MHD flow and heat transfer over stretching/shrinking sheets with external magnetic field,viscous dissipation and Joule effects

The present article considers the steady magnetohydrodynamic (MHD) laminar boundary layer flow of a viscous and incompressible electrically conducting fluid near the stagnation point on a horizontal stretching or shrinking surface, with variable surface temperature and a constant magnetic field applied normal to the surface of the sheet. The governing system of partial differential equations is first transformed into a system of ordinary differential equations by introducing an appropriate similarity transformation, which is then solved numerically using a finite‐difference scheme known as the Keller‐box method. The effects of the governing parameters on the skin friction coefficient, the local Nusselt number as well as the velocity and temperature profiles are determined and discussed. Results indicate that for the stretching sheet, solution exists and is unique for all values of the stretching/shrinking parameter $\lambda $ , while for the shrinking sheet, solutions only exist up to some critical values $\lambda = \lambda _{{\rm c}} $ , and these solutions may be unique, dual and sometimes triple. © 2011 Canadian Society for Chemical Engineering     

Ultra-fast catalytic reduction of dyes by ionic liquid recoverable and reusable mefenamic acid derived gold nanoparticles

We synthesized mefenamic acid (MA) derived gold nanoparticles (MA-AuNps) in aqueous solution (MA-Au sol). Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) of the sol at 1, 5, 15 and 60 min showed changes in size and shape of formed AuNps. Fourier Transform Infrared (FTIR) Spectroscopy revealed the interaction between AuNps and MA. Each Au sol exhibited exceptional catalytic activity for the reduction of Methylene Blue (MB), Rose Bengal (RB) and Eosin B (EB) dye individually as well as collectively. However, complete reduction of dye(s) was accomplished by Au sol of 5 min in just 15s. The catalytic performance of Ma-Au sol was far superior to that adsorbed on glass. AuNps were recovered with the help of water insoluble room temperature ionic liquid and reused with enhanced catalytic potential. This finding is a novel, rapid and highly economical alternative for environmental safety against pollution by dyes and extendable for control of other reducible contaminants as well.     

Diagnostics of First Wall Materials in Device by Polarization-Resolved a Magnetically Confined Fusion Laser-Induced Breakdown Spectroscopy

Laser-induced breakdown spectroscopy （LIBS） is a powerful analytical tool for real- time diagnostics and detection of multiple elements deposited at the first wall of magnetically confined plasma ft~sion devices. Recently, we have tested LIBS in our laboratory for application to in situ real-time diagnostics in the fusion device EAST. In this study, we applied polarization- resolved LIBS （PR-LIBS） to reduce the background continuum and enhance the resolution and sensitivity of LIBS. We used aluminium （A1） （as a substitute for Be） and the first wall materials tungsten （W） and molybdenum （Mo） to investigate polarized continuum emission and signal-to- background ratio （SBR）. A Nd：YAG laser with first, second and third harmonics was used to produce plasma. The effects of the laser polarization plane, environmental pressure and polarizer detection angle were investigated. The spectra obtained without using a polarizer （i.e. LIBS） were compared with those obtained with a polarizer （PR-LIBS）. Distribution of emission spectral intensity was observed to follow Malus＇ law with respect to variation in the angle of detection of the polarizer. The spectra obtained by PR-LIBS had a higher SBR and greater stability than those obtained by LIBS, thereby enhancing the reliability of LIBS for quantitative analyses. A comparison of A1, Mo and W showed that W exhibited a higher continuum with stronger polarization than the low-Z elements.     

Microemulsions in Enhanced Oil Recovery: A Review

Abstract

Microemulsions have recently made advances in enhanced oil recovery processes in which chemicals, especially surfactants, are used to recover the oil from natural oil reservoirs. This technique relies on the knowledge of interfacial properties among oil, water, and solid rock reservoirs in the occasional presence of natural gas under extreme conditions. Surfactant-based chemical systems have been reported in many academic studies and their technological implementation is a potential candidate in enhanced oil recovery (EOR) activities. For instance, it was determined that a mobilized buffer (polymer) with viscosity either equal to or greater than the mobilized oil enhanced the recovery efficiency considerably. However, EOR based on chemicals like alkaline–surfactant–polymer (ASP) is a complex technology requiring a high level of expertise for its industrial implementation. The surfactant–polymer interaction is a rapidly growing research area for efficient oil recovery by improving slug integrity, adsorption, and mobility control. This review article evaluates the injecting fluid system to highlight some recent advances in the use of chemicals in EOR, especially with microemulsions. It further reveals the current status and future outlook for EOR technology in oil fields and describes the opportunities for strategic utilities and load growth in petroleum industry.     

