Mathematical Modeling of VOD Oxygen Nozzle Jets

This study has focused on numerically exploring the oxygen flow in the convergent‐divergent De Laval nozzle. The De Laval nozzle has been commonly used as oxygen outlet at the lance tip in the vacuum oxygen decarburization (VOD) process. The nozzle geometry used in an active VOD plant was investigated by isentropic nozzle theory as well as by numerical modeling. Since an optimal nozzle design is only valid for a certain ambient pressure, one VOD nozzle will be less efficient for a large part of the pressure cycle. Different ambient pressures were used in the calculations that were based on the De Laval nozzle theory. Flow patterns of the oxygen jet under different ambient pressures were studied and the flow information at different positions from the nozzle was analyzed. In addition, the study compared the effects of different ambient temperatures on jet velocity and dynamic pressure. The predictions revealed that the modeling results obtained with the CFD modeling showed incorrect flow expansion, which agreed well with the results from the De Laval theory. Moreover, a little under‐expansion is somewhat helpful to improve the dynamic pressure. The jet dynamic pressure and its width for the specific nozzle geometry have also been studied. It has been observed that an altering ambient pressure can influence the jet momentum and its width. In addition, a high ambient temperature has a positive effect on the improvement of the jet dynamic pressure.     

聚合射流氧枪射流特性的实验研究

利用带有中心主孔的Laval喷管和16个副孔的聚合射流氧枪喷头的氧枪射流检测系统研究氧枪射流中心速度的衰减规律,测试常温氦气代替高温燃烧的保护气体作为伴流而产生的聚合射流,以及高温以主孔通空气,两副孔分别通入氧气和丙烷来产生保护气体模拟的聚合射流。结果表明,聚合射流特性优于传统射流特性,常温下随氦气入口压力增加,中心射流的轴向衰减变缓,获得比传统超音速射流更长的超声速区域;高温下通过调节燃气和氧气流量可改变环状火焰长度,同时可以根据生产实际情况变化主射流长度,满足冶炼工艺要求。     

Effect of shrouding Mach number and ambient temperature on the flow field of coherent jet with shrouding Laval nozzle structure

The coherent jet technology was widely used to improve the stirring effect of molten bath in steelmaking field, and the key to this technology was to form a low-density zone around the main oxygen jet by a high-temperature shrouding flame. With this revelation, a shrouding nozzle was processed to a Laval nozzle structure fitted with a loop arrangement for increasing the velocity of shrouding jet. For further increasing the area of the low-density zone, the preheating method was also adopted in this new coherent lance structure. In this paper, the effect of Mach number of the shrouding nozzle on the flow field of the coherent jet was investigated at room and high ambient temperature using numerical simulation and experimental studies. The result represented the simulation model used in this research showed good agreement with the experimental data at the texted conditions. Although the shock wave formed by the shrouding jet removed more kinetic energy form the main oxygen jet, the impaction ability of the coherent jet was much bigger than that of conventional supersonic jet, and this phenomenon would be further strengthen if ambient temperature and Mach number of the shrouding nozzle increases.     

完全膨胀的目标设计改进喷砂枪喷管

为改变普通喷砂枪效率低下只适用于处理小型工件的现状,运用 CFD 方法系统计算了 Laval 喷管和同口径 普通收缩喷管的流场,提出并论证了以完全膨胀状态气流为目标的 Laval 喷管设计观点。以提高喷气速度和超声 速气流长度为有效途径提高喷砂枪效率。     

激波在转炉炼钢中的应用

激波是超音速气流中液体属性的不连续面,气流通过激波时速度下降,温度和压强升高。氧气转炉炼钢的氧气是通过拉瓦尔管以超音速射流状态吹入转炉。在氧枪喷头设计和制定供氧制度时要减小激波损失。在转炉的某些特殊吹炼工艺中要把激波控制在适当范围内,以取得良好的冶金效果。     

预热温度对超音速氧气射流特性影响的数值模拟研究

超音速氧气射流特性是影响金属冶炼的重要因素之一。相同条件下,超音速氧气射流的特性会受到喷管入口氧气预热温度的影响。通过数值模拟的方法研究了不同预热温度条件下超音速氧气射流的特性,并与文献值进行了对比分析。结果表明：不同预热温度条件下,超音速氧气射流的速度,温度和压力沿轴向分布趋势相同,首先保持稳定,然后不断地衰减,最终趋于环境参数;与低预热温度相比,高预热温度条件下的超音速氧气射流的出口速度,温度和压力较大;随着预热温度的提高,射流的密度变小,导致射流稳定段的长度有所减小。     

