气-液并流通过堆叠筛板填料的脉冲流特性

通过高速摄像机和压力传感器测量,对脉冲流的产生机理、筛板数的影响、液相脉冲传播速度及频率进行了系统的研究。实验发现：脉冲流是重力和气流曳力作用下,孔口液相波动在向下传播过程中被叠加放大的动力学过程,且与气、液流量及筛板数密切相关;一定气量下,脉冲流的产生需要有一个最小（临界）液相流量,且增加液量可促进局部脉冲的产生,并使液相脉冲传播速度与频率均增大;临界液量之上,增大气量,气相的扰动作用增强,局部脉冲越容易产生,从而导致脉冲传播速度与频率均增大;进一步增大气量,液相脉冲会被逐渐分散,导致脉冲传播速度与脉冲频率均减小。增加筛板数,有利于增强脉冲流强度,从而导致脉冲流范围变宽,当筛板数少于三块时不会出现脉冲流。最后,基于实验结果分析,提出了脉冲传播速度及频率的预测关联式。     

气液并流筛板流态的模拟

文章利用CFX软件对开孔率为17%、150×120 mm的矩形气液并流筛板的气液两相流态进行模拟,分析了气液两相并流筛板的传质传热机理及筛板压降产生的主要原因。通过模拟研究了气液两相并流时气相和液相流量变化分别对塔板压降产生的影响。     

气液两相并流向下通过筛板孔口单元的压降特性

针对堆叠筛板填料的基本单元,采用12种不同规格的孔板,研究了气液两相并流向下通过孔口的压降特性,阐明了气液流量、孔板结构对压降的影响规律。结果表明：压降随气液流量的增加而增大;随孔径的增大而减小;在筛板常用厚度范围内,孔口锐缘效应使得压降随板厚减小而增大。根据孔口压降行为不同,以气相雷诺数Re_G=5000分界,建立了单一气相向下通过孔口的压降预测关联式;然后利用气相折算因子对关联式进行修正,得到了Re_G>5000时气液并流向下通过孔口的压降预测关联式;当Re_G<5000时,通过直接对单一气相阻力系数进行修正,得到了相应气相雷诺数范围内的气液两相压降预测关联式。     

气液两相并流下行通过堆叠筛板填料的压降特性

堆叠筛板填料已在核电站放射性气体除气塔中得到成功应用。针对这一新型填料的应用设计,在较广泛的气液流量下,对气液并流下行通过不同规格堆叠筛板填料的阻力特性进行了系统的实验。实验填料共6种规格,孔径参数包括6、10和14 mm,不同孔径填料对应不同的孔间距、板间距,每种孔径填料具有正方形和正三角形两种筛孔分布方式。通过压降数据分析,研究了流动参数和几何参数（孔径、开孔率、布孔方式、板间距）对气液两相并流通过填料的流动行为及压降特性的影响;结合多孔板阻力系数经验公式提出了堆叠筛板填料干板阻力系数的计算模型,模型很好地反映了不同几何参数对干板阻力系数的影响,预测偏差在5%范围以内;基于均相流模型提出了堆叠筛板填料气液两相压降的预测模型,模型预测偏差在10%范围以内。研究工作对堆叠筛板填料塔的应用设计及进一步的传质动力学研究有一定参考价值。     

气液并流填料塔的持液量

本文提出用静持液准数E对文献及本试验静持液数据进行关联;在受力分析基础上得到单相持液的半经验关系式,使用范围及精度均比文献值有所提高。对脉冲流区后的动持液量提出了单独的经验关联。     

