Dispersed Phase Flow Rate Research Articles

Direct measurement of droplet breakage in a pulsed disc and doughnut column

The lack of experimental data for the droplet breakup has been one of the limitations for the application of population balance model (PBM). In this work, a high‐speed camera was used to directly measure the droplet breakup frequency and daughter size distribution in a pulsed disc and doughnut column. It was found from the captured video that multiple breakup events were more frequently observed than binary breakup. The multiple breakup was treated as an original breakup and several intermediate breakups to characterize the process quantitatively. The effects of pulsation intensity, dispersed phase flow rates, and the spatial locations were investigated in detail. Empirical correlations were finally established for both the breakup frequency function and the daughter droplet size distribution function and fitted well with the experimental data. The correlation equations were then used in a simplified PBM to calculate the droplet number density, which further proved the feasibility of the correlations. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4188–4200, 2017

Mass transfer in a pulsed and non-pulsed disc and doughnut (PDD) solvent extraction column

Mechanical agitation or pulsation is usually introduced to a solvent extraction column to improve the efficiency. Recently a number of industrial scale pulsed disc and doughnut (PDD) solvent extraction columns have been found to have higher extraction efficiency while running with non-pulsing. In this study, the mass transfer performance of a PDD column was measured under pulsing and non-pulsing conditions using a 72.5mm diameter disc and doughnut column. The effects of pulsation intensity and dispersed and continuous phase velocity on the mass transfer performance have been investigated. The results show that, under non-pulsing conditions, the overall mass transfer coefficient increased with increasing continuous phase flow rate and slightly decreased with increasing dispersed phase flow rate. With increasing pulsation intensity, the overall mass transfer coefficient decreased at first and then increased. Two correlations are proposed to predict the height of mass transfer unit and overall mass transfer coefficient in a PDD column including pulsing and non-pulsing conditions.

CFD with population balance model to predict droplet size distribution in submerged turbulent multiphase jets

During deepwater oil spill events, oil is released into a relatively stagnant environment (ocean water) in an uncontrolled manner. The oil phase initially emerges as a jet and the gushing oil loses its momentum energy and results in entrainment of surrounding water. The shear interaction between the oil mass and the ambient fluid results in generation of droplets with wide size distribution. In this study, we present a numerical model for predicting the droplet size distribution resulting from the interaction of turbulent oil jets with the surrounding quiescent environment. We achieve this objective by integrating traditional multiphase CFD models with a population balance approach. The developed model has been validated against the experimental observations reported in Johansen et al.[12] The ‘Mixture model’ has been employed for evaluating flow fields in the system. We restrict our study to the atomization regime, where the droplet disintegration process has a greater significance over the competing coalescence mechanism. The population balance equation has been solved using the ‘Class method’ and the disintegration of droplets has been modelled by including the breakage kernel suggested by Lehr.27 The developed model has been used to analyze the effect of dispersed (oil) phase flow rates, the presence of dispersants, and the presence of air in the jet phase on the overall size distribution of oil droplets. We also present a case which compares the droplet size distributions obtained by using the flow field evaluated by a more rigorous Eulerian Two‐Fluid model over Mixture model.

Drop generation from a vibrating nozzle in an immiscible liquid-liquid system

Drop generation from an axially vibrating nozzle exhibits a transition in drop diameter when varying the vibration amplitude. Below a threshold amplitude, forcing has essentially no effect on drop size and drops form in dripping mode. Above the threshold, drop size is controlled by forcing: drops detach at resonance, i.e., when the first eigenfrequency of the growing drop coincides with the forcing frequency. We experimentally study the impact of the nozzle inner diameter, dispersed phase flow rate, interfacial tension, and dispersed phase viscosity on this transition. Drop diameter is well correlated to the mode 1 eigenfrequency of Strani and Sabetta for a drop in partial contact with a spherical bowl. We propose a transient model to describe drop dynamics until detachment. The drop is modelled as a linearly forced harmonic oscillator, with the eigenfrequency of Strani and Sabetta. Since the dispersed phase does not wet the nozzle tip, an additional damping coefficient is introduced to account for the viscous dissipation in the film of continuous phase between the drop and nozzle surface. The model adequately reproduces the effect of the different parameters on the threshold amplitude.

