压力型雾化喷嘴射流喷雾气-液两相流数值模拟

为了研究喷雾压力和环境气流速度对射流喷雾的雾化效果及喷雾雾场的均匀性的影响,基于流体力学理论,建立压力型喷嘴喷雾的数值计算模型,利用计算流体动力学软件Fluent对喷雾雾场进行气-液两相流数值模拟研究,并通过大量的数据统计定量分析雾滴粒径的分布情况。结果表明:在喷射压力一定时,风速越大雾滴飘移能力越强,风速过大或过小都将严重影响雾化雾场的均匀性;在一定范围内喷射压力越大,雾化效果越好,所形成的雾滴平均粒径越小。     

街道峡谷内细微颗粒物扩散特性的DPM数值模拟

应用离散相模型(DPM)对城市中典型的街道峡谷内细微颗粒污染物浓度场进行了模拟,计算湍流模型选择标准k-ε双方程模型.计算结果表明,城市风场作用于街谷内导致涡旋流动,进而影响颗粒物的扩散分布.背风侧壁面颗粒物的浓度场呈现明显的"爬墙效应".不同几何结构影响颗粒物的浓度场,递增型街谷模型更有利于颗粒污染物的扩散.     

影响柴油机喷雾数值模拟精度的若干因素分析

为探明影响柴油机喷雾数值模拟精度的若干因素，采用通用商业软件FLUENT对柴油机喷雾特性进行了CFD模拟计算，分别研究了网格尺寸、喷雾粒子数和最大时间步长对油束几何形状及油束贯穿距的影响．结果表明，网格划分的精度和喷雾粒子数量的多少对计算结果的正确性和油束的几何形状有直接的影响，网格尺寸过大或喷雾粒子数过少则喷雾几何形状失真．最大时间步长对数值模拟的精度在一定的范围内影响是比较小的．     

基于激光粒度仪测量油品喷雾粒径的方法研究

为了测量油品喷雾过程的雾化性能,通过对喷嘴雾化粒径的指标和雾化粒径测定方法的分析,利用激光粒度仪及粒径发生装置设计喷嘴雾化实验系统,并对实验系统的工作原理进行描述;在不同喷雾压力下测定煤基柴油特征平均粒径dv10、dv50、dv90、d[3,2]、d[4,3]数据。结果表明:柴油雾化过程分为形成阶段、扩散阶段、稳定阶段;喷雾压力越大,雾滴特征平均粒径dv10、dv50、dv90、d[3,2]、d[4,3]参数值越小,雾化效果越好,并且随着喷雾压力的增大,液滴雾化粒径减小的趋势变缓。     

无人机静电喷雾治理开放性粉尘的数值模拟

将静电喷雾技术与无人机技术相结合用于治理开放性粉尘,使用Fluent对粉尘的扩散模型进行数值模拟.模拟得出无人机工作高7m,喷雾压力为0.2MPa时,无人机静电喷雾的平均降尘效率能达到85.87％,并在自然风速为1m/s、空气相对湿度为70％时,局部区域的降尘效率高达95.93％.本文提出的无人机静电喷雾控制开放性粉尘...     

真空闪蒸喷雾冷却中非等温液滴闪蒸特性的研究

真空闪蒸喷雾冷却是利用液体工质在真空环境下相变吸热来冷却加热表面的新型冷却手段。具有散热能力强、所需工质少,与加热表面没有接触热阻等优点,在航天器电子元器件冷却方面具有广阔的应用前景。液滴闪蒸是真空闪蒸喷雾冷却闪蒸过程的重要组成部分,要研究整个真空闪蒸喷雾冷却系统的闪蒸过程就必须对液滴的闪蒸特性进行研究。本文考虑液滴闪蒸过程中液滴内部存在的温度梯度和对流的影响,采用扩散控制蒸发模型并结合导热方程,对液滴的热导率进行修正,建立了热导率修正模型计算直径为微米级液滴在毫秒量级时间内的真空闪蒸特性,并通过实验验证。研究结果表明,导热模型较等温模型能更准确地预测液滴温度的变化;液滴闪蒸导致液滴到达被冷却表面时,其温度下降明显,但体积几乎没有变化;并且,环境压力越低,液滴的初始半径越小,液滴速度越大,液滴闪蒸对液滴温度的影响越明显。     

