Calculated Film Thickness Research Articles

A quantitative research of water distribution characteristics inside shale and clay nanopores

Understanding the fluid distribution characteristics inside nanopores are of great significance to evaluate shale gas reservoirs. In this work, the quantitative evaluations for water saturation distribution of porous shale and clay are performed by experiments. The experimental results show that the capillary condensation is remarkable for clay pores during the process of water adsorption, the pores less than 6.76 nm would be blocked by the capillary water when the relative humidity is approximate to 0.98; moreover, the inorganic pore is hydrophilic while the organic pore is hydrophobic, the coupled effect make less water uptake inside shale sample. Meanwhile, a mathematic model for studying the effect of pore shape on water adsorption is established based on the difference of morphology characteristics between organic and inorganic pore. The results indicate that the slit pore is better similar with the actual condition, and the calculated film thickness and water saturation is more coincide with the measured value. Thus, the slit pore is more appropriate than the circular pores for studying the water uptake characteristic of shale. Our work lays the foundations for better understanding and evaluating the fluids occurrence pattern and gas generation mechanism of different pores in shale reservoir.

Measurement and calculation of oil film thickness in a ball bearing

PurposeThe oil film thickness provides a key performance indicator of a ball bearing lubrication condition. This paper aims to propose an approach to calculate and measure the oil film thickness of the bearing.Design/methodology/approachOn a specially designed test rig, measurement of the capacitance is used to monitor the oil film thickness of ball bearing. A corrected film thickness formula taking account of the influences of non-Newtonian shear thinning and thermal is introduced to predict the oil film thickness of ball bearing. And then the film thickness distribution and the corresponding capacitances are calculated.FindingsMeasurement and calculation of oil film thickness in a ball bearing are carried out under various rotating speeds and external loads. By comparing the calculated capacitances with measured results, it can be concluded that the calculated results obtained by the amended film thickness formula are much closer to the test findings than the classical computed values according to Hamrock–Dowson.Originality/valueA new corrected film thickness formula is introduced in predicting oil film thickness of ball bearing and verified by the series of experiments according to capacitance method.

Superlubricity of 1-Ethyl-3-methylimidazolium trifluoromethanesulfonate Ionic Liquid Induced by Tribochemical Reactions.

The robust liquid superlubricity of a room-temperature ionic liquid induced by tribochemical reactions is explored in this study. Here, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate ([EMIM]TFS) could realize stable superlubricity (μ < 0.01) with water at the interfaces of Si3N4/SiO2. A superlow and steady friction coefficient of 0.002-0.004 could be achieved under neutral conditions (pH of 6.9 ± 0.1) after 600 s of running-in process. Various factors that could affect superlubricity were explored, including concentration of [EMIM]TFS, sliding speed, applied load, and volume of the lubricant. The results reveal that superlubricity can be achieved with [EMIM]TFS aqueous solution under a broad scope of conditions. The results of surface analysis show that a steady composite tribochemical layer comprising [EMIM]TFS, silica, ammonia-containing compounds, and sulfides was formed by tribochemical reactions between [EMIM]TFS and Si3N4 during the running-in period. The film thickness calculation reveals that the achieved superlubricity is in a mixed lubrication regime that comprises boundary lubrication and thin film lubrication. The superlubricity state is governed by a firm composite tribochemical layer, a molecular adsorption layer (electric double layer of [EMIM]TFS), and a fluid layer. The liquid superlubricity achieved by the ionic liquid is helpful for the development of new ionic liquids with superlubricity characteristics and is of great significance for scientific understanding as well as engineering applications.

Liquid Superlubricity of Polyethylene Glycol Aqueous Solution Achieved with Boric Acid Additive.

Boric acid is a weak acid and has been used as a lubrication additive because of its special structure. In this study, we report that boric acid could achieve a robust superlubricity (μ < 0.01) as an additive in polyethylene glycol (PEG) aqueous solution at the Si3N4/SiO2 interfaces. The superlow and steady friction coefficient of approximately 0.004-0.006 could be achieved with boric acid under neutral conditions (pH of approximately 6.4), which is different from the acidic conditions leading to superlubricity. The influence of various factors, including boric acid concentration, sliding speed, applied load, PEG molecular weight, and the volume of lubricant on the superlubricity, were investigated. The results reveal that the PEG aqueous solution with the boric acid additive could achieve superlubricity under a wide range of conditions. The surface composition analysis shows that the synergy effect between boric acid and PEG provides sufficient H+ ions to realize the running-in process. Moreover, a composite tribochemical film composed of silica and ammonia-containing compounds were formed on the ball surface, contributing to the superlubricity. The film thickness calculation shows that superlubricity was achieved in a mixed lubrication region, and therefore, the superlubricity state was dominated by both the composite tribochemical film formed via the tribochemical reaction on the contact surfaces and the hydrodynamic lubricating film between the contact surfaces. Such a liquid superlubricity achieved under neutral conditions is of importance for both scientific understanding and engineering applications.

