圆形封闭水箱非稳态数值模拟

采用数值方法对圆形封闭水箱内放置两根加热管的二维流动传热进行了非稳态数值模拟,探讨了Ra数从104到107四种情况和封闭水箱的加热管不同摆放位置下的流动和换热;对流场和温度场进行了分析,讨论了不同情况下加热管平均努赛尔数(Nuavg)的变化情况。数值模拟结果表明,随着Ra数增大水箱内的流动表现出了很大变化,决定了传热是导热或者是对流;两个水平加热管在水箱存在最佳的放置距离,这样可以使自然对流情况下的换热达到最好。     

Surface and Subsurface Deformation of Wear-Resistant Steels Exposed to Impact Wear

The impact wear resistance of four different wear-resistant steel grades was investigated using different impact bodies. Post-test evaluation of the impact tested samples was performed by different techniques including 3D surface profilometry, microhardness indentation, optical and scanning electron microscopy, and energy dispersive x-ray spectroscopy. The tribological response of the steel plates during the impact is strongly dependent on the properties of the impacting body. The subsurface deformation was found to increase with increasing impact energy and/or impact velocity and decreasing steel hardness. On a microscopic scale, a number of interesting mechanisms were revealed within the deformed impact sites. Besides an overall plastic deformation, localized deformation resulting in narrow adiabatic shear bands with an ultra-fine microstructure was observed. Within these shear bands, showing intense shearing strain, nucleation of microvoids was frequently observed. Growth and linkage of these voids lead in crack formation along the shear bands and eventually flake-like wear fragments are detached when these cracks reach the surface.     

Measurement of in-plane effective thermal conductivity in PEM fuel cell diffusion media

Gas diffusion media used in polymer electrolyte membrane (PEM) fuel cells are highly anisotropic with significantly different transport property values in the through- and in-plane directions. In this study, experimental measurements of the in-plane effective thermal conductivity k for gas diffusion media used in PEM fuel cells have been carried out using a parallel thermal conductance technique. Conductivity values are measured at a mean sample temperature of 70 °C for six different material types and two different orientations in order to quantify the effect of PTFE content on thermal conductivity and to reveal any anisotropic behavior. The results vary from a minimum of k = 3.54 W/(m °C) to a maximum value of 15.1 W/(m °C) for various samples and configurations tested in this study, with an uncertainty between 1% and 2% for all the cases investigated.     

Successful Use of Geoelectrical Surveys in Area 3 of the Gol-e-Gohar Iron Ore Mine,Iran

Geoelectrical surveys were conducted in Area 3 of the Gol-e-Gohar iron ore mine to provide geological and hydrogeological information. Open pit mining is currently underway in the northern part of the Area, and underground mining operations are planned for the southern section. Groundwater has already been encountered in the open pit mine. Twenty five resistivity soundings were first performed in the mine area; then, induced polarization (IP) measurements were carried out to remove ambiguities between clay and water-bearing layers. To investigate fault zones as water conduits, combined resistivity profiling surveys were also carried out. These measurements provided a detailed structural map of the pit area. Resistivity and IP results have subsequently been confirmed by observations at three monitoring wells and the mine pit wall. Monitoring and piezometric wells will be drilled at locations suggested by the results of the geoelectrical surveys. Drainage galleries may be developed to dewater the open pit mine. However, another option being considered is to start the underground mining with the idea that it will initially simply serve as a dewatering mechanism.     

Effect of long-chain monoacrylate on the residual monomer content, swelling and thermomechanical properties of SAP hydrogels

Residual monomer is an important factor, particularly in hygienic materials such as superabsorbent polymer (SAP) hydrogels. Recently, we reported different approaches to minimizing residual monomer content in SAPs. In this paper, the effect of a long-chain monomer, poly(ethylene glycol) methylether methacrylate (PEG.MEMA), on the residual monomer content of SAP networks of partially neutralized acrylic acid–PEG.MEMA is investigated. The aim of using PEG.MEMA in SAP synthesis was to reduce the glass transition temperature (T _g) of SAP. As the temperature that is conventionally used to dry SAP (70–110 °C) is lower than the T _g of ordinary SAPs, the polymer is in the glassy state during the heating stage. It was assumed that converting SAP from the glassy state to the rubbery state during drying would facilitate the removal of acrylic acid monomer (AA) from the gel, thus reducing the residual monomer content. The results showed that the use of PEG.MEMA led to a reduction in residual AA when the drying temperature was 100 °C. The residual AA was decreased from 169 to 95 ppm when the drying time was increased from 3 to 15 hours at 100 °C. This positive effect of PEG.MEMA on the level of unwanted residual AA became insignificant at a higher drying temperature (140 °C). The effects of PEG.MEMA content on the thermal and mechanical properties (in the dried state) and the rheological properties (in the water-swollen state) of the SAP hydrogels were also investigated. The swelling capacity and rate was studied in relation to the PEG.MEMA content. It was found that a high level of PEG.MEMA restricted both the absorption capacity and the rate of water absorption.     

