氢气爆炸特性研究(英文)

本文研究、总结了氢气与空气(氢气与氧气)的混合物的爆炸特性。即氢气在空气中,在比较低燃烧界限的情况下,只有向上的传播和非常少的超压可以观测得到。正因为氢气的这种特性,将氢应用于科技将极大地推进社会进步,氢燃料将成为一种主要的能源。然而,氢技术应用的成功与否主要取决于氢使用的安全性。所以,必须掌握实际使用时氢气燃烧的性能。本文在日本过去十年实验数据的基础上,通过实验研究了氢气与空气混合物的燃点。研究了氢气、氧气混合物经氮气稀释后,按化学当量比例将不同浓度的氢气与空气进行混合,并得出了低温下的爆炸压力特性。随后,分别讨论了在初始压力下一致的情况下,试管直径相同的状况下,氢气与空气混合浓度相同的情况下,这三种爆轰传播限制之间的关系。得出了在空气中直接点燃的发生爆轰的最小试管直径,最小的装药量之间的关系,进行了爆轰危险性分级。最后,文章概括比较了氢与其他燃料的燃烧特性,评估了氢气燃烧过程中的危险与安全因素。

Evolution mechanism of crystallographic orientation in grain continuator bars of a Ni-based single-crystal superalloy prepared by Bridgman technology during directional solidification

Single-crystal rods with different diameters and deviation angles with respect to the solidification direction were produced by Bridgman rapid solidification method at withdrawal rates of 3 and 6 mm·min^(-1) and used as grain continuators.The crystallographic orientation of the rods,which cross-sections were perpendicular to the solidification direction at different solidification heights,was measured by electron backscattered diffraction,while the corresponding microstructures were observed by optical microscopy.The mushy zone morphology and the distribution of the temperature gradient were simulated by the finite element analysis software ProCAST.The experimental results indicate that the crystallographic orientation of the single-crystal rods corresponds to the statistical average value of all the dendrite orientations in cross-section.The crystallographic orientation of the primary and secondary dendrites of each single-crystal rod at different cross-sections fluctuates irregularly within a small range(less than 4°).The crystallographic orientation of the dendrite in each single-crystal rod is not exactly consistent with each other and is affected by their branching mode of dendrites in the solidification space.In addition,the simulation results show that the mushy zone shapes and the temperature gradient of single-crystal rods change with the increase of solidification height during the solidification process.Finally,the evolution mechanism of the crystallographic orientations and the corresponding influence factors were analyzed and discussed.

Grid Model for High-accuracy Coordinate Transformation of China Geodetic Coordinate System 2000

After implementing CGCS2000,establishing grid models for high-accuracy coordinate transformation which are mainly used to transform border lines and coordinate grids of topographic maps becomes an important issue in mapping applications.Consequently,a grid model for high-accuracy coordinate transformation of CGCS2000 is proposed.Specifically,we firstly analyze a minimum curvature equation of coordinate transformation,which possesses the characteristics of both the global and local smoothness,achieving better consistency with the consecutive smoothness for the coordinate transformation of map’s linear feature.Then an iterative calculation method of grid nodes and an approach for establishing regional grid models based on collocation by two-step minimization are proposed.Meanwhile,a data structure of grid model is constructed.Finally we give the optimized grid interval and transformation accuracy in China corresponding to the proposed grid model.Using 48 433 points of 2000 National Geodetic Control Network of China,we take the proposed model into practice by constructing grid models for coordinate transformation from BJS54 and XAS80 to CGCS2000,and the external positional accuracies for both models are 0.26 m and 0.03 m respectively.

Downward continuation of airborne gravimetry data based on Poisson integral iteration method

The research and application of airborne gravimetry technology has become one of the hottest topics in gravity field in recent years. Downward continuation is one of the key steps in airborne gravimetry data processing, and the quality of continuation results directly influence the further application of surveying data. The Poisson integral iteration method is proposed in this paper, and the modified Poisson integral discretization formulae are also introduced in the downward continuation of airborne gravimerty data. For the test area in this paper, compared with traditional Poisson integral discretization formula, the continuation result of modified formulae is improved by 10.8 mGal, and the precision of Poisson integral iteration method is in the same amplitude as modified formulae. So the Poisson integral iteration method can reduce the discretization error of Poisson integral formula effectively. Therefore, the research achievements in this paper can be applied directly in the data processing of our country＇s airborne scalar and vector gravimetry.

