Coalescence Effects Research Articles

Laminar and turbulent flow effects in high-pressure homogenization of liposomes and perfluorocarbon nanoemulsions

AbstractSince flow characteristics are still largely unexplored for high-pressure homogenization, we investigated particle break-up at different Reynolds numbers and transition ranges in two channels (Y- and Z-channel). While the channel geometries are often treated as “black boxes”, opening the channels and measuring their geometries allowed a detailed analysis of flow conditions. Transitions from laminar to turbulent flow for pressures of 250–2,000 bar have measurable effects on the sizes of perfluorocarbon (PFC)-nanoemulsion droplets emulsified by phospholipids processed simultaneously in liposomal conformation. Laminar flow has a higher size-reducing rate with growing pressure compared to turbulent flow and leads to a minimum in polydispersity. A density-driven sucrose gradient allows differential analysis of size-reducing effects on liposomes and PFC-nanoemulsion droplets separately. Liposomes can be broken up in both laminar and turbulent flow at the same size reduction rate. In contrast, emulsion droplets have much smaller size reduction rates in turbulent flow and need sufficient emulsifiers, made available by liposomal break-up, to enable size decreases. Repetitive homogenization is only effective for a limited number of cycles. Beyond this threshold, size distributions remain similar or can be deteriorated because of increased particle collisions and aggregation or coalescence effects.

Changes in cross-boundary coalescence effects induce the unsynchronized states shift of microbial structure and microbial-mediated nitrogen-cycle pathways in coupled-ecosystem

Understanding the coalescence of materials and microorganisms across pre-configured functional zones in coupled ecosystems is crucial for refining ecological restoration strategies. Deciphering how this coalescence triggers changes in state and functionality is key. However, the emergence of alternative states due to coalescence impacts could lead to abrupt ecological changes near boundaries, with unknown implications. This study focused on a typical coupled ecosystem, constructed wetland (CW), to investigate the impact of coalescence on shifts in aquatic microbial community states. A quantitative method and hierarchical linear models with Bayesian inference were used. Results showed a gradual increase in coalescence from inlet to outlet, with upstream points significantly influencing downstream points (54.13%, 62.35%, 84.03% for each pond). Alternative stable states were found in microbial-mediated nitrogen cycle pathways, leading to a transition from robust denitrification to diminished ammonification and denitrification states. This shift correlated strongly with community cohesion and nitrogen concentration. The observed change in state shift lagged 5% of the total CW length compared to the change in functional states. This research highlights the potential for targeted manipulation of microbial assemblages in CWs for ecological management and restoration.

Interface area density model for Large-Eddy Simulation of assisted atomization in fiber regime

In the context of simulating liquid rocket engines (LREs), accurately reproducing the complex combustion chamber environment poses a significant challenge. Recent works have shown that Direct Numerical Simulation has made good progress in achieving the simulation of the whole range of temporal and spatial two-phase flow scales involved. However, due to the computational costs, it is currently out of reach in an industrial context. Large-Eddy Simulations (LES) considerably reduce the computational cost but require modeling the two-phase flow at sub-grid level. A promising approach for such modeling is the interface area density (IAD) approach, which was developed initially for LES of flame fronts and subsequently adapted to Diesel jet atomization to recover spray droplet size distributions. In this method, a subgrid density of interface area is transported with an advection equation, while opportune source terms simulate its growth by breakup or its reduction by coalescence effects. In the context of the LREs assisted atomization, the complex mechanism of the assisted atomization in fiber regime must be taken into account by the subgrid model to recover the correct spray size distribution. The present work proposes a new interface area density evolution modeling for two-phase LES of coaxial assisted atomization in fiber regime. The proposed model focuses on recovering a realistic liquid-gas relative velocity at all the scales, enabling accurate modeling of sub-grid scales by using the IAD as a measure of liquid structure sizes.

