Characterization of gas bubbles injected into molten metals under laminar flow conditions

Velocity and volume measurements of gas bubbles injected into liquid metals under laminar flow conditions (at the orifice) have been achieved. A novel experimental approach utilizing noises generated by bubbles was used to collect the necessary data. Argon gas was bubbled through tin, lead, and copper melts, and gas bubble formation frequencies (and hence bubble sizes) were determined. It was found that the bubble size generated for a particular orifice diameter was dependent upon the magnitudes of the orifice Froude and Weber numbers. Maximum formation frequencies increased slightly with decreasing orifice diameter, and the transition point from varying to constant frequency occurred at an orifice Weber number of approximately 0.44. Velocities of gas bubbles rising through the metals were greater than those previously reported for studies in which only one bubble was in the melt at any time. Effective drag coefficients of the rising bubbles were found to agree with data previously generated in aqueous systems. R. J. ANDREINI, Formerly Graduate Student, Michigan Technological University,     

3Cr钢在油水两相层流工况下的腐蚀行为

油水两相是海底管道和集输管线常见的腐蚀工况之一。以3Cr钢为代表的低Cr合金钢是目前具有良好耐蚀性能的重要材料,但是,在油水两相层流工况下,特别是加注了一定缓蚀剂的条件下,3Cr钢的适用性尚不明确。通过高温高压反应釜模拟了油水两相层流工况的腐蚀环境,结合扫描电子显微镜（SEM）、X射线衍射谱（XRD）、激光共聚焦拉曼光谱、电化学交流阻抗等测试表征方法,研究了3Cr钢的腐蚀行为及缓蚀剂对其耐蚀性能的影响。结果表明,在油水分层工况下,3Cr钢的腐蚀产物膜为明显的双层膜结构,其内层腐蚀产物膜为结构致密的富Cr层,表现出良好的抗CO₂腐蚀性能,但加入100 mg·L?1十七烯基胺乙基咪唑啉季铵盐缓蚀剂后,3Cr钢并未得到有效的缓蚀保护。腐蚀产物分析和电化学研究表明,烷烃分子、缓蚀剂分子及富Cr层间存在竞争关系,烷烃分子干扰了缓蚀剂分子的有序排列,影响了3Cr钢的耐蚀性。      

A novel probe for detecting gas bubbles in liquid metals

A novel probe intended for detecting gas bubbles within a liquid metal has been tested both in water and in a low melting point alloy. The probe is inexpensive in itself and in the cost of processing signals from the probe. It is also rugged in that the part (a simple tube) inserted into the liquid can be selected from materials resistant to the liquid. It is also rugged in that accidental damage to the tube is not costly. The probe functions by measuring, using a microphone, the pressure fluctuation as a bubble passes the probe tip. Use of two probes to measure a bubble rise velocity in water is also described.     

Experimental studies on the flow velocity of molten metals in a ladle model at centric gas blowing

Experimental measurements of the flow velocity were carried out with liquid Wood's metal in a ladle-shaped vessel with an inner diameter of 40 cm at centric gas blowing. By means of permanent magnet probes the liquid flow field was measured under various blowing conditions. The results show that a circulating flow field is established in the vessel. In the bubble plume zone an upwardly directed liquid flow is formed. The radial distribution of the flow velocity in this zone follows a Gaussian function. The axial flow velocity increases with growing gas flow rate and is nearly constant in vertical direction. The width of the upward flow becomes larger with increasing distance from the nozzle and its dependence from the gas flow rate is not considerable. At centric gas blowing the liquid in the upper part of the bath streams quickly, whereas in the lower part so-called “dead zones” with very low flow velocity are present. Besides the time-averaged value of the flow velocity, the turbulent behaviours of the liquid flow such as fluctuation velocity, the turbulent kinetic energy and its dissipation rate were investigated on the basis of measured data. It was found that the liquid flow is turbulent particularly in the region of bubble plume and of bath surface. The radial profiles of these parameters can also be described by a Gaussian function. Only a small part of the gas stirring energy is changed into the kinetic energy of the directed liquid flow. Most of the stirring energy is already dissipated in the bubble plume zone.     

