Mathematical modelling and numerical optimization of particle heating process in copper flash furnace

A mathematical model of the particle heating process in the reaction shaft of flash smelting furnace was established and the calculation was performed.The results indicate that radiation plays a significant role in the heat transfer process within the first 0.6 m in the upper part of the reaction shaft,whilst the convection is dominant in the area below 0.6 m for the particle heating.In order to accelerate the particle ignition,it is necessary to enhance the convection,thus to speed up the particle heating.A high-speed preheated oxygen jet technology was then suggested to replace the nature gas combustion in the flash furnace,aiming to create a lateral disturbance in the gaseous phase around the particles,so as to achieve a slip velocity between the two phases and a high convective heat transfer coefficient.Numerical simulation was carried out for the cases with the high-speed oxygen jet and the normal nature gas burners.The results show that with the high-speed jet technology,particles are heated up more rapidly and ignited much earlier,especially within the area of the radial range of R=0.3−0.6 m.As a result,a more efficient smelting process can be achieved under the same operational condition.

Effect of Particle Orientation on Heat Transfer in Arrays of Prolate Particles

Direct Numerical Simulations have been carried out to study the forced convection heat transfer of flow through fixed prolate particles for a variety of aspect ratios ar={5/4,5/3,5/1}with Reynolds number(Re)up to 100.Three variations of the solid volume fraction c={0.1,0.2,0.3}with four Hermans orientation factors S={−0.5,0,0.5,1}are studied.It has been found that changes in S cause prominent variations in the Nusselt number.In general,Nusselt number increases with the decrease of S.For all three aspect ratios,the Nusselt number remains a linear function of S at different c and Re.Therefore,it is concluded that,for heat transfer from prolate muti-particle system,the effects of orientations cannot be ignored.A new correlation for Nusselt number has been developed for arrays of prolate particles using the simulation data as a function of Re,c,S and ar.

Characteristics of turbulence transport for momentum and heat in particle-laden turbulent vertical channel flows

The dynamic and thermal performance of particle-laden turbulent flow is investigated via direction numerical simulation combined with the Lagrangian point-particle tracking under the condition of two-way coupling, with a focus on the contributions of particle feedback effect to momentum and heat transfer of turbulence. We take into account the effects of particles on flow drag and Nusselt number and explore the possibility of drag reduction in conjunction with heat transfer enhancement in particle-laden turbulent flows. The effects of particles on momentum and heat transfer are analyzed, and the possibility of drag reduction in conjunction with heat transfer enhancement for the prototypical case of particle-laden turbulent channel flows is addressed. We present results of turbulence modification and heat transfer in turbulent particle-laden channel flow, which shows the heat transfer reduction when large inertial particles with low specific heat capacity are added to the flow. However, we also found an enhancement of the heat transfer and a small reduction of the flow drag when particles with high specific heat capacity are involved. The present results show that particles, which are active agents, interact not only with the velocity field, but also the temperature field and can cause a dissimilarity in momentum and heat transport. This demonstrates that the possibility to increase heat transfer and suppress friction drag can be achieved with addition of particles with different thermal properties.

Effects of Particle Stacking Angle on Heat Transfer Characteristics of Particles Close to the Wall

The primary energy demand increases, but a large amount of waste heat resources were not effectively used. To explore the influence of particle stacking structure on waste heat recovery process, CFD method was used to simulate. An unsteady heat transfer model of two particles was established, effect of particle stacking angle on heat transfer characteristics of the particles close to the wall under different initial temperature conditions was studied. Results show that: higher initial temperature, resulting in increased heat transfer time, the larger particle stacking angle causes the shortening of heat transfer time. When initial temperature is 1073 K, the average wall heat flux shows a trend of rapid decline first and then a slow one. At the same moment, the larger stacking angle causes smaller particle average temperature. The change of particle stacking angle shows a greater impact on the temperature of the particles close to adiabatic wall. The increase in the stacking angle resulting in better heat transfer characteristics between particles.

Heat transfer analysis in particle-laden flows using the immersed boundary method

This paper investigates an efficient immersed boundary method(IBM)for multiple-core CPU machines with local grid refinement for the calculation of heat transfer between fluids and finite-sized particles.The fluid momentum equations are solved by using the fractional step method,while the energy equation is solved by employing the second-order Adams-Bashforth method.For efficient load balancing between the CPU cores,the coupling between particles and fluid is obtained by applying the body force in the fluid equations,which depends on the solid volume fraction of particles contained in each grid cell,and then by linearly interpolating the particle temperature and velocity on the fluid grid cell(in place of the delta function commonly used in literature).Several test cases from the literature are studied,and good agreement is observed between the simulation results and the literature.Finally,a scaling study on multiple core machines is performed,demonstrating the proposed IBM's capabilities for a significant reduction in processing time.