Lose-lose consequences of bacterial community-driven invasions in soil

BackgroundCommunity-driven invasion, also known as community coalescence, occurs widely in natural ecosystems. Despite that, our knowledge about the process and mechanisms controlling community-driven invasion in soil ecosystems is lacking. Here, we performed a set of coalescence experiments in soil microcosms and assessed impacts up to 60 days after coalescence by quantifying multiple traits (compositional, functional, and metabolic) of the invasive and coalescent communities.ResultsOur results showed that coalescences significantly triggered changes in the resident community's succession trajectory and functionality (carbohydrate metabolism), even when the size of the invasive community is small (~ 5% of the resident density) and 99% of the invaders failed to survive. The invasion impact was mainly due to the high suppression of constant residents (65% on average), leading to a lose-lose situation where both invaders and residents suffered with coalescence. Our results showed that surviving residents could benefit from the coalescence, which supports the theory of “competition-driven niche segregation” at the microbial community level. Furthermore, the result showed that both short- and long-term coalescence effects were predicted by similarity and unevenness indexes of compositional, functional, and metabolic traits of invasive communities. This indicates the power of multi-level traits in monitoring microbial community succession. In contrast, the varied importance of different levels of traits suggests that competitive processes depend on the composition of the invasive community.ConclusionsOur results shed light on the process and consequence of community coalescences and highlight that resource competition between invaders and residents plays a critical role in soil microbial community coalescences. These findings provide valuable insights for understanding and predicting soil microbial community succession in frequently disturbed natural and agroecosystems.DpDvMjk1dTeXPyYscPCMZPVideo Graphical

Unraveling Partial Coalescence Between Droplet and Oil-Water Interface in Water-in-Oil Emulsions under a Direct-Current Electric Field via Molecular Dynamics Simulation.

When the electric field strength (E) surpasses a certain threshold, secondary droplets are generated during the coalescence between water droplets in oil and the oil-water interface (so-called the droplet-interface partial coalescence phenomenon), resulting in a lower efficiency of droplet electrocoalescence. This study employs molecular dynamics (MD) simulations to investigate the droplet-interface partial coalescence phenomenon under direct current (DC) electric fields. The results demonstrate that intermolecular interactions, particularly the formation of hydrogen bonds, play a crucial role in dipole-dipole coalescence. Droplet-interface partial coalescence is categorized into five regimes based on droplet morphology. During the contact and fusion of the droplet with the water layer, the dipole moment of the droplet exhibits alternating increases and decreases along the electric field direction. Electric field forces acting on sodium ions and the internal interactions within droplets promote the process of droplet-interface partial coalescence. High field strengths cause significant elongation of the droplet, leading to its fragmentation into multiple segments. The migration of hydrated ions has a dual impact on the droplet-interface partial coalescence, with both facilitative and suppressive effects. The time required for droplet-interface partial coalescence initially decreases and subsequently increases as the field strength increases, depending on the competitive relationship between the extent of droplet stretching and the electric field force. This work provides molecular insights into the droplet-interface coalescence mechanisms in water-in-oil emulsions under DC electric fields.

Hong–Ou–Mandel interference of spin–orbit hybrid entangled photons

Structured photons are a crucial resource in both classical and quantum technologies, particularly in spin–orbit hybrid photons, enabling various practical applications ranging from ultra-sensitive metrology techniques to quantum-enhanced information processing tasks. However, the two-photon interference of spin–orbit hybrid photons, which combines polarization modes and complex transverse spatial structures across the beam profile, remains unexplored. Here, we present an experimental observation of Hong–Ou–Mandel (HOM) interference of spin–orbit hybrid photons. The tunable q-plates that work as spin–orbit coupler devices are used to prepare various forms of spin–orbit hybrid entangled photons. By harnessing the match degree in the temporal domain, the coalescence and anti-coalescence effects resulting from the symmetric and anti-symmetric properties of the incident quantum states are observed. Moreover, we demonstrated the feasibility of quantum-enhanced photon polarization gears through HOM interference and theoretically analyze the noise-resilient advantages based on coherent HOM measurements. These results provide an alternative route toward quantum experiments with structured photons that allows for controlling their quantum interference in a compact, stable, and efficient way.

