Entrainment Control Using a Newly Developed Telecentric Inline Probe

This contribution presents a novel approach to investigate entrainment in distillation and absorption columns. An image-based probe allows precise droplet detection at various radial and axial positions above trays. Validations achieve an average error of 6.4 % (monospheres 9.2–114.4 µm) and 3 % (monodisperse droplet stream up to 19 m s⁻¹ and 74.5 µm). Experiments in a DN 450 cold flow test rig show an increasing (decreasing) share of larger droplets with higher gas (liquid) loads. Locally measured droplet sizes depend on probe position as well as tray design and enable an extrapolation to integral entrainment rates.     

旋流塔板的板效率模型

引　言板式塔的操作通常可分为气体为分散相的鼓泡、泡沫工况和液体为分散相的喷射工况 .喷射态操作的塔板 ,虽然其效率一般较低 ,但具有通量大、压降低等重要优点 ,符合现代大工业发展趋势的要求 ,正受到越来越多的重视[1～ 3] .有关鼓泡、泡沫工况下的流体力学和传质过程的研     

An investigation of the droplet size distributions in a cyclone reactor for liquid-liquid heterogeneous reactions using FBRM and PVM

A multi-element process coupled cyclone reactor for the liquid-liquid heterogeneous reaction was proposed. This paper presents the investigation of dispersed phase droplet size distributions near the wall surface using FBRM and PVM. To translate a chord length distribution (CLD) measured by the FBRM instrument into its droplet size distribution (DSD), a CLD-DSD transformation model was proposed. Moreover, the effects of operational parameters on the droplet size distributions were studied. The results show that the total inlet flow plays a decisive role on the dispersed phase droplet size distributions, while the influence of feed ratio is mainly reflected in inhibiting the probability of droplet coalescence. In comparison, the influence of overflow ratio on the droplet size distributions can be neglected.     

湍流分散体系中液滴破碎频率模型的黏性修正

在分析研究分散相黏度对液滴变形和破碎影响的基础上,提出了一个改进的液滴破碎频率模型并拓展了液滴破碎判据标准.同时通过Monte Carlo模拟的随机方法,得到了湍流搅拌槽中液-液分散体系的液滴直径分布和Sauter平均直径d₃₂.通过与文献中关于d₃₂的实验结果比较发现,该模型预测的Sauter平均直径更接近实验值,对于黏性分散相改进的液滴破碎频率模型要优于Coulaloglou和Tavlarides提出的模型.计算结果表明对于黏性分散相液滴,其黏度限制了液滴变形,使得液滴破碎频率被大大减少, 液滴直径明显增加,液滴直径分布向右偏移.     

喷射状态下大孔径复合筛板塔中的液滴分布

The droplet size distribution with large-holed compound sieve tray operating in the spray regime is measured by using a double electrical probes technique in a cold model column of 400 mm diameter. The results indicate that the hole F-factor Fo and surface tension are the main factors which influence the liquid dispersion expressed by the Sauter mean diameter D32. A correlation of D32 on surface tension, viscosity, F-factor, weir height and liquid flow rate is proposed.     

不溶液-液分散在搅拌槽内的CFD模拟

液滴平均尺寸和液滴尺寸分布是描述不溶液-液分散程度的2个重要参数,决定着两相接触面积的大小,进而决定着相间的传质、传热和化学反应速率。利用CFD方法详细研究了水-油两相在搅拌槽内的分散过程,发现叶轮转速、分散相体积分数和连续相黏度对分散效果有显著影响。当两相组成一定时,增大叶轮转速和连续相黏度均有利于两相的分散。在一定范围内,液滴平均直径与叶轮转速、分散相体积分数均为对数线性关系,相关系数高达0.999。基于个数的液滴尺寸分布在不同转速和连续相黏度条件下出现了双峰分布,而基于体积的液滴尺寸分布则始终为单峰分布。     

EXPERIMENTAL AND THEORETICAL INVESTIGATION OF GAS FLOWFIELD ON A ROTATING STREAM TRAY

The rotating stream tray is a new type of column tray operating in the spray regime, through which the gas stream rotates. Combinations, performances and applications of the rotating stream tray are introduced briefly. On a 300 mm diameter rotating stream tray, the gas flowfield was investigated with a DANTEC 55X laser Doppler anemometer. The data of velocity distributions in tangential, axial and radial directions on sections at different heights above the tray were obtained. A numerical model for computing the turbulence flow on the tray was also proposed. The predicted results of three-dimensional velocities and pressures were found to be in qualitative agreement with experimental data. The main gas flow features are clarified.     

