微界面扩散过程对二元合金凝固过程数值模拟的影响

针对反向凝固工艺实验研究的传热传质现象，进行了数值模拟，讨论分析了微界面质扩散过程对二元合金凝固过程数值模拟的影响。结合实验数据，认为微观偏析模型的选择对新生相生长的影响不可忽略。     

枝晶尺度溶质再分配对连续铸造凝固过程的影响

阐述了凝固微细尺度结构上的溶质再分配与宏现尺度传热传质现泉之问的关联，总结比较了多种徽现健析模型，并针对反向凝固工艺和传统的薄板坯连铸连轧(CSP)工艺的传热传质现泉进行了数值模拟，与实验数据进行对比分析。结果表明，微细尺度固—液相界面上的溶质再分配对凝固宏观传输过程的影响不可忽略。     

燃煤链条炉排工业锅炉燃烧数值模型研究

针对燃煤链条炉排工业锅炉的燃烧过程中床层内部存在复杂的传热、传质及物理化学反应过程等特点开发了三维床层和炉膛耦合的燃烧数值计算模型,模型包含了煤燃烧过程中水分蒸发、挥发析出、气相反应、焦炭燃烧和传热传质等基本的化学物理过程,同时考虑了大粒径煤颗粒内部的非等温传热特性,并通过实验测试与数值模拟对数值模型进行校核,实验结果与模型计算吻合得较好,从而验证了计算模型的准确性。燃煤链条炉排工业锅炉燃烧数值模型的建立为实现燃煤工业锅炉的优化设计和运行指导提供了先进的设计手段和理论支持。     

埋地原油管道停输期间温降及原油凝固传热模型及数值模拟

假设原油凝固区域为一固相和液相组成的动态多孔介质区域,建立了土壤、管道能量方程与原油质量、动量和能量方程相互耦合的传热模型,并对埋地原油管道停输温降过程进行了数值模拟.数值模拟结果能够合理解释停输期间温度场、凝固界面和自然对流规律.     

含湿毛细多孔介质湿区相变传热传质干燥三方程模型

含湿毛细多孔介质的干燥过程是复杂的相变传热传质过程。该过程涉及渗流、扩散、传热、毛细效应和相变等机理，建立了含湿毛细多孔介质湿区干燥过程相变传热传质数学模型，采用全隐式有限差分方法对一维模型进行了数值计算。得到了含湿毛细多孔介质湿区干燥过程中的液相饱和度、温度和混合气体压力的变化，并分析了该计算结果。     

涡轮薄层污泥干化的热质传递过程与关键参数研究

涡轮薄层污泥干化是涉及导热、对流传热与传质、高速旋流相耦合的复杂过程,掌握污泥的耦合干化机理与规律、确定干化设备核心参数,是该技术成功应用的关键。本文用机理分析方法构建涡轮薄层干化过程传热、传质的数学模型,基于该模型对污泥干化过程开展数值模拟,揭示涡轮薄层干化过程单一气相和气固两相流的速度、温度和含水率的分布规律,探究涡轮薄层干化的关键技术及参数。设计开发涡轮薄层污泥干化系统并开展实验研究。结果表明：干化机内部的桨叶阵列设计能够实现物料的顺利运输,桨叶末端是干化机内混合传热效果最佳位置,最优桨叶安装角度为45°,出口污泥含水率可降至20%。     

双层壁幕墙传热特性的数值模拟

建立了双层壁中层空间的流体动力学和传热学二维稳态数学模型。将内、外层玻璃幕墙的传热模型、遮阳板的传热模型相耦合计算出双层壁的热力性能。给出了不同高度上的温度和速度分布数据。计算结果与相关文献中的实验数据较吻合。     

HAT循环饱和器数学模型及实验研究

在分析饱和器内的传热传质过程基础上,建立了一维数学模型,并通过引入广义传质系数CC,简化了饱和器的计算过程。经实验验证表明该模型具有较好的精度,可以比较准确的模拟饱和器内加湿过程,并且对含有填料的饱和器也具有通用性。通过计算得到的饱和器性能曲线图对设计和研究饱和器工作性能和传热传质规律有较大帮助。     

建筑装饰玻璃窑炉蓄热室的模拟优化设计

玻璃熔窑蓄热室的燃烧依靠空气和废气交替流动来提供动力。数值模拟方法能够揭示玻璃窑炉蓄热室在工作时内部流体的传热传质过程,以便进行相关的传热传质机理研究,并提出新的改进方法。采用计算流体力学软件ANSYS Fluent对蓄热室内的流场进行模拟,将固相的真实几何模型化为多孔固相与气流。数据拟合结果证明了该方法的可靠性,相关研究结果为提高蓄热室内的热能的利用率提供理论依据。     

板坯连铸动态二冷配水技术的工业应用

基于耦合多元合金两相区凝固模型的板坯连铸凝固传热数学模型和恒间距切片单元跟踪方法,开发了板坯连铸动态二冷配水软件平台,其中内嵌二冷分区有效拉速和目标表面温度曲线两种控制模式,前者充分考虑了铸坯的冷却历史,后者则关注对铸坯表面温度沿铸流方向的合理控制,在实际生产中可以方便灵活地加以选择应用.该技术控制功能丰富、安全机制完...     