Raincloud conditioning by thunder

AbstractThis article considers the role of thunder in the production of rain by gravitational processes. A previous numerical work has shown that a thunder event consisting of four consecutive thunderclaps can alone produce small but significant droplet growths in a lean cumulus cloud in less than 2 s. Here we consider, also numerically, the coalescence effects produced by both thunderclaps and gravity in a cumulus congestus cloud that had more than four times the liquid content of that lean cloud. Those effects are studied separately and in tandem, using the same set of assumptions. Therefore, the results presented here provide a basis for the comparison of the effectiveness of each type to produce droplet growth in thunderclouds. For thunder alone, these results show that a small number of thunderclaps can in less than 2 s produce mean size growths larger than 50%. For gravity alone, it is found that after 60 s, the longest time considered, gravitational coalescence increases the mean diameter of the original droplet size distribution by 20%. The tandem study considers the effects produced by gravitation on the droplet size distribution that resulted after the original distribution was modified by four or five thunderclaps. Significant increases are found in both cases. For four claps it was found that the mean size increased by 71% in 60 s. The corresponding growth for five claps was slightly larger than 100%. These substantial increases also show that the growths produced by the thunderclaps are not simply additive, but significantly accelerate those produced by gravitation. This acceleration implies that the droplet size growths produced by thunderclaps can substantially decrease the time required by gravitational coagulation to produce raindrops in rainclouds.

Asymmetric PCM melting and thermal convection in a rectangular enclosure with straight and wavy heat transfer passages

Experimental and numerical investigations of thermal convection in the vicinity of a straight and wavy horizontal heat transfer fluid passage (HTF)s placed in a rectangular enclosure filled with phase change material (PCM) are presented. The enthalpy-porosity-based finite volume solver is used to simulate the spatiotemporal evolution of the thermal convection, which is well-complemented by experimental visualization and thermocouple measurements. Heat transfer from the horizontal HTF exhibits asymmetrical melting. Heat diffusion is the dominating energy transfer mechanism on the bottom part of the HTF passage and is compared with the Stefan problem. The temporal evolution of thermal convection on the top part of HTF passage involves three distinct phases of melting, viz. initial conduction phase, Rayleigh–Bénard (R-B) convection with linear convection, and vortex coalescence effects. The final stage of the melting process is influenced by the topography of a peninsula of unmelt PCM, which is influenced by specific top-boundary conditions. Thermal convection in PCM above the wavy HTF passage exhibits restricted plume development leading to an improved melting rate and a higher average melt height. Augmentation of internal convection characteristics of HTF with the evolution of melting is also explored. A systematic investigation of the convection plume development and heat transfer characteristics in PCM by varying the HTF Reynolds (1700<Re<2750) and Stefan numbers (0.4<Ste<0.6) has been carried out, and analyzed the nature of thermal plumes, melt fraction, and average penetration length with the Fourier number. Additionally, novel correlations are proposed between Nusselt and Rayleigh numbers for straight and wavy tubes in the intermediate melting stage (1.3×104<Ra<4.7×107).

Three-dimensional simulations of liquid/gas flow through radial centrifugal pumps and the effect of bubble coalescence and breakup on the formation of gas accumulations

Three-dimensional liquid/gas flow mixture simulations of a centrifugal pump are performed by a hybrid two-phase solver, which comprises a blending between a Volume-of-Fluid-like interface-sharpening scheme and a classical homogeneous mixture two-fluid model. The hybrid solver is combined with a population balance model and a turbulence-scale adaptive simulation approach. The experimentally measured head drop due to adherent gas pockets at elevated gas loadings is well reproduced. By a thorough validation with optical measurement data, it is shown that the transition from dispersed bubbles to coherent gas accumulations as well as the steady core of gas pockets and their unsteady wake could be captured without any parameter fitting of coalescence and breakup kernels. Regions of high coalescence activity correlate with locations of gas accumulations, stabilizing the gas pockets in the impeller region. Bubble breakup, in contrast, was primarily found in the wake of the accumulation zones where the tip leakage flow of the semi-open impeller re-enters the blade passage. The particular hybrid solver architecture, together with the resolution of turbulence scales and bubble populations, facilitates the reproduction of bubble coalescence and breakup effects on the formation of gas pockets in centrifugal pumps.

One-pot in-situ deposition toward fabricating superhydrophobic fiberglass membranes with composite microstructure for fast water-in-oil emulsions separation

