Drop Shape Research Articles

Dual stabilization of O/W/O double emulsions by proteins: An interfacial perspective

Oil-in-water-in-oil (O/W/O) double emulsions are regarded as a promising emulsion system to accomplish multifunctionality in the food industry. However, the stability of the complex structure of O/W/O double emulsions is still a problem to be solved due to the presence of two completely opposite water-oil interfaces. To overcome this issue, the application of proteins was investigated to demonstrate their stabilization effect on the O/W/O double emulsion. In this study, a model O/W/O double emulsion was formulated with the commercial emulsifiers Tween 80 and polyglycerol polyricinoleate (PGPR), and then different proteins were introduced to alternate Tween 80. The results showed that the release rate of the inner oil to the outer phase in O/W/O double emulsions stabilized by proteins and PGPR was significantly reduced by about 30% after 2 weeks of storage compared to Tween 80. The stabilization mechanism was verified using drop shape tensiometry, and it was found that whey protein isolate (WPI) and modified pea protein isolate (MPPI) could improve the interfacial moduli of both the inner and outer W–O films, further strengthening the mechanical properties of W–O interfaces against deformation and hence achieving the dual stabilization of O/W/O double emulsions. On the other hand, sodium caseinate (SC) only enhanced the interfacial properties of the PGPR-covered external interface compared to Tween 80. Taken together, this work provides a better understanding of how the composition of the intermediate water phase affects the stability of O/W/O double emulsions and paves the way to design highly stable O/W/O emulsions for food application.

The Shape of a Compressible Drop on a Vibrating Solid Plate

The influence of high-frequency vibrations on the shape of a compressible drop placed on an oscillating solid substrate is studied in this paper. Due to the significant difference in characteristic temporal scales, the average and pulsating motions of the drop can be considered separately. For nearly hemispherical drop, the solution to the problem of pulsating motion is found in the form of series in Legendre polynomials. Frequencies of natural sound oscillations of hemispherical axisymmetric drop are obtained. Resonances of the acoustic mode of drop oscillations are found. The problem of forced oscillations of hemispherical drop in the limit of weakly compressible liquid is considered. It is found that drop oscillation amplitude grows with vibration intensity according to quadratic law, which is consistent with the solution of the pulsation problem for finite compressibility assumption. A variational principle for calculation of average drop shape is formulated based on minimization of energy functional for the case, so the compressibility of the liquid should be taken into account. It is shown that the functional (the sum of the kinetic and potential energies of the pulsating flow, the kinetic energy of the averaged flow, and the surface tension energy of the drop) decreases and reaches a minimum value at quasi-equilibrium state, in which the average shape of the drop becomes static. The influence of vibrations on the drop shape is studied for small values of the vibrational parameter. The surface of the drop in the absence of vibrations is assumed to be hemispherical. Calculations showed that under vibrations, drop height decreases, while the area of the base increases.

Analyzing the impact of the interaction between hydraulic fracturing fluid and Kerogen on its wettability alteration

The increasing demand for exploring and developing unconventional reservoirs has sparked active research into hydraulic fracturing. However, the effect of hydraulic fracturing fluid on kerogen wettability alteration resulting from their interaction remains inadequately understood. This study aims to experimentally quantify the impact of hydraulic fracturing fluid on kerogen wettability alterations as a function of thermal maturity level. To achieve this objective, kerogens isolated from various organic-rich shale rocks of different types and maturities were mixed with synthetic hydraulic fracturing fluid at a temperature of 80 °C for 14 days. The resulting kerogen wettability was analyzed with the sessile drop method, Ion Chromatography (IC), and Attenuated Total Reflectance Fourier-Transform Infrared spectroscopy (ATR-FTIR), while Rock-Eval pyrolysis experiments were conducted as well to determine the kerogen geochemistry changes. After experiments, ANSYS-CFD was utilized to conduct numerical simulations of two-phase fluid flow to identify the impact of wettability on gas-water relative permeability.This study experimentally demonstrated that hydraulic fracturing fluid interacting with kerogen results in significant wettability alterations, which depend on the type and maturity of the kerogen. The Drop Shape Analyzer (DSA) results revealed that the air/water-contact angle decreased after the reaction for every type and maturity of kerogen, although the wettability alteration was greater with higher kerogen maturity. The ATR-FTIR findings revealed that mature kerogen isolates experienced a reduction in their hydrophobic functional groups, whereas kerogen isolates with relatively lower maturity demonstrated a potential loss of such groups, possibly resulting from oxidation. This trend toward hydrophilicity is consistent with the DSA results. The numerical modeling results indicated that the relative permeability was strongly influenced by the wettability of the formation. A water-wet formation led to a higher water relative permeability compared to the relative permeability of gas, and vice versa. These results represent a significant step forward in assessing multiphase fluid transport in organic-rich shales and hydrocarbon production.