Jurassic-Cretaceous Stratigraphy of Malaysia

In Peninsular Malaysia, the Jurassic-Cretaceous sequences are represented by continental deposits in several isolated basins. Generally, the sequences are characterised by the fining upward sequences, comprising reddish brown to red siltstone, sandstone and conglomerate often interpreted as molasse sequences. In Sabah and Sarawak, the Jurassic-Cretaceous sequences are represented by the marine deposits comprising argillaceous, some arenaceous and calcareous rocks and associated chert, lava, and pyroclastics.

A Micromixer Using the Taylor-Dean Flow: Effects of Aspect Ratio and Inflow Condition on the Mixing

Chaotic mixing in three different types of curved-rectangular channels flow has been studied experimentally and numerically. Two walls of the channel (inner and top walls) rotate around the center of curvature and a pressure gradient are imposed in the direction toward the exit of the channel. This flow is a kind of Taylor-Dean flow. There are two parameters dominating the flow, the Dean number De (∝ the pressure gradient or the Reynolds number) and the Taylor number Tr (∝ the angular velocity of the wall rotation). In this paper, we analyze the physical mechanism of chaotic mixing in the Taylor-Dean flow by comparing experimental results and numerical ones. We produced three micromixer models of the curved channel, several centimeters long, with rectangular cross-section of a few millimeters side. The secondary flow is measured using laser induced fluorescence (LIF) method to examine secondary flow characteristics. Also we performed three-dimensional numerical simulations with the open source CFD solver, OpenFOAM, for the same configuration as the experimental system to study the mechanism of chaotic mixing. It is found that good mixing performance is obtained in the case of De ≤ 0.1 Tr, and it becomes more remarkable when the aspect ratio tends to large. And it is found that the mixing efficiency changes according to the aspect ratio and inflow condition.

A Micromixer Using the Taylor-Dean Flow: Effect of Inflow Conditions on the Mixing

Chaotic mixing in a curved-square channel flow is studied experimentally and numerically. Two walls of the channel (inner and top walls) rotate around the center of curvature and a pressure gradient is imposed in the direction toward the exit of the channel. This flow is a kind of Taylor-Dean flows. There are two parameters dominating the flow, the Dean number De (∝ the pressure gradient or the Reynolds number) and the Taylor number Tr (∝ the angular velocity of the wall rotation). In the present paper, we analyze the physical mechanism of chaotic mixing in the Taylor-Dean flow by comparing experimental and numerical results. We produced a micromixer model of the curved channel several centimeters long with square cross section of a few millimeters side. The secondary flow was measured using laser induced fluorescence (LIF) method to examine secondary flow characteristics. We also performed three-dimensional numerical simulations for the exactly same configuration as the experimental system to study the mechanism of chaotic mixing. It is found that good mixing performance is achieved for the case of De ≤ 0.1Tr, and that mixing efficiency changes according to the difference in inflow conditions. The flow is studied both experimentally and numerically, and both results agree with each other very well.

Reshaping Agriculture Using the Nuclear Techniques: The Pakistan Case

The field of nuclear agriculture is introduced very briefly. Nuclear agriculture research/development system in Pakistan is described highlighting the achievements of the system partners. Description and discussion are generalized in concluding remarks at the end of the article. This article is an experimental guide for a developing nuclear agriculture system.

Comparative H₂S Sensing Characteristics of Fe₂O₃: Thin Film vs. Bulk

Comparative investigations of gas sensing characteristics of Fe2O3 in both thin film as well as bulk forms have been performed. Thin film sensors were realized by first depositing Fe films using electron-beam evaporation followed by thermal oxidation. Bulk sensors in the form of pellets were prepared by cold pressing commercial Fe2O3 powder with subsequent sintering. Both thin film and bulk Fe2O3 sensors exhibited a selective and reversible response characteristics towards H2S with maximum response at an operating temperature of 250°C and 200°C, respectively. A negligible response towards other interfering gases was observed. Thin film sensors exhibited an enhanced response in comparison to that of pellets.

