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Recently, we demonstrated that the local heating of degassed water can generate water vapor microbubbles and induce a rapid flow around the bubble. Although flow generation involves the self-excited oscillation of bubbles at a local heating point, the conditions under which the bubbles oscillate are not fully understood. In this study, the dependence of microbubble size and oscillation frequency on the concentration of non-condensable gases in water was investigated. A continuous-wave laser beam was focused on a β -FeSi 2 thin film, and water was locally heated using the photothermal conversion properties of the film. The results showed that the lower the concentration of non-condensable gases dissolved in water, the smaller the bubble size and the higher the oscillation frequency. Furthermore, it was found that the bubbles oscillate when the amount of non-condensable gas absorbed by the bubbles, i.e., the bubble size, falls below a specific level. This study can provide a new understanding of the bubble oscillation mechanism and lead to the development of fluid control technology using bubbles. [ABSTRACT FROM AUTHOR]

Carbonate reservoirs exhibit varying pore sizes that significantly impact gas distribution and flow dynamics. Current models fail to adequately address the flow mechanisms within the diverse matrix pores of carbonate reservoirs. To address this gap, we propose a triple-porosity model that incorporates small pores, large pores, and fractures, alongside a capillary pressure equation that accounts for pore radius and saturation. Additionally, a new transient shape factor was derived. Utilizing the triple-porosity model, we investigated the processes of gas separation and dissolution from oil, gas distribution, and the effects of gas on water flow. Our findings reveal that gas is primarily dissolved during the initial water injection stage or at low gas saturation levels. Once the pressure reaches the gas initiation threshold, gas transport becomes the dominant mechanism. Both dissolution and transport can reduce gas saturation by a factor of 1:10. In small pores, capillary pressure induces a gas locking phenomenon, resulting in higher free gas presence compared to large pores. Moreover, the presence of the gas phase accelerates the spread of injected water. Implementing depletion followed by water injection decreases oil recovery. This study elucidates the processes of gas separation, distribution, flow, and dissolution, providing theoretical guidance for managing complex flow dynamics in volatile carbonate reservoirs. [ABSTRACT FROM AUTHOR]

A series of experiments have been performed studying the displacement of water by gas in consolidated porous media at an adverse viscosity ratio of μw/μg = 100, from the perspective of subsurface gas storage. The gas/water relative permeability functions (RPs) produced in the laboratory to model these processes generally use short cores from which the RPs are derived using conventional analysis and assumptions. In this work, we present results that challenge some of these assumptions and bring into question some of the currently used RP functions to design storage scenarios gas/water systems. Using a novel visualization technique, large two-dimensional sandstone slabs are imaged via x-rays during the gas → water unstable drainage processes. Three experiments were carried out evaluating the impact of rate and vertical flow direction. In the bottom-to-top experiments, we observed the rate dependence on the evolution of viscous fingers from an initially stable bank resulting from the effect of capillary dispersion stabilizing the early finger growth. In the case of top-to-bottom displacement, we observe that the combined capillary and gravity forces are not sufficient to fully stabilize the system, although a visible "stable" bank is formed prior to the emergence of the gas fingering instability. Finally, these results are compared to a water → oil drainage carried out under the same conditions and viscosity ratio. The results are then discussed in the context of subsurface gas storage, and recommendations are made for future experiments designed to derive appropriate gas/water RP functions and for upscaling the results from the laboratory to the field. [ABSTRACT FROM AUTHOR]

The pulsation of bubbles and the impact load from reverse flow, generated by the evolution of semiclosed initial intermittent bubble multiphase flow during underwater launches, are crucial factors affecting launch safety. This paper employs the mixture multiphase flow model and the interphase heat and mass transfer model to simulate the interaction between the gas inside a partially enclosed cylinder and the water medium outside the cylinder, combined with simulation and piggybacking experiments, to analyze the flow process and load state. The numerical model is further utilized to study the evolution of the multiphase flow field of the semienclosed initial intermittent bubble, the pulsating load of the bubble, the impact load of the inverted water flow, and the influence of structural dimensions on the load. The results show that the initial intermittent bubble in the mouth of the cylinder experiences an expansion–contraction–expansion pulsation process, and as the migration of the interface between the phases results in significant pressure pulsation, the peak pulsation can exceed twice the pressure difference between the initial gas pressure inside the cylinder and the hydrostatic pressure at the mouth of the cylinder. At the late stage of bubble pulsation, a large amount of water with pulsating bubbles flows into the semiclosed cylinder, and the pulsation-induced velocity and gravity are used to form a high-speed inverted water flow. The interaction between the inverted water and the gas inside the cylinder generates an oscillating shock load where the maximum shock load is significantly greater than the ambient pressure load. Additionally, the effect of structural dimensions on the load state under the same intermittent conditions is examined. [ABSTRACT FROM AUTHOR]