A rapid benchtop NMR method for determination of droplet size distributions in food emulsions

The determination of water and oil droplet size distributions in food emulsions by low‐field NMR has the advantage of a simple and non‐perturbing sample preparation. Furthermore, NMR performs very well with respect to precision. The current implementation on most benchtop NMR spectrometers deploys a variation of gradient duration and requires continuous corrections for gradient imbalances, thus making the whole procedure a time‐consuming one. By using variation of gradient strength and further stretching the capability of commercial benchtop NMR spectrometers, both water and oil droplet sizes can be measured in a more rapid manner, typically two to three times faster. The measured droplet size distributions are equivalent to those assessed by the current (slow) method, for both O/W and W/O emulsions. Furthermore, the rapid method shows a good performance with respect to precision. In addition, the method is able to determine droplet sizes in samples with much smaller amounts of dispersed phase.     

The Investigation of Intermediate Stage of Template Etching with Metal Droplets by Wetting Angle Analysis on (001) GaAs Surface

In this work, we study metal droplets on a semiconductor surface that are the initial stage for both droplet epitaxy and local droplet etching. The distributions of droplet geometrical parameters such as height, radius and volume help to understand the droplet formation that strongly influences subsequent nanohole etching. To investigate the etching and intermixing processes, we offer a new method of wetting angle analysis. The aspect ratio that is defined as the ratio of the height to radius was used as an estimation of wetting angle which depends on the droplet material. The investigation of the wetting angle and the estimation of indium content revealed significant materials intermixing during the deposition time. AFM measurements reveal the presence of two droplet groups that is in agreement with nanohole investigations. To explain this observation, we consider arsenic evaporation and consequent change in the initial substrate. On the basis of our analysis, we suggest the model of droplet evolution and the formation of two droplet groups.     

MODEL FOR PREDICTION OF ROTATING STREAM TRAY EFFICIENCY

Based on the results of the gas flow field, the droplet size distribution and the droplet initial flow rate distribution on a Φ300 mm rotating stream tray (RST), a three-dimensional droplet projection trajectory model, and a mass transfer model have been developed. The calculation of the models was carried out by a finite-difference procedure. The predicted results of the tray efficiency agree quite well with the experimental data measured with absorbing NH₃ or SO₂ in water on a Φ300 mm RST column and with the industrial data from a Φ3600 mm RST column. Meanwhile, the influence of absorbing system and the RST structure on the tray efficiency is discussed.     

变截面通道内流动聚焦微液滴生成数值研究

化学分析研究的不断深入,对液滴微流控精度提出了更高的要求。设计了不同孔径尺寸的流动聚焦通道模型,模拟油-水两相流动剪切微液滴生成过程。采用Level Set方法处理两相流动界面,研究了流动聚焦模型下通道尺寸和油-水两相流量比对生成液滴尺寸的影响。研究结果对实现微液滴生成过程的精准操控具有一定的参考意义。     

Predicting the diameters of droplets produced in turbulent liquid–liquid dispersion

The droplet size distribution in liquid–liquid dispersions is a complex convolution of impeller speed, impeller type, fluid properties, and flow conditions. In this work, we present three a priori modeling approaches for predicting the droplet diameter distributions as a function of system operating conditions. In the first approach, called the two-fluid approach, we use high-resolution solutions to the Navier–Stokes equations to directly model the flow of each phase and the corresponding droplet breakup/coalescence events. In the second approach, based on an Eulerian–Lagrangian model, we describe the dispersed fluid as individual spheres undergoing ongoing breakup and coalescence events per user-defined interaction kernels. In the third approach, called the Eulerian–Parcel model, we model a sub-set of the droplets in the Eulerian–Lagrangian model to estimate the overall behavior of the entire droplet population. We discuss output from each model within the context of predictions from first principles turbulence theory and measured data.     

Oil droplet movement and micro-flow characteristics during interaction process between gas bubble and oil droplet in flotation

Flotation is an efficient pre-treatment technology for oily water. In this work, the interaction process between the moving oil droplet and the gas bubble was studied by high-speed camera and Bassset-Boussinesq-Oseen (BBO) theoretical model, and the experimental and simulation results of the oil droplet trajectory were compared. Moreover, the micro-particle image velocimetry system was utilized to observe the flow inside and outside of the moving oil droplet. The results show that the BBO model with the mobile bubble’s surface can reflect the velocity change trend of the oil droplet during the interaction process between the moving oil droplet and the gas bubble, but there are some significant differences between the experimental and simulation results. While the oil droplet is moving on the bubble’s surface, the velocity of the area near the contact point of oil droplet–gas bubble is less than that of the other areas inside the oil droplet. Meanwhile, the flow of water above the oil drop is more biased towards the gas bubble.     

