Separation Of Droplets Research Articles

Controlled evaporation-induced phase separation of droplets containing nanogels and salt molecules.

Droplets without protection from surfactants or surfactant-like objects normally experience merging or a coalescence process since it is thermodynamically favored. However, division or replication of droplets is thermodynamically unfavored and comparably more difficult to realize. Herein, we demonstrate that a population of droplets that are composed of nanogels and salt spontaneously undergo a separation process under a slow solvent evaporation condition. Each individual droplet underwent changes in size, shape and eventually developed into two domains, which was caused by the screening effect due to the increased salt concentration as a result of solvent evaporation. The two domains gradually separated into nanogel-rich and salt-rich parts. These two parts eventually evolved into nanogel aggregates and branched structures, respectively. This separation was mainly due to the salting out effect and dewetting. Comparison studies indicate that both the nanogels and salt are indispensable ingredients for the phase separation. These discoveries may have profound applications in the fields of biomimetics and offer new routes for self-replication systems.

EXPERIMENTAL INVESTIGATIONS ON THE ROLE OF GROUP COMBUSTION MODE IN LIFTED SPRAY FLAMES WITH KEROSENE FUEL

In the present work, detailed experimental investigations on lifted spray flames have been carried out to identify the various combustion modes using group combustion number analysis with kerosene fuel. Solid cone pressure swirl nozzle N1 ((m_f ) ̇ =1.7 kg/hr at ΔPinj = 9 bar) is considered and fuel injection pressure varied from 3 - 48 bar. Detailed droplet size and droplet velocity measurements using shadowgraphy and PIV helped obtain the group combustion number and dimensionless droplet separation distance. A Chiu (1977, 1982) criterion of group combustion number is used along with experimental observations to understand the spray combustion mode in lifted spray flames. Internal group combustion mode is observed at lower injection pressures (3 bar) in which individual droplet combustion is significant. At intermediate pressures, the combustion mode is defined by internal group combustion with a double reaction zone. The inner reaction zone burns with local extinction, and the outer reaction zone burns like a diffusion flame. A group combustion number range of 1 - 103 is investigated for various combustion modes in lifted spray flames without coflow air. For air coflow conditions (Vcoflow = 0.4 m/s), both individual droplet burning mode and double reaction zone flame structure disappear from the flame. At higher injection pressures, small fuel vapor cloud burning with external group combustion mode is observed in the G range of 103 - 106.

Application of multiphase flow and droplet separation theory in modeling cough droplets contamination range to mitigate COVID-19 transmission: Do not stand too close to me!

On March 11, 2020, the World Health Organization (WHO) declared that COVID-19 is a pandemic, warning the world of a health catastrophe and social, economic, and political disruptions. According to WHO, COVID-19 is transmitted by the transport of respiratory droplets generated by a violent respiratory event such as sneeze and cough directly to susceptible persons, or indirectly through surfaces. The aim of this study is to propose simple physical and mathematical models based on two-phase flow dynamics and droplet separation theory. The proposed mathematical model predicts the contamination range of ejected cough droplets, estimating the safe person-to-person social distance. As a result, the proposed simple model predicted a contamination range of 2.3 m for a male adult. In addition, to understand the behavior of ejected cough droplets, a sensitivity analysis is carried out to investigate the effect on contamination range of cough air flowrate, i.e., body/lung size, droplet size, and droplet drag coefficient. It is found that as the body/lung size decreases, i.e., lower cough flow rate, contamination range decreases, resulting in 1.9 m for an adult female, and 1.4 m for a child. In addition, the model predictions show an appreciable effect of droplet size, and droplet drag coefficient on cough contamination range. In particular, the effect of droplet drag coefficient is of interest, because of its relationship to ambient conditions such as temperature and relative humidity, in which both affect ambient air viscosity, and thus drag coefficient. This is important in investigating the contamination range and person-to-person social-distance as climate changes.

Treatment of hydrothermal liquefaction wastewater with ultrafiltration and air stripping for oil and particle removal and ammonia recovery

This study aims to evaluate the application of ultrafiltration technology for the separation of particles and oil droplets and the recovery of ammonia from hydrothermal liquefaction (HTL) wastewater. Real HTL wastewater from the hydrothermal liquefaction of municipal sewage sludge was used in this study. Experiments were carried out using a submerged polyethersulfone ultrafiltration membrane with molecular weight cutoff of 100 kDa in combination with air stripping and addition to acid and base traps for recovery of volatiles. Results showed, that the best operation mode of ultrafiltration is with backwash cycles of the permeate, maintaining a flux lower than the critical flux of 6 L/h·m2. The setup led to fast stripping of ammonia, which was successfully recovered by 88% in the acid trap. This application can be considered an adequate first stage treatment of the HTL wastewater. The importance of this work is that it proves that membrane technology can be successful in treating complex real HTL wastewater, and is not only limited for applications using model solutions.