Convective heat-transfer measurements in liquid metals under different fluid flow conditions

In this study an experimental method to measure convective heat transfer characteristics in liquid metals is presented. This method involves the immersion into a metal bath of a solid specimen whose melting point is equal to or lower than that of the metal or alloy in the metal bath, and which will not react chemically with the liquid metal or alloys used. The specimen should have a hollow bore whose opening is held above the surface of the liquid metal; immersion continues until such a time as the liquid metal penetrates the hollow bore. The apparent weight of the specimen is monitored to determine the rate at which the net downward force changes. Experimental results are reported for liquid aluminum, liquid copper, and liquid steel. Those experimental results were conducted under different fluid flow conditions. The applicability of this method to liquid slags is also discussed. Formerly Postdoctoral Research Fellow with the Department of Metallurgy and Materials Science, University of Toronto     

Penetration of molten nickel into sintered titanium carbide hard metals

Conclusions A study was made of some aspects of molten nickel penetration into titanium carbide hard metals. It is shown that, when such a liquid phase migrates through a semiinfinite rod, the variation of the concentration of the binder metal along the length of the rod may be described by a hyperbolic function. The dependence of the thickness of the layer of increased nickel content on time of contact between the specimen and the melt was determined. It is demonstrated that, by employing the method of infiltration of a hard metal with a liquid metal, it is possible to produce parts possessing varying physicomechanical properties.Translated from Poroshkovaya Metallurgiya, No. 11(215), pp. 25–38, November, 1980.     

Characterization of Plasmodium falciparum-infected erythrocyte and P-selectin interaction under flow conditions

Plasmodium falciparum-infected erythrocytes (IRBC) roll on the adhesion molecule P-selectin in vitro under flow conditions that approximate the shear stress in capillary and postcapillary venules in which cytoadherence occurs in vivo. The pathological significance of this adhesive interaction is currently unknown. In this study, we further investigated the molecular interactions between IRBC and P-selectin by using a laminar flow system that allowed for the direct visualization of IRBC-substratum interactions. The results showed that the IRBC-P-selectin interaction was Ca2+-dependent and involved the lectin domain of P-selectin and a sialic acid residue on IRBC. The sialylated P-selectin ligand was trypsin-sensitive, which suggests that it could be part of the parasite antigen PfEMP1 that interacts with CD36 and intercellular adhesion molecule-1 (ICAM-1), but different from a trypsin-resistant IRBC ligand that adheres selectively to chondroitin sulfate A. Studies on the rolling and adhesion of IRBC on activated platelets that express both CD36 and P-selectin showed that inhibition of rolling on P-selectin reduced the adhesion of some clinical parasite isolates to CD36, whereas other parasite isolates appeared to interact directly with CD36. Thus, cytoadherence under physiological flow conditions may be mediated by multiple IRBC ligands that interact with different adhesion molecules in a cooperative fashion. These findings underscore the complexity of the interactions betweeen IRBC and vascular endothelium.     

A simulation study of ostwald ripening of gas bubbles in metals accounting for real gas behaviour

The Ostwald ripening kinetics of bubbles containing non-ideally behaving gas is studied by a computer simulation approach. The temporal evolution of mean radii and bubble size distributions under transient and steady state conditions is examined. In comparison with ideal gas, the results for real gas show large differences for mean radii r_m ⩽ 50 nm, which is the usual range of Transmission Electron Microscopy investigations.     