Are all yeast biosurfactants really capable of lowering surface tension below 30 mN/m ?

The study discusses pitfalls in attempts to determine reliable surface tension values for the culture media and their extracts for two biosurfactant-producing yeast strains: Rhodotorula graminis and Rhodotorula babjevae. The values obtained from an Axisymmetric Drop Shape Analysis (ADSA) tensiometer showed systematically more and more shallow dynamic surface tension decays, suggesting a deterioration of their surface activity. The rate of this apparent surface activity loss was shown to depend on the sample history, with slower changes observed in vigorously shaken samples. On the other hand, the force-based Wilhelmy plate method provided apparently stable surface tension values of the order of 30 mN/m, in accordance with numerous previous literature reports on similar yeast biosurfactants. Both observations can be justified by the presence of an oil emulsified by biosurfactants produced by the yeast. We show that the odd (apparent) surface tension results are in fact the measurement artifacts resulting from slow demulsification and subsequent oil-spreading assisted by the yeast biosurfactants. The apparent surface tension reduction is thus indeed caused by the presence of biosurfactants, but its value does not represent their real adsorption in a thermodynamic sense. Consequently, the often reported in the literature very low surface tension values for the yeast culture media, of the order of 30±5 mN/m, should be treated with caution, especially if the emulsion stabilized with the biosurfactant had not been fully destabilized prior to the measurement.

Evaluation of hydrogen peroxide wetting properties in the context of safe application in aseptic milk filling

Introduction: In aseptic filling systems, packaging materials are sterilized using various methods to eliminate microorganisms. One of the most popular methods for sterilizing packaging materials is the use of hydrogen peroxide. The wetting property of the surface plays a crucial role in ensuring effective inactivation of microorganisms and uniform treatment of the aseptic packaging. Improving the wetting properties of hydrogen peroxide solutions by adding surfactants will enhance the contact of the sterilant with the lyophobic multilayer packaging material's treated surface, providing the necessary sterilizing ability and disinfectant action during the aseptic filling of milk and dairy products.Purpose: To study the wetting properties of concentrated hydrogen peroxide solutions on various substrates and the possibility of their correction with surfactants to ensure better packaging wetting and safe disinfection processes.Materials and Methods: The objects of the study included the disinfecting substance and sterilant - hydrogen peroxide, surfactants used as technological aids in the food industry, and combined multilayer packaging materials based on paper, cardboard, aluminum foil, and polymer materials used in aseptic milk filling processes. Wetting ability was evaluated by the contact angle in a 3-phase system: adhesive (hydrogen peroxide, water, surfactant solutions) - substrate (packaging material, steel plate, glass) - air using the drop shape analysis based on the Young-Laplace method; surface tension was determined by the optical drop shape analysis using the DSA25S device; surface tension of solutions at temperatures ranging from 30 to 70 °C was determined using the maximum bubble pressure method. The presence of residual amounts of the surfactant polysorbate on the sterilized packaging material was analyzed by HPLC.Results: The Tetra Brik®Aseptic packaging material exhibits pronounced lyophobic properties. The introduction of 0.1% polysorbate surfactant into the hydrogen peroxide solution (~35% w/w) reduced the contact angle by more than 50%, from 93.75° to 40.99°, and significantly decreased the surface tension (45-48%).Conclusion: Improving the wetting properties of hydrogen peroxide solutions will enhance the contact of the sterilant with the treated surface of the lyophobic multilayer packaging material by adding a surfactant, ensuring the necessary sterilizing ability and disinfectant action during the aseptic filling of milk and dairy products. The application conditions of hydrogen peroxide solutions with the addition of 0.1% nonionic surfactant polysorbate in aseptic filling, considering both effectiveness in disinfecting packaging material and safety related to the removal of its residual amounts, allow considering it as a technological aid.