The Effect of Lubrication on the Vibration of Roller Bearings

Proper lubrication is crucial to ensure smooth operation in machineries. In rolling bearing, the improper lubrication may induce high friction and vibration level due to metal to metal contact between the rolling elements. In this study, the roller bearings with and without lubrication are investigated. the natural surface degradation of the roller bearing is monitored and the surface roughness is measured for the lubricant film thickness calculation. the film thickness is determined by the Hamrock-Dowson equation which showed that the grease lubricated bearing operated under the elastro-hydrodynamic lubrication, with the ratio of lubrication film thickness to the surface roughness of λ in the range of 0.9 to 3.65. the un-lubricated bearing was damaged after 20 minutes whereas the grease lubricated bearing continued to operate for 6600 minutes. the observation under microscope showed that the surface underwent smoothening process where the surface roughness decreases initially (running-in state) followed by roughening at the steady state where the surface roughness increases. At damage, the value of λ = 0.9 can be associated with the high level of the bearing vibration. the increase of vibration level becomes rapid at the critical value of λ = 1.6. As such the overall vibration level of the bearing can be related to the surface degradation and low film thickness.

Effect of a SiO₂ Anti-reflection Layer on the Optoelectronic Properties of Germanium Metal-semiconductor-metal Photodetectors

The interdigitated germanium (Ge) metal-semiconductor-metal (MSM) photodetectors (PDs) with and without an SiO₂ anti-reflection (AR) layer was fabricated, and the effect of SiO₂ AR layer on their optoelectronic response properties were investigated in detail. The lowest reflectance of 15.6% at the wavelength of 1550 nm was obtained with a SiO₂ AR layer with a thickness of 260 nm, which was in a good agreement with theoretically calculated film thickness for minimizing the reflection of Ge surface. The Ge MSM PD with 260 nm-thick SiO₂ AR layer exhibited enhanced device performance with the maximum values of responsivity of 0.65 A/W, the quantum efficiency of 52.2%, and the detectivity of 2.49 × 10SUP9/SUP cm HzSUP0.5/SUPWSUP-1/SUP under the light illumination with a wavelength of 1550 nm. Moreover, timedependent switching analysis of Ge MSM PD with 260 nm- thick SiO₂ AR layer showed highest on/off ratio with excellent stability and reproducibility. All this investigation implies that 260 nm-thick SiO₂ AR layer, which is effective in the reduction in the reflection of Ge surface, has a great potential for Ge based optoelectronic devices.

Quantitative Elastohydrodynamic Film-Forming for an Oil/Refrigerant System

The first calculations of film thickness for an oil/refrigerant system using quantitative elastohydrodynamics are reported in this work. It is demonstrated that primary measurements of the properties of the oil/refrigerant system can be employed to accurately predict film thickness in concentrated contacts. An unusual response to lubricant inlet temperature is revealed, wherein the film thickness may increase with temperature as a result of decreasing refrigerant solubility in oil when the inlet pressure is high. There is competition between the reduction in viscosity of the oil and the reduction of refrigerant concentration with increased temperature. For high inlet pressure, the dilution effect is dominant, whereas for low inlet pressure, the temperature dependence of the viscosity of the solution dominates over the range of inlet temperatures considered. It seems that only central film thicknesses have been experimentally measured for oil/refrigerant systems leaving these calculations as the only means of assessing the minimum.

Calculation of the film flowing over horizontal tube surface

Hydrodynamic processes taking place during the motion of liquid droplets and the formation of a liquid film flowing over surface of a horizontal tube are considered. Mathematical modelling of motion of two-phase medium is based on the Lagrangian approach. The results of numerical calculations of the liquid film thickness over surface of the tube are presented.