Dual solutions in mixed convection flow near a stagnation point on a vertical surface in a porous medium

The steady stagnation point flow through a porous medium bounded by a vertical surface is investigated in this study. The external velocity, which normally impinges the vertical surface and the surface temperature are assumed to vary linearly with the distance from the stagnation point. The governing system of partial differential equations is first transformed into a system of ordinary differential equations, and then they are solved numerically by a finite-difference scheme, namely the Keller-box method. The features of the flow and heat transfer characteristics for different values of the governing parameters are analyzed and discussed. Both cases of assisting and opposing flows are considered. It is found that dual solutions exist for assisting flow, besides that usually reported in the literature for opposing flow. Therefore, the reported results are completely new.     

Mixed convection boundary layer flow past an isothermal horizontal circular cylinder with temperature-dependent viscosity

The problem of steady laminar mixed convection boundary layer flow past an isothermal horizontal circular cylinder placed in a viscous and incompressible fluid of temperature-dependent viscosity is theoretically considered in this paper. The partial differential equations governing the flow and heat transfer are shown to be non-similar. Full numerical solutions of these governing equations are obtained using an implicit finite-difference scheme known as the Keller-box method. The solutions are obtained for various values of the Prandtl number Pr, the mixed convection parameter λ and the viscosity/temperature parameter θ_r. The obtained results show that the flow and heat transfer characteristics are significantly influenced by these parameters.     

Optimized production and advanced assessment of biodiesel: A review

Biodiesel production is profitable only under special conditions. Technical challenges including methods to make the transesterification reaction more energy efficient and faster by using catalysts, controlling reaction conditions more efficiently in narrow range, or selection of appropriate feedstocks should be properly addressed to make biodiesel economical viable fuel. Cradle to grave assessment of biodiesel is provided in the present review article. Transesterification reaction variables that affect the purity and performance of biodiesel including quality of raw materials, molar ratio of alcohol to oil, type and concentration of used catalysts, concentration of free fatty acids, water content, temperature, and time required for the reaction are critically described to provide complete understanding and obtaining economical and optimal biodiesel yields. This article also provides a critical review of biodiesel properties such as density, viscosity, cetane number, cloud point, pour point, and flash point. The importance of analytical methods including gas chromatography, high‐performance liquid chromatography, nuclear magnetic resonance spectroscopy, infrared spectroscopy, and Raman spectroscopy is presented and highlighted here in a novel way. Finally, this review will provide complete understanding to readers about biodiesel.     

Source code fragment summarization with small-scale crowdsourcing based features

Recent studies have applied different approaches for summarizing software artifacts, and yet very few efforts have been made in summarizing the source code fragments available on web. This paper investigates the feasibility of generating code fragment summaries by using supervised learning algorithms.We hire a crowd of ten individuals from the same work place to extract source code features on a corpus of 127 code fragments retrieved from Eclipse and Net- Beans Official frequently asked questions (FAQs). Human annotators suggest summary lines. Our machine learning algorithms produce better results with the precision of 82% and performstatistically better than existing code fragment classifiers. Evaluation of algorithms on several statistical measures endorses our result. This result is promising when employing mechanisms such as data-driven crowd enlistment improve the efficacy of existing code fragment classifiers.     

Encapsulation and characterization of controlled release flurbiprofen loaded microspheres using beeswax as an encapsulating agent

The aim of the present study was to extend the use of flurbiprofen in clinical settings by avoiding its harmful gastric effects. For this purpose, we designed the controlled release solid lipid flurbiprofen microspheres (SLFM) by emulsion congealing technique. Drug was entrapped into gastro resistant biodegradable beeswax microspheres which were prepared at different drug/beeswax ratios 1:1, 1:2 and 1:3 using gelatin and tween 20 as emulsifying agents. The effect of emulsifiers and the effect drug/beeswax ratios were studied on hydration rate, encapsulating efficiency, micromeritic properties, scanning electron microscopy (SEM), fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), X-ray diffraction (X-RD) analysis and in vitro drug release at pH 1.2 for 2 h and at pH 6.8 for 10 h. SEM revealed that microspheres made with tween 20 were smooth while microspheres made with gelatin showed porous morphology, however, they were all spherical in nature. The practical yield (recovery) showed a dependence on drug-beeswax ratio and it was variable from 53 to 84%. High loading encapsulating efficiency of flurbiprofen from 8 to 94% was achieved. FTIR and DSC analysis confirmed the absence of any drug polymer interaction indicating drug stability during microencapsulation. X-RD of pure flurbiprofen shows sharp peaks, which decreases on encapsulation, indicating decrease in the crystallinity of drug in microspheres. The micromeritic studies confirmed the presence of excellent and good flow properties of microspheres. Entrapment efficiency, morphology, practical yield, hydration rate, flow properties demonstrated their dependence on the HLB value of emulsifiers and emulsifiers with higher HLB were found more appropriate for effective microencapsulation of flurbiprofen. The release kinetics followed zero order mechanism of drug release at pH 6.8. Release pattern depends on the morphology of flurbiprofen microspheres and amount of beeswax used in the microspheres preparation. The microspheres prepared with high HLB values i.e., tween 20 showed effective control of drug release from microspheres. The absence of drug release at pH 1.2 proved the suitability of beeswax for its use as a gastro resistant material.