Rate Of Droplet Coalescence Research Articles

Effects of Inorganic Salts on the Phase Separation of Partially Miscible Solutes.

Partially miscible solutions with a lower critical solution temperature have promising applications in the field of physical chemistry. To better guide the utilization of these solutions in practice, we conduct an in-depth study about the phase separation behavior of the solution added with inorganic salts. The addition of the inorganic salts into the solution is found to consequently reduce the phase separation temperature. The variation of concentrations of inorganic salts does not notably affect the mass fraction of the separation. Moreover, the addition of inorganic salts in the solutions at lower mass fractions improves the separation mass fraction, while the addition of inorganic salts decreases the separation mass fraction at the mass fractions above 30%. It sheds light on selecting the proper mass fractions and inorganic salt concentrations. Furthermore, we explore the phase separation behavior of mixed solutions under different inorganic salt additions by means of a high-speed camera. The phase separation behavior under different inorganic salt systems shows a similar trend. However, calcium ions and Fe3+ ions in the solutions can greatly decrease the rate of droplet coalescence and result in an increase in phase separation. For better regulating the solutions with a lower critical solution temperature through inorganic salts, sodium chloride or potassium chloride is recommended with an appropriate concentration.

Formation and properties of zein Particle-GMS Co-stabilized pickering emulsions: Insights into the complex interface

The interplay between colloidal particles and surfactant co-adsorption plays a pivotal role in determining interface properties and emulsion stability. This study delves into the influence of the Zp/GMS ratio on the physical stability of Zein particle-GMS co-stabilized emulsions (CPEs) and how co-adsorption and interfacial interactions impact this stability. Results indicated that the preferential adsorption of GMS facilitated the diffusion (Kdiff increased from 0.083 mNm−1 s−0.5 to 0.206 mNm−1 s−0.5) and penetration of Zp (KP increased from −17.0 × 104 s−1 to −23.6 × 104 s−1), triggering interface rearrangement. Consequently, intricate interfaces formed, inducing a synergistic reduction in interfacial tension. Moreover, the decreased Zp/GMS ratio bolstered the lateral molecular interactions between Zp and GMS at the interface, while also enhancing the longitudinal relaxation of GMS during interface deformation. Therefore, the Zp/GMS ratio played a pivotal role in controlling the stiffness, elasticity, and deformability recovery of complex interfaces in both lateral and longitudinal dimensions. Furthermore, in both O/W and W/O CPEs, a decreased Zp/GMS ratio improved the physical stability of CPEs by reducing the rate of droplet coalescence. To summarize, the enhanced stability of CPEs can be attributed to the reduction in droplet aggregation. This reduction is influenced by a combination of improved mechanical properties resulting from lateral molecular interactions at the interface and enhanced deformability recovery due to the longitudinal relaxation of GMS. These findings not only deepen our understanding of particle-surfactant interactions in Pickering emulsions but also pave the way for formulating emulsions with specific textures and stabilities.

A Numerical Simulation of Multiple‐Droplet Coalescence Characteristics under an Electric Field

AbstractA phase field method based on the Cahn‐Hilliard equation was used to establish a numerical model for the motion and coalescence of multiple droplets under an electric field. The influencing factors of the droplet coalescence rate, velocity field and pressure field distributions, and droplet cluster motion and coalescence were investigated. The observations showed that the dynamic behaviors of droplets under the action of the electric field can be characterized as not coming together, coalescence, and breakup after coalescence. High‐speed (low‐speed) and high‐pressure (low‐pressure) regions are generated inside the droplet or near the interface under the action of the electric field, and the size, number, and location of these regions change over time. The results of this study offer an essential guide for developing new electrostatic coalescers.

Effect of salt addition on the coalescence process of droplets on fiber

Fiber coalescence is an economical and effective technology for the treatment of oily wastewater. In this paper, the microscopic coalescence process of salt droplets on the fiber is studied using a high-speed camera and PIV, and the effect of salt on hydrodynamics and morphological evolution is discussed. The results show that the increase of salt concentration leads to a decrease of double layer force, a larger liquid bridge expansion, and a higher capillary wave propagation velocity. When the salt concentration is too high, the capillary wave propagation velocity decreases. A catchment region with a high velocity is formed near the traveling region of the capillary wave, and the velocity can reach 0.03 m/s. The attenuation coefficient of the oscillation process increases with the increase of salt content. By combining fiber and salt, the rate of droplet coalescence can be increased, and the production of secondary droplets can be reduced.

