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 trajectories and distribution of particles in a turbulent axisymmetric gas jet injected into a flash furnace shaft

Numerical computations have been performed for the behavior of a vertical turbulent particle-laden gas jet exemplified by the shaft region of a flash-smelting furnace. The two-equation(k-ε) model was used to describe turbulence. Model predictions for the gas and solid flow fields give a satisfactory representation of experimental data taken from the literature. The predictions of flow properties of the two phases under flash-smelting conditions have been obtained for various inlet conditions, particle sizes, particle loading, and oxygen enrichment. Model predictions show that the axial velocity of the particle phase is substantially higher than that of the gas phase. The presence of solid particles causes the axial velocity of the gas phase to be greater near the centerline and lower in the outer region than in a single-phase gas jet. A more uniform distribution of particles was obtained by introducing a strong radial velocity of the distribution air at the inlet. The implications of the behavior of a particle-laden gas jet on flash-smelting processes arc discussed.     

Electric-pulse disintegration of a jet of liquid metal

Conclusions Electric-pulse disintegration of a jet of molten metal can be employed for producing both granules and powders. In this process the yield of fine fractions can be increased by: increasing voltage between the electrodes; decreasing to the permissible minimum the distance between the electrodes and the initial jet diameter; using a dc supply; employing a discharge circuit of low inductance and high capacitance; disintegrating a hollow jet.Translated from Poroshkovaya Metallurgiya, No. 10(178), pp. 6–10, October, 1977.     

Mass transfer between a horizontal,submerged gas jet and a liquid

The rate of reaction between a horizontal, submerged gas jet and a liquid has been measured in a model system under conditions where mass transfer in the gas phase is rate limiting. The gas was 1 pct SO₂ in air, and the liquid was a 0.3 pct solution of hydrogen peroxide in water. SO₂ absorption rates were measured as a function of jet Reynolds number (10,000 < N_Re < 40,000) and jet orifice diameter (0.238 < d₀ < 0.476 cm). The product of the gas phase mass transfer coefficient and the interfacial area per unit length of jet trajectory, k_SO2 α was found to increase linearly with increasing Reynolds number and to be a strong function of the orifice diameter. The ratio of k_so2 α to volumetric gas flow rate was shown to be independent of Reynolds number for a given orifice diameter. Extrapolated values of k_so2 α are lower than the coefficients measured for vertical CO jets blown upward through liquid copper. Extrapolation of the measured mass transfer data to the jet conditions in copper matte converting and in the gaseous deoxidation of copper has indicated that the gas utilization efficiencies in these processes should approach 100 pct if gas phase mass transport is rate controlling.     

The influence of gas phase resistance on mass transfer to a liquid metal

When a dilute gas is absorbed in a liquid metal in which Sievert’s law is obeyed, the gas phase resistance is likely to be significant. The influence of gas phase resistance will de-pend on the concentration of the transferred species in both the gas and the liquid as well as on the mass transfer coefficients in both the gas and liquid phases. An overall mass transfer coefficient is defined by: n″(X)₁=k_ov√pb -cb and equations are developed relating this to the variables mentioned. Experimental work has been carried out with dilute oxygen jets (p(O₂) = 0.1 and 0.2 atm) blowing onto molten silver, and the results have confirmed that the resistance in the gas phase contributes to the overall resistance. From these results it has been possible to estimate gas phase mass transfer coefficients which range from 1.4 cm/s for a jet momentum of 8000 dyne and lance height of 18.5 cm to 4.8 cm/s for a jet momentum of 56,000 dynes and lance height of 10.5 cm. A. CHATTERJEE, formerly in The John Percy Research Group in Process Metallurgy, Imperial College of Science and Technology, University of London, England     

Mixing of concentric gas jets issuing vertically into a liquid

Mixing of two concentric jets of dissimilar gases blown vertically upward through wafer was investigated experimentally. Air was blown through the inner pipe and carbon dioxide through the annular space between the inner and the outer pipes. The two jets mixed rapidly upon emergence from the nozzle. This made physical shielding of the air jet by CO₂ ineffective. It was caused by the fact that the air bubbles during and upon emergence from the nozzle were large. Moreover, they exhibited oscillations which made them spread over the annulus. Pursuing this argument it has been inferred that physical shielding would be ineffective in OBM/Q-BOP converter process of steelmaking as well. Therefore, protection of tuyere lining by shrouding gas seems to be due to thermal and chemical shielding, primarily. N.B. BALLAL, formerly a Graduate Student at Indian Institute of Technology, Kanpur, is presently     

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,     

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. Formerly Graduate Student, Michigan Technological University     

The spout of air jets upwardly injected into a water bath

The spout region of gas jets in liquids has received little attention, although it has both theoretical and practical significance. In this study, the spout of upwardly injected gas jets in water was characterized experimentally in terms of gas fraction, bubble frequency, and axial velocity distributions for ultimate incorporation into turbulent recirculating flow models. The measurements were made with a two-element electroresistivity probe coupled to a microcomputer. For the turbulent flow conditions prevailing in the jet plume and spout, special hardware and software were developed to analyze the signals generated by contact of the bubbles with the sensor in real time. Correlations of the gas fraction with axial and radial position for different gas flow rates have been established from the measurements. The dimensions of the spout were obtained from time-exposure photographs; when compared with the gas-fraction measurements, the spout boundary always corresponded to values ranging from 0.82 to 0.86. The radial profiles of bubble frequency at different levels in the spout exhibit a bell shape; the bubble frequency decreases with increasing height. The velocity of the bubbles in the spout drops linearly with increasing axial position. Formerly Graduate Student. Formerly Postdoctoral Fellow, The Centre for Metallurgical Process Engineering.     

