Dispersed Flow Rate Research Articles

Effect of Intersection Angle of Input Channels in Droplet Generators.

In this paper, we studied the effects of the intersection angle between the inlet channels on the droplet diameter using a COMSOL Multiphysics® simulation. We employed the level-set method to study the droplet generation process inside a microfluidic flow device. A flow-focusing geometry was integrated into a microfluidics device and used to study droplet formation in liquid–liquid systems. Droplets formed by this flow-focusing technique are typically smaller than the upstream capillary tube and vary in size with the flow rates. Different intersection angles were modeled with a fixed width of continuous and dispersed channels, orifices, and expansion channels. Numerical simulations were performed using the incompressible Navier–Stokes equations for single-phase flow in various flow-focusing geometries. As a result of modeling, when the dispersed flow rate and the continuous flow rate were increased, the flow of the continuous flow fluid interfered with the flow of the dispersed flow fluid, which resulted in a decrease in the droplet diameter. Variations in the droplet diameter can be used to change the intersection angle and fluid flow rate. In addition, it was predicted that the smallest diameter droplet would be generated when the intersection angle was 90°.

Development of a Semi-Empirical Model for Droplet Size Determination of a Three-Channel Spray Nozzle for Pellet Coating Based on the Optical Method Concept

The purpose of this study was to investigate the droplet size obtained with a three-channel spray nozzle typically used in fluid bed devices and to construct a semi-empirical model for prediction of droplet size. With the aid of a custom-made optical method concept, the impact of the type of polymer and solvents used through dispersion properties (viscosity, density, and surface tension), dispersion flow rate, atomization pressure, and microclimate pressure on droplet size was investigated. A semi-empirical model with adequate predictability for calculating the average droplet size (R2 = 0.90, Q2 = 0.73) and its distribution (R2 = 0.84, Q2 = 0.61) was constructed by employing dimensional analysis and design of experiments. Newtonian and non-Newtonian dispersion and process parameters on laboratory and on production scale were included, thereby enabling constant droplet size irrespective of the scale. Based on the model results, it would be possible to scale-up the atomization process (e.g., coating process) from laboratory to production scale in a systematic fashion, regardless of the type of solvent or polymer used. For the system investigated, this can be performed by understanding the dispersion properties, such as viscosity, density, and surface tension, as well as the following process parameters: dispersion flow rate, atomization, and microclimate pressure.

The breakup dynamics of bubbles stabilized by nanoparticles in a microfluidic Y-junction

The breakup flow patterns, the neck dynamics and the tip dynamics of bubbles stabilized by adsorptive nanoparticles in microfluidic Y-junction were investigated. Three flow patterns were observed in the Y-junction: non-breakup, breakup with partial obstruction, and breakup with permanent obstruction. Compared with bubbles stabilized only by surfactants (conventional bubbles), bubbles stabilized by nanoparticles (hardening bubbles) are more difficult to breakup. The breakup process with partial obstruction could be divided into three stages: squeezing, transition and pinch-off. Nanoparticles have little effect on the squeezing stage, but could greatly prolong the transition stage while accelerate the pinch-off stage. The difference between hardening and conventional bubbles is weakened, even disappears as the dispersion flow rate increases. Besides, the “rigid” surface of hardening bubbles could cause the decrease of the curvature of daughter bubble tips and the tunnels between the daughter bubbles and the channel wall in comparison with conventional bubbles.

