An improved radial impulse turbine for OWC

Traditionally, wells turbines have been widely used in OWC plants. However, an alternative has been studied over recent years: a self-rectifying turbine known as an impulse turbine. We are interested in the radial version of the impulse turbine, which was initially proposed by M. McCormick. Previous research was carried out using CFD (FLUENT^®), which aimed to improve knowledge of the local flow behavior and the prediction of the performance for this kind of turbine. This previous work was developed with a geometry taken from the literature, but now our goal is to develop a new geometry design with a better performance. To achieve this, we have redesigned the blade and vane profiles and improved the interaction between them by means of a new relation between their setting angles. Under sinusoidal flow conditions the new design improves the turbine efficiency by up to 5% more than the geometry proposed by Professor Setoguchi, in 2002. In this paper, the design criteria we have used is described, and the flow behavior and the performance of this new design are compared with the previous one.     

Numerical modelling in wave energy conversion systems

This paper deals with a numerical modelling devoted to predict the flow characteristics in the components of an oscillating water column (OWC) system used for the wave energy capture. In the present paper, the flow behaviour is modelled by using the FLUENT code. Two numerical flow models have been elaborated and tested independently in the geometries of an air chamber and a turbine, which is chosen of a radial impulse type. The flow is assumed to be three-dimensional (3D), viscous, turbulent and unsteady. The FLUENT code is used with a solver of the coupled conservation equations of mass, momentum and energy, with an implicit time scheme and with the adoption of the dynamic mesh and the sliding mesh techniques in areas of moving surfaces. Turbulence is modelled with the k–ε model. The obtained results indicate that the developed models are well suitable to analyse the air flows both in the air chamber and in the turbine. The performances associated with the energy transfer processes have been well predicted. For the turbine, the numerical results of pressure and torque were compared to the experimental ones. Good agreements between these results have been observed.     

Optimization of mechanical properties of in situ polymerized poly(methyl methacrylate)/alumina nanoparticles nanocomposites using Taguchi approach

Polymer Bulletin - Alumina nanoparticles are among important metal oxides with specific properties but chemically incompatible with an organic matrix such as poly(methyl methacrylate) (PMMA). In...     

Graphene oxide grafted poly(acrylic acid) synthesized via surface initiated RAFT as a pH-responsive additive for mixed matrix membrane

Incorporation of nanostructured materials into the membrane matrix is a new strategy to improve mechanical and performance properties. Graphene oxide (GO) is one of the advantageous carbon-based nanomaterials, which recently has been used extensively in this field. However, in the most cases, the surface modification of GO has been considered for the creation of new properties like a response to different stimuli such as temperature, pH, and pressure. In the present study, a well-defined poly(acrylic acid) was grafted on GO using reversible addition–fragmentation chain transfer polymerization technique. This modified GO was incorporated into the mixed matrix membrane as a pH-sensitive additive and its effect on the membrane performance was investigated. The membrane with 5 wt % of modified GO provides better hydrophilicity, flux, antifouling, and rejection properties and so the effect of pH change on the aforementioned characteristic properties was studied for this membrane. It is indicated that modified membrane shows different behaviors in acidic and alkaline conditions. In addition, excellent heavy metal separation was observed among rejection tests, especially for Hg ions. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47213.     

A 3D analytical modeling of tri-gate tunneling field-effect transistors

In this paper, a three-dimensional (3D) analytical solution of the electrostatic potential is derived for the tri-gate tunneling field-effect transistors (TG TFETs) based on the perimeter-weighted-sum approach. The model is derived by separating the device into a symmetric and an asymmetric double-gate (DG) TFETs and then solving the 2D Poisson’s equation for these structures. The subthreshold tunneling current expression is extracted by numerical integrating the band-to-band tunneling generation rate over the volume of the device. It is shown that the potential distributions, the electric field profile, and the tunneling current predicted by the analytical model are in close agreement with the 3D device simulation results without the need of fitting parameters. Additionally, the dependence of the tunneling current on the device parameters in terms of the gate oxide thickness, gate dielectric constant, channel length, and applied drain bias is investigated and also demonstrated its agreement with the device simulations.     