The separation of oily wastewater, especially surfactant-stabilized water-in-oil emulsions, has become a pressing global challenge. Herein, to achieve ultrafast and efficient separation of water-in-oil emulsions, this work took advantage of the Dodecyltrimethoxysilane (DTMS)-modified TiO2 sol to prepare a superhydrophobic fiberglass (FG) membrane via a facile one-pot in-situ deposition technique. The unique composite microstructure: stalactite-shaped TiO2-SiO2 composite nanoparticles and multi-layer rough fibers were constructed on the fibrous membranes, which significantly increased the roughness and led to a water contact angle of 162.7°. As-prepared composite microstructures combined the capture, coalescence, and interception effects to achieve ultrafast gravity-driven separation of surfactant-stabilized emulsions, with a flux up to 3130.4 L m−2h−1 for surfactant stabilized water-in-hexane and high separation efficiency above 99% for various emulsions. Additionally, the prepared membrane exhibited an excellent cyclic adsorption capacity of 4.25–19.07 gg−1 and high stability. Such an easy, cost-efficient one-pot in-situ deposition method provides a brand-new solution to fabricate superhydrophobic membranes for efficient separation of water-in-oil emulsions, thus exhibiting great potential in applications of domestic wastewater treatment, oil spill treatment, and oil industry development.

Can Enzymatic Treatment of Sugar Beet Pectins Reduce Coalescence Effects in High-Pressure Processes?

While sugar beet pectins (SBPs) are well known for effectively stabilizing fine oil droplets in low-fat food and beverages, e.g., low-fat dressings and soft drinks, it often fails in products of higher oil contents. The aim of this study was to improve the emulsifying properties of SBPs and, consequently, their ability to reduce coalescence during high pressure homogenization of products with increased oil content. Therefore, the molecular size of SBPs was reduced by partial cleavage of the homogalacturonan backbone using the enzymes exo- and endo-polygalacturonanase and varying incubation times. The sizes of SBPs were compared based on the molecular size distribution and hydrodynamic diameter. In addition, to obtain information on the interfacial activity and adsorption rate of SBPs, the dynamic interfacial tension was measured by drop profile analysis tensiometry. The (non)modified SBPs were used as emulsifying agents in 30 wt% mct oil–water emulsions stabilized with 0.5 wt% SBP at pH 3, prepared by high-pressure homogenization (400–1000 bar). By analyzing the droplet size distributions, conclusions could be drawn about the coalescence that occurred after droplet breakup. It could be shown that SBPs modified by exo-polygalacturonanase stabilized the oil–water interface more rapidly, resulting in less coalescence and the smallest oil droplets. In contrast, SBPs modified with endo-polygalacturonanase resulted in poorer emulsification properties, and thus larger oil droplets with increasing incubation time. The differences could be attributed to the different cleavage pattern of the enzymes used. The results suggest that a minimum molecular size is required for the stabilization of fine oil droplets with SBPs as emulsifiers.

Iron Based Catalysts for Nitrogen Reduction Reaction

Ammonia (NH3) is a fundamental feedstock for the global population not only for its wide use as fertilizer and chemical, but also for its potential as energy storage medium. Its synthesis at the industrial scale is based on the well-known Haber Bosch process, operating at high temperature (400-500°C) and high pressure (150-300atm), thus making it highly pollutant. Considering the global climate emergency, it is mandatory to develop a green ammonia synthesis that relies on milder conditions and may adopt renewable energy sources. The electrochemical synthesis, of NH3 from N2 and H2O at ambient conditions and using renewable energy driven electricity could be a promising approach. An efficient electrochemical ammonia synthesis however, is currently still lacking. The main reasons are the absence of adequate catalysts capable of dissociating the N2 triple bond and the competition with the hydrogen evolution reaction (HER) at the cathode, since the required potential is close to that of nitrogen reduction reaction (NRR), required for the ammonia formation.There are some reaction models in the literature but it is commonly accepted that the dissociative adsorption of N2 is the rate limiting step and extensive research has been done on nitrogen interaction with metal surfaces. Ru, Co, Bi, Au, Fe, Mo, etc based materials have been extensively tested for the green ammonia synthesis, but results are still conflicting also because a complete evaluation of environmental contaminations is still lacking.In this work we adopted as NRR catalyst Fe based nanoparticles on carbon cloth substrate via a simple and fast electroless deposition technique. We prepared a FeCl3 solutions with different concentrations in the range 1-10mM and deposited a drop on (3x1.5) cm2 samples of carbon cloth, on a hot plate, at 80°C. After evaporation of the water, the as deposited substrates were dipped in NaBH4 solution while stirring.The catalyst morphology has been studied by Scanning Electron Microscopy (SEM), as a function of the concentration. Very small particles, with a size ranging from 10 to 70nm, were obtained with the most diluted solution. The cluster size increases with increasing FeCl3 concentration in the solution, giving rise to strong coalescence effects and to the formation of a thicker and continuous layer in the case of the most concentrated solution. Scanning Transmission electron Microscopy (STEM) and Electron Energy Loss Spectroscopy (EELS) have been adopted to determine the composition. EELS spectra showed that the iron L-edge is that typical of Fe3O4 materials.The electrochemical ability to reduce nitrogen, with the formation of ammonia, was evaluated in a standard two compartment cell, with a phosphate buffered solution (PBS 0.1M) adopting a Zirfon membrane as a gas separator. Ar or N2 gas (both with a purity of 99.9999%) flowed in the cathode chamber after going through an acidic trap and a water trap, to be further purified. A rigorous protocol has been adopted to evaluate the ammonia production, including a two steps measurement of the environmental ammonia at the open circuit potential. The ammonia was measured by spectrophotometric analysis using the indophenol blue method. The electrochemical production of ammonia was obtained by chronoamperometry under constant voltage.For the iron-based catalysts, a very efficient activation procedure has been developed, based on cyclic voltammetry under N2 flow. The activation process allows an improvement up to 10 times in the ammonia generation rate. Moreover, a strong correlation has been found between the particle size of the catalyst and its activity for NRR, with the best results achieved with the sample covered with nanoparticles, exhibiting also the highest electrochemical active area. Iron based nanoparticles showed excellent activity for NRR, with a faradaic efficiency of 15% at -0.35 V vs RHE and a maximum ammonia production rate of 85µg mg-1 cat h-1. Acknowledgements:This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No101006941.