影响血浆冷冻效果因素的数值模拟研究

血浆袋中心点温度降至-30℃是衡量血浆冷冻过程的最终指标,冷冻过程中的降温速率和温度分布均匀性是决定血浆冷冻质量的关键因素。本文通过实验测定了血浆的热物性参数,结合数值模拟方法研究不同冷冻温度对血浆冷冻过程中降温速率和温度分布均匀性的影响。结果表明:降低冷冻温度,可缩短血浆中心达到-30℃所需的冷冻时间,但使血浆内温度均匀性变差;不同冷冻温度时,由于空气与血袋壁面换热能力相对较弱,血浆最高温度均分布在与空气接触壁面附近;通过增大血袋与冷冻箱内壁的接触面积或提高空气的流速、湍流度,可能成为增大血浆降温速率和温度均匀性的重要措施。     

基于数值模拟方法的循环流化床的颗粒特性分析

主要采用数值模拟的方法,以一台75t/h级额定蒸发量为90t/h次高压,自然循环、单炉膛、平衡通风、半露天布置、全钢架悬吊结构,燃料发热量为3000大卡,燃料采用混煤(50%)和煤泥(50%)混合燃烧,固态排渣,配国产15MW抽凝式汽轮发电机组的循环流化床锅炉为研究对象,从判断高浓度颗粒相的方法、高浓度气固流动的数值研究以及气固两相间的耦合三方面出发,对其高浓度颗粒相进行模拟分析,以得到循环流化床的浓相气固两相流动特性。     

基于离散元法的催化剂密相装填过程数值模拟

基于颗粒离散元法,对一种椭圆形密相装填器的催化剂密相装填过程进行数值模拟研究,分析布料盘转速和颗粒直径对装填过程的影响。结果表明:催化剂颗粒装填速度不等于布料盘上方料斗下料速度,而是随着布料盘转速增大而增大,随颗粒直径增大而减小。催化剂颗粒在反应器底部分布的直径范围与颗粒直径大小无关,它随着布料盘转速增大而增大。颗粒与反应器的碰撞是造成颗粒破碎的主要因素。利用该设备装填球形催化剂颗粒时,催化剂床层中心会出现凹陷现象,当颗粒直径较小时,床层中心附近会出现驼峰状的凸起。     

喷雾半干法脱硫塔内射流卷吸特性的数值模拟

喷雾半干法烟气脱硫塔内射流卷吸特性对塔内烟气与吸收剂的混合以及流场分布均匀有着重要影响。该文通过数值模拟的方法,分析双流体雾化喷嘴的射流卷吸混合特性,得到喷雾半干法烟气脱硫塔内射流流场分布。结果表明：双流体雾化喷嘴在塔内流场呈现中间大两边小的对称分布,并且在靠近塔壁的两侧产生了回流;射流流体与周围气体发生动量交换,对周围气体有明显的卷吸作用,沿着射流轴线方向,射流卷吸量逐渐增加,随着伴随风量的增加,射流卷吸量也逐渐增加。     

Numerical simulation of the thermal history of droplets during multi-stage atomization

Analyses are made on the characteristics of cooling and undercooled solidification of multi-stage atomized aluminum droplets. Models are established for Newtonian cooling, highly undercooled heterogeneous nucleation and steady-state continuous growth. They are used for numerical simulation of the thermal history of the droplets and the effects of the main atomization process parameters such as the extent of superheat and the speed of the rotating disk. Results show that large undercooling occurs mainly in the later stage of multi-stage atomization while recalescence and rapid quenching take place mainly in the forced cooling stage. The undercooling and cooling rates of the droplets are primarily dependent on the droplet diameter, and the main atomization parameters have little effect on the nucleation and solidification behavior of the droplets.     

Numerical simulation of the thermal history of droplets during multi-stage atomization

Analyses are made on the characteristics of cooling and undercooled solidification of multi-stage atomized aluminum droplets. Models are established for Newtonian cooling, highly undercooled heterogeneous nucleation and steady-state continuous growth. They are used for numerical simulation of the thermal history of the droplets and the effects of the main atomization process parameters such as the extent of superheat and the speed of the rotating disk. Results show that large undercooling occurs mainly in the later stage of multi-stage atomization while recalescence and rapid quenching take place mainly in the forced cooling stage. The undercooling and cooling rates of the droplets are primarily dependent on the droplet diameter, and the main atomization parameters have little effect on the nucleation and solidification behavior of the droplets.     

