壁面润湿性对微通道内二氧化碳-水两相流流动及传质性能的影响

在1 mm×1 mm矩形截面下微通道内,以二氧化碳-水为工作流体,研究壁面润湿性和气液表观流速对气-液两相流型和气液传质的影响,并研究了气、液表观流速对弹状流流体力学性质的影响。在亲水微通道中观测到了泡状流、泡状-弹状流、弹状流;在疏水微通道中观测到了非对称弹状流、拉长的非对称弹状流、分层流。实验表明亲水微通道中弹状流区域下气泡长度大体上随气相表观流速的增大而增大,随液相表观流速的增大而减小;液弹长度大体上随气相表观流速的增大而减小,随液相表观流速的增大先增大后减小;液侧体积传质系数k_La均随气、液相表观流速的增大而增大,随通道壁面润湿性的增强而增大。     

下倾管段塞流液塞速度特性研究

为探究段塞流液塞在下倾管中的耗散规律,利用段塞产生器和电导探针数采系统对液塞的速度演变规律进行了试验研究。结果表明:液塞在下倾管运动过程中由于液塞前方气泡渗入将发生耗散,当耗散作用明显时,液塞速度减小;液塞初始长度、下倾管倾角和表观气速对液塞耗散程度的影响体现在液塞形态改变和液塞速度上:液塞初始长度大或表观气速小时,液塞速度慢,利于耗散;倾角大时,液塞速度较快,但液塞形态变化大,综合而言,液塞耗散受形态变化影响更大;液塞尾部速度总是大于头部速度,且差值随液塞初始长度和表观气速的增大而增加;相同表观气速下,液塞头尾速度差值越大,液塞耗散越快,且耗散主要发生在头部。     

垂直上升管中的液弹长度分布

根据气液相不同的电导性质,通过实验测得了气液二相弹状流中气液弹的长度及速度。利用统计方法研究了在垂直上升管内不同位置以及不同气液表观速度下的液弹长度分布。结果表明该分布能够与对数正态分布关系式符合得很好,气液表观速度对液弹长度影响并不显著。同时还研究了气泡上升速度与前方液弹长度的关系,该关系可以用R.van Hout得到的经验关系式来描绘。     

垂直管内弹状气泡上升中壁面传递的实验研究

垂直管内弹状流壁面传递是诸多工业应用中需研究的重要问题之一。今用极限扩散电流技术,对弹状气泡上升时瞬时壁面剪应力和传质系数进行了测定,结果显示:当基于表观气速的Froude数FrG < 0.74时,壁面剪应力随弹状气泡和液塞的到来呈现方向相反的交替变化,壁面传质系数亦相应变化;而当FrG > 0.74时,剪应力方向一直向下,说明液膜向下流动,且弹状气泡和液塞的到来对壁面传质系数的影响很小。这说明下落液膜射流穿透了液塞段,控制了整个壁面传递过程。研究还对下落液膜区、尾迹区及液塞段的不同传递特征及机理进行了分析, 并结合气泡塔熔融结晶器中弹状气泡上升时的传热,对结晶操作条件的合理选择进行了讨论。     

微通道气液两相流研究进展

介绍了国内外微化工发展背景及发展现状,微通道内气液两相流流动气泡特性和传质特性。微通道中(横向及竖向微通道)气液两相流流型划分主要有泡状流、弹状流、环状流、搅拌流等。气泡形成过程中流体挤压力对气泡表面进行破坏致使分离,表面张力则在整个过程中维持着气泡形状及长度。着重介绍了微通道内气泡形成过程及经验长度计算,比较了不同研究者提出的经验公式中气液相表观速度比和气泡长度的关系,得出气泡长度均随气液相表观速度比的增加而增加,但依据研究者实验条件不同增加趋势也不尽相同。传质方面,研究基本集中在气液相比表面积较大的泡状流、环状流上,而气液表观速度、当量直径、压强等都会影响传质系数。微通道气液两相流虽然在传热、传质方面有很大的应用前景,但仍存在研究手段单一、理论数据不完善等问题,指出在未来的研究中研究者们要扩大领域范围,为传质传热的实际应用提供更可靠的理论依据。     

