双喷嘴喷射成形柱状坯传热过程模拟

利用移动边界条件,对双喷嘴喷射成形柱状坯不同时刻热过程做出了表征,模拟了两组不同工艺参数下得到沉积坯的传热过程.研究结果表明,稳定生长条件下得到的柱状沉积坯除底部区域外各处温度比较均匀,且温度随时间变化趋势相似,可得到整体性能良好的沉积坯;非稳定生长条件下得到的沉积坯除中心区域外其余各处温度相差较大,顶部和底部冷却速度明显大于中心部分,得到沉积坯整体性能较差.利用数值模拟方法可以理解喷射沉积动态热过程,有效优化沉积工艺,对获得优质沉积材料具有一定指导意义.     

喷射成形生产圆管坯复合材料的沉积及传热过程模拟

运用数学模型及计算机模拟技术,对喷射成形法生产圆管坯复合材料过程中的沉积和传热过程进行了模拟研究.采用多道次往返反复沉积的方法,在控制喷射速度和管坯运行速度的条件下,可以形成均匀稳定的圆管坯复合材料.传热过程采用跟踪沉积过程外界面的方法,得到了不同沉积厚度情况下圆管坯和基体材料的温度分布情况,以及圆管坯内的凝固情况和冷却速度.     

喷射成形沉积坯凝固过程和温度场的数值模拟

结合沉积坯的实际沉积过程,利用跟踪计算沉积坯表面轮廓线坐标而建立沉积坯形状的预测模型,模拟结果与实验基本吻合,表明该方法可以获得较合理外形的沉积坯;使用有限元分析方法,对沉积坯动态凝固过程做出了表征,并对其温度场做出数值模拟,结果表明,利用数值模拟方法可以理解喷射沉积动态凝固过程,有效优化沉积工艺,对获得优质沉积材料具有一定指导意义.     

金属喷射成形过程的数学模型

应用数学模型模拟了金属喷射成形过程,并在宝钢的喷射成形设备上进行了测试,验证了研究结果.该过程的数学模型由4部分组成:喷射气体在沉积室中的流动、单一液滴沿其轨道的运动、大量液滴运动的概率统计分析、对喷射成形过程中沉积坯形状和温度分布的预测.在原型实验中,测定了射流中心的速度、沉积坯的形状以及沉积率.预测值和实验值吻合得较好.     

喷射沉积坯GCr15合金致密化研究

利用Gleeble1500模拟实验机对喷射沉积坯GCr15进行了致密化处理.通过正交实验,研究了变形温度、变形速度、变形量和升温速度对试样致密化效果Y的影响,其中致密化效果通过密度、晶粒度、晶粒均匀度3个指标综合测评,结果表明,变形温度显著影响喷射沉积坯GCr15的致密化效果,致密化优化条件为:升温速度10℃/s,变形温度850℃,变形量60%,变形速度0.1mm/s.经优化工艺处理后,喷射沉积坯致密化效果得到改善:相对密度增加了12.31%,晶粒度降低了79.27%,晶粒均匀度增加了24.8%.     

3D挤出吹塑型坯吹胀的数值模拟

采用超弹本构模型对挤出吹塑型坯吹胀进行了3D数值模拟，得到了型坯在吹胀过程中的型坯轮廓曲线分布以及吹胀完毕时的型坯壁厚分布，模拟的结果与文献的实验结果相吻合；探讨了材料的性能、初始条件和吹胀压力等工艺条件对吹胀完毕后的壁厚分布影响，这为在实际生产获得最佳的加工工艺参数提供了依据。     

喷射电沉积枝晶生长数值模拟及实验研究

介绍了喷射电沉积的基本原理,并根据喷射电沉积原理对凝聚扩散模型进行了改进,对电铸过程中的二维枝晶生长过程进行了数值模拟,并进行了实验验证.结果表明,利用改进的凝聚扩散模型模拟得到的粒子簇与实验获得的枝晶相似度较高,用该模型来说明枝晶的生长规律是真实的、可靠的.随着粒子相对运动速度的加快,得到的粒子簇的形貌由疏松分枝逐步发展为致密结构;在不同的粒子数目模拟枝晶图中表现出了明显的屏蔽效应;结合概率越小,粒子越容易进入内层生长点,使枝晶结构较致密;喷射高度对枝晶形貌的影响没有明显规律,波动性很强.     