Paraffin–graphene oxide hybrid nano emulsions for thermal management systems

Phase change material nano-emulsions are investigated as potential working fluids for various applications including heat transfer and solar applications. Main hindrances to their application are the difficulty in maintaining emulsion stability and the subcooling effect. In this study, new phase change material nano-emulsions (PCMEs) were designed and characterized as possible heat transfer media to be used at 21 and 55 °C, by investigating two commercial phase change materials melting at these temperatures. In particular, the influence of graphene oxide (GO) and reduced graphene oxide (rGO) on emulsion stability and on thermal and optical properties of PCMEs has been investigated. The stability of emulsions was verified and no phase separation or significant growth of PCM droplets were observed through storage and after freeze–thaw cycles. GO was less successful in case of paraffin melting at 21 °C, while it was effective in reducing subcooling to only 1 °C for nanoemulsion with paraffin melting at 55 °C and strongly influenced heat transfer capability. This resulted in a fluid thermal capacity increase of more than 20% within 10 °C from PCM melting temperature. The partial reduction of GO did not result in significantly changing the thermal properties of nanoemulsions and slightly increased the optical absorption, due to higher optical absorption of rGO with respect to GO.

High dielectric properties, TiO2 nanoparticles doped PDLC devices for lower switching voltage

ABSTRACT Polymer dispersed liquid crystal (PDLC) films were prepared using a nematic liquid crystal, photo-curable polymer and TiO2 nanoparticles by polymerisation-induced phase separation (PIPS) method. Electro-optical properties of doped and undoped samples including transmittance, driving voltage, contrast ratio and response time of the transmittance-voltage were measured, compared and analysed. The morphology of polymer network has been investigated by means of SEM. The phase separation of LC droplets was found to be dependent on the content of prepolymer, LC and nanoparticles used. The high dielectric properties and high refractive index of TiO2 nanoparticles make PDLC have low driving voltage and high contrast. In particular, the nanoparticles concentration can be optimised to obtain promising electronic materials with minimum threshold and high contrast for display applications.

Microfluidic Preparation of Janus Microparticles With Temperature and pH Triggered Degradation Properties.

Based on the phase separation phenomenon in micro-droplets, polymer-lipid Janus particles were prepared on a microfluidic flow focusing chip. Phase separation of droplets was caused by solvent volatilization and Janus morphology was formed under the action of interfacial tension. Because phase change from solid to liquid of the lipid hemisphere could be triggered by physiological temperature, the lipid hemisphere could be used for rapid release of drugs. While the polymer we selected was pH sensitive that the polymer hemisphere could degrade under acidic conditions, making it possible to release drugs in a specific pH environment, such as tumor tissues. Janus particles with different structures were obtained by changing the experimental conditions. To widen the application range of the particles, fatty alcohol and fatty acid-based phase change materials were also employed to prepare the particles, such as 1-tetradecanol, 1-hexadecanol and lauric acid. The melting points of these substances are higher than the physiological temperature, which can be applied in fever triggered drug release or in thermotherapy. The introduction of poly (lactic-co-glycolic acid) enabled the formation of multicompartment particles with three distinct materials. With different degradation properties of each compartment, the particles generated in this work may find applications in programmed and sequential drug release triggered by multiple stimuli.

Spin-affected droplet coalescence and separation undergoing off-center collision

Spin-affected droplet coalescence and separation undergoing off-center collision

Influence of Modification of the Geometry of the Wave-Plate Mist Eliminators on the Droplet Removal Efficiency—CFD Modelling

This study is concerned with droplet separation using wave-plate mist separators. The influence of continuous phase velocity, droplet size, and geometry on droplet removal efficiency has been investigated. The following modifications were analysed: drainage channel presence, length, angle, and modification to the streamlined shape. Furthermore, the influence of the physical parameters of the separated substances on separator efficiency was investigated. Calculations were conducted using computational fluid dynamics (CFD). The results were compared with the experimental data from the literature. Based on the results obtained, a new shape of drainage channels was proposed, which is characterised by high droplet removal efficiency with relatively low pressure drop.

