稀疏固液搅拌体系流动特性

引　言在固液两相搅拌反应器中 ,固体颗粒的运动行为直接影响到固液两相流的流体力学及传质特性 ,因此 ,近年来对固液两相体系中颗粒的运动行为研究愈来愈受到重视 .对于流体机械混合操作 ,许多情况下流动均处于湍流区域 ,涉及到多相态时 ,问题变得更为复杂 .颗粒和湍流的相互作用 ,很久以来一直是人们研究的基本问题之一[1～ 3] ,对有固体颗粒存在下液相流体速度及湍流脉动变化规律 ,也是研究人员和工程技术人员关注的重点 .现有文献中用激光测量搅拌槽内固液两相流动的数据很少 ,仅Ｎｏｕｒｉ[3] 测量了六直叶涡轮搅拌槽内固液两相速度分…     

多相反应器的非均相特性测量技术进展

为了增大传质和传热面积，多相反应器中分散相通常以颗粒形式（气泡、液滴或固体颗粒）分散、运动于连续相流体中，与周围的连续相及其他分散相颗粒的相互作用使颗粒和颗粒群呈现复杂的时空非均相行为。多相反应器中非均相特性的准确描述是发展准确的反应器模型、进行定量诊断分析和优化设计高效反应器的必要基础。本文总结了多相反应器中颗粒和颗粒群的复杂时空行为，提出了当前多相反应器非均相特性测量正面临的在线测量、高分散相浓度和多分散相等主要难题；综述了多相反应器测量技术研究的进展，指出了PC和PV等光纤测量技术是较经济的高浓度两相反应器的在线测量技术，而侵入式照相法测量结果更准确，具备解决上述测量难题方面的可行性，具备较好的应用前景，但要实现工业在线测量仍存在一些高难度的技术问题需要解决。     

海上含液天然气流量计开发

阐述在线多相流量计的开发原理和国内外低含液率气液两相流计量技术研究的主要技术路线.结合海上含液天然气流量计开发工作,全面系统地总结了流量计开发的技术路线和研究成果.详细介绍槽式孔板的单相流与两相流测量特性、基于双槽式孔板组合测量原理与软测量技术的流量计计量算法等内容,指出了需要进一步深入研究的方向.     

磁共振成像应用于多相流体动力学研究进展

多相流反应器广泛应用于化工、冶金、能源及医药等过程工业,其内部具有非稳态、非线性、非平衡的自然属性,因而对多相流检测技术提出了挑战。准确检测并理解多相流体力学特性、进而揭示并掌握多相流反应器设计及放大规律,一直是当今过程工程领域的前沿课题之一。磁共振成像(MRI)作为一种非侵入式、多维瞬态全流场先进检测手段,可获得准确详尽的多维流场信息,包括颗粒浓度与速度(脉动)场、流型识别、气泡尾涡、颗粒聚团等多尺度流场参数及介尺度流动结构。此外,MRI在数值模型验证与改进方面也具有良好的应用前景。概述了MRI技术原理,重点论述了MRI近年来在气固及气液反应器中的研究现状,展望了MRI在多相流反应器中有待拓展的方向。     

磁共振成像应用于多相流体动力学研究进展

多相流反应器广泛应用于化工、冶金、能源及医药等过程工业,其内部具有非稳态、非线性、非平衡的自然属性,因而对多相流检测技术提出了挑战。准确检测并理解多相流体力学特性、进而揭示并掌握多相流反应器设计及放大规律,一直是当今过程工程领域的前沿课题之一。磁共振成像（MRI）作为一种非侵入式、多维瞬态全流场先进检测手段,可获得准确详尽的多维流场信息,包括颗粒浓度与速度（脉动）场、流型识别、气泡尾涡、颗粒聚团等多尺度流场参数及介尺度流动结构。此外,MRI在数值模型验证与改进方面也具有良好的应用前景。概述了MRI技术原理,重点论述了MRI近年来在气固及气液反应器中的研究现状,展望了MRI在多相流反应器中有待拓展的方向。     

多相流搅拌反应器研究进展

综述了近五年冷态气液固三相搅拌反应器的研究成果,阐明近期研究热点已转为热态多相流搅拌反应器的流体力学行为。概述了热态气液两相体系中通气功率、混合时间、局部及总体气含率的研究结果。指出今后研究重点应为热态的固液悬浮、气液传质过程及其机理,同时说明用计算流体力学（CFD）对气液固三相搅拌反应器的数值模拟仍属起步阶段。     