聚合物熔体在纺黏非织造牵伸器中的气流牵伸模型 与数值模拟研究

介绍了有关纺黏非织造过程建模与数值求解的方法。首先在继承前人研究成果的基础上,给出了纺黏非织造过程理论模型;其次,对实际生产中应用的宽狭缝牵伸器的喷射流场进行数值模拟,求出了气流速度在牵伸器中的数值分布。通过对牵伸器喷射流场的数值模拟,得到了气流速度在流场中的数值分布,从而为聚合物熔体的气流牵伸模型求解提供了有利的条件。本研究也显示了在对纺黏非织造布工艺和设备进行计算机辅助设计方面具有较好的应用前景。     

喷射电沉积喷嘴流场的数值分析

用ANSYS软件对喷射电沉积喷嘴流场进行分析.将解析结果以可视化的速度场给出,从而针对喷嘴过流特性的分析结果,对喷嘴的结构进行改进.在实验中利用自行研制的喷射电沉积装置电沉积镍.结果表明,结构改进后,明显减小了压力损失,提高了喷嘴的轴向速度,电镀液冲击镀件的冲击力得到提高,有效地减少了扩散层的厚度,改善了电沉积过程,而且使镀层组织致密,晶粒细化,性能得到提高.     

冷轧Q195L钢带鱼鳞状掉皮缺陷成因分析

结合SEM及EDS、金相分析、数值模拟方法研究了冷轧Q195L钢带冷轧过程中出现的鱼鳞状掉皮现象.试样检测表明,非金属夹杂物和氧化铁共同作用导致这种缺陷,前者来源于钢水夹杂驱除不净或保护渣卷渣,后者根源在于连铸坯内部裂纹发生脱碳氧化,最终在冷轧中暴露于表面.数值模拟表明,铸坯角部裂纹发生在结晶器内,钢水开始浇注的前6s内铸坯角部降温速率为124.9℃/s,凝固收缩速率达0.07mm/s.凝固前裂纹指数呈增长趋势,在凝固末端达0.75,伴随疏松与缩孔形成中心裂纹;凝固坯壳内从近表面到距离边部41mm处裂纹指数均出现过大于1的情况,中间裂纹形成于此,铸坯二冷II段内回温会导致中间裂纹沿弱化的柱状晶晶界扩展.     

A 1D model for the description of mixing-controlled inert diesel sprays

The paper reports an investigation focusing on the transient evolution of diesel sprays. In order to understand the relationship between fuel–air mixing and spray penetration, a one-dimensional spray model is developed, which is capable of predicting the spray behaviour under transient conditions. The main assumptions of the model are the mixing-controlled hypothesis and the validity of self-similarity for conservative properties. Validation of such concepts is achieved by comparing model predictions with both CFD gas jet simulations and experimental diesel spray measurements. Results show that a reasonable estimation of the spray evolution can be obtained for both non-vaporising and vaporising conditions.     

Experimental investigation of the elastoplastic response of aluminum silicate spray dried powder during cold compaction

Mechanical experiments have been designed and performed to investigate the elasto-plastic behaviour of green bodies formed from an aluminum silicate spray dried powder used for tiles production. Experiments have been executed on samples obtained from cold compaction into a cylindrical mould and include: uniaxial strain, equi-biaxial flexure and high-pressure triaxial compression/extension tests. Two types of powders have been used to realize the green body samples, differing in the values of water content, which have been taken equal to those usually employed in the industrial forming of traditional ceramics. Yielding of the green body during compaction has been characterized in terms of yield surface shape, failure envelope, and evolution of cohesion and void ratio with the forming pressure, confirming the validity of previously proposed constitutive models for dense materials obtained through cold compaction of granulates.     

Role of the scaling factor in the process of SHS extrusion based on the example of a TiC + Co system

The effect of the scaling factor (the influence of the height and diameter of the initial cylindrical billet) on the temperature distribution in a material and on the completeness of the extrusion of long samples obtained the method of self-propagating high-temperature synthesis (SHS) extrusion has been theoretically studied. A numerical analysis has been carried out based on the mathematical simulation of the thermal conditions of the SHS extrusion process. It has been shown that the change in the scaling factor significantly affects the length and quality of extruded rods due to the uniformity of the temperature field. It has been found that there is a limiting value for the diameter of the initial billet above which material is hardly squeezed out of the camera.     

