Axial Dispersion in a Three-Phase Gas-Agitated Spray Extraction Column

1998 ◽  
Vol 63 (2) ◽  
pp. 283-292 ◽  
Author(s):  
Milan Sovilj
Keyword(s):  
Gas Phase ◽  
Dispersion Coefficient ◽  
Continuous Phase ◽  
Axial Dispersion ◽  
Superficial Velocity ◽  
Extraction Column ◽  
Dispersed Phase ◽  
Dispersion Coefficients ◽  
Axial Dispersion Coefficient ◽  
Three Phase

The continuous-phase axial dispersion coefficients of the three-phase gas-liquid-liquid system in a gas-agitated spray extraction column 10 cm i.d. at 20 °C were examined. The system used was water as continuous phase, toluene as dispersed phase, and air as gaseous phase. The rise in the gas phase superficial velocity increased the continuous-phase axial dispersion coefficient. A non-linear dependence between the continuous-phase axial dispersion coefficient and the continuous phase superficial velocity was observed. No correlation was found between the continuous-phase axial dispersion coefficient and dispersed phase superficial velocity. The increase in the gas phase hold-up corresponded to a slight increase in the continuous-phase axial dispersion coefficient. The increase in the dispersed phase hold-up generated a growth of the continuous-phase axial dispersion coefficient. A comparison was made of the continuous-phase axial dispersion coefficients of the three-phase (air-water-toluene) and two-phase (water-toluene) systems.

scholarly journals Hydrodynamics of pulsed sieve-plate extraction columns

2020 ◽  
Vol 74 (1) ◽  
pp. 1-14
Author(s):  
Milan Sovilj ◽  
Momcilo Spasojevic
Keyword(s):  
Continuous Phase ◽  
Liquid System ◽  
Axial Dispersion ◽  
Superficial Velocity ◽  
Dispersed Phase ◽  
Geometrical Parameters ◽  
Drop Diameter ◽  
Sieve Plate ◽  
Axial Dispersion Coefficient ◽  
Hydrodynamic Parameters

This paper presents a review of some hydrodynamic parameters in pulsed sieve-plate extraction columns. The hydrodynamic parameters in liquid-liquid systems in these columns were analyzed regarding the effects of operating and geometrical parameters. The values of Sauter mean drop diameter were function of the existing work flow regimes in the column device defined as mixer-settler, emulsion and dispersion regimes. It was concluded that the dispersed-phase holdup was a function of the mean drop diameter and dispersed-phase superficial velocity. An increase in the dispersed-phase holdup induced an increase in the interface area in the liquid-liquid system. Knowledge of the value of the dispersed-phase holdup can be used for calculation of the volumetric mass transfer coefficient, one of the important factor in the design of the column extractor. It was concluded that the increase in the dispersed-phase superficial velocity is causing a decrease in axial dispersion. On the other hand, an increase in the continuous-phase superficial velocity is causing the increase in the axial dispersion coefficient. Some of the empirical equations proposed in literature for calculations of the hydrodynamic parameters were presented. These correlations, derived for determination of the hydrodynamic parameters in pulsed sieve-plate extraction columns, can be used for the design of these liquid-liquid extraction columns.

scholarly journals Hydrodynamics of a pilot plant spray extraction column

2018 ◽  
pp. 159-168 ◽  
Author(s):  
Milan Sovilj ◽  
Branislava Nikolovski ◽  
Momcilo Spasojevic
Keyword(s):  
Pilot Plant ◽  
Droplet Diameter ◽  
Great Influence ◽  
Continuous Phase ◽  
Liquid System ◽  
Superficial Velocity ◽  
Hydrodynamic Characteristics ◽  
Extraction Column ◽  
Dispersed Phase ◽  
Axial Dispersion Coefficient