Numerical and Experimental Investigation on the In-Flight Melting Behaviour of Granulated Powders in Induction Thermal Plasmas

An innovative in-flight glass melting technology with thermal plasmas was developed for the purpose of energy conservation and environment protection. In this study, modelling and experiments of argon-oxygen induction thermal plasmas were conducted to investigate the melting behaviour of granulated soda-lime glass powders injected into the plasma. A two-dimensional local thermodynamic equilibrium （LTE） model was performed to simulate the heat and momentum transfer between plasma and particle. Results showed that the particle temperature was strongly affected by the flow rate of carrier gas and the particle size of raw material. A higher flow rate of carrier gas led to lower particle temperature and less energy transferred to particles which resulted in lower vitrification. The incomplete melting of large particles was attributed to the lower central temperature of the particle caused by a larger heat capacity. The numerical analysis explained well the experimental results, which can provide valuable practical guidelines for the process control in the melting process for the glass industry.

基于CFD的烟叶松散润叶筒气固耦合数值模拟

针对烟叶松散润叶筒内部的“黑箱”问题,基于计算流体力学(CFD)对其进行气固双向耦合的数值模拟,通过建立可视化的流场和温度场模型,探讨润叶过程的影响因素和影响机理。结果表明:流场模拟中,颗粒的存在能有效改善气体流动形式,总体气相速率从1.0 m/s降低到0.3 m/s,增加了气固间的接触,强化了两相间的传热;温度场模拟中,温度变化呈现阶段式变化,在润叶筒前半段气固之间传热显著,气相平均温度由81.0℃下降至68.8℃,颗粒平均温度从25.0℃迅速升温到64.8℃,后半段温度维持相对稳定,气固间传热的热流密度随着轴向位置呈现先逐步下降后平稳的趋势;气相、颗粒温度的模拟值与试验实测值的相对误差分别为0.7%、-2.5%,模拟值与试验实测值整体吻合良好,说明模型合理有效;随着筒体倾角、转速增大,两相间的传热效果随之减弱,为满足润叶工艺要求,筒体倾角应小于8°,综合考虑生产速率与能耗,转速应选择15 r/min。

Numerical Study and Performance Analyses of Mems-Based Particle Velocity Sensor with Combined Inclined Rib Pair

The combined inclined rib pair(CIRP)is the first time proposed to improve the sensor performance of particle velocity sensor(PVS)by using a three-dimensional numerical method.The method is verified by the experiment results in the literature.The optimal plain channel parameters are determined as the basic sensor structure.In comparison of plain channel,both heat transfer characteristics and sensor performance are enhanced effectively by arranging the CIRP.The reason is that the high flow rate region caused by the CIRP can maintain strongly in the whole fluid field if there are enough rib pairs.Furthermore,the produced longitudinal vortex pair can get a better fluid mix,which is more conductive to heat transfer.The increasing height and number of the CIRP can improve the heat transfer characteristics,but the flow resistance will increase as well.For the purpose of finding the best overall performance,the effects of the parameters including the geometric sizes and the position of the CIRP have been investigated.The results show that PVS will get the best sensitivity when the rib length and width are 0.2 mm and 0.03 mm respectively,and the distance between rib pair and between ribs in the same pair are 0.15 mm and 0.3 mm respectively.Besides,the most suitable crossing angle is 45°.Thus,the performance of PVS can be significantly improved by this novel structure.

换热管束壁面颗粒沉积状况的数值模拟

随着计算流体力学的不断发展,许多学者提出了受热面结渣沾污状况的预测模型,然而,由于灰颗粒的沉积过程较为复杂,为了简化计算,很多因素在现有模型中并未考虑。本研究在现有模型的基础上,综合考虑了还原性气氛对灰颗粒黏度的影响以及灰中碱金属对颗粒黏结概率的影响,基于数值模拟研究了不同模型下换热管束颗粒沉积状况,并探究了纵向节距和壁面温度对管束壁面颗粒沉积状况的影响。结果表明:考虑不同的修正模型后,颗粒沉积效率均有一定程度的增加,且同时考虑还原性气氛及碱金属对沉积过程的影响时,其颗粒沉积效率相对于基础模型颗粒沉积效率的变化率为22.24%。颗粒在同列管束壁面上沉积质量的分布并不一致,对于第一排管束,颗粒主要沉积在30°~150°位置上,且90°附近区域颗粒沉积质量最大;而随着管排数的增大,颗粒沉积质量分布越来越均匀。随着纵向节距的增加,第一排管束颗粒沉积质量基本不变,而后排管束的颗粒沉积质量逐渐增加;随着温度的升高,各管束颗粒沉积质量略有增加,但变化并不明显,这是因为沉积过程受到多种机理耦合作用。