Heat transfer measurement in a three-phase spray column direct contact heat exchanger for utilisation in energy recovery from low-grade sources

Energy recovery from low-grade energy resources requires an efficient thermal conversion system to be economically viable. The use of a liquid-liquid-vapour direct contact heat exchanger in such processes could be suitable due to their high thermal efficiency and low cost in comparison to a surface type heat exchanger.In this paper, the local volumetric heat transfer coefficient (Uv) and the active height (Hv) of a spray column three-phase direct contact heat exchanger (evaporator) have been investigated experimentally. The heat exchanger comprised a cylindrical Perspex tube of 100cm height and 10cm diameter. Liquid pentane at its saturation temperature and warm water at 45°C were used as the dispersed phase and the continuous phase respectively. Three different dispersed phase flow rates (10, 15 and 20 L/h) and four different continuous phase flow rates (10, 20, 30 and 40 L/h) were used throughout the experiments. In addition, three different sparger configurations (7, 19 and 36 nozzles) with two different nozzle diameters (1 and 1.25mm) were tested. The results showed that the local volumetric heat transfer coefficient (Uv) along the column decreases with height. An increase in both the continuous and dispersed phase flow rates had a positive effect on Uv, while an increase in the number of nozzles in the sparger caused Uv to decrease. The active height was significantly affected by the dispersed and continuous phase flow rates, the sparger configuration and the temperature driving force in terms of the Jacob number.

Use of axial dispersion model for determination of Sherwood number and mass transfer coefficients in a perforated rotating disc contactor

The mass transfer process in a perforated rotating disk contactor (PRDC) using a toluene–acetone–water system was investigated. The volumetric overall mass transfer coefficients are calculated in a PRDC column. Both mass transfer directions are considered in experiments. The influences of operating variables containing agitation rate, dispersed and continuous phase flow rates and mass transfer in the extraction column are studied. According to obtained results, mass transfer is significantly dependent on agitation rate, while the dispersed and continuous phase flow rates have a minor effect on mass transfer in the extraction column. Furthermore, a novel empirical correlation is developed for prediction of overall continuous phase Sherwood number based on dispersed phase holdup, Reynolds number and mass transfer direction. There has been great agreement between experimental data and predicted values using a proposed correlation for all operating conditions.

Measuring the average volumetric heat transfer coefficient of a liquid–liquid–vapour direct contact heat exchanger

The average volumetric heat transfer coefficient in a spray column liquid–liquid–vapour direct contact evaporator has been experimentally investigated. The experiments were carried out utilising a cylindrical Perspex tube of diameter 10cm and height and 150cm. Saturated liquid n-pentane and warm water at 45°C were used as the dispersed and continuous phases, respectively. Three different dispersed flow rates (10, 15 and 20L/h) and four different continuous phase flow rates (10, 20, 30 and 40L/h) were used in the study. The effect of different parameters, such as the initial drop size, continuous and dispersed phase flow rates and sparger configuration, on the average volumetric heat transfer coefficient in the evaporator was studied. The results showed that the average volumetric heat transfer coefficient was reduced as the initial drop size increased. Also, both the continuous phase and the dispersed phase flow rates have a significant positive impact on the average volumetric heat transfer coefficient.

Extraction of heavy metals from aqueous solutions in a modified rotating disc extractor

Extraction of Cu+2 from dilute aqueous solutions as a case study by liquid cation exchanger in a modified rotating disc extractor was studied. The liquid cation exchanger consisted of naphthenic acid dissolved in an inert carrier kerosene. Variables studied were: initial concentration of Cu+2, disc rotational speed, concentration of naphthenic acid, flow rates of continuous and dispersed phase, degree of roughness, and number of rotating discs. The rate of extraction increased with increasing rotational speed, concentration of naphthenic acid, flow rate of dispersed phase, degree of roughness and number of discs to a certain number, while increasing Cu+2 concentration and flow rate of continuous phase decreased the rate of extraction. All variables were correlated by the dimensionless mass transfer equation. Possible practical applications of the present data in treating aqueous waste from different sources such as petrochemical industries, electroplating, and hydrometallurgical processes was highlighted.

Study on the transient interfacial tension in a microfluidic droplet formation coupling interphase mass transfer process

In two‐phase dispersion coupling interphase mass transfer process, the variation of interfacial tension is an important factor affecting the dispersion. In this study, we described a microfluidic method for the determination of the transient interfacial tension (TIFT). The method has the advantage of determining TIFT during the whole droplet formation process, rather than only at the rupture moment as reported in previous studies. The TIFTs of several systems were determined. In certain systems, it has been found that the droplet size decreased with the increase of the dispersed phase flow rate, which is obviously different from the constant interfacial tension system. It has also been found that TIFT was mainly affected by two‐phase flow rates, solute type and concentration, and droplet size. A semiempirical equation was finally established to predict TIFT. It has the potential to be used in a variety of industrial equipment with dispersion–mass transfer coupling process. © 2016 American Institute of Chemical Engineers AIChE J, 62: 2542–2549, 2016