熔渣颗粒空冷相变换热的三维数值模拟

利用VOF方法结合凝固和熔化模型对熔渣颗粒在空气流中的冷却相变过程进行了三维数值模拟,讨论了熔渣颗粒直径和空气速度对冷却凝固过程演变的影响。结果表明：空冷方法能够实现熔渣颗粒表面的快速凝固成型,但同时也造成了颗粒内部的非均匀凝固。熔渣直径越小,完全凝固时间越短;空气流速越大时, 其表面换热越强, 完全冷却时间越短。颗粒初温为1673.15 K、直径为0.5~2 mm,风速为1~5 m·s^-1条件下熔渣颗粒在2 s内释放出全部凝固热,后续空气最高温度能达到900 K以上。     

A unified theoretical model for breakup of bubbles and droplets in turbulent flows

Pressure has a significant effect on bubble breakup, and bubbles and droplets have very different breakup behaviors. This work aimed to propose a unified breakup model for both bubbles and droplets including the effect of pressure. A mechanism analysis was made on the internal flow through the bubble/droplet neck in the breakup process, and a mathematical model was obtained based on the Young–Laplace and Bernoulli equations. The internal flow behavior strongly depended on the pressure or gas density, and based on this mechanism, a unified breakup model was proposed for both bubbles and droplets. For the first time, this unified breakup model gave good predictions of both the effect of pressure or gas density on the bubble breakup rate and the different daughter size distributions of bubbles and droplets. The effect of the mother bubble/droplet diameter, turbulent energy dissipation rate and surface tension on the breakup rate, and daughter bubble/droplet size distribution was discussed. This bubble breakup model can be further used in a population balance model (PBM) to study the effect of pressure on the bubble size distribution and in a computational fluid dynamics‐population balance model (CFD‐PBM) coupled model to study the hydrodynamic behaviors of a bubble column at elevated pressures. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1391–1403, 2015     

蒸发式过冷水制冰中单个水滴的蒸发过冷特性

为分析蒸发式过冷水制冰中单个水滴在此低温低湿空气环境中的蒸发特性,建立了水滴蒸发过冷过程的数理模型。通过悬挂水滴实验与模拟结果的对比,验证了模型的有效性。因此利用该数学模型预测微小直径水滴的蒸发特性是可行的。通过模拟计算获得了水滴初始直径、初始水温、空气温度、空气含湿量和空气流速对水滴蒸发过冷过程的影响。结果表明,水滴初始直径越小、温度越低或空气流速越大,水滴的冷却速率就越大,达到稳态时的过冷时间就越短。另外,通过降低空气温度或含湿量不仅提高了水滴的冷却速率,而且增加了水滴达到稳态时的过冷度。通过水滴蒸发过冷特性的分析,可为制冰系统的优化设计及提高系统制冰效率提供理论参考。     

Spray characterization: Numerical prediction of Sauter mean diameter and droplet size distribution

A simplified equation of the Nukiyama-Tanasawa type for droplet size distribution in sprays is obtained from the synergetic concept of entropy information, assuming spherical droplets and zero and infinity as their limit sizes. The introduction of Sauter mean diameter (SMD) definition in that equation yields a new distribution function dependent solely on SMD, which is calculated from available correlations for pressure-jet and pre-filming airblast atomizers. For plain-jet airblast atomizers a new and dimensionally consistent correlation is determined. Several droplet size distributions are then predicted. Experimental data are compared with predictions of SMD; the agreement is satisfactory.     

农药雾滴空间运行中的变形特征分析

以化学农药雾滴的空间运行过程为背景，构建了二维气液相界面追踪模型，通过COMSOL Multiphysics系统地研究了雾滴特征参数及风速等多因素耦合下单雾滴在横向风场中下落时的形变特征。结果表明，雾滴的形变会受黏性力、表面张力等内部因素和重力、曳力等外部因素的共同作用，外部作用力能够促进雾滴发生形变，而内部作用力阻碍雾滴的形变。雾滴的形变量随着雾滴尺寸和横向速度的增大而增大，随着动力黏度和表面张力的增大而减小；雾滴下落过程中的形变存在振荡周期，雾滴的形变周期随着雾滴尺寸的增大而增大，随着表面张力的增大而减小，但基本不受横向风速和动力黏度的影响。将雾滴的形变量、形变周期与韦伯数We、奥内佐格数Oh和雷诺数Re等量纲为1数进行拟合，可以预测雾滴的空间形变特性。研究结果对农药雾滴的空间飘移机理及其阻控技术的研发具有重要意义。     

气流式雾化过程的有限随机分裂模型

滴径分布是描述喷嘴雾化性能的一个重要指标.从液滴分裂的自相似性出发,提出了描述气流式雾化过程的液滴有限随机分裂模型.实验和模拟计算结果表明,该模型能较好地模拟三通道喷嘴气流式雾化过程的平均滴径和滴径分布的非线性关系.     

APPLICATION AND FUNDAMENTAL RESEARCH OF ROTATING STREAM TRAY

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