Presence Of Water Film Research Articles

Effect of aqueous layer thickness on nano-scratching of single-crystal γ-TiAl alloys

ABSTRACT The study of nano-scratching under water lubrication is helpful to understand the role of lubrication mechanism in the machining of single crystal γ-TiAl alloy. In this paper, through the comparative analysis of nano-scratching under different thicknesses of water layers, it was found that under a water layer thickness of 1 nm, nano-scratching not only improves the surface quality but also achieves multiple reductions in scratch force, stress, temperature and subsurface structural damage. In order to deeply reveal the internal mechanism of workpiece temperature variation under different thicknesses of water layer lubrication, a fitting formula was innovatively adopted to conduct quantitative analysis. In addition, with the increase of the thickness of the water layer, it was observed that the water film effect was continuously enhanced, and this change caused the matrix stress to gradually increase, which hindered the forward motion of the nanoscratch, ultimately resulting in an increase in the friction coefficient. These findings provide valuable insights into the nanoscratching mechanism of monocrystalline γ-TiAl alloy in the presence of water film, and provide a new perspective for understanding the complex mechanism of nanoscratch behaviour under water lubrication, thus promoting the understanding of nanoscale lubrication effects.

Smoothed particle hydrodynamics based numerical study of hydroplaning considering permeability characteristics of runway surface

The presence of water films on a runway surface presents a risk to the landing of aircraft. The tire of the aircraft is separated from the runway due to a hydrodynamic force exerted through the water film, a phenomenon called hydroplaning. Although a lot of numerical investigations into hydroplaning have been conducted, only a few have considered the impact of the runway permeability. Hence, computational problems, such as excessive distortion and computing efficiency decay, may arise with such numerical models when dealing with the thin water film. This paper presents a numerical model comprising of the tire, water film, and the interaction with the runway, applying a mathematical model using the smoothed particle hydrodynamics and finite element (SPH-FE) algorithm. The material properties and geometric features of the tire model were included in the model framework and water film thicknesses from 0.75 mm to 7.5 mm were used in the numerical simulation. Furthermore, this work investigated the impacts of both surface texture and the runway permeability. The interaction between tire rubber and the rough runway was analyzed in terms of frictional force between the two bodies. The SPH-FE model was validated with an empirical equation proposed by the National Aeronautics and Space Administration (NASA). Then the computational efficiency of the model was compared with the traditional coupled Eulerian-Lagrangian (CEL) algorithm. Based on the SPH-FE model, four types of the runway (Flat, SMA-13, AC-13, and OGFC-13) were discussed. The simulation of the asphalt runway shows that the SMA-13, AC-13, and OGFC-13 do not present a hydroplaning risk when the runway permeability coefficient exceeds 6%.

Pore-scale modelling of water sorption in nanopore systems of shale

Water vapor sorption in nanoporous media with complex pore structures, like shale, is not well understood. To address this, a pseudopotential lattice Boltzmann method (LBM) is developed to investigate water sorption behavior. The LBM model incorporates long-range molecular forces using a modified Shan-Chen model based on the Carnahan-Starling equation of state. The simulation results show that the presence of water films in nanopores can create a liquid pressure difference of up to 100 MPa between confined and free states. The adsorption theories based on simple pore shapes are not applicable to nanoporous systems with complex pore geometries. Additionally, when the relative humidity exceeds 1, water vapor condenses inside hydrophobic nanostructures while being attracted by neighboring liquid, leading to cluster formation. In water-wet nanoporous media, capillary condensation occurs progressively from small throats to large pores, and the sorption curves vary smoothly with pressure variation. In mixed-wet nanoporous media, the sorption curves exhibit no hysteresis in the early desorption stage, where the adsorption and desorption processes occur in the region around the hydrophobic particles and are reversible. Overall, this study provides valuable insights into water sorption behavior in nanopore systems of shale and sets the foundation for modelling liquid-vapor distribution in nanoporous media at the pore scale.

