Lifted flames on fuel jets in co-flowing air

The three principal theories for the stabilization of lifted flames on turbulent jets of fuel are reviewed in the light of the most recent flame imaging experiments in the literature. Most of these experiments have been conducted with a small co-flow of air, but the observations are relevant to lift-off with higher ratios of co-flowing air to fuel jet velocity. The similarity solutions for jets in co-flow are developed, and data from a variety of fluid dynamic sources are assessed to yield the governing parameters for mean flow, turbulence and mixture fraction. New data for lifted flames on a methane jet in diffusing streams of co-flowing air are then presented. These data provide essential information on the intermittency, and on the properties of the jet conditioned on the presence of turbulent fluid. However, the co-flow lifts the flame to stabilize in better-mixed regions than in its absence. The ‘premixture’ model is confirmed for this situation, in which the lift-off heights were more than 20 jet diameters and where there is little intermittency at the stabilization radius. Nevertheless, mixing data for this geometry in the absence of a flame show that, with lift-off heights less than 20 jet diameters, the base of the flame would have been in the outer regions of the jet where the mixture of fuel in air only reaches stoichiometric proportions intermittently, with the passage of large eddies. Trading on many papers from the recent literature where this was the case, both experimental and computational insights as to the processes in this region are reviewed. A question remains about how ignition is maintained in these experiments with low turbulent lift-off. It is hypothesized that the mechanism is the diffusive heating of the slowly moving surrounding air which then provides an energy store for the incoming eddies. Further time-resolved observations of reaction zone and high temperature gas structure are required to test this model.     

Bulk modulus and thermal expansion coefficient of mechano-chemically synthesized Mg2FeH6 from high temperature and high pressure studies

Mg₂FeH₆ was synthesized by ball milling MgH₂ and Fe (2:1 molar ratio) mixture for 72 h followed by heating at 400 °C under H₂ pressure. The hydride formation, its structure and homogeneity were investigated by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and Raman spectroscopy. High pressure in situ synchrotron X-ray diffraction and Vienna ab initio simulation were used to determine bulk modulus of the sample. The bulk modulus of Mg₂FeH₆ was found to be 75.4(4) GPa by optimized experiment and 76.3 GPa by theoretical simulation. From high temperature in situ X-ray diffraction study the volumetric thermal expansion coefficient of Mg₂FeH₆ was found to be α_v = 5.85(3) × 10⁻⁵ + 7.47(7) × 10⁻⁸ (T − T_o)/°C. Decomposition of Mg₂FeH₆ was observed at 425 °C and the decomposition products were Mg, Fe and H₂.     

Thermodynamic analysis of supercritical water gasification of methanol,ethanol, glycerol,glucose and cellulose

In the present work the Gibbs free energy minimization, using a non-linear programming formulation and an approximation in the gas fugacities, was used to calculate the equilibrium composition for supercritical water gasification of methanol, ethanol, glycerol, glucose and cellulose. The proposed formulation mathematically ensures finding the global optimal solution with no need of an initial estimate and the numerical results are close to the ones calculated using non-ideal gas formulation. Therefore, the proposed approach is reliable and easy to use, without numerical difficulties, such as an undesirable local minimum. The model predictions show a good agreement with the experimental studies in all cases studied in this work.     

Electrochemical hydriding as method for hydrogen storage?

Electrochemical hydriding of magnesium alloys in alkaline solutions is proposed as a method of storing hydrogen in a solid phase. In this article, we present a new approach to hydrogen storage for mobile applications. Rapidly solidified ribbons of Mg–14Ni alloy were prepared by melt spinning. Subsequently, they were exposed to electrochemical hydriding at 90 °C/120 min in various alkaline electrolytes. It was found that hydrogen reached up to 1.4 wt.%. Higher hydrogen concentrations might be achieved by proper adjustment of hydriding conditions.     

棉织物低温漂白新工艺

本文采用自制的双氧水活化剂,在低温下对棉织物进行双氧水漂白,用中心旋转法并借助微机对漂白工艺进行优化。结果表明,此工艺是可行的,当漂白在70℃进行时,漂白效果优于常规气蒸漂白,而与常规浸漂相似。中心旋转法和回归分析是寻找染整工艺优化区域最为有效的方法之一。     

镍氢二次电池和储氢电极材料

本文叙述了镍金属氢化物二次电池的工作原理和电池的主要工作参数,稀土储氢电极材料及电极对材料的要求,电极的制备途径,电池在工业应用中存在的主要技术问题,开发现状和技术经济展望。     

42CrMo钢氢致开裂行为过载效应研究

氢致开裂(HIC)是一种工程中常见的零部件失效方式。本文针对工程常用材料42CrMo钢,就短时过载对氢致开裂行为的影响展开了研究,并就试验结果进行了理论阐述。     

18—8钢制换热器U形管失效分析

通过宏观与微观测定分析，提出临氢环境下１８—８钢制Ｕ形换热器Ｕ形区局部开裂失效的根本原因如下：粗糙的冷加工产生过大的残余应力，从而使钝化膜严重损伤，材料表面活性增大，硫腐蚀加速；使表面吸附环境中的Ｃｌ－量增大，氯腐蚀加速；冷加工和氢渗入量增大，使马氏体相变倾向增强，马氏体相变量增大．综上所述，在给定的工况介质中腐蚀被加速，脆性迅速增大，过早地发生开裂失效．     

石化设备湿硫化氢应力腐蚀失效及其防护

本文介绍了湿硫化氢应力腐蚀机理并分析了影响石化设备湿硫化氢应力腐蚀失效的诸种因素，提出石化设备防止湿硫化氢应力腐蚀失效的一些有效措施。     

Ni-MH电池负极材料的产业化

本文叙述了Ni-MH电池的产业化现状,AB_5型储氢合金的生产与质量保证及研究与开发的新趋势。