多流中间包内流体浪动模式的分析方法

提出了多流中间包内流体流动的联合RTD曲线分析方法,并从整体上对多流中间包平均停留时间作出新的解释.以某钢厂多流中间包为模拟对象,进行了水力学模拟实验,采用联合RTD曲线分析方法对多流中间包内流体流动模式进行分析,并与常用的方法进行了比较.实验结果表明,不考虑死区的缓慢流动将会使死区的计算结果产生较大偏差.运用联合RTD曲线分析计算多流中间包内流体流动模式,能够更真实地反映中间包内实际流动状况.     

多流中间包内流体流动模式的分析方法

提出了多流中间包内流体流动的联合RTD曲线分析方法,并从整体上对多流中间包平均停留时间作出新的解释.以某钢厂多流中间包为模拟对象,进行了水力学模拟实验,采用联合RTD曲线分析方法对多流中间包内流体流动模式进行分析,并与常用的方法进行了比较.实验结果表明.不考虑死区的缓慢流动将会使死区的计算结果产生较大偏差.运用联合RTD曲线分析计算多流中间包内流体流动模式,能够更真实地反映中间包内实际流动状况.     

弓形折流板换热器壳程流体流动过程模拟及结构优化

折流板的结构参数是决定换热器性能的重要指标.采用传统弓形折流板,对折流板不同板距和不同缺口高度条件下换热器壳程流体的流动过程进行数值模拟.研究了换热器壳程流体的流动行为,全面分析了折流板结构参数对壳程流体流动、停留时间分布及压降的影响;综合考虑设备的能耗和性能,提出了折流板结构参数的合理取值范围,为工业上弓形折流板换热...     

折流杆气-气换热器

该换热器是华南工学院在研究成功强化换热技术的基础上与桂林化工机械厂联合研制开发的。这种换热器把传统的折流板换热器中的折流板改成了杆式折流支承结构,其壳程流体的流动由折流式变为流体经支承杆网格造成局部湍动的平流式。因此,其特点是强化了管外壳程传热;传热面积得到了充分利用,减少了死区;防止了流体引起的振动;减少了阻力降。     

折流杆气—气换热器的试制和试用

一、概况折流杆换热器是把传统的折流板换热器中的折流板改成秆式折流支承结构。其壳程流体的流动由折流式改变为流体经支承杆网格造成局部湍动的平行流方式。因此有以下四方面的特点: (1)强化了管外壳程传热; (2)传热面积得到充分利用,减少了死区; (3)防止流体引起的振动; (4)大大减少了阻力降。以上第三和第四个优点,使该换热器的流体壳程流速可比普通的折流板式列管换热器大     

基于ANSYS-CFX的管壳式换热器壳程性能的数值研究

利用Pro/E对弓形折流板换热器进行了参数化建模,采用ANSYS-CFX对换热器壳程流体的流动与传热做了模拟分析。从数值模拟的角度分析了单弓形折流板换热器壳程振动和传热"死区"产生的原因,研究了不同折流板间距、不同折流板缺口高度及不同进口流速对换热器壳侧传热和压降的影响,并在此基础上对换热器的结构提出了优化措施。     

网状孔板纵向流换热器壳程流体流动及换热特性的数值模拟

应用CFD软件对网状孔板换热器壳程流体流动及换热特性进行了数值模拟研究,揭示了网状孔板强化传热的机理,分析了孔板间距及开孔率对其换热、压降性能的影响,推导出网状孔板纵向流换热器壳程换热与流动的准数关系式. 结果表明,流体流过网状孔板产生射流及二次流现象,强化了壳程流体的传热;在Re=2300~6300范围内,网状孔板换热器比弓形折流板换热器的Nu数增大约50%,但压降比弓形折流板换热器高约2.5倍;在研究范围内,孔板间距减小、开孔率减小均能使壳程流体的Nu数及压降增大,且Re数越大,开孔率、折流板间距对Nu数及压降的影响越大;但随开孔率、折流板间距减小,流体压降增加的速度明显比Nu数快.     

异波折流板反应器水力特性试验研究

以Cl~-为示踪剂,采用停留时间分布法(RTD)研究在清水和有污泥稳定运行条件下,HRT对异波折流板反应器和平板折流板反应器水力特性的影响,并进行了对比分析.结果表明,进水为清水、HRT为2～8 h,HRT对平板折流板反应器的水力特性的影响比异波折板反应器更为显著,异波折板反应器的流动模式处于平推流和完全混合的"中间状态".相同HRT条件下异波折板反应器的死区率小于平板折板反应器,异波折板反应器内接种污泥后,死区比清水反应器时有所增加,生物死区成为死区大小的主要贡献者.     

