浮法玻璃熔窑内液流运动和传热三维数学模拟

本文从流动力学和传热学原理出发，结合浮法玻璃熔化作业特性，提出了浮法玻璃熔窑的三维液流运动及配合料熔化数学模型，建立了火焰与配合料和玻璃液之间的传热过程的半经验模型，通过计算，研究了浮法玻璃熔窑内液流运动特性，发现在投料池中存在一个独特的循环液流，并发现在配合料层覆盖下的上层玻璃液帻两侧池壁流向中心线，与热点处清情况刚好相反。     

人工汽化中心表面核状沸腾传热的研究——(Ⅱ)关于核状沸腾传热机理以及汽化中心的大小和密度对沸腾给热系数的影响

本文在前人提出的各种沸腾传热机理模型的基础上,建立了一个关于核状沸腾传热机理的综合模型,并在规则排列的、不同汽化中心密度和孔径的人工汽化中心表面上进行了沸腾传热实验,对所提出的模型进行了验证.模型计算结果与实验结果符合良好,文中根据所建立的模型分析了汽化中心的大小和密度对沸腾传热速率的影响.     

滚塑工艺在加热阶段的两种传热模型的比较研究

为一个圆筒形滚塑模具在其内部粉料开始熔融之前的加热阶段建立了两种传热理论模型.在第一种传热模型中,将模具内的空气当作主要相的流体,将粉料当作次要相的流体.采用FLUENT软件中多相流模块的Mixture模型对模具内的流动与换热进行仿真计算.第二种传热模型是一种简化的传热模型.即忽略模具的结构形状和温度梯度,同时假设模具...     

溴化锂溶液垂直降膜过程中流动与传热的数值模拟

采用流体体积(VOF)法捕捉自由界面,并应用连续表而力(CSF)模型,建立了垂直降膜波动模型,研究了溴化锂溶液垂直降膜过程中的波动过程,根据波动模型得到的界面信息,建立了以波速为动坐标系的固定界面传热模型,同时考察了波动对传热的影响,并建立了垂直降膜波动模型和固定界面传热模型.结果表明:一定入口频率的扰动发展为孤波和毛...     

引入液固界面效应的滴状冷凝传热模型

针对液固界面相互作用对滴状冷凝传热的影响,以Rose滴状冷凝传热模型为基础,考虑接触角、脱落直径对冷凝传热的影响,对滴状冷凝过程中液滴空间序列上的构象,作时间序列上的重构,建立了包含液固界面效应的滴状冷凝传热模型.模型计算结果表明液固表面自由能差越大、接触角滞后越小则越有利于冷凝传热.为滴状冷凝文献数据间存在差异的原因提供了一个新的解释,即液固界面效应的影响.模型可计算得到在不同界面条件下的不同传热结果,模型计算结果与Rose实验值以及本文滴状冷凝传热实验较为吻合.     

引入接触角的滴状冷凝分形传热功当量模型

以Rose模型为基础,引入接触角因素建立单个液滴传热模型,基于液滴在冷凝表面的分形分布特性,考虑接触角对分形维数的影响建立液滴分布函数,进而建立不同接触角表面通用传热模型.采用不同液滴分布模型分别计算求得通过冷凝生长的液滴的分布函数f(r)以及通过合并生长的液滴的分布函数F(r),并将总冷凝传热表示为上述两种方式生长液...     

布朗工艺一段转化炉的模拟计算

在建立炉膛燃烧传热模型和管内气固相催化反应模型的基础上对布朗工艺合成氨装置一段炉辐射段进行模拟计算.炉膛燃烧传热过程采用Hottle区域法建立三维辐射换热模型,与管内的气固相催化反应动力学模型迭代求解,得出了炉膛三维温度分布以及管内温度、压力、组成随高度的分布.计算结果与实测值基本吻合.由于炉膛燃烧传热模型采用三维模型,与传统的一维和二维模型比较,计算结果更为精确.计算方法和结果对于节能降耗以及设备的改进等都有非常重要的意义.     