Enhanced oil recovery (EOR) strategies, particularly CO2 flooding, play a crucial role in optimizing oil reservoir exploitation while addressing carbon sequestration. Despite their effectiveness, the application of these techniques is often hindered by complex reservoir dynamics and the computational intensity of traditional simulation models. This study introduces a novel approach utilizing the FlowNet model, which combines data-driven analytics and physics-based modeling, aimed at expediting history matching and production optimization processes. The FlowNet model simplifies the representation of reservoirs by using virtual well points along flow paths and employs a non-linear solver for quick resolution of flow equations. Our method significantly enhances the efficiency of history matching by reducing computational overheads and leveraging streamlined network structures, thereby facilitating faster and more accurate production forecasts. We implement the model in several case studies involving CO2 and water alternating gas flooding, which demonstrate an 11% increase in the economic net present value compared to traditional methods. These findings highlight the potential of integrating data-driven techniques with physical modeling to improve EOR performance predictions and optimize production strategies, ultimately promoting more sustainable and economically viable oil recovery practices. [ABSTRACT FROM AUTHOR]

An underwater shooting method with a novel barrel structure featuring spiral grooves is designed by opening multiple spiral grooves on the gun barrel's tail inner wall, and the combustion-gas flows are guided to create multiple gas jets that are sprayed into the barrel to form a gas curtain for water drainage. A three-dimensional unsteady multiphase mathematical model was created, and the correctness of the numerical model established was verified by comparing it with the experimental results of underwater gun gas curtain drainage visualization. On this basis, the influence of different spiral grooves on the evolution process of gas jet and liquid and the drainage effects were simulated. The results indicate that the phase change happens in close proximity to the gas–liquid boundary; nonetheless, the volume percentage of vapor generated by phase change during gas–liquid interaction is less than 1%. The more grooves there are, the greater the maximum pressure at each moment inside the fully filled circular tube; the temperature at the front end of the circular tube becomes higher. When the number of grooves is increased from 4 to 6, the drainage completion time is shortened by 29.7%, the amount of gas in the circular barrel increased by 5.2%, and the drainage rate is significantly increased. However, as the amount of grooves increased from 6 to 8, the gas volume fraction and drainage rate in the tube only increased slightly. On the contrary, it takes a little more time to complete the drainage. [ABSTRACT FROM AUTHOR]

In order to visualize multiphase fluid seepage in porous reservoir media due to gravitational differentiation, a series of innovative experimental devices for individual or composite repulsion were fabricated to study and analyze the effects of repulsion mode, glass bead diameter, inclination angle, settling time, and crude oil viscosity on the gravitational differentiation of oil, gas, and water. The results show that compared with the actual production process in the reservoir, which requires a long time for the transport and aggregation of multiphase fluids under the action of gravity, this device can make the oil, gas, and water to produce gravity differentiation quickly and obviously. Compared with water flooding and gas flooding, combination flooding mainly extracted the emulsion of the oil–water mixture. The gravity differentiation effect of the oil–water mixture is much more significant than that of the oil–gas mixture. Static treatment of the emulsion is also required for reading numbers and producing a clear oil–water interface by oil–water gravity differentiation. Neither too low nor too high, the bank angle of a pipe filled with sand is conducive to the oil–water gravity differentiation. The effect of gravity differentiation within a specific time is directly proportional to the standing time. The change in the displacement mode can further amplify the three-phase gravity differentiation of oil, gas, and water. The greater the viscosity of crude oil, the harder the displacement. Finally, the microscopic experiment witnessed the oil–water gravity differentiation process of the extracted emulation. This experimental study identifies the main factors affecting the gravitational differentiation of multiphase fluids and methods to improve the gravitational differentiation rate of oil and water or oil and gas. The findings provide a theoretical basis for the rational and effective development of oil reservoirs. [ABSTRACT FROM AUTHOR]

In the initial stage of coal seam water injection, due to the high density and low permeability of coal bodies, an obvious startup pressure gradient is observed in relation to water seepage; this phenomenon leads to low-velocity nonlinear seepage. In this paper, we study the nonlinear seepage law and the main influencing parameters of the water injection process. First, based on the startup pressure gradient, the nonlinear seepage equation, and the fractal theory, we formulated a nonlinear seepage model of coal seam water injection that considered the fractal characteristics of a complex coal structure. Subsequently, we carried out coal seam water injection and gas radial seepage experiments under a high overburden pressure, obtaining the startup pressure gradient according to the seepage characteristics and the changes of dynamic parameters. Then, the dynamic parameters of water injection, the structural parameters of the coal samples, the physical parameters, and the fractal dimension were substituted into the theoretical model to obtain the theoretically calculated value. Finally, through comparative analysis of theoretical and experimental startup pressure gradient calculation results, it is found that with the increase in the overburden pressure, the permeability of coal and the connectivity effect are reduced, while the fracture tortuosity and the startup pressure gradient increase. Moreover, coal seam permeability does not seem to be the single decisive factor for the nonlinear startup pressure gradient. [ABSTRACT FROM AUTHOR]