帘式折流片换热器壳程流体流动死区

对帘式折流片换热器壳程流体流动死区大小及分布规律进行了数值模拟和实验研究。研究表明,帘式折流片换热器壳程流体流动死区大小随着Re的增加而降低;流动死区的大小和分布规律受折流栅装配方式的影响,折流栅同向装配时壳程死区小于折流栅对称装配,当壳程Re分别为5000、10000和15000时,折流栅同向装配时的帘式折流片换热器壳程死区分别为折流栅对称装配时的50.5%、51.6%、43.0%。     

帘式折流片换热器壳程流体流动死区

对帘式折流片换热器壳程流体流动死区大小及分布规律进行了数值模拟和实验研究。研究表明,帘式折流片换热器壳程流体流动死区大小随着Re的增加而降低;流动死区的大小和分布规律受折流栅装配方式的影响,折流栅同向装配时壳程死区小于折流栅对称装配,当壳程Re分别为5000、10000和15000时,折流栅同向装配时的帘式折流片换热器壳程死区分别为折流栅对称装配时的50.5%、51.6%、43.0%。     

白钨矿连续酸浸槽内固体颗粒的流动特性实验及模型研究

以停留时间分布（RTD）为评价指标,对硫磷混酸浸出白钨矿的连续浸出槽内固相颗粒流动行为进行实验研究。同时探究了进料流量、搅拌转速、连续浸出槽中物料进出口位置组合对固相颗粒流动行为的影响。实验结果表明：随着进口流量的增大,一开始槽内的返混程度得到了增强,量纲为1化方差变大,但是继续增大进口流量,进口处物料的横向迁移速度加强,使槽内流体流动趋向平推流,导致量纲为1化方差减小;量纲为1化方差随着搅拌转速的增大而增大,但是此时在槽下部区域会逐渐形成循环死区,槽内死区体积分数随之增大;平均停留时间随着物料进出口位置的变化而发生变化,下进下出的进出料位置组合其平均停留时间最大,且最接近理论平均停留时间。最后利用非理想流动模型来表征实验过程中的停留时间分布,模型拟合的停留时间曲线与实验测量的曲线吻合程度良好。     

CFD simulation of solids residence time distribution in a multi-compartment fluidized bed

The present work focuses on a numerical investigation of the solids residence time distribution(RTD)and the fluidized structure of a multi-compartment fluidized bed,in which the flow pattern is proved to be close to plug flow by using computational fluid dynamics(CFD)simulations.With the fluidizing gas velocity or the bed outlet height rising,the solids flow out of bed more quickly with a wider spread of residence time and a larger RTD variance(σ2).It is just the heterogeneous fluidized structure that being more prominent with the bed height increasing induces the widely non-uniform RTD.The division of the individual internal circulation into double ones improves the flow pattern to be close to plug flow.     

Stochastic Modeling of the Particle Residence Time Distribution in an Opposed Multi‐Burner Gasifier

The gasification technology of impinging streams has been extensively applied to chemical production and power generation. Particle residence time distribution (RTD) is an important parameter required for modeling, designing and optimization of an impinging stream gasifier. A stochastic mathematical model based on the Markov chains model is developed for the opposed multi‐burner gasifier (OMBG), which closely describes the behavior of the flow pattern and particle RTD in the gasification system. The model simulates the motion of single particle moving in the gasifier using the Markov chains. The predicted results give a reasonable fit to the experimental data. This shows that the flow process of particles in the gasifier has recirculation eddies, which have a downward flow direction near the downflow core and an upward flow direction near the wall, but no short‐circuit. Finally, the effect of particle flux rate on the RTD is predicted, and the contrast between gas and particles RTDs at a laboratory scale and in an industrial gasifier are presented.     

流量控制方式对离心泵停留时间分布的影响

采用脉冲示踪法研究离心泵的停留时间分布(RTD),将离心泵与等径等体积空管对比,定性描述了离心泵的返混特征,考察了泵前阀控、泵后阀控、转速控制对RTD的影响. 结果表明,RTD曲线呈单峰分布,泵内有死区存在,返混大于等径等体积空管,无因次方差为0.39~0.61;离心泵的返混程度既不靠近平推流,也不靠近全混流,受流量影响显著,随流量增大,返混显著减小. 3种流量控制方式对离心泵返混有一定影响,转速控制的返混情况明显大于2种阀控方式,2种阀控方式的影响较接近;随流量减小,流量控制方式引起的RTD差异更显著,3种方式的无因次方差的最大相对偏差达13.6%.     