超音速氧枪射流特性的数值模拟

利用GAMBIT建立了轴向计算长度2 200 mm和径向计算长度800 mm的超音速氧枪的数学模型,并采用FLUENT软件对氧枪射流特性进行数值仿真研究。分析了单孔氧枪超音速射流特性,以及操作压力(0.6~1.0 MPa)和环境温度(298~1 873 K)对流动特性的影响。结果表明,入口滞止压力在设计压力±25%内对射流轴向衰减及径向扩展影响不大,其与射流的超音速区长度呈二次曲线关系变化,随环境温度升高,射流轴向衰减变缓慢,核心区长度增加,超音速区长度和环境温度呈线性关系,环境温度对射流径向影响很小。     

环氧温度对超音速主射流特性的影响

超音速氧气射流喷吹工艺是炼钢过程的重要技术,通过在主氧周围增加环状高温伴随流是改善主氧射流特性、提高冶炼效率的重要途径。通过数值模拟的方法研究集束射流条件下环氧温度对超音速氧气射流特性的影响。研究结果表明,高温环氧可抑制超音速主射流速度的衰减,环氧温度越高,速度衰减越慢,射流核心区长度明显延长;不同环氧温度下,主射流温度均呈现先增大后减小的趋势,环氧温度的升高使得主射流温度的快速增长受到抑制;环氧在主射流周围形成高温低密度区域,将主射流与环境介质隔离,延缓主射流与周围介质的掺混,对主射流起到封套作用。     

Computational Fluid Dynamics Simulation of Supersonic Oxygen Jet Behavior at Steelmaking Temperature

Supersonic oxygen jets are used in steelmaking and other different metal refining processes, and therefore, the behavior of supersonic jets inside a high temperature field is important for understanding these processes. In this study, a computational fluid dynamics (CFD) model was developed to investigate the effect of a high ambient temperature field on supersonic oxygen jet behavior. The results were compared with available experimental data by Sumi et al. and with a jet model proposed by Ito and Muchi. At high ambient temperatures, the density of the ambient fluid is low. Therefore, the mass addition to the jet from the surrounding medium is low, which reduces the growth rate of the turbulent mixing region. As a result, the velocity decreases more slowly, and the potential core length of the jet increases at high ambient temperatures. But CFD simulation of the supersonic jet using the k−ε turbulence model, including compressibility terms, was found to underpredict the potential flow core length at higher ambient temperatures. A modified k-ε turbulence model is presented that modifies the turbulent viscosity in order to reduce the growth rate of turbulent mixing at high ambient temperatures. The results obtained by using the modified turbulence model were found to be in good agreement with the experimental data. The CFD simulation showed that the potential flow core length at steelmaking temperatures (1800 K) is 2.5 times as long as that at room temperature. The simulation results then were used to investigate the effect of ambient temperature on the droplet generation rate using a dimensionless blowing number.     

Simulation of Gas Flow Field in Laval Nozzle and Straight Nozzle for Powder Metallurgy and Spray Forming

Gas flow field in nozzles and out of nozzles was calculated for Laval orifice and straight orifice nozzles. The results showed that the flow generated by the Laval nozzle had a higher exit velocity in the vicinity of the nozzle, in comparison with that of the straight nozzle, that is to say, a Laval nozzle was more efficient than a straight one in disintegrating the melt stream and was apt to produce finer powders. The flow generated by the Laval nozzle was less convergent and the velocity gradient along the radial direction was more moderate than that of a straight nozzle, which could contribute to a broad distribution of melt particles. According to their flow characteristics, the Laval nozzle was reckoned as a better choice of producing larger spray-formed billets.     

环境压力对超音速氧气射流特性影响的数值模拟

超音速氧气射流技术是炼钢精炼过程中的重要环节,关于常压条件下超音速氧气射流的特性已进行了大量的研究,但对真空精炼过程中低压环境下的超音速氧气射流特性目前研究较少。通过数值模拟的方法研究了不同环境压力条件下超音速氧气射流的特性,并与试验结果进行了对比分析。研究结果表明：低压环境条件与高压环境条件相比,超音速氧气射流速度的衰减受到抑制,射流核心段的长度得到延长;不同环境压力条件下,射流压力与射流速度分布趋势一致,均沿轴向不断降低,但压力衰减程度大于速度衰减的程度;不同环境压力条件下,氧气射流的温度随着氧气射流的扩散不断升高,最终趋于环境温度。     

Effect of oxygen flow rate and temperature on supersonic jet characteristics and fluid flow in an EAF molten bath

A new operation method for the oxygen lance of an electric arc furnace (EAF) was proposed, meeting the simultaneous demand for low oxygen flow rate and high stirring power in a particular smelting stage. When the oxygen flow rate needs to be reduced, the stirring power of the jet can be improved by increasing oxygen temperature properly. Free supersonic jet characteristics at different flow rates and stagnation temperatures were studied by numerical simulation and validated by a jet measurement experiment. The results showed that the designed Mach number can be maintained by coupling adjustment of flow rate and stagnation temperature. Meanwhile, a three-phase, full-scaled numerical model for a commercial 75t EAF with three oxygen lances on the side-wall was established to study the fluid flow in the molten bath. The velocity distribution, cavity profile and total kinetic energy of the EAF bath induced by the impingement of supersonic jets onto the liquid bath were discussed and compared. It was found that the fluid flow characteristics of the EAF molten bath can be improved even if the oxygen flow rate was reduced as long as the oxygen temperature could be increased reasonably.     

