气泡微细化实验中均混时间的研究

在水模型实验的指导下,依照佐野先生提出的高效的镁精炼铁水计划进行实验.本文采用电导率法测定溶池的均混时间,考察喷镁脱硫钢包内钢液的一些主要工艺和结构参数对均混时间的影响,通过比较均混时间来衡量气泡的微细化程度;通过水模型实验,讨论钢包喷吹镁粉脱硫精炼过程中,不同的搅拌桨结构、搅拌模式、搅拌速度、气体流量、搅拌桨的潜入深度和喷嘴结构等一系列因素对均混时间的影响,分别做了单机械搅拌,单吹气搅拌和机械搅拌加上吹气搅拌的铁水包水模型实验.对实验结果进行对比分析,把上述不同参数条件下的均混时间列出表格,绘出曲线,进行了以铁水包脱硫效率为最终考察目标的铁水包单吹镁脱硫的工艺优化研究,得到最佳的优化参数,并把这些参数运用到实验中,来研究讨论气泡微细化的程度,指导本水模型实验.通过水模型实验,最终确定130t钢包的最佳工艺优化参数.     

铁水包喷镁脱硫预处理动力学模型

依据对铁水喷镁脱硫机理的理论分析,同时考虑熔池均混时间和镁气泡在铁水中停留时间等重要参数对喷镁脱硫的影响,开发了铁水包喷吹颗粒镁铁水预处理脱硫动力学模型.并采用四阶龙格库塔法对该模型进行求解.模型计算结果与实际生产数据吻合较好,可用于对国丰钢铁公司铁水包喷镁脱硫过程的预测.     

180 t转炉底吹气体与熔池相互作用的水模型实验

通过10:1水模型研究了转炉底吹流量0.55～0.75 m3/h和底吹喷嘴4孔对称、2孔对称、2孔不对称分布以及喷嘴位置d/D=0.1～0.9(d-喷嘴所在同心圆直径,D-转炉熔池直径)对熔池均混时间的影响.结果表明,d/D=0.3,底吹流量0.70 m3/h,4孔对称底吹时熔池搅拌效果最佳;2孔不对称喷吹时,最佳流量为0.60～0.70m3/h,最佳喷嘴位置d/D=0.3～0.5;2孔对称喷吹时最佳流量与喷嘴位置分别为0.65 m3/h和d/D=0.7.     

RH上升管喷嘴数量及其布置对流动、混合与传质的影响

通过物理模拟测定了RH精炼过程的循环流量、钢包的均混时间、真空室内物料的平均停留时间及容量传质系数，重点分析了RH上升管内的提升气体用喷嘴个数及其布置对上述4个方面特性的影响．结果表明，提升气体用喷嘴个数及其布置对RH内钢水流动有很大的影响，循环流量随喷嘴个数和气泡行程的增加而增大，但均混时间、平均停留时随喷嘴个数和气泡行程的增加而减小．     

180 t转炉底吹和顶-底复吹射流与熔池作用的水模型研究

根据180 t转炉的实际生产情况,以修正的Froude准数为相似准数,建立几何相似比10 ： 1水模型,进 行了四孔对称单纯底吹试验,并在最佳的底吹工艺参数下(底吹最佳位置为喷嘴所在同心圆直径:转炉熔池直径= 0. 3处;最佳流量为0. 7 m³/h,均混时间18. 2 s),通过改变顶吹氧枪的气体流量和吹炼枪位进行了顶底复吹转炉射 流与熔池作用的试验。结果表明,在底吹条件下,增加顶吹工艺(最佳枪位150 mm,最佳流量39 m³/h),熔池平均 的均混时间减少了 5.6 s, 180 t转炉顶底复吹可显著提高经济效益。     

高效铜侧吹熔炼反应器内均混时间的物理模拟

采用相似原理指导下的物理模拟试验,通过实时测定溶液电导率研究高效铜侧吹熔炼反应器内均混时间。结果表明,在喷嘴排布紧凑的1#排布下,熔池内流体的混合时间相对较短;随着喷嘴直径的增加,气体流速减小,均混时间变长;随着气体流量的增大,均混时间不断减小,但减小的幅度变小。     