The late-stage development of gas reservoirs often encounters the paradox of significant remaining formation pressure coupled with low wellhead pressure, which indicates small drainage volume, low gas production rate, and low recovery efficiency, reducing gas supply and economic benefit. Owing to the lack of experimental research, the reasons behind this contradiction between gas production and producing pressure differential are unclear. The key factors affecting the development outcomes are reservoir permeability and initial water saturation, while the evaluation parameters include gas and water production rates, reservoir pressure, and recovery efficiency. Based on the characteristic properties of typical gas fields, physical simulation experiments of constant-rate gas production are conducted on spliced long cores with average permeabilities of 2.300, 0.486, and 0.046 millidarcy (mD). Furthermore, leveraging the multi-point embedded pressure measurement technique, the pressure drawdown propagations and the macroscopic and microscopic characteristics of connate water production at the initial water saturations of 0%, 20%, 40%, and 55% are investigated. By connate water, we mean water that occurs naturally within the pores of rock. Pre- and post-experiment core weighing and nuclear magnetic resonance testing are performed. In addition to the mercury injection tests, the results indicate that during gas reservoir depletion, connate water primarily stems from macropores and mesopores, with micropores and nanopores capturing water through capillary imbibition. Moreover, lower permeability and higher initial water saturation lead to greater pressure gradients, increased connate water production, and reduced recovery efficiency. Reservoirs with permeabilities below 0.1 mD are significantly affected by connate water, exhibiting steep pressure profiles. Owing to connate water, the near-wellbore pressure quickly decreases, while distant reservoir pressure barely decreases, implying a limited drainage area. To enhance the recovery efficiency, measures like infill drilling and reservoir stimulation are recommended for low-permeability gas reservoirs. [ABSTRACT FROM AUTHOR]

The present study aims to reveal two-phase flow characteristics as gas is injected into co-flowing water. A computational fluid dynamics work was conducted using the volume of fluid model and the delayed detached eddy simulation. The numerical scheme was validated through experimental results. Effects of the upstream water velocity and the gas injection rate on flow patterns were investigated. Characteristics of gas cavities were compared under different operating conditions. In both experimental and numerical results, unique patterns of gas cavities are obtained. A large cavity is attached to the nozzle outlet, and simultaneously, bubbles are shed from the cavity front. With increasing gas injection rate, the attached cavity is pinched off as it extends in a streamwise direction. As the velocity of water increases, scattered pinch-off frequencies are evidenced and cavity instability is enhanced. Liquid wake downstream of the nozzle contributes significantly to the collapse of the gas cavity. A long and stable gas cavity is produced at high upstream water velocities and gas injection rates. [ABSTRACT FROM AUTHOR]

In this paper, we have studied the vibrational spectral features for the collagen triple helix using a dispersion corrected hybrid density functional theory (DFT-D) approach. The protein is simulated by an infinite extended polymer both in the gas phase and in a water micro-solvated environment. We have adopted proline-rich collagen models in line with the high content of proline in natural collagens. Our scaled harmonic vibrational spectra are in very good agreement with the experiments and allow for the peak assignment of the collagen amide I and III bands, supporting or questioning the experimental interpretation by means of vibrational normal modes analysis. Furthermore, we demonstrated that IR spectroscopy in the THz region can detect the small variations inherent to the triple helix helicity (10/3 over 7/2), thus elucidating the packing state of the collagen. So far, identifying the collagen helicity is only possible by means of crystal x-ray diffraction. [ABSTRACT FROM AUTHOR]

The recently developed efficient protocols to implicit [Grimme et al., J. Phys. Chem. A 125, 4039–4054 (2021)] and explicit quantum mechanical modeling of non-rigid molecules in solution [Katsyuba et al., J. Phys. Chem. B 124, 6664–6670 (2020)] are applied to methyl lactate (ML). Building upon this work, a new combination scheme is proposed to incorporate solvation effects for the computation of infrared (IR) absorption spectra. Herein, Boltzmann populations calculated for implicitly solvated single conformers are used to weight the IR spectra of explicitly solvated clusters with a size of typically ten solvent molecules, i.e., accounting for the first solvation shell. It is found that in water and methanol, the most abundant conformers of ML are structurally modified relative to the gas phase, where the major form is ML1, in which the syn conformation of the –OH moiety is stabilized by a OH⋯O=C intramolecular hydrogen bond (HB). In solution, this syn conformation transforms to the gauche form because the intramolecular HB is disrupted by explicit water molecules that form intermolecular HBs with the hydroxyl and carbonyl groups. Similar changes induced by the gas-solution transition are observed for the minor conformers, ML2 and/or ML3, characterized by OH⋯OCH3 intramolecular HB in the gas phase. The relative abundance of ML1 is shown to decrease from ∼96% in gas to ∼51% in water and ∼92% in methanol. The solvent strongly influences frequencies, IR intensities, and normal modes, resulting in qualitatively different spectra compared to the gas phase. Some liquid-state conformational markers in the fingerprint region of IR spectra are revealed. [ABSTRACT FROM AUTHOR]