Mass transfer of dissolved gas from a liquid into a rising bubble swarm

Mass transfer of dissolved gas from a liquid into a rising bubble swarm of inert gas is a transitoric reaction. The theory of such processes is described. The extraction of carbon dioxide dissolved in water by air purging was measured as a model reaction. It was found that the overall rate constant of the reaction is almost exclusively determined by the purging-gas blowing-rate. Nozzle position and number of nozzles have no influence on the reaction rate. This finding is explained by the fact, observed elsewhere, that the bubble size distribution function is constant and only a function of the liquid's physical properties. The measured rate constants agree with theoretically calculated ones, if the influence of turbulence on mass transfer into the bubbles is considered.     

Discussion of “physical chemistry of gas liquid solder reactions”

BAHRI OZTURK, P. BARRON, and R.J. FRUEHAN:Metall. Trans. B, 1987, vol. 18B, pp. 577-82.     

The mechanical behavior of a hybrid metal matrix composite

The mechanical behavior of a unidirectionally reinforced hybrid metal matrix composite in two different states has been studied: one with a “weakly bonded” interface and the other with a “strong” interface. Similarities and contrasts in mechanical behavior have been related to the properties of the interface. The longitudinal tensile strength and the crack growth initiation resistance are found to be insensitive to the condition of the interface. However, the material with the “weak” interface exhibits extensive debonding, resulting in a steeply increasing resistance curve and a large work of rupture. Furthermore, the weak interface reduces the transverse and torsional strength of the composite. This study illustrates how the tailoring of interfacial properties can improve the mechanical performance of composites for certain structural applications.     

微波加热金属液体的实验研究

研究微波加热液态金属的升温特征,在MobileLab-W-R型微波工作站中进行了微波直接加热铜液和铁液的实验研究,实现了微波直接加热铜液和铁液实验,对比研究了微波直接加热和间接加热铜液与铁液的加热效果,并研究了微波功率、金属液质量、温度等对微波直接加热效果的影响,探讨了微波直接加热金属液体的机理.结果表明,微波可以以较快的升温速度直接加热铜液和铁液,且升温速率与微波加热功率呈近似线性递增关系;在相同微波直接加热条件下,同等质量的铜液和铁液的升温速度相近,但不同质量铁液加热时,由于其表面积、微波场强分布等因素的影响,铁液质量对微波加热效果的影响没有明显的线性关系.理论分析认为,铜和铁在熔化后电阻率增大,磁导率明显下降,导致微波在铜液和铁液内部的趋肤深度显著大于固态铜和铁;电导损耗是实现微波直接加热液态金属的主要机制,液态金属可通过电子与原子核碰撞、表面快速更新、内部缺陷阻碍电子运动、原子运动及碰撞等形式吸收微波,将微波能量转化为自身热量.     

微波加热金属液体的实验研究

研究微波加热液态金属的升温特征,在MobileLab-W-R型微波工作站中进行了微波直接加热铜液和铁液的实验研究,实现了微波直接加热铜液和铁液实验,对比研究了微波直接加热和间接加热铜液与铁液的加热效果,并研究了微波功率、金属液质量、温度等对微波直接加热效果的影响,探讨了微波直接加热金属液体的机理。结果表明,微波可以以较快的升温速度直接加热铜液和铁液,且升温速率与微波加热功率呈近似线性递增关系;在相同微波直接加热条件下,同等质量的铜液和铁液的升温速度相近,但不同质量铁液加热时,由于其表面积、微波场强分布等因素的影响,铁液质量对微波加热效果的影响没有明显的线性关系。理论分析认为,铜和铁在熔化后电阻率增大,磁导率明显下降,导致微波在铜液和铁液内部的趋肤深度显著大于固态铜和铁;电导损耗是实现微波直接加热液态金属的主要机制,液态金属可通过电子与原子核碰撞、表面快速更新、内部缺陷阻碍电子运动、原子运动及碰撞等形式吸收微波,将微波能量转化为自身热量。      

Bubble formation during horizontal gas injection into downward-flowing liquid

Bubble formation during gas injection into turbulent downward-flowing water is studied using high-speed videos and mathematical models. The bubble size is determined during the initial stages of injection and is very important to turbulent multiphase flow in molten-metal processes. The effects of liquid velocity, gas-injection flow rate, injection hole diameter, and gas composition on the initial bubble-formation behavior have been investigated. Specifically, the bubble-shape evolution, contact angles, size, size range, and formation mode are measured. The bubble size is found to increase with increasing gas-injection flow rate and decreasing liquid velocity and is relatively independent of the gas injection hole size and gas composition. Bubble formation occurs in one of four different modes, depending on the liquid velocity and gas flow rate. Uniform-sized spherical bubbles form and detach from the gas injection hole in mode I for a low liquid speed and small gas flow rate. Modes III and IV occur for high-velocity liquid flows, where the injected gas elongates down along the wall and breaks up into uneven-sized bubbles. An analytical two-stage model is developed to predict the average bubble size, based on realistic force balances, and shows good agreement with measurements. Preliminary results of numerical simulations of bubble formation using a volume-of-fluid (VOF) model qualitatively match experimental observations, but more work is needed to reach a quantitative match. The analytical model is then used to estimate the size of the argon bubbles expected in liquid steel in tundish nozzles for conditions typical of continuous casting with a slide gate. The average argon bubble sizes generated in liquid steel are predicted to be larger than air bubbles in water for the same flow conditions. However, the differences lessen with increasing liquid velocity.