合金元素对20CrMnTi凝固组织影响的数值模拟

利用CA（元胞自动机）和FE（有限元）耦合模型，模拟齿轮钢中Si、 Mn、 Cr、 Ti 4种元素对连铸坯凝固组织的影响。模拟所得温度场和凝固组织跟实际数据基本吻合。在国标规定的成分范围内， Si含量增加可降低钢种液相线温度，增加形核动力，从而增加晶粒数目，细化晶粒； Ti含量可增加钢中异相形核数，从而增加晶粒数目，细化晶粒； Si， Ti含量增加还可降低枝晶尖端生长速度，从而减小柱状晶区域，扩大等轴晶区域； Mn， Cr含量变化对于钢种的液相线温度以及枝晶尖端生长速度影响不大，因此对于晶粒数目，等轴晶面积影响较小。     

真空自耗熔炼工艺参数对齿轮钢凝固组织的影响

为进一步提高Cr-Co-Mo-Ni齿轮钢材料的均匀性和细晶化,建立了直径290 mm的齿轮钢钢锭真空自耗熔炼过程三维数学模型,研究了熔炼工艺参数对钢锭凝固组织分布及晶粒大小的影响规律。结果表明：在工艺参数可调范围内,冷却强度越大,晶粒尺寸越小、数目越多,二次枝晶间距越小;熔池温度越低,晶粒的细化效果越好,二次枝晶间距也越小;降低冶炼速率,形核数目增多,晶粒尺寸减小,但对二次枝晶间距的影响较小。对齿轮钢真空自耗熔炼工艺参数优化调整后,模拟结果显示,自耗锭内部等轴晶区域增大将近一倍,晶粒尺寸得到明显细化;最大二次枝晶间距减小了4.88%,合金元素分布实现均匀化。     

电弧炉用氧技术的多相流数值模拟研究

对150 t电弧炉冶炼过程中单支氧枪供氧流量分别为500,1 450,1 800,2 000 m<'3>/h时氧气射流冲击熔池进行了三维三相流数值模拟.模拟研究表明,随着供氧流量的增加,熔池中钢液和渣液的流动速度、裸露钢液面面积及射流的冲击深度均增大.由数值模拟和水模得到的供氧流量与射流冲击深度的规律得到了很好的吻合....     

重型燃机涡轮空心叶片定向凝固数值模拟

文章采用铸造模拟软件Procast,模拟了重型燃机涡轮空心叶片的定向凝固过程,研究了不同的抽拉速度对凝固时固液界面形态及铸件微观组织的影响,得到了较优抽拉速度.模拟结果表明,随着抽拉速度减小,固液界面趋于水平,定向柱晶分布均匀,取向良好.对模拟得到的较优抽拉速度进行试验验证,制备了具有较为理想的晶粒组织的实物叶片.     

不同锭型及热负荷下均热炉内对流换热系数的模拟分析

均热炉是钢锭轧前加热过程的主要设备,其炉内的对流换热对于钢锭的加热过程有着很大的影响.文中以均热炉内对流换热过程为研究对象,通过对模拟研究得到了不同锭型在不同热负荷下加热过程中表面对流换热系数的变化情况,为钢锭加热过程工艺优化提供了基础.     

用于太阳能超临界CO2布雷顿循环的流态化颗粒换热试验与模拟

搭建30 kW浅层多级流态化颗粒换热试验台,在约1.5倍临界流化速度、换热器采用直管管束逆流形式布置时颗粒侧换热系数可达590～860 W/(m2·K).采用双欧拉流体模型对流化床内水平埋管管束换热进行数值模拟,模拟结果与试验结果偏差在10％以内.利用析因设计与线性回归模型研究颗粒粒径、颗粒导热系数和流化气体速度对流态...     

电弧炉炼钢氧枪优化布置研究

为了消除电弧炉熔池中的死区,以电弧炉熔池钢渣液为研究对象,采用CFD数值模拟软件模拟了氧枪氧气射流作用下熔池中钢液、渣液两相的速度场,通过对偏转氧枪水平角度的研究,发现氧枪形成对熔池切向方向上的冲击,使钢液水平面上形成围绕熔池中心旋转的涡流,数模研究表明,其涡流的形成促进了熔池中钢渣液的速度均匀分布,搅动熔池,加速反应,均匀成分和温度。同时,数值模拟与他人所做的水模的射流冲击深度进行了对比,两者反应出的规律一致。     