Experimental Investigation of Flooding and Drop Size in a Kuhni Extraction Column

In this research, Sauter-mean drop diameters and the flooding behavior have been investigated experimentally in a pilot scale Kuhni extraction column. The experiments were carried out in the absence of mass transfer for two different standard chemical systems. In the experiments operating parameters including agitation speed, flow rate of both liquid phases and interfacial tension have been studied. The results showed that Sauter-mean diameter are strongly affected by agitation speed and interfacial tension but the effects of continuous phase and dispersed phase flow rates are negligible. An empirical correlation for prediction of mean drop size as a function of column geometry, operating conditions and physical properties of liquid systems is suggested with a mean deviation of 9.54 %. Flooding rate is also influenced mainly by rotor speed and interfacial tension. An empirical correlation for predicting flooding velocities is also proposed with a mean deviation of 11.54 %.

Dispersed-Phase Holdup and Characteristic Velocity in a Pulsed and Nonpulsed Disk-and-Doughnut Solvent Extraction Column

The dispersed-phase holdup and characteristic velocity, which are important hydrodynamic performance parameters for solvent extraction columns, were measured and compared to literature correlations under pulsing and nonpulsing conditions using a 75 mm diameter disk-and-doughnut column. The results show that the dispersed-phase holdup increased with increasing dispersed-phase flow rate, while there was no noticeable change in holdup with the continuous-phase flow rate. With increasing pulsation intensity from zero, the dispersed-phase holdup decreased at first and then increased. A minimum holdup was found in the transition from the mixer-settler to the emulsion regime, and it increased with increasing dispersed-phase velocity. The experimental holdup and minimum holdup were correlated over a range of pulsation rates to within 13.3% and 8.8%, respectively. The characteristic velocities under different pulsation conditions were calculated from the measured holdup for the pulsing conditions. The characterist...

미세유체 장치에서 수거 방법에 따른 펙틴 하이드로겔 입자의 특성 비교

본 연구는 미세유체 장치를 통해 제조가 이루어진 펙틴 하이드로겔 입자의 수거 방법을 다르게 하였을 때 각 방법에 따른 하이드로겔의 물리적 특성을 비교한 것이다. 펙틴 하이드로겔 입자는 미세유체 채널 내에서 미네랄 오일에 분산된 칼슘 이온에 의해 겔화되고 이후 각각 파이펫팅법, 튜브법, 침전법을 통해 수거하였다. 각 방법으로 수거된 펙틴 하이드로겔 입자의 단분산성을 분석한 결과 침전법의 변동 계수(Coefficient of variation)는 3.46으로 파이펫팅법(18.60)과 튜브법(14.76)의 변동 계수보다 월등히 낮아 가장 우수한 단분산성 하이드로겔 입자를 만들 수 있었다. 상기 침전법을 이용한 조건에서 분산상과 연속상의 부피유속 및 펙틴 용액의 점도를 조절함으로써 <TEX>$30{\mu}m$</TEX>에서 <TEX>$180{\mu}m$</TEX>까지의 다양한 크기를 갖는 단분산성 펙틴 하이드로겔을 제조할 수 있었다. 본 논문에서 제시한 펙틴 하이드로겔 입자는 생체 물질을 손쉽게 함입할 수 있으므로 이는 향후 약물전달, 식품, 그리고 생체적합성 재료 등으로 활용 가능할 것으로 기대된다. This study investigated the effect of different collection methods on physical properties of pectin hydrogels in microfluidic synthetic approach. The pectin hydrogels were simply produced by the incorporation of calcium ions dissolved in continuous mineral oil. Then, different collection methods, pipetting, tubing, and settling, for harvesting pectin hydrogels were applied. The settling method showed most uniform and monodispersed hydrogels. In the case of settling, a coefficient of variation was 3.46 which was lower than pipetting method (18.60) and tubing method (14.76). Under the settling method, we could control the size of hydrogels, ranging from <TEX>$30{\mu}m$</TEX> to <TEX>$180{\mu}m$</TEX>, by simple manipulation of the viscosity of pectin and volumetric flow rate of dispersed and continuous phase. Finally, according to the characteristics of simple encapsulation of biological materials, we envision that the pectin hydrogels can be applied to drug delivery, food, and biocompatible materials.

Structured Biodegradable Polymeric Microparticles for Drug Delivery Produced Using Flow Focusing Glass Microfluidic Devices.