Development of a fully integrated falling film microreactor for gas–liquid–solid biotransformation with surface immobilized O2‐dependent enzyme

Microstructured flow reactors are powerful tools for the development of multiphase biocatalytic transformations. To expand their current application also to O2 -dependent enzymatic conversions, we have implemented a fully integrated falling film microreactor that provides controllable countercurrent gas-liquid phase contacting in a multi-channel microstructured reaction plate. Advanced non-invasive optical sensing is applied to measure liquid-phase oxygen concentrations in both in- and out-flow as well as directly in the microchannels (width: 600 μm; depth: 200 μm). Protein-surface interactions are designed for direct immobilization of catalyst on microchannel walls. Target enzyme (here: d-amino acid oxidase) is fused to the positively charged mini-protein Zbasic2 and the channel surface contains a negatively charged γ-Al2 O3 wash-coat layer. Non-covalent wall attachment of the chimeric Zbasic2 _oxidase resulted in fully reversible enzyme immobilization with fairly uniform surface coverage and near complete retention of biological activity. The falling film at different gas and liquid flow rates as well as reactor inclination angles was shown to be mostly wavy laminar. The calculated film thickness was in the range 0.5-1.3 × 10(-4) m. Direct O2 concentration measurements at the channel surface demonstrated that the liquid side mass transfer coefficient (KL ) for O2 governed the overall gas/liquid/solid mass transfer and that the O2 transfer rate (≥0.75 mM · s(-1) ) vastly exceeded the maximum enzymatic reaction rate in a wide range of conditions. A value of 7.5 (±0.5) s(-1) was determined for the overall mass transfer coefficient KL a, comprising a KL of about 7 × 10(-5) m · s(-1) and a specific surface area of up to 10(5) m(-1) . Biotechnol. Bioeng. 2016;113: 1862-1872. © 2016 Wiley Periodicals, Inc.

Lubrication film thickness calculation from contact resistance measurement in point contact

Purpose– The purpose of this study is to solve this problem. Different lubrication states play a huge role in friction, wear and service life of parts. To ensure the reliability and power of the internal combustion engine, it is necessary to ensure that the friction pair has been in the best lubrication state. One of the key problems of lubrication state and transformation characteristics is to achieve real-time measurement of lubrication state.Design/methodology/approach– Previous studies show that the contact resistance method is very effective in the qualitative analysis of lubrication state test. The circuit is simple and does not require expensive test equipment. But this method could not accurately reflect the film thickness ratio. Through a combination of experimental and theoretical analysis methods, the limitation of the contact resistance method could be overcome.Findings– The relationship between the point contact film-thickness ratio and contact resistance was established, then the film-thickness ratio could be obtained through the contact resistance, thus providing the basis for determining the point contact lubrication state.Research limitations/implications– According to existing research, the lubrication state of the friction pair mainly was determined through two methods, the friction coefficient and film-thickness ratio. But there are limitations on either using Stribeck curves or optical interference methods. The method used in this paper not only provides a verified way of design theory and model, but is also beneficial to the formation of a new design theory.Originality/value– A new real-time measurement method of lubrication state based on contact resistance is established and its practicability and veracity are verified by series experiments.

蒸发式冷凝器传热传质数值模拟研究

采用VOF法，建立二维水蒸气传热传质顺流和逆流的计算模型，计算所得的平均液膜厚度模拟值比实验测量值大3.03%~6.90%，比Nusselt理论的预测值大8.33%~10.34%，在合理的误差范围，说明该模型切实可行。运用该模型计算并分析水与空气顺流和逆流过程中，液态水的流动分布、空气与水流速度分布以及空气中水蒸气的质量含量分布情况，结果表明：在气–液两相逆流过程的气–液界面的总传热量中，潜热传热量所占比值在90%以上，比气–液两相顺流时高，在气–液相界面处是以水蒸发传质引起的潜热换热为主、温差引起的显热传热为辅的换热形式，逆流比顺流更有利于传热。 The VOF (volume of fluid) method is used to establish a two-dimensional water vapor heat and mass transfer parallel flow and counter flow model. The deviation of calculated film thickness, which is changed with Re values, is greater than the experimental measurement’s value by 3.03% - 6.90%, and the predicted value of the Nusselt theory by 8.33% - 10.34%; it indicates that the model is feasible. The model is used to calculate and analyze liquid water flow distribution, air and water quality and velocity distribution, water vapor quality content distribution in the air, in water and air’s parallel flow and counter flow processes. The results show that: in gas-liquid two- phase counter flow process, the ratio of latent heat transfer rate in total heat transfer rate is above 90% at gas-liquid interface, higher than that of gas-liquid two-phase parallel flow; at air-liquid interface, the main heat transfer is latent heat transfer caused by water’s evaporation and mass transfer, and the supplemented heat transfer is sensible heat transfer caused by temperature difference; counter flow is more conducive to heat transfer than parallel flow.