Modeling of an industrial mixing valve and electrostatic coalescer for crude oil dehydration and desalination

ABSTRACT This paper aims to present a new model for an industrial desalination system including a mixing valve and an electrostatic coalescer. This model uses a one-dimensional population balance equation in steady-state conditions. The effect of hydrodynamic, diffusion and electrostatic mechanisms on the collision or breaking of water droplets dispersed in crude oil was considered. Also, using the film drainage model, the droplet coalescence rate has been determined. The developed model can predict the outlet droplet size distribution as well as the desalination and dehydration efficiency. The simulation results showed good agreement with the industrial data. Finally, the effect of some important parameters on the electrostatic desalination process, such as mixing valve pressure drop, electric field intensity, crude oil viscosity, crude oil temperature, diluting water flow rate, and crude oil API on the efficiency of the process was analyzed. The results indicated that by increasing the crude oil temperature from 314 to 334 K, the efficiency of dehydration improves from 97.95% to 99.02%. Also, reducing crude oil API from 33 to 30 and crude oil viscosity from 4 to 2 mPa.s caused a decrease in water separation by 2.88% and 1.16%, respectively.

On the Possibility of Modeling the IMF By-Weather Coupling through GEC-Related Effects on Cloud Droplet Coalescence Rate

The meteorological response to the fluctuation of the interplanetary magnetic field (IMF), known as the Mansurov effect, is well established. It is hypothesized that the IMF By fluctuation can modulate the atmospheric global electric circuit (GEC) over the polar regions and affect surface meteorology. The influence of electric charges on the rate of droplet coalescence in fair-weather clouds is one of several cloud microphysical mechanisms that have been hypothesized to be involved. However, although meteorological effects associated with IMF By have been observed, the role of cloud droplet coalescence in this solar–weather coupling mechanism has not yet been confirmed. In addition, studies demonstrating the solar wind-driven effects are based on observations without using global climate models to support the IMF By-weather linkage. In this study, we investigate the Mansurov effect over the period 1999–2002 using ensemble experiments modeled with the chemistry-climate model (CCM) SOCOLv3 (SOlar Climate Ozone Links, version 3.0). Using observed IMF By, we model its effect on ground-level air pressure and temperature to examine one of the proposed GEC-cloud hypotheses: that surface meteorology response on IMF By fluctuations occurs through the Jz-associated intensification of cloud droplet coalescence rate. The results showed that we cannot explain and confirm the hypothesis that the rate of cloud droplet coalescence is an intermediate link for the IMF By-weather coupling. Anomalies in surface air pressure and temperature from the control run, where IMF By is omitted, do not robustly differ from experiments in which the dependence of cloud droplet coalescence rate on IMF By is included. In addition, the standard deviation of anomalies in surface air pressure and temperature between ensemble members is consistent with the magnitude of the observed effect even in the control run, suggesting that the model has a strong internal variability that prevents the IMF By effect from being properly detected in the model.

Stability of PAM/PEI emulsified gels under HTHS conditions for water shut-off treatment

Emulsification has been widely used in the oil industry. The thermal stability of emulsified systems, such as emulsified gels or acids, is critical for the placement success of the emulsified system. Early separation of the system in a tubular well leads to corrosion. In the present study, the stability of emulsified polyacrylamide/polyethylenimine (PAM/PEI) gels is investigated in high-temperature and high-salinity (HTHS) environments. The influences of different parameters such as surfactant concentration, water–oil ratio, salinity, intensity of mixing and temperature on the droplet size and the emulsion thermal stability are studied. The droplet size of the PAM/PEI system, which is emulsified in diesel, decreases, and the separation time increases with increasing mixing speed, surfactant concentration, and salinity. The emulsions with smaller droplets are thermally stable compared with large droplets since the rate of droplet coalescence is low. The effect of emulsion stability on gelation kinetics and gel strength is investigated. The emulsification reduces both the gel strength and the gelation rate. The cross-linking (gelation) rate in the unemulsified PAM/PEI is almost ten times higher than that in the emulsified gels. This gelation process is slow in the case of stable emulsified PAM/PEI solution and is believed to be the result of limited heat and mass transfer. The emulsion stability achieved in this work adds to the current understanding of how to control emulsion stability through different parameters to withstand HTHS environments and how this stability influences the gelation process.