Deformation of a magnetic fluid droplet with an immersed magnetizable body under uniform magnetic fields

The effect of a uniform applied tilted magnetic field on the deformation of a magnetic fluid droplet (resting on a horizontal plane) with an immersed magnetizable ball is investigated numerically and compared with experimental data. It is shown that the ball takes its equilibrium position in the droplet at a certain levitation height above the plane under a uniform tilted field. A 3D mathematical model is used to predict the deformation of the droplet under uniform fields of different directions and magnitudes. The calculated drop shapes are in good agreement with the experimental ones, especially for small volumes and high magnetic fields.

CO2 rich cushion gas for hydrogen storage in depleted gas reservoirs: Insight on contact angle and surface tension

Hydrogen storage in porous media (aquifers and depleted reservoirs) is an effective means of achieving large-scale inter-seasonal demand for energy. In particular, the depleted gas reservoir provides substantial storage capacity and additional economic incentives due to the preexistence of the storage infrastructure as well as the requisite reservoir integrity. However, the interfacial phenomenon between the injected hydrogen, the native gas (cushion gas), the formation brine, and the host rocks require further investigation for efficient gas containment. In this study, we conducted a comprehensive examination of the application of CO2 as a cushion gas. Our investigation involved performing contact angle and surface tension experiments using the drop shape analyzer (DSA) 100 equipment. We examined various gas mixtures (H2–CO2 – CH4–N2) under different pressure ranges (500–3000 psi), temperature levels (30, 40, 50, 60, 70 °C), and salinities (2, 5, 10, 15, and 20 wt%).Results indicate that the wettability behavior of the studied gas-mixture compositions remains relatively consistent unless there are changes in the initial wetting state of the rock. The contact angles observed ranged from 29 to 51°, independent of reservoir pressure, temperature, and salinity. The contact angle values increased with higher pressure but decreased with higher temperature. Furthermore, the contact angle was lower for a gas mixture with a lower CO2 fraction compared to a gas mixture with a higher CO2 fraction. Conversely, the gas mixture brine surface tension exhibited a decrease with increasing pressure, temperature, and CO2 fraction. However, it increased with increasing salinity for all gas mixtures. Based on the results obtained from the contact angle and surface tension analysis, mixture 4 emerged as the ideal fraction for designing CO2 cushion gas in terms of both hydrogen storage and withdrawal. These findings present precise and valuable input parameters and data that can be utilized in reservoir-scale simulations to optimize geo-storage in depleted natural gas reservoirs.

Machine learning (ML)-assisted surface tension and oscillation-induced elastic modulus studies of oxide-coated liquid metal (LM) alloys

Pendant drops of oxide-coated high-surface tension fluids frequently produce perturbed shapes that impede interfacial studies. Eutectic gallium indium or Galinstan are high-surface tension fluids coated with a ∼5 nm gallium oxide (Ga2O3) film and falls under this fluid classification, also known as liquid metals (LMs). The recent emergence of LM-based applications often cannot proceed without analyzing interfacial energetics in different environments. While numerous techniques are available in the literature for interfacial studies- pendant droplet-based analyses are the simplest. However, the perturbed shape of the pendant drops due to the presence of surface oxide has been ignored frequently as a source of error. Also, exploratory investigations of surface oxide leveraging oscillatory pendant droplets have remained untapped. We address both challenges and present two contributing novelties- (a) by utilizing the machine learning (ML) technique, we predict the approximate surface tension value of perturbed pendant droplets, (ii) by leveraging the oscillation-induced bubble tensiometry method, we study the dynamic elastic modulus of the oxide-coated LM droplets. We have created our dataset from LM’s pendant drop shape parameters and trained different models for comparison. We have achieved >99% accuracy with all models and added versatility to work with other fluids. The best-performing model was leveraged further to predict the approximate values of the nonaxisymmetric LM droplets. Then, we analyzed LM’s elastic and viscous moduli in air, harnessing oscillation-induced pendant droplets, which provides complementary opportunities for interfacial studies alternative to expensive rheometers. We believe it will enable more fundamental studies of the oxide layer on LM, leveraging both symmetric and perturbed droplets. Our study broadens the materials science horizon, where researchers from ML and artificial intelligence domains can work synergistically to solve more complex problems related to surface science, interfacial studies, and other studies relevant to LM-based systems.

