Flow Rate Of Continuous Phase Research Articles

Liquid-liquid dispersions in intensified impinging-jets cells

The formation of dispersions of two immiscible liquids in a confined impinging-jets cell was studied experimentally. The jets of the liquids formed at two opposing channels and collided in a main channel, which was perpendicular to the previous two. Jet channels with diameters either 0.25 or 0.5mm and main channels with diameters either 2 or 3mm were used. The jet velocities varied from 0.17 to 6.2m/s and the dispersed to continuous phase ratios varied from 0.05 to 0.28. Deionised water and kerosene (Exxsol D80: ρ=795kg/m3 and μ=1.73mPas) were used as test fluids. Drop sizes were measured with high-speed imaging. It was found that the total velocity of the two jets was the main parameter that affected both the average drop size and the interfacial area, whilst the dispersed to continuous phase flow rate ratio was less significant. Both phases could become continuous depending on the phase flowrate ratio; drops were, however, larger in the organic continuous dispersions. The interfacial area produced with the impinging-jets cell was almost 3 times larger than in capillary contactors at similar conditions (umix=0.024–0.19m/s). The size of the main channel affected the drop size and smaller drops formed in the large channel compared to the small one. With increasing energy dissipation rate, ε, in the impingement zone, the Sauter mean diameter decreased following a relation of the form ∼ε−b. Apart from the lower velocities, the drop sizes did not change significantly at distances equal to 15 channel diameters downstream the impingement area.

The effect of packing on direct contact evaporation in spray column

AbstractThe direct contact evaporation in countercurrent spray column has been experimentally investigated. Two kinds of random packing were added into the column independently to study their influence on heat transfer process. Three different continuous phase flow rates (150, 200, 250 L/h) and two different dispersed flow rates (6.565, 13.13 L/h) were used in the experiment. The inlet continuous phase temperature ranged from 42 to 57 °C, and the inlet dispersed phase temperature was near its boiling point. The effect of variable factors on the optimal column height, the volumetric heat transfer coefficient, the pressure drop, and the thickness of foam layer were studied. The results showed that packing had positive effects on heat transfer, such as decreasing the optimal column height and the thickness of foam layer, increasing heat transfer coefficient. But extra pressure was also obvious. Dixon rings performed better than Raschig rings in the experiments due to their finer structure.

Gellan microgels produced in planar microfluidic devices

Microgels were obtained from the droplets gelation of a water-in-oil emulsion containing gellan in the aqueous phase. Gellan gum (0.6% w/w) and calcium acetate (0.5 and 2.0% w/w) as gelling agent were used to produce the microgels. The effect of the continuous phase flow rate and salt concentration on the particle size and size polydispersity of the gellan microgels was evaluated, as well as microchannels configuration for encapsulation of hydrophilic compounds in these particles using planar microfluidics devices. The microgels exhibited uniform and spherical shape. A highly monodisperse particle size distribution was observed showing coefficient of variation below 5% and average size ranging from 63 to 113 μm. Increasing salt concentration caused an increase of the mean particle diameter and a decrease of the size polydispersity. However at high salt concentration the continuous flow rate did not exert significant effect on the microgel size since average size ranged from 106 to 113 μm. A potential use of gellan microgels as encapsulating matrix of active compounds was evaluated by adding a hydrophilic dye, Rhodamine B, in the aqueous phase. Results showed good retention capacity of the dye and stability over time of storage, indicating that microgels obtained by microfluidics technique may be used for the encapsulation of hydrophilic compounds, including those sensitive to temperature and pressure, as well as in drug delivery.

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.

Two-phase pressure drop and flooding characteristics in a horizontal-vertical pulsed sieve-plate column

In this paper, an experimental investigation on the two-phase pressure drop has been carried out in a novel class of extractors entitled "horizontal-vertical pulsed sieve-plate column". The liquid-liquid systems used in this work are toluene–water, n-butyl acetate–water and butanol-water. The effects of operating parameters including the dispersed and continuous phases flow rates and pulsation intensity on total pressure drop under and at the flooding points have been studied. It is achieved that the pressure drop is strongly affected by the continuous and dispersed flow rates as well as pulsation intensity. In fact, the column experiences higher pressure drop with an increase in the values of Af, Q c and Q d. The interfacial tension is a physical property which has significant impact on pressure drop. Two theoretical-experimental correlations for prediction of pressure drop under and at the flooding in the column, and one correlation for maximum throughput are proposed by using dimensional analysis method with Average Absolute Relative Error (AARE) values of 2.15%, 3.56 and 6.85% respectively. Moreover, a particular approach for preventing flooding in pulsed extraction columns is developed based on evaluation of pressure drop through the column length.

Microfluidic production of degradable thermoresponsive poly(N-isopropylacrylamide)-based microgels.

Highly monodisperse and hydrolytically degradable thermoresponsive microgels on the tens-to-hundreds of micron size scale have been fabricated based on simultaneous on-chip mixing and emulsification of aldehyde and hydrazide-functionalized poly(N-isopropylacrylamide) precursor polymers. The microfluidic chip can run for extended periods without upstream gelation and can produce monodisperse (<10% particle size variability) microgels on the size range of ∼30-90 μm, with size tunable according to the flow rate of the oil continuous phase. Fluorescence analysis indicates a uniform distribution of each reactive pre-polymer inside the microgels while micromechanical testing suggests that smaller microfluidic-produced microgels exhibit significantly higher compressive moduli compared to bulk hydrogels of the same composition, an effect we attribute to improved mixing (and thus crosslinking) of the precursor polymer solutions within the microfluidic device. The microgels retain the reversible volume phase transition behavior of conventional microgels but can be hydrolytically degraded back into their oligomeric precursor polymer fragments, offering potential for microgel clearance following use in vivo.