合金枝晶生长及微细界面热质传递模拟

利用元胞自动机法(CA)耦合对流和热质传递模型模拟了Al-Cu二元合金微观组织在多种影响因素下的二维生长过程,分析了枝晶凝固、微界面热质传递以及微流动等微细现象之间的相互作用,得到了单枝晶以及多个枝晶在微流作用下的生长规律。模拟结果表明:(1)枝晶凝固过程中溶质富集于生长前沿。随着枝晶生长,凝固前沿远离冷源,枝晶尖端温度逐渐增大,而浓度逐渐变小;(2)流动对于枝晶的生长有着重要影响。流动破坏了枝晶生长的对称性,下游溶质浓度大于上游,枝晶在上游方向优先生长,而在下游方向有所抑止;(3)多个枝晶生长时,枝晶彼此间有阻碍生长的作用,二次枝晶臂的形成相对减少,枝晶间几乎不存在微流动。     

小方坯帘线钢末搅参数的优化研究

以小方坯帘线钢的连铸生产为研究对象,采用ProCast商业软件根据实际生产的工艺参数建立铸坯的凝固传热模型,并利用射钉试验对模型进行校正以提高模型的准确性。结果表明,该凝固传热模型可以模拟帘线钢的连铸生产过程。根据射钉试验和数值模拟结果,对末搅位置进行改进,可发现铸坯中心缩孔等级下降,等轴晶率增大。     

椭圆管内对流换热与流动阻力特性研究

通过CFD技术,分别对5种长短轴之比的椭圆管管内湍流和层流状态时的换热与流动进行数值研究,分析了流体流动状态和椭圆管长短轴之比对换热系数与流动阻力的影响,并根据数值计算结果拟合出湍流区椭圆管管内换热系数的准则关系式,最后绘制每种类型椭圆管的局部换热系数曲线。研究结果表明:数值计算结果与实验值吻合良好;采用当量直径的方法计算椭圆管内换热系数误差较大;随着雷诺数的增加,每种类型的椭圆管管内阻力系数逐渐减小;而在相同的雷诺数下,随着长短轴之比K的增大,管内阻力系数逐渐增加;每种类型的椭圆管具有类似的局部换热特性,即长半轴两端点处局部换热系数最低,而短半轴两端点处具有最大局部换热系数。     

Simulation of Slag-Skin Formation in Electroslag Remelting Using a Volume-of-Fluid Method

A modified volume-of-fluid method is implemented in a fixed-grid, finite-volume model simulating transport phenomena, solidification, and electromagnetics. The VOF model agrees well with published results, and the complete model is used to investigate process variations in the electroslag remelting process, in which liquid metal is melted from a consumable electrode immersed in an electrically resistive slag. The molten metal sinks through the slag cap floating on the liquid metal pool while a slag skin freezes to the mold. Here a VOF tracks slag skin formation and its effects on melt rate with different current levels and ingot diameters.     

NUMERICAL SIMULATIONS OF ELECTRO-SLAG REMELTING PROCESS

Flow and heat transfer characteristics in the electro-slag remelting process (ESR) are important in manufacturing steel of good quality. An integrated numerical model is developed to compute the flow field and the temperature distribution inside ESR units with a metal pool profile which is solved simultaneously. In addition to the conservative equations of mass, momentum, energy, and turbulent properties, Maxwell's equations are employed to obtain the electromagnetic field by either AC or DC power supply. The results include the effects of power supply type, current amplitude, casting rate, and flow field patterns (laminar or turbulent) on flow and heat transfer characteristics. Different flow patterns and turbulent properties have been predicted using a pool profile close to the real one for AC and DC power supplies. The present model concludes that the casting rate and current amplitude are very effective in affecting the pool shape.     

恒渣阻恒熔速重熔高铝钛合金研究

高铝钛含量高温合金在恒渣阻恒熔速下电渣重熔，锭熔池形状变化和铝钛含量变化作了研究，找出ESR锭最佳成分段，对电极提出合理铝钛含量要求。     

Heat transfer enhancement for thermal energy storage using metal foams embedded within phase change materials (PCMs)