Several oil–water separation techniques have been proposed to improve the capacity of cleaning water. With the technological possibility of producing materials with antagonist wetting behavior, for example, a substrate that repels water and absorbs oil, the understanding of the properties that control this selective capacity has increased with the goal of being used as the mechanism to separate mixed liquids. Besides the experimental advance in this field, less is known from the theoretical side. In this work, we propose a theoretical model to predict the wetting properties of a given substrate and introduce simulations with a four-spin cellular Potts model to study its efficiency in separating water from oil. Our results show that the efficiency of the substrates depends both on the interaction between the liquids and on the wetting behavior of the substrates itself. The water behavior of the droplet composed of both liquids is roughly controlled by the hydrophobicity of the substrate. Predicting the oil behavior, however, is more complex because the substrate being oleophilic does not guarantee that the total amount of oil present on the droplet will be absorbed by the substrate. For both types of substrates considered in this work, pillared and porous with a reservoir, there is always an amount of reminiscent oil on the droplet, which is not absorbed by the substrate due to the interaction with the water and the gas. Both theoretical and numerical models can be easily modified to analyze other types of substrates and liquids. [ABSTRACT FROM AUTHOR]

The Ar( 3 P 2) metastable density in the effluent of the cold atmospheric pressure plasma jet kINPen was investigated as a function of the feed gas humidity, the gas curtain composition, and the distance from the nozzle by means of laser atomic absorption spectroscopy. The filamentary character of the plasma jet was considered as the absorption signals are from single individual events. From the effective lifetime, the quenching coefficient for Ar( 3 P 2) by water was determined. A maximum Ar( 3 P 2) density of (6.0 ± 0.7) × 10 13 cm − 3 was obtained close to the nozzle for a feed gas humidity of 20 ppm. The densities near the nozzle decreased inversely proportional to the water content in the feed gas leveling off at approximately 1 × 10 13 cm − 3 , independently from the gas curtain composition. With the addition of water to the feed gas, the excitation dynamics changed, and the production and lifetime of Ar( 3 P 2) was reduced. The impact of Ar( 3 P 2) on the reactive species composition in the effluent was found to be smaller than within the plasma zone inside the plasma jet device. [ABSTRACT FROM AUTHOR]

The process of water evaporation, although deeply studied, does not enjoy a kinetic description that captures known physics and can be integrated with other detailed processes such as drying of catalytic membranes embedded in vapor-fed devices and chemical reactions in aerosol whose volumes are changing dynamically. In this work, we present a simple, three-step kinetic model for water evaporation that is based on theory and validated by using well-established thermodynamic models of droplet size as a function of time, temperature, and relative humidity as well as data from time-resolved measurements of evaporating droplet size. The kinetic mechanism for evaporation is a combination of two limiting processes occurring in the highly dynamic liquid–vapor interfacial region: direct first order desorption of a single water molecule and desorption resulting from a local fluctuation, described using third order kinetics. The model reproduces data over a range of relative humidities and temperatures only if the interface that separates bulk water from gas phase water has a finite width, consistent with previous experimental and theoretical studies. The influence of droplet cooling during rapid evaporation on the kinetics is discussed; discrepancies between the various models point to the need for additional experimental data to identify their origin. [ABSTRACT FROM AUTHOR]

Bimetallic alloys have attracted considerable attention due to the tunable catalytic activity and selectivity that can be different from those of pure metals. Here, we study the superior catalytic behaviors of the Pt3Ni nanowire (NW) over each individual, Pt and Ni NWs during the reverse Water Gas Shift (rWGS) reaction, using density functional theory. The results show that the promoted rWGS activity by Pt3Ni strongly depends on the ensemble effect (a particular arrangement of active sites introduced by alloying), while the contributions from ligand and strain effects, which are of great importance in electrocatalysis, are rather subtle. As a result, a unique Ni–Pt hybrid ensemble is observed at the 110/111 edge of the Pt3Ni NW, where the synergy between Ni and Pt sites is active enough to stabilize carbon dioxide on the surface readily for the rWGS reaction but moderate enough to allow for the facile removal of carbon monoxide and hydrogenation of hydroxyl species. Our study highlights the importance of the ensemble effect in heterogeneous catalysis of metal alloys, enabling selective binding–tuning and promotion of catalytic activity. [ABSTRACT FROM AUTHOR]