Transgranular Pore Formation in Nanocrystalline Coatings Condenced in the “Openess” of Vacuum and Quasi-Closed Volume

It has presented a review of the results of the survey on the formation and behavior of submicropores (SMP) in mono- and poly-crystalline systems, condensed in the “open vacuum” and quasi-closed volume. The mechanisms, patterns and characteristics of these processes, depending on the physical and technological factors are reviewed.

Effect of Camphor Sulfonic Acid Doping on Structural, Morphological, Optical and Electrical Transport Properties on Polyaniline-ZnO Nanocomposites

In the present work, we report on effect of camphor sulfonic acid (CSA) doping on polyaniline-ZnO (50%) nanocomposites prepared by spin coating method on glass substrates. The XRD analysis revealed that the addition of CSA has no effect on crystallinity of PANi-ZnO nanocomposites. Surface morphological studies (SEM) showed that CSA has a strong effect on morphology of PANi-ZnO. The FTIR & UV-Vis spectroscopy confirmed the interaction between CSA and PANi-ZnO nanocomposite. DC electrical conductivity studies showed an increase in conductivity of PANi-ZnO nanocomposites by one order due to addition of CSA (10% - 50%).

Investigations on luminescence of rare earths doped CaTiO_3:Pr^(3+) phosphor

Calcium titanate doped with praseodymium was prepared through solid state reaction and it exhibited intense red emission at 612 nm. Phosphors were characterized for photoluminescence, thermo-luminescence and afterglow emissions. Study of effects of rare earths on photoluminescence as well as afterglow intensity was reported. Presence of gadolinium enhanced luminescence. Presence of some monovalent ions enhanced both afterglow and photoluminescence emission. Thermo-luminescence glow curves were analyzed and ...

Effects of irrigation and weed-control methods on growth of weed and rice

A field experiment was conducted to study the effects of weeds control methods and an irrigation model on rice growth as well as water consumption and weed quantity in the paddy field.In conventional paddy rice production,one of the most important irrigated crops,a significant amount of irrigation water is lost due to percolation and evaporation.A new irrigation model called the Rain-Catching and Controlled Irrigation(RCCI)model has been developed as a viable water-saving technology in the production of paddy rice.In this study the performance of the RCCI model has been analyzed under mulching,hand weeding and weedy conditions in Jiangsu Province of China.The experiment was laid out in Randomized Complete Block Design(RCBD)with three replications and nine treatments.The three replicates consisted of three water management regimes:high dry high flooding(HD-HF),high dry low flooding(HD-LF),and shallow and frequent irrigation(SF)water treatment.The RCCI model was adopted in HD-HF and HD-LF while Flooding Irrigation(CFI)was adopted in SF as a control.The nine treatments were equally divided under mulching,hand weeding and weedy conditions.The lowest and maximum irrigation water delivery was 244.86 mm in mulching and 429.22 mm in hand weeding,respectively at HD-HF.And the lowest and maximum irrigation water delivery was 300.1 mm in the mulching field and 680.72 mm under hand weeding,respectively at HD-LF.The Nanjing 44 rice variety was used.It was observed that weed density and dry weight were significantly influenced by the amount of irrigation water in all the mulching,hand weeding and weedy plots.Considering yield and the number of irrigations,the RCCI model produced better results than CFI.Mulching under RCCI was an effective method to control weeds and reduce labor cost.In addition,mulching decreases the use of herbicides and the risk of pollution.On the other hand,mulching could improve yield and save water.

Rheological Properties of Polyamide: Experimental Studies and Constitutive Modeling

This work is focused on simulating the rheological effects in polyamide. An experimental study is carried out in order to assess such features of polyamide as: the hysteretic behavior, the strain rate dependence, and the stress relaxation. The material response in tension is investigated. Digital images correlation method(DIC) is employed in order to measure the material compressibility. A newly developed constitutive model, which was previously used to simulate the mechanical response of polyethylene subjected to moderate strains and compressive loadings, is applied to capture the large strain, inelastic behavior of polyamide in tension. The gathered experimental data are utilized to determine the values of constitutive constants of viscoelasticity and plasticity, which describe the rheological properties of polyamide. The determined material parameters are included in the text. Different strategies for evaluating the material parameters are discussed. The proposed constitutive equation is implemented into the finite element(FE) system, ABAQUS, by taking advantage of the user subroutine UMAT, which allows to define custom material laws. Some exemplary FE simulations that were used to investigate the performance of the developed subroutine are described.