Paper-based dual-mode liquid manipulation system: Oil/water separation and time-lapse droplet switch

Multi-mode liquid handling system integrated different types of liquid behaviors on super-wetting surfaces has attracted great interest from both academia and industries due to their promising applications in the field of surface science. Herein, a paper-based dual-mode droplet manipulation system that combines oil/water separation and time-delay droplet switch was designed by spray-coating α-cellulose 10-undecenoyl ester (CUE) particles on filter paper with further “reverse sizing” by polydimethylsiloxane (PDMS) based on capillary action and “like dissolve like” principle. Such novel binding technique leaded to a remarkably robust superhydrophobicity of the as-fabricated PDMS@CUE-coated paper (PDMS@CCP), including outstanding mechanical resistance and environmental durability. In particular, the front side of PDMS@CCP displayed excellent separation efficiency (higher than 99.89%) for light oil/water mixture, heavy oil/water mixture, and even surfactant-stabilized water-in-oil emulsion. Interestingly, based on the hydrophobicity of the back side of PDMS@CCP and the intrinsic hygroscopicity of paper itself, a time-delay droplet switch was simply achieved in between by the Laplace pressure derived from the curvature difference of the droplet on two paper surfaces with surface energy gradient. By adjusting the width of the filter paper and the volume of the droplet, the switch time could be rationally modulated between 0.8 and 202.1 s. The designed functional paper would enrich the application field of the liquid manipulation system.

Simulation and experimental study on droplet breakup modes and redrawing of their phase diagram

Dimensionless numbers are often used to characterize the various modes of droplet breakup processes. However, the current methods of calculating these dimensionless numbers are not uniform—consequently, the calculation results are different, resulting in different phase diagrams of droplet separation. This paper first summarizes the methods of calculating the Weber number. The maximum transient velocity at the center of a nozzle is then used as the characteristic velocity for calculating the Weber number, and this formulation is used to solve certain scenarios in which the traditional Weber number cannot be applied, such as the strange phenomenon of the upward flight of separated droplets. A mathematical model is established to simulate the various separation forms of droplets, and the experimental study is also carried out. This upward flight of droplets is found to be the result of competition between the liquid inertial force, surface tension force, and suction effect of the nozzle mouth. The final velocity of the droplets depends on the existence of a stagnation surface and the corresponding sweep effect. Finally, the phase diagram of different droplet separation modes is drawn in the Ohnesorge–Weber number space.

Preparation of modified membrane of polyvinylidene fluoride (PVDF) and evaluation of anti-fouling features and high capability in water/oil emulsion separation

The conventional Polyvinylidene Fluoride (PVDF) membrane was modified by polymerization Reversible addition−fragmentation chain-transfer (RAFT) with copolymer (PEGMA-co-BVIm-Br) on the upper bulk. This copolymer was obtained from the synthesis of (BVIm-Br) 3-butyl-1-vinyl-1-H-imidazole-3-ium bromide and the vinyl imidazole (VI) monomer N-vinyl imidazole (a hydrophilic monomer) and 1-bromobutane (C4H9Br). The analysis of such as ATR-FTIR, the magnetic resonance of H-NMR nuclei, zeta potential, Water Contact Angle (WCA), and Scanning Electron Microscopy (SEM) confirmed the presence of copolymer on the surface of the modified membrane. The bonding of this copolymer on the membrane surface reduced the WCA of the membrane water (from 89.5 ±1.96 to 33.8 ±1.55). The raw PVDF membrane (M1) and modified membrane (with total ratio-P(PEGMA-co-BVIm-Br) copolymer 2.5 % (M2), 5 % (M3), 10 % (M4), 20 % (M5), and 40% (M6) to (raw PVDF membrane) membrane showed appropriate hydrophilic nature and excellent separation of oil droplets from water/oil emulsions in the simulated effluent on the surface.This operation was performed for a comprehensive study on the determined parameters and by filtration with simulated petrochemical industry effluent (containing water/oil emulsion). Therefore, the recovery efficiencies of water flux, flow flux, oil recovery amount, as well as total fouling of M6 membrane were reported 96.14±0.99 and 428±2.6 L/ (m2 h), 96.1±1.3%, and 17.18±0.37%, respectively. This study aimed to prepare a copolymer-modified membrane that can show high performance in cleaning and resistance to various fouling, such as Rt, Rr, and Rir at the specified temperature, after long-term emulsion separation.