Accurate prediction of water properties in its gas and condensed phases, including the interaction of water with surfaces, is of prime importance for many scientific disciplines. However, accurate simulation of all water properties together within semilocal approximations of the density functional theory possesses great challenges. The Strongly Constrained and Appropriately Normed semilocal density functional, which satisfies 17 known exact constraints and includes the intermediate range van der Waals interaction, performs quite well for different properties of water including the correct energy ordering of isomers. Despite its impressive performance, the energy overestimation for water isomers, ice lattice energies, and volume underestimation for ice are noticeable. However, it is recently shown that [S. Jana et al., J. Chem. Theory Comput. 16(2), 974–987 (2020)] meta-generalized gradient approximations based on the density matrix expansion [i.e., Tao-Mo (TM) and revised TM (revTM)] can achieve quite a good accuracy for the diverse properties of water. In this paper, we assess the performance of the dispersion corrected counterparts of the TM and revTM functionals. It is shown that the dispersion corrected counterparts of both methods are also quite accurate for diverse water properties, especially for the water–solid interactions. Moreover, the extent of accuracy of TM-based functionals is also analyzed from the viewpoint of the density and functional-driven error. Finally, a comparison in the performance of the dispersion corrected functionals is exhibited. It is shown that the "Optimized Power" damping function together with Grimme's D3 correction and revTM functional is in excellent agreement for the water adsorption on carbon nanostructure materials and ice-lattice mismatch problem without deviating accuracy of other water properties compared to its bare functional. [ABSTRACT FROM AUTHOR]

We present a systematic analysis of state-of-the-art polarizable and flexible water models from a many-body perspective, with a specific focus on their ability to represent the Born–Oppenheimer potential energy surface of water from the gas to the liquid phase. Using coupled cluster data in the completed basis set limit as a reference, we examine the accuracy of the polarizable models in reproducing individual many-body contributions to interaction energies and harmonic frequencies of water clusters and compare their performance with that of MB-pol, an explicit many-body model that has been shown to correctly predict the properties of water across the entire phase diagram. Based on these comparisons, we use MB-pol as a reference to analyze the ability of the polarizable models to reproduce the energy landscape of liquid water under ambient conditions. We find that, while correctly reproducing the energetics of minimum-energy structures, the polarizable models examined in this study suffer from inadequate representations of many-body effects for distorted configurations. To investigate the role played by geometry-dependent representations of 1-body charge distributions in reproducing coupled cluster data for both interaction and many-body energies, we introduce a simplified version of MB-pol that adopts fixed atomic charges and demonstrate that the new model retains the same accuracy as the original MB-pol model. Based on the analyses presented in this study, we believe that future developments of both polarizable and explicit many-body models should continue in parallel and would benefit from synergistic efforts aimed at integrating the best aspects of the two theoretical/computational frameworks. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations were performed to study the interfacial behavior of the pure carbon dioxide–water system and a binary 40:60 mol. % gas mixture of (carbon dioxide + methane)–water at the temperatures of 275.15 K and 298.15 K and pressures near 4 MPa for CO2 and up to 10 MPa for methane. The simulations are used to study the dynamic equilibrium of the gases at the water–gas interface, to determine the z-density profiles for the gases and water, and calculate the interfacial tension γ under the different temperature/pressure conditions close to those of the formation of clathrate hydrates of these gases. At the same hydrostatic gas phase pressure, the CO2–water interface has a lower interfacial tension than the CH4–water interface. A greater number of CO2 molecules, as much as three times more than methane at the same pressure, were adsorbed at the interfacial layer, which reflects the stronger electrostatic quadrupolar and van der Waals interactions between CO2 and water molecules at the interface. The water surfaces are covered by less than a monolayer of gas even when the pressure of the system goes near the saturation pressure of CO2. The surface adsorbed molecules are in dynamic equilibrium with the bulk gas and with exchange between the gas and interface regions occurring repeatedly within the timescale of the simulations. The effects of the changes in the CO2–water interfacial tension with external temperature and pressure conditions on the formation of the clathrate hydrates and other CO2 capture and sequestration processes are discussed. [ABSTRACT FROM AUTHOR]

