KBN新型双通道燃烧器的可视化模拟

本文利用酸碱水模拟技术,对KBN新型双通道燃烧器出口情况进行了可视化模拟.模拟试验结果表明KBN燃烧器在不改变一次风量的情况,对于旋流强度和出口动量的调节都是可靠的、灵敏的.     

催化燃烧蒸发器内气体浓度冷态分布规律

催化燃烧蒸发器作为一种强化传热的有效手段,具有高效、结构紧凑和易放大等优点.催化燃烧蒸发器中的浓度场分布对其传热性能具有重要的影响.运用多空介质模型对燃烧蒸发器内部流体分布特性进行了CFD模拟,分析计算了冷态时N₂和H₂ 在混合腔内浓度的分布特性,同时进行了实验验证.模拟和实验结果具有相同的变化趋势,而且结果表明不同空速下燃烧蒸发器中存在较大的浓度分布不均匀性,改变出口位置对浓度场的分布具有一定的改善作用.通过对燃烧腔中浓度场分布的模拟为燃烧蒸发器的进一步优化设计提供了理论依据.     

化学反应器的电路模拟

<正> 化工过程模拟指对某一化工过程的数学模型或相似模型进行研究,它具有安全、重复性好,可进行稳定性及参数敏感性实验等优点,因而在化工技术中得到了广泛的应用。本文提出的用电路模拟反应器,属于相似模型的模拟法。与其它相似模型方法比较,电路模拟更加经济、安全,当需要改变反应器的设计和操作参数时,只需更换几个相应的     

煤粉空气分级燃烧中还原性气氛的模拟预测及分析

空气分级燃烧是广泛采用的煤粉低氮燃烧技术,使用数值模拟方法对其进行模拟预测,有助于燃烧设备的改进并优化燃烧,实现在燃烧中进一步降低污染物排放。空气分级燃烧数值模拟中对还原区的准确模拟是预测氮氧化物排放、硫化氢高温腐蚀等的基础。笔者旨在提出一种合理预测煤粉空气分级燃烧还原性气氛的数值模拟方案,并将其应用于实际锅炉的模拟,并探讨了还原性气氛预测准确性对氮氧化物排放、焦炭燃烧等的影响。主要内容包括:①对煤粉空气分级燃烧过程进行原理分析,提出数值模型开发及其应用的研究思路,即是通过小型电加热沉降炉模拟实际锅炉分级燃烧温度和组分浓度场,测量组分、焦炭转化等参数用于模型开发和验证,最后将开发的模型嵌入商用数值模拟平台,实现分级燃烧全过程模拟。基于此,搭建了能够反映实际锅炉空气分级燃烧温度场和组分浓度场特性的电加热沉降炉试验平台,并通过在线称重给煤速率、气体浓度组分测量,对试验系统的稳定性进行了验证。②设计不同工况的空气分级燃烧试验,并获取沿程CO、H_2、焦炭转化率等关键数据,基于数值模拟的动力学优化方法获取空气分级燃烧状态下还原区焦炭的气化反应动力学参数。通过开发用户自定义函数的方式在Fluent平台上实现了焦炭气化以及还原性气氛的模拟预测,并将其应用于600 MWe超临界墙式对冲炉分级燃烧的数值模拟。③分析比较了在模拟中不考虑气化和考虑气化时对炉内温度、还原区气氛、氮氧化物的分布和焦炭转化的影响。结果表明,文中提出的空气分级燃烧数值模拟方案能实现对实际锅炉空气分级燃烧特别是还原区的合理预测;在模拟中不考虑焦炭气化将导致还原性气体浓度明显偏低,导致颗粒燃尽推迟,炉膛出口氮氧化物浓度偏高。     

膜式水冷壁结构燃磷塔的开发与传质传热的数值模拟（Ⅱ）传热特性影响因素分析

利用已建立的数学模型考察了燃磷量、过剩空气系数、壁面温度、辐射吸收系数对新型燃磷塔的最高燃烧温度、烟气排放温度、壁面最大热流和平均热流的影响.模拟结果表明,无论过剩空气系数固定还是空气流量固定,随燃磷量的增大,最高燃烧温度、烟气出口温度、壁面平均热流和最大热流都呈上升趋势.在燃磷量不变情况下,最高燃烧温度、壁面最大热流和平均热流均随过剩空气系数的增大而减小,但烟气出口温度缓慢增加.壁面温度对最高燃烧温度、壁面最大热流和平均热流影响不明显,但烟气出口温度随壁面温度的升高而增加较大.辐射吸收系数对最高燃烧温度和壁面最大热流影响很大,随辐射吸收系数的增大,最高燃烧温度和烟气出口温度会下降,而壁面最大热流和平均热流会上升.     