The hydrodynamic characteristics of the liquid-liquid system of toluene-water in a pilot plant spray extraction column were experimentally determined. The experimental data for hydrodynamic characteristics such as the dispersed phase holdup, mean droplet size, and the axial dispersion coefficient were obtained. The dispersed phase superficial velocity had a great influence on toluene holdup. At the same time, a strong effect of the continuous phase superficial velocity on the dispersed phase holdup was evident. The dispersed phase holdup had a tendency to increase when the ratio of the dispersed phase superficial velocity and characteristic velocity increased. The Sauter mean droplet diameter decreased with increasing dispersed phase superficial velocity when the continuous phase superficial velocity remained constant. In contrast, it was not affected by the changes in the continuous phase superficial velocity while the dispersed phase superficial velocity remained constant. It was concluded that the Peclet number increased as a result of an increase of the Reynolds number.

scholarly journals Axial dispersion and mixing of coolant gas within a separate-effect prismatic modular reactor

2018 ◽  
Vol 4 (3) ◽  
pp. 167-178 ◽  
Author(s):  
Ibrahim Said ◽  
Shaoib Usman ◽  
Muthanna Al-Dahhan ◽  
Mahmoud Moharam ◽  
Vineet Alexander
Keyword(s):  
Gas Phase ◽  
Flow Rate ◽  
Dispersion Coefficient ◽  
Dispersion Model ◽  
Heat Fluxes ◽  
Axial Dispersion ◽  
Experimental Setup ◽  
Gas Dispersion ◽  
Axial Dispersion Coefficient ◽  
Separate Effect

Multiphase Reactors Engineering and Applications Laboratory performed gas phase dispersion experiments in a separate-effect cold-flow experimental setup for coolant flow within heated channels of the prismatic modular reactor under accident scenario using gaseous tracer technique. The separate-effect experimental setup was designed on light of local velocity measurements obtained by using hot wire anemometry. The measurements consist of pulse-response of gas tracer that is flowing through the mimicked riser channel using air as a carrier. The dispersion of the gas phase within the separate-effect riser channel was described using one-dimensional axial dispersion model. The axial dispersion coefficient and Peclet number of the coolant gas phase and their residence time distribution within were measured. Effect of heating intensities in terms of heat fluxes on the coolant gas dispersion along riser channels were mimicked in the current study by a certain range of volumetric air flow rate ranging from 0.0015 to 0.0034 m3/s which corresponding to heating intensity range from 200 to 1400 W/m2. Results confirm a reduction in the response curve spreads is achieved by increasing the volumetric air velocity (representing heating intensity). Also, the results reveal a reduction in values of axial dispersion coefficient with increasing the air volumetric flow rate.

scholarly journals Reactive Zinc Extraction in MRDC Column; Case Study by Mathematical Modelling and Applying the Droplet Size Distribution with Forward Mixing Approach

2021 ◽  
Author(s):  
Benyamin Shakib ◽  
Rezvan Torkaman ◽  
Meisam Torab-Mostaedi ◽  
Mojtaba Saremi ◽  
Mehdi Asadollahzadeh
Keyword(s):  
Mathematical Modeling ◽  
Mass Transfer ◽  
Solvent Extraction ◽  
Mass Transfer Rate ◽  
Continuous Phase ◽  
Axial Dispersion ◽  
Extraction Column ◽  
Dispersed Phase ◽  
Rotor Speed ◽  
Zinc Extraction

Abstract In this survey, the reactive mass transfer data are determined for zinc extraction from chloride solution using D2EHPA in the MRDC extraction column. The numerical analysis for evaluating the column performance is applied to describe mass balance equations. Four mathematical models (backflow, forward mixing, plug flow, and axial dispersion) are investigated to compute the mass transfer coefficients of the dispersed phase. The solvent extraction experiments showed that the optimum zinc transport efficiency in rotor speed of 410 rpm in this column is equal to 98.85% and 99.85 for extraction and stripping stages, respectively. The model's achievement is compared with the solvent extraction data and a significant validity is obtained by coupling the forward mixing approach. The mathematical modeling expresses that the coefficients of axial dispersion and backflow based on the continuous phase increase by an increase in the rotor speed and inlet continuous phase rate. While these coefficients reduce at a higher inlet dispersed phase rate. The FMM method is preferred to predict the reactive mass transfer rate in the MRDC column due to the lowest relative deviation. The experimental study and mathematical modeling in this report provide beneficial information about the metallurgical industry to design solvent extraction equipment.