The activity of Pt-Re surfaces was studied for the water-gas shift (WGS) reaction in order to understand how Pt-Re interactions and cluster-support interactions influence activity. The results from these studies were also compared with previous reports of WGS activity on Pt-Re clusters grown on TiO2. Platinum on Re surfaces were prepared by annealing Re films on Pt(111) to form Pt-Re surface alloys, depositing Pt on Re/Pt(111), and depositing Pt on Re clusters supported on highly oriented pyrolytic graphite (HOPG) surfaces. In all cases, the turnover frequency (TOF) for the WGS reaction was higher for Pt with subsurface Re compared to pure Pt. Furthermore, the TOF for 2 ML Pt/TiO2 clusters was greater than that of Pt(111) and 2 ML Pt/HOPG clusters, indicating that the TiO2 support enhances activity for the WGS reaction on Pt. For Pt/TiO2 clusters, a plot of the fraction of perimeter/surface sites as a function of Pt coverage closely follows TOF vs Pt coverage, strongly suggesting that activity occurs at the Pt-TiO2 interface. Notably, the fraction of undercoordinated sites as a function of Pt coverage does not follow the same behavior as the TOFs. [ABSTRACT FROM AUTHOR]

Water–gas flow in heterogeneous porous media is a ubiquitous natural phenomenon. A pore-scale investigation can help to understand the mechanisms of water–gas flow. This study employs a direct simulation method to model the immiscible water–gas flow while tracking the phase interface via the phase-field method. We first verified the mathematical model by layered two-phase flow and capillary intrusion tests. Then, the quartet structure generation set was used to generate a heterogeneous porous media, based on which water–gas displacement was simulated. The characteristics of drainage and imbibition displacements were systematically investigated. Results show that the forced imbibition process shows stable displacement due to cooperative filling, yet with local capillary fingering. Capillary valve effects always exist during the process, making the capillary force act as both driving and resistance forces in heterogeneous porous media. Nevertheless, these pore-scale events inhabit the rapid breakthrough in the small pore-throat zone, ensuring the uniform advancement of the interface. During drainage, viscous fingering in the wide pore-throat zone and capillary fingering in the narrow pore-throat zone are simultaneously observed. Compared with the imbibition process, the water–gas front advances faster due to the smaller viscous force of invading fluid. The phase distribution after drainage displacement at different capillary numbers is quite different due to inconsistent flow patterns. Nevertheless, the final phase saturation of the imbibition process under different capillary numbers is similar, but the area of each type is different. For both the imbibition and drainage processes, the larger the capillary number, the higher the final displacement efficiency. [ABSTRACT FROM AUTHOR]

Manganese (II) oxide (MnO), manganese (IV) oxide (MnO2), cobalt (II,III) oxide (Co3O4), and nickel (II) oxide (NiO) were analyzed with time-of-flight secondary ion mass spectrometry using 70 keV gas cluster ion beams. The obtained mass spectra are influenced by projectile chemistry and to a lesser extent velocity. Gas cluster ion beams containing CO2 or H2O enhanced the relative yield of metal oxide and metal hydroxide secondary ions compared to beams containing only Ar. For all gas cluster ion beams tested, steady-state ion ratios [MxOy]+/[Mx]+ were reached. For manganese oxides, the [MnxOy]+/[Mnx]+ ratio reflected the metal oxidation state whereas the [MnxOyHz]+/[Mnx]+ ion ratios did not. This study demonstrates that secondary ion mass spectrometry using 70 keV gas cluster ion beams provides a novel approach to the quantitative analysis of the surface and subsurface regions of metal oxides related to energy-storage materials. [ABSTRACT FROM AUTHOR]

Although two-phase flows containing gas and water have received extensive attention, the pulsating pressurization effect of a two-phase fluid in a pipe is unclear and the influence of the gas-phase content has not been revealed. This paper discusses the pulsating pressurization of such a two-phase fluid. First, the two-phase Navier–Stokes equations are derived and an algorithm is developed based on MacCormack's method. The reliability of the algorithm is examined and validated using Poiseuille's theory and existing experimental two-phase flow data. Finally, the influence of several key factors is discussed, including the gas-phase fraction and pipe slenderness. Our results show that a significant pulsating supercharging phenomenon occurs when the gas-phase fraction is less than 10−3. When the gas-phase fraction is greater than this critical value, the pulsating supercharging effect decreases significantly with the increasing gas-phase fraction. The equivalent elastic modulus of the two-phase fluid rapidly decreases as the gas-phase fraction increases, and the pressure disturbance is absorbed by the gas bubbles, causing an apparent weakening of the pulsating supercharging effect. Thus, decreasing the gas-phase content can enhance the pulsating supercharging effect. The pipe slenderness has a very limited influence on the pulsating pressurization process, and the maximum reduction is only 7.3% for slenderness ratios of up to 2000. Moreover, we derive and propose a new mathematical expression for the inlet boundary that is applicable to gas–liquid two-phase flows. To our knowledge, this paper extends the pulsating pressurization range from the single-phase to two-phase fluid for the first time and reports different physical phenomena and regularity. The present research clarifies the pulsating pressurization phenomenon in two-phase flows, providing a valuable reference for pulsating pressurization design. [ABSTRACT FROM AUTHOR]