膜式水冷壁结构燃磷塔的开发与传质传热的数值模拟(Ⅰ)模型建立

针对热法磷酸生产中一方面要求外部供热,另一方面又浪费自身燃烧热的现状,提出能回收余热的新工艺,开发成功膜式水冷壁结构新型燃磷塔.建立了考虑新型燃磷塔内流动、燃烧、传热过程的三维数学模型,通过数值模拟得到塔内湍流场、温度场和组分浓度场的分布.模拟结果显示,燃磷塔内存在明显的涡流射流结构,磷的燃烧主要在喷磷枪雾化角范围内,塔内最高燃烧温度约为1790 K,出现在喷磷枪轴线上偏离燃磷塔中心的一侧.烟气出口温度约为970 K,与测量值符合较好.     

波瓣喷嘴燃烧室燃烧特性的数值模拟

建立了波瓣式燃油多点喷射燃烧室模型,考察了波瓣诱发涡系对燃烧室燃烧特性的影响。采用文献的多点喷射燃烧室实验的空载、30%载荷、巡航与起飞4种工况,对波瓣喷嘴燃烧室内的流场涡系结构、燃烧多物量场及燃烧特性进行了数值模拟。结果表明,不同油气质量比下随空气质量流量增加,每个工况下的流向涡、正交涡等无量纲涡量逐渐增大,出口温场品质逐渐提高,NOx排放逐渐降低,燃烧效率和出口温度场改善。波瓣喷嘴燃烧室实验台的水流模型实验结果验证了模型计算结果的正确性。     

旋风分离器出口边界条件对其流场模拟的影响

研究比较了不同的出口边界条件对旋风分离器内流场CFD模拟结果的影响.模拟结果同LDV试验测量值的对比表明:采用充分发展出口边界条件进行模拟所得的流场在旋风分离器的升气管、内旋流部分与LDV测量结果相比存在一定的误差,而压力出口边界条件模拟的流场更接近于LDV测量值.因此,进行旋风分离器流场模拟时,应用压力出口边界条件得到的计算结果更为精确.     

5 000 t/d线DD型分解炉燃料燃烧组份 浓度场的数值模拟

分解炉是水泥窑外预分解技术的核心设备之一,承担着煤粉燃烧、碳酸盐分解等多种复杂的化学反应。本文对国内某厂5000t/d水泥熟料生产线的DD型分解炉内煤粉的燃烧进行了数值模拟,得到了分解炉内煤粉燃烧过程中挥发分、O_2、CO和CO_2的质量浓度变化规律。模拟发现本分解炉配风比例合理,没有出现过氧燃烧或缺氧燃烧,煤粉燃烧产物浓度分布符合燃烧规律,煤粉燃烧平稳有序进行,符合煤粉燃烧反应机理。     

CPFD在细颗粒料仓下料中的应用

借助计算颗粒流体力学(CPFD)的数值模拟方法,研究了细颗粒玻璃微珠在不同结构料仓内的下料特性,获得了料仓出口直径和半锥角对颗粒下料流动的影响。在实验室可视化下料平台开展了验证实验,模拟结果与实验结果吻合较好。模拟结果表明:下料流率与料仓出口直径2.5次方呈正比;料仓半锥角增大,下料流型从质量流过渡至漏斗流。CPFD模拟给出了料仓下料过程的细节信息,并获得了料仓结构对颗粒流动形态转变的临界面相对高度的影响。     

露天矿汽车运输系统模拟的一种新方法

应用元胞自动机模型，提出了露天矿汽车运输系统动态模拟新方法，该方法将时间、空间和系统行为三者紧密地联系在一起，在较为形象、直观和真实的条件下对运输系统进行了模拟。     

Distribution of the estimated lyapunov exponents from noisy chaotic time series

Abstract. In this paper, we give statistical analyses and simulation studies on the Lyapunov exponents estimated from noisy chaotic time series. Through the Jacobian estimation approach, the asymptotic distribution of the estimated Lyapunov exponents are studied and characterized from the observed noisy chaotic time series. Theoretical results are visualized and verified by numerical simulations.     

Numerical Simulation of Oil‐water Hydrocyclone Using Reynolds‐Stress Model for Eulerian Multiphase Flows

A three‐dimensional oil‐water turbulent flow and oil separation process in a double‐cone liquid‐liquid hydrocyclone (LLHC) is numerically simulated using FLUENT software. The Euler‐Euler approach and Reynolds‐stress model are combined and adopted in this simulation to handle the challenging situation of anisotropic turbulent two‐phase flow with a higher volumetric ratio (over 10%) in the dispersed phase. It is visualized well in the simulation how separation, aggregation and shift of oil and water proceed in the LLHC. The oil separation efficiency is determined based on flow field and phase concentration distribution. The simulation is verified by comparing predicted and measured separation efficiency in the LLHC.     