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.

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.

Solvent extraction performance of Ce(III) from chloride acidic solution with 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (EHEHPA) by using membrane dispersion micro-extractor

By using membrane dispersion micro-extractor, Ce(III) solvent extraction experiments were conducted. Cerium chloride solution with certain acidity was used as aqueous phase and 2-ethylhexyl phosphoric acid-2-ethylhexyl ester (EHEHPA) kerosene solution as organic phase. The effects of system physicochemical properties and operational conditions, such as initial EHEHPA concentration, initial aqueous acidity, total flow rate and continuous phase flow rate, etc., on the extraction efficiency and the overall volume mass transfer coefficient were evaluated. As the total flow rate increased from 20 to 160 mL/min, the overall volume mass transfer coefficient was enhanced from 0.1 to 0.54 s−1. Under the optimal conditions, the Ce(III) extraction efficiency could reach 99.92% in 2.98 s. A mathematical model was set up to predict the overall volume mass transfer coefficient, and the calculation results agreed well with the experimental results, most relative error was within ±10%.

Heat transfer efficiency and capital cost evaluation of a three-phase direct contact heat exchanger for the utilisation of low-grade energy sources

Low-grade energy cycles for power generation require efficient heat transfer equipment. Using a three-phase direct contact heat exchanger instead of a surface type exchanger, such as a shell and tube heat exchanger, potentially makes the process more efficient and economic. This is because of its ability to work with a very low temperature driving force, as well as its low cost of construction. In this study, an experimental investigation of the heat transfer efficiency, and hence cost, of a three-phase direct contact condenser has been carried out utilising a short Perspex tube of 70cm total height and 4cm internal diameter. Only 48cm was used for the direct contact condensation. Pentane vapour with three different initial temperatures (40°C, 43.5°C and 47.5°C) was contacted with water with an inlet temperature of 19°C. In line with previous studies, the ratio of the fluid flow rates was shown to have a controlling effect on the exchanger. Specifically, the heat transfer efficiency increased virtually linearly with this ratio, with higher efficiencies also being observed with higher flow rates of the continuous phase. The effect of the initial temperature of the dispersed phase was shown to have a lower order impact than flow rate ratio. The capital cost of the direct contact condenser was estimated and it was found to be less than the corresponding surface condenser (shell and tube condenser) by 30 times. An optimum value of the continuous phase flow rate was observed at which the cost of the condenser is at a minimum.

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.

Microfluidic generation of aqueous two-phase system (ATPS) droplets by controlled pulsating inlet pressures.

We present a technique that generates droplets using ultralow interfacial tension aqueous two-phase systems (ATPS). Our method combines a classical microfluidic flow focusing geometry with precisely controlled pulsating inlet pressure, to form monodisperse ATPS droplets. The dextran (DEX) disperse phase enters through the central inlet with variable on-off pressure cycles controlled by a pneumatic solenoid valve. The continuous phase polyethylene glycol (PEG) solution enters the flow focusing junction through the cross channels at a fixed flow rate. The on-off cycles of the applied pressure, combined with the fixed flow rate cross flow, make it possible for the ATPS jet to break up into droplets. We observe different droplet formation regimes with changes in the applied pressure magnitude and timing, and the continuous phase flow rate. We also develop a scaling model to predict the size of the generated droplets, and the experimental results show a good quantitative agreement with our scaling model. Additionally, we demonstrate the potential for scaling-up of the droplet production rate, with a simultaneous two-droplet generating geometry. We anticipate that this simple and precise approach to making ATPS droplets will find utility in biological applications where the all-biocompatibility of ATPS is desirable.

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.

Alternating and merged droplets in a double T-junction microchannel

In this work, we report experimental and numerical studies of alternating and merged droplets in a double T-junction microchannel. The microchannel device is fabricated using PDMS substrate and experiments are performed with mineral oil with surfactant as the continuous phase and aqueous glycerol as the discrete phase. Based on the flow rate fraction ϕ and Capillary number Ca, four different flow regimes are identified: merging, stable alternating droplets, alternating droplets with transition and laminar. A numerical model that employs volume-of-fluid formulations is used to predict the alternating droplet generation process. In the stable alternating droplet regime, the effect of the discretephase flow rate ratio α on the droplet diameter ratio β is experimentally studied and compared with that predicted from the simulations. It is observed that the droplet diameter ratio β increases linearly with increase in the flow rate ratio α and a good match between experiments and simulations is observed. The diameters of droplets at different Capillary numbers Ca generated using single and double T-junction microchannels are compared and it is observed that, at low Ca, the double T-junction generates larger droplets as compared to single T-junction. In merged droplet regime, the effect of the continuous phase flow rate Qc and discrete phase viscosity μd on diameter dm and interdistance between the droplets λ of the merged droplets are studied. It is observed that the merged droplet diameter dm is reduced and interdistance between the droplets λ increases with increase in the continuous phase flow rate Qc. As the viscosity of the discrete phase μd increases, the diameter dm and interdistance between the droplets λ of the merged droplets decreases.