Molecular dynamics (MD) simulations of methane–water mixtures were performed using ab initio force fields for the CH4–H2O, H2O–H2O, and CH4–CH4 interactions. Both methane and water molecules were polarizable. From these calculations, the potential of mean force (PMF) between two methane molecules was extracted. Our results are compared with PMFs from a density-functional-theory (DFT) based Born-Oppenheimer type MD (BOMD) simulation, from a Monte Carlo (MC) simulation with ab initio-based force fields, and from MD simulations with empirical force fields. Our PMF is qualitatively similar to that obtained from the simulations with empirical force fields but differs significantly from those resulting from the DFT-BOMD and MC simulations. The depth of the PMF global minimum obtained in the present work is in a much better agreement with the experimental estimate than the result of the DFT-BOMD simulation, possibly due to the inability of DFT to describe the dispersion interactions and the lack of extensive sampling in the BOMD simulations. Our work indicates that, for a pair of methane molecules, there are configurations where the solvent increases the attraction between the solutes, but there are also conformations in which the solvent causes a weak net repulsion. On average, the methane molecules are more likely to be in the configuration where they are separated by a water molecule than in the one in which they are in contact even though the minimum of the PMF at the latter configuration is deeper than that at the former. Finally, we found that the water structure around methane solutes does not show a greater tetrahedral ordering than in neat bulk water. [ABSTRACT FROM AUTHOR]

This study presents a numerical investigation of the solitary wave breaking over a slope by using the multi-phase smoothed particle hydrodynamics (SPH) method. Four different computational models are proposed to solve the gas-related far-field boundary conditions, and the model with the least disturbance to the internal flow field is selected. Since the artificial viscous coefficient can greatly affect the wave-breaking location, an empirical equation is fitted to quickly determine the optimal value of the artificial viscous coefficient. In addition, the turbulence model and three-dimensional effect on the wave breaking are discussed in this study. The results show that the present two-dimensional multi-phase SPH without a turbulence model can capture the macroscopic characteristics of the flow before the vortices convert to three dimensional flow structures caused by the wave breaking. Then, the processes of shoaling solitary wave breaking with different slopes and relative wave heights are simulated. Compared with the single-phase SPH, the multi-phase SPH is of great help in improving the prediction of wave breaking. A vortex similar to the Rankine Vortex is observed near the wave crest. Its intensity affects the pressure distribution of the gas, and its relative position to the wave crest is relevant to the energy transfer from the water to the gas. During the solitary wave propagating from deep water to shallow water, energy dissipation of gas and water shows four different stages. In the stage of energy dissipation, the gas can absorb the great energy from the water, which effectively dissipates the wave energy. [ABSTRACT FROM AUTHOR]

To reduce the energy dissipation of the submerged water jet, a series of experiments of the submerged water jet wrapped in an annular gas jet are performed under different gas ventilation rates, annular sizes, water jet nozzle diameters, and water jet velocities in a transparent water tank. In the experiments, a ventilated cavity is created by the annular gas jet that encloses the submerged water jet. The submerged water jet is separated from the surrounding water within a certain distance after leaving the nozzle exit by the ventilated cavity, which contributes to the effective working length of the submerged water jet significantly increasing, referring to the energy dissipation decrease. Furthermore, the geometry of the ventilated cavity changes periodically, i.e., the cavity length and diameter decrease after increasing to the peak values in each cycle. Moreover, the ventilated cavity development process can be mainly divided into formation, collapse, and intermission stages. The maximum cavity length of the ventilated cavity decrease with the per unit time momentum ratio between the water jet and the gas jet. Namely, the per unit time momentum ratio between the water jet and the gas jet is the dominating parameter of the cavity geometry. [ABSTRACT FROM AUTHOR]

High voltage nanosecond pulse driven electric discharges in de-ionized water with an argon bubble suspended between two electrodes were experimentally investigated. Two electrode configurations were used to temporally resolve the time scales of the discharge from the applied voltage rise time (7 ns), through the end of the first pulse (∼ 30 ns), and longer (>50 ns). We found that, in positive and negative applied voltage polarities, discharge initiates in the water at the tip of the anode. The discharge in the water rapidly extends (∼ 10 4 m/s) to the apex of the bubble and light emitted from inside the bubble begins to form. The steep rate of rise of the applied voltage (d V / d t < 4 kV/ns) and the short time for the development of discharge in the water suggest that cavitation is a likely mechanism for discharge initiation and propagation in water. In addition, the short duration of the applied voltage pulse results in only a partial Townsend discharge inside the bubble. [ABSTRACT FROM AUTHOR]