Numerical simulation of gas-solid flows in fluidized bed gasification reactor

A numerical model for simulating a fluidized bed gasifier should include appropriate parameters to capture the dynamics of gas-solid flows, gasification kinetics and the interaction between these two. The focus of the present study is to analyze the effects of coal gasification chemistry models reported in literature on the prediction of product gas composition in a fluidized bed gasification reactor. Numerical results are validated against the experimental data available in literature. The validated model is used to examine the available chemical kinetics schemes for water gas shift reaction, steam methane reforming reaction and char heterogeneous reactions. It is also used to assess the effects of hydrodynamic models parameters such as drag model, particle-particle restitution coefficient and specularity coefficient on exit gas composition. Results show that the predictions of product gas composition are notably affected by the choices of the kinetics schemes for water gas shift and steam methane reforming reactions. Systematic analysis using the available choices to simulate initial processes such as moisture removal, volatile and tar cracking is reported. Drag models and the value of specularity coefficient are shown to have no effect on product gas composition, and the particle-particle restitution coefficient slightly influences the predicted gas composition.     

热熔融流化床液固接触包衣特性的CFD-DEM模拟

为了研究热熔融流化床包衣的影响因素,优化包衣过程,采用计算流体力学(CFD)与离散单元法(DEM)耦合的方法,在4种流化速度下(u_(mf),1. 5 u_(mf),2. 5 u_(mf),3. 5 u_(mf))模拟熔融液滴与流化粉体的接触过程;研究热熔融流化床包衣过程中的参数变化对包衣过程的影响。结果表明,当液滴与粉体接触成粒时,产生聚并和破碎现象;顶喷流化床比中喷流化床的液滴与粉体的接触次数更多更充分;较理想的流化速度为1. 5 u_(mf)。     

蒸汽动能磨粉碎腔内颗粒加速特性的数值模拟

为研究颗粒经超音速喷嘴加速后在蒸汽动能磨粉碎腔内的加速情况,采用Fluent软件模拟蒸汽动能磨内的过热蒸汽流场和颗粒加速特性,获得不同物料在多种粒径和密度条件下的颗粒加速特性。结果表明:由于受喷嘴出口气流与环境压力匹配的影响,导致加速区域激波与膨胀波交替出现,使得过热蒸汽气流速度上下波动,最大波动幅度约为5%;在相同的过热蒸汽加速流场中,4种不同粒径的颗粒加速过程相似,粒径越小,颗粒的加速性能越好,其中直径为5μm的物料被加速达到的最大速度是直径为45μm的2倍左右,并且颗粒的加速性能与颗粒的密度呈反比关系。     

3D simulation on pressurized oxy-fuel combustion of coal in fluidized bed

Pressurized oxy-fuel combustion technology is considered as a perspective carbon capture technology in industrial process. A computational fluid dynamics (CFD) model based on Multi-Phase Particle-In-Cell (MP–PIC) method was developed to predict pressurized oxy-coal combustion process in fluidized bed. The heterogeneous and homogeneous combustion reactions of coal were considered in this model. The predicted results were validated the accuracy of this model with experimental data from a 15 kW_th pressurized fluidized bed combustor in terms of the gas component and temperature characteristics. The characteristics of gas–solid flow and combustion under different pressure (0.1–2 MPa) and oxygen atmosphere were studied in this work. The predicted results show that the intensity of particle motion and the expansion degree in the fluidized bed was gradually decreased with an increase in pressure. A correlation was proposed based on the simulation results to maintain suitable fluidization conditions in pressurized circulating fluidized bed at different pressures. The temperature of particle phase region gradually increased with combustion pressure and inlet O₂ concentration increased. In addition, the CO₂ concentration in outlet increased while the emission of CO and NO_x decreased as the combustion pressure increased.     

Semi-empirical mathematical simulation of larger-diameter fluidized bed coal combustors

The assumptions underlying a previously presented mathematical model for the simulation of fluidized bed coal combustors are tested Based on experimental results obtained in a larger-diameter combustor, the number of tran sfer units of the bed has been estimated. The value obtained is significantly lower than that expected assuming uniform bubble properties throughout the bed.