scholarly journals Hydrodynamics in spray and packed liquid-liquid extraction columns: A review

2019 ◽  
Vol 38 (2) ◽  
pp. 267
Author(s):  
Milan N. Sovilj ◽  
Branislava G. Nikolovski ◽  
Momčilo Đ. Spasojević
Keyword(s):  
Slip Velocity ◽  
Drop Size ◽  
Dispersion Coefficient ◽  
Packed Bed ◽  
Axial Dispersion ◽  
Hydrodynamic Characteristics ◽  
Dispersed Phase ◽  
Drop Diameter ◽  
Axial Dispersion Coefficient ◽  
Experimental Findings

This work provides a review of hydrodynamic characteristics such as the slip velocity, the dispersed-phase holdup, mean drop size, and axial dispersion of non-mechanically agitated liquid-liquid (L-L) extractors, with special reference to spray and packed bed columns. The complexity and importance of hydrodynamic behavior in designing and scaling up L-L extractors was a driving force to analyze, compare and discuss some important experimental findings available in the literature. The effects of phase velocities and the dispersed-phase holdup on the slip velocity, the mean drop size and the axial dispersion coefficient were studied and presented. Empirical correlations for slip velocity, the Sauter mean drop diameter and the axial dispersion coefficient, which were taken from the literature, were commented in terms of their applicability.

scholarly journals The Hydrodynamics and Mixing Performance in a Moving Baffle Oscillatory Baffled Reactor through Computational Fluid Dynamics (CFD)

Processes ◽  
2020 ◽  
Vol 8 (10) ◽  
pp. 1236
Author(s):  
Hamid Mortazavi ◽  
Leila Pakzad
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Dispersion Coefficient ◽  
Velocity Ratio ◽  
Axial Dispersion ◽  
Shear Strain Rate ◽  
Turbulent Length Scale ◽  
Mixing Performance ◽  
Axial Dispersion Coefficient ◽  
Computational Fluid Dynamics Cfd

Oscillatory baffled reactors (OBRs) have attracted much attention from researchers and industries alike due to their proven advantages in mixing, scale-up, and cost-effectiveness over conventional stirred tank reactors (STRs). This study quantitatively investigated how different mixing indices describe the mixing performance of a moving baffle OBR using computational fluid dynamics (CFD). In addition, the hydrodynamic behavior of the reactor was studied, considering parameters such as the Q-criterion, shear strain rate, and velocity vector. A modification of the Q-criterion showed advantages over the original Q-criterion in determination of the vortices’ locations. The dynamic mesh tool was utilized to simulate the moving baffles through ANSYS/Fluent. The mixing indices studied were the velocity ratio, turbulent length scale, turbulent time scale, mixing time, and axial dispersion coefficient. We found that the oscillation amplitude had the most significant impact on these indices. In contrast, the oscillatory Reynolds number did not necessarily describe the mixing intensity of a system. Of the tested indices, the axial dispersion coefficient showed advantages over the other indices for quantifying the mixing performance of a moving baffle OBR.

