受限空间内浮升气泡与液体间传质行为实验研究

采用紫外诱导荧光(UIF)实验方法,研究Hele-Shaw狭缝受限尺度对受限空间内浮升气泡流体力学与气液传质行为的影响。实验中以二苯并[b,e]吡啶作为荧光剂实现了受限空间内CO₂溶液浓度分布及其气泡运动速度的定量测量,获得了CO₂在受限空间内运动过程中的传质量和气泡动力学参数,并分别计算气泡受限空间内液膜区和自由接触区的传质速率。分析得到受限空间中不同狭缝宽度内CO₂的传质行为,分析了受限尺度对CO₂-水体系传质过程的影响。     

液相中气泡上升行为与界面传质:实验研究与数值计算

在工业生产过程中，气泡在液相中的上升行为及气液界面的传质行为极为常见。本文针对不同条件下气泡上升过程的实验研究方法以及数值计算方法进行了总结。从实验与数值计算的角度，综述了单气泡上升过程的影响因素、多气泡上升过程聚并与破裂的现象和机理以及工业装置中气液两相流型和气泡特性，并对传质模型进行了归纳，主要关注了气侧-界面传质模型的研究现状。综述结果表明：当前对于单气泡上升行为的研究较为充分，而对于多气泡的行为机理的研究尚需深入。此外，受到研究手段的限制，进行气侧-界面传质模型研究具有一定挑战性。针对当前的相关研究进展和存在的问题，对今后气泡上升行为和传质行为的研究提出以下建议，即开展气泡聚并与破裂可控性研究，强化对气侧-界面传质过程的研究，包括泡内流体行为可视化研究和相关传质模型的建立。     

液体中气泡上浮与传质过程的耦合模型

针对液体中气泡上浮与传质这一非稳态、强耦合过程,分析气泡的受力情况,考虑到非恒定Basset力的影响,得出了气泡瞬态加速度模型;利用绕球流动传质边界层模型,并引入非平衡传质理论,构建了气泡的瞬态非平衡传质模型;进而依据气泡质量变化率将两模型耦合,以此构建了完整描述这一过程的耦合模型。计算实例表明,Basset力对难溶性气泡的运动过程无明显影响,但对易溶性气泡影响显著;传质条件则对两类气泡都具有重要影响,且该模型中引入非平衡传质理论后,计算值与难溶性气泡的实验结果吻合更好。     

过冷流动沸腾中气泡浮升直径的实验及理论研究

研究气泡浮升直径对揭示过冷流动沸腾的传热机理至关重要。为探究流动工况对气泡浮升直径的影响机制,针对发动机缸盖沸腾区域的冷却通道设计了一个水动力相似的矩形实验通道,搭建了过冷流动沸腾可视化实验循环系统。基于该可视化实验系统,研究了系统压力、壁面过热度、流速以及液体过冷度对气泡浮升直径的影响,发现气泡浮升直径随着系统压力、流速以及过冷度的增大而变小,随着壁面过热度的增大而增大。建立了气泡在浮升时刻的力平衡模型,该力平衡模型的预测值与实验值的平均相对误差为12.25%。为了便于工程应用,基于气泡浮升直径的力平衡模型,建立了气泡浮升直径的经验模型,该经验模型的预测值与实验值的平均相对误差为6.80%。     

基于传质强化的微气泡塔盘流动特性实验的研究

筛板塔塔内件的作用主要是增大气液比表面积,改变气液接触形式,以提高塔内传质、传热。研究者提出了新型微气泡塔盘,通过在筛板上方的泡沫层内增加破泡组件,利用破泡组件使大气泡破裂为小气泡,增加气液接触面积,提高气液传质、传热效果。利用自行设计的筛板塔和微气泡塔盘实验平台及PIV测速系统,测定了塔板上气泡的直径分布和上升速度。实验结果显示:与普通筛板相比较,微气泡塔盘上气泡的上升速度较小,气泡停留时间更长,且径向分布更平坦;气泡直径也仅为筛板的1/16,气液接触的比表面积增大,更利于传质过程的进行。     