决定铁水包喷粉脱硫效率的三个基本参数

熔池均混时间、粉剂穿透比和粉剂停留时间是决定铁水包喷粉脱硫效率的三个基本参数。通过实验考察了喷枪喷嘴结构不同和喷枪平面位置不同条件下吹气对熔池搅拌的影响 ;理论分析了影响单个粉剂穿越气 -液界面的主要因素 ,并得到在本实验粉剂粒度分布条件下理论粉剂穿透比的表达式。将实测粉剂穿透比与理论粉剂穿透比进行比较 ,提出了粉剂穿透比理论值的修正公式 ;利用流场计算结果 ,回归出了粉剂停留时间与载气流量和喷嘴离包底距离的关系     

决定铁水包喷粉脱硫效率的三个基本参数

熔池均混时间、粉剂穿透比和粉剂停留时间是决定铁水包喷粉脱硫效率的三个基本参数。通过实验考察了喷枪喷嘴结构不同和喷枪平面位置不同条件下吹气对熔池搅拌的影响;理论分析了影响单个粉剂穿越气－液界面的主要因素,并得到在本实验粉剂粒度分布条件下理论剂穿透比的表达式。将实测粉剂穿透比与理论粉剂穿透进行比较,提出了粉剂穿透比理论值的修正公式;利用流场计算结果,回归出了粉剂停留时间与载气流量和喷嘴离包底距离的关系     

复吹转炉底吹喷粉实验研究

在1:6物理模型上,通过水模实验对复吹转炉底吹喷粉时熔池搅拌情况进行了研究.结果表明:喷粉对熔池搅拌有明显的促进作用.喷粉条件下,均混时间随顶吹气体流量的增加存在最小值,最佳顶吹气体流量为117.0 m3/h,增加底吹气体流量对降低均混时间有利.在本实验范围内最佳顶吹流量为117.0 m3/h、最佳底吹流量为2.36 m3/h.     

喷镁脱硫过程中氮化作用的热力学和动力学分析

本文运用热力学和动力学对喷镁过程中载气如何影响脱硫进行了研究,研究表明,用氮作为载气会降低镁的利用率,但用氩和氮作为载气对镁利用率影响的不同还不清楚。热力学和动力学分析表明,当用氮作为载体导入镁粒到金属液时,在喷枪喷嘴处可能形成镁的氮化物,在喷枪处形成的镁氮化物可能堵塞喷枪。氮化镁的分解或在熔池表面未分解氮化镁的存在都会增加镁在气体中的损失。可通过优化喷吹条件,使由于氮化作用损耗的镁和喷枪堵塞问题降到最低程度。     

The kinetics of molten iron desulfurization using magnesium vapor

Magnesium vapor was injected into 60 kg heats of carbon-saturated iron at 1523 K. The magnesium dissolution and desulfurization rates as well as magnesium bubble size were monitored over sulfur contents ranging from 0.0002 to 0.2 pct S. The magnesium dissolution mass transfer coefficient was found to be 0.046 ± 0.034 mm · s⁻¹ (for 30 mm diam bubbles). Further analysis indicated that most of the desulfurization took place at magnesium sulfide inclusions present in the bath; there was good agreement between the experimental precipitation rate constant and that predicted for diffusion to the number of inclusions observed by chemical analysis and inclusion counts. The seed magnesium sulfide inclusions were probably stripped from the ascending magnesium bubbles. These particles were quickly eliminated from the melt by bubble and induction stirring, resulting in a steady-state number of inclusions. This allowed a pseudosteady-state model to be developed.     

Thermochemistry of ternary liquid Cu-Mg-Si alloys

The thermodynamic properties of ternary liquid Cu-Mg-Si alloys with a constant concentration ratio of x _Cu/x _Si=7/3 were determined using a combination of different experimental methods. Enthalpies of mixing were measured by isoperibolic calorimetry, and magnesium vapor pressures were obtained by an isopiestic method. Partial thermodynamic properties of magnesium were derived from the vapor pressure data, and the composition dependence of the magnesium activities is given for 1173 K. Integral Gibbs energies of mixing for liquid alloys were calculated by a Gibbs-Duhem integration. The agreement of the thermodynamic data obtained from different methods was found to be very good.     