Experimental and numerical evaluation of the performances of type‐C and three‐segment demisters used in cooling towers

AbstractDemisters have become a key vapour‐liquid separation device for eliminating mist and preventing any escape of liquid droplets from cooling towers. In this paper, the overall performances of two types of demisters, namely type‐C and three‐segment demisters, are systematically investigated by using both experimental and numerical methods. The validation results show that the numerical results agree well with experimental data. On this basis, the underlying influences of key operating parameters, such as the circulating pressure of the pump, spray water flow rate, inlet gas velocity, and droplet size on the overall performance, are revealed. The results show that the overall separation efficiency is more sensitive to the gas velocity and increasing the gas velocity leads to two distinct declining stages of the overall separation efficiency for both demisters. The first stage appears due to the competition between the drag force and the inertial/centrifugal forces, while the next stage arises mainly due to the droplet re‐entrainment. The geometric design of the type‐C demister is more conducive to the separation of the fine droplets due to the presence of the hook plate, even at a relatively low gas velocity. Besides, the type‐C demister has more potential to reduce the power consumption while achieving a higher profit for a given grade separation efficiency.

Design and analysis of de-oiling coalescence hydrocyclone

ABSTRACT De-oiling hydrocyclones are extensively applied in oilfield wastewater purification for fluid separation, because of their efficient and rapid processing performance. However, it is difficult for a hydrocyclone to separate tiny oil droplets owing to the inadequate centrifugal force. A type of coalescence hydrocyclone (CHC) is designed based on the principle of centrifugal separation and hydraulic droplet collision coalescence. The structure, coalescence theory, and separation principle of the CHC are introduced. Based on the Euler–Euler method, the population balance model (PBM) is applied to a continuous equation to simulate the distributions of the velocities, oil volume fraction, and oil droplet size in the CHC. The simulation method is verified by conducting particle image velocimetry tests in a polymethyl methacrylate hydrocyclone. The results indicate that the CHC can improve the separation performance by enlarging the oil droplet size by collision coalescence before entering the hydrocyclone. The results of separation efficiency experiment indicate that the CHC can not only improve the oil–water separation efficiency but also clearly enhance the processing capability. The optimal inlet flow rate is 5.5 m3·h-1 and the split ratio is 25%. The feasibility of the structure design and the reliability of the separation performance are validated by experiments.

Mathematical modeling and experimental study on solid–liquid suspension separation in ultrasonic standing wave field

A new method of removing waste chips is proposed by focusing on the key factors affecting the processing quality and efficiency of high energy beams. Firstly, a mathematical model has been established to provide the theoretical basis for the separation of solid–liquid suspension under ultrasonic standing wave. Secondly, the distribution of sound field with and without droplet has been simulated. Thirdly, the deformation and movement of droplets are simulated and tested. It is found that the sound pressure around the droplet is greater than the sound pressure in the droplet, which can promote the separation of droplets and provide theoretical support for the ultrasonic suspension separation of droplet; under the interaction of acoustic radiation force, surface tension, adhesion, and static pressure, the droplet is deformed so that the gas fluid around the droplet is concentrated in the center to achieve droplet separation, and the droplet just as a flat ball with a central sag is stably suspended in the acoustic wave node.

Computational fluid dynamics (CFD) assisted design and prototyping of the immiscible drop separation section for an intensified perstraction system

Bioprocesses development is a fundamental research area nowadays, and downstream processing is one of the main bottlenecks due to its high contribution to production cost. In that regard, process intensification of separation technology is still needed. Particularly, a novel liquid membrane in Taylor flow (LMTF) has demonstrated to intensify organic acid separation performance and potentially facilitate economic bioprocesses viability (Fontalvo and Pérez-Ávila, 2019). However, the current challenge is designing a separation mechanism for the immiscible phases once the extraction has been performed. In this work, a computational fluid dynamic (CFD) approach is used for fast prototype design followed by prototype construction and experimental evaluation. The device aims an immiscible droplets separation based on wettability in a LMTF used for the extraction of lactic acid. Simulation results indicate that a low contact angle for the hydrophilic ramification and a low division angle allowed the best separation performance, where complete phases separation was possible but experimentally some challenges limit the separation performance. CFD simulations have shown to be a powerful tool to assess geometric degrees of freedom which accelerate prototyping and reduce the initial experiments required. The combined LMTF system and drop separation device offers a continuous downstream alternative for bioprocesses further intensification.

A CFD study of the transport and fate of airborne droplets in a ventilated office: The role of droplet-droplet interactions.