Finite element analysis of deformation and fracture of an exploded gas cylinder

This paper presents the finite element simulations of deformation and fracture of a gas cylinder which catastrophically failed as a result of an accidental explosion. The results of a previous detailed investigation of this incident indicated that detonation of a low-pressure oxygen-rich mixture of hydrogen and oxygen was the cause of the cylinder failure. In the current study, the finite element method was used to provide a more realistic modeling of geometry, material behavior, and boundary conditions of the cylinder. The overall transient dynamic response of the cylinder to gaseous detonation loading was studied using the ANSYS/LS-DYNA V10 package and the crack growth simulations were performed using the WARP3D-R15 research code. The crack growth analyses were performed using interface cohesive elements. The finite element results were validated using analytical solutions and data collected from the remains of the cylinder. The simulations clearly showed that the stresses caused by the assumed loading profile were indeed capable of creating local ruptures at the actual crack initiation sites. It was also shown that the self-similar growth of the initial axial crack in the main body of the cylinder was a fatigue-type incremental growth governed by the structural waves. The subsequent cyclic bulging of the crack flaps and the resultant crack curving and branching were also simulated.     

Analysis of MTHFR and MTRR Gene Polymorphisms in Iranian Ventricular Septal Defect Subjects

Ventricular septal defect (VSD) is one of the most common types of congenital heart defects (CHD). There are vivid multifactorial causes for VSD in which both genetic and environmental risk factors are consequential in the development of CHD. Methionine synthase reductase (MTRR) and methylenetetrahydrofolate reductase (MTHFR) are two of the key regulatory enzymes involved in the metabolic pathway of homocysteine. Genes involved in homocysteine/folate metabolism may play an important role in CHDs. In this study; we determined the association of A66G and C524T polymorphisms of the MTRR gene and C677T polymorphism of the MTHFR gene in Iranian VSD subjects. A total of 123 children with VSDs and 125 healthy children were included in this study. Genomic DNA was extracted from the buccal cells of all the subjects. The restriction fragment length polymorphism polymerase chain reaction (PCR-RFLP) method was carried out to amplify the A66G and C524T polymorphism of MTRR and C677T polymorphism of MTHFR genes digested with Hinf1, Xho1 and Nde1 enzymes, respectively. The genotype frequencies of CC, CT and TT of MTRR gene among the studied cases were 43.1%, 40.7% and 16.3%, respectively, compared to 52.8%, 43.2% and 4.0%, respectively among the controls. For the MTRR A66G gene polymorphism, the genotypes frequencies of AA, AG and GG among the cases were 33.3%, 43.9% and 22.8%, respectively, while the frequencies were 49.6%, 42.4% and 8.0%, respectively, among control subjects. The frequencies for CC and CT genotypes of the MTHFR gene were 51.2% and 48.8%, respectively, in VSD patients compared to 56.8% and 43.2% respectively, in control subjects. Apart from MTHFR C677T polymorphism, significant differences were noticed (p < 0.05) in C524T and A66G polymorphisms of the MTRR gene between cases and control subjects.     

A Comparison Between Cold-Welded and Diffusion-Bonded Al/Cu Bimetallic Rods Produced by ECAE Process

In this research, the application of equal channel angular extrusion process to produce both the cold-welded and diffusion-bonded Al/Cu bimetallic rods is assessed. The joints shear strength for both of the methods are measured and compared. The microstructure examinations were also carried out using scanning electron microscope equipped with EDX system and x-ray diffraction analysis. The results exhibit that the strength of the bond in cold-welded specimens is dependent on the amount of stretch and pressure at the materials interface. But in the diffusion-bonded specimens, it is depended on the struggle between the oxidation rate of the mating surfaces accompanied by inter-metallic compounds formation and the aluminum and copper atoms ability to diffuse in the joint interface.     

Recycling of aluminium alloy turning scrap via cold pressing and melting with salt flux

Among the various steps of aluminium production from liquid metal, a lot of scrap is generated due to machining operations. Therefore, recycling of aluminium scrap is an interesting subject because of the broad applications of this metal and low efficiency of processes used to recycle metal scrap. In this paper, the recyclability of aluminium alloy AA 336 turnings with different cold compacting pressures and a protective salt flux (NaCl–KCl–KF) has been experimentally studied. Various categories of compacted samples were melted at 750 °C in molten aluminium alloy AA 336 and also in the protective salt flux to recover aluminium alloy. In order to understand the amount of recycling of different samples, weight loss measurement was applied. From recyclability stand point it is shown that using protective salt flux is the best route, from the point of view of recyclability. Mechanical properties and chemical analysis of samples were approximately the same as the primary material produced by conventional casting process.     

Computer simulation of the effect of post annealing parameters on the microstructure inhomogeneity of the non-uniformly deformed copper

A computer simulation on the basis of the Finite Element Method and Monte Carlo Model is developed to simulate the microstructure of the non-uniformly deformed copper workpiece after annealing. Using the computer simulation, the effects of annealing time and temperature on the microstructure inhomogeneity of the workpiece are simulated and investigated quantitatively, by defining an Inhomogeneity Factor, to design an annealing program for reducing the microstructure inhomogeneity. The results show that with increasing the parameters of annealing time and temperature, the inhomogeneity is decreased when one of the parameters is constant. Also, at high annealing temperature, the annealing time changes the inhomogeneity slowly compared with which occurs at low annealing temperature. The simulation results agree well with the experimental values.