数值模拟在焙烧炉设计中的应用

针对焙烧炉的运行特点进行分析，提出将焙烧炉分为两个模型(火道模型和传热模型)进行模拟。其中，火道模型解决火道结构设计问题，传热模型解决温度曲线等问题。分别介绍了这两个模型的几何模型和数学模型，并通过计算实例说明了其在焙烧炉设计中的应用。文中对两种模型的耦合和模型参数取值问题亦进行了说明。     

PYRO-JET燃烧器冷模特性的数值模拟试验

采用 CFD(Calculation of Fluid Dynamics)三维湍流场数值摸拟软件研究 PYRO- JET燃烧器和传统三通道燃烧器的冷模湍流场 ,结果表明 :PYRO- JET燃烧器的卷吸率远大于传统的燃烧器 ,中心区回流率比传统的燃烧器低 ,外风速最佳操作值应控制在 30 0 m /s左右 ,且外风速度大小对回流量影响不明显     

NUMERICAL SIMULATION OF THE EFFECT OF VELOCITY RATIO ON THE FLOW CHARACTERISTICS IN A COAXIAL JET

Previous experimental work shows that velocity ratio is the principal independent variable to determine the flow behavior of coaxial jets. This study focusing on the effect of velocity ratio on the flow characteristics such as the velocity and kinetic energy profiles, centerline velocity decaying, flow growing and entraining of the jet, presents a detailed numerical simulation of a coaxial jet with a secondary parallel moving stream. It is found that radial profiles of the mean velocity component u depending on the velocity ratio show good similarity in the fully developed zone. Compared with available experimental data, the results show that the use of standard κ-ε model leads to good agreement between the numerical results and experimental data.     

NUMERICAL SIMULATION OF THE GAS-PARTICLE FLOW IN RISERS I: THE MACRO FLOW BEHAVIOR

The steady gas-particle flow in risers under variant operating conditions was predicted based on a k-?-k_p-?_p-Θ two-fluid model, which describes the dense turbulent gas-particle flow by the Eulerian method, considering the turbulence of both gas and particles as well as the particles' collisional effects. Much information on the macro flow behavior in risers, such as the profiles of local particle axial velocity, solids volume fraction, and solids mass flux in different operating regimes was obtained, and the predicted results show satisfactory agreement with experimental data. Further analysis of the predictions gives the comprehension of flow characteristics on the macro scale.     

NUMERICAL SIMULATION OF THE GAS-PARTICLE FLOW IN RISERS I: THE MACRO FLOW BEHAVIOR

The steady gas-particle flow in risers under variant operating conditions was predicted based on a k-ε-k_p-ε_p-Θ two-fluid model, which describes the dense turbulent gas-particle flow by the Eulerian method, considering the turbulence of both gas and particles as well as the particles' collisional effects. Much information on the macro flow behavior in risers, such as the profiles of local particle axial velocity, solids volume fraction, and solids mass flux in different operating regimes was obtained, and the predicted results show satisfactory agreement with experimental data. Further analysis of the predictions gives the comprehension of flow characteristics on the macro scale.     

NUMERICAL SIMULATION OF THE GAS-PARTICLE FLOW IN RISERS II: THE MICRO AND MESO FLOW BEHAVIORS

The steady gas-particle flow in risers under variant operating conditions was simulated using a k-ε-k_p-ε_p-Θ two-fluid model, which describes the dense turbulent gas-particle flow. The particle temperature Θ, the scale of the fluctuant energy of particles in micro scale, and the particle turbulent energy k_p that describes the particle fluctuation in meso scale can be predicted by the numerical simulation. Further investigation shows that different flow parameters influence the particle fluctuation in different ways and that solid volume fraction significantly affects the particle fluctuation and particle dispersion behavior.     

NUMERICAL SIMULATION OF THE GAS-PARTICLE FLOW IN RISERS II: THE MICRO AND MESO FLOW BEHAVIORS

The steady gas-particle flow in risers under variant operating conditions was simulated using a k-?-k_p-?_p-Θ two-fluid model, which describes the dense turbulent gas-particle flow. The particle temperature Θ, the scale of the fluctuant energy of particles in micro scale, and the particle turbulent energy k_p that describes the particle fluctuation in meso scale can be predicted by the numerical simulation. Further investigation shows that different flow parameters influence the particle fluctuation in different ways and that solid volume fraction significantly affects the particle fluctuation and particle dispersion behavior.     

