Estimating the Aquifer’s Renewable Water to Mitigate the Challenges of Upcoming Megadrought Events

Water Resources Management - In arid and semi-arid regions of the world, the occurrence of prolonged drought events (megadroughts) associated with climate change can seriously affect the balance...     

Radiation and slip effects on MHD Maxwell nanofluid flow over an inclined surface with chemical reaction

The numerical solutions of the upper-convected Maxwell (UCM) nanofluid flow under the magnetic field effects over an inclined stretching sheet has been worked out. This model has the tendency to elaborate on the characteristics of “relaxation time” for the fluid flow. Special consideration has been given to the impact of nonlinear velocity slip, thermal radiation and heat generation. To study the heat transfer, the modified Fourier and Fick's laws are incorporated in the modeling process. The mass transfer phenomenon is investigated under the effects of chemical reaction, Brownian motion and thermophoresis. With the aid of the similarity transformations, the governing equations in the ordinary differential form are determined and then solved through the MATLAB's package “bvp4c” numerically. This study also brings into the spotlight such crucial physical parameters, which are inevitable for describing the flow and heat transfer behavior. This has been done through graphs and tables with as much precision and exactitude as is possible. The ascending values of the magnetic parameter, the Maxwell parameter and the angle of the inclined stretching sheet cause decay in the dimensionless velocity while an assisting behavior of the thermal and concentration buoyancy parameters is noticed.     

Hydrogen production by silica membrane reactor during dehydrogenation of methylcyclohexane: CFD analysis

A comprehensive computational fluid dynamic model has been developed using COMSOL Multiphysics 5.4 software to predict the behavior of a membrane reactor in dehydrogenation of methylcyclohexane for hydrogen production. A reliable reaction kinetic of dehydrogenation reaction and a permeation mechanism of hydrogen through silica membrane have been used in computational fluid dynamic modeling. For performance comparison, an equivalent traditional fixed bed reactor without hydrogen removal has been also modeled. After model validation, it has been used to evaluate the operating parameters effect on the performance of both the silica membrane reactor and the equivalent traditional reactor as well. The operating temperature ranged between 473 and 553 K, pressure between 1 and 2.5 bar, sweep factor from ?6.22 to 25 and feed flow rate from 1 to 5 × 10^?6 mol/s. The membrane reactor performed better than the equivalent traditional reactor, achieving as best result complete methylcyclohexane conversion and 96% hydrogen recovery.     

Aircore mechanism during draining based on influence of pressure difference and drain port diameter

An understanding of the mechanism of aircore phenomenon during draining is very important. In this study, numerical simulations were conducted for different pressurized and suction pressure water tanks, as well as for different drain port diameters, to explain and validate the proposed aircore mechanism. It was found that increasing the pressure at the top surface of the tank results in suppression of the aircore, whereas an increase in the suction pressure at the drain port outlet enhances the development of the aircore. For different drain port diameters, it was observed that the duration of the aircore during draining decreases with a decrease in the drain port diameter, and that the aircore is suppressed for a very small drain port diameter.     

A compact CMOS DC-DC buck converter based on a novel complement value leaping PWM technique

A very compact ultra-low power DC-DC buck converter is presented. The proposed buck converter employs a novel complement value leaping pulse-width modulation (PWM) technique to realize the desired DC mean-value for various loads. Incorporating just two counters with a simple digital controller to load the repeatedly complemented value of the 4bit up/down counter as the initial value of the least significant bits of the 5bit up counter, a PWM pulse is created to manage the charge/recharge period. The realized PWM signal maintains the same desired output voltage mean value for any load resistance between 80 and 140 Ω. The switching frequency is 160 kHz, and the overall power consumption is 26.9 nW, while the efficiency is 93.4% for current range of 1.7 to 3 mA. The performance of the proposed converter is validated by Cadence post-layout simulations utilizing TSMC180nm CMOS technology for 1-V supply voltage providing the output voltage mean value of 0.24 V.     

Effect of Shot Peening Operation on the Microstructure and Wear Behavior of AZ31 Magnesium Alloy

Protection of Metals and Physical Chemistry of Surfaces - Shot peening is a treatment used to increase surface hardness and wear resistance. In this study, the effect of shot peening on the...     

Synthesis and characterization of yttrium aluminum garnet nanostructures by cathodic electrodeposition method

Pure nanostructures of yttrium aluminum garnet (YAG) was prepared based on the cathodic electrodeposition method from the mixture of YCl₃ and AlCl₃ dissolved in water/ethanol solution. At first, hydroxide precursors cathodically were grown on the steel substrates then, the hydroxide powders heat treated at 850 °C for 4 h in dry air atmosphere. The formation of crystalline YAG nanopowder was confirmed by X-ray diffraction (XRD), thermogravimetric analysis (DSC-TGA), scanning electron microscopy (SEM) and Fourier transformed infrared spectroscopy (FT-IR). The results of the SEM showed that applied current density and bath temperature have the prominent effect on the morphology and particle size of the products. The results revealed that cathodic electrodeposition followed by heat-treatment can be used as a facile method for preparation of YAG nanostructures with different morphology.