加压下规整填料塔内气液两相流返混的实验研究:气相返混系数

规整填料因具有生产能力大、分离效率高、压降低、操作弹性大、持液量低等诸多优点 ,目前已被广泛应用于精馏、吸收及萃取等多种化工单元操作中 .通常只在常压或减压条件下操作 ,而在高压或大液相负荷下 ,因流体物性的变化及流动状态的改变 ,使塔内产生严重的返混 ,塔效率显著降低 .因此 ,研究加压下规整填料塔内流体的流动状态具有重要意义 .对于加压下填料塔内气相返混的研究 ,中国台湾的ＴａｎＣｈｕｎｇ -Ｓｕｎｇ[1] 在低实验气速 (0 .0 0 2～ 0 .1ｃｍ·ｓ- 1)下做过初步的研究 ,其实验填料为散堆填料 .Ｋｕｒｔｚ[2 ] 在这方面的研究…     

气液向下并流填料塔的持液量

用φ15mm的陶瓷拉西环和塑料鲍尔环填料,在内径153mm的有机玻璃塔内,采用空气-水体系,测量了气液向下并流流动时的持液量数据。以Bemer等人提出的颈缩管模型为基础,推导了向下并流填料塔内的持液量计算式,较好地关联了本实验和Dodds等人的结果。并检验Larkins,Charpentier,佐藤等人提出的持液量关联式。     

气-液-液萃取的流体力学研究

在液-液萃取过程中,提高分散相的表面更新速率可有效提高萃取的传质效率。研究发现,在萃取过程中使用气体搅拌可以增加液液之间的接触面积,促进液相内的湍动和循环。本文研究了气-液-液三相下油滴的流动形态,并对不同填料的流体力学性能进行了测定。实验结果表明,气相速度的增加可导致气含率、液含率的增加,从而提高分散相在填料萃取塔中的停留时间,在一定的速度范围内明显降低萃取的表观传质单元高度,极大地强化传质效果。通过与散装填料对比,发现规整填料更利于强化萃取效果,其液泛速度平均增加25%。     

新型规整填料——脉冲填料的流体力学性能研究

本文研究了新型规整填料——脉冲填料(impulse packing)的流体力学性能。研究结果表明,该填料比一般乱堆填料性能为好,它的压降较小,处理量较大。     

填料塔气液并流接触时压降的研究

以内径72 mm的玻璃吸收塔为主体,分别采用Mellapack-250X型金属孔板波纹规整填料以及Dg16塑料阶梯环散堆填料作为传质媒介。以水-SO2作为研究体系,结合气液逆流接触吸收试验对比分析气液并流接触时填料层压降的情况,并分别考察了气相动能因子F和液气比L/V对填料吸收塔气液并流接触时填料层压降的影响。填料层压降随着气相动能因子F的增大呈指数型增长,随着液气比的增加而升高,并流操作时的影响相对逆流操作时变化幅度较小。通过试验结果拟合出相应压降的关联式,为进一步的工艺设计与优化提供相关依据与理论指导。     

气液并流筛板式填料压降的数值模拟

基于欧拉-欧拉模型,采用CFX软件对筛板式填料的气液两相并流流动进行了模拟。将模拟所得的压降与填料的出厂特性值进行了对比,发现在液气动能参数较小的情况下,两者吻合较好。分析了该流场内的速度分布和压力分布的特点,射流卷吸作用使流场内两相流体混合,但涡旋使筛板下方压强减小,射流撞击使筛板上方压强增加。对不同结构的矩形筛板式填料的压降进行研究,结果表明：筛板孔径和液相流量是影响筛板压降的重要因素,开孔直径越小,液相流量对单板压降的影响越大;上层筛孔投影与下层筛孔相交的结构更能有效降低单板压降。液相流量较大时,两个不同板间距的单板压降曲线将相交于一点,气相流量低于此交点时,板间距越小,单板压降越大;气相流量高于此交点时,则相反。     

Hydrodynamics and mass transfer in gas-liquid flow through static mixers

The objective of this study was to characterize the two-phase flow hydrodynamic behaviour and mass transfer in a static mixer in a horizontal pipe. Different arrangements of elements of the static mixer were tested and their performances compared. The pressure drop, bubble diameters and mass transfer coefficient were measured. The influence of operating conditions was also studied. A different correlations are proposed and compared with other correlations found in the literature.     

