New Predictive Correlations for the Drop Size in a Rotating Disc Contactor Liquid‐Liquid Extraction Column

Sauter mean drop sizes (d₃₂) generated from a hole distributor in liquid extraction RDC columns were studied under various conditions. Experiments were designed to generate data required to determine the main variables that control the drop sizes in RDCs. Two precise correlations were proposed for predicting d₃₂ in a RDC extraction column. The first was based on operating variables, hole‐distributor diameter, disc speed, column geometry, and system physical properties. The second one considered the same variables, except the column geometry. This model can be used for design purposes. The two correlations are the first of their type to consider the distributor hole inlet diameter in a RDC column. This diameter has been neglected by previous investigators. The maximum standard deviation for all data is 0.75 %, with a maximum absolute error of 6.8 %.     

Effect of Impeller Blade Height on the Drop Size Distribution in Agitated Dispersions

A common method to achieve a contact of two liquid phases – required for many chemical engineering operations – is the dispersion of one into the other by mechanical agitation. The drop size distribution in such an agitated dispersion is a result of the dynamic equilibrium existing between the breaking and coalescing drops. A comparison has been made of drop diameters produced by four disk type impellers differing only in blade height (D_W = 1, 2, 4 and 6 cm). Measurements in situ at 200, 250, 300, 350, 400, 450 rpm and at holdup fractions 0.02, 0.05, and 0.07, showed that the Sauter mean drop diameters increased up to 140 % as the impeller blade height decreased from 6 to 1 cm. Plots of ln α₃₂ vs. ln N, lnα₃₂ vs. ln D_T and ln α₃₂ vs. ln α_max gave straight lines.     

Influence of Different Silica Nanoparticles on Drop Size Distributions in Agitated Liquid‐Liquid Systems

The impact of different silica nanoparticles on rheology, interfacial tension and drop size distributions in liquid‐liquid systems is determined experimentally. The particles vary in wettability and specific surface area. In contrast to commonly used high‐energy devices for Pickering emulsion preparation, low energy input by stirring allows to quantify drop breakage and coalescence in steady state and dynamic conditions. The experiments can provide essential information for drop size model development in nanoparticle‐stabilized emulsions.     

Droplet Size in Two‐Phase Liquid Dispersed Pipeline Flows

Few experimental data exists on drop size distribution during dispersed liquid‐liquid pipeline flows. In the majority of cases dilute dispersions have been used and the results have mainly been compared with models for drop breakup. A review of this work shows that the Rosin‐Rammler distribution represents satisfactorily the existing experimental data. However, the commonly used Hinze model (Hinze, 1955) often underpredicts the experimentally found maximum drop sizes. Later models, many of which are developments of the Hinze one, are also unable to predict the resulting maximum drop size for a wide range of experimental conditions. A more comprehensive database is needed for the further development and refinement of theoretical models.     

Effect of Impeller Vertical Position on Drop Sizes in Agitated Dispersions

The effect of impeller height relative to the vessel bottom was studied by measuring the drop size distributions of kerosene dispersions in water at two positions inside a stirred tank. Measurements were taken at 1/3, 1/ 2, and 2/3 of total vessel height for rotational speeds 250, 300, 350 and 400 RPM and for hold‐up fractions 0.02 and 0.04. Results show an influence of impeller height on drop sizes ranging from a Sauter mean diameter decrease of 7.8 % to an increase of 35 % relative to the ones obtained with the impeller at the center of the vessel     

An Analysis of Pressure Drop and Holdup for Liquid‐Liquid Upflow through Vertical Pipes

The present study has attempted to investigate pressure drop and holdup during simultaneous flow of two liquids through a vertical pipe. The liquids selected were kerosene and water. The measurements were made for phase velocities varying from 0.05–1.2 m/s for both liquids. The pressure drop was measured with a differential pressure transducer while the quick closing valve (QCV) technique was adopted for the measurement of liquid holdup. The measured holdup and pressure drop were analyzed with suitable theoretical models according to the existing flow patterns. The analysis reveals that the homogeneous model is suitable for dispersed bubbly flow whereas bubbly and churn‐turbulent flow pattern is better predicted by the drift flux model. On the other hand, the two fluid flow model accurately predicts the pressure drop in core annular flow.     

