Mass transfer from an oxygen jet to liquid silver

A subsonic jet of pure oxygen discharging from a converging nozzle with a throat diameter of 2.5 mm was directed vertically on the surface of molten silver maintained at 1000°C. The effects of variation in lance height (5 to 25 cm), jet momentum (3000 to 56000 dyne), jet temperature (600° to 1000°C) and interfacial area (45 sq cm to 182 sq cm) were studied. In all cases the oxygen concentration in the silver was measured by lime stabilized zirconia probes. The mean liquid phase mass transfer coefficients calculated for transfer across the total surface area of the bath of 182 sq cm, ranged from 0.001 to 0.015 cmJs. The higher values were obtained with high jet momentums or with low values of the lance height. A decrease in the surface area of the bath to 45 sq cm only slightly reduced the rate of transfer and resulted in a threefold increase in the mass transfer coefficient based on the reduced area. The mass transfer coefficients were independent of the jet temperature providing the jet momentum was maintained constant and there were no thermal gradients in the liquid silver. A. CHATTERJEE, formerly Member of the John Percy Research Group in Process Metallurgy, Imperial College of Science and Technology, London, England. D. H. WAKELIN, formerly Member of the John Percy Research Group in Process Metallurgy, Imperial College of Science and Technology.     

Dynamic variations of lance distance in impinging jet steelmaking practice

The behaviour of a free gas jet is used to study the dynamic variations of lance distance to supply oxygen in impinging jet steelmaking practice. It is shown that the dimensionless momentum flow rate within the jet describes satisfactorily the plant data on variation of lance distance to supply oxygen. Correlations are proposed to determine the lance distance to supply oxygen and its variation during the blow.     

Turbulent fluid flow phenomena in metals processing operations: Mathematical description of the fluid flow field in a bath caused by an impinging gas jet

A mathematical representation is developed for describing the flow field in liquids or melts, agitated by a symmetrically placed impinging gas jet. The problem is formulated by the statement of the axi-symmetrical turbulent fluid flow equations using the Prandtl-Komogorov model for the eddy viscosity. The resultant differential equations are solved numerically and the computed results are shown to be in reasonable agreement with experimental data reported in the literature. This problem is thought to be relevant to various metals refining operations and the results should also be helpful for the interpretation of laboratory scale studies in which molten metals are contacted with impinging gas jets.     

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 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.     

Penetrability of impinging gas jets in molten steel bath

An experimental study is carried out to determine the penetrability of impinging gas jets in molten steel baths of BOF and combined blown steelmaking. Depth and diameter of the depression produced by an impinging single jet or multi-nozzle jets are measured and correlated successfully with dimensionless momentum flow rate number. The equations are represented in the form of a nomogram by which the depth and diameter of the depression in a molten steel bath during the blow can be determined from easily available top blowing parameters.     

孔排射流冲击换热过程数值模拟研究及结构优化

运用数值仿真技术对带钢连续热处理快速冷却过程中的孔排射流冲击换热进行了三维数值模拟,主要研究了几何参数对射流冲击传热特性的影响规律。在研究的参数范围内,获得了孔排射流冲击换热装置的最优结构。分析表明:展向孔间距S2的影响最为显著,其次是流向孔间距S1,板间距H的影响作用最小。     

Dynamic behavior of a liquid/liquid interface at an oscillating wall

The dynamic behavior of the meniscus between two liquids has been investigated experimentally using mercury and silicon oil and theoretically by solution of the equations of motion applying the marker and cell (MAC) method. The liquids were contained in a plexiglass tube which could be moved relative to the liquids with constant and superposed sinusoidal velocities. Special attention was focused on the movement of the three-phase contact line (TPL) at the wall. Depending on the parameters of the motion, the TPL may be drawn above the flat part of the oil/mercury meniscus so that the normally convex contour of the meniscus disappears and a concave contour is formed. Good agreement was found between the measured and computed shapes of the meniscus.     

圆形喷口紊流冲击射流流动与传热过程数值模拟

中厚板无约束淬火主要采用上下集管圆形射流冲击冷却方式，使淬火钢板在向前行进的过程中得到冷却。本文通过建立单股圆形喷口紊流冲击射流流动与传热过程数学模型，对单股射流冲击热钢板的射流流场、温度场、压力场和自由液面进行了数值模拟，得到了冲击射流各物理场的变化规律及钢板表面的换热特性。数值计算结果不仅为钢板淬火过程的温度场模拟、热应力应变场模拟提供了较为准确的换热边界条件，也为优化钢板淬火控冷工艺、保证钢板淬火质量提供了坚实的理论基础。     

An experimental study on the behaviour of an underexpanded supersonic gas jet

The velocity decay and radial spreading characteristics of an underexpanded supersonic jet have been determined by a hot film anemometer. It is shown that the axial velocity in the subsonic portion of an underexpanded jet decays exponentially in a way similar to that of a fully expanded gas jet.     

高雷诺数射流冲击对流系数的计算及数值分析

为了确定高雷诺数条件下射流与挡板之间的换热系数,采用理论分析和数值计算的方法,建立流场模型,分析流场各物理量的基本规律、流动特性和对流传热系数分布规律,并与已有实验数据进行比较。结果表明:驻点附近,流体与壁面之间的对流换热系数较低;板面上,随着到驻点的距离增大,对流换热系数增大并出现峰值然后降低,峰值出现在约0.2倍扩散半径处。数值计算与理论分析得到的换热系数较为接近。     

Machines employing a hot gas jet to cut metals and nonmetallic materials

Energomash UNPTs. Translated from Metallurg, No. 11, pp. 29–32, November, 1994.     