Process intensification of Tetrabromobisphenol S removal with a bubble-film hybrid plasma reactor

In order to improve the efficiency of removal of organic contaminants in wastewater treatment, a bubble-film hybrid plasma reactor has been designed in this study. Both the generation and mass transfer processes of active species can be intensified with the presence of water film. On one hand, the water film makes streamer discharge and surface dielectric barrier discharge initiated simultaneously, which reduces the initiation voltage and increases the intensity of electric discharge, and then improves the production efficiency of active species. On the other hand, the water film expands the plasma-water interface, which improves the utilization efficiency of active species by enhancing the mass transfer process. The results show that, benefiting from the water film, the maximum yield of active species can be increased by over 80%, and the efficiency of gas–liquid mass transfer can be improved by over 20%. For the initial Tetrabromobisphenol S (TBBPS) concentration of 0.5 mg/L, the time needed to get a nearly 100% removal is about 1 min at the discharge voltage of 12.8 kV. This time increases with the increase in TBBPS concentration, and increases to 9 min for 50 mg/L. The maximum energy efficiency is 700 mg/kWh and decreases with the increase in discharge voltage.The results demonstrate that the bubble-film multistage process is of great significance to the enhancement of removal of organic pollutants in wastewater with plasma.

Semi-convertible Hydrogel Enabled Photoresponsive Lubrication

Summary A semi-convertible hydrogel with reversible photoresponsive supramolecular lubricating ability is demonstrated by integrating a responsive supramolecular system of α-cyclodextrins/polyethylene glycol (α-CD/PEG) and competitive guest 1-[p-(phenylazo)benzyl]pyridinium bromide (AzoPB) within a poly(vinyl alcohol) (PVA) and polyacrylamide (PAAm) framework. The competitive host-guest interaction between α-CD/PEG supramolecular network and AzoPB after UV and visible-light irradiation enables the appearance and disappearance of the sol-state layer on the hydrogel surface while the PVA and PAAm consistently keeps the framework. This semi-convertible process realizes the reversible photoresponsive lubricating ability and variable toughness. We envision that this finding will offer a possible way for fabricating novel smart devices far beyond lubrication, leading to an emerging branch of interdisciplinary materials science that integrates supramolecular chemistry, hydrogel, and surface science.

The influence of transient evaporation and geometric characteristics on shale gas transmission in inorganic nanopores

Transient evaporation characteristics of water film in inorganic nanopores play an important role in the shale gas storage and transmission. Meanwhile, Inorganic nanopores in shale minerals exhibit complex geometric characteristics. In this work, TESCAN MAIA3 is used to observe the pore shape and size of inorganic nanopores. The pore shapes of rectangular or wedge-shaped are frequently occurred in inorganic nanopores. Water distribution characteristic influenced by surface wettability and disjoining pressure in slit-like nanopores is then analyzed in detail. We divide the water film attached to the surface of the inorganic nanopores into two layers: the high-viscosity water film and the bulk water film. The Moving Mesh Method is used to simulate the evaporation of water film and a mass flow prediction model synthetically considering the pore shape, evaporation, water film slip and layering is established in a single inorganic nanopore. Based on this model, the influence of four different parameters including pressure gradient, water-methane diffusivity coefficient, pore size and wedging coefficient on the shale gas production are investigated. The results show that the presence of water film and its evaporation have significant influence on the production of shale gas. This phenomenon can be interpreted by the increase of pore size caused by evaporation. However, the water film slip and layering have little effect on the shale gas flow rate. With the increase of pressure gradient, the mass flow rate increases significantly. The water-methane diffusion has a considerable influence on the time to reach the steady state. Lower wedging coefficient and larger pore size contribute to higher mass flow rate. Meanwhile, as the wedging coefficient increases from 1.0 to 1.8, the contribution of evaporation increases from 39.34% to 45.33%. Generally, the effective migration space of shale gas directly determines the amount of gas production.

Effect of different polar organic compounds on wettability of calcite surfaces

The average oil recovery by conventional water flooding from oil-wet and naturally fractured carbonate reservoirs is often less than 30%. Removal of adsorbed acidic components and/or asphaltene from the carbonate surface results in wettability alteration towards water-wet which is an effective approach to enhance oil recovery. Long chain fatty acids, long chain naphthenic acids and asphaltene are major components in crude oil which are responsible for wettability alteration in carbonate reservoirs while unsaturated acids have minor effect. In this study, a more accurate quantification of the effects of different types and structures of polar components that contribute to the initial oil-wetting extent of the reservoir rocks were used (aliphatic saturated acids, aliphatic unsaturated acids, naphthenic acids, aromatic acids and asphaltene). Different analytical tools (contact angle, zeta potential, Fourier transform infrared spectroscopy and thermal analysis) were utilized for all acids in order to study surface characteristics. The results indicated that polar organic compounds act in different ways according to their structure and properties. Presence of double bond could make the acid molecule more polar, reactive and less hydrophobic. In addition, it can affect the spatial arrangement of the molecule and hence its orientation on the surface. Presence of benzene ring increases the reactivity and polarity of carboxylic group. Moreover, it enhances hydrophilic properties of the acid due to electrons of π double bonds that can resonate over aromatic carbon atoms. The results revealed that, in the presence of water film, combination of acid dissociation in water, surface activity of acid and water solubility controls the acid adsorption and hence wettability alteration of the surface during aging process. Chemisorption of carboxylic acids/asphaltene changes the wettability of calcite surface. In addition to chemical adsorption, some acids adsorb physically on the surface. Physical adsorption of polar compounds may happen via hydrogen bonding between carboxylic groups and carbonate ions on the surface. Although physical adsorption is reversible and forms weak bonds between adsorbate and adsorbent, it may partially contribute to wettability alteration.

