Surface Water Film Research Articles

Effects of nanoactive fluids on water wettability reversal of shale: Implications for CO2 geo-sequestration

CO2 geo-sequestration (CGS) is crucial in tackling global climate change, and the safety of CO2 storage within the reservoir is intricately linked to wettability. The utilization of nanofluids-surfactants for adjusting reservoirs’ wettability has emerged as a promising approach to enhance the security of CGS. However, the mechanism underlying their impact on reservoir wettability and carbon sequestration remains elusive. Regarding nanoactive fluid (ASNF) compounded with nano-SiO2 and AOS, to explore its potential for wettability reversal of CO2-exposed shale under in situ conditions, comparative experiments were conducted with Longmaxi Formation shale as the subject. The chemical structures and microstructures of shale before and after the experiments were comprehensively characterized. The results showed that a maximum of 67.93 % enhanced the water wettability of samples co-treated with ASNF and ScCO2. The primary reason for shale wettability reversal was increased hydrophilic chemical groups and enhanced interaction energy between organic matter and water molecules, stemming from nanoactive particle retention on the shale surface. The alteration in wettability decreased the mobility of CO2 and increased the distribution of surface water films, enhancing the carbon sequestration capabilities of the trapping mechanism. These findings provided an important foundation for improving the effectiveness and safety of CGS in shale reservoirs.

Elucidating the role of water films on solute diffusion in unsaturated porous media by improved pore‐scale modeling

AbstractSolute diffusion in partially saturated porous media is an important fundamental process in many natural and environmental systems. At low water saturation, the solute transport is governed by the diffusion in thin water films on the surfaces of solids. In this study, we established an improved pore‐scale simulation framework successfully describing the solute diffusion in variably saturated porous media (e.g., soils), which considers the contribution of the diffusion within the thin water film on the surface of the solid matrix. The model takes into account the liquid–gas distribution in the underlying porous media by the Shan‐Chen lattice Boltzmann Method (LBM) and simulates the solute diffusion in the bulk liquid phase and the water film. Based on the numerical results, an easy‐to‐use theoretical formula was also developed to predict the effective diffusivity in microporous materials at low saturation levels. The average relative error of its prediction with respect to the experimental data from the literature is about 30%, while that of the classical power law exceeds 70%. A simple phase diagram was defined, which allows us to identify the situations under which it is necessary to take the influence of surface water films on the effective diffusivity in unsaturated microporous media into account. The present study improves the pore‐scale model to address solute diffusion in the water films at low water saturation and elucidates the contribution of thin water films on solute transport.

Numerical simulation of droplet impingement and film flow for three-dimensional wings

Abstract In order to investigate the three-dimensional effects on the flow characteristics of the thin water film for the three-dimensional wings, the numerical simulation of the droplet impingement and film flow on the MS-0317 wing is implemented based on the open-source package OpenFOAM. The simulation focuses on the effects of the angle-of-attack and the angle of sweepback. The movement and impingement of the droplets are calculated using the Lagrangian method, and the film flow is simulated using the thin film assumption and the finite area method. The simulation of the water film flow of the three-dimensional MS-0317 wing shows that there is a spanwise flow of the water film due to the three-dimensional effects. This suggests that more research should be conducted on the warm glaze ice with surface water film of three-dimensional ice accretion on three-dimensional geometries.

Analysis of temperature characteristics of the plunger pair of the ceramic plunger pump for hemodialysis

Through the design of the ceramic plunger pump for hemodialysis, the mathematical model of the water film of the plunger pair of the ceramic plunger pump was built. The distribution characteristics of the speed and pressure of the water film of the plunger pair were analyzed, and the temperature distribution characteristics of the water film surface were obtained. The effects of inlet pressure, inlet temperature, rotational speed, and chamber temperature on the water film temperature of the plunger pair were studied. Experiments and analysis show that the closer the temperature of the plunger pair is to the inlet of purified water, the smaller the temperature change. The farther the ceramic plunger rod is from the inlet of purified water, the greater the temperature change, and the main influencing points are concentrated inside the plunger pair. Therefore, maintaining a certain amount of purified water temperature, pressure, and flow rate for lubrication is crucial for the service life of ceramic piston pumps.