Microemulsion based hybrid biofuels using glycerol monooleate

The present investigation aims to highlighten the effect of monoglyceride surfactant (GMO) on structure and dynamic behavior and other fuel characteristics of microemulsion based hybrid biofuels (MHBFs). Fuel quality of MHBFs formulated using purified GMO (>90%), which was prepared by esterification of glycerol, was investigated in the study. Phase behaviors, droplet size distribution, number of droplets present in the system, average droplet size and average length of surface active agents were studied as a part of structural investigations of the GMO based MHBFs. Diffusion coefficient, energy barrier to droplet coalescence and rate of coalescence of droplets were also investigated for the formulated MHBFs. The number of droplets, length of surface active agent and the diffusion co-efficient were in the ranges of 1.87×1021–5.66×1021/m3, 0.92–1.07nm and 1.00×10−11–1.79×10−11m2/s, respectively. The rate of droplet coalescence was obtained in the range 2.77×10−4–8.78×10−4 times the collision factor. MHBFs incorporating the glycerol derived bio-based nonionic surfactant GMO exhibited viscosity of 4.12mm2/s (at 40°C), gross calorific value (GCV) of 39.17MJ/kg and pour point of −7°C.

Injection of nanosized CO2 droplets as a technique for stable geological sequestration

Geological sequestration of carbon dioxide (CO2) is considered an important technology to achieve a substantial reduction in CO2 emissions. However, leakage is a risk of geological sequestration because CO2 migrates upwards by buoyancy. This study proposes a new technique using nanosized CO2 droplets injected into a porous structure to decrease the buoyancy effect, thereby preventing the upward migration of CO2. We focus on the formation of nanosized CO2 droplets, their subsequent size variation over time, and their behavior in porous media. Experiments are performed using a volume ratio of CO2 to water of 1:1 and trisiloxane (0.4–1.6%) as a surfactant. In the experiments, nanosized CO2 droplets with initial diameters in the range of 20–100nm are successfully generated. The droplet coalescence rate depends on both temperature and CO2 density. Experimental results also indicate that sufficiently small CO2 droplets can be maintained throughout the injection process and readily introduced into an aquifer. Microfocus X-ray computed tomography shows that CO2 is stably trapped in a porous medium. This study suggests that nanosized CO2 droplets hold considerable promise as a means of stable geological sequestration. Surfactant optimization and cost reduction need to be addressed for field application of this approach.

Multiwalled Carbon Nanotubes at the Interface of Pickering Emulsions.

Carbon nanotubes exhibit very unique properties in biphasic systems. Their interparticle attraction leads to reduced droplet coalescence rates and corresponding improvements in emulsion stability. Here we use covalent and noncovalent techniques to modify the hydrophilicity of multiwalled carbon nanotubes (MWCNTs) and study their resulting behavior at an oil-water interface. By using both paraffin wax/water and dodecane/water systems, the thickness of the layer of MWNTs at the interface and resulting emulsion stability are shown to vary significantly with the approach used to modify the MWNTs. Increased hydrophilicity of the MWNTs shifts the emulsions from water-in-oil to oil-in-water. The stability of the emulsion is found to correlate with the thickness of nanotubes populating the oil-water interface and relative strength of the carbon nanotube network. The addition of a surfactant decreases the thickness of nanotubes at the interface and enhances the overall interfacial area stabilized at the expense of increased droplet coalescence rates. To the best of our knowledge, this is the first time the interfacial thickness of modified carbon nanotubes has been quantified and correlated to emulsion stability.

Movement of dispersed droplets of W/O emulsion in a uniform DC electrostatic field: Simulation on droplet coalescence

Considering the droplet coalescence, the motion of a group of dispersed droplets in W/O emulsion in a DC electric field is simulated. The simulation demonstrates the evolutions of droplet number, size as well as its distribution, local concentration distribution and droplet size-velocity relation with the applied time of electric field. The simulated average droplet size is roughly consistent with the experimental value. The simulated variation of droplet number with time under several applied voltages shows that increasing voltage is more effective for raising the rate of droplet coalescence than extending exerting time. However, with the further raise of applied voltage, the improvement in droplet coalescence rate becomes less significant. The evolution of simulated droplet size–velocity relationship with time shows that the inter-droplet electric repulsion force is very strong due to larger electric charge on the droplet under higher applied voltage, so that the magnitude and the direction of droplet velocity become more random, which looks helpful to droplet coalescence.