基于滴膜共存理论热虹吸管冷凝段传热模型

引入滴膜共存冷凝传热理论分析管内存在滴状冷凝的热虹吸管冷凝段传热,将热虹吸管冷凝段传热表示为滴状区和膜状区传热之和建立传热模型。滴状区,以Rose冷凝传热模型计算单个液滴的传热,基于随机分形理论建立了液滴的空间和尺度分布函数,进而求解整个滴状区的热通量。膜状区,根据Nusselt竖壁层流膜状凝结理论进行热通量的计算。通过沟流级别计算滴状区和膜状区的面积比率,从而建立滴膜共存冷凝传热模型。传热模型计算结果与实验结果较为吻合,能够反应热管冷凝段传热本质。     

过渡状态冷凝传热模型

引入沟流级别的概念解释过渡状冷凝形态的形成特征,并在此基础上,将过渡状冷凝传热表示为通过滴状区与沟流区上的传热之和,建立了反映界面效应影响的过渡状冷凝传热模型.设计了人工形成沟流形态的冷凝表面,其实验结果与模型计算结果吻合;模型计算也与实际自然形成沟流冷凝形态的传热过程吻合.模型对滴状区的传热计算,以液滴分布时间序列构象模型为基础,并将滴状区最大液滴与沟流级别相关联,得到与界面效应相关的滴状区传热模型;沟流区传热计算,以在一定厚度液膜上的冷凝传热模型为基础,并根据沟流形态模型,求出液膜厚度与沟流区所占面积分率.模型描述了过渡状冷凝形态形成特征以及过渡状冷凝传热系数随表面自由能差渐进变化的规律.     

基于红外技术的工业窑炉池壁冷却风控制

在玻璃生产过程中,窑炉池壁区域由于缺乏池壁温度、冷却风风量、风压、风速等相关数据的检测,工艺人员大多凭借经验调节冷却风,导致在温度偏低的季节,冷却强度却高于夏季。通过开发池壁风机变频控制技术体系,建立冷却风相关数据的检测方法,借助红外测温技术及热流密度检测技术,建立池壁区域相关数据的数据库。通过监控池壁温度来合理地调节池壁风机的风量,进而达到节约用电和降低燃料消耗的目的。     

液化石油气储罐在喷射火焰作用下的热响应模型

Abstract This paper describes a mathematical model developed to study the behavior of liquefied petroleum gas (LPG) tanks when subjected to jet fire. The model consists of a number of field and zone sub-models which are used to simulate the various physical phenomena taking place during the tank engulfment period. The model can be used to predict the pressure and temperature of the LPG in the tank, the temperature of the wall of tank, and the time of tank explosion. The comparisons between the model predicted results and the test data show good agreement. The results show that the jet fire partially impinging on tank wall led to higher wall temperature and the time to failure was shorter than that in engulfing pool fire. And the exposure of the upper wall in the vapor zone to the fire is more dangerous than that of the LPG contacted wall.     

The Model of Thermal Response of Liquefied Petroleum Gas Tanks Partially Exposed to Jet Fire

This paper describes a mathematical model developed to study the behavior of liqupfied petroleum gas (LPG) tanks when subjected to jet fire. The model consists of a number of field and zone submodels which are used to simulate the various physical phenomena taking place during the tank engulfment period. The model can be used to predict the pressure and temperature of the LPG in the tank, the temperature of the wall of tank, and the time of tank explosion. The comparisons between the model predicted results and the test data show good agreement. The results show that the jet fire partially impinging on tank wall led to higher wall temperature and the time to failure was shorter than that in engulfing pool fire. And the exposure of the upper wall in the vapor zone to the fire is more dangerous than that of the LPG contacted wall.     

Laser transmission welding of PMMA to alumina ceramic

In this paper, a method of laser transmission welding on ceramic surface after pulse laser microtexture pretreatment was proposed to address the problem that welding ceramics with high transparency polymers is demanded but difficult to be performed. In this method, the polymer flows into the micro-texture of the blind hole on the surface to form mechanical riveting to enhance the welding strength. The formation characteristics and welding mechanism of PMMA welded joint with micro-texture alumina ceramics were studied experimentally and simulatively. The effects of blind hole microtexture size, continuous laser power and continuous laser scanning rate on solution flow and welding strength were studied. The results showed that the air bubbles formed in the welded seam by entering the micro-texture blind hole and trapped air in the blind hole were the key factors affecting the strength of the joint. A 3D finite element model of the transient temperature field and flow field of polymer during laser welding was established. The simulation results showed that the polymer on the left side of the blind hole melted first when heated and inflowed along the wall due to the effects of self-gravity and buoyancy caused by temperature differences. The gas expanded and extruded upward to the left, forming bubbles in the polymer melt pool and pushing the polymer melt into the blind pore microtexture. Finally, a complete molten pool was formed. The flow of polymer melt, the formation of bubbles and the formation of joint were revealed.     

Velocity and temperature profiles in compressible turbulent wall jets

The results of an experimental study on compressible turbulent wall jets resulting from a normally impinging round jet are presented. A finite difference technique was used for the calculation of velocity and temperature profiles. The eddy transfer coefficients used were functions of the distance from the plate throughout the flow field of the wall jet. The nozzle exit Mach number ranged up to 0.85. The nozzle exit temperature to the ambient temperature ratio ranged up to 2.92. The applicability of the calculational method has been thoroughly checked for a region of flow extending up to 12 nozzle diameters from the axis of symmetry. Using the empirical eddy transfer coefficients presented in this paper only starting profiles are needed to generate the solution for any point in the wall jet flow field which is described by a system of parabolic (boundary layer) equations.     