Microfluidic emulsification: Process and formulation variables effects in flow behavior pattern on a flow-focusing device

Formulation and process variables in surfactant/oil/water (SOW) systems can strongly modify the water/oil interfacial tension leading to different behaviors. Pre-equilibration time of the SDS/toluene/1-butanol/NaCl(aq) system was studied as a process variable and the flow regimes were described at different continuous and dispersed flow rates through a flow focusing geometry. Salinity and oil nature for the SDS/n-alkane/alcohol/NaCl(aq) equilibrated system were studied as formulation variables at fixed dispersed flow rates, changing the continuous flow rate and the formulation variable in order to get O/W or W/O emulsions in hydrophilic and hydrophobic chips, respectively. Pre-equilibration time modifies the flow regimes depending on the differences observed in the interfacial tension at t = 0 and t = 24 h of equilibration. Under very hydrophilic conditions, when γt=24 > γt=0, the entire droplet area is slightly higher for equilibrated systems. At WIII condition, when γt=0 >> γt=24, droplets are formed only in jetting regime for not equilibrated systems. For salinity scan, monodispersed oil droplets were obtained at low salinities, S = 0−0.25 % and in the oil scan, water droplets were obtained when using cyclohexane and cyclohexane-hexane mixtures. In both cases, flow regimes are reported into the formulation maps, using the Hydrophilic Lipophilic Deviation as formulation variable (HLD vs flow rate ratio). Droplet size was fitted into the same equation ( di≈αCac-0.264), and it is noteworthy that the interfacial tension in CaC is lower than in most of reported works using flow-focusing geometries and both emulsions (W/O and O/W) were obtained with the same surfactant.

Effects of a Dynamic Injection Flow Rate on Slug Generation in a Cross-Junction Square Microchannel

The injection flow rates of two liquid phases play a decisive role in the slug generation of the liquid-liquid slug flow. However, most injection flow rates so far have been constant. In order to investigate the effects of dynamic injection flow rates on the slug generation, including the slug size, separation distance and slug generation cycle time, a transient numerical model of a cross-junction square microchannel is established. The Volume of Fluid method is adopted to simulate the interface between two phases, i.e., butanol and water. The model is validated by experiments at a constant injection flow rate. Three different types of dynamic injection flow rates are applied for butanol, which are triangle, rectangular and sine wave flow rates. The dynamic injection flow rate cycles, which are related to the constant slug generation cycle time t0, are investigated. Results show that when the cycle of the disperse phase flow rate is larger than t0, the slug generation changes periodically, and the period is influenced by the cycle of the disperse phase flow rate. Among the three kinds of dynamic disperse flow rate, the rectangular wave influences the slug size most significantly, while the triangle wave influences the separation distance and the slug generation time more prominently.

Aerosol drug delivery to the lungs during nasal high flow therapy: an in vitro study

BackgroundAerosol delivery through a nasal high flow (NHF) system is attractive for clinicians as it allows for simultaneous administration of oxygen and inhalable drugs. However, delivering a fine particle fraction (FPF, particle wt. fraction < 5.0 μm) of drugs into the lungs has been very challenging, with highest value of only 8%. Here, we aim to develop an efficient nose-to-lung delivery system capable of delivering improved quantities (FPF > 16%) of dry powder aerosols to the lungs via an NHF system.MethodsWe evaluated the FPF of spray-dried mannitol with leucine with a next generation impactor connected to a nasopharyngeal outlet of an adult nasal airway replica. In addition, we investigated the influence of different dispersion (20–30 L/min) and inspiratory (20–40 L/min) flow rates, on FPF.ResultsWe found an FPF of 32% with dispersion flow rate at 25 L/min and inspiratory flow rate at 40 L/min. The lowest FPF (21%) obtained was at the dispersion flow rate at 30 L/min and inspiratory flow rate at 30 L/min. A higher inspiratory flow rate was generally associated with a higher FPF. The nasal cannula accounted for most loss of aerosols.ConclusionsIn conclusion, delivering a third of inhalable powder to the lungs is possible in vitro through an NHF system using a low dispersion airflow and a highly dispersible powder. Our results may lay the foundation for clinical evaluation of powder aerosol delivery to the lungs during NHF therapy in humans.