Microemulsion based hybrid biofuels from Thevetia peruviana seed oil: Structural and dynamic investigations

Abstract The structure and dynamics of microemulsion based hybrid biofuels (MHBFs) from Thevetia peruviana seed oil (TPO) were investigated for the first time in this study. Nonionic surfactants like fatty esters (FAME), oleyl alcohol (OA) and ethylene glycol butyl ether (EGBE) were introduced into the system to investigate their influence on MHBF characteristics. Introduction of these surfactants resulted in modification of structure and dynamics of simple systems comprising of vegetable oil, butan-2-ol and ethanol. The diffusion co-efficient increased from 0.13 × 10 −11 to 5.10 × 10 −11 m 2 /s, which indicated the formation of reverse micellar system. Besides, decrease in the rate of droplet coalescence from 10 −1 to 10 −5 times the collision factor signified the increase in physical stability of MHBFs. The number of droplets increased from 1.88 × 10 18 to 6.60 × 10 22 and average length of surface active agent decreased from 8.8 to 0.26 nm. The introduction of OA and FAME also increased the gross calorific value (GCV) (from 38.91 to 40.21 MJ/kg). Moreover, the introduction of EGBE resulted in decrease in pour points of MHBFs from 1 °C to −8 °C. Conclusively, the conversion of fatty acids to corresponding esters (FAMEs), introduction of long chain alcohol (like OA) and anti freezing agent (EGBE) contributed towards improvement in fuel quality of simple MHBF.

Controlled droplet coalescence in miniemulsions to synthesize zinc oxide nanoparticles by precipitation

The precipitation of zinc oxide with a coalescence controlled emulsion technique is introduced. This technique involves the preparation of two stable water-in-oil submicron sized emulsions (miniemulsions). Each emulsion contains one water soluble precipitation precursor. In a second high pressure emulsification step droplet coalescence is induced leading to particle precipitation. In this contribution we present parameters influencing droplet coalescence rate such as emulsifier and emulsifier content as well as local flow conditions. Considering the precipitation of zinc oxide we furthermore investigate the influence of droplet coalescence rate on the size and composition of the particles synthesized. The results approve the importance of full coalescence of droplets prior to particle synthesis: Remaining uncoalesced droplets lead to a wide particle size distribution with a fraction of larger particles. If all droplets coalesce to some extent, we observe a decrease in particle size with increasing reactant concentration depicting a precipitation process dominated by homogeneous nucleation.

Linear relation between convective cloud drop number concentration and depth for rain initiation

Coalescence of cloud droplets is essential for the production of small raindrops at a given vertical distance above the cloud base (Dp). The rate of droplet coalescence is determined mainly by droplet size, spectrum width and concentrations. The droplet condensational growth is determined by the number of activated CCN (Na) and height above cloud base. Here we show that when the droplet mean volume radius, rv, exceeds ∼13 μm, or when droplet effective radius (re) exceeds ∼14 μm, considerable precipitation mass (>0.03 g kg−1) is likely to be present in growing convective clouds. This is because the rate of droplet coalescence is proportional to ∼rv5 which practically implies the existence of a threshold rv above which efficient warm rain formation can occur, and also because the vertical profile of rv, even in diluted clouds, nearly follows the theoretical adiabatic condensational growth curve. The small observed deviations are mainly caused by deviations from purely inhomogeneous mixing which cause partial droplet evaporation. Consequently, Dp must theoretically change nearly linearly with Na. This is confirmed here observationally, where increasing Na by 100 per milligram (≈cm3 at cloud base) of air, resulted in an increase of ∼280 m in Dpfor both Israeli and Indian deep convective clouds. This means that in highly polluted clouds or where strong cloud‐base updrafts occur, clouds have to grow well above the freezing level, even in tropical atmosphere, before precipitation forms either by warm or by mixed‐phase processes.