DIRECT NUMERICAL SIMULATION OF VORTEX STRUCTURES AND PARTICLE DISPERSION IN TURBULENT FREE SHEAR FLOWS

In order to provide references for the study of jets from combustor and associated industrial applications, direct numerical simulation was employed to study a three-dimensional temporally evolving plane mixing layer laden with particles in the upper region initially. The coherent structures in the mixing layer between two parallel streams were simulated using a pseudo-spectral method. Particles with different Stokes numbers were traced using the Lagrangian approach based on one-way coupling between the continuous and the dispersed phases. Both the large-scale vortex structures and the particle dispersion patterns with different Stokes numbers were investigated. The results clearly showed that particle dispersion is closely related to the large-scale organized structures and the three-dimensionality. Particles with Stokes number of the order of unity were found to have the largest concentration on the outer edges of the large-scale vortex structures, and the variation of particle concentration along the spanwise direction increased with the development of the three-dimensionality, which was mainly due to the presence of the streamwise large-scale structures. When the counter-rotating “rib” large-scale vortices paired, part of the particles were thrown out from the high concentration area in the upper region to the lower region of the mixing layer and finally developed into a “mushroom” pattern of the particle distribution along the spanwise direction.     

DIRECT NUMERICAL SIMULATION OF VORTEX STRUCTURES AND PARTICLE DISPERSION IN TURBULENT FREE SHEAR FLOWS

In order to provide references for the study of jets from combustor and associated industrial applications, direct numerical simulation was employed to study a three-dimensional temporally evolving plane mixing layer laden with particles in the upper region initially. The coherent structures in the mixing layer between two parallel streams were simulated using a pseudo-spectral method. Particles with different Stokes numbers were traced using the Lagrangian approach based on one-way coupling between the continuous and the dispersed phases. Both the large-scale vortex structures and the particle dispersion patterns with different Stokes numbers were investigated. The results clearly showed that particle dispersion is closely related to the large-scale organized structures and the three-dimensionality. Particles with Stokes number of the order of unity were found to have the largest concentration on the outer edges of the large-scale vortex structures, and the variation of particle concentration along the spanwise direction increased with the development of the three-dimensionality, which was mainly due to the presence of the streamwise large-scale structures. When the counter-rotating “rib” large-scale vortices paired, part of the particles were thrown out from the high concentration area in the upper region to the lower region of the mixing layer and finally developed into a “mushroom” pattern of the particle distribution along the spanwise direction.     

NUMERICAL SIMULATION OF ELECTROKINETIC MICROFLUIDICS IN COLLOIDAL SYSTEMS

A numerical scheme is presented for simulating electrokinetic microfluidics in systems with arbitrary morphology. This scheme is based on a numerical solution of the coupled Poisson, Nernst-Planck, and Navier-Stokes equations. While traditional finite-difference methods were used to resolve the first two problems, the lattice Boltzmann method was applied to the latter. The developed numerical approach was used for the simulation of electroosmotic flow through a simple cubic array of hard (impermeable, nonconducting) micro-sized spheres. Volumetric electroosmotic flow was studied for dependence on electrical field strength, ζ-potential at the solid-liquid interface, electrical double layer interaction, and numerical grid resolution. Colloid stability and electrokinetics in microfluidic devices with particulate or monolithic fixed-bed elements represent two potential applications of this work.     

NUMERICAL SIMULATION OF ELECTROKINETIC MICROFLUIDICS IN COLLOIDAL SYSTEMS

A numerical scheme is presented for simulating electrokinetic microfluidics in systems with arbitrary morphology. This scheme is based on a numerical solution of the coupled Poisson, Nernst–Planck, and Navier–Stokes equations. While traditional finite-difference methods were used to resolve the first two problems, the lattice Boltzmann method was applied to the latter. The developed numerical approach was used for the simulation of electroosmotic flow through a simple cubic array of hard (impermeable, nonconducting) micro-sized spheres. Volumetric electroosmotic flow was studied for dependence on electrical field strength, ζ-potential at the solid-liquid interface, electrical double layer interaction, and numerical grid resolution. Colloid stability and electrokinetics in microfluidic devices with particulate or monolithic fixed-bed elements represent two potential applications of this work.     

NUMERICAL SIMULATION OF LAMINAR SOLID-LIQUID TWO-PHASE FLOW IN STIRRED TANKS

Laminar flow of solid-liquid suspension has been rarely reported in the literature. In this article, the laminar solid-liquid two-phase flow in a lab-scale stirred tank is measured with digital particle image velocimetry (DPIV) and numerically simulated with the improved inner-outer iterative method. The simulation results show good agreement with the present data. In the range of low solid volume concentration under investigation, solid particles have minor impact on two-phase flow, and the simulated flow fields of both phases are similar to the counterpart of single-phase laminar liquid flow. The comparison of simulation with experiments of single-phase laminar flow shows reasonable agreement. These observations suggest that the numerical method employed in the present study is reliable for analysis of stirred tanks. The influence of impeller off-bottom clearance on velocities is found significant: the lower the impeller, the smaller the radial and axial velocities, and the higher the solid concentration.     