The breakup of bubbles into jets during submerged gas injection

There has never been any fundamental explanation presented for the transition from the bubbling regime to the jetting regime when gas is injected into liquid at high velocity through submerged tuyeres. This is an important issue in metallurgical processes, since the flow regime is known to influence refining rates, refractory erosion, and the penetration of the liquid into the tuyere. Based on the observation that many small droplets of liquid and gas bubbles are formed to create the jets, a combined Kelvin-Helmholtz and Rayleigh-Taylor instability analysis has been applied to bubbles forming at submerged tuyeres. For particular wavelengths of disturbances, the interface will be unstable and create bubbles and droplets. The critical injection velocity for instability depends on surface tension, tuyere diameter, and the gas-to-liquid density ratio, which can be summarized by We = 10.5(ρ*)^−1/2, where We is the Weber number based on the gas velocity and density and tuyere diameter, and ρ* is the gas-to-liquid density ratio. The importance of surface tension had not been appreciated previously for this regime of gas injection. There is considerable controversy in the literature concerning the measurement of the transition from bubbling to jetting. The 70 pct “linking” point, proposed by Ozawa and Mori, describes the situation where 70 pct of the bubbles link with the preceding bubbles and produce a reasonably steady jet. The theoretical correlation developed above predicts the velocity to reach this point ±20 pct (95 pct confidence level) in a variety of systems from six different groups of workers. The theoretical analysis demonstrates that the instabilities are primarily capillary in nature, not gravity waves, which explains the observation that orientation has little effect on the jetting transition.     

Dissolution of solid antimony in molten bismuth under static conditions

The dissolution of solid antimony in molten bismuth was studied under static and isothermal conditions using the reaction couple and immersion methods between 623 and 773 K. The dissolution of antimony under the antimony upper position, using reaction couple method, was governed by diffusion, and the diffusion coefficient of antimony in molten bismuth was obtained as follows:D _L = 2.08 X 10-⁸exp(-ll kJ mol^-1/RT), (m²/s). The dissolution of antimony under the immersed condition was governed by the natural convection resulting from the density difference in the melt, and the dissolving antimony was distributed uniformly by natural convection in molten bismuth. The apparent activation energy for the dissolution of solid antimony in molten bismuth was the same as that for the diffusion of antimony in the melt.     

电弧炉EBT区不同底吹搅拌条件的钢液流动数值模拟

底吹工艺在电弧炉炼钢过程中的应用能有效缩短熔池混匀时间, 加速碳、磷、硫的去除, 提高生产效率及产品质量.本文利用数值模拟软件模拟了EBT (偏心底部出钢) 区底吹孔不同气体流量下的电弧炉钢液速度场, 发现当EBT区域底吹气体流量从100 L·min^-1升至267 L·min^-1 (其他两孔气体流量稳定保持为133 L·min^-1) 时, EBT区域钢液的平均流速由2.805×10^-3m·s^-1升至3.268×10^-3m·s^-1, 钢液整体平均流速由4.126×10^-3m·s^-1升至4.610×10^-3m·s^-1, 并耦合得出EBT区域不同底吹流量下的钢液流动速度经验公式.由于钢液流动是影响熔池内反应的动力学因素, 本文提出了电弧炉炼钢基于底吹熔池搅拌的碳成分预报模型, 为冶炼终点均匀熔池成分、合理供氧操作提供理论建议.     

Physical characteristics of gas jets injected vertically upward into liquid metal

The time-averaged structure of plumes has been measured with a two-element electroresistivity probe during upward injection of nitrogen or helium into mercury in a ladle-shaped vessel. From these measurements and data obtained earlier for air jets in water, general correlations linking the spatial distribution of gas fraction with the Froude number and gas/liquid density ratio have been developed. Early evidence suggests that these correlations should be applicable to gas-stirred metallurgical baths. Measurements of the profiles of bubble velocity and bubble pierced length reveal that the kinetic energy of the gas is dissipated close to the nozzle, and buoyancy dominates flow over most of the plume. Castillejos E., formerly with the Centre for Metallur-gical Process Engineering, The University of British Columbia,     

The siliconizing of refractory metals under nonequilibrium conditions

Summary It is shown that, during the vacuum siliconizing of refractory metals in the absence of an equilibrium silicon concentration at the phase boundaries, the growth of the silicide layer as a function of time may obey, a linear law. This is observed during the initial period of siliconizing, when new phases are formed, as well as in the presence of impurities whose vapor pressure is much higher than that of silicon.     