High-temperature degradation of butadiene-based model elastomers by reactive molecular dynamics simulation

Thermal degradation of butadiene-based model elastomers was analyzed via a novel reactive molecular dynamics simulation (ReaxFF) method. The molecular simulation was carried out on 40 monomer units connected together. Degradation pathways of both homopolymer and copolymer of butadiene-based model elastomers such as polybutadiene (BR) and poly (styrene-co-butadiene) (SBR) were studied. The evolution of different fragmented products was examined as a function of time and heating rate. The formation mechanisms of different degraded fragments were visualized via the simulation method. The major decomposition products obtained from these model compounds were the monomers and comonomers. Pyrolysis gas chromatography–mass spectrometry (py-GC–MS) analysis was performed on the commercial samples of BR and SBR to verify the simulation results. The results obtained from the reactive simulation were very consistent with the experimental results. The activation energy required for the thermal decomposition of butadiene-based model elastomers were calculated both from the ReaxFF simulation and thermogravimetric analysis (TGA). The results were also in good agreement. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48592.     

SIMULATION OF A TWO PHASE FLOW BY CFD: ANALYSIS OF THE COMPUTATIONAL METHOD

When using a Computational Fluid Dynamics (CFD) code for the simulation of a two phase system, special attention must be given to the solution procedure. Fluid dynamics in CFD codes are obtained by iterative computations, and criteria must be established to decide the number of iterations needed to obtain a convergent solution under certain defined conditions. In this work, the predicted liquid and gas flow patterns obtained in the simulation of hydrodynamics in bubble columns are analysed throughout the computational process, and the effects of some parameters affecting the computation are studied (dimension of the grid, working conditions, scale-up, relaxation used in the calculations, free surface performance). It was found that each of these parameters affects considerably the solution procedure (though in a different manner) and therefore no general criteria can be established to decide the number of sweeps necessary for a certain simulation. It is concluded that every simulation should be analysed individually each time the conditions are changed. This analysis clearly helps to understand the reliability of CFD predictions in complex systems.     

多孔介质电渗流动计算流体力学模拟与实验研究（Ⅰ）多孔介质电渗流动的CFD模拟

采用周期性空间模型描述多孔介质,根据电动力学理论及计算流体动力学方法对多孔介质内的电渗流动行为进行数值模拟,得到多孔介质孔内与颗粒表面可视化的流场,并对比了多孔介质中压力场驱动与电场驱动的流体流动特性,显示出电渗在强化固体表面流体流动所具有的优势.     

啮合同向三螺杆挤出机中三维等温流动的数值模拟

Three-dimensional isothermal flow of polymer melt in the kneading-disc element of an intermeshing co-rotating tri-screw extruder was simulated by using finite element package POLYFLOW. Based on the velocity fields calculated, flow patterns of the melt were analyzed, and particle trajectories were visualized. The numerical results indicated that, in intermeshing co-rotating tri-screw extruders, particles went through three intermeshing regions during one cycle around the screws, thus achieving better plasticating and mixing than intermeshing co-rotating twin-screw extruders. Flow in the central region was also studied by using particle tracking technique, and residence time distribution (RTD) and trajectories for particles in this region were presented. The simulation results showed that there was no stagnation in the central region. This study provided a clear insight into the flow mechanism of tri-screw extrusion. It also provided a new method for studies of flow mechanisms in other complicated mixers.     

Global sensitivity analysis in the flowsheet simulation of solids processes

This paper proposes a strategy for the global sensitivity analysis in the flowsheet simulation on solid processes which allows to examine and quantify the influences of given parameters on specific target criteria. The strategy is basically divided into two parts: The first is the effect analysis which provides the range of possible values of a target variable. This permits an estimation of the accuracy of a simulation with uncertain parameters. As the second part the influence analysis builds a hierarchy of the different uncertain parameters according to their impacts on a specific target criterion. This latter information can be used to decrease the efforts for parameter estimation in a given process simulation by focussing the efforts on the most influential parameters. The strategy for global sensitivity analysis suggested here is applied to a soil washing process where an oil-contaminated soil is to be cleaned such that both the amount of the contaminant concentrate to be disposed and the residual oil contamination of the cleaned soil are to be minimized.     

临界热流的数值模拟

建立了以加热板为计算域的核沸腾瞬态数值模型,以沸腾表面局部换热为边界条件,对多种工质在不同压力条件下的控制方程、边界条件和计算过程进行了量纲1化处理,并考虑了由核心随机分布产生的气泡重叠效应.数值研究包括模拟整个核沸腾曲线和临界热流（CHF）.研究结果表明平均瞬态活化核心间距和气泡覆盖率可以作为沸腾到达CHF的判据.数值模拟的CHF与表面粗糙度无关,而与饱和压力有关,这与Kutateladze和Zuber等的关系式的结果相符合.     

水／二甘醇两级升温吸收式热泵的性能模拟

通过对水／二甘醇两级升温吸收式热泵理论循环过程进行模拟,从热力学原理出发,讨论了评价热泵系统性能的参数,提出了较全面反映热泵效率的判据。