小长径比组合立管的液塞耗散作用

试验研究了小长径比组合立管的液塞耗散作用,分析了组合立管进出口持液率、液塞频率及液塞长度的变化规律。结果表明:组合立管中的扩径管使出口段液膜区与液塞区的持液率均小于入口段,出口段液塞区随折算气速增加而减小直至消失,而随折算液速的增加变化不大;液塞频率变化率随折算气速增加而增大;在中低气速下,液塞频率变化率随折算液速增加而增大,在高气速下,液塞频率变化率先稳定在最大值而后又下降;液塞长度变化率随折算气速增加而增大,在最低与最高气速下,液塞长度变化率随折算液速增加先稳定后减小,在中等气速下,液塞长度变化率稳定在0.6附近。     

垂直上升弹状流中液弹长度分布

提出了计算垂直上升弹状流中尾随Taylor气泡上升速度的关系式;并基于气泡追赶合并机理,建立了预测沿管路任意位置液弹长度分布模型,提供了弹状流发展过程中弹长分布的变化情况。     

低温气液两相弹状流动中Taylor气泡的统计特征?I. Taylor气泡长度

为了研究倾角(q)和管径对低温气液两相流中Taylor气泡长度分布规律的影响,在6种管路倾角下,以液氮为工质,使用高速相机对4种内径透明抽真空Pyrex玻璃管内的弹状流动进行了可视化实验. 结果表明,低温弹状流动中Taylor气泡长度分布的统计特征可由对数正态分布函数描述,Taylor气泡长度分布的标准偏差受到液膜射流直接影响,并随q减小先增大后减小. Taylor气泡无量纲平均长度随管路轴向位置增大而线性增加,随管路内径增加呈指数下降趋势,随q减小而增大,最小值出现在70o≤q≤90o.     

采用电阻层析成像技术测量气液加压鼓泡塔局部气泡参数

在内径0.3 m,高6.6 m的加压气液鼓泡塔反应器中,采用电阻层析成像技术(ERT)研究了空气-水体系中气泡群平均上升速度、局部气含率及其径向分布。在表观气速0.119~0.312 m s 1,压力0.5~2.0 MPa,考察了表观气速、压力对气泡群上升速度、局部气含率及其径向分布的影响。实验结果表明,鼓泡塔中局部气含率随着表观气速与压力的增大而增大,其径向分布呈现出中心高边壁低的分布特征,但整个截面的分布并非严格对称,在r/R=0~0.3,气含率变化较小,且极大值出现在该范围内;气泡群的局部上升速度随着表观气速的增大而增大,但是随着压力的增大而减小。     

鼓泡塔反应器的两级气泡模型参数研究

为了研究鼓泡塔反应器两级气泡模型在高黏度下的适用性,采用动态气体逸出法,在内径为286 mm,总高为7 200 mm的鼓泡塔中考察了液体黏度(1.2×10-3—210.4×10-3Pa·s)和操作条件对塔内总气含率,大、小气泡相含率和大、小气泡上升速度等两级气泡模型参数的影响。结果表明:床层总气含率随表观气速的增加而增大,大气泡相含率受液体黏度的影响较小,受表观气速的影响较大;小气泡相含率随黏度的增加而迅速下降,在高气速时受表观气速的影响较小。大、小气泡上升速度均随液体黏度的增加而降低,但随表观气速的升高有着不同的变化关系:前者明显升高,后者略有降低。大气泡直径随着黏度增大而稍有增大,小气泡直径随着黏度增大急剧减小。     