Molecular-level study of hydrophobic interactions during low-rank coal particle-bubble attachment

Particle-bubble attachment is a crucial part of coal and mineral flotation processes. The attachment of two different hydrophobic low-rank coal particles to bubble surface were simulated by a non-equilibrium molecular simulation method. Both particles were subjected to water film drainage resistance when approaching the bubble. Eventually, CPC (low-rank Coal Particle with mixed Collector adhered) jumped in and attached to bubble, but CP (low-rank Coal Particle) had only repulsive effect with bubble. The surface water film of CPC generated tiny hole under the entropy effect of water molecule rearrangement, and the presence of gas–water and oil–water interfacial tension promoted the rapid expansion of the hole until the water film rupture. The critical rupture thickness of the water film on CPC surface was about 1 nm and the rupture was completed in a very short time of 0.4 ns. The CPC jumped in and attached to the bubble surface under the action of oil–water interfacial tension. This suggests that the long-range hydrophobic force originates from the combined action of various interfacial tensions. Our results demonstrate the important role of interfacial tension in the attachment of hydrophobic particle to bubble, and contribute to the connection between microscopic and macroscopic mechanism of particle-bubble attachment.

Study on the influence mechanism of water reducing agent on the properties of anhydrite-based self-leveling mortar

Gypsum-based self-leveling has been widely used for its good construction performance and economy. This paper investigated the influence mechanisms of three kinds of water-reducing agents (WRAs) on the properties of anhydrite-based self-leveling floor screeds (ASLF) through macroscopic performance characterization, rheological model fitting, TG-DSC, MIP, SEM, et al. The outcomes conducted that the types, densities, and lengths of the side chain groups of the WRAs had diverse effects on the hardening, rheological parameters, and crystal morphology of ASLF. In descending order, the influence was PCE > SMF > SNF. The anionic groups of PCE affected the crystal growth by adsorbing on the dominant surface of CaSO4·2H2O and reducing the crystal length-diameter ratio. Simultaneously, with the increase of PCE content, the steric resistance effect increased, and the thickness of the surface water film layer increased, resulting in a decrease in the final viscosity and yield strength. ASLF is a power-law fluid that fits the Hershel-Bulkle (H-B) model well. Compared with PCE, the hydration and hardening characteristics of ASLF mixed with SMF and SNF were similar, and the influence was smaller, but a larger amount was required to ensure flowability. The pore size distribution of ASLF-hardened bodies mixed with various superplasticizers was similar. The hardening properties of ASLF were investigated using a variety of methods in this study. Various types of WRAs were investigated for their effects on the hydration and hardening of anhydrite, providing important reference information for ASLF preparation and production.

High speed water droplet impact erosive behavior on dry and wet pulsed waterjet treated surfaces

During water droplet impact onto a dry or wet rough solid surface, several phenomena affect the surface erosion process, such as splashing, crown formation, and small droplet emission to name a few. These phenomena have been extensively studied for various simple target surface geometries. However, droplet impact studies on complex irregular and asymmetric target surface topographies resulting from a waterjet treatment have never been conducted. Furthermore, very limited reports are found on the role of target surface topography and water droplet deformation development on the resulting target stress state. In the present study, high speed droplet impingements on surfaces exhibiting coarse topographical features associated with ultrasonic pulsed waterjet treatment are modeled to understand the underlying mechanisms causing erosion. Impacts on surfaces with various roughness values and water film thicknesses are modeled using a three-dimensional coupled Eulerian–Lagrangian approach. A detailed comparative analysis of the model with experimental ultrasonic pulsed waterjet erosion features and material loss is provided. It was found that the synclastic curvature of the modeled coarse surface features increases the shock wave's strength as many compression wavelets are simultaneously emitted at each water droplet contact location with the surface, resulting in concentrated high-pressure zones. The ultrasonic pulsed waterjet treated surface features and water film thickness also greatly influence the onset of water droplet splashing, subsequent finger, secondary droplet characteristics, and crown stability. According to the numerical results, strong splashing patterns and droplet breakup are generated and create high stress zones capable of accelerating surface erosion, explaining the enhanced performance of ultrasonic pulsed waterjet process.

