Computer simulation-based method to predict packing density of aggregates mixture

A key theory in concrete mix design is maximizing aggregate packing density (PD) of aggregate mixture. Different methods have been presented by researchers to estimate PD of aggregate mixture. One such method is computer simulation that has become increasingly common over the last decade; however, it is usually a time-consuming procedure. In the current study, a method based on computer simulation is proposed for estimating aggregate PD. In this method, aggregates with specific shapes, grading and PDs are substituted by monosized spherical aggregates. An equation is also presented for determining the diameter of equivalent monosized aggregates. The coefficient of friction between the equivalent monosized aggregates is determined in a way that the monosized aggregates will have a PD equal to that of actual aggregates. The proposed method is also used to simulate laboratory experiments conducted by the present authors and other researchers. Comparisons reveal the high accuracy of the proposed simple method in predicting the PD of aggregate mixtures.     

Preparation of tin ferrite–tin oxide by hydrothermal,precipitation and auto-combustion: photo-catalyst and magnetic nanocomposites for degradation of toxic azo-dyes

In this work, tin ferrite nanoparticles were first synthesized by simple chemical procedures such as co precipitation, sol–gel auto combustion and hydrothermal methods. In general, all three methods were compared in the synthesis of nanoparticles. Then tin ferrite–tin oxide (50%:50%) nanocomposites were prepared using co precipitation method. Crystal structures of nanoparticles and nanocomposite were studied using X-ray diffraction pattern. The particle size was determined by Scanning Electron Microscopy. Vibrating sample magnetometer was used to study the magnetic property of the products. And also, by applying Fourier transform infrared spectrometer, the purity of the material was determined. Photocatalytic activity of nanoparticles and nanocomposites was investigated under ultra-violet and visible spectroscopy (UV–Vis). The results show that prepared nanocomposites are applicable for magnetic and photocatalytic performance and they were able to degrade azo dyes (organic dyes) under UV–Vis radiation.     

Thermally induced nonlinear stability and imperfection sensitivity of temperature- and size-dependent FG porous micro-tubes

International Journal of Mechanics and Materials in Design - An attempt is made in the current research to analyse the nonlinear thermal stability and imperfection sensitivity of functionally...     

A high‐voltage gain nonisolated noncoupled inductor based multi‐input DC‐DC topology with reduced number of components for renewable energy systems

This paper proposes a modular nonisolated noncoupled inductor‐based high‐voltage gain multi‐input DC‐DC converter. Despite the high‐voltage gain of the proposed topology, the average of normalized voltage stress (NVS) on its switches/diodes is low. This property leads to less loss and cost of switches/diodes. Using the same number of components, the proposed topology produces higher voltage gains, in comparison with recently presented high step‐up topologies. Also, the proposed topology utilizes less number of components (capacitors, inductors, diodes, and switches) for producing a desired voltage gain, which can reduce the size, mass, cost, complexity, and losses and improve the efficiency of converter. Continuous current of input sources is another main advantage of the proposed topology. All the abovementioned characteristics have made the proposed topology very suitable for renewable energy systems (or even hybrid/electric vehicles). Design considerations of the proposed topology have also been presented. For better evaluation, the proposed topology has been compared with some of recently presented high step‐up structures, from viewpoints of producible voltage gain, number of components, and normalized voltage stress (NVS) on switches/diodes. Finally, the prototype of 2‐input version has been experimentally implemented. Obtained experimental results confirm appropriate performance of the proposed topology.     

A solution method for frictional contact problems of a crack in FGMs under mechanical and thermal loads

This article provides a numerical treatment of a finite crack in an interfacial layer with spatially varying elastic properties under in-plane mechanical and thermal loading conditions. The variation of stress intensity factors and energy release rates with the functions which are governing the material properties of the interfacial layer is studied. Transient and steady-state response of a central crack in FGMs subjected to the mechanical and thermal loads are investigated. Unlike earlier studies which consider the cracks encountered as open, the current investigation studies cracks in an essentially compressive environment in which the crack faces are in contact and frictional effects play an important role. To solve this contact problem, a simple and efficient, iterative finite element method developed by authors is used. Numerical examples are provided to verify the technique and the results are compared with those of the published papers. This revised version was published online in July 2006 with corrections to the Cover Date.     

Reactivity stabilization and capacity study of fabricated alumina and zirconia-supported CaO-based sorbents for high-temperature CO2 capture in a fixed-bed reactor

Calcium looping process is a promising approach for CO₂ capture from the flue gas of fossil fuel power plants and the cement industry. Even though the advantages of calcium-based sorbents are low cost and high uptake capacity, they suffer from low durability during cycles. Modified sorbents were fabricated by adding alumina and zirconia and the mixture of alumina and zirconia to calcium oxide via the co-precipitation method. The performance of synthesized sorbents in terms of stability and CO₂ capture capacity were evaluated using a fixed bed reactor in various CO₂ sorption/desorption cycles. The sorbents were fabricated by a co-precipitation methodology using 10% binders (alumina and/or silica). X-ray diffraction (XRD), BET/BJH, and scanning electron microscopy (SEM) were conducted for characterization of synthesized sorbents. CaO-10% ZrO₂ showed the best performance among the fabricated sorbents in terms of stability during 5 cycles and CO₂ capacity (14 mmol CO₂/g sorbent). The formation of CaZrO₃ with a perovskite structure and high-temperature resistance could be attributed to well performance of zirconia-supported sorbent. On the other hand, no sign of aluminum zirconate formation was approved in XRD analysis for the fabricated sorbent using mixed binders of zirconia and alumina to enhance its stability during cycles.     

Compensation of voltage disturbances in distribution systems using single-phase dynamic voltage restorer

In this paper, a new topology is proposed for a single-phase dynamic voltage restorer (DVR) using direct ac/ac converter. This topology does not require dc-link energy storage elements. The proposed topology has a simple structure and can compensate several types of voltage disturbances such as voltage sags, swells, harmonics and flickers. This topology will not face any problem in long time compensation due to the fact that it provides the required energy directly through grid. The proposed topology can be easily extended to n-phase systems such as three-phase based on the same principle of the operation. In n-phase systems, the voltage sags and swells can be properly compensated regardless of the balanced or unbalanced operation. A new control method is also proposed for direct ac/ac converter in the proposed topology. The simulation and experimental results verify the effectiveness of the proposed topology and its control method in voltage restoration.     

CFD modeling of a radiant tube heater

This paper reports experimental and Computational Fluid Dynamics (CFD) studies on combustion and radiation heat transfer from a real radiant tube heater. The temperature along the radiant tube as well as at different positions in a test room has been measured. A good agreement between the experimental and predicted results has been found. Based on this validation, the effect of excess air, presented by Air Factor (AF) on efficiency of heater has been studied, theoretically. Moreover, the effect of inlet air preheating on heater efficiency has been examined. The results show that the higher values of excess air can reduce the heater efficiency. The air preheating temperature caused positive effect on heater efficiency. In addition, the results show at higher preheating temperature the effect of AF value on heater efficiency is negligible.