Effect of Geometry on Droplet Generation in a Microfluidic T-Junction

2013 ◽  
Author(s):  
Katerina Loizou ◽  
Wim Thielemans ◽  
Buddhika N. Hewakandamby
Keyword(s):  
Aspect Ratio ◽  
Cross Section ◽  
Droplet Formation ◽  
Continuous Phase ◽  
Main Channel ◽  
Superficial Velocity ◽  
Droplet Generation ◽  
Dispersed Phase ◽  
Aspect Ratios ◽  
The Cross

The main aim of this study is to examine how the droplet formation in microfluidic T-junctions is influenced by the cross-section and aspect ratio of the microchannels. Several studies focusing on droplet formation in microfluidic devices have investigated the effect of geometry on droplet generation in terms of the ratio between the width of the main channel and the width of the side arm of the T-junction. However, the contribution of the aspect ratio and thus that of the cross-section on the mechanism of break up has not been examined thoroughly with most of the existing work performed in the squeezing regime. Two different microchannel geometries of varying aspect ratios are employed in an attempt to quantify the effect of the ratio between the width of the main channel and the height of the channel on droplet formation. As both height and width of microchannels affect the area on which shear stress acts deforming the dispersed phase fluid thread up to the limit of detaching a droplet, it is postulated that geometry and specifically cross-section of the main channel contribute on the droplet break-up mechanisms and should not be neglected. The above hypothesis is examined in detail, comparing the volume of generated microdroplets at constant flowrate ratios and superficial velocities of continuous phase in two microchannel systems of two different aspect ratios operating at dripping regime. High-speed imaging has been utilised to visualise and measure droplets formed at different flowrates corresponding to constant superficial velocities. Comparing volumes of generated droplets in the two geometries of area ratio near 1.5, a significant increase in volume is reported for the larger aspect ratio utilised, at all superficial velocities tested. As both superficial velocity of continuous phase and flowrate ratio are fixed, superficial velocity of dispersed phase varies. However this variation is not considered to be large enough to justify the significant increase in the droplet volume. Therefore it can be concluded that droplet generation is influenced by the aspect ratio and thus the cross-section of the main channel and its effect should not be depreciated. The paper will present supporting evidence in detail and a comparison of the findings with the existing theories which are mainly focused on the squeezing regime.

scholarly journals New regimes of dispersion in microfluidics as mediated by travelling temperature waves

2019 ◽  
Vol 475 (2230) ◽  
pp. 20190382 ◽  
Author(s):  
Debashis Pal ◽  
Suman Chakraborty
Keyword(s):  
Dispersion Coefficient ◽  
Dna Amplification ◽  
Temperature Wave ◽  
Axial Dispersion ◽  
Stable Regime ◽  
Axial Dispersion Coefficient ◽  
Time Period ◽  
Fluidic Devices ◽  
Periodic Temperature ◽  
Short Time

We unveil new regimes of dispersion in miniaturized fluidic devices, by considering fluid flow triggered by a travelling temperature wave. When a temperature wave travels along a channel wall, it alters the density and viscosity of the adjacent fluid periodically. Successive expansion–contraction of the fluid volume through a spatio-temporally evolving viscosity field generates a net fluidic current. Based on the temporal evolution of the axial dispersion coefficient, new regimes of dispersion—such as a short-time ‘oscillating regime’ and a large-time ‘stable regime’—have been identified, which are absent in traditionally addressed flows through miniaturized fluidic devices. Our analysis reveals that the oscillation of axial dispersion persists until the variance of species concentration becomes equal to half of the square of the wavelength of the thermal wave. The time period of oscillation in the dispersion coefficient turns out to be a unique function of the thermal wavelength and net flow velocity induced by thermoviscous pumping. The results of this study are likely to contribute towards the improvement of microscale systems that are subjected to periodic temperature variations, including microreactors and DNA amplification devices.

scholarly journals Measurement of the axial dispersion coefficient of powders in a rotating cylinder: dependence on bulk flow properties

2016 ◽  
Vol 292 ◽  
pp. 298-306 ◽  
Author(s):  
Sara Koynov ◽  
Yifan Wang ◽  
Agnesa Redere ◽  
Prashani Amin ◽  
Heather N. Emady ◽  
...  
Keyword(s):  
Dispersion Coefficient ◽  
Rotating Cylinder ◽  
Axial Dispersion ◽  
Bulk Flow ◽  
Flow Properties ◽  
Axial Dispersion Coefficient
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