Previous studies reported that specially designed ventilation systems provide good air quality and safe environment by removing airborne droplets that contain viruses expelled by infected people. These water droplets can be stable in the environment and remain suspended in air for prolonged periods. Encounters between droplets may occur and droplet interactions should be considered. However, the previous studies focused on other physical phenomena (air flow, drag force, evaporation) for droplet transport and neglected droplet interactions. In this work, we used computational fluid dynamics (CFD) to simulate the transport and fate of airborne droplets expelled by an asymptomatic person and considered droplet interactions. Droplet drag with turbulence for prediction of transport and fate of droplets indicated that the turbulence increased the transport of 1 µm droplets, whereas it decreased the transport of 50 µm droplets. In contrast to only considering drag and turbulence, consideration of droplet interactions tended to increase both the transport and fate. Although the length scale of the office is much larger than the droplet sizes, the droplet interactions, which occurred at the initial stages of release when droplet separation distances were shorter, had a significant effect in droplet fate by considerably manipulating the final locations on surfaces where droplets adhered. Therefore, it is proposed that when an exact prediction of transport and fate is required, especially for high droplet concentrations, the effects of droplet interactions should not be ignored.Electronic Supplementary MaterialSupplementary material is available in the online version of this article at 10.1007/s11783-021-1465-8 and is accessible for authorized users.

Nanopore-based active oil droplet filtration under negative DC dielectrophoresis for oily wastewater treatment

Efficient separation of oil droplets from oily wastewater is an essential task for handling the world water crisis and environmental pollution. However, existing passive oil/water separation technologies suffer from the drawbacks of relatively low separation efficiency and strict material requirements. We present an active dielectrophoretic oil/water separation technique without inducing further environmental contamination. Based on the non-uniform electric field generated through insulated nanopores under direct current (DC) voltage, an oil droplet experiences a negative dielectrophoresis (nDEP) force because of its weaker dielectric property compared with wastewater. Meanwhile, electroosmotic flow also occurs in oil/water separation devices due to the ion motion inside the electric double layer of the nanopore solid surface. Through developing a multiphysical model for immiscible oil/water flow under hybrid electrokinetic effects, the oil/water separation is investigated at different parametric conditions. Electrokinetic filtration of oil droplets through nanopores is successfully achieved when the nDEP force is dominant rather than the electroosmotic electrohydrodynamic (EHD) force for oil droplet movement. To enhance the oil/water separation rate, the relative strength between nDEP force and EHD force on an oil droplet is consolidated via increasing DC voltage, decreasing surface charge density, and optimizing the nanopore configuration. The designed active oil/water separation using DC-DEP offers significant potential for future oily wastewater treatment.

Superhydrophobic modification of the surface of cellulosic materials based on honeycomb-like zinc oxide structures and their application in oil–water separation

Honeycomb-like zinc oxide structures were prepared on the surface of cellulosic materials including cotton fabric fiber and filter paper fiber through plasma treatment followed by wet chemical reaction, the effect of plasma treatment is to increase the wettability and reactivity of cellulosic materials, so that the zinc oxide can nucleate and grow into a honeycomb-like structure on the cellulose fibers. The superhydrophobic surface was then obtained by modifying stearic acid on the zinc oxide structure. The microstructure, chemical composition and state, and wettability of the cellulosic materials were studied in detail. After the modification, the water contact angle and water sliding angle of the modified cotton fabric were 151° and 3.4°, respectively, and those of the modified filter paper is 154° and 4.5°, which indicates super-hydrophobicity. Due to the structural characteristics of zinc oxide-stearic acid structure, the superhydrophobic structure can maintain superhydrophobic performance in strong acidic or strong alkaline environments or after ultrasonic vibration treatment. Further, superhydrophobic modified cotton fabric and filter paper can be used for oil–water separation and adsorption of oil droplets in aqueous solution, and the oil–water separation efficiency is greater than 90%. This method of superhydrophobic modification of cellulosic materials has broad application prospects.

Continuous separation of submicron-scale oil droplets in aqueous electrolyte by electrophoretic migration

Separation of tiny oil droplets, which is not readily achieved by conventional oily wastewater treatment, is becoming important in the petrochemical industries with regard to public health and the global environment. Herein, we report a continuous and filterless separation of submicron-scale oil droplets based on electrophoretic migration in a three-dimensional (3D) printed microfluidic free-flow electrophoresis (μFFE) device which is miniaturized system of conventional electrodialysis (ED). Microscale electrodialysis system with commercial ion exchange membrane (IEM) is proposed to control the dynamics of negatively (or positively) charged tiny oil droplets. We examined separation performance for various parameters, such as applied voltage, recovery ratio, flow velocity, solution concentration, and flow-channel dimension, with visualization of fluorescent oil droplets. Separation of several non-fluorescent submicron-scale oil droplets (e.g. gasoline engine, diesel engine, gear, and palm oils) were also investigated, including measurement of droplet diameters and surface charge (zeta potential). Future scale-up of the proposed microfluidic ED system will be a promising method for the treatment and relevant applications of industrial oily wastewater.