A new classification of pre-ovulatory oocyte maturation stages in pikeperch, Sander lucioperca (L.), and its application during artificial reproduction

This study aimed at improving the reproduction effectiveness and synchronization of ovulation in the pikeperch, Sander lucioperca (L.), during induced spawning, which is one of the main bottlenecks in the aquaculture of this species. For this purpose, a new categorization of maturation stages in pre-ovulatory oocytes was applied. It is generally based on two morphological indicators: germinal vesicle migration or its breakdown (GVBD) and different oil droplet coalescence rates. This categorization covered seven stages (from I to VII) – from the end of vitellogenesis to ovulation. The categorization was verified by controlled reproduction with the use of hormonal stimulation (500 IU of hCG per kg of female body weight) and low spawning temperature (12 °C), which extended the latency time. In addition, some morphological indicators (pseudo-gonadosomatic index, Fulton's condition coefficient) of females were calculated in order to determine their usability in determining the maturation stage. However, these indicators proved to be ineffective for this purpose, further highlighting the need to determine the maturational stages in pre-ovulatory oocytes to synchronize ovulation in pikeperch. During the experiment, ovulation seemed to be synchronized among the experimental treatments. Statistical differences were found in terms of latency time between experimental groups at different maturity stages (II – 78–98 h; III – 57–78 h; IV – 48–58 h; V – 32–49 h; VI – 5–30 h) according to the proposed classification. This classification and the results presented in the study significantly improved the synchronization of ovulation, which may positively affect the effectiveness of pikeperch production under controlled conditions.

Development of a new reflectance technique to investigate the mechanism of emulsification

A new reflectance technique has been developed to measure the droplet size evolution during the process of emulsification in real-time. This has been used to investigate the dynamic behaviour of 50% oil-in-water emulsions. The performed experiments were designed in order to investigate the occurring droplet break-up and droplet coalescence phenomena individually, by carefully creating processing conditions where each of those events is dominant. The effect of emulsifier (Tween 20) concentration and different hydrodynamic conditions on the droplet break-up and coalescence phenomena and the emulsion droplet size evolution during processing were all investigated. The concentration of Tween 20 was shown to be a key parameter affecting the droplet size of the emulsion at the early stages of processing (within the first 3 min). However, during the later stages of processing, hydrodynamic conditions have a more pronounced effect on determining the final droplet size. Unlike droplet break-up, droplet coalescence rate decreases by intensifying the hydrodynamic conditions of the process as a consequence of the high capillary pressure of the smaller droplets being produced.

Influence of CaCl 2 on the water vapor permeability and the surface morphology of mesquite gum based edible films

Oil-in-water (O/W) emulsions with a dispersed phase mass fraction (φ m ) of 0.175 were prepared by dispersing a blend of candelilla wax/mineral oil (2:1 ratio) in 10 g of mesquite gum per 100 g of water containing either CaCl 2 (0.0, 0.1, 0.2, 0.3, 0.4 or 0.5 g) alone or combined with 1.5 g of glycerol. The mean volumetric droplet size ( d 3,0), the rate of droplet coalescence (C) and the viscosity-shear rate behavior of the emulsions were affected by the addition of CaCl 2 alone or combined with glycerol. The Carreau–Yasuda model fitted best the viscosity-shear rate data of all the emulsions. The surface morphology of the edible films, analyzed by Atomic Force Microscopy (AFM), exhibited a strong dependence on the CaCl 2 concentration. Maximum roughness occurred with a CaCl 2 concentration of 0.3 g per 100 g. Films with glycerol showed significantly higher roughness than those with only CaCl 2. Water vapor permeability (WVP) was significantly lowered as the concentration of CaCl 2 increased from 0.1 to 0.3 g per 100 g in the coatings, but increased again at CaCl 2 concentrations of 0.4–0.5 g per 100 g. Coatings containing glycerol displayed significant higher WVP.