The shape of things to come: Axisymmetric drop shape analysis using deep learning

HypothesisIn the traditional approach to Axisymmetric Drop Shape Analysis (ADSA), the determination of surface tension or interfacial tension is constrained by computational speed and image quality. By implementing a machine learning-based approach, particularly using a convolutional neural network (CNN), it is posited that analysis of pendant drop images can be both faster and more accurate. ExperimentsA CNN model was trained and used to predict the surface tension of drop images. The performance of our CNN model was compared to the traditional ADSA, i.e. direct numerical integration, in terms of precision, computational speed, and robustness in dealing with images of varying quality. Additionally, the ability of the CNN model to predict other drop properties such as Volume and Surface Area was evaluated. FindingsOur CNN demonstrated a significant enhancement in experimental fit precision, predicting surface tension with an accuracy of (+/-) 1.22×10−1 mN/m and at a speed of 1.50 ms−1, outpacing the traditional method by more than 5×103 times. The model maintained an average surface tension error of 2.42×10−1 mN/m even for experimental images with challenges such as misalignment and poor focus. The CNN model also demonstrated showcased a high degree of accuracy in determining other drop properties.

From Biological Source to Energy Harvesting Device: Surface Protective Ionic Liquid Coatings for Electrical Performance Enhancement of Wood-Based Electronics.

This study explores task-specific ionic liquids (TSILs) in smart floor systems, highlighting their strong electrical rectification abilities and previously established wood preservative properties. Two types of TSILs, featuring a "sweet" anion and a terpene-based cation, were used to treat selected wood samples, allowing for a comparison of their physical and electrical performance with untreated and commercially treated counterparts. Drop shape analysis and scanning electron microscopy were employed to evaluate the surface treatment before and after coating. Near-IR was used to confirm the presence of a surface modifier, and thermogravimetric analysis (TGA) was utilized to assess the thermal features of the treated samples. The different surface treatments resulted in varied triboelectric nanogenerator (TENG) parameters, with the molecular structure and size of the side chains being the key determining factors. The best results were achieved with TSILs, with the instantaneous voltage increasing by approximately five times and the highest voltage reaching 300 V under enhanced loading. This work provides fresh insights into the potential application spectrum of TSILs and opens up new avenues for directly utilizing tested ionic compounds in construction systems.

Ultra-hydrophobic biomimetic transparent bilayer thin film deposited by atmospheric pressure plasma

An open-air atmospheric pressure plasma was used to deposit ultrahydrophobic bilayer coatings. The plasma set-up was tuned, allowing the successive injection in the post-discharge of two monomers. To the best of our knowledge, no study describes the successive deposition by atmospheric plasma of two precursors, which could work in synergy and allow designing composite coatings of high added value. In this study, two liquid precursors were chosen for the deposition of single and bilayer coatings: (i) hexamethyldisiloxane (HMDSO) and (ii) 1H,1H,2H,2H-perfluorooctyltriethoxysilane (pFOTES). Single layer coatings (HMDSO and pFOTES) as well as bilayer coating (HMDSO/pFOTES) were analysed using multiscale techniques: Scanning Electron Microscopy (SEM), profilometer, Atomic Force Microscopy (AFM), Fourier-Transformed Infrared Spectroscopy (FTIR), Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) and drop shape analysis. The bilayer system (HMDSO/pFOTES), resulting from the successive deposition of HMDSO and pFOTES precursors, was confirmed by ToF-SIMS characterization while contact angle measurements highlighted the ultrahydrophobic property of the bilayer: water was fully repelled, with a zero contact angle hysteresis. This resulted from the combination of the multiscale roughnesses of the HMDSO-based and pFOTES based layers, combined with the intrinsic hydrophobicity of the pFOTES layer.