Powder aerosol delivery through nasal high-flow system: In vitro feasibility and influence of process conditions

We aimed to obtain fundamental information for potential pulmonary delivery of powder aerosols using a clinically-approved nasal high-flow system (AIRVO), with spray-dried mannitol (SD-Man) being a model powder. Compressed air exiting the AIRVO at set ‘dispersion’ air flow rates dispersed SD-Man loaded in an Osmohaler® into a human nasal airway replica (NAR) coupled downstream to a Next Generation Impactor (NGI) running at specific ‘inspiratory’ flow rates. Increasing the dispersion flow rate from 30 to 60L/min increased powder deposition in the NAR from 50 to 70% of the emitted dose, while decreased the NGI deposition from 50 to 30% of the emitted dose. The inspiratory flow rate did not affect powder deposition in the NAR and NGI. In contrast, as the inspiratory flow rate was increased from 15 to 40L/min, powder recovery, emitted fraction, and fine particle fraction below 5μm (as aerosol performance indices) were increased from 90, 30 and 5% to 97, 45 and 8% of the loaded dose, respectively. The dispersion flow rate did not change the performance indices. Importantly, heating and humidification of dispersion airflow, loaded doses, and nasal cannula sizes did not greatly affect the aerosol characteristics.

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.

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.

Comparative performance of in-line rotor-stators for deagglomeration processes

In-line rotor-stators are used for a wide range of power intensive dispersion applications, including the breakup of immiscible liquid droplets or agglomerates. This study, performed within the DOMINO project at BHR Group, aimed at studying the performance of three different rotor-stator head designs for deagglomeration processes. A given test system, nanoscale silica particles-in-water, was used to identify the mechanism and kinetics of break-up and determine the smallest attainable size. Three rotor-stator head designs used were the GPDH-SQHS and EMSC screens from Silverson and Ytron Z-Lab from Ytron. These in-line rotor-stators were used in the recirculation loop of a stirred tank with a total dispersion volume of 100l. Power input and residence time were varied by changing the rotor speed and dispersion flow rate. Breakup was found to occur through erosion regardless of the operating conditions or rotor-stator design. The smalleachieves a higher fraction of finesst fragments obtained were aggregates, rather than primary particles, and these were of a mean diameter of 150–200nm; also independent of the operating conditions or rotor-stator head design. With a given rotor-stator operated at a given flow rate, increasing the rotor speed and hence the power input increased the break up kinetics. For a given design at a given specific power input, whilst the break up rate per tank turnover decreased when the flow rate was increased, the total processing time could be reduced. There were differences in the volume of the mixer head and chamber volumes; in addition, a smaller flow rate range could be covered with the Ytron design. Comparison of the different designs was therefore not straightforward. It could however be shown that the rotor-stator designs with a high number and small size of holes and/or gaps have a faster break up rate.

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.

Generation of Oil Droplets in a Non-Newtonian Liquid Using a Microfluidic T-Junction

We have compared the formation of oil drops in Newtonian and non-Newtonian fluids in a T-junction microfluidic device. As Newtonian fluids, we used aqueous solutions of glycerol, while as non-Newtonian fluids we prepared aqueous solutions of xanthan, a stiff rod-like polysaccharide, which exhibit strong shear-thinning effects. In the squeezing regime, the formation of oil droplets in glycerol solutions is found to scale with the ratio of the dispersed flow rate to the continuous one and with the capillary number associated to the continuous phase. Switching to xanthan solutions does not seem to significantly alter the droplet formation process. Any quantitative difference with respect to the Newtonian liquid can be accounted for by a suitable choice of the capillary number, corresponding to an effective xanthan viscosity that depends on the flow rates. We have deduced ample variations in the viscosity, on the order of 10 and more, during normal operation conditions of the T-junction. This allowed estimating the actual shear rates experienced by the xanthan solutions, which go from tens to hundreds of s−1.