受限空间内高效硫化氢吸消液性能评价实验研究

设计搭建了两套不同规模的受限空间硫化氢吸消液性能评价装置,评价了SJ-1型吸消液对不同浓度硫化氢气体的清除性能。结果表明,SJ-1型吸消液对高浓度硫化氢气体(> 1 500 mg/m³)具有良好的清除能力,可快速将泄漏的硫化氢气体降至安全浓度以下;同时,在高浓度硫化氢持续泄漏过程中,连续喷射SJ-1型吸消液,同样可有效降低其浓度,具有良好的清除性能。     

相间传质对气泡聚并过程影响的实验研究

设计了一套双气泡聚并实验系统,考察了相间传质对气泡聚并过程的影响,气相采用非相变的N2,液相为挥发性的丙酮和乙醇水溶液. 利用该系统测定了25~50℃温度下,不同组分浓度、鼓泡频率和气泡直径时气泡的聚并特性. 结果表明,相间传质诱导的Marangoni效应使聚并时间随温度升高呈先减小后增大的趋势,聚并时间的分散性在较高温度下显著增大,采用聚并效率描述气泡聚并特性更合适;聚并效率在温度升高到一定程度后开始降低并趋于最小值,该值随溶液浓度增加而减小,稳定因子可定量描述Marangoni效应;鼓泡速率和气泡直径增加1倍,最小聚并效率分别减小50%和67%.     

微小通道内液体扰流微孔逸出气泡串的迁移行为

对微小矩形通道内,液体扰流下微孔孔口逸出气泡串的迁移行为进行了可视化实验。基于图像处理方法,分别研究了液体流量和通道倾斜角度对气泡串尺寸、运动速度以及运动轨迹的影响。发现了不同工况下通道内的微气泡堆积现象,并对其进行了分析。结果表明：增大液体流量或者通道倾角,使得形成的气泡尺寸减小,气泡运动轨迹与通道壁面夹角减小,气泡运动速度增大。液体流量与通道倾角影响了通道内微气泡堆积的位置及数量。     

局部开口受限空间油气爆燃的超压瞬变与火焰行为

开展了油气在局部开口受限空间内油气爆燃的实验研究,获得了不同初始浓度下油气爆燃超压及火焰特性。研究结果表明：内场有两个超压峰值,外场仅有一个,开口处出现负压区。内外最大超压大小基本相同,均由外部爆燃形成。随着浓度的升高,超压先增后减,最大超压对应初始浓度为1.88%。火焰的传播过程分为3个阶段,火焰的形态、颜色、各阶段持续时间、直径、平均速度均受初始浓度的影响。随着初始浓度升高,火焰从淡蓝色层流光滑火焰变为亮黄色褶皱火焰,层流传播阶段和加速变形阶段的持续时间先增后减,溃散熄灭阶段的持续时间增加。火球直径与浓度的关系可用三次多项式描述,火焰平均速度随时间的变化可用二次多项式描述。随着开口率的升高,爆燃超压和火焰速度逐渐减小,火球直径先增大后减小。     

小型受限撞击流反应器内混合特征及激励强化

利用平面激光诱导荧光技术(planar laser induced fluorescence,PLIF)研究了小型受限撞击流反应器(confined impinging jets reactor,CIJR)内混合特征及激励强化,射流入口Reynolds数范围为75~150。研究结果表明,在受限撞击流反应器内,由分离流模式向自持振荡模式转变过程中,两股流体间的混合效果逐渐提升;当流动为分离流模式时,激励能有效地强化两股流体间的混合,而当流动转变为自持振荡模式时,激励对流体混合的影响较小。     

垂直管内弹状气泡上升时的壁面传质

Wall-liquid mass transfer for Taylor bubbles rising through liquid column in vertical tubes is an important and fundamental topic in industrial processes.In this work,the characteristics of wall-liquid mass transfer for this special case of slug flow were studied experimentally by limiting diffusion current technique (LDCT). Based on the experimental results and the analysis of hydrodynamic mechanisms,it was proposed that four different zones exist,i.e.the laminar falling film zone,the turbulent falling film zone,the wake region and the remaining liquid slug zone.The corresponding correlations for all these zones were developed.     