不同形状拉伐尔喷嘴中气流行为的研究

在考虑不同形状收缩段的基础上，建立描述不同形状拉伐尔喷嘴中沿喷嘴长各部气流行为的数学模型。数值计算表明，气体速度随入口段曲率半径的增大而增大，拉伐尔喷嘴和长度则随曲率半径的增大而减小。本数学模型可为不同形状超音速氧枪的设计提供理论依据。     

Characteristics of Flow Field for Supersonic Oxygen Multijets with Various Laval Nozzle Structures

Metallurgical and Materials Transactions B - The Laval nozzle is used widely in steelmaking processes to increase the velocity of an oxygen jet up to approximately 2 Mach numbers. The present...     

超音速射流流场中湍流模型

为了确定适用于超音速射流流场数值模拟的湍流模型,首先从理论上分析常用的五种湍流模型之间的差异及其适用范围;其次,采用五种湍流模型,分别对不同马赫数下超音速射流流场进行数值模拟,将数值模拟结果与实测值和理论值进行对比分析.结果表明:剪切压力传输k-ω模型与其他模型相比,通过对输运方程的修正,保证其在计算射流流场时具有较高的准确性;在喷管内部和外部射流流场的模拟中,剪切压力传输k-ω模型的计算结果与理论值和实测值具有较高的吻合度,在五种湍流模型中最适合于超音速射流流场的数值模拟研究.      

环境温度对超音速氧气射流特性影响的数值模拟

通过数值模拟的方法研究了不同环境温度条件下超音速氧气射流的特性,并与前人的实验结果进行了对比分析.研究结果表明:与低温环境条件相比,高温环境条件下超音速氧气射流的速度衰减受到抑制,射流核心段长度得到延长;不同环境温度条件下,氧气射流的温度随着氧气射流的扩散不断升高,最终趋于环境温度;射流的压力分布趋势与射流速度分布趋势一致.数值模拟得到的射流速度、温度和压力结果与实测值吻合度较高.      

Computational Fluid Dynamics Modeling of Supersonic Coherent Jets for Electric Arc Furnace Steelmaking Process

Supersonic coherent gas jets are now used widely in electric arc furnace steelmaking and many other industrial applications to increase the gas–liquid mixing, reaction rates, and energy efficiency of the process. However, there has been limited research on the basic physics of supersonic coherent jets. In the present study, computational fluid dynamics (CFD) simulation of the supersonic jet with and without a shrouding flame at room ambient temperature was carried out and validated against experimental data. The numerical results show that the potential core length of the supersonic oxygen and nitrogen jet with shrouding flame is more than four times and three times longer, respectively, than that without flame shrouding, which is in good agreement with the experimental data. The spreading rate of the supersonic jet decreased dramatically with the use of the shrouding flame compared with a conventional supersonic jet. The present CFD model was used to investigate the characteristics of the supersonic coherent oxygen jet at steelmaking conditions of around 1700 K (1427 °C). The potential core length of the supersonic coherent oxygen jet at steelmaking conditions was 1.4 times longer than that at room ambient temperature.     

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.     

200 t转炉交错氧枪设计优化研究

以200t转炉5孔氧枪为原型,优化设计内外喷孔相同倾斜角度下不同流量配比的交错氧枪.基于射流特性仿真研究,通过数值模拟方法,分析交错氧枪喷头射流特性与传统5孔氧枪的不同,探讨内外孔流量比变化对氧枪射流轴向速度衰减和有效冲击面积的影响规律.结果 表明:交错氧枪内孔射流轴向速度大于传统氧枪,外孔的轴向速度与传统氧枪相近,但...     

低密度伴随湍流流场的仿真研究

借助商业软件Fluent,采用数值模拟的方法,分析了副孔压力0.12～0.20 MPa时中心射流轴线上速度分布,副孔压力和环境温度(300～2000 K)对射流横截面速度分布的影响,以及环境温度对中心射流轴线上速度衰减规律的影响。结果表明,中心射流在高温低密度伴随流保护下,可显著减少对周围介质的卷吸量,更大程度减缓轴线上速度衰减,使核心区长度明显增加。