수치해석 모델링을 이용한 교차 흐름 미세유체 액적 생성 디바이스 채널 교차각이 액적 직경에 미치는 영향

In this paper, we studied the effects of intersection angles of the flow-foucusing type droplet generation device inlet channel on droplet diameter using numerical simulation modeling. We modeled different intersection angles with a fixed continuous channel width, dispersed channels width, orifices width, and expansion channels width. Numerical simulations were performed using COMSOL Multiphysics ® to solve the incompressible Navier-Stokes equations for a two-phase flow in various flow-focusing geometries. Modeling results showed that an increase of the intersection angle causes an increase in the modification of the dispersed flow rate ( ), and the increase of the mod- ification of the continuous flow rate ( ) obstructs the dispersed phase fluid flow, thereby reducing the droplet diam- eter. However, the droplet diameter did not decrease, even when the intersection angle increased. The droplet diameter decreased when the intersection angle was less than 90 o , increased at an intersection angle of 90 o , and decreased when the intersection angle was more than 90 o . Furthermore, when the intermediate energy deceased, there was a decrease in the droplet diameter when the intersection angle increased. Therefore, variations in the drop- let diameter can be used to change the intersection angle and fluid flow rate.

Supported liquid membranes with organic dispersion for recovery of Cephalexin

Supported liquid membranes with organic dispersion (SLM-OD) have been proposed and investigated for simultaneous removal and recovery of Cephalexin from aqueous solutions by using the carrier Aliquat 336 and a commercially available hollow-fiber module (HFM). The organic dispersion, formed by dispersing a small amount of organic membrane solution in the feed solution with a mixer, flowed through the shell side of the HFM. Investigated various parameters including organic-to-feed volume ratio, Aliquat 336 concentration, initial Cephalexin concentration, KCl concentration, shell-side organic dispersion flow rate, and lumen-side strip solution flow rate. The mass transfer mechanism of the SLM-OD technique was elucidated, and a mathematical model was developed to calculate the overall mass transfer coefficient. The results showed that the overall mass transfer coefficient increased with an increase of organic-to-feed volume ratio or increase of Aliquat 336 concentration, but reduced with the increase of initial Cephalexin concentration. Furthermore, the results indicated that the lumen and shell side flow rates had little effects on mass transfer performance and that an excess amount of KCl was necessary for the facilitated transport. The fractional mass transfer resistances of SLM-OD were calculated based on the resistance-in-series model, showing that the extraction reaction resistance was greatly reduced. In addition, the SLM-OD was shown to be superior to the supported liquid membranes with strip dispersion (SLM-SD) in terms of the improvement of mass transfer performance and the reduced volume requirement of the organic membrane solution.

Biodegradation of methyl tert-butyl ether by cometabolism with hexane in biofilters inoculated with Pseudomonas aeruginosa

Biodegradation of methyl tert-butyl ether (MTBE) vapors by cometabolism with gaseous hexane (n-hexane > 95%) was investigated using Pseudomonas aeruginosa utilizing short chain aliphatic hydrocarbon (C5-C8). Kinetic batch experiments showed that MTBE was degraded even when hexane was completely exhausted with a cometabolic coefficient of 1.06 ± 0.16 mg MTBE mg hexane−1. Intermediate tert-butyl alcohol (TBA) accumulation was observed followed by its gradual consumption. A maximum MTBE elimination capacity (ECMAX) of 35 g m−3 h−1 and removal efficiency (RE) of 70% were attained in mineral medium amended biofilters having an empty bed residence time (EBRT) of 1 min. For these experimental conditions, a maximum hexane EC of approximately 60 g m−3 h−1 was obtained at a load of 75 g m−3 h−1. Experiments under transient conditions revealed a competitive substrate interaction between MTBE and hexane. Biomass densities between 5.8 and 12.6 g Lbiofilter −1 were obtained. Nevertheless, production of biopolymers caused non-uniform distribution flow rates that reduced the performance. Residence time distribution profiles showed an intermediate dispersion flow rate with a dispersion coefficient of 0.8 cm2 s−1.