Overview of open heavy-flavour and quarkonia measurements with ALICE

Heavy-flavour hadrons, i.e. hadrons containing charm or beauty quarks, are effective probes to test perturbative-QCD (pQCD) calculations, to investigate the different hadronisation mechanisms, and to study the quark–gluon plasma (QGP) produced in relativistic heavy-ion collisions at the LHC. Measurements performed in pp and p–Pb collisions have recently revealed unexpected features not in line with the expectations based on previous measurements from e+e− and ep collisions, showing that charm fragmentation fractions are not universal. The investigation of initial-state effects such as shadowing in the collision of a proton with a heavy nucleus is also performed. Measurements of open heavy-flavour and quarkonia production in Pb–Pb collisions allow for testing the mechanisms of heavy-quark transport, energy loss, and coalescence effects during the hadronisation in the presence of a QCD medium. In this contribution, the most recent results on open heavy-flavour and quarkonia production in pp, p–Pb, and Pb–Pb collisions obtained by the ALICE Collaboration are discussed.

Modelling of spall damage evolution and fragment distribution for melted metals under shock release

A strong shock-wave, produced by plate impact, explosive detonation or laser irradiation, can induce metal materials to melt. Reflection of the triangular pressure wave from the free surface generates a strong tensile stress in the liquid state, resulting in the creation of an expanding cloud of liquid debris. This phenomenon is called micro-spalling. The understanding of spall damage evolution and dynamic fragmentation of melted metal under shockwave loading and subsequent releasing is an issue of considerable importance for both basic and applied science, to predict the evolution of engineering structures subjected to explosive detonation in implosive dynamics or inertial confinement fusion, the latter involving high energy laser irradiation of thin metallic shells. For dynamic failure processes, spall fracture in solid material has been extensively studied for many years, while scarce data can be found about how such a phenomenon can evolve after being melted partially or fully when being compressed or released. In this paper, by studying the physical laws of void evolution in melted metals, we expect to reveal the mode and criterion of void coalescence, inertial and temperature effects on void distribution and evolution, and the relationship between fragment distribution and characteristics of breakup of damaged material. According to these physical laws, we can develop theoretical model to describe the damage evolution and fragment distribution of metal that melts when shock releases. This model is implemented as a failure criterion in a one-dimensional hydrocode. The experimental results and computational results are in fairly good agreement with each other. Some discrepancies are explained by using both experimental uncertainties and model limitations which are carefully pointed out and discussed. We believe that these results can deepen our physical understanding of the damage evolutions of metals and improve the credibility of numerical simulation on the damage and fragmentation of materials under implosive loading.