Effect of Composite Bionic Micro-Texture on Bearing Lubrication and Cavitation Characteristics of Slipper Pair

The slipper pair is the crucial friction pair of the seawater axial piston pump. Taking seawater as the working medium will inevitably affect the bearing performance of the slipper pair. In this paper, a seawater axial piston pump slipper pair model with a composite bionic micro-texture of the first-stage circular pit and the second-stage circular ball is established. Using the CFD simulation method, 18 groups of orthogonal tests are designed to explore the effects of seven test factors, such as rotational speed, first-stage diameter, first-stage aspect ratio, second-stage diameter, second-stage aspect ratio, area ratio, and distribution angle, on the bearing characteristics of the water film of the slipper pair. Study whether cavitation can further improve the bearing characteristics of the water film. The research shows that there is a vortex behind the circular pit, and there is a pressure difference in the calculation domain of the water film. The existence of the pressure difference causes the bearing force of the water film surface to increase. The cavitation phenomenon mainly occurs at the divergent wedge behind the circular pit. Among them, the total pressure bearing force of the 5th test group increased by 90% after introducing cavitation effect, and the total pressure bearing force of the 17th test group increased by about 86% compared with other test groups at the same speed. The order of the test factors affecting the water film bearing features is: A (rotational speed) > C (first-stage aspect ratio) > B (first-stage diameter) > E (second-stage aspect ratio) > F (area ratio) > D (second-stage diameter) > G (distribution angle). The optimal model is A6B2C1D3E3F2G3.

Humic Substance Photosensitized Degradation of Phthalate Esters Characterized by 2H and 13C Isotope Fractionation.

The photosensitized transformation of organic chemicals is an important degradation mechanism in natural surface waters, aerosols, and water films on surfaces. Dissolved organic matter including humic-like substances (HS), acting as photosensitizers that participate in electron transfer reactions, can generate a variety of reactive species, such as OH radicals and excited triplet-state HS (3HS*), which promote the degradation of organic compounds. We use phthalate esters, which are important contaminants found in wastewaters, landfills, soils, rivers, lakes, groundwaters, and mine tailings. We use phthalate esters as probes to study the reactivity of HS irradiated with artificial sunlight. Phthalate esters with different side-chain lengths were used as probes for elucidation of reaction mechanisms using 2H and 13C isotope fractionation. Reference experiments with the artificial photosensitizers 4,5,6,7-tetrachloro-2',4',5',7'-tetraiodofluorescein (Rose Bengal), 3-methoxy-acetophenone (3-MAP), and 4-methoxybenzaldehyde (4-MBA) yielded characteristic fractionation factors (-4 ± 1, -4 ± 2, and -4 ± 1‰ for 2H; 0.7 ± 0.2, 1.0 ± 0.4, and 0.8 ± 0.2‰ for 13C), allowing interpretation of reaction mechanisms of humic substances with phthalate esters. The correlation of 2H and 13C fractions can be used diagnostically to determine photosensitized reactions in the environment and to differentiate among biodegradation, hydrolysis, and photosensitized HS reaction.

A new mechanism of the interfacial water film dominating low ice friction.

It is generally accepted that ice is slippery due to an interfacial water film wetting the ice surface. Despite the current progress in research, the mechanism of low ice friction is not clear, and especially little is known about the behavior of this surface water film under shear and how the sheared interfacial water film influences ice friction. In our work, we investigated the ordering and diffusion coefficient of the interfacial water film and the friction of ice sliding on an atomically smooth solid substrate at the atomic level using molecular dynamics simulations. There are two layers of water molecules at the ice-solid interface that exhibit properties very different from bulk ice. The ice-adjacent water layer is ice-like, and the solid-adjacent water layer is liquid-like. This liquid-like layer behaves in the manner of "confined water," with high viscosity while maintaining fluidity, leading to the slipperiness of the ice. Furthermore, we found that the interfacial water exhibits shear thinning behavior, which connects the structure of the interfacial water film to the coefficient of friction of the ice surface. We propose a new ice friction mechanism based on shear thinning that is applicable to this interfacial water film structure.