Supported liquid membranes with strip dispersion for the recovery of Cephalexin

The removal and recovery of Cephalexin from aqueous solutions by supported liquid membranes (SLMs) with strip dispersion has been studied. Experiments used a Liqui-Cel ® hollow-fiber module as a mircoporous support and an organic membrane solution consisting of Aliquat 336, Isopar L (isoparaffinic hydrocarbon solvent), and 1-decanol. The aqueous strip solution was composed of potassium chloride and citrate buffer. The presence of the strip dispersion, formed by dispersing the aqueous strip solution in the organic membrane solution with a mixer, on the shell-side of the hollow-fiber module ensures SLM stability. Various experimental parameters such as strip dispersion mixing rate, Aliquat 336 concentration in the organic membrane phase, KCl and citrate buffer concentrations in the aqueous strip solution, volume of aqueous strip solution, and feed and strip dispersion flow rates were investigated. High extraction and recovery rates were achieved when maintaining a proper pH in the aqueous strip solution combined with an excess of KCl. Typical results using an Aliquat 336 concentration of 2.5 wt% (48 mM) have shown >99% extraction, recovery rates of 96–98%, and enrichment ratios of 1.6–3.3 from a feed solution containing 15 mM of Cephalexin. Mass transfer resistances were analyzed, showing the resistance from the extraction reaction to be dominant.

Lattice Boltzmann simulations of droplet formation during microchannel emulsification

In this study, we compared microchannel droplet formation in a microfluidics device with a two phase lattice Boltzmann simulation. The droplet formation was found to be qualitatively described, with a slightly smaller droplet in the simulation. This was due to the finite thickness of the interface in the simulations. Dependence on dispersed flow rate could be very nicely predicted by the model, while a better insight was obtained on the internal pressures and flow velocities during droplet formation. These were found to be well described by simple relations; (1) the pressure inside the dispersed phase was predicted very well by the Laplace pressure while (2) the flow rate through the neck could be estimated by the flow through an orifice. These insights simplify the development of design rules for new microchannel devices.

Preparation and characterization of water in oil emulsion via drop break-off

Water in oil emulsion with drop sizes ranging from 15 to 400 μm was produced via drop break-off in a co-flowing environment. A phase diagram illustrating the drop break-up formation mechanism and size distribution as a function of disperse and continuous phase flow rate is presented. The drop break-up dynamic dominated by the disperse flow rate gives the transition point between monodisperse and polydisperse emulsion production. In addition, we studied the formation of 2D and 3D emulsion crystalline structures by mixing droplets with two distinct diameters with a certain size ratio, which may lead to a novel type of chemical reaction setup and new materials.

The effect of elasticity on drop creation in T-shaped microchannels

Polymeric microdrops of low viscosity, elastic fluids have been generated in T-shaped microfluidic devices using a cross-flow shear-induced drop generation process. Dilute ( c/ c * ∼ 0.5) aqueous solutions of polyethylene oxide (PEO) of various molecular weights (3 × 10 5–2 × 10 6 g/mol) were used as the drop phase fluids whilst silicone oils (5 mPa s ≤ η ≤ 50 mPa s) were used as the continuous phase fluids. The effects of viscosity ratio and fluid elasticity on the mechanism of drop detachment and break-up, final drop size and frequency of drop formation were studied in this non-Newtonian–Newtonian multiphase system. The generation of thinning filaments between subsequent drops of these low viscosity fluids signifies the presence of elastic stresses in this low Reynold's number flow. Two distinct regions of filament thinning dynamics, a ‘pre-stretch’ region and an exponential self-thinning region, were observed for the highest molecular weight of PEO studied. The ‘experimental’ relaxation times extracted from the exponential self-thinning region were of the same order of magnitude as the calculated Zimm relaxation time but were shown to increase as the cross-flow shear was increased. This increase is associated with substantial pre-stretching of the polymer molecules within the forming neck prior to the onset of thread self-thinning. The presence of elasticity within these low viscosity fluids resulted in the production of secondary drops of varying sizes upon final breakup. The substantial threads between the primary drop and the nozzle display traditional bead-on-a-string morphologies, with the final drop size and polydispersity being a distinct function of cross-flow rate, dispersed flow rate and polymer molecular weight.