金属镁粒铁水脱硫过程动力学

通过对金属镁粒铁水脱硫过程动力学的研究发现,金属镁粒的粒径越大,镁粒气化后的气泡在铁液中的停留时间和平均上浮速率就越大,铁液中镁脱硫反应的传质系数减小;上浮速率及停留时间与铁液温度几乎没有关系,但传质系数随温度的增加而增加;在一定的铁液深度和铁液硫含量时,金属镁粒铁水脱硫时镁的利用率随镁粒的粒径增加而减小;温度对镁的利用率的影响在镁粒粒径小时比粒径大时要大,在铁液硫含量小时比硫含量大时影响要大;就脱硫过程动力学而言,温度越高越有利于铁液中镁的脱硫反应,这与热力学结论相反;铁液温度为1573 K,铁液中的w([S])为0.06%,铁水包的深度为3 m,在镁粒半径范围为(3～16)×10-4 m时,理论计算镁脱硫时镁的平均利用率为83.1%,与宣化钢铁公司生产得到的数据进行了对比,得到很好的吻合.     

Mixing time and fluid flow phenomena in liquids of varying kinematic viscosities agitated by bottom gas injection

A model experiment was carried out to investigate the mixing condition and related fluid flow phenomena in a slag layer of metal-refining processes agitated by bottom gas injection. Silicone oil was used as a model for the molten slag. Mixing time in a silicone oil bath was measured with a newly developed laser optical sensor. Measured mixing time values increased with an increase in the kinematic viscosity of the silicone oil. In order to explain the relation between mixing time and the kinematic viscosity of silicone oil, the rising velocity of bubbles and the vertical and horizontal velocities of silicone oil flow were measured with an electroresistivity probe and a laser Doppler velocimeter, respectively. The increase in the mixing time with the kinematic viscosity of silicone oil was caused mainly by the suppression of upward motion of bubbles and silicone oil in the bubbling jet region. An empirical correlation for the mixing time was derived as a function of the kinematic viscosity of silicone oil, in addition to conventionally used parameters such as the gas flow rate, bath diameter, and bath depth.     

Mixing and mass transfer by bubbling in treating ferrocarbon melts with alkaline-earth metals

The desulfurization of ferrocarbon melts as a result of mixing by bubbles of Ca and Mg vapor and carrier gas is investigated. The calculation results are in satisfactory agreement with experimental data. The introduction of calcium by powder wire is shown to be more effective than Ca injection.     

Fundamentals of Bubble Formation during Coagulation and Sedimentation Processes

Conventional coagulation and sedimentation processes can be significantly disrupted by gas bubbles, attaching to, and then floating coagulant floc. This study sought to understand the fundamental factors that lead to bubble formation and corresponding floating floc during coagulation and sedimentation. Gas bubbles (causing the floating floc) can form whenever the total dissolved gas pressure exceeds the local solution pressure, which can occur at localized minimum pressures during rapid mixing at high fluid velocities. Very high rate rapid mixers can cause bubble formation and floating floc even in waters undersaturated with dissolved gas. The formation and stability of floating floc are dependent on the local solution pressure, amount and type of dissolved gas supersaturation, temperature, length of rapid mixing, surface chemistry of the mixing paddle, floc, and attachment forces.     