新型湿法除尘系统内气液两相流动的数值模拟

结合湿法除尘及挡板绕流技术,本文设计开发了一种带有挡板结构的新型湿法除尘系统。为探究该系统内挡板结构诱导产生的涡旋流动特性及其内部离散相运动规律,基于计算流体力学（CFD）方法,文章选用重整规划群（RNG）k-ε湍流模型数值对比了不同挡板参数下的涡旋结构、速度分布及压降情况等气相流场特性。同时利用离散相模型（DPM）分析了不同工况下喷淋液滴的运动轨迹、逃逸率及驻留时间表现。结果表明,集尘区内弓形挡板的设置可诱导产生涡旋流动,不仅能够抑制低速“流动死区”,同时还可不同程度改善喷淋液滴逃逸情况、有效延长其在装置内的驻留时间。综合考虑气相入口速度v、挡板安放角θ及喷淋液滴粒径D_p的影响,文章推导获得了液滴逃逸率的计算公式,可较为准确地预测喷淋液滴的运动情况。     

Modelling of flow in a wiped film evaporator

In a wiped film apparatus, the hydrodynamic conditions of the flow have a direct effect on the film thickness and on the residence time of the molecules and thus on the effectiveness of mass and heat transfer. Measurements of the residence time distribution (RTD), for different stirring velocities, allowed to propose a model for the flow as a series of perfectly mixed cells in parallel with a series of perfectly mixed cells exchanging mass with a dead zone.     

Residence time distribution of a pharmaceutical grade polymer melt in a single screw extrusion process

The residence time distribution (RTD) of a flowing polymer through a single screw extruder was studied. This extruder allows injecting supercritical carbon dioxide (scCO₂) used as physical foaming agent. The tested material is Eudragit E100, a pharmaceutical polymer. RTD was measured at various operating conditions and a model describing RTD has been developed. High screw speed or high temperature implies short residence time, but these parameters do not have the same effect on polymer flow. In the flow rate range studied, scCO₂ has no significant influence. A mathematical model consisting of a plug flow reactor in series with a continuous stirred tank reactor (CSTR) cross-flowing with a dead volume fitted well the experimental data.     

The flow pattern of solids in a gravity column

Flow pattern of solids in a gravity column (150 mm diam.) with peripheral discharge was studied by measuring the residence time distribution (RTD) of coloured solids tracer in the exit stream. The data were used to calculate dispersion numbers and flow volumes by applying a dispersion model and a multiparameter model respectively. The results show that the flow pattern of solids in the upper 75% of the column height was plug and that this flow pattern was virtually unaffected by the flow rate in the range investigated (35 – 75 g/s millet seed). The flow pattern of the solids in the bottom section of the column is shown to be markedly mixed and to depend on the flow rate. The paper also notes the usefulness of RTD analysis in providing flow models of bulk flow equipment which can give supplementary design and operating information not available by traditional methods.     

单流中间包气幕挡墙物理模拟研究

通过在实验室的物理模拟,研究透气砖底吹氩技术对中间包内钢液流动和夹杂物去除行为的影响。结合中间包内的停留时间曲线(RTD曲线)、平均停留时间及死区、活塞流体积分数,研究不同位置的透气砖对钢液流动特性的影响,并与不安装透气砖进行对比。结果表明,中间包底吹入气体后,能够有效改善钢液的流动状态,延长钢液的平均停留时间,并能延长响应时间、降低死区体积。当多孔导流隔墙距离中间包上沿600mm、气幕挡墙距多孔导流隔墙500mm时位置最优,平均停留时间最长,死区体积最小。     

撞击流气化炉内颗粒停留时间分布的随机模拟

根据多喷嘴对置式气化炉流场测试,将气化炉划分为若干区域,运用时间离散、状态离散的马尔可夫链随机模型,模拟了气化炉内颗粒相的停留时间分布(RTD)。当颗粒在撞击区和射流区间的回流比为0.5,向下撞击流股区和管流区为平推流模型,其他区域按全混流模型处理时,模拟值与实验值吻合较好。随着进料流量的增大,平均停留时间减小,量纲1方差减小;随着回流比的增加,平均停留时间增大;气固两相平均停留时间接近,但RTD存在一定差异。