We have used the Maxwell–Stefan diffusion theory to model the mass transfer between tertiary-injected gas and residual oil blocked by water, in order to predict the time required for the rupture of the water barrier due to oil swelling. We have also designed and conducted a set of visualization micromodel experiments on various pure and multicomponent oil–gas systems to measure the water rupture time in tertiary gas injection processes. The experimental results show that the initial pressure and dimensions of the system, the oil and gas composition, and the gas solubility in water control the oil swelling process. The experimentally measured rupture times are then employed to evaluate the reliability of the model and to compare its accuracy with that of a similar one using classical Fick's law. Our modeling results show that both models are able to estimate the water rupture time for pure systems with an acceptable precision. As for multicomponent mixtures, however, only the Maxwell–Stefan theory is capable of modeling the molecular diffusion process correctly and yields values close to reality, while the use of Fick's law would lead to erroneous results. Deficiency of the latter model becomes more acute when the diffusion direction in reality is contrary to what the model indicates, which leads to failure in calculating any value for rupture time at all for these cases. [ABSTRACT FROM AUTHOR]

Passive acoustic inversion techniques for measuring gas flux into the water column have the potential to be a powerful tool for the long-term monitoring and quantification of natural marine seeps and anthropogenic emissions. Prior inversion techniques have had limited precision due to lack of constraints on the initial amplitude of a bubble's excitation following its release into the water column ( R ε 0 i ). R ε 0 i is determined by observing the acoustic signal of bubbles released from sediment in a controlled experiment and its use is demonstrated by quantifying the flux from a volcanic CO2 seep offshore Panarea (Italy), improving the precision by 78%. [ABSTRACT FROM AUTHOR]

Composed of methane gas and cage-like water molecules, methane hydrate is expected to have innovative engineering applications, such as gas transportation. In this study, a methane hydrate decomposition interface is visualized qualitatively, and the decomposition rate is discussed. To clarify the decomposition mechanism, consideration is given to the dynamic decomposition interface and the variation of the decomposition rate. In the present experiment, methane hydrate is formed around a water droplet and decomposed by depressurization in the gas phase, the dynamic variation of the decomposition interface is observed precisely using a high-resolution camera, and three different depressurization conditions are used to confirm the interfacial change. It is found that the decomposition rate and dynamic shape change of the decomposition interface depend on the difference between the equilibrium pressure and that of the gas phase. In addition, the decomposition time is discussed using the decomposition model, and it is estimated that the present experimental decomposition rate corresponds to a lower activation energy for decomposition compared with that of the model by other authors. It is assumed that the decomposition proceeds under nearly reaction-limited conditions. Additionally, the interfacial deformation and collapse are observed in the case of pressure reduction near the equilibrium pressure, and validation is provided by a numerical simulation considering the heat and mass transfer near the interface. The numerical results suggest that the decomposition is affected by the interfacial configuration and the nearby temperature and concentration distributions. [ABSTRACT FROM AUTHOR]

An optical gas sensing technique based on in-plane quartz-enhanced photoacoustic spectroscopy (IP-QEPAS) is reported. In IP-QEPAS, the laser beam is aligned in the plane of the quartz tuning fork (QTF) to increase the interaction area between the acoustic wavefront and the QTF. A custom T-shaped QTF with a prong length of 9.4 mm and a resonance frequency of 9.38 kHz was designed and employed in the IP-QEPAS sensor. For comparison, the traditional QEPAS sensor in which the laser beam is perpendicular to the QTF plane (PP-QEPAS) is investigated with the same operating conditions. Theoretical calculations of strain and displacement of the QTF prong were performed to support the advantage of using the IP-QEPAS technique. By selecting water vapor as the gas target, the IP-QEPAS sensor results in a signal more than 40 times higher than that measured with the PP-QEPAS configuration, confirming the potential of this approach. [ABSTRACT FROM AUTHOR]

Near ambient pressure-x-ray photoelectron spectroscopy (NAP-XPS) is a less traditional form of XPS that allows samples to be analyzed at relatively high pressures, i.e., at ca. 2500 Pa, or higher in some cases. With NAP-XPS, XPS can probe moderately volatile liquids, biological samples, porous materials, and/or polymeric materials that outgas significantly. In this submission, we show an NAP-XPS survey spectrum, and also O 1s and C 1s narrow scans, of a commercial soft drink, Coca-Cola. Clearly this is a material that could not be analyzed at moderate pressures by conventional XPS. The C 1s narrow scan is fit to five synthetic components. The O 1s narrow scan shows strong contributions from both liquid and gas phase water. A small N 1s signal in the survey spectrum is attributed to background nitrogen. The shape of the uniqueness plot corresponding to the C 1s fit suggests that the fit parameters are statistically significant. [ABSTRACT FROM AUTHOR]