Multi-Scale Numerical Simulation of Flow,Heat and Mass Transfer Behaviors in Dense Gas-Solid Flows:A Brief Review

Dense gas-solid flows are very common in actual production and industrial fields,so it is significant to understand their hydrodynamic characteristics and heat and mass transfer behaviors.This article provides a brief review of multi-scale numerical simulation of flow,heat and mass transfer behaviors in dense gas-solid flows.It describes multiscale models(direct numerical simulation,discrete particle model,and two-fluid model)and the results of related research.Finally,it discusses possible future developments in research on the flow,heat and mass transfer characteristics of dense gas-solid two-phase flows.

堆积石墨颗粒蓄放热性能仿真模拟研究

选用堆积石墨颗粒作为固体蓄热材料,利用Ansys软件进行仿真模拟,分析堆积石墨颗粒模型的蓄放热性能。以250 kW的加热功率对蓄热体加热10 h,通入温度为523 K的空气进行8 h放热。结果显示:经过10 h加热,蓄热体整体升温曲线差异较大,靠近热源位置呈现外凸的升温趋势,而蓄热体边缘呈现内凹趋势,整体温度分布不均匀,最大温差大于400 K。经过8 h的空气冷却,蓄热体模型出口界面温度分布呈现H形,紧贴通风管道周围的蓄热体经过空气对流换热温度迅速降低,剩余H形部分中大量的热量不能均匀释放,最大温差达到195 K。

射频热等离子体制备球形氧化铝粉末的数值模拟及实验研究

研究粉末颗粒在热等离子体(ICTP)中的行为可以为射频等离子体制备球形粉末工艺过程的优化提供参考。首先,利用FLUENT软件对具有不同粒径分布的氧化铝粉末颗粒在射频热等离子体中的运动轨迹及加热历程进行了数值模拟;然后,根据模拟结果所确定的实验参数范围进行了射频热等离子体粉末球化实验,并将实验测量与数值模拟的结果相结合,研究了输入功率、送粉速率等参数的改变对具有不同粒径分布的氧化铝粉末球化效果的影响。研究结果表明:粒径较小的氧化铝粉末颗粒在飞行过程中可以从等离子体内吸收更多的热量,因此能够被充分加热至完全熔化;增加系统输入功率、降低送粉速率均能提高单位质量的颗粒从等离子体中获得的能量,从而在一定程度上提升氧化铝粉末的球化率。

基于离散单元法的丝状颗粒传热数学模型

丝状颗粒作为一类长径比较大的非球形颗粒,其传热特性及相关技术广泛应用于工农业生产的诸多领域。但目前颗粒在运动过程中传热问题的研究还很不充分,特别是对于丝状颗粒,更是缺乏有效的数学模型进行描述。从颗粒传热机理出发,提出了一种基于离散单元法的丝状颗粒传热模型,模型中综合考虑了颗粒碰撞(接触)传热、颗粒的内部导热以及颗粒与气体间的对流换热。利用该模型,对固定床中堆积丝状颗粒的热量迁移过程进行了数值模拟,着重比较了各种传热方式对传热过程的影响。研究表明,对流换热对整体传热量的贡献较大。此外,还获得了不同工况下颗粒温度随时间的变化规律。

三维颗粒有序堆积多孔介质内强制对流换热数值研究

采用N-S方程和RNGk-ε湍流模型及比例缩放的壁面函数法对三维圆球颗粒有序堆积多孔介质孔隙内的强制对流换热进行了数值研究。详细研究了Re数变化及不同颗粒堆积方式对多孔介质强制对流换热性能的影响。计算结果表明:在相同条件下,通过对颗粒进行合理有序堆积,可以使相应多孔介质内的压降显著降低,其综合换热效率明显提高;传统经验公式用于颗粒有序堆积多孔介质须进行合理修正;在不同堆积方式中,简单立方体均匀堆积(SC)模型的综合换热效率最高;在相同堆积方式下,均匀颗粒堆积多孔介质内的综合换热性能明显高于非均匀颗粒堆积多孔介质。