A framework for characterizing RAP clustering in asphalt concrete mixtures

Recycled Asphalt Pavement (RAP) is commonly used in asphalt for road rehabilitation or new constructions. Nevertheless, some physical and chemical phenomena that occur during production, laying and compaction of mixtures containing RAP are not yet completely explored. One of the main aspects is represented by the interaction between the aged bitumen from RAP and the virgin bitumen added to the mixture as well as the creation of clusters among small-size RAP particles. In this paper several combinations of mixtures are studied, varying the amount of RAP, the type of new binder and the testing temperature in order to obtain a suitable data set for the development of a framework for characterizing clustering of RAP during mixing hot recycled asphalt concrete based on the parameters mentioned above. For analyzing the experiments, the Response Surface Methodology (RSM) was applied. The set of points (combinations tested) for calibration of the models was selected using the Dohelert network, which is a design optimization strategy that allows the effective estimation of the models coefficients. The agglomeration of RAP particles is investigated for all virgin binders used and for all the percentages of RAP. It was shown that the quantity and the quality of virgin aggregates play a significant role in the clusters formation. Moreover, this experimental work suggested that revised formula for the calculation of the bitumen film thickness is needed, in order to include the combined effect of bitumen penetration and fabrication temperature.

Quantitative elastohydrodynamic film forming for a gear oil with complex shear-thinning

Perhaps the most thorough characterization of the elevated pressure properties of any commercial EHL lubricant is presented here for a gear oil. Compressibility, thermal conductivity, and low-shear viscosity were measured. Of particular interest is the shear dependence of viscosity, measured across four decades of stress, which shows two transitions each with a specific value of power-law exponent. An attempt to capture a suspected third transition at very high stress resulted in mechanical degradation of the liquid in the viscometer. Numerical simulations of a point contact between a steel ball and a glass disc showed good agreement over a range of slide-to-roll ratio for the measured central thickness. The agreement for the minimum thickness was excellent. A new result is that shear-thinning of a higher molecular weight component that occurs from 3 to 200 kPa had little effect on the film thickness and could therefore be neglected in a film thickness calculation.

Repassivation behaviour of 316L stainless steels using new type of abrading electrode technique

In this paper, a novel electrode abrading technique is designed to improve the conventional methods. By employing the new depassivation method, 316L stainless steel has been tested in 0.05M H2SO4 solution with and without chloride ion. The repassivation kinetics has been analysed in terms of the current density flowing through the abraded surface bare metal surfaces. The results are described by the linear relationship of log i(t) versus log t. At potentials within the passive region, the passive film grew according to the high field ion conduction model in which log i(t) is linearly proportional to 1/q(t). The repassivation process was analysed in three stages according to different kinetics. The effect of applied potential and chloride ion concentration on repassivation kinetics was also discussed, and the change of calculated film thickness is more sensitive to applied potential than chloride ion concentration.

Surface and interfacial interactions of multilayer graphitic structures with local environment

In order to exploit the potential of graphene in next-generation devices, such as supercapacitors, rechargeable batteries, displays and ultrathin sensors, it is crucial to understand the solvent interactions with the graphene surface and interlayers, especially where the latter may be in competition with the former, in the medium of application deployment. In this report, we combine quartz crystal microbalance (QCM) and ultrasonic force microscopy methods to investigate the changes in the film–substrate and film–environment interfaces of graphene and graphene oxide films, produced by diverse scalable routes, in both polar (deionised water) and non-polar (dodecane) liquid and vapour environments. In polar liquid environments, we observe nanobubble adsorption/desorption on the graphene film corresponding to a surface coverage of up to 20%. As no comparable behaviour is observed for non-polar environment, we conclude that nanobubble formation is directly due to the hydrophobic nature of graphene with direct consequences for electrode structures immersed in electrolyte solutions. The amount of water adsorbed by the graphene films was found to vary considerably from 0.012 monolayers of water per monolayer of reduced graphene oxide to 0.231 monolayers of water per monolayer of carbon diffusion growth graphene. This is supported by direct nanomechanical mapping of the films immersed in water where an increased variation of local stiffness suggests water propagation within the film and/or between the film and substrate. Transferred film thickness calculations performed for QCM, atomic force microscopy topography and optical transmission measurements, returns results an order of magnitude larger (46±1 layers) than Raman spectroscopy (1 - 2 graphene layers) on pristine pre-transferred films due to contamination during transfer and possible turbostratic structures of large areas.

NUMERICAL AND EXPERIMENTAL STUDY OF SPRAY COATING USING AIR-ASSISTED HIGH-PRESSURE ATOMIZERS

Airless and Air-assisted Airless spray guns are widely used in the spray painting industry. The present contribution summarizes ongoing investigations on the spray painting processes of these two atomizers using real paint material. Atomization processes under airless