The movement of particles in liquid metals due to gravity

The buoyancy of a single crystal copper cube in a lead tin melt was examined. A neutral buoyancy melt density of 8828 Kg/m³ at 250 °C was obtained which corresponds to a copper density of 8930 Kg/m³ at 20 °C. The copper cube was found to change from a floating to sinking position with changes in melt density of 1 Kg/m³. Contact with the crucible walls or meniscus prevented the copper cube from moving under buoyancy forces resulting from density differences as high 12 Kg/m³. This is attributed to surface tension forces at the points of contact of the copper, melt, crucible wall, and meniscus. Very small density variations in the copper due to micro-porosity and other imperfections was found to have a very large effect on the movement of the copper under buoyancy forces. In experiments in which grains of tin in partially solidified pure tin were allowed to settle under controlled conditions, it was found that many grains appeared to be separated from neighboring grains. In addition, regions clear of grains were observed in the settling region. It is suggested that this results from clumping of the grains and bridging of the clumps as they settle in the melt.     

Studies of left-ventricular function in anemia due to beta-thalassemia

Left-ventricular (LV) function was studied in 23 patients with anemia due to beta-thalassemia, of whom seven had thalassemia intermedia and the remainder thalassemia major. Two-thirds of the patients wih thalassemia intermedia and almost all the patients with thalassemia major were in clinical congestive heart failure. Despite this, resting measurements of ventricular size and systolic ventricular function were normal, indicating high-output cardiac failure. However, effort testing showed a flat response or decrease in the LV shortening fraction in patients with thalassemia major, and serial studies showed a decrease in the shortening fraction over a 4-yr period in some patients. LV diastolic function was studied by calculating peak LV filling rate and the pattern of LV filling in early diastole. Three patient with thalassemia major showed a pattern indicating abnormal LV distension. Since LV end-diastolic dimension was increased, volume overload was present in all patients. The results indicate that the following factors contribute to the genesis of cardiac failure in beta-thalassemia: 1) diminished response of systolic ventricular performance to exercise and later at rest; 2) ventricular volume overload; and 3) abnormal ventricular distension in diastole. Although the ventricular filling suggests abnormal LV compliance, the effect of right-ventricular volume overload or a pericardial factor cannot be excluded.     

Liquid-solid mass transfer from a wall in contact with a gas/liquid interface undergoing wave motion

Experimental data are presented for mass transfer from a discrete area on a vertical wall near an air/water interface undergoing wave motion. The local mass transfer rate near the interface was found to be well correlated by Sh=Re ₀ ^0.5 Sc^1/3, which is much higher than that for a steady unidirectional flow over a flat plate with the same mean velocity considering the contact time between the wall and the liquid. Visualization studies showed that the high local mass transfer rate was related to the periodic renewal of the boundary layer near the wall and the extremely high initial mass transfer rate during the establishment of a new concentration field.     

液气组合雾化过程的多相流动研究

在液气组合雾化过程中,当雾化器上端存在正压时,易造成钢液堵塞,影响雾化的正常进行。本文采用数值模拟的方法,针对液气组合雾化中空气-水-模拟钢液3相流动过程展开研究。结果表明:在液气组合雾化过程中,水流入射夹角决定了雾化器上端抽吸正压力的存在;通过对比不同水流入射夹角下中心线上的空气流速和负压区域的大小,得到使该液气组合雾化过程达到最佳雾化效果的水流入射夹角为45.0～50.0°。     

转炉顶吹气体射流的冲击特性

 利用Fluent软件研究了转炉炼钢不同枪位条件下的顶吹气体射流特性,并与理论计算结果对比分析。发现单孔氧枪数值模拟的冲击深度小于理论计算值、冲击面积大于理论计算值,且随着枪位的提高,冲击深度差值变小,冲击面积差值变大。在此基础上,研究了100 t转炉采用4孔超音速氧枪的射流冲击特性,发现当枪位为1.0 m时,冲击深度为0.21 m,冲击面积仅为1.328 m2,与计算值相差较大;当枪位提高至1.5 m时,冲击深度模拟结果为0.12 m,计算值为0.83 m,冲击面积模拟结果和计算值相差增大。     

An analytical model for the interaction between an insoluble particle and an advancing solid/liquid interface

In this article, the behavior of particles in front of an advancing solidJliquid interface was analyzed. In the analytical model presented, the critical velocity for the transition from particle pushing to engulfment by the interface was calculated as a function of relevant material parameters and processing variables. In particular, the effect of the difference in the thermal properties of the particle and the matrix on the particle/interface interaction was examined. It was demonstrated that the presence of particles could destabilize the interface which, in turn, affected the behavior of particles at the interface. Based on the analysis, a particle behavior map was constructed to illustrate the complex particle behaviors in different material systems under various growth conditions. Theoretical predictions were compared against experimental results obtained in transparent organic materials as well as in metallic systems. The relevance of these observations to the melt processing of particulate-reinforced metal matrix composites (MMCs) was discussed. Formerly Assistant Research Engineer, The University of Alabama, is now Manufacturing Engineer