NNumerical investigation of bubble interaction mechanisms in gas-liquid bubbly flows: Harmonisation of bubble breakup and coalescence effects

Numerical investigation of the dynamics of gas-liquid bubbly flow has been performed by using the population balance approach. Using the homogeneous MUSIG model coupled with the two-fluid model, the evolution of bubble size distribution in vertical pipes has been simulated with appropriate consideration of bubble interaction mechanisms. In particular, the study focuses on harmonising the imbalance often associated with breakup and coalescence rates by performing extensive numerical investigations for the examination and comparison of different model formulations to harmonise the coalescence calibration factor of Prince and Blanch (1990) model. To avoid the fine-tuning procedure of selecting calibration factors to harmonise the breakup and coalescence effects, a breakup calibration factor of 1.0 (default setting in ANSYS CFX) was used and three different expressions area-averaged and included as the coalescence calibration factor for the model of Prince and Blanch (1990) modelled using CFX Expression Language (CEL). The performance of the three different “cases” (modifications) has been investigated, compared with each other and validated against the experimental data reported by Monrós et al. (2013). In general, the comparison has shown that all the “cases” yielded satisfactory results when the numerical results were compared with five primitive experimental parameters, namely: gas volume fraction, interfacial area concentration, Sauter mean bubble diameter, gas velocity and liquid velocity. The encouraging results obtained clearly show the capability of the “cases” modelled in capturing the evolution of the bubble sizes. The agreement with the gas volume fraction profiles indicates a level of confidence in the interfacial force models used. Similarly, the agreement seen with the interfacial area concentration indicates that the “cases” modelled for the birth and death processes are reasonably adequate to describe the bubble dynamics. Overall, the comparison shows that the model labelled as “case 2” presented the best results in most of the experimental conditions simulated.

Influence of Cavitation and Mixing Conditions on Oil Droplet Size in Simultaneous Homogenization and Mixing (SHM)

High-pressure homogenizers (HPH) equipped with a Simultaneous Homogenization and Mixing (SHM) orifice allow for inducing a mixing stream directly into the disruption unit. Previous studies show that by doing so, synergies between the unit operations “emulsification” and “mixing” can be used to save energy, e.g., in homogenization of dairy products, or to extend the application range of HPH. Up to now, process design has mainly been based on the trial and error principle due to incomplete understanding of flow conditions and droplet break-up in the SHM unit. This study aims at a higher level of understanding of cavitation and mixing effects on emulsion droplet size. Experimental data were obtained using a model emulsion of low disperse phase concentration in order to avoid coalescence effects. The different flow conditions are created by varying the process and geometric parameters of an SHM unit. The results show that the oil droplet size only depends on mixing conditions when the emulsion droplets are added in the mixing stream. Furthermore, a smaller oil droplet size can be achieved by reducing cavitation, especially for droplets fed in the high-pressure stream.

Early-Stage Growth Mechanism and Synthesis Conditions-Dependent Morphology of Nanocrystalline Bi Films Electrodeposited from Perchlorate Electrolyte.

Bi nanocrystalline films were formed from perchlorate electrolyte (PE) on Cu substrate via electrochemical deposition with different duration and current densities. The microstructural, morphological properties, and elemental composition were studied using scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray microanalysis (EDX). The optimal range of current densities for Bi electrodeposition in PE using polarization measurements was demonstrated. For the first time, it was shown and explained why, with a deposition duration of 1 s, co-deposition of Pb and Bi occurs. The correlation between synthesis conditions and chemical composition and microstructure for Bi films was discussed. The analysis of the microstructure evolution revealed the changing mechanism of the films’ growth from pillar-like (for Pb-rich phase) to layered granular form (for Bi) with deposition duration rising. This abnormal behavior is explained by the appearance of a strong Bi growth texture and coalescence effects. The investigations of porosity showed that Bi films have a closely-packed microstructure. The main stages and the growth mechanism of Bi films in the galvanostatic regime in PE with a deposition duration of 1–30 s are proposed.