Prediction of multi-bead profile of robotic wire and arc additive manufactured components recursively using axisymmetric drop shape analysis

ABSTRACT Dimension prediction of robotic wire and arc additive manufacturing (WAAM) part is fundamentally dependent on the modelling accuracy of single-bead profile and its subsequent overlapping ones. Current multi-bead overlapping models are still not capable of describing the flatten valley area of WAAM parts. This paper proposes a new recursive model, based on coordinate transformation and axisymmetric drop shape analysis (ADSA), to predict multi-bead overlapping profiles. First, a single-bead profile model for WAAM is established based on ADSA, followed by detailed description of conventional and proposed modified recursive ADSA profile model. The properties of developed recursive ADSA model are then investigated to reveal the effects of overlapping ratio and single-bead aspect ratio. Finally, multi-bead overlapping deposition experiment is carried out to validate the model feasibility. The results show that the modified recursive ADSA model is more accurate than the conventional one for its better accountability of valley areas. It is also indicated that the modified recursive ADSA model is suitable for the robotic WAAM process. The research outcome is beneficial to improving the forming accuracy of WAAM parts and geometry prediction of other additive manufactured products.

Dynamics of Drop Formation in the Presence of Interfacial Mass Transfer.

The dynamics of drop formation have been investigated in the presence of interfacial mass transfer through controlled flow visualization experiments. The mixtures of n-hexane (solvent) and acetone (solute) were used as a dispersed phase, having different initial compositions varying over a broad range. Drops were formed at the submerged position in the continuous phase (water) at the same operating flow conditions. The unsteady force balance model is developed to analyze the implications of the simultaneously occurring interfacial transfer of the solute on the formation dynamics in real time, and predictions are validated with experimental results. Based on initial compositions, the analysis of the transient drop shape shows a sharp transition in the drop formation regime. At lower initial solute concentrations, i.e., ϕ0 < 0.2, axisymmetric drop formation occurs and the interfacial solute transfer has negligible effects on the formation dynamics. Over an intermediate range of solute concentrations, i.e., 0.2 < ϕ0 < 0.5, Marangoni instability is triggered along the evolving interface, and therefore, the interface deformations and contractions occur during the drop formation. At ϕ0 = 0.5, the drop takes highly nonaxisymmetric shapes and remains away from equilibrium until its detachment from an orifice. For ϕ0 > 0.5, the spontaneous ejection of plumes of the solute results in the rapid generation of multiple droplets of smaller size. This work shows that higher solute concentration gradients not only lead to faster solute transport but also induce strong interfacial instability simultaneously. Thus, the coupled effects of transient change in composition and fluid properties govern the drop size and its formation time in such systems under non-equilibrium.

One Material-Opposite Triboelectrification: Molecular Engineering Regulated Triboelectrification on Silica Surface to Enhance TENG Efficiency.

Molecular engineering is a unique methodology to take advantage of the electrochemical characteristics of materials that are used in energy-harvesting devices. Particularly in triboelectric nanogenerator (TENG) studies, molecular grafting on dielectric metal oxide surfaces can be regarded as a feasible way to alter the surface charge density that directly affects the charge potential of triboelectric layers. Herein, we develop a feasible methodology to synthesize organic-inorganic hybrid structures with tunable triboelectric features. Different types of self-assembled monolayers (SAMs) with electron-donating and withdrawing groups have been used to modify metal oxide (MO) surfaces and to modify their charge density on the surface. All the synthetic routes for hybrid material production have been clearly shown and the formation of covalent bonds on the MO's surface has been confirmed by XPS. The obtained hybrid structures were applied as dopants to distinct polymer matrices with various ratios and fiberization processes were carried out to the prepare opposite triboelectric layers. The formation of the fibers was analyzed by SEM, while their surface morphology and physicochemical features have been measured by AFM and a drop shape analyzer. The triboelectric charge potential of each layer after doping and their contribution to the TENG device's parameters have been investigated. For each triboelectric layer, the best-performing tribopositive and tribonegative material combination was separately determined and then these opposite layers were used to fabricate TENG with the highest efficiency. A comparison of the device parameters with the reference indicated that the best tribopositive material gave rise to a 40% increase in the output voltage and produced 231 V, whereas the best tribonegative one led to a 33.3% rise in voltage and generated 220 V. In addition, the best device collected ~83% more charge than the reference device and came up with 250 V that corresponds to 51.5% performance enhancement. This approach paved the way by addressing the issue of how molecular engineering can be used to manipulate the triboelectric features of the same materials.

