自蔓延高温合成Ti—Ni合金

研究了热爆法和预热燃烧法合成 Ti-Ni 合金的自蔓延高温合成工艺。试验结果表明:低加热速度也能实现 Ti-Ni 的热爆合成;预热温度对燃烧法反应影响很大。探讨了 TiNi、Ti_2Ni、TiNi_3的形成温度,提出了燃烧合成 TiNi 的反应过程模型。大量液相的出现对燃烧反应合成 Ti-Ni 至关重要。     

自蔓延燃烧合成Mg2Ni的淬熄试验

采用在试样顶部添加Al-Ti-C引燃剂的方法,在圆柱形钢模具内成功淬熄了Mg-Ni反应。对不同区域的XRD分析表明:反应直接生成了Mg2Ni而没有中间产物,而且在较低的温度下Mg-Ni发生固—固反应生成Mg2Ni。结合SEM及EDS分析结果,燃烧合成Mg2Ni的结构形成过程可以描述为:(1)预热阶段的固—固反应;(2)燃烧阶段的液相反应;(3)燃烧完成阶段的产物冷却结晶;(4)保温阶段的成分均匀化过程。     

陶瓷内衬复合铜管的自蔓延高温合成

开发了离心自蔓延高温全成陶瓷内衬复合铜管制造工艺，研究了离心力和添加剂对复合铜管性能的影响。随着离心力增大，陶瓷层的孔隙度降低、压溃强度和压剪强度明显提高，离心力超过200G后，压剪强度反应而降低。铝热剂中加入SiO2也可降低孔隙度，提高压剪强度。提高铝热剂预热温度，可加快铝热反应速度，改善复合铜管质量。     

高温空气燃烧炉内燃烧特性的数值研究

采用数值模拟法,研究了高温空气燃烧炉内不同空气预热温度、氧气浓度和燃气入口温度对火焰特性和NOx生成和排放的影响规律。研究表明,在提高空气预热温度、降低氧气浓度条件下,在较大范围内进行燃烧,火焰体积变大,炉内温度的峰值相应降低,温度分布更均匀,NOx的生成量大幅度降低。提高燃气入口温度,可抑制燃料和空气在主燃烧区的混合,使火焰内反应物的分布更加均匀,抑制了热力NO的生成,从而减少了NOx的排放量。     

取向硅钢高温环形退火炉用低NOx天然气烧嘴的试验与数值模拟

确定了一种低NO_x天然气烧嘴结构参数,采用CFD数值模拟方法建立了该烧嘴的燃烧传热模型,并通过试验验证了模型的准确性;研究了烧嘴多级空气配比(一、二级风量之和与总风量之比)、空气过量系数、空气预热温度、烟气再循环量等参数对NO_x生成的影响.研究结果表明：热力型NO_x的生成主要与燃烧温度和高温区的氧浓度有关;可以通过改变烧嘴的多级空气配比和烟气再循环量控制燃烧区域的温度和氧浓度,进而抑制热力型NO_x的生成;增大空气过量系数会增加高温区的氧浓度,提高空气预热温度会提高燃烧温度,两者均会增加NO_x的生成浓度.对不同参数进行正交数值模拟优化分析,发现在炉内温度为1 623.15 K时,低NO_x天然气烧嘴燃烧烟气中NO_x浓度可达到低于150 mg/m³的指标,满足我国钢铁行业对NO_x排放的要求.在天然气中掺入再循环烟气可以降低燃烧烟气中的NO_x浓度,当空气预热温度为723.15 ...     

反射炉炉膛燃油数值模拟及污染物生成分析

对燃烧过程的数值模拟已成为工业炉窑辅助设计、优化运行、故障诊断等环节的重要手段。运用PDF燃烧机理模型对反射炉燃油雾化燃烧及污染物的生成过程进行了数值模拟仿真,定量考察了燃料射流速度、空气预热温度和燃料预热温度、氧浓度的不同对炉膛内温度场变化和热力型NO浓度分布的影响规律。计算结果符合燃烧规律和污染物生成机理,为炼铜厂反射炉的节能减排,设计及优化提供了理论计算依据。     

高炉煤气无焰纯氧燃烧过程数值模拟

采用ANSYS FLUENT对高炉煤气的无焰纯氧燃烧过程进行数值模拟,获得燃烧反应后燃烧室内的温度场以及组分浓度场。研究结果表明:无焰纯氧燃烧(OF)技术与同等条件下的空气燃烧(AF)相比,火焰区域的温度分布比较均匀,实现了"无焰化",炉内最高温度将近2100K;OF组在整个炉膛轴向范围内NO_x浓度增加缓慢且趋于稳定,OF组中NO_x生成速率及生成量均远低于AF组,无焰纯氧燃烧大幅度降低了NO_x生成。     