Biodegradable poly(DL-lactic acid) (PLA) and poly(lactic-co-glycolic acid) (PLGA) microparticles with tunable size, shape, internal structure and surface morphology were produced by counter-current flow focusing in axisymmetric (3D) glass capillary devices. The dispersed phase was composed of 0.5-2 wt % polymer solution in a volatile organic solvent (ethyl acetate or dichloromethane) and the continuous phase was 5 wt % aqueous poly(vinyl alcohol) solution. The droplets with a coefficient of variation in dripping regime below 2.5% were evaporated to form polymeric particles with uniform sizes ranging between 4 and 30 μm. The particle microstructure and surface roughness were modified by adding nanofiller (montmorillonite nanoclay) or porogen (2-methylpentane) in the dispersed phase to form less porous polymer matrix or porous particles with golf-ball-like dimpled surface, respectively. The presence of 2-4 wt % nanoclay in the host polymer significantly reduced the release rate of paracetamol and prevented the early burst release, as a result of reduced polymer porosity and tortuous path for the diffusing drug molecules. Numerical modeling results using the volume of fluid-continuum surface force model agreed well with experimental behavior and revealed trapping of nanoclay particles in the dispersed phase upstream of the orifice at low dispersed phase flow rates and for 4 wt % nanoclay content, due to vortex formation. Janus PLA/PCL (polycaprolactone) particles were produced by solvent evaporation-induced phase separation within organic phase droplets containing 3% (v/v) PLA/PCL (30/70 or 70/30) mixture in dichloromethane. A strong preferential adsorption of Rhodamine 6G dye onto PLA was utilized to identify PLA portions of the Janus particles by confocal laser scanning microscopy (CLSM). Uniform hemispherical PCL particles were produced by dissolution of PLA domes with acetone.

Numerical investigation on the velocity fields during droplet formation in a microfluidic T-junction

In this paper, we present the findings from a numerical investigation of the droplet formation process in a T-junction microchannel. A volume-of-fluid (VOF) model that is refined with smoothing operations was used to minimise spurious or non-physical velocities at the micro-scale, in order to obtain more accurate velocity results from the microchannel simulations. The model was validated with experimental results and was able to yield a closer match to the experimental data compared to the standard VOF model. Subsequently the refined VOF model was used to investigate the velocity field evolution during the droplet formation process to further understand the underlying physics. For the squeezing regime, we observed regions of large recirculation after droplet break-up with reversed flows. These recirculation regions were also seen in the transition and dripping regimes but reversed flows did not occur. We also studied the effects of varying the dispersed phase flow rate under a constant capillary number (Ca) of the continuous phase. The results show that increasing the dispersed phase flow increases the droplet length and formation frequency. In addition, the frequency of the velocity fluctuation at the junction vicinity was found to coincide with the rate of new droplet formation. Finally, the effects of Weber number on droplet length was also investigated and it was found that inertial forces significantly influence droplet formation, albeit being the least dominant force.

The Effect of Nanoparticles on Liquid Holdups in a Randomly Packed Liquid-Liquid Extraction Column

In the present study, the dispersed phase holdup was measured in a randomly packed column filled with stainless steel Raschig ring packings using water-toluene chemical system. Based on holdup data, the results were analyzed with the aim of determining the influence of dispersed phase flow rate and drop diameter in the presence and absence of silica nanoparticles with particle sizes of 10, 30, and 80 nm and concentrations of 0.01, 0.05, and 0.1 vol%. The results indicate that liquid holdups increase with increase in dispersed phase flow rate. The presence of the nanoparticles influence in both static and dynamic holdups. The experimental results showed that increasing nanoparticle content in dispersed phase increases the dynamic holdup while static holdup decreases. However, by increasing the size of nanoparticles the dynamic and static holdup also follow a similar trend. Finally a successful correlation is proposed for total liquid holdup, which yielded an average error of 6% and shows a good agreement between predicted and experimental results. This is for the first time that a correlation is proposed to estimate total liquid holdup as a function of nanoparticle size and concentration in liquid-liquid extraction systems.

Removal of tributyl phosphate from aqueous stream in a pilot scale combined air-lift mixer-settler unit: Process intensification studies

This work reports the removal of tributyl phosphate (TBP) from aqueous stream using organic solvent in an industrial scale combined air-lift mixer-settler unit (CAL-MSU) having 10 stages. The solute i.e., TBP is transferred from aqueous continuous (0.3M HNO3 saturated with TBP) to organic dispersed phase i.e., normal paraffin hydrocarbon (NPH). Effect of phase flow ratios on steady state, number of stages as well as mass transfer coefficient on TBP removal and mass transfer coefficient, is observed. The maximum TBP extraction efficiency of about 96% (201ppm to 8ppm) and maximum overall volumetric mass transfer coefficient of 13.3×10−5s−1 was observed at continuous phase flowrate 36 LPH and dispersed phase flowrate 24 LPH. For optimized operating parameters, the energy input per unit volume for 10-stage CAL-MSU and similar configuration 10-stage pump-mix mixer-settler are found to be 37.0kJ/m3 and 77.7kJ/m3, respectively.