Hydrogen storage in depleted gas reservoirs using nitrogen cushion gas: A contact angle and surface tension study

The utilization of depleted natural gas reservoirs is a significant consideration for large-scale hydrogen (H2) storage and production. However, accurate knowledge of cushion gas compositions such as nitrogen (N2), methane (CH4), and carbon dioxide (CO2) is crucial, as they are critical components that affect the rock-fluid interfacial phenomenon, thereby impacting deployment feasibility. Moreover, there are limited reported studies on rock/brine/gas-mixture wettability and gas-mixture/brine surface tension for this type of reservoir. To address this gap, we explore the possibility of using N2 as a cushion gas (in the presence of CH4 and CO2) on a pristine quartz for H2 storage across various pressure (500–3000) psi, temperature (30–70) °C, and salinity (2–20) wt.%. We conducted extensive contact angle (CA) and surface tension (ST) experiments for different gas mixtures (H2–N2–CH4–CO2) to generate relevant data for H2 storage in depleted natural gas reservoirs using drop shape analyzer (DSA 100) equipment. Our findings suggest that the wettability behavior of the gas-mixture compositions studied is likely to remain consistent unless the rock's initial wetting state is altered. The CAs were observed to range between 28 and 46°, regardless of reservoir pressure, temperature, and salinity. It also increased with increasing pressure but decreased with increasing temperature. In addition, CA was lower at a lower N2 fraction (Mix 1–80% H2 – 10% N2 – 5% CH4 –5% CO2) compared to a higher N2 fraction (Mix 4–20% H2 – 70% N2 – 5% CH4 –5% CO2). The ST of the gas-mixture/brine systems declined with increasing (i) pressure, (ii) temperature, and (iii) N2 fraction but increased with increasing salinity for every gas mixture. Based on our investigation, mixtures 2 and 3 with H2 (40–60%) and N2 (30–50%) fractions (at constant 5% CH4 and 5% CO2) were identified as the optimal cushion gas for H2 storage and withdrawal under the studied conditions. The results of this study provide accurate and valuable input parameters and data for reservoir-scale simulations utilized in optimizing geo-storage in depleted natural gas reservoirs.

Identification of machine learning neural-network techniques for prediction of interfacial tension reduction by zein based colloidal particles

In this work, five different models of the artificial neural networks (ANNs) called feedforward, cascadeforward, timedelay, layrec and narx were used for IFT prediction as a function of biopolymers (zein and water-soluble portion of Zedo gum (WZG)) contents, pH, and time based on the experimental data. The architecture of the ANN models consisted of four inputs, one hidden layer and one output layer by considering the range of 1–60 neurons and the tansig activation function in the hidden layer. The experimental IFT data obtained from pendant drop method and drop shape analyzer (DSA) instrument were used to train the ANN models. The relative root mean square error (rRMSE) for the mentioned models were in the range of 0.68%− 2.51% and the overall score of timedelay model was higher than other models. Moreover, the relative importance index of the input data for more detailed assessment of IFT was determined for time delay model as the best model to predict IFT. Analysis showed that the impacts of time and zein content on IFT were greater than other factors. The results of this research showed the considerable ability of timedelay model (a data-based and knowledge-based combined approach) to predict IFT. This model can be used by food industry engineers as a very useful and cost-effective tool for process optimization and control the stability of emulsions.