矩形截面螺旋通道内气液两相流局部含气率分布实验研究

应用电导探针测量技术,对矩形截面螺旋通道内气液两相流局部含气率进行实验研究。在不同的气相折算速度下,应用电导探针测量了弹状流弹单元的长度,并与可视化方法进行对比,验证了电导探针的可靠性,并为信号处理选择合适的阈值。分别在泡状流、弹状流及环状流三种流型的条件下,分析了气相与液相折算速度对局部含气率分布的影响。实验结果发现,螺旋通道气液两相局部含气率呈非对称的抛物线形分布,这种非对称性受流型和液相折算速度的影响。     

Influence of hydrodynamics on liquid mixing during Taylor flow in a microchannel

The miscible liquid‐liquid two phases based on Taylor flow in microchannels was investigated by high‐speed imaging techniques and Villermaux/Dushman reaction. The mixing based on Taylor flow was much better compared with that without introducing gas in microchannels, even the ideal micromixing performance could be obtained under optimized superficial gas and liquid velocities. In the mixing process based on Taylor flow, the superficial gas and liquid velocities affected the lengths and the velocities of Taylor bubble and liquid slug, and finally the micromixing performance. The formation process of Taylor flow in the inlets, the initial uniform distribution of reactants and the internal circulations in the liquid slug, and the thin liquid films all improved the mixing performance. Furthermore, a modified Peclet number that represented the relative importance of diffusion and convection in the mixing process was proposed for explaining and anticipating micromixing efficiency. © 2011 American Institute of Chemical Engineers AIChE J, 58: 1660–1670, 2012     

Hydrogenation of 2‐ethylanthraquinone under Taylor flow in single square channel monolith reactors

The hydrogenation of 2‐ethylanthraquinone (EAQ) to 2‐ethylanthrahydroquinone (EAHQ) was carried out under Taylor flow in single square channel monolith reactors. The two opening ends of opaque reaction channel were connected with two circular transparent quartz‐glass capillaries, where Taylor flow hydrodynamics parameters were measured and further used to obtain practical flow state of reactants in square reaction channels. A carefully designed gas‐liquid inlet mixer was used to supply steady gas bubbles and liquid slugs with desired length. The effects of various operating parameters, involving superficial gas velocity, superficial liquid velocity, gas bubble length, liquid slug length, two‐phase velocity and temperature, on EAQ conversion were systematically researched. Based on EAQ conversion, experimental overall volumetric mass transfer coefficients were calculated, and also studied as functions of various parameters as mentioned earlier. The film model, penetration model, and existing semi‐empirical formula were used to predict gas‐solid, gas‐liquid, and liquid‐solid volumetric mass transfer coefficients in Taylor flow, respectively. The predicted overall volumetric mass transfer coefficients agreed well with the experimental ones. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

Pressure drop in monolith reactors

A theoretical model for the computation of pressure drop in bubble-train flow inside capillaries of square cross-section was developed. The model is based on three contributions: hydrostatics, viscous pressure drop, and capillary pressure drop. Capillary pressure drop is related to the shape of the fronts and ends of the bubbles. The model does not include entrance or exit effects, has no adjustable parameters, and agrees very well with available experimental data.

For a given set of flow parameters, bubble velocity and liquid slug average velocity are computed as a function of gas and liquid superficial velocities. The length of the unit cell determines the number of bubbles inside the capillary for a given flow situation. The model requires experimental information of average bubble lengths to compute the length of a unit cell consisting of a bubble and a liquid slug.

The three pressure contributions for a unit capillary length are linear functions of the number of bubbles inside the capillary. The length of the bubbles in bubble-train flows is a critical parameter in the computation of pressure drop.     