不同黏度下气液体系流体力学行为的PBM模拟

基于Eulef-Euler双流体模型,分别采用均一气泡尺寸和PBM方法对鼓泡床内气液两相流体系中的流体力学行为进行了数值模拟,经与实验结果比较表明,采用PBM方法获得的模拟结果更为准确,表明了PBM方法的优越性.采用PBM模型模拟了不同黏度气液体系中的流体力学行为,获得了包括平均及局部气含率分布、气泡尺寸分布,循环液速和大小气泡的空间分布等流体力学信息,并将模拟结果与相应操作条件下的实验结果进行了比较,吻合较好,说明PBM方法不仅可以用于鼓泡床反应器内气液两相流体系的模拟研究,还能对不同液相黏度下气液体系中的流体力学行为作出正确的预测和描述,为多相流反应器的设计和放大提供了有益的参考.     

气液流经标准孔板压差特性数值研究

本文以油井多相流的在线测量系统研究为背景,在既定多相流量计实验平台上,基于计算流体动力学理论,利用软件CFX对单相水、空气和气液两相流三种流体仿真．得出不同流体对于标准孔板的压差特性,从理论上验证了利用标准孔板进行气液两相流流量测量的可行性,为进一步将标准孔板应用到油、气、水三相流测量提供依据。     

多相光催化反应工程介绍

多相光催化反应工程是化学反应工程学科的新领域.对近年来国内外有关多相光催化反应器模拟和设计研究现状进行了总结,探讨了辐射能传递行为、反应动力学和反应的温度效应;阐述了多相光催化反应器的设计因数,包括光源、几何形状、制造材料、热交换、混合和流动特性以及催化剂的放置;介绍了气固相和气液固3相光催化反应器的类型并分析了优缺点.认为现今反应器的设计方法仍然是用经验和半经验近似处理,仍需进行大量的基础研究和开发工作,以促进多相光催化技术的应用.     

环管反应器内液固两相流的数值模拟

为了对环管反应器内液固两相的流动形态进行研究,建立了以颗粒动力学为基础的Euler-Euler双流体模型.在浆液流速远大于自由沉降速度的情况下,模拟了不同浆液入口速度时的环管反应器上升段压力降,同时对管道内液固两相流中的一些重要参数进行了数值研究:在入口液固两相体积分布均匀的情况下,环管反应器上升段、弯管段以及下降段液固两相体积分布和液固两相速度均不一样,在弯管段由于离心力存在而引起管道内二次流,使得固相颗粒甩向弯管的外侧壁,引起固相体积分数在弯管外侧壁明显增大,管道内固体颗粒相分布不均.在浆液速度v =3 m·s-1时,液相和固相的速度有一定的速度差,随着入口速度增大,速度差变小;当浆液速度v =7 m·s-1时,固体颗粒相速度分布与液相速度基本相同,两者之间的滑移速度可以忽略.计算结果与传统经验公式的比较表明模型能有效地描述环管反应器内压力降和反应器内浆液流动形态.     

Hydrodynamics and bubble behaviour in a three-phase two-stage internal loop airlift reactor

Local hydrodynamics of a gas–liquid–solid system,such as bubble circulation regime,gas holdup,liquid velocity and axial profile of solid concentration,are studied in a two-stage internal loop airlift reactor.Empirical correlations for gas holdup and liquid velocity are proposed to ease the reactor design and scale-up.Different bubble circulation regimes were displayed in the first(lower) and second(upper) stages.Increasing superficial gas velocity and solid loading can promote regime transition of the second stage,and the gas holdup of the second stage is higher than that of the lower stage.In addition,the effects of solid loading on bubble behaviour are experimentally investigated for each stage.It is found that bubble size in the downcomer decreases with the presence of solid particles,and bubble size distribution widens under higher superficial gas velocity and lower solid loading.     

Local hydrodynamic properties of gas phase in an internal-loop airlift reactor

The local hydrodynamic properties of the gas phase in an internal-loop airlift reactor were investigated in this study. The hydrodynamic properties including gas holdup, bubble velocity and bubble chord length were measured by dual electrical resistivity probes. The chord length distribution was then transformed to the bubble size distribution by modeling the bubbles as ellipsoids. It was found that the gas holdup increased with decreasing bubble velocity. In addition, most bubbles tended to rise along the riser central axis. Thus, the gas holdup in the axis was higher. The bubble size, bubble velocity and gas holdup were relatively constant in the axial direction of the riser except in the zones near the gas sparger and the gas–liquid separator. The bubble velocity became slower when the bubbles approached the gas–liquid separator. Moreover, the bubble size and bubble velocity for the three-phase system were relatively insensitive to the radial direction compared to those for the two-phase system. It was also found in this study that the bubble rise velocity and bubble size for the three-phase system were lower than that for the two-phase system. However, the gas holdup for the three-phase system were higher than that for the two-phase system due to bubble breakage caused by the solid particles.     