A Dual Scale Model for Macrosegregation in Alloy Solidification

A numerical approach for coupling the temperature and concentration fields using a micro/macro dual scale model for a solidification problem is presented. The dual scale modeling framework is implemented on a hybrid explicit-implicit solidification scheme. The advantage of this model lies in more accurate consideration of microsegregation occurring at micro-scale using a subgrid model. The model is applied to the case of solidification of a Pb–40% Sn alloy in a rectangular cavity. The present simulation results are compared with the corresponding experimental results reported in the literature, showing improvement in macrosegregation predictions. Subsequently, a comparison of macrosegregation prediction between the results of the present method with those of a parameter model is performed, showing similar trends.     

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。     

Effect of micro mass transfer through phase interface on numerical simulation of solidification process

Existing models for the solute redistribution during solidification have been reviewed. Some typical models are applied for the numerical simulation of heat and mass transfer with phase change under experimental condition of inverse casting. The results show that the effect of micro mass transfer models on the formation of the new phase cannot be omitted. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(6): 393–401, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20024     

Numerical simulation of filling and solidification of permanent mold castings

Filling of a mold is an essential part of the permanent mold casting process and affects significantly the heat transfer and solidification of the melt. For this reason, accurate prediction of the temperature field in permanent mold castings can be achieved only by including simulation of filling in the analysis. In this work we model filling and solidification of a casting of an automotive piston produced from an aluminum alloy. Filling of the three-dimensional mold is modeled by using the volume-of-fluid method. Fluid mechanics and heat transfer equations are solved by a finite element method. Comparisons of numerical results to available experimental data show that the formulated model provides a solution of acceptable accuracy despite some uncertainty in material properties and boundary and initial conditions. This implies that the model can be a viable tool to design permanent molds.     

Applicability of a Mechanistic Model for the Prediction of Boiling Heat Transfer for Refrigerants

Among the different mechanisms of heat transfer during nucleate pool boiling, evaporation from the micro layer, evaporation from the macro layer, and transient heat transfer from the fluid mass above the macro layer play very crucial roles. Based on these three mechanisms, a model made earlier by the authors can predict the pool boiling heat transfer of water from flat and tubular surfaces quite accurately. To the best of our knowledge no model has so far been constructed for refrigerants considering evaporation from micro and macro layers. This leaves an opportunity for extending the generic micro–macro layer-based boiling heat transfer model for refrigerants. In the present work the authors' earlier model has been used to predict boiling heat transfer for a number of refrigerants. Experimental data for both flat and tubular surfaces have been considered for the validation of the model. Good agreements have been observed in most of the cases. Although the model is developed for nucleate boiling, it has been extended for a higher degree of superheat, and a matching trend can be seen beyond the critical heat flux for various heat input rates. Values of critical heat flux are also well predicted by the present model.     

Direct numerical simulation of interphase heat and mass transfer in multicomponent vapour–liquid flows

A Volume-of-Fluid methodology for direct numerical simulation of interface dynamics and simultaneous interphase heat and mass transfer in systems with multiple chemical species is presented. This approach is broadly applicable to many industrially important applications, where coupled interphase heat and mass transfer occurs, including distillation. Volume-of-Fluid interface tracking allows investigation of systems with arbitrarily complex interface dynamics. Further, the present method incorporates the full interface species and energy jump conditions for vapour–liquid interphase heat and mass transfer, thus, making it applicable to systems with multiple phase changing species. The model was validated using the ethanol–water system for the cases of wetted-wall vapour–liquid contacting and vapour flow over a smooth, stationary liquid. Good agreement was observed between empirical correlations, experimental data and numerical predictions for vapour and liquid phase mass transfer coefficients. Direct numerical simulation of interphase heat and mass transfer offers the clear advantage of providing detailed information about local heat and mass transfer rates. This local information can be used to develop accurate heat and mass transfer models that may be integrated into large scale process simulation tools and used for equipment design and optimization.     

Dendritic growth in Al-Si alloys during brazing. Part 1: Experimental evidence and kinetics

This work provides empirical evidence needed for an in depth phenomenological study of dendrite growth phenomena during brazing of aluminum alloys in form of composite brazing sheets. The main objective of this study was (1) a collection of experimental evidence associated with heat and mass transfer modeling of the Al + Si solid solution dendrite macro morphology evolution inherent to joint formation during brazing, and (2) the dendrite growth kinetics analysis. The isothermal dwell and the quench that follow the clad molten aluminum binary alloy surface-tension-driven flow into the joint at the peak brazing temperature upon melting lead to the solidification of the metal micro layer and joint formation. Before, during and after the isothermal dwell a significant reduction of Si content in the melt is found. So, a subsequent dissolution may affect the interface zone between the molten clad and substrate. α-phase dendrite assemblies imbedded in an irregular eutectic in the joint zone are the main morphological features of the solidification microstructures. The major characteristic of the phenomenon is a sensitivity of the dendrite pattern selection and dendrite population on brazing process parameters, in particular on the temperature during the dwell.