多层百页窗式挡板对三相流化床中液相混合行为的影响

在矩形气液固三相流化床反应器中,采用脉冲应答技术测定了液相混合时间、液体下降速度及液体混合现象。考察了挡板结构对床层液体混合行为的影响。采用多釜串联模型表征液体混合程度。结果表明,在床中设置挡板构件,对床下段液体混合时间、液体下降速度以及液体混合程度的影响不太明显。     

底部挡板与进气位置对水力喷射空气旋流器传质性能的影响

水力喷射空气旋流器(water-sparged aerocyclone,WSA)是一种利用液体射流在气体旋流场中雾化强化气液传质的新型传质设备,可广泛用于废水、废气处理等环境工程中。为了改进水力喷射空气旋流器结构,提高其气液传质性能,本文通过废水氨氮吹脱实验研究了进气口轴向位置以及底部挡板的设置对气液传质性能的影响。实验结果表明,进气位置与底部挡板对水力喷射空气旋流器的气液传质性能存在影响。在相同工作条件下,气相进口沿轴向下移对WSA内气液传质性能作用较小,但能够使其气相压降降低约为10%。在WSA主筒体底部液封区域设置挡板,能够强化WSA底部气液两相的混合,进而提高低液相循环流量下WSA内的气液传质性能,且随进气速度的增加,其效果越显著,研究结果可为设计传质性能良好的WSA提供设计依据。     

混合池模型推算气液返混对精馏效率的影响

精馏操作过程中 ,气液返混现象对精馏传质效率有重要影响。为预测其影响规律 ,文内针对含有错流塔板且气相预混合的精馏塔 ,提出了气液返混发生时计算精馏效率的混合池模型。所得计算结果与实验数据的比较说明模型是可靠的。在此基础上 ,根据计算结果 ,探讨了不同情况下气液相返混对精馏效率的影响 ,发现气体返混和液体返混的发生均导致板效率下降 ,且过程的汽提因子和点效率越大 ,板效率随返混的发生而下降的速度越快。     

筛孔塔板上气相错流对液相流场影响的实验测量

利用热膜流速仪、测量了矩形塔内光板上液体单相流动以及筛孔板上气液两相流动时的液体流速分布，实验主要考察气液两相错流时，气体鼓泡作用对鼓泡区下游液体流速分布的影响，实验结果表明，单相流动时，受壁面效应的影响，靠近塔壁的液体的速度最低，气液两相错流时，受气体阻力作用的影响，靠近壁面液体的速度反而大于远离壁面处液体的速度，气相流量越大对液相流场的影响作用越强。     

气液搅拌釜中不同因素对混合时间的影响

在液体石蜡中通入氮气的气液搅拌釜中,通过光差法确定特定混合状态和达到该状态的混合时间,研究了多种因素对气液混合时间的影响。进气流量较小时,随进气流量增加,混合时间明显缩短;但当进气流量达一定值时,混合时间变化很小。比较了12个搅拌桨,转速和进气流量均相同时,6叶大圆盘涡轮桨混合时间最短;列出了4种桨型混合时间的长短顺序。转速和进气流量一定时,用4挡板替换3挡板,混合时间略有缩短。     

漏斗型导流内构件对内循环三相流化床流体力学与传质特性的影响

通过增加新型内构件来改善内循环三相流化床的流体力学与传质特性,以实现化工、环保领导中追求高氧利用率的过程。针对此过程设计了3种不同结构参数的漏斗型导流内件并设置于导流筒顶端,分别测定反应器内气含率、液相混合时间、液体循环速度、体积氧传质系数的数据并分析其变化规律,以解析内件的作用机制。实验在有效体积39L,以空气为气相、水为液相、多孔泡沫颗粒为固相的反应器中进行,研究发现：漏斗型导流内件的设置使升流区气含率平均增大10%,体积氧传质系数kLa提高了15%,液相混合时间下降10%-25%;内件的设置可以改变液体循环速度,当表观气速<0.5cm/s时,液体循环速度加快,当表观气速>0.5 cm/s时,液体循环速度下降;此外,漏斗型导流内件的结构参数变化对流化床流体力学与传质特性有较大影响。结果表明,流化床内增加新型内构件并合理设置能够实现反应器效能的提高。     

机械搅拌反应器中挡板的结构设计

研究了内径为0．786m的搅拌釜中挡板尺寸及结构对圆盘透平桨RT和翼型桨k5及其组合在气液两相中的气体分散与混合特性的影响。对不同形式的挡板的搅拌功率、气含率及气液混合特性进行了对比分析。研究结果表明：挡板尺寸结构应根据搅拌特性需要进行优化设计;挡板系数为0．12时,组合浆的功率输入已与同一转速下的全挡板系数时的功率输入相近,它同时可改善微观混合、提高混合效率：采用开槽挡板可提高复杂快反应的选择性,混合效率提高20％～25％。     