底吹炉氧枪喷口形式对气泡形态及混合状况的影响

针对4种不同的氧枪喷口结构进行了冷态试验研究，采用高速相机获得了不同喷口下的炉内气泡形态，采用电导率法测试了不同喷口下炉内流体的混合状况。试验结果表明，在相同的气体流量下，不同的气体喷口时炉内气泡的形态十分相似，当采用结构最复杂的喷口时，炉内的混合状态是最好的，结构最简单的喷口混合效果最差，其最小响应时间较最复杂喷口增加约11%，均混时间增加约4.7%。     

Excimer laser induced bubble: dimensions, theory, and implications for laser angioplasty

BACKGROUND AND OBJECTIVE: Previous studies have demonstrated that during Xenon-Chloride excimer laser ablation of tissue, rapidly expanding and imploding bubbles (diameter < 3 mm), predominantly containing water vapor, are formed. These short lived bubbles (life time < 300 microseconds) induce mechanical damage in adjacent tissue. In the present study, a theoretical analysis of the volume of vaporized water is correlated with measured bubble volumes formed in hemoglobin solution. STUDY DESIGN/MATERIALS AND METHODS: The dimensions of the rapidly expanding and imploding vapor bubble induced by the XeCl excimer laser pulses (308 nm, 115 ns), delivered via a 300, 550, or 950 microns diameter monofiber in 16% w/v hemoglobin solution (at 37 degrees C), were measured. RESULTS: Theoretical analysis and the experimental data correlated well (correlation coefficient r = 0.97). The diameter of excimer laser induced bubbles increased with increasing pulse energy. For a given radiant exposure, the bubble size was decreased by either decreasing the fiber tip area or by decreasing the absorption coefficient of the hemoglobin solution. CONCLUSION: We conclude that, for a wide range of conditions, theory agrees well with experimental data. Thus, during delivery of excimer laser pulses in blood, bubble dimensions can be reduced by flushing with saline or by reduction of the area radiated with each laser pulse, for example, by pulse multiplexing or using a smaller multifiber catheter.     

Experimental Research of External Desulfurization in Situ Mechanical Stirring

This paper presents a new idea about desulfurization with in-situ mechanical stirring method on the basis of desulfurization by single blow grain magnesium and KR method, that is, the inner gases carry the magnesium vapor formed in-site in molten iron by magnesium-based desulfurization, and bubble dispersed and disintegrated under the condition of mechanical stirring, thence to improve the efficiency of desulfurization by single blow grain magnesium .It has been proved by research of cold water model experiment that the bubble dispersion and disintegration can not only improve the desulphurization efficiency but also increase the utilization rate of magnesium. Obviously, the bubble dispersion and disintegration of magnesium vapor is the key problem in improving the desulphurization efficiency and increasing the utilization rate of magnesium. Thus the research focus on exploring the performance of bubble dispersion and disintegration on the base of refining process and gas-liquid mass transfer. According to the literature and cold water model experimental result basing on principle of similitude, the influencing factors and interaction of bubble dispersion and disintegration have been studied from the perspectives of physical and numerical simulation. The study would provide the theoretical and experimental data for the new method of desulfurization with in-situ mechanical stirring.     

Probing the initial stage of synthesis of Al2O3/Al composites by directed oxidation of Al-Mg alloys

In the directed oxidation of Al-Mg alloys, the amount of MgO that forms in the initial stage prior to the incubation period affects the rate of oxidation of Al to Al₂O₃ in the composite growth stage. The mechanism of formation of MgO and the duration of the initial stage were investigated experimentally and theoretically. The variables studied were total pressure in the reaction chamber, partial pressure of oxygen, and the nature of the diluent gas which affects the diffusion coefficients of magnesium vapor and oxygen in the gas phase. The oxidation rate in the initial stage was proportional to both the oxygen partial pressure and the diffusivity of oxygen. The duration of the initial stage decreased with the increase in oxygen pressure. To understand the role of magnesium evaporation in the oxidation behavior of the alloy, the velocity, temperature, and concentration fields in the gas phase were simulated numerically. The calculated concentration profiles of magnesium vapor and oxygen as a function of time were consistent with the experimentally measured oxidation rates and confirm reaction-enhanced gaseous diffusion-limited vaporization of magnesium in the initial stage of oxidation of Al-Mg alloys. The region where the magnesium vapor is oxidized in the gas phase moved progressively closer to the alloy surface during the initial stage of oxidation. The end of the initial stage and the start of the incubation period corresponded to the arrival of the oxygen front close to the surface when the spinel formation occurred.