Engineering highly effective nanofibrous membranes to demulsify surfactant-stabilized oil-in-water emulsions

Demulsification of oil-in-water emulsions is challenging but significant for oily wastewater treatment, especially for surfactant-stabilized oil-in-water (S–O/W) emulsions. Electrospun nanofibrous membranes exhibit promising performance as demulsification medium but the underline mechanisms are still unclear. In this work, the effects of membrane pore size and nanofiber surface wettability on the demulsification of the S–O/W emulsions were investigated. Two polyvinylidene difluoride (PVDF) nanofibrous membranes with different nanofiber diameter (#P2: 200 nm and #P10: 1000 nm) were developed by electrospinning. The superhydrophilic membranes (#Dopa-P2 and #Dopa-P10) were obtained by coating polydopamine layers on both membranes #P2 and #P10. The silver nanoparticle deposition and subsequent fluorination were conducted on the surfaces of the polydopamine-activated membranes to prepare superhydrophobic nanofibrous membranes (#Ag–P2 and #Ag–P10). The superhydrophilic membrane #Dopa-P10 with a membrane pore size matching the oil droplets performed the best demulsification result. The oil droplets size increased up to 15 times (from 6.5 ± 1.0 μm to 98 ± 7 μm) after passing through #Dopa-P10. The underlying mechanism should be the superhydrophilic nanofibers possessed excellent affinity to the surfactants layer surrounding oil droplets, which could destroy the stable status and facilitate the coalescence of the oil droplets in S–O/W emulsions. The hydrophobic and superhydrophobic membrane #P10 and #Ag–P10 showed little coalescence effects as they exhibited a negative repulsive force to oil droplets. The physical cutting effect dominated the coalescence process when oil droplets passing through the membranes (#P2, #Dopa-P2, and #Ag–P2) with pore size much smaller than oil droplets. The various surface wettability didn't show any obvious difference on the coalescence results.

Elaboration of the Demulsification Process of W/O Emulsion with Three-Dimensional Electric Spiral Plate-Type Microchannel.

Rapid and efficient demulsification (destabilizing of an emulsion) processes of a water in oil (W/O) emulsion were carried out in a three-dimensional electric spiral plate-type microchannel (3D-ESPM). In this experiment, the demulsifying efficiency of emulsions by 3D-ESPM was compared with that by gravity settling, the factors influencing demulsifying efficiency were investigated, and the induction period, cut size and residence time in the demulsification process were studied. The results showed that in contrast to the gravity settling method, 3D-ESPM can directly separate the disperse phase (water) instead of the continuous phase (oil). The maximum demulsifying efficiency of W/O emulsion in a single pass through the 3D-ESPM reached 90.3%, with a microchannel height of 200 μm, electric field intensity of 250 V /cm, microchannel angle of 180°, microchannel with 18 plates and a flow rate of 2 mL /min. An induction period of 0.6 s during the demulsification process was simulated with experimental data fitting. When the residence time of emulsion in 3D-ESPM was longer than the induction period, its demulsifying efficiency increased as the increase of the flow velocity due to the droplet coalescence effects of Dean vortices in the spiral microchannel. For this device a cut size of droplets of 4.5 μm was deduced. Our results showed that the demulsification process of W/O emulsion was intensified by 3D-ESPM based on the coupling effect between electric field-induced droplets migration and microfluidic hydrodynamic trapping.

Joint analysis of the magnetic field and total gradient intensity in central Europe

Abstract. In the European region, the magnetic field at satellite altitudes (∼350 km) is mainly defined by a long-wavelength magnetic low, called the Central European Magnetic Low (CEML) here, located to the southwest of the Trans-European Suture Zone (TESZ). We studied this area through a joint analysis of magnetic and total gradient (∇T) anomaly maps for a range of different altitudes of 5, 100 and 350 km. Tests on synthetic models showed the usefulness of the joint analysis at various altitudes to identify reverse dipolar anomalies and to characterize areas in which magnetization is weak. This way we identified areas where either reversely or normally magnetized sources are locally dominant. At a European scale these anomalies are sparse, with a low degree of coalescence effect. The ∇T map indeed presents generally small values within the CEML area, indicating that the Paleozoic Platform is weakly magnetized. At 350 km of altitude, the TESZ effect is largely dominant: with intense ∇T highs above the East European Craton (EEC) and very small values above the Paleozoic Platform, this again denotes a weakly magnetized crust. Small coalescence effects are masked by the trend of the TESZ. Although we identified sparsely located reversely magnetized sources in the Paleozoic Platform of the CEML, the joint analysis does not support a model of a generally reversely magnetized crust. Instead, our analysis strongly favors the hypothesis that the CEML anomaly is mainly caused by a sharp contrast between the magnetic properties of the EEC and Paleozoic Platform.