In this paper the experimental investigation on the solid/liquid phase change (melting and solidification) processes have been carried out. Paraffin wax RT58 is used as phase change material (PCM), in which metal foams are embedded to enhance the heat transfer. During the melting process, the test samples are electrically heated on the bottom surface with a constant heat flux. The PCM with metal foams has been heated from the solid state to the pure liquid phase. The temperature differences between the heated wall and PCM have been analysed to examine the effects of heat flux and metal foam structure (pore size and relative density). Compared to the results of the pure PCM sample, the effect of metal foam on solid/liquid phase change heat transfer is very significant, particularly at the solid zone of PCMs. When the PCM starts melting, natural convection can improve the heat transfer performance, thereby reducing the temperature difference between the wall and PCM. The addition of metal foam can increase the overall heat transfer rate by 3-10 times (depending on the metal foam structures and materials) during the melting process (two-phase zone) and the pure liquid zone. The tests for investigating the solidification process under different cooling conditions (e.g. natural convection and forced convection) have been carried out. The results show that the use of metal foams can make the sample solidified much faster than pure PCM samples, evidenced by the solidification time being reduced by more than half. In addition, a two-dimensional numerical analysis has been carried out for heat transfer enhancement in PCMs by using metal foams, and the prediction results agree reasonably well with the experimental data.     

Thermal and heat transfer characteristics in a latent heat storage system using lauric acid

The thermal and heat transfer characteristics of lauric acid during the melting and solidification processes were determined experimentally in a vertical double pipe energy storage system. In this study, three important subjects were addressed. The first one is temperature distributions and temporal temperature variations in the radial and axial distances in the phase change material (PCM) during phase change processes. The second one is the thermal characteristics of the lauric acid, which include total melting and total solidification times, the nature of heat transfer in melted and solidified PCM and the effect of Reynolds and Stefan numbers as inlet heat transfer fluid (HTF) conditions on the phase transition parameters. The final one is to calculate the heat transfer coefficient and the heat flow rate and also discuss the role of Reynolds and Stefan numbers on the heat transfer parameters. The experimental results proved that the PCM melts and solidifies congruently, and the melting and solidification front moved from the outer wall of the HTF pipe (HTFP) to the inner wall of the PCM container in radial distances as the melting front moved from the top to the bottom of the PCM container in axial distances. However, it was difficult to establish the solidification proceeding at the axial distances in the PCM. Though natural convection in the liquid phase played a dominant role during the melting process due to buoyancy effects, the solidification process was controlled by conduction heat transfer, and it was slowed by the conduction thermal resistance through the solidified layer. The results also indicated that the average heat transfer coefficient and the heat flow rate were affected by varying the Reynolds and Stefan numbers more during the melting process than during the solidification process due to the natural convection effect during the melting process.     

Modeling of transport phenomena in hybrid laser-MIG keyhole welding

Mathematical models and associated numerical techniques have been developed to investigate the complicated transport phenomena in spot hybrid laser-MIG keyhole welding. A continuum formulation is used to handle solid phase, liquid phase, and the mushy zone during the melting and solidification processes. The volume of fluid (VOF) method is employed to handle free surfaces, and the enthalpy method is used for latent heat. Dynamics of weld pool fluid flow, energy transfer in keyhole plasma and weld pool, and interactions between droplets and weld pool are calculated as a function of time. The effect of droplet size on mixing and solidification is investigated. It is found that weld pool dynamics, cooling rate, and final weld bead geometry are strongly affected by the impingement process of the droplets in hybrid laser-MIG welding. Also, compositional homogeneity of the weld pool is determined by the competition between the rate of mixing and the rate of solidification.     

Parametric study of multi-splat solidification/remelting including contact resistance effects

Solidification and remelting behavior of a series of deposited splats is investigated through numerical modeling. The non-perfect thermal contact at the interface between the splat and the substrate surface is accounted for by introducing a heat transfer coefficient. The effect of the interfacial thermal contact resistance as well as the effect of splat solidification parameters such as splat superheats, splat thickness, substrate temperature and splat deposition frequency on the resulting remelting depth of the previously solidified layer are discussed. Numerical results show that in the absence of thermal contact resistance between the splat and substrate interface, the remelting depth is underestimated. It is also found that the remelting depth increases for either an increase in substrate temperature or increasing splat thickness. In addition, the findings in the present study imply that in some practical applications, decreasing the deposit frequency would be a valid method to ensure the constant remelting thickness for depositing layers.     

蓄能互联热泵系统相变装置熔化与凝固过程特性分析

介绍了一种新型的蓄能互联热泵系统。利用数值模拟的方法对填充石蜡C17的球型蓄热单元的熔化与凝固过程进行研究,分析了球壁温度、相变单元尺寸和相变材料初始温度三种影响因素对熔化过程和球壁温度对凝固过程的影响。通过对两个过程对比发现相变单元尺寸对相变过程影响最大,在相同温差条件下完全熔化时间少于完全凝固时间,熔化过程中始终存在的石蜡-壁面与液相石蜡-固相石蜡之间的对流换热过程增加了熔化速率。