumina membranes: effect of barrier layer

Deposition into nanoporous alumina membranes is widely used for nanowire fabrication. Herein using AC electrodeposition ternary Fe–Co–Ni nanowires are fabricated within the nanoscale-pores of alumina membranes. Using an electrodeposition frequency of 1,000 Hz, 15 V_rms, consistently and repeatably yield nanowire arrays over membranes several cm² in extent. Electrochemical Impedance Spectroscopy (EIS) is used to explain the effects of AC electrodeposition frequency. The impedance of the residual alumina barrier layer, separating the underlying aluminum metal and the nanoporous membrane, decreases drastically with electrodeposition frequency facilitating uniform pore-filling of samples several cm² in area. Anodic polarization studies on thin films having alloy compositions identical to the nanowires display excellent corrosion resistance properties.