Monte Carlo simulations to determine coating uniformity in a Wurster fluidized bed coating process

This paper presents a coating model to predict the mass coating uniformity in a Wurster fluid bed coater using a Monte Carlo method. The velocity and voidage data obtained using imaging techniques on the same Wurster coater are used as inputs to the model. The semi-circular Wurster fluid bed used in this work was 22.9 cm in diameter. A batch of 3.6 kg tablets was used to conduct coating experiments and the coating weight gain distribution results were compared to predictions from the simulation. The model rigorously considers the sheltering effect of particles as they move in the spray zone. Good agreement was obtained when comparing the results with an analytical model.Spray shape and orientation of discretization were found to play an important role in predicting the coating uniformity. A simple spray experiment in a particle-free bed showed that the direction of spray material, in general, was vertically upward. Simulation results confirmed that an upward cylindrical spray model gives better agreement with experimental results compared to a solid cone spray model. Finally, the model was used to predict the changes in coating uniformity with bed operating conditions such as gas velocity and gap height. A wider coating distribution was found for the case with the lower gas velocity and gap height.     

Modeling and prediction of morphology and crystallinity for cylindrical‐shaped crystals during polymer processing

To describe and predict the crystallization and morphology evolution of semicrystalline polymers, the shape of crystals is often modeled as spheres and/or cylinders. The Kolmogoroff–Avrami model, which is often used to model the crystallinity and spherulite growth of polymer materials under isothermal and nonisothermal conditions, has shortcomings in dealing with conditions when spherulites and cylindrical crystals form simultaneously. This study adopted the Monte Carlo method, a method based on the random theory, to model and predict the morphological evolution of crystallization and the degree of crystallinity for polymers that exhibit concurrently growing spherulites and cylindrical crystals. A case study on predicting the morphology and crystallinity of a solidifying polymer melt with the memory effect (self‐seeding) from prior stretching is presented. The effectiveness of this Monte Carlo approach vs. the original Kolmogoroff–Avrami model was demonstrated when compared with experimental results. In addition, for the ideal cylindrical growth of crystals, a modified Kolmogoroff–Avrami model based on the Monte Carlo method solutions is proposed to predict the crystallinity without intensive computation. The results showed that the modified expression performs better than the original Avrami prediction. POLYM. ENG. SCI., 2010. © 2010 Society of Plastics Engineers     

Identification of thermal zones and population balance modelling of fluidized bed spray granulation

Air temperature measurements in a fluidized bed of glass beads top sprayed with water showed that conditions for particles growth were fulfilled only in the cold wetting zone under the nozzle which size and shape depended on operating conditions (liquid spray rate, nozzle air pressure, air temperature, and particles load). Evolution of the particle size distribution during agglomeration was modelled using population balance and representing the fluidized bed as two perfectly mixed reactors exchanging particles with particle growth only in the one corresponding to the wetting zone. The model was applied to the agglomeration of non-soluble glass beads and soluble maltodextrin particles spraying respectively an acacia gum solution (binder) and water. Among the three adjustable parameters, identified from experimental particle size distributions evolution during glass beads agglomeration, only one describing the kinetics of the size distribution evolution depended on process variables. The model allowed satisfying simulation of the evolution of the particle size distribution during maltodextrin agglomeration.     

EFFECT OF SPRAY MIXING ON TRAY EFFICIENCY I. One Dimensional Mixing

The usual models for predicting the effect of liquid mixing assume a diffusion model as is reasonable for the foam and froth regimes. Here a one-dimensional spray regime model is developed with finite spray “throw,” allowing for inlet and outlet conditions and the effect of spray mixing on tray efficiency is evaluated. The extension to less restricted models is indicated.     

EFFECT OF SPRAY MIXING ON TRAY EFFICIENCY I. One Dimensional Mixing

The usual models for predicting the effect of liquid mixing assume a diffusion model as is reasonable for the foam and froth regimes. Here a one-dimensional spray regime model is developed with finite spray “throw,” allowing for inlet and outlet conditions and the effect of spray mixing on tray efficiency is evaluated. The extension to less restricted models is indicated.     

Numerical modeling of an evaporative spray in a riser

A numerical model is developed for modeling the evaporative spray in a hot gas-solid flow. Phenomenological sub-models for the interaction between the cold evaporative spray droplets and hot particles, including momentum exchange, heat and mass transfer, are proposed based on previous experimental and numerical studies in the literature. Simulation of an evaporative water spray through a hollow cone spray nozzle in a riser operated at an elevated temperature is conducted. Comparison with available experimental measurements in terms of the spray expansion and spray width is performed, and reasonable agreement is obtained. The effect of various parameters introduced into the model is investigated in parametric studies, and appropriate values for those parameters are suggested. In addition, influences of various operating conditions including droplet size, bed temperature, and spray angle are evaluated.