On the chemical compatibility between Zr-4 substrate and well-bonded Cr_2AlC coating

Accident tolerant fuel(ATF) for the light water reactor has gained wide attentions after the Fukushima accident. To enhance the accident-tolerance of the nuclear system, one strategy is to modify the Zr-based alloy cladding surface with advanced ceramic coating. In this work, monolithic and dense Cr_2AlC coating has been synthesized by magnetron sputtering. The as-grown Cr_2AlC coating exhibits good chemical compatibility with Zr-based alloy substrate as well as mechanical integrity under both pull-off and scratch tests. The coating system also presents moderate thermochemical compatibility at 800℃ but degrades above 1000℃ under simulated loss-of-coolant accident(LOCA) conditions.

A catalyst-free new polyol method synthesized hot-pressed Cu-doped Bi2S3 nanorods and their thermoelectric properties

This is the first report on the thermoelectric properties of a catalyst-free polyol method used to prepare stoichiometric Bi2-xCuxS3 samples, x = 0.1, 0.2, 0.3, 0.4, via hot pressing. Various systematic approaches to arrive at in their stoichiometric compositions are explored precisely with introduction of excess precursor of S. X-ray diffraction data analysis using Rietveld refinement confirms a polyhedral orthorhombic crystal structure with a space group Pnma, in contrast to Pbnm reported earlier. Raman data further substantiates this. X-ray photoelectron spectroscopy confirms the valence states of the constituent elements （Bi^3＋, Cu^2＋, and S^2-） and energy dispersive X-ray analysis corroborates their compositions. The particle sizes of the pure Bi2S3 nanoparticles were 20, 35, and 82 nm as determined from the Scherrer formula, atomic force microscopy, and dynamic light scattering, respectively. Their transmission electron microscopy image shows rod-like nanostructures elongated in the 〈010〉 direction with an average diameter of 23 nm and a length of several hundreds of nanometers. A 34% improvement in the thermoelectric figure of merit is observed for Bi.6Cu0.4S3 as compared to pure Bi2S3 at 300 K.

板材轧机厚度自动控制的发展

1.前言 在钢板制造中,改进钢板的厚度偏差,改善产品的质量,降低成品价格,是满足用户要求的重要条件。开发自动厚度控制(AGC)就是为了改善钢板厚度精度,减少纵向偏差,提高板与板间厚度精度。 电动压下AGC最初取得了一些成功。但从可控轧制表明,电动AGC根据负载和响应特性,不适应大轧制力下的大量生产和满足高精度要求。因此,需要采取其它强有力的措施。

Preliminary study on the fabrication of 14Cr-ODS FeCrAl alloy by powder forging

A simple powder forging process was presented herein to fabricate an Fe-14 Cr-4.5 Al-2 W-0.4 Ti-0.5 Y_(2)O_(3)ODS Fe Cr Al alloy.The forged alloy exhibits a high density that exceeds 97%of the theoretical density.The ODS alloy was investigated in terms of the residual porosity,morphology and phase structure of oxide nanoparticles,impact toughness and tensile properties.It was found that refined grains were obtained during powder forging.A residual porosity less than 1.1%has no impact on the precipitation of oxide nanoparticles.The average diameter of the oxide particles is 7.99 nm,with a number density of 2.75×10^(22)m^(-3).Almost all of the oxides are identified as orthorhombic YAl O3 particles.The refined grains and uniformly distributed oxide nanoparticles enable the alloy to show excellent mechanical strength and ductility below 700℃,and enable the ductile-to-brittle transition temperature to be close to room temperature.However,a slight decrease in strength at 1000℃and the Charpy upper shelf energy has been suggested to be due to the residual porosity.These results indicate that powder forging can be used as a promising technique for the fabrication of ODS alloys.