整体钢锭模生产锻造钢锭工艺的试验研究

根据凝固理论，采用整体钢锭镶绝热冒口套生产锻造镇静钢锭。整体钢锭模解决了钢锭悬挂裂纹问题，减少两道操作工序，防止了穿钢包模现象的发生，绝热冒口套良好的绝热保温性能使冒口钢水冒容比大大降低，提高了锭身质量，节约大量钢水。     

钢锭系统热送热装热过程数学模型的研究

在全面系统分析了某公司钢锭热送热装系统热过程传热机理的基础上,建立了钢锭冷却、加热过程二维传热数学模型。并采用交替隐式TDMA法对所建立的数学模型进行了数值求解。利用现场的实测数据对所建立的数学模型进行了对比分析计算,模型计算值和实测值的最大相对误差仅为2．46％,完全满足工程应用的要求,证明所建模型是正确可信的,可以作为计算机在线控制的理论基础。     

炉内钢锭热应力计算的数学模型

具有多段温度场的炉内钢锭应力计算问题的解决，取决于钢锭内热过程的数学模拟水平。研究目的在于对在炉内运动着的分段加热的钢锭建立三维数学模型。计算以非耦合准静态弹性理论为基础。首先确定研究对象的温度场，即求解三维傅里叶导热微分方程；其次按线性弹性理论计算应力。介绍了详细计算过程，并举有计算实例，研究成果可以用来对炉内复杂形状的料坯加热过程编制工业加热制度的优化算溃．图3参4     

高品质钢锭生产质量控制研究

通过钢水质量控制、凝固过程控制及退火工艺优化等研究,实现了钢中合金含量的窄成分控制、夹杂物控制和凝固结构控制,改善了钢锭的纯净度、组织均匀性和性能稳定性,稳定了生产过程控制、提高了钢锭的质量。     

电渣重熔过程中传热及凝固组织的数值模拟

在凝固传热数学模型基础上,采用正态分布形核模型和二维偏心生长模型,模拟了钢锭重新凝固过程温度场及钢锭凝固组织的生长情况.数值结果表明：电渣重熔钢锭以倒“V”形的柱状晶为主,中心和底部为等轴晶,模拟结果与实验结果符合良好.随着渣温的提高,熔池变得深且宽;随着侧壁换热系数的增大,熔池深度变浅;随着重熔速度的减小,熔池深度也逐渐变浅;较低的渣池温度、较大的对流换热系数有利于等轴晶形成,而重熔速度对凝固组织的影响不大.     

谈汽轮机转子轴颈无损检测的超标缺陷及国外对大型钢锭冶金技术的开发

电站用汽轮机服役条件日益苛刻，对核心部件汽轮机转子锻件的要求亦日趋严格。文章列举了汽轮机转子锻件进厂复验中，轴颈无损检测超标缺陷分析的典型实例。论述了轴颈缺陷与大型钢锭凝固特征与偏析的关系；介绍了国外在改进转子大型钢锭冶金质量及开发新型转子材料方面所具有的先进生产制造技术。     

第三类边界条件下环形空腔内凝固问题的研究

采用积分近似法对第三类边界条件下环形空腔内相变介质的凝固问题进行求解，得出计算凝固总时间的关系式，分析讨论内外管径比η＾＊和Ｂｉ数对凝固时间的影响。     

快速冷却条件下凝固潜热处理模型的研究

深入分析了有限差分法模拟凝固过程时，采用等效比热法处理相变潜热的原理；从理论和实际计算角度分析了快速冷却条件下常规的等效比热法会造成热量“虚增”，模拟计算结果失真的原因和影响程度；并进一步建立了快速冷却条件下凝固潜热处理的模型。计算结果表明，该模型可以充分保证模拟计算的精度和效率。     

200MW汽轮机调峰启动优化初探

从200MW汽轮机组冷态和热态启动应力的分析和计算入手论述了机组启动时间优化问题,给出了经过优化计算程序运算后的结果,对现场机组启动提供了一定的参考依据,尤其是热态启动的优化分析对现场机组两班制调峰运行具有一定的参考价值。     

两侧对流条件下平面冻结凝固相变换热分析

通过无因次分析的方法,在相界面两侧均是对流条件下,得到了平面冰层厚度和速度的时变规律、生长条件、极限厚度、温度场分布特点等重要结论,提出了凝固换热全传热系数和衰减特征时间的概念,并给出了理论公式用于换热量计算.结果表明,凝固换热是一个非稳态过程,初始阶段凝固潜热释放强化了换热,衰减特征时间之后,冰层热阻开始恶化换热效果,并最终无限趋近于一稳定状态.     

Experimental verification of immune recruitment mechanism and clonal selection algorithm applied for solving the inverse problems of pure metal solidification

In the paper an application of two immune algorithms — Immune Recruitment Mechanism and Clonal Selection Algorithm — in procedures for solving the inverse problems of pure metals solidification is presented. Discussed problems consist in reconstruction of boundary conditions (forms of the heat transfer coefficient and the heat flux) on the basis of temperature measurements. For verifying the effectiveness of investigated algorithms the experimental data obtained in the solidification of aluminum have been used. An example of applying considered procedures for determining the cooling conditions of the continuously cast ingot is also presented.     