Numerical modelling framework of continuous salt precipitation from super-critical water

Salt separation at super-critical condition is a promising technology to separate dissolved salts from water by utilizing sharp changes in thermal and physical properties of water close to its critical point in a tube in tube separator. To capture flow complexity and geometric asymmetry, a three-dimensional CFD model of salt separator is developed in Fluent ver 16. Simulation results are compared and validated with experimental work by Schubert et al. [19]. The axial temperature profiles predicted by model at different wall temperature are well in agreement with the reported data [19]. The model provides insight to axial and radial flow field, temperature gradients, and so on within the salt separator. The blurred boundary between super-critical and sub-critical regions is captured by accounting sharp changes in physical properties of water close to critical temperature and pressure. Sensitivity of key process parameters (e.g., vessel wall temperature, feed pre-heat temperature, flow rates and forced cooling in cold region) was carried out to check effect of operating parameters on deviation in performance of salt separator. No pre-heat feed condition (25°C) is best since it ensures no salt deposition in dip tube without affecting the salt separator performance. Optimum wall temperature lies between 390°C to 470°C to avoid salt deposition and maintain desired temperature gradient between hot and cold section. The modelling framework will aid in efficient design and scale up of salt separator.     

甲烷化固定床反应器床层反应过程与场分布数值模拟

以甲烷化固定床反应器床层为研究对象,使用CFD软件编写CEL语言,将甲烷化反应以源项的形式添加到模拟过程中,对比多孔介质模型与填充球床模型模拟的准确性,选择填充球床模型进行模拟,获得了床层的速度场、组分浓度以及温度场分布。研究结果表明:与填充球床模型比较,由于多孔介质模型简化了内部的孔隙结构,使用其对固定床反应器进行模拟时存在较大误差,其中出口温度模拟值比实测值低13.6%;固定床的壁效应使近壁面处10%的圆环面积上通过20%的质量流量,进而显著影响床层内部场的分布;床层内部轴向温升显著,从250℃ 升高到 685℃,同时径向温度分布不均,变化范围在20～40℃内波动。     

微型机械运动副模内微组装成型热流固耦合变形模拟

提出了一种新型规模化高效低成本聚合物微型机械系统模内微组装成型加工技术,并针对其成型过程特点,建立了描述模内微组装成型过程成型热流固耦合变形机理的理论模型。通过有限元数值模拟,研究了模壁温度对模内微组装成型过程的影响规律。结果表明,模内微组装成型的微装配加工精度受控于热流固耦合压力场和不均匀温度场,且其热流固耦合变形随着模壁温度的升高而增大;减小模壁温度有利于提高其微装配加工精度。     

核态池沸腾换热的数值模拟

以沸腾壁为研究对象 ,以气泡或核心为边界建立了沸腾换热的数学模型 ,进行了核态池沸腾换热的直接数值模拟 ,模拟结果与现有的实验数据具有很好的一致性 ,从而验证了数值模拟的可靠性 .通过数值模拟得到了气泡影响面积系数和气泡扰动强度系数的计算方法 ,揭示了气泡等待时间和沸腾表面温度波动的非线性特征 .     

Viscous dissipation in packed beds

Factors affecting the magnitude of viscous dissipation in packed beds under conditions used in high pressure liquid chromatography are investigated. The free surface model is employed to characterize packed beds, to evaluate the flow field and to derive the appropriate similitude criterion for the effect of viscous dissipation. Equations for the calculation of radial temperature profiles due to internal heat generation in beds with axially uniform and non-uniform wall temperatures are given and the results are illustrated for typical cases. The evaluation of the temperature profiles in beds with non-uniform wall temperature is based on experimentally measured wall temperatures.     

二次氧量对分级气化炉气化特性的影响

分级给氧气流床气化炉具有碳转化率高、炉内混合过程强烈、喷嘴附近温度较低等优点。本文采用CFD数值模拟的方法研究了二次氧量变化对气化炉运行特性的影响,分析比较了不同二次给氧量下相交射流火焰特性的变化,及相交射流对煤气化炉炉内整体混合过程、煤气化特性的影响。发现当二次给氧量下降时,受炉内回流流场的影响,二次火焰明显随回流发生偏斜,壁面温度升高。当二次给氧量小于总给氧量的8%时,其射流动量不足以影响主射流产生的宏观流场。