管壳式换热器壳程流动和传热的三维数值模拟

提出了一种管壳式换热器壳程单相流动和传热的三维模拟方法 .用体积多孔度、表面渗透度、分布阻力和分布热源来考虑壳程复杂几何结构造成的流道缩小和流动阻力、传热效应 ,通过数值求解平均的流体质量、动量、能量守恒方程 ,得到壳程流动和换热的分布 .用该方法对一实验换热器进行了流动和传热的模拟 ,计算结果和实验结果吻合良好 .     

SIMULATION OF TRANSPORT DYNAMICS IN FLUIDIZED-BED DRYERS

ABSTRACT

A mathematical model for predicting three-dimensional, two-phase flow, heat and mass transfer inside fluidized-bed dryers has been developed. The model consists of the full set of partial-differential equations that describe the conservation of mass, momentum and energy for both phases inside the dryer, and is coupled with correlations concerning interphase momentum-, heat-, and mass-transfer.

It is shown that the model can predict the most important engineering aspects of a fluidized-bed dryer including pressure drop, particle holdup, temperature distribution in both phases as well as drying efficiency all over the fluidized-bed. Plug-flow conditions are predicted for the gas phase, while back-mixing is predicted for the particles.

The effect of particle mass-flow-rate on fluidized-bed dryer performance is evaluated. It is shown that the lower the particle mass flow-rate, the more intense the horizontal moisture gradients, while the higher the particle rate the more uniform the moisture distribution throughout the bed.     

IGCC示范工程煤气化炉的数值模拟

采用Aspen Plus流程模拟软件对某拟建的IGCC示范工程的德士古煤气化炉进行数值模拟,通过考虑碳的不完全转换对计算流程进行了改进,并运用CPD模型预测煤热裂解的产物分布.研究了煤气化炉的重要操作参数(即水煤浆浓度、氧煤比、气化压力和气化温度)对气化结果的影响.在计算区间内,发现高浓度水煤浆浓度范围内,随浓度的增加,煤气的主要成分(H2+CO)的总含量增加.气化温度增大到1400℃左右时,煤气的主要成分随气化温度的进一步增加会趋于一个恒定值.     

底部局部辐射加热窑炉内温度场数值模拟

提出了底部局部辐射加窑炉内温度场数值分析的控制方程组，分别对平面加热及半圆柱形加热面两种算例进行了数值计算，得了影响烤花烤窑炉内温度场均匀性的主要因素和有加热面发射率，加热面形状，加热面相对位置及窑炉墙体热阻和墙体与外界的换热热阻。     

分解炉中气体成分分布的数值模拟

对水泥生产中广泛使用双喷腾分解炉系统进行了3D数值模拟研究,深入研究和分析了分解炉中气体成分来源对煤粉燃尽率和碳酸钙分解率之间的影响关系.在前人研究的基础上运用适用于工业研究的碳酸钙分解模型,数值模拟求解了煤粉总体燃尽率和碳酸钙总体分解率.提出了一种预测分解炉内不同来源气体成分分布的方法,为工业研究分解炉中煤粉燃烧和碳酸钙分解问题提供了理论依据.     

浮法玻璃熔窑烟气处理系统流场数值模拟

本文采用湍流κ-ε模型及随机轨道模型,运用通用的计算流体力学软件Fluent进行脱硫塔内流场模拟.从模拟结果上看,喷雾液滴极大地影响了塔内的流场.混合喷雾效果比单排效果好,高位喷雾效果比低位效果好,根据这一结果做出了相应的设计和优化,为研究脱硫过程提供了一种可行的方法.     

板坯结晶器内电磁制动过程流场的数值模拟

应用描述结晶器电磁制动过程的三维流动数学模型,并利用所开发的计算程序ＭＯＬＤ－ＥＭＢＲ ３Ｄ１．０进行了数值模拟．结果表明：电磁制动能明显减缓钢水主流股的流速,缓解对铸坯窄面的冲击,有效地抑制表面波动,减小钢水的冲击深度;磁场和流场的相互作用程度直接影响电磁制动效果,磁场位置的升高或降低会出现双涡现象．     

搅拌槽内三维流场的数值模拟

应用商业计算流体力学软件CFX对搅拌槽内的流场进行了模拟,并与PIV测试结果进行了比较,流型吻合良好.速度分量的对比结果表明不同情况与各种模型的吻合情况不尽相同,标准k-ε双方程模型、RNG k-ε模型和代数应力模型在主流域内都能较准确地模拟搅拌槽内的流动场.