Influences of Relative Humidity and Dwell Time on Silica/Graphene Adhesion Force of a Cone-Plane Contact.

Graphene has exceptional electronic, mechanical, and thermal properties, and it is expected to have important applications in integrated circuits and other microelectronic fields. Its performances are greatly affected by surface adhesion force when it is used in a humid environment. In this paper, based on the law of variable water contact angle changing in the process of water vapor condensation, we established a cone-plane contact model, which is related to relative humidity and dwell time, to reveal the internal mechanism of the influence of relative humidity and dwell time on silica/graphene adhesion force. First, the silica/graphene adhesion force dependence of dwell time was measured by atomic force microscopy (AFM) at 45-85% RH. Then, the changing process of the meniscus between the AFM tip and the graphene surface was discussed, and the function of adhesion force with variables of dwell time and contact angle was established. Furthermore, the theoretical and experimental results were compared and analyzed. The results show that with the increase of relative humidity and dwell time, the capillary condensation increases, but the water contact angle of the cone material decreases. This causes the adhesion force to increase first and then decrease after it reaches a threshold value. Furthermore, the variable water contact angle of the graphene surface increases, but the adhesion force decreases gradually with the increase of surface water film. The theoretical results are in good agreement with the experimental results.

Impingement and splashing of a supercooled large droplet on a freezing water film

In the present study, we report for the first time the detailed dynamic processes of a supercooled large droplet (SLD) impacting on a freezing water film at different freezing moments. At the beginning of the experiment, the deionized water film was first set to a desired temperature and then triggered to freeze by further cooling. Then, a supercooled large droplet was released to impact the freezing water film at different freezing moments. Its impact and splashing processes were recorded by a high-speed camera. Besides, under room-temperature conditions, the impinging and splashing processes of a water droplet on the water film with different thicknesses were also measured. The results showed that, at the early stage of the water film freezing process, the dendritic ices could be pushed out of the water film surface due to the impact of the supercooled large droplet. Besides, the dendritic ices significantly affected the formation and growth of crowns, which could lead to the earlier crown breaks or the formation of the irregular crowns. Moreover, compared to its counterpart of the room-temperature droplet case, the evolution characteristics of the crown generated by the supercooled large droplet case were significantly different in terms of the crown top diameter, the crown base diameter, the crown height, the crown angle, and the crown lifetime. In addition, the correlations between the number of the secondary droplets and the dimensionless water film thickness were obtained and compared as for the room-temperature droplet cases and the supercooled large droplet cases.

Study on freezing characteristics of the surface water film over glaze ice by using an ultrasonic pulse-echo technique

This study proposes an ultrasonic pulse-echo technique to examine the freezing characteristics of a thin film of water over ice, and uses it to develop a method to measure the thickness of glaze ice. A multilayer model is first introduced to simulate ultrasonic transmission through multiple media. A transition layer is then inserted between the layers of ice and water, and its properties were in gradient form along the direction of thickness. Following this, a high-frequency ultrasonic experimental device is developed to dynamically measure variations in the thickness of the layers of ice and water. The accuracy of the proposed model of the transition layer was validated by showing that its numerical results agreed well with those of experiments. The results show that the amplitude of echo from the top of the ice layer was at its minimum when the thickness of the film of water was in the range of [40, 45] μm, and increased when the film of water was thinner than 40 μm. A delay in echo from the top of the layer of ice was observed when measuring its thickness because the film of water froze, which yielded a relative error of 3.34%. The proposed numerical model can thus efficiently measure the thickness of glaze ice.