A model for simultaneous measurement of gas and solid holdups in a bubble column using ultrasonic method

The ultrasonic method developed to measure the dispersed phase holdups in dispersion systems is based on the fact that the velocity of ultrasound in the dispersion is different from that in the liquid. The relationships between velocity differences in the term of transmission time differences of ultrasound and gas holdup in a gas-liquid system and solid holdup in a liquid-solid system were derived. The holdups became linearly dependent on the time differences, which is in agreement with the experimental data. Based on those relations, a model for simultaneous measurement of gas and solid holdups in three-phase systems is proposed. The model permits measurement of the dispersed phase holdups by measuring the transmission time of ultrasound transmitted through the dispersions in two frequencies. It allows investigation of local holdups distributions in a bubble column and in a suspended bubble column.     

Experimental Study on Bubble Rising and Descending Velocity Distribution in a Slurry Bubble Column Reactor

To determine bubble rising and descending velocity simultaneously, a BVW‐2 four‐channel conductivity probe bubble parameters apparatus and its analysis are used in gas‐liquid and gas‐liquid‐solid bubble columns. The column is 100 mm in internal diameter and 1500 mm in height. The solid particles used are glass beads with an average diameter of 17.82 μm, representing typical particle size for catalytic slurry reactors. The effects of superficial gas velocity (1.0 cm/s ≤ U_g ≤ 6.4 cm/s), solid holdup (0 % ≤ ?_s ≤ 30 %), and radial location (r/R = 0, 0.4, and 0.7) on bubble velocity distributions are determined. It is found that increasing U_g can increase the velocity of bubbles but do not exert much influence on bubble velocity distribution. Solid holdup mainly affects the distribution of bubble velocity while the radial direction affects bubble velocity distribution only slightly. The ratio of descending bubbles to rising bubbles increases from the bubble column center to the wall. It can be proved experimentally that large bubbles do not always rise faster than small bubbles at higher U_g (for example 6.4 cm/s).     

LOCAL HYDRODYNAMICS IN AN EXTERNAL LOOP AIRLIFT SLURRY REACTOR WITH AND WITHOUT A RESISTANCE-REGULATING ELEMENT

The hydrodynamic behavior of an external loop airlift slurry reactor (ALSR) with and without a resistance-regulating element was studied with a fiber optic probe and ultrasound Doppler velocimetry. The influences of the superficial gas velocity and solid holdup on the global gas holdup and radial profiles of the suspension circulation velocity in the downer and of gas holdup, bubble size, and bubble rise velocity in the riser were studied. Local measurements allow a better understanding of the flow behavior in the reactor and can be used for CFD modeling and validation. Experimental results show that the resistance-regulating element increases the gas holdup and decreases the suspension circulation velocity, indicating that an optimum design of the flow resistance is needed to obtain the maximum gas-liquid volumetric mass transfer coefficient for a specific superficial gas velocity. A high superficial gas velocity and low solid holdup are favorable for increased uniformity of the radial profile of the gas holdup and bubble rise velocity. Hydrodynamic models that predict the gas holdup and suspension circulation velocity were developed for an ALSR with and without a resistance-regulating element. Good agreement was obtained between measured and predicted values.     

浆态床鼓泡反应器中气含率的分布

为了解浆态床鼓泡反应器中气含率的分布规律,在浆态床鼓泡反应器冷模试验装置中,以空气-液体石蜡-氧化铝微球为试验介质对装置内部的气含率进行研究。利用压差法研究了表观气速、浆液固含量等操作条件对反应器床层总体气含率的影响,利用光纤探针法研究了浆态床反应器不同操作条件对局部气含率的影响,总结了反应器内部气含率的分布规律,并由此对工业浆态床鼓泡反应器的设计进行了研究。结果表明:浆态床反应器的总体气含率随表观气速的增大而增大,固体细颗粒的加入能适当降低总体气含率;在反应器底部,分布器对气体的均布作用明显,但表观气速的增大能够弱化分布器的作用;在反应器的中上部气含率不受分布器的影响,沿反应器径向呈现"中间高,边缘低"的分布趋势;在工业费托浆态床中,表观气速不宜低于0.12 m/s,内过滤系统适宜设置于反应器中上部靠近器壁的位置。     