抽鼓自平衡式U型辐射管烧嘴的实验研究

对抽鼓式U型辐射管烧嘴进行了实验研究,通过实验得到辐射管内零压面的调节手段。实验表明,采用鼓风和吸风相结合的供风方式,同时添加分级燃烧装置,能够在保证辐射管内负压的前提下,提高换热器预热温度和温度效率,改善辐射管的表面温度分布。同时分级燃烧对抑制NOx的生成有重要的作用。     

Ti-W-C体系的自蔓延高温合成与反应机理

研究了Ti-W-C体系自蔓延高温合成(SHS)的燃烧温度和燃烧速度与W含量、Ti粉粒度及预热温度的关系。分析了不同W含量和预热温度时SHS产物的相组成,并对体系的SHS反应机理进行了研究。结果表明:W/(Ti+W)≤ 0.3时,基本能合成单相(W/Ti)C;而预热可促进(W,Ti) C的SHS合成;体系的SHS反应过程中存在两种反应机制,即溶解-析出机制和扩散-固溶机制     

烟气自循环加热炉内预热空气温度对燃烧过程的影响

高温空气燃烧技术中预热空气温度对炉膛内的燃烧特性及火焰特性有重要的影响。就不同预热空气温度对烟气自循环加热炉的影响进行了模拟研究。结果发现：预热空气温度一般加热到900～1100K为最佳。NOx浓度随着预热空气温度的升高而增大,一旦预热空气温度超过1500K,NOx的生成量将急剧升高。     

氧压力对自蔓延高温合成Ni-Zn铁氧体粉体的影响

在自蔓延高温合成（SHS）Ni-Zn铁氧体粉体的研究中，以XRD、TEM分析， 考察了氧压力对燃烧温度、燃烧波速度以及产物微观相组成和形貌的影响，并结合理论分析，确定了以SHS方法合成Ni-Zn铁氧体粉体的最佳氧压力值。     

自蔓延高温合成氮化硅的研究

本文在106炉生产规模氮化硅的合成试验中,通过对高压釜内氮气温度与压力的变化计算出在合成过程中耗氮量的变化,计算结果表明,氮化硅燃烧合成的特点属自蔓延高温合成中非稳态合成。其燃烧模式为振荡燃烧及螺旋燃烧。此外,氮气渗透率与高压釜内氮压及氮气渗透阻力有关。     

Combustion of Powder Mixtures Forming Reaction Products - Synthesis of NiAl

Abstract

Combustion of powder mixtures under adiabatic conditions -Self-propagating High-temperature Synthesis (SHS)-is an efficient and attractive technique to synthesize a host of materials for high technology applications, namely, ceramics, intermetallics, composites and functionally graded materials. Conditions necessary for and general features of this technique are briefly reviewed.

Experimental investigations on synthesis of nickel monoaluminide from stoichiometric mixtures of component powders by this technique using plane-wave propagation mode is carried out. Effects of reaction parameters namely, bulk density of compacts, amount of inert dilutions and atmospheres on velocity of combustion wave propagation and combustion peak temperature are investigated. From the dependence of propagation velocity on combustion temperature an activation energy of 170.99 kJ/mole is obtained for SH-synthesis of NiAl. The synthesized products showed equiaxed large grained microstructures.     

Effect of composition of starting materials of Mo–Si on self-propagating high temperature SHS reaction

Abstract

An experimental study of the self-propagating high temperature synthesis of Mo–Si alloys was conducted from elemental powder compacts. Test specimens with seven compositions, including Mo/Si?=?1∶1·25, 1∶1·50, 1∶1·75, 1∶2·00, 1∶2·25, 1∶2·50 and 1∶2·75 respectively, were employed. Experimental evidence showed that a combustion wave featuring a spinning reaction zone can be observed. When the powder compacts are from Mo∶1·25Si to Mo∶1·75Si, the combustion temperature and the propagation velocity of combustion wave increase with increasing silicon in the sample, and the combustion products are composed of MoSi₂, Mo₅Si₃ and Mo. However, when the powder compacts are from Mo∶2·25Si to Mo∶2·75Si, the combustion temperature and the propagation velocity decrease rapidly as the silicon in the compact increases, and the combustion products are composed of MoSi₂ and Si. The sample with Mo/Si?=?1∶2·00 possesses the highest combustion temperature (1628·9 K) and propagation velocity (3·13 mm s^?1). A single-phase MoSi₂ is synthesised by the Mo/Si?=?1∶2·00 sample.     