Experimental Study on Influences of Self-Preservation Effects and Memory Effects on the Hydrate Decomposition Process

Abstract In order to explore the characteristics of the hydrate decomposition behavior at the pore scale, this study carries out a pore-scale experimental study of methane hydrate decomposition based on the high-pressure visual model under the etched glass. A mathematical model is also constructed to analyze the behavioral characteristic of the self-preservation effect and memory effect during the hydrate decomposition period. This study draws the following conclusions: (1) The self-preservation effect and memory effect exist during the methane hydrate decomposition lead by depressurization, which generally inhibits the hydrate decomposition process. (2) The hydrate self-preservation effect is a transition of the surface water film’s phase state to inhibit the methane hydrate decomposition, in which the liquid phase transforms into a metastable “quasiliquid film”. (3) The multiple syntheses induced by the hydrate memory effect are a periodic attenuation process. The times of synthesis are a critical factor affecting the hydrate gas production and decomposition rate. (4) The self-preservation and memory effects during the hydrate decomposition period are associated with each other. The two are correlated at some degree with playing a dominant role alternately at different stages. The self-preservation effect is an abnormal behavior of the hydrate, which refers to the hydrate’s transition from the solid phase to the gas-liquid mixed phase. The memory effect is another abnormal behavior, which refers to the transition from the gas-liquid mixed phase to the solid phase. The sustaining pressure drop is the key reason of the disappearance of the two effects. This research was aimed at providing a theoretical basis for the exploitation and optimization of marine natural gas hydrates.

Improving laser-EMAT ultrasonic energy conversion efficiency using surface constraint mechanism

To address the problem of low signal-to-noise ratio (SNR) of ultrasonic echo generated by laser-electromagnetic acoustic transducer (EMAT) ultrasonic method in metal materials, a method to improve the energy conversion efficiency of laser-EMAT ultrasonic testing using the surface constraint mechanism is proposed. Based on numerical simulation and experiment, the excitation mechanism of a laser surface heat source with and without a surface constraint mechanism is investigated, and the effect of the water film surface constraint on the laser-EMAT ultrasonic testing echo of different metal materials is analyzed. The effects of laser spot radius, laser power density, laser pulse duration, EMAT design parameters, and water film parameters on the ultrasonic echo amplitude and multimode ultrasonic energy distribution ratio are also investigated, and the optimal combination of laser excitation and EMAT reception parameters is provided. The results show that the laser power density and spot radius significantly affect the multimode ultrasonic amplitudes. Under the water film surface constraint, the energy distributions of shear waves (SWs) and longitudinal waves (LWs) change significantly, and the energy of the SW change rules of different metal materials are different. After using the surface constraint mechanism, the LW amplitude improves significantly, and the SNR of the LW is increased by at least 13.0 dB, the main bang duration is reduced by at least 29.4%, and the main bang amplitude is reduced by more than 80.5%. The relevant information of the surface constraint mechanism provides an effective reference for designing the laser-EMAT testing system with LW detections and reducing the dead zone in ultrasonic testing.

Characteristics of a nanosecond pulsed dielectric barrier plasma actuator with a surface water film

Aircraft icing is one of the most serious hazards for airflight operations. The nanosecond pulsed surface dielectric barrier discharge (NSDBD) plasma actuator is recognized as an extremely promising anti-icing technology. In this paper, a multi-physics coupling simulation is used to study the plasma-discharge characteristics and responses of the air–water flow field generated by an NSDBD plasma actuator with a surface water film. The computational model describes air flows through an NSDBD plasma actuator with a water film at the center of two upper powered electrodes. The multi-physics model is solved using the drift-diffusion and energy-conservation equations for the plasma discharge and the mass, momentum, energy, and concentration equations for the air–water flow. The results show that, at the beginning of the voltage pulse, the surface water film has no effect on the plasma discharge. Then, during the pulse plateau time, the film leads to a longer plasma-discharge time and a larger plasma-discharge region. Furthermore, the film causes the plasma-actuator surface to develop a virtual positive electrode that would otherwise be absent and results in the plasma actuator generating more intense shock waves, higher gas temperatures, and larger heated regions.