Unsteady mass transfer between a slender bubble and a viscous liquid in a simple extensional flow

Unsteady mass transfer between a slender bubble and a viscous Newtonian liquid in a simple extensional and creeping flow has been studied. The exact analytical solution, at large Peclet numbers, has been obtained using similarity transformations and by the method of characteristics. It was determined that when a dimensionless time (the strength of the flow multiplied by the time) is greater than 2, then steady state is, in practice, obtained.     

限域传质分离膜

阐述了限域传质分离膜的研究背景及现状,分析了该领域面临的关键科学问题及研究思路,介绍了我国在此领域的研究进展,并提出了未来的发展方向。     

An improved subgrid scale model for front-tracking based simulations of mass transfer from bubbles

Gas–liquid bubble column reactors are often used in industry because of their favorable mass transfer characteristics. The bubble mass boundary layer in these systems is generally one order of magnitude thinner than the momentum boundary. To resolve it in simulations, a subgrid scale model will account for the sharp concentration variation in the vicinity of the interface. In this work, the subgrid scale model of Aboulhasanzadeh et al., Chem Eng Sci, 2012, 75:456–467 embedded in our in-house front tracking framework, has been improved to prevent numerical mass transfer due to remeshing operations. Furthermore, two different approximations of the mass distribution in the boundary layer have been tested. The local and global predicted Sherwood number has been verified for mass transfer from bubbles in the creeping and potential flow regimes. In addition, the correct Sherwood number has been predicted for free rising bubbles at several Eötvös and Morton numbers with industrial relevant Schmidt numbers (10³–10⁵).     

Numerical study of the coupling between reaction and mass transfer for liquid‐liquid slug flow in square microchannels

While the benefits of miniaturization on processes have been widely demonstrated, its impact on microfluidics and local mechanisms such as mass transfer is still little understood. The coupling between reaction and mass transfer in microchannels is simulated for liquid‐liquid slug flow. First, the extrapolation to confined flow of the classical model used to calculate interfacial mass fluxes in reactive infinite media was studied. This model consists in estimating transferred fluxes between two phases as a function of the enhancement factor E. Its expression depends on the model used to represent interfacial mass transfer. In infinite media, Lewis and Whitman's stagnant film theory is generally preferred for its simplicity and its reliability. In the case of confined slug flow, the limitation of such a model to predict interfacial fluxes is highlighted. Second, the case of liquid‐liquid competitive consecutive reactions in microchannels is considered. The unfavorable impact of the length between droplets on selectivity is emphasized. This is a direct consequence of mass‐transport mechanisms in microchannels. © 2010 American Institute of Chemical Engineers AIChE J, 2011     

Heat and mass transfer between bubbles and a liquid

The understanding of the heat and mass transfer phenomena between hot bubbles and a liquid is particularly relevant to the design of direct contact heating and evaporation systems such as submerged combustion equipment. In this process, exhaust gas from a burner is dispersed in a liquid to be heated or evaporated. Various models for the prediction of the temperature and vapor content of the bubbles as a function of their residence time in the liquid are presented. Based on the experimental measurements of the bubble size and of the heating time and evaporation rate in an actual submerged combustion system, models using spherical, ellipsoidal and spherical-cap bubbles, with or without internal circulation, are discussed and assessed. It is found experimentally that the bubbles are of a spherical cap shape. Bubble equivalent diameters between 15 and 25 mm and bubble velocities between 0.4 and 1.2 m/s are observed. The proposed models are used to compute the heating time and evaporation rate of the bath during a submerged combustion operation; the predictions are then compared to the experimental values. The rigid spherical cap bubble model is found to predict satisfactorily the heat and mass exchanges between the bubbles and the liquid.