Ferrous bisglycinate content and release in W 1/O/W 2 multiple emulsions stabilized by protein–polysaccharide complexes

ABSTRACT Ferrous bisglycinate aqueous solution was entrapped in the inner phase (W1) of water-in-oil-in-water (W1/O/W2) multiple emulsions. The primary ferrous bisglycinate aqueous solution-in-mineral oil (W1/O) emulsion contained 15% (w/w) ferrous bisglycinate, had a dispersed phase mass fraction of 0.5, and was stabilized with a mixture of Grindsted PGPR 90:Panodan SDK (6:4 ratio) with a total emulsifiers concentration of 5% (w/w). This primary emulsion was re-emulsified in order to prepare W1/O/W2 multiple emulsions, with a dispersed mass fraction of 0.2, and stabilized using protein (whey protein concentrate (WPC)):polysaccharide (gum arabic (GA) or mesquite gum (MG) or low methoxyl pectin (LMP)) complexes (2:1 ratio) in the W2 aqueous phase. The W1/O/W2 multiple emulsion stabilized with WPC:MG (5% w/w total biopolymers concentration) provided smaller droplet sizes (2.05 μm), lower rate of droplet coalescence (7.09 × 10−7 s−1), better protection against ferrous bisglycinate oxidation (29.75% Fe3+) and slower rate of ferrous bisglycinate release from W1 to W2 (KH = 0.69 mg mL−1 min−0.5 in the first 24 h and 0.07 mg mL−1 min−0.5 for the next 19 days of storage time). Better encapsulation efficiencies, enhanced protection against oxidation and slower release rates of ferrous bisglycinate were achieved as the molecular weight of the polysaccharide making up protein:polysaccharide complex was higher. Thus, the factor that probably affected most the overall functionality of multiple emulsions was the thickness of the complex adsorbed around the multiple emulsion oil droplets. These thicknesses determined indirectly by measuring the z-average diameter of the complexes, and that of the WPC:MG (529.4 nm) was the largest.

Steady and Dynamic Shear Rheological Properties, and Stability of Non-Flocculated and Flocculated Beverage Cloud Emulsions

Rheological properties of single-phase, and emulsions containing modified starch and gum arabic as surface active hydrocolloids, as well as xanthan and tragacanth gums as stabilizers were evaluated under steady and dynamic shear testing conditions using a control stress rheometer. Emulsions were formed by 9% and 14% gum concentrations with oil concentration maintained at 9% thus giving a 1:1 and 1.5:1 surface active agent to oil ratio, respectively. The rates of droplet coalescence and creaming, for a total of 8 emulsions, as a function storage time before and after dilution in a simulated fruit beverage were then investigated. Steady shear (flow curve) were well described by the Carreau model at shear stress ranging from 0.01 to 100 Pa. All prepared water phases indicated a zero-shear viscosity plateau followed by shear thinning behavior with flow behavior index (n) ranging from 0.51 to 0.79 for 14% starch-0.3% xanthan and 14% gum arabic-0.8% tragacanth stabilized emulsions, respectively. The water phase flow property data were well fitted by the Einstein equation and its expansions. The dynamic rheological properties of water phase and emulsions were also evaluated for G′(ω) and G″(ω) from 1 to 50 rad/s. Similar curves were obtained with varying degrees of deviations (G′ from G″) for different emulsions. Starch-xanthan emulsion and associated water phase at 1.5/1 agent to oil ratio demonstrated viscoelastic behavior (G′ ≥ G″) with lower droplet coalescence and creaming rates. On the other hand, gum arabic-xanthan emulsion at 1:1 agent to oil ratio showed the highest rate of droplet coalescence and a greater degree of creaming. It was speculated that the lower stability of gum arabic-xanthan emulsion could be related to the denaturation of proteinaceous part in the gum and loss of emulsification capacity due to lower pH and pasteurization.

The dynamics of montmorillonite clay dispersion and morphology development in immiscible ethylene–propylene rubber/polypropylene blends

The evolution of morphology during the melt compounding of polypropylene (PP), maleated ethylene–propylene rubber (EPR-g-MAn) and onium-ion exchanged montmorillonite clay (NR4+-MM) is described. Irrespective of the ratio of components, clay partitions into the EPR-g-MAn phase exclusively, with significant amounts of mineral exfoliation occurring in the very early stages of compounding. These changes in filler distribution and dispersion are accompanied by reductions in the size of the dispersed PP phase, as the rate of droplet coalescence falls in response to an elevated EPR-g-MAn matrix viscosity. However, when NR4+-MM is localized in a dispersed EPR-g-MAn phase, coalescence increases as a result of hindered particle break-up.