Interfacial rheology insights: particle texture and Pickering foam stability

Interfacial rheology studies were conducted to establish a connection between the rheological characteristics of particle-laden interfaces and the stability of Pickering foams. The behavior of foams stabilized with fumed and spherical colloidal silica particles was investigated, focusing on foam properties such as bubble microstructure and liquid content. Compared to a sodium dodecyl sulfate-stabilized foam, Pickering foams exhibited a notable reduction in bubble coarsening. Drop shape tensiometry measurements on particle-coated interfaces indicated that the Gibbs stability criterion was satisfied for both particle types at various surface coverages, supporting the observed arrested bubble coarsening in particle-stabilized foams. However, although the overall foam height was similar for both particle types, foams stabilized with fumed silica particles demonstrated a higher resistance to liquid drainage. This difference was attributed to the higher yield strain of interfacial networks formed by fumed silica particles, as compared to those formed by spherical colloidal particles at similar surface pressures. Our findings highlight that while both particles can generate long-lasting foams, the resulting Pickering foams may exhibit variations in microstructure, liquid content, and resistance to destabilization mechanisms, stemming from the respective interfacial rheological properties in each case.

Liquid drops on compliant and non-compliant substrates: an ellipsoid-based fitting for approximating drop shape and volume

Liquid drops on compliant and non-compliant substrates: an ellipsoid-based fitting for approximating drop shape and volume

Impact of water on miscibility characteristics of the CO2/n-hexadecane system using the pendant drop shape analysis method

Miscible CO2 flooding has shown bright prospects for improving oil recovery from unconventional reservoirs as well as for storing greenhouse gas in underground formations. Although the favorable water presence effect has been reported in the near miscible CO2 flooding practices, there is still a lack of target research works on the impact of water on the miscibility characteristics of the oil/gas systems. Therefore in this paper, the effect of water presence on the Minimum Miscibility Pressure (MMP) of the CO2/n-Hexadecane (n-C16H34) system is experimentally investigated based on the Oil Droplet Volume Measurement (ODVM) method. By pre-saturating CO2 with water in the high-pressure high-temperature cell, the water component is introduced at the CO2/oil interface. Measurement results show the water presence could result in lower MMPs of the CO2/oil system. Under five temperature levels of 40 °C, 51 °C, 61 °C, 72 °C, and 82 °C, the water presence decreases the MMPs of the CO2/n-C16H34 system from 8.2 to 7.8 MPa, from 9.6 to 8.8 MPa, from 11.6 to 10.2 MPa, from 13.0 MPa to 12.2 MPa and from 14.6 MPa to 13.2 MPa respectively. Thermodynamic calculations provide consistent results as the experimental observations, indicating the main mechanism behind the lower MMPs of the water presence CO2/oil system could be the decreased CO2 molar fraction in the water presence system. This research is expected to provide an innovative viewpoint to understand the water presence effect in the CO2 flooding processes.

Dynamics of the spontaneously accelerative equatorial expansion of a droplet in a high-intensity acoustic standing wave field

This work reports an investigation of the acoustically induced accelerated deformation of drops in high-intensity acoustic standing wave fields generated by a single-axis acoustic levitator. The dynamic characteristics of droplet deformation are obtained and discussed based on high-speed visualization and in-house Python codes. Based on the actual physical characteristics, the finite element method numerical model has been developed for intercoupling the sound field and flow field, allowing for bidirectional feedback between the drop shape and the acoustic wave. The experimental results indicate that during the deformation process of droplets, their equatorial radius expands at an increasing speed without artificially increasing the sound field intensity. The simulation shows that the acoustic radiation suction acting on the equator dominates droplet deformation. Furthermore, there is a kind of positive feedback loop between the acoustic radiation pressure (pr) amplitude at the drop’s equator and the aspect ratio (AR) during the deformation period. It is confirmed that this causes the spontaneous accelerated expansion of the droplet’s equator. In addition, the functional relationship between pr at the drop’s equator and the AR has been obtained through theoretical derivation, which is consistent with the simulation results. Finally, the critical Bond number (Ba,s) of the rim instability is also obtained. This work provides deeper insights into contactless liquid manipulation and ultrasonic atomization technology applications.