Drop Size Distribution in a Standard Twin‐Impeller Batch Mixer at High Dispersed‐Phase Volume Fraction

The preparation of concentrated aqueous silicone oil emulsions has been investigated with particular attention to the effect of the dispersed‐phase volume fraction ? from 0.01 to 0.5 for a wide range of oil viscosities (50 to 1000 cSt). Oil was added on the top surface of a 6‐L vessel. Drop size distribution and Sauter mean diameter, d₃₂, measurements were carried out over 24 h mixing time. Emulsification was found to be relatively sensitive to the oil phase viscosity, μ_d, for the same ? yielding a narrower drop size distribution for low oil viscosity (50 cSt) and a wider drop size distribution for the highly viscous oil (1000 cSt). For the same ?, increasing μ_d resulted in increasing d₃₂. The equilibrium d₃₂ was found to be well correlated to the viscosity number by for ? = 0.5. For the same oil viscosity, d₃₂ was found to increase with increasing ?. A multiregression of d₃₂ with both ? and V_i for various silicone oil viscosity grades was successfully correlated by with a regression coefficient (R²) of 0.975. This shows a very weak dependence of the equilibrium d₃₂ on ?.     

具有高粘度分散相的油-水分散体系的液滴破碎与粒径分布研究

对湍流搅拌槽中原油-水分散体系的液滴破碎进行了研究。在不同的温度下原油表现出不同的流变学特征，对分散过程中的液滴破碎产生不同的影响。实验研究对比了不同温度下原油-水分散体系的液滴分布及最大稳定粒径，分析了触变性对破碎过程及最大稳定粒径的影响。经过模型计算与实验结果比较，发现以初始粘度计算的理论值预测最大稳定粒径更为合适。     

Dispersion and Phase Separation of Water‐Oil‐Amphiphile Systems in Stirred Tanks

Drop size distributions and phase separation behavior of water‐oil‐nonionic amphiphile systems are investigated using an in situ endoscope measurement technique and an external camera in stirred tanks in batch mode. The fitting procedure and the simulation results of a phase separation model are analyzed under the condition that either the swarm sedimentation speed or the mean drop size during sedimentation is known. The steady‐state drop size distributions are self‐similar over the whole range of process parameters, but not in the decaying turbulence field after agitation stop. The coalescence rate in the first seconds after agitation stop clearly affects the separation behavior, so that a prediction of the separation time based on the initial conditions in steady state is not trivial.     

Flow Field Analysis of Stirred Liquid‐Liquid Systems in Slim Reactors

Previous studies have shown the great potential, but also the great challenges, in handling slim reactors often used for polymerization reactions. Experiments and simulations were carried out in reactors with aspect‐to‐diameter ratios of up to 5, to test and to evaluate the mixing and dispersion efficiency for liquid‐liquid systems of single‐ and multiple‐stage impellers. Therefore, power consumption, mixing time and minimum dispersion speed were determined for five different stirrer types under turbulent conditions. It was found that the dimensionless mixing time is highly sensitive to the configuration of the impellers, with almost no dependency on the turbulent power number. Another focus was the analysis of the effect of the baffles. The influence of the baffle length in slim reactors on the mixing time and the macroscopic flow field was determined.     

Effect of Structural Parameters on Drop Size Distribution in Pulsed Packed Columns

The effect of packing type on drop size distribution in pulsed packed columns was investigated by means of different columns and three packing types with three liquid systems including n‐butyl acetate, toluene, and kerosene with water. These liquid systems cover a wide range of interfacial tensions. Also the influence of operating variables in terms of pulse intensity and volumetric flow rates of dispersed and continuous phases was examined. Pulse intensity, interfacial tension, and packing shape were found as the main important factors for drop size distribution while volumetric flow rates had no significant effect. Correlations are presented to predict drop distribution and mean drop size in pulsed packed columns.     

Behavior of Elongated Liquid Jets in Viscous Liquid‐Liquid‐Systems

The stability of jets in elongational flow is exploited to obtain thin threads before breakup. Fine drops can be generated in suitable geometries with comparably large ducts. The examination deals with the stability of liquid threads simultaneously extended with the continuous phase in convergent flow. Breakup limits and regimes are discussed.     

CFD Prediction of the Critical Agitation Speed for Complete Dispersion in Liquid‐Liquid Stirred Reactors

A computational fluid dynamics (CFD) model is adopted to simulate the turbulent immiscible liquid‐liquid flow in a stirred vessel based on a two‐fluid model with a k‐ϵ‐A_P turbulence model. An improved inner‐outer iterative procedure is adopted to deal with the impeller rotation in a fully baffled stirred tank. Different drag formulations are examined, and the effect of the droplet size on both the dispersed phase holdup distribution and the velocity field is analyzed. Two different numerical criteria are tested for determining the critical impeller speed for complete dispersion. The simulated critical impeller speeds are generally in good agreement with the correlations in the literature when the fixed droplet size is properly selected. This demonstrates that the modeling approach and the numerical criteria proposed in this work are promising for predicting the dispersion characteristics in liquid‐liquid stirred tanks.