LOCAL HYDRODYNAMICS IN AN EXTERNAL LOOP AIRLIFT SLURRY REACTOR WITH AND WITHOUT A RESISTANCE-REGULATING ELEMENT

The hydrodynamic behavior of an external loop airlift slurry reactor (ALSR) with and without a resistance-regulating element was studied with a fiber optic probe and ultrasound Doppler velocimetry. The influences of the superficial gas velocity and solid holdup on the global gas holdup and radial profiles of the suspension circulation velocity in the downer and of gas holdup, bubble size, and bubble rise velocity in the riser were studied. Local measurements allow a better understanding of the flow behavior in the reactor and can be used for CFD modeling and validation. Experimental results show that the resistance-regulating element increases the gas holdup and decreases the suspension circulation velocity, indicating that an optimum design of the flow resistance is needed to obtain the maximum gas-liquid volumetric mass transfer coefficient for a specific superficial gas velocity. A high superficial gas velocity and low solid holdup are favorable for increased uniformity of the radial profile of the gas holdup and bubble rise velocity. Hydrodynamic models that predict the gas holdup and suspension circulation velocity were developed for an ALSR with and without a resistance-regulating element. Good agreement was obtained between measured and predicted values.     

Experimental investigation on multiscale hydrodynamics in a novel gas–Liquid–Solid three phase jet-Loop reactor

Multiphase flow hydrodynamics in a novel gas–liquid–solid jet-loop reactor (JLR) were experimentally investigated at the macroscales and mesoscales. The chord length distribution was measured by an optical fiber probe and transformed for bubble size distribution through the maximum entropy method. The impacts of key operating conditions (superficial gas and liquid velocity, solid loading) on hydrodynamics at different axial and radial locations were comprehensively investigated. JLR was found to have good solid suspension ability owing to the internal circulation of bubbles and liquid flow. The gas holdup, axial liquid velocity, and bubble velocity increase with gas velocity, while liquid velocity has little influence on them. Compared with the gas–liquid JLRs, solids decrease the gas holdup and liquid circulation, reduces the bubble velocity and delays the flow development due to the enhanced interaction between bubbles and particles (Stokes number >1). This work also provides a benchmark data for computational fluid dynamics (CFD) model validation. © 2019 American Institute of Chemical Engineers AIChE J, 65: e16537, 2019     

Experimental and numerical investigations of scale-up effects on the hydrodynamics of slurry bubble columns

Experiments and simulations were conducted for bubble columns with diameter of 0.2 m(180 mm i.d.), 0.5 m(476 mm i.d.) and 0.8 m(760 mm i.d.) at high superficial gas velocities(0.12–0.62 m·s-1) and high solid concentrations(0–30 vol%). Radial profiles of time-averaged gas holdup, axial liquid velocity, and turbulent kinetic energy were measured by using in-house developed conductivity probes and Pavlov tubes. Effects of column diameter, superficial gas velocity, and solid concentration were investigated in a wide range of operating conditions. Experimental results indicated that the average gas holdup remarkably increases with superficial gas velocity, and the radial profiles of investigated flow properties become steeper at high superficial gas velocities. The axial liquid velocities significantly increase with the growth of the column size, whereas the gas holdup was slightly affected. The presence of solid in bubble columns would inhibit the breakage of bubbles, which results in an increase in bubble rise velocity and a decrease in gas holdup, but time-averaged axial liquid velocities remain almost the same as that of the hollow column. Furthermore, a 2-D axisymmetric k–ε model was used to simulate heterogeneous bubbly flow using commercial code FLUENT 6.2. The lateral lift force and the turbulent diffusion force were introduced for the determination of gas holdup profiles and the effects of solid concentration were considered as the variation of average bubble diameter in the model. Results predicted by the CFD simulation showed good agreement with experimental data.     

鼓泡床反应器内流动与传质行为的研究进展

总结了有关浆态鼓泡床反应器内流动、混合用气液传质特性的研究成果,详细地介绍了鼓泡床反应器内气含率、液速、液体轴向扩散系数、传质系数的测量方法,阐述了鼓泡床反应器性能的主要影响因素,如系统压力、温度、气体表观气速、液体性质及固含率等对流动、液相混合和传质特性的影响,并对鼓泡床反应器的应用前景进行了详述.