Three dimensional accurate morphology measurements of polystyrene standard particles on silicon substrate by electron tomography

Polystyrene latex (PSL) nanoparticle (NP) sample is one of the most widely used standard materials. It is used for calibration of particle counters and particle size measurement tools. It has been reported that the measured NP sizes by various methods, such as Differential Mobility Analysis, dynamic light scattering (DLS), optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM), differ from each other. Deformation of PSL NPs on mica substrate has been reported in AFM measurements: the lateral width of PSL NPs is smaller than their vertical height. To provide a reliable calibration standard, the deformation must be measured by a method that can reliably visualize the entire three dimensional (3D) shape of the PSL NPs. Here we present a method for detailed measurement of PSL NP 3D shape by means of electron tomography in a transmission electron microscope. The observed shape of the PSL NPs with 100nm and 50nm diameter were not spherical, but squished in direction perpendicular to the support substrate by about 7.4% and 12.1%, respectively. The high difference in surface energy of the PSL NPs and that of substrate together with their low Young modulus appear to explain the squishing of the NPs without presence of water film.

Three Dimensional Accurate Morphology Measurements of Polystyrene Standard Particles on Silicon Substrate by Electron Tomography

Polystyrene latex (PSL) nanoparticle (NP) sample is one of the most widely used standard materials. It is used for calibration of particle counters and particle size measurement tools. It has been reported that the measured NP sizes by various methods, such as Differential Mobility Analysis, dynamic light scattering (DLS), optical microscopy (OM), scanning electron microscopy (SEM) and atomic force microscopy (AFM), differ from each other. Deformation of PSL NPs on mica substrate has been reported in AFM measurements: the lateral width of PSL NPs is smaller than their vertical height. To provide a reliable calibration standard, the deformation must be measured by a method that can reliably visualize the entire three dimensional (3D) shape of the PSL NPs. Here we present a method for detailed measurement of PSL NP 3D shape by means of electron tomography in a transmission electron microscope. The observed shape of the PSL NPs with 100 nm and 50 nm diameter were not spherical, but squished in direction perpendicular to the support substrate by about 7.4% and 12.1%, respectively. The high difference in surface energy of the PSL NPs and that of substrate together with their low Young modulus appear to explain the squishing of the NPs without presence of water film.

Parameters affecting wedge disc brake performance

A new wedge disc brake is introduced in the last few years to increase brake shoe factor. The present work is conducted to investigate the frictional properties of commercial brake pad materials. Several tests have been carried out to examine the effect of the presence of water film, oil film and wet dust between the disc and brake pads on the performance of classical and wedge disc brakes. The results showed that the presence of water film between brake pads and disc increases friction coefficient, thereby increasing the brake shoe factor. This effect is significant in the case of wedge disc brake. The presence of oil film between the friction surfaces remarkably reduces the coefficient of friction; hence, there is a reduction in the brake shoe factor. However, at high applied loads, the presence of wet dust between friction surfaces has a negligible effect.

Controls over ozone deposition to a high elevation subalpine forest

Ecosystem level ozone (O 3) fluxes during four different years were examined at a subalpine forest site in the Colorado Rocky Mountains. The local mountain–valley wind system and the proximity of the Denver Metropolitan area leads to high summertime ozone episodes on many afternoons. The timing between these episodes and the ecosystem processes controlling photosynthesis during the growing season plays a critical role in determining the amount of ozone deposition. Light and vapor pressure deficit (VPD) were the most dominant environmental drivers controlling the deposition of O 3 at this site through their influence on stomatal conductance. 81% of the daytime O 3 uptake was predicted to occur through the stomata. Stomatal uptake decreased at high VPD and temperatures leading to an overall decrease in O 3 flux; however, we did observe a non-stomatal conductance for O 3 that increased slightly with temperature before leveling off at higher values. During the growing season, O 3 deposition fluxes were enhanced after midday precipitation events and continued at elevated levels throughout the following night, implying a role for surface wetness. From nighttime data, evidence for both the presence of water films on the needles and non-closure of the plant stomata were observed. During the winter (non-growing) season, the ozone deposition velocity showed a consistent dependency on the latent heat flux. Although the mechanism is unclear, it is apparent that precipitation events play a role here through their influence on latent heat flux.