Pressure Waves in Porous Medium Saturated with Liquid Containing Gas Bubbles

Theoretical analyses on nonlinear pressure waves evolution in porous medium saturated with a liquid containing gas bubbles is carried out. The evolution equations for fast and slow longitudinal modes are derived for slightly nonlinear, disperse, and dissipation processes. The pressure wave distribution in gas bubble liquid-saturated porous media was investigated experimentally. It was revealed that both modes might have oscillating structure induced by bubble oscillation in the wave. It is shown that the wave damping is determined by a combined impact of heat losses due to gas cooling in the bubbles and dissipation due to longitudinal displacement of liquid and porous skeleton, both influenced by the wave. Experimental data on the velocity and structure of fast and slow modes are compared with results of theoretical modeling.     

首钢京唐BSK顶燃式热风炉的燃烧技术

 为开发5500m3高炉BSK顶燃式热风炉技术,对顶燃式热风炉的燃烧机制和燃烧特性进行了研究。采用CFD数学仿真模拟研究了BSK顶燃式热风炉环形陶瓷燃烧器的燃烧机制,解析了顶燃式热风炉燃烧室内气体的混合、流动以及燃烧过程,计算分析了顶燃式热风炉燃烧过程的速度场、温度场以及浓度场分布。通过对实体热风炉的冷态测试,验证了CFD数学仿真计算的结果。研究结果表明,BSK顶燃式热风炉采用旋流扩散燃烧技术使燃烧过程速度场、温度场和浓度场分布均匀对称,并可以有效控制火焰长度和火焰形状,使煤气在拱顶空间内充分燃烧。速度场、温度场和浓度场的分布与煤气和助燃空气的初始分布有直接关系。通过燃烧器喷嘴结构优化设计可以显著提高空气与煤气混合的均匀性,改善燃烧室内浓度、温度分布以及火焰形状。     

工业气体在多孔介质燃烧器中的燃烧研究

主要考查工业混合煤气在多孔介质内燃烧情况.建立二维数学模型,通过Fluent软件计算出燃烧稳定情况下的温度分布和主要组分浓度分布.数值模拟结果证明,工业煤气在多孔介质内燃烧污染物排放量极少,可以有效地利用工业煤气和工业废气,节约能源.     

Effect of methane-hydrogen mixtures on flow and combustion of coherent jets

Coherent jets are widely used in electric arc furnace(EAF)steelmaking to increase the oxygen utilization and chemical reaction rates.However,the influence of fuel gas combustion on jet behavior is not fully understood yet.The flow and combustion characteristics of a coherent jet were thus investigated at steelmaking temperature using Fluent software,and a detailed chemical kinetic reaction mechanism was used in the combustion reaction model.The axial velocity and total temperature of the supersonic jet were measured via hot state experiments.The simulation results were compared with the experimental data and the empirical jet model proposed by Ito and Muchi and good consistency was obtained.The research results indicated that the potential core length of the coherent jet can be prolonged by optimizing the combustion effect of the fuel gas.Besides,the behavior of the supersonic jet in the subsonic section was also investigated,as it is an important factor for controlling the position of the oxygen lance.The investigation indicated that the attenuation of the coherent jet is more notable than that of the conventional jet in the subsonic section.     

The effect of gravity on the combustion synthesis of metal-ceramic composites

The effects of gravity on the combustion characteristics and microstructure of metal-ceramic composites (HfB₂/Al and Ni₃Ti/TiB₂ systems) were studied under both normal and low gravity conditions. Under normal gravity conditions, pellets were ignited in three orientations relative to the gravity vector. Low gravity combustion synthesis (SHS) was carried out on a DC-9 aircraft at the NASA-Lewis Research Center. It was found that under normal gravity conditions, both the combustion temperature and wave velocity were highest when the pellet was ignited from the bottom orientation; i.e., the wave propagation direction was directly opposed to the gravitational force. The SHS of 70 vol pct Al (in the Al-HfB₂ system) was changed from unstable, slow, and incomplete when ignited from the top to unstable, faster, and complete combustion when ignited from the bottom. The hydrostatic force (height × density × gravity) in the liquid aluminum was thought to be the cause of formation of aluminum nodules at the surface of the pellet. The aluminum nodules that were observed on the surface of the pellet when reacted under normal gravity were totally absent for reactions conducted under low gravity. Buoyancy of the TiB₂ particles and sedimentation of the Ni₃Ti phase were observed for the Ni₃Ti/TiB₂ system. The possibility of liquid convective flow at the combustion front was also discussed. Under low gravity conditions, both the combustion temperature and wave velocity were lower than those under normal gravity. The distribution of the ceramic phase, i.e., TiB₂ or HfB₂, in the intermetallic (Ni₃Ti) or reactive (Al) matrix was more uniform.