An experimental investigation of gas-liquid two-phase flow in single microchannel contactors

This paper describes two-phase flow pattern and pressure drop characteristics during the absorption of CO₂ into water in three horizontal microchannel contactors which consist of Y-type rectangular microchannels having hydraulic diameters of 667, 400 and , respectively. With the help of a high-speed photography system, flow patterns such as bubbly flow, slug flow (including two sub-regimes, Taylor flow and unstable slug flow), slug-annular flow, churn flow and annular flow were observed in these microchannels. The applicability of the currently available correlations for describing flow pattern transitions in microchannels has been examined. Generally, the predicting performance of these correlations deteriorates as the channel diameter further reduces. Toward solving this discrepancy, an empirical correlation based on the superficial Weber numbers was developed to interpret the transition from Taylor flow to unstable slug flow in three microchannels. Taylor bubble formation process in microchannels was found to be in the squeezing regime at lower superficial liquid velocities (Ca ranging from 0.0019 to 0.029) while the transition to the dripping regime was observed at the highest superficial liquid velocity of 1.0 m/s. Lengths of Taylor bubbles formed in the squeezing regime can be well represented by the scaling relation proposed by Garstecki et al. [Formation of droplets and bubbles in a microfluidic T-junction—scaling and mechanism of break-up. Lab on a Chip, 6, 437-446]. For flow patterns including slug-annular flow, annular flow and churn flow, a simple analysis based on the separated flow model has been performed in order to reveal the observed effect of the superficial liquid velocity on two-phase frictional multiplier in the present microchannels. Then, reasonable correlations for the prediction of two-phase frictional pressure drop under these flow patterns were suggested.     

水平管道油气二相段塞流稳态流动特性

使用通过自行设计并搭建的实验装置,对水平管道油气二相段塞流稳态流动特性进行了实验研究。采用压力信号互相关方法测量了段塞流平均液塞速度,通过分析得到了液塞速度、液塞长度和液塞频率随气、液相折算速度的变化规律。结果表明,当液相折算速度恒定时,随着气相折算速度的增大,液塞速度基本上呈线性增大,而液塞长度呈双曲线减小;当气相折算速度恒定时,随着液相折算速度的增大,液塞频率基本呈线性增大,而液塞长度呈双曲线减小。     

Vertical slug flow in laminar regime in the liquid and turbulent regime in the bubble wake—Comparison with fully turbulent and fully laminar regimes

An experimental and simulation study on free bubbling vertical slug flow in laminar regime in the main liquid and turbulent regime in the near-wake bubble region is reported. A non-intrusive image analysis technique and a previously developed slug flow simulator (SFS) were used. Two aqueous glycerol solutions (0.012-0.013 and 0.022 Pa s) were studied. A single bubble-to-bubble interaction curve was obtained. Strong interaction was found for bubbles flowing less than 3-4D apart, with slight interaction persisting for longer distances. The shape of the interaction curve bridges those for fully turbulent and fully laminar regimes. The experimental average bubble velocity in undisturbed conditions was shown not to follow the correlation-based predictions for laminar regime in the liquid. Alternative fitting coefficients are proposed. An entrance length of 50-80D (or 90-170D) was obtained for normal inlet slug length distributions centred on 2-5D (or 2-6D), for superficial gas and liquid velocities up to 0.40 and 0.30 m/s, respectively. More contrasting inlet slug length distributions were found not to converge within the length of the column (6.5 m). An overall comparison between the three regimes is presented.     

气液两相流差压测量波动信号的符号序列统计分析

将符号时间序列分析方法应用到两相流测量波动信号分析，并讨论了关键参数对符号统计量影响问题。在此基础上，利用垂直上升管中采集到的80组气液两相流差压动态波动信号，提取了时间不可逆转性Tfb及χ2fb统计量。当气相表观速度小于002 m·s-1时，随着气相表观速度增加，泡状流随机可变的运动特征逐渐加剧，其动力学特性变得相对复杂；当气相表观速度大于002 m·s-1时，在流型从泡状流向段塞流转变过程中，随着气相表观速度增大，流型演化的动力学特性逐渐变得相对简单；在流型从段塞流向混状流转变过程中，随着气相表观速度增加，混状流的动力学特性逐渐变得愈加复杂。研究结果表明，时间不可逆转性Tfb及χ2fb统计量两个符号是表征气液两相流流型的敏感特征量，考察这两个统计量随两相流流动参数变化规律有助于更好地理解两相流流型动力学特性。