300 kA铝电解槽中氧化铝颗粒的溶解模拟

在铝电解下料过程中,氧化铝颗粒吸热、结块、溶解并受到传热与传质溶解机制的综合作用。基于Open FOAM计算平台,有效区分主导颗粒溶解的控制机制,考虑气泡作用和下料后的电解质温度响应,开发铝电解槽中氧化铝颗粒传热、传质耦合溶解计算模型;利用Rosin-Rammler分布函数计算下料后电解质中氧化铝颗粒粒径分布,对实际300 k A铝电解槽中氧化铝溶解过程进行数值模拟。结果表明:前18 s氧化铝溶解50%(质量分数),属于快速溶解阶段;一个下料周期144 s结束后,剩余约1.5%(质量分数)的氧化铝未溶解,未溶解颗粒聚集,并在电解槽底部形成沉淀;仅考虑氧化铝溶解吸热的情况下,下料区位置电解质温度在前1 s快速下降,随后,电解质温度快速回升并在60 s之后呈现震荡趋势。

大颗粒流化床传热数值模拟与气固传热模型比较

采用欧拉-欧拉模型对GeldartD类颗粒气固流化床的非定常传热过程进行了模拟,比较了包括Gunn模型在内的6种不同的气固传热系数模型.通过模拟二维流化床发现,基于6种气固传热模型得出的平均壁面传热系数与文献的实验关联式相差不大,但是6种模型给出的局部气固传热系数呈现较大的差别,其原因在于不同模型中的两个主要影响参数颗粒雷诺数和床层空隙率的贡献不同.比较了6种气固传热模型之后,采用Gunn模型对D类颗粒的流化床进行了模拟和分析,结果表明:尽管存在较大的气泡和一定程度的腾涌,D类颗粒流化床可以实现稳定的流化.从流化床内的温度分布的演化来看,D类颗粒流化床的传热均匀性不存在问题,较大的颗粒直径和较大的气泡并未造成传热问题.

冶金渣颗粒与空气间的换热和阻力特性

对空气绕流高温冶金熔渣颗粒进行非稳态三维数值模拟,研究不同绕流雷诺数下熔渣颗粒与空气的换热性能以及熔渣所受空气的阻力特性。结果表明:空气冷却渣粒时,高温渣粒与空气换热出现了不均匀性,熔渣迎风面换热迅速,背风面的回流加强换热,空气温度较高;熔渣颗粒的平均努塞尔数(Nu)随着绕流雷诺数(Re)增大而增大,粒径越小,则平均努塞尔数越小,空气流速越大则平均努塞尔数越大,同等条件下粒径对平均努塞尔数的作用比空气流速的作用更强烈。不同粒径的绕流雷诺数可将平均努塞尔数一元拟合为非线性幂次函数,得到空气绕流熔渣颗粒对流换热计算关联式;熔渣阻力系数随着绕流雷诺数的增大而增大,最终趋于恒定,空气流速需要优化控制。绕流雷诺数将阻力系数CD进行一元非线性拟合,得到熔渣绕流阻力系数的计算关联式。

层流曳带流反应器内流动和温度特性的数值模拟

用计算机模拟方法对层流曳带流反应器内的流动和加热特性进行了详细的数值计算，描述了煤粒在该反应器内的加热速率、停留时间以及煤粒的温度－时间曲线，为正确地解释该反应器内的燃烧和热解试验数据提供参考。

固定床中丝状颗粒的传热传质特性

目前对于固定床中丝状填充颗粒传热传质特性的认识仍处于初始阶段。为了能够从颗粒尺度的微观层面揭示丝状颗粒与气体、颗粒与颗粒之间的热、质传递机理,建立了一种丝状颗粒传热传质数学模型,之后将离散单元法与计算流体力学相结合,对实验中较难获得的床层局部流动及传递信息进行了数值模拟,并着重分析比较了气流入口温度以及表观气速等关键因素对固定床中丝状颗粒温度和含水率变化的影响规律。通过模拟结果与实验数据的对比,验证了所建模型的可行性。研究结果表明:同一时刻,固定床中颗粒温度大体上是随着床层高度的增加而降低,含水率则是随着床层高度的增加而升高;气流入口温度对于固定床中丝状颗粒平均温度的提升起着主导作用,而颗粒的传质速度则受表观气速的影响更为明显。

颗粒传热增强对微型脉冲推力器点火过程的影响

为了分析点火药产物中炽热颗粒对固体脉冲推力器点火过程的影响,采用了颗粒对壁面的冲击热增强模型来模拟炽热颗粒对推进剂表面的传热增强效应,进行了微型脉冲推力器点火过程的数值分析。结果表明,颗粒热增强效应显著影响脉冲推力器的点火启动过程,颗粒的热增强效应显著缩短了点火延迟时间,并使点火启动过程的压强增大,点火过程对颗粒含量较少的点火药更敏感;设计微型脉冲推力器点火器时要严格匹配产物颗粒含量,并严格控制点火药量范围。