底隙设置挡板内循环流化床水力特性分析

针对流化床反应器中多相流体混合碰撞的复杂性、突变性的问题,以底隙设置十字形挡板反应器的水力特性改变为研究对象,采用电导法测定反应器内液体循环速度和混合时间等动力学数据及其变化,分析新型内构件的强化作用原理。研究结果发现,两相条件下,十字形挡板的设置使反应器的升流区及降流区的液体循环速度分别提高9.5%±1.0%和11.8%±1.0%,低流速时,液相混合时间变长,高流速时,混合时间反而短缩,变化范围在±5%,计算的摩擦阻力系数由4.13降低为2.75,证明了流体在反应器底部碰撞能量消耗的下降。通过全环路能量衡算得到液体循环速度模型计算参数的实验关联式,应用于三相条件,计算值与实验值误差在8%以内。表明在急剧湍流内循环流化床底部设置挡板所实现的流态有序、矢量归一的目标能有效改善反应器中流体的水力特性而使流体稳定,并进一步实现稳态运行条件下的节能。     

改良型CO2湿壁塔内气液两相流动规律及传质特性

基于Fluent软件，采用层流模型、VOF模型及非稳态类型，模拟基准湿壁塔和改良型湿壁塔的气液两相流场，分析稳定液膜边界气液两相流场对传质过程的影响。结果表明，随液相入口流量的增大，在稳定液膜边界气相涡旋运动逐渐增强，气液两相混合程度加强，利于改良型湿壁塔的气液两相传质。在一定气相入口流量范围内，随气相入口流量的增大，液膜界面涡旋运动增强，气液两相混合程度加强，利于改良型湿壁塔的气液两相传质；气相入口流量不宜过大，否则导致液相不能沿湿壁柱向下流动形成稳定的液膜，不利于传质。改良型湿壁塔的变径结构和气体挡板均利于气液两相混合，利于传质。改良型湿壁塔的传质过程在液膜边界发生，随液相入口流量的增大液膜厚度增加，液膜表面积增大，有效传质面积增大，利于气液两相传质。通过对比基准湿壁塔和改良型湿壁塔的气液两相流场，改良型湿壁塔内气液两相混合程度加强，更利于传质。     

不同出入口条件下气液喷射器喷射性能的数值模拟

针对气液喷射器传统二维几何模型和模拟中未考虑温度导致气液相变的不足,建立三维几何模型,导入考虑时间、温度影响的气液相变UDF程序,用CFD软件模拟气液喷射器喷射性能.40000 s条件下有相变的模拟结果与实际情况符合较好.改变气液喷射器出入口气液相的速度和压力条件,得到气液喷射器轴线速度、压力、温度、引射比及气液相体积分数等参数.结果表明,随液化天然气(LNG)入口速度增加,气液喷射器引射比增大,合理的LNG入口速度能使喷射器内各相体积分数及引射比趋于稳定,有利于喷射器正常喷射;随混合出口压力增加,引射比减小,LNG体积分数增大,过大的出口压力会导致气液喷射器内喷射偏斜、扩散室出口气相闪蒸汽(BOG)液化现象,不利于喷射器正常喷射.液相入口速度11~12 m/s、混合出口压力0.101~0.304 MPa时,气液喷射器喷射性能最优.     

EFFECT OF BAFFLE ON TRAY UNDER OSCILLATING CONDITION

Effect of baffle on a tray under oscillating conditions has been examined experimentally. To reduce the degree of liquid mixing and liquid channeling under oscillating conditions, it is necessary to install the baffles on tray.

Experiments were conducted with the air-water system, ft was found that the pressure drop change can be expressed as a sinusoidal function and the period coincides with tray oscillation. The degree of liquid mixing decreases when the baffles are installed on tray and it also decreases with the increase of liquid flow rate. The pressure drop increases with the installation of baffle on tray.

The suitable baffle number on tray is from 4 to 8 and in this region, the degree of liquid mixing reaches minimum and the liquid holdup takes a maximum value. @KEYWORDS: Tray, Oscillating, Liquid mixing, Baffle, Pressure drop, Liquid holdup.     

搅拌釜中自浮颗粒三相体系的混合时间

液相混合时间是搅拌过程中的重要内容。在釜径３８６ｍｍ的搅拌釜内,采用热电偶温差法考察了搅拌桨型、挡板、等操作因素对自浮颗粒三相搅拌混合的液相混合时间的影响。     

Improvement of granular mixing of dissimilar materials in rotating cylinders

We have found that periodic flow inversions of free-flowing materials may be used to effectively eliminate both size and density segregation in free-surface flows. In a rotating cylinder, these inversions may be induced by placement of an axially located baffle within the flow. In this work, we report on an experimental study of radial mixing and segregation for binary mixtures of granular materials in a rotating cylinder both with and without an axially-located baffle. Qualitative and quantitative measures of the segregation/mixing are shown via digitized images and the intensity of segregation, respectively. We define a mixing improvement factor (ψ) to quantify the relative impact of the axial baffle for a variety of baffle placements and geometries. We find that the maximum extent of mixing is achieved when the baffle size is equal to the radius of the cylinder and fixed either at the free surface or within the shear layer. In contrast, we show that segmenting the baffle, baffle placement outside the shear layer (in fixed bed), or placement at the periphery of the cylinder resulted in an insignificant increase in mixing. Mixing was found to be independent of the shape of a baffle.     