Hydrodynamics and mass transfer characteristics in gas-liquid flow through a rectangular microchannel

Researches on two-phase transfer and reaction processes in microchannnels are important to the design of multiphase microchemical systems. In the present work, hydrodynamics and mass transfer characteristics in cocurrent gas-liquid flow through a horizontal rectangular microchannel with a hydraulic diameter of have been investigated experimentally. Liquid side volumetric mass transfer coefficients were measured by absorbing pure CO₂ into water and a 0.3 M NaHCO₃ / 0.3 M Na₂CO₃ buffer solution. Interfacial areas were determined by absorbing pure CO₂ into a 1 M NaOH solution. Two-phase flow patterns and pressure drop data were also obtained and analyzed. This paper shows that two-phase frictional pressure drop in the microchannel can be well predicted by the Lockhart-Martinelli method if we use a new correlation of C value in the Chisholm's equation. Liquid side volumetric mass transfer coefficient and interfacial area as high as about and , respectively, can be achieved in the microchannel. Generally, liquid side volumetric mass transfer coefficient increases with the increasing superficial liquid or gas velocity, which can be described satisfactorily by the developed empirical correlations. A comparison of mass transfer performance among different gas-liquid contactors reveals that the gas-liquid microchannel contactor of this study can provide at least one or two orders of magnitude higher liquid side volumetric mass transfer coefficients and interfacial areas than the others.     

气体通过堆叠筛板填料的压降特性研究

单一气相通过堆叠筛板填料的压降是研究气液两相并流通过筛板填料压降的基础。文章对气体通过不同规格堆叠筛板填料的压降进行了系统的测试,并利用Realizable k-ε模型进行了数值模拟,揭示了气相流量、筛板开孔率、相对板厚、填料板间距等因素对气体压降的影响。结果表明:气相流量与筛板开孔率是压降的2个主要影响因素,压降随气量的增大而增大,随开孔率的增大而减小;受锐缘效应影响,随着相对板厚的增加,阻力系数逐渐减小;流体通过筛板后会冲击下层筛板,使得压降阻力系数随填料板间距的减小而增大。在此基础上,综合实验与模拟结果获得了气体通过堆叠筛板填料的阻力系数预测公式。     

Comparative study of dry pressure drop and flow behaviour of gas flow through sieve plate packing

Sieve plate packing is a newly developed packing that has been used in several industries due to its simple structure and operating flexibility, and no liquid flooding. In this work, first, systematic experiments were conducted to measure the pressure drop of gas flow through six sieve plate packings. The results indicated that the geometric characteristics of the packing have complicated effects on the pressure drops. Based on this, CFD simulations on the gas flow field were conducted using the realizable k-ε model, and flow behaviours such as the pressure drop, pressure nephogram, and velocity distributions within different packings were obtained. The simulation results clearly showed interesting flow patterns, including the contraction and expansion of the gas stream through the sieve hole, the flow separation on the sharp edge of the hole, and the vortexes formed when gas impacts the downstream plate. By comparing the flow patterns and the pressure drop under different packings operating at different conditions, the effects of the geometric characteristics of the packing on the pressure drop could be clearly distinguished from the flow behaviours, so that the variations in pressure drop with various packing structures were clearly indicated. Finally, based on the experimental data and the simulated results, correlations for the prediction of the pressure drops were proposed. This work will provide a useful basis for understanding the flow behaviour of gas and liquid two-phase flow in sieve plate packing.     

Hydrodynamics in down flow jet loop reactor

Gas holdup and liquid circulation time were measured in a down flow jet loop reactor for air–water system. It was observed that the circulation time decreases with an increase in nozzle diameter, draft tube to column diameter ratio and liquid velocity. Th gas holdup increases with an increase in gas and liquid velocities. The optimum draft tube to column diameter ratio was found to be 0.438. Correlations for gas holdup and circulation time involving operational and geometrical variables are presented.