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     

The Influence of Macroscopic Elongational Flow on Dispersion Processes in Agitated Tanks

The influence of elongational and shear gradients in the macroscopic flow field in agitated tanks on dispersion processes is investigated. Measurements of droplet size distribution for a liquid‐liquid dispersion process using phase‐Doppler anemometry (PDA) reveal that axial‐flow impellers, such as the 24°‐pitched‐blade turbine and propeller, produce smaller droplets than the Rushton turbine at the same average specific power and energy input. These results stand in contradiction to the usual assumption that only the maximum turbulent shear stress determines the breakup process and the Rushton turbine is well known to produce higher turbulent shear stresses. Particle image velocimetry (PIV) measurements of the macroscopic flow field indicate that the 24°‐pitched‐blade turbine and propeller produce larger areas with higher elongational gradients. Therefore, the proposed consideration of particle breakup due to macroscopic elongational flow in addition to turbulent stresses improves the understanding of dispersion processes in agitated tanks.     

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.     

Effect of Impeller Blade Geometry on Drop Size in Stirring of Immiscible Liquids

The stirring of immiscible liquids is considered, and the effect of impeller geometry on the dynamic equilibration of the emulsion and on the maximum drop size is analyzed. The dissipation rate of turbulent energy in the wake of an impeller blade is estimated.     

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.     

Interrelation among Liquid Velocity,Impeller Speed and Gas Flow Rate in the Stirred Airlift Reactor

We investigate the liquid circulation velocity in the draft‐tube airlift reactor, with mechanical agitation in the internal column as a riser, at the impeller speed of up to 40 s^–1. An influence of the gas flow rate and the stirrer speed on the riser and downcomer gas hold‐up difference and on the liquid circulation velocity is also investigated. The character of the liquid circulation velocity changes depends on the relation between the gas flow rate and the impeller speed. A monotonic increase of the liquid circulation velocity with an increase of the gas velocity is observed at the impeller speed of lower than 15 s^–1. A distinct decrease of the liquid velocity is found at higher impeller speeds and at low gas velocities. The decrease is larger for higher impeller speeds. We observe the minimum on the curve of the liquid velocity dependence on the gas velocity followed by the monotonic increase of the liquid velocity with an increase of the gas flow velocity. The minimum of the liquid circulation velocity appears if the ratio of the gas flow number to the impeller speed is about 0.0006. The minima are shifted towards the higher gas velocities at higher impeller speeds. An experimental equation for the prediction of the liquid circulation velocity in the stirred airlift reactor is presented.     

离心光散射法测定乳液液珠大小与分布

用日本 Shimadzu SA-CP3型粒度分布仪测定由低分子量挥发性有机物构成的 O/W型和 W/O型乳液中液珠大小与分布。讨论了稀释液种类、稀释倍数和离心速度对测试结果的影响     

旋风筒阻降浅论

介绍了旋风筒阻降(压降)的定义及其测量方法、旋风筒阻降的计算公式,分析了操作参数和结构尺寸对旋风筒阻降的影响、旋风筒阻降的种类及各种减阻措施。     

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。     

Correlation of the Drop Size in a Modified Scheibel Extraction Column

Experiments were designed to ascertain the main factors for the Sauter mean drop size (d₃₂) of the dispersed phase in a three‐stage modified Scheibel extraction column with no mass transfer. A precise correlation applied to the liquid‐liquid systems with low interfacial surface tension was proposed for calculating d₃₂. The maximum relative error for all data was 16.0 % and the mean relative error ±4.6 %.     

Flow and Turbulence in the Discharge of Radial Pumping Turbines: Influence of the Turbine Type

Velocity measurements were made in the impeller discharge of 6SRGT‐ and Rushton‐type impellers in a 0.6 m³ tank using constant temperature anemometry with a direction sensitive split‐film probe. The reproducibility error of the measurement system was found to be greater than 5 % for all measured properties. The main flow and turbulent parameters measured at three agitation rates in the impeller discharge are compared for the two turbines with respect to both agitation rate and the measured power input. For comparison of the flow properties in the centerline of the two turbines having different diameter and blade height, a uniform representation was used treating the impeller stream as a special kind of free jet. Using this representation, we obtained similar results for both turbines on all measured parameters. The profile measurements showed a similar main flow field for both turbines, but significant differences were found in the axial distribution of turbulent kinetic energy and the energy dissipation rate.     

Size Distribution of Drops Formed from Nozzles in Air at Velocities below Jetting

The drop size distribution of drops formed from four nozzles (d = 0.5, 1.8, 2.7 and 3.6 mm) were measured for the flow rate range Q = 0.1–1.17 cm³/s and Reynolds number 56–448. Distilled water was used as the dispersed phase and air as the continuous one. The experimental drop size distributions were described satisfactorily by the theoretical upper limit number and volume distributions. The experimental data of minimum and maximum diameters versus the respective Sauter mean diameters gave straight lines with slopes of 0.81 and 1.18, respectively.     

Effect of Ultrasonication on Droplet Size in Biodiesel Mixtures

Biodiesel fuels have become more attractive recently because of their environmental benefits and cost competitiveness compared to diesel fuel. Many processing improvements have been proposed to increase the conversion rates and the yields of vegetable oil in order to lower production costs and improve biodiesel product quality. In conventional biodiesel production chemistries, alkaline transesterifications of alcohol/oil dispersions should occur primarily near the interface. Ultrasonic mixing has already been shown to increase overall conversion rates for alcohol/vegetable oil mixtures. Our data show that ultrasonic mixing produced smaller droplet sizes than conventional agitation, leading to more interfacial area for the reaction to occur. Droplet size distributions have been measured for conventional impeller and ultrasonic mixing systems using methanol/soybean oil as a model system. The dispersions were stabilized by surfactant in order to obtain droplet size distribution for mixture samples. Ultrasonic mixing produced dispersions with average droplet sizes 42% smaller than those generated using standard impellers.     

Influence of Nanoparticles and Drop Size Distributions on the Rheology of w/o Pickering Emulsions

The rheological behavior of particle/oil suspensions and w/o Pickering emulsions consisting of water, 1‐dodecene and different fumed silica nanoparticles was investigated. The particles varied in hydrophobicity and specific surface area. The influence of particle concentration and water content on rheology was determined and the emulsion drop size distributions were examined. Emulsions with different drop sizes were created by either varying the particle concentration or the water content. It was found that the particles in the continuous oil phase and not the drop size distribution seem to be the major influencing factor on the Pickering emulsion rheology.