基于循环灰热载体煤热解的固-固颗粒冷态混合特性

以开发循环流化床（CFB）燃烧/煤热解分级转化工艺为应用背景,为在移动床混合段内利用有限高度空间达到理想的灰/煤混合效果,建立了内置锥面形挡板结构的固-固冷态混合实验装置,并对颗粒的混合特性进行了研究。分别以石英砂和硅胶模拟CFB循环灰和煤,采用挡板重力混合的方法,探究了挡板角度、层数、放置方式（对向和旋转放置）以及物料混合比等因素对混合效果的影响,并与机械混合实验进行了对比。结果表明,在混合过程中颗粒的混合和分散是并存的,旋转放置30°的挡板层数越多,硅胶和石英砂颗粒混合越均匀,混合物料中石英砂比例越高,混合效果越好。通过优化挡板结构及设置方式强化对流混合和剪切混合可明显改善固-固混合效果。虽然与机械混合相比,挡板混合效果略差,但在一定操作范围内仍可满足灰/煤混合热解工艺的要求。     

Flow Field Analysis of Stirred Liquid‐Liquid Systems in Slim Reactors

Previous studies have shown the great potential, but also the great challenges, in handling slim reactors often used for polymerization reactions. Experiments and simulations were carried out in reactors with aspect‐to‐diameter ratios of up to 5, to test and to evaluate the mixing and dispersion efficiency for liquid‐liquid systems of single‐ and multiple‐stage impellers. Therefore, power consumption, mixing time and minimum dispersion speed were determined for five different stirrer types under turbulent conditions. It was found that the dimensionless mixing time is highly sensitive to the configuration of the impellers, with almost no dependency on the turbulent power number. Another focus was the analysis of the effect of the baffles. The influence of the baffle length in slim reactors on the mixing time and the macroscopic flow field was determined.     

On the effect of gap size between baffle outer diameter and tube inner diameter on the mixing characteristics in an oscillatory‐baffled column

We report our experimental investigation on the effect of gaps between baffle outer diameter and inner tube diameter on the mixing characteristics, in terms of mixing time and axial dispersion coefficient, in a batch oscillatory‐baffled column. Local concentration profiles are measured using conductivity probes at two locations along the height of the column. The mixing time was determined based on the equilibrium concentration concept, and the axial dispersion coefficient was obtained by solving the axial dispersion governing equation. Comparison of mixing time between the ‘push‐fit’ and ‘loose‐fit’ baffle arrangements was carried out and the results showed that the existence of a gap of various sizes between the baffle outer and the tube diameters lengthened the time at which the state of uniform mixing is achieved in such a device. © 1999 Society of Chemical Industry     

组合桨聚合釜内非牛顿流体的混合特性

在φ476mm的椭圆底有机玻璃聚合釜中,以羧甲基纤维素-甘油水溶液(前者质量分数为1.3％)为实验物系。利用酸碱中和法测定了9种不同的搅拌桨直径与聚合釜直径比接近于1的组合搅拌桨沿聚合釜轴向及径向的混合特性。结果表明：内外螺带-锚式组合桨的轴向混合最强,但径向混合较差。框板式搅拌桨的轴向混合较内外螺带-锚式组合桨弱,但比改进偏框式桨强,其径向混合较后者弱。改进偏框桨的7种不同组合方式沿径向的混合良好,多数组合桨沿轴向的混合较前2种组合桨弱,更接近于平推流。     

Effects of Geometrical Factors on Liquid Mixing in a Gas-Induced Agitated Tank

An agitated tank having two 45° pitched blade downward turbines in series and four thin baffles which were narrower than the conventional ones was studied. At higher impeller speeds, a gas and liquid vortex induces the gas above the liquid surface vertically downward into the turbines, which in turn cuts the gas stream into bubbles which then circulate in the liquid. Consequently gas-induction increases the gas utilization ratio as well as simplifying the ancillary equipment otherwise required to recycle the escaped gas. The relationship between tank geometrical factors and the liquid mixing time was also investigated. The experimental variables investigated were the impeller speed, the baffle width, the turbine diameter, the space between two impellers, the liquid level, and the clearance between the lower turbine and the bottom of the tank. The results showed that all but the clearance between the lower turbine and the bottom of the tank had significant effects on the mixing time under normal gas-induction, revealing results in contrast to the conventional agitated tank. © 1997 SCI.