Experimental analysis of the solidification of Sn–3 wt.%Pb alloy under natural convection

A quasi-two-dimensional solidification benchmark experiment with controlled thermal boundary conditions is proposed. The experiment consists in solidifying a rectangular ingot of Sn–3 wt.%Pb alloy using two lateral heat exchangers to extract the heat flux from one or two sides of the sample. The temperature difference between the two sides of the heat exchangers may vary from 0 to 40 K and the cooling rate from 0.02 to 0.04 K/s. This slow-cooling condition has been used to promote segregation formation. An array of fifty thermocouples placed on the corresponding sample walls is used to determine the instantaneous temperature distribution. During the solidification process, the temperature field is recorded versus time and analyzed. This makes it possible to estimate the change in temperature due to natural convection, the velocity field and the solidification macrostructure and segregation behavior. After each experiment, the segregation patterns are obtained by X-ray analysis and confirmed by eutectic fraction measurements. The local solute distribution is determined by means of induction coupled plasma analysis.     

A benchmark solidification experiment on an Sn–10%wtBi alloy

The solidification of a 90/10%wt tin–bismuth alloy has been analyzed experimentally for a 50 × 60 × 10 mm ingot. The heat flux was extracted from one vertical side of the ingot. Instantaneous temperature measurements were performed using a lattice of 25 thermocouples located on one of the large sides of the sample. The temperature versus time curve exhibits the classical pseudo-plateau as well the eutectic step. A post-mortem analysis of the samples was carried out. Solidification is almost columnar over the range of solidification rates considered. Two types of segregations are observed. X-ray analysis reveals the development of segregated channels near the cold wall. Analysis of the solute composition shows the existence of significant macro-segregations. The locations of the segregations are confirmed by the measurements of the eutectic fraction.     

Mathematical Model for Predicting Solidification and Cooling of Steel Inside Molds and in Air

A two-dimensional mathematical model is presented to describe the solidification and cooling of liquid steel. The liquid steel is poured into a mold to obtain a solid mass of desired shape, called an ingot. After cooling of the steel in the mold for some time, the mold is removed. Then the leftover ingot mass is cooled in air. This article is concerned with the above process. Nevertheless, the technique can be very applicable to other processes such as continuous casting.

Partial differential equations describing the process have been discretized using control-volume (or finite-volume) technique. The discretization equations obtained are of tridiagonal matrix form, which have been solved using the well-known tridiagonal matrix algorithm (TDMA) and the alternate direction implicit (ADI) solver. The model has been validated by measuring surface temperatures of molds and ingots using an infrared thermo-Vision scanner. This is then used to compute temperature distribution and solidification status of the ingot as a function of time and type of ingot.     

Analysis of solidification in a finite PCM storage with internal fins by employing heat balance integral method

Here, a simplified analytical model has been proposed to predict solid fraction, solid–liquid interface, solidification time, and temperature distribution during solidification of phase change material (PCM) in a two‐dimensional latent heat thermal energy storage system (LHTES) with horizontal internal plate fins. Host of boundary conditions such as imposed constant heat flux, end‐wall temperature, and convective air environment on the vertical walls are considered for the analysis. Heat balance integral method was used to obtain the solution. Present model yields closed‐form solution for temperature variation and solid fraction as a function of various modeling parameters. Also, solidification time of PCM, which is useful in optimum design of PCM‐based thermal energy storages, has been evaluated during the analysis. The solidification time was found to be reduced by 93% by reducing the aspect ratio from 8 to 0.125 for constant heat flux boundary condition. While, for constant wall temperature boundary condition, the solidification time reduces by 99% by changing the aspect ratio from 5 to 0.05. In case of convective air boundary surrounding, the solidification time is found to reduce by 88% by reducing the aspect ratio from 8 to 0.125. Based on the analytical solution, correlations have been proposed to predict solidification time in terms of aspect ratio and end‐wall boundary condition.     

A remedy for the temperature recovering method of solidification simulation

One of the methods of phase change simulation is the “temperature recovering method.” It has two main difficulties in practical application. The first one is the explicit nature of the method. The second one is the slow convergence of the solidification ratio. In this study, a method has been proposed to improve these difficulties. The method consists of two procedures. First, the solidification range is clustered into a discrete variable. A solidification ratio is sorted within a cluster as an integer variable. Second, the source term related to the change of the latent heat is reformulated into an implicit form by the “numerical linearization method” as previously proposed by the author. The benchmark test cases show that: (1) The convergence is faster, even for large latent heat cases, than the existing method. (2) The stability is independent of the time increment. © 2000 Scripta Technica, Heat Trans Asian Res, 29(5): 400–411, 2000