Mesostructured Hollow Siliceous Spheres for Adsorption of Dyes

A facile and one-pot strategy for the preparation of novel diamino-functionalized hollow siliceous spheres (DAF-HSS) is suggested. Field-emission scanning electron microscopy (FE-SEM) images of DAF-HSS showed a monodispersed hollow sphere morphology. Also, TEM images revealed that the DAF-HSS has a porous structure with parallel semi-long-range channels. DAF-HSS material was used as an adsorbent for the removal of hazardous monocationic dyes in aqueous solution. Neutral red (NR) and crystal violet (CV) were selected as model compounds. Isotherm and kinetic studies were carried out and their different linear forms were applied and compared. The equilibrium data fitted better with the Langmuir model.     

MapReduce scheduling algorithms: a review

Recent trends in big data have shown that the amount of data continues to increase at an exponential rate. This trend has inspired many researchers over the past few years to explore new research direction of studies related to multiple areas of big data. The widespread popularity of big data processing platforms using MapReduce framework is the growing demand to further optimize their performance for various purposes. In particular, enhancing resources and jobs scheduling are becoming critical since they fundamentally determine whether the applications can achieve the performance goals in different use cases. Scheduling plays an important role in big data, mainly in reducing the execution time and cost of processing. This paper aims to survey the research undertaken in the field of scheduling in big data platforms. Moreover, this paper analyzed scheduling in MapReduce on two aspects: taxonomy and performance evaluation. The research progress in MapReduce scheduling algorithms is also discussed. The limitations of existing MapReduce scheduling algorithms and exploit future research opportunities are pointed out in the paper for easy identification by researchers. Our study can serve as the benchmark to expert researchers for proposing a novel MapReduce scheduling algorithm. However, for novice researchers, the study can be used as a starting point.

     

Ethanol purification using polyamide‐carbon nanotube composite membranes

This work presents synthesis and characterization of polyamide‐carbon nanotube (CNT) composite membranes for purification of ethanol. The solution‐casting method was applied for preparation of nanocomposite membranes. The nanocomposite membranes were characterized using scanning electron microscopy to ensure the fine dispersion of nanoparticles in polymer matrix. The effect of CNT loading on membrane performance was investigated. The separation performance of synthesized membranes was evaluated in separation of ethanol from ethanol/water mixture using pervaporation. Effect of feed temperature and feed concentration on separation of ethanol was investigated. The results showed that increasing temperature increases flux of ethanol through the membrane, but decreases separation factor. The results also confirmed that the best separation performance can be obtained at CNT loading of 0.5 wt%. Furthermore, a mathematical model was developed to simulate the separation process. The model was based on solving the continuity equation for ethanol in the feed side and membrane. The simulation results were compared with the experimental data and were in good agreement. POLYM. ENG. SCI., 54:961–968, 2014. © 2013 Society of Plastics Engineers     

Development of a Group Contribution Method Based on UNIFAC Groups for the Estimation of Vapor Pressures of Pure Hydrocarbon Compounds

A group contribution method based on UNIFAC groups was developed to estimate the vapor pressures of pure hydrocarbons at reduced temperatures (0.45–0.95). The maximum pressure for the correlation is 35 atm. Experimental vapor pressures for 456 hydrocarbons were collected and used to calculate model parameters. The developed model utilizes the combinatorial and the residual UNIFAC terms and the fugacity of pure hydrocarbons. The model parameters were fitted in two modes, using contributions from first‐order groups. In the first case, the Gibbs free energy was considered only as an explicit function of temperature, and in the second one, in addition to the temperature effect, the effect of the molecular structure was also considered. Taking the molecular structure into account significantly decreases the prediction error. Hence, a uniform linear relationship to structure is considered. In the modified models, the error in prediction of the vapor pressure in the temperature range discussed is less than 15 %.     

Separation of CO2 by single and mixed aqueous amine solvents in membrane contactors: fluid flow and mass transfer modeling

Removal of carbon dioxide from gas mixtures is of vital importance for the control of greenhouse gas emission. This study presents a numerical simulation using computational fluid dynamics of mass and momentum transfer in hollow-fiber membrane contactors. The simulation was conducted for physical and chemical absorption of CO₂. A mass transfer model was developed to study CO₂ transport through hollow-fiber membrane contactors. The model considers axial and radial diffusions in the contactor. It also considers convection in the tube and shell side with chemical reaction. The model equations were solved by numerical method based on finite element method. Moreover, the simulation results were validated with the experimental data obtained from literature for absorption of CO₂ in amine aqueous solutions as solvent. The simulation results were in good agreement with the experimental data for different values of gas and liquid velocities. The simulation results indicated that the removal of CO₂ increased with increasing liquid velocity in the tube side. Simulation results also showed that hollow-fiber membrane contactors have a great potential in the area of gas separation specially CO₂ separation from gas mixtures.