Study on surface conductivity distribution of pollution layer during the propagation of local arc on the wet polluted insulation surface

The surface conductivity of the pollution layer plays a pivotal role in the investigation of flashover voltage and the propagating mechanism of the local arc. In order to study the characteristics of the pollution layer, an experimental system is designed in this paper. Ferric chloride is employed as the color indicator for demonstrating the dry state distribution of the pollution layer. Thus, the surface conductivity is calculated by analyzing the red–green–blue value of the pollution layer. In addition, a numerical model for calculating the heat transfer on the surface of the pollution layer is also established. It has been revealed that the dry state distribution of the pollution layer is affected by the leakage current and the speed of the local arc. Moreover, the relationship between the surface conductivity of the pollution layer and the thickness of the surface water film is obtained. The comparative analysis shows that the calculated results are in good agreement with the experimental data.

Non-invasive on-skin sensors for brain machine interfaces with epitaxial graphene

Objective. Brain–machine interfaces are key components for the development of hands-free, brain-controlled devices. Electroencephalogram (EEG) electrodes are particularly attractive for harvesting the neural signals in a non-invasive fashion. Approach. Here, we explore the use of epitaxial graphene (EG) grown on silicon carbide on silicon for detecting the EEG signals with high sensitivity. Main results and significance. This dry and non-invasive approach exhibits a markedly improved skin contact impedance when benchmarked to commercial dry electrodes, as well as superior robustness, allowing prolonged and repeated use also in a highly saline environment. In addition, we report the newly observed phenomenon of surface conditioning of the EG electrodes. The prolonged contact of the EG with the skin electrolytes functionalize the grain boundaries of the graphene, leading to the formation of a thin surface film of water through physisorption and consequently reducing its contact impedance more than three-fold. This effect is primed in highly saline environments, and could be also further tailored as pre-conditioning to enhance the performance and reliability of the EG sensors.

Simple method to detect and to isolate entomopathogenic fungi (Hypocreales) from mosquito larvae

Entomopathogenic fungi are important agents for mosquito vector control. We report on the utility of a simple method to detect fungi on living larvae of Aedes aegypti that had been exposed to a fungal entomopathogen. Four species of the hypocrealean genera Metarhizium, Beauveria, Tolypocladium and Culicinomyces, known for their larvicidal activity against mosquito species, were tested. Living larvae previously exposed to a suspension of different conidial concentrations were set directly into the surface water film on non-nutritive agar supplemented with chloramphenicol, thiabendazole and crystal violet and then incubated. Except for C. clavisporus ARSEF 964 (which developed and produced conidia mostly inside the cadaver rather than on its surface in the present study), this method favored external fungal development and conidiogenesis on larvae of different instars after death. The dead larva on the water agar represents the unique and specific source of nutrition for the fungus that killed it. The technique facilitates the detection and posterior isolation of entomopathogenic fungi, and offers a compact, convenient, and rapid means to survey larval mosquito populations for fungal pathogens at the field.

Analysis of vehicle skidding potential on horizontal curves

High crash rates on horizontal curves during wet weather are a major road safety concern. Among the various causes of crashes on horizontal curves, wet-weather skidding is a major contributing factor. This study analyzed the mechanisms of three possible modes of vehicle skidding on horizontal curves based on theories of mechanics. The three modes of skidding analyzed were: (i) forward skidding of front steering wheel, (ii) sideway skidding of front steering wheel, and (iii) sideway skidding of rear wheel. The main objective was to provide useful information to researchers and practitioners in identifying the important factors that contribute to horizontal curve crashes. A computer simulation procedure was developed to evaluate the maximum safe vehicle speeds against the three modes of skidding on wet horizontal curved pavements. This offers a much improved method for skidding potential evaluation compared to the conventional approximate method using estimated coefficient of friction. The skidding potential of a vehicle is defined as the difference between its speed and the maximum safe speed against skidding. The smaller the difference, the higher is the skidding potential. The relative magnitudes of skidding potential for the three skidding modes were considered for different operating conditions. Different operating conditions were represented by different values of pavement curve radii, super-elevations, and wet-weather conditions represented by the thickness of pavement surface water-film. The analysis identified five key factors that affect the skidding potential of vehicles negotiating a horizontal curve. They are: vehicle speed, curve radius, superelevation, water film thickness and pavement skid resistance state.