Multicomponent mass transfer across water films during hydrocarbon gas injection

Understanding the dynamics of pore-scale multicomponent gas and oil mass transfer across water films during hydrocarbon gas injection in petroleum reservoirs is important in the design of tertiary oil recovery schemes at the field scale. The water films prevent oil and gas coming into direct contact and, for miscible gas injection, delay the onset of miscibility. We use a pore-scale model to describe the diffusion-controlled mass transfer through the water films. The following different processes are found: (i) rapid oil swelling which results in short times needed to rupture the water films shielding the oil, (ii) slow oil swelling resulting in very long water film rupture times and (iii) both oil swelling and oil shrinking. The rate of oil recovery and the way it is recovered (either by rupturing the water film or being vaporized into the displacing gas) is critically dependent upon the oil and gas compositions, the oil droplet size and the water film thickness. We show cases at the pore scale where the time for gas and oil to be brought into direct contact and reach equilibrium in the presence of water films during miscible gas displacement is so long that water-blocking will adversely affect oil recovery at the field scale.

Effects of water films and sliding speed on the frictional behavior of truck disc brake materials

Friction materials for car and truck disc brake pads are typically complex composites containing metals, ceramics, and polymers that are designed to provide stable frictional performance over a range of vehicle operating conditions, exhibit acceptable wear life, and produce minimal noise and vibration. Despite the fact that brakes must operate under a variety of environmental conditions, most standardized and developmental laboratory tests for brake materials are conducted under dry sliding conditions. Studies of wet braking behavior are rare in the tribology literature. The present work investigated the frictional behavior of commercial truck brake pad materials sliding on gray cast iron simulated brake discs in the presence of water films. An instrumented sub-scale testing machine equipped with a water spray was used. There was a significant effect of water films on reducing pad/disc friction compared with dry tests on the same materials and at the same sliding speeds. The friction coefficient under water spray conditions was inversely proportional to the square of the sliding speed. The reduction of friction with increasing speed was principally due to hydrodynamic effects, although the water spray also reduced frictional heating and changed the nature of the transfer film formation on the cast iron contact surface. Frictional recovery occurred within seconds after the water spray was removed.

THE INFLUENCE OF N-ALKANES ON WETTABILITY DF LOW COAL RANKS

Abstract Contact angle measurements were carried out in coal / n-alkanes film - air bubble - water systems. Then theoretical an analysis of the equilibrium state of that system was carried out on the basis of the components of the surface free energy of coal of various ranks. The contact angles were measured for four ranks of Polish coal which surfaces were covered with n-alkanes film in the homological series from n-hexane to n-hexadecane. On the basis of the studies and calculations carried out we have concluded that the values of the contact angle depend on the rank of coal, a thickness of n-alkane film and its structure and the presence of water film under the air bubble. It was also found that the changes of the- values of the contact angles measured in the mentioned sytems as a function of the number of contacted air bubbles were similar to those calculated on the basis of the solution of Young equation in function of the surface free energy of coals precovered with n-alkane film.

Absolute power factor of air capacitors

In this investigation seven air capacitors of different types of construction were studied. In the preliminary tests it was determined that the power factor was independent of the voltage stress and that it varied with the separation of the plates. The results of these studies led to the development of a method of determining the absolute power factor of an air capacitor. In addition, data are presented on the effects produced by the degree of polish of the electrode surfaces, by the width of the gap between the measuring electrode and its guard ring, and by the presence of water films on the plates.

Absolute power factor of air capacitors

STANDARD air capacitors are used with measuring equipment of high sensitivity for comparison with test capacitors in investigations such as the study of dielectric materials; therefore the absolute power factor of the standard should be known. In the investigation reported in this paper, <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">∗</sup> seven air capacitors of different types of construction were studied. A method of determining the absolute power factor of an air capacitor was developed, and data were obtained on the effects produced by the degree of polish of the electrode surfaces, by the width of gap between the measuring electrode and its guard ring, and by the presence of water films on the plates.