燃气轮机进气喷雾冷却下层流火焰的特性

建立了燃气轮机进气喷雾冷却条件下燃烧室的一维层流预混燃烧模型,研究了在不同化学当量比、温度和压力下H₂O体积分数对火焰传播速度、火焰温度、燃烧产物分布的影响.研究结果表明:火焰传播速度随H₂O体积分数升高而近似线性减小,采用进气雾化冷却技术时,可适当提高燃烧室中扩散燃烧所占比例,以此来稳定燃烧工况;火焰温度随混合气中H₂O体积分数升高而急剧降低,燃烧尾气排放中NO_x体积分数降低;CH₄燃烧过程中H₂O降低了O, H, OH自由基的体积分数,高H₂O体积分数下基元反应R38对促进CH4燃烧的作用效果减弱,火焰传播速度降低.     

Investigation of the kinetics of breakup of gas bubbles in liquid metals with digital simulation method

The method of digital system simulation can be effectively used to quantify the complex multiphase interactions within a gas injection process. Process simulation results yield a better understanding and a better aimed engineering of gas dispersion techniques in metallurgical processes. In this paper the breakup phenomenon of gas bubbles in stagnant liquids is simulated and the dependencies between breakup of bubbles and various parameters of a gas dispersion process such as operative parameters, system parameters and mass transfer rates are investigated. The bubble diameter after breakup is almost independent of the nozzle diameter and gas flow rate. The frequency of bubble breakup and critical bubble size depend on the rate of mass transfer into the bubble. An almost constant rising velocity is achieved only in those cases investigated where mass transfer and bubble breakup are considered. In all other cases no stationary rising velocity is obtained. The interplay between bubble size, rising velocity and the inertia of the surrounding liquid and the influence of mass transfer and breakup are investigated. Simulation results reveal that the behaviour of an ascending bubble is strongly influenced by the mass transfer rate, i. e. by the composition of the melt. Verification of the simulation results with empirical equations from literature shows a very good agreement in all dispersion systems investigated.     

The physical behavior of a gas jet injected horizontally into liquid metal

The gas fraction and bubble frequency distributions in a submerged air jet, injected horizontally into mercury, have been measured under isothermal, nonreactive conditions for nozzle diameters of 0.325 and 0.476 cm and jet Froude numbers ranging from 20.5 to 288. The measurements reveal that the jets expand extremely rapidly upon discharge from the nozzle with an initial expansion angle of 150 to 155 deg. This value, which is over seven times greater than is found with air jets in water, indicates that the physical properties of the liquid exert considerable influence on the jet behavior. In conjunction with the rapid expansion, the air jets in mercury were also found to penetrate extensively behind the nozzle, and in many respects resembled a vertically injected jet. The extent of backward penetration of the jets was constant for all blowing conditions studied while the forward penetration increased with both increasing jet Froude number and nozzle diameter. The measured jet penetration in both the forward and backward directions were considerably larger than expected from model predictions. The core of the jets consists of a high concentration of gas bubbles. Both the gas volume fraction and bubble frequency in the core increase with increasing jet Froude number and nozzle diameter. The gas concentration and bubble frequency decrease with increasing distance along the jet trajectory due presumably to entrainment of liquid metal and bubble coalescence. On the basis of these findings, it is likely that process jets, such as are injected into copper converters, also expand rapidly and penetrate only a short distance into the bath. Thus rather than reacting in the middle of the bath, the jets may be impinging on the backwall refractory and contributing to the erosion observed there.     

增氮析氮法生成气泡去除钢液中显微非金属夹杂物

为了进一步完善增氮析氮法生成气泡去除钢液中显微非金属夹杂物技术,研究了真空处理时间、充氮压力、气体类型等因素对钢中全氧和显微非金属夹杂物的影响.结果表明:减压处理过程中,钢液中非金属夹杂物可为过饱和气体氮气形成气泡提供非均相形核核心;增氮析氮法可有效地降低钢中全氧,去除钢中显微非金属夹杂物;真空处理时间越长,钢中全氧和显微非金属夹杂物数量越低,当真空处理时间为30 min时钢中全氧去除率达到了81.6%,而且全氧质量分数最低达到7×10^-6.