Prediction of drop size distribution in a horizontal pulsed plate extraction column

Mean drop size and drop size distribution in a horizontal pulsed plate extraction column were investigated using different four binary systems. The effects of pulse intensity (af) and flow rates of both liquid phases have been investigated. The drop size decreased more rapidly with the increase of pulse intensities. It was observed that an increase in intensity of the pulses will lead to narrower ranges of distribution for the drop size. Increasing the flow rate of dispersed phase tends to increase the drop size. The effect of continuous phase flow rate is weaker than the effect of the dispersed phase flow rate. By using results, a semi empirical correlation obtained for the estimation of mean drop size which proves to be in good agreement to the experimental data. The average absolute relative error (AARE) of this correlation is about 15.6%. In order to find a predictive correlation for drop size distribution, four models of distribution functions are tested. The normal probability density function is the only suitable way for representing the experimental drop size distributions with an AARE of 13.7%.

Axial dispersion model in predictive mass transfer correlation for random pulsed packed column

The continuous phase volumetric overall mass transfer coefficient in a ceramic intalox saddle pulsed packed extraction column using axial dispersion model was studied for two different liquid-liquid systems containing water/acetone/toluene and water/acetone/n-butyl acetate. The effects of pulsation intensity, continuous and dispersed phase flow rates on mass transfer coefficient were investigated. The experimental results indicated that the mass transfer coefficient was enhanced by increasing pulsation intensity and dispersed and continuous phase flow rates. The utilization of nonlinear least square method provided a new predictive correlation for the continuous phase overall mass transfer coefficient. The developed mass transfer model was validated via the comparison of the modeling data with experimental results with 18.7% average absolute relative error (AARE). Furthermore, one empirical correlation was developed for prediction of the continuous phase overall mass transfer coefficient as the function of the aforementioned operating variables.

Investigation of Copper Extraction from Aqueous Sulfate Solution in a Rotating Disc Contactor

The extraction of copper from aqueous sulfate solution with new extractant Cupromex-3302 (active substance is the 5-nonylsalicylaldoxime) using a rotating disc contactor (RDC) was investigated. It was observed from batch experiments that the best results were obtained with the initial aqueous pH and concentration of Cupromex-3302 of 1.9 and 10% (v/v) respectively. In continuous experiments, the first critical rotor speed based on drop breakage probabilities was determined. Then the effects of rotor speed, dispersed and continuous phase flow rates on hydrodynamic parameters such as static hold-up, mean drop sizes and extraction efficiency were studied. The experimental results were compared with the ones obtained by the empirical correlations for prediction of the dispersed phase static hold-up and mean drop sizes in terms of the operating variables and the physical properties. The results of experiments proved the feasibility of operating the solvent extraction of copper from the aqueous solution using rotating disc contactor.

Centrifugal step emulsification applied for absolute quantification of nucleic acids by digital droplet RPA.

Aqueous microdroplets provide miniaturized reaction compartments for numerous chemical, biochemical or pharmaceutical applications. We introduce centrifugal step emulsification for the fast and easy production of monodisperse droplets. Homogenous droplets with pre-selectable diameters in a range from 120 μm to 170 μm were generated with coefficients of variation of 2-4% and zero run-in time or dead volume. The droplet diameter depends on the nozzle geometry (depth, width, and step size) and interfacial tensions only. Droplet size is demonstrated to be independent of the dispersed phase flow rate between 0.01 and 1 μl s(-1), proving the robustness of the centrifugal approach. Centrifugal step emulsification can easily be combined with existing centrifugal microfluidic unit operations, is compatible to scalable manufacturing technologies such as thermoforming or injection moulding and enables fast emulsification (>500 droplets per second and nozzle) with minimal handling effort (2-3 pipetting steps). The centrifugal microfluidic droplet generation was used to perform the first digital droplet recombinase polymerase amplification (ddRPA). It was used for absolute quantification of Listeria monocytogenes DNA concentration standards with a total analysis time below 30 min. Compared to digital droplet polymerase chain reaction (ddPCR), with processing times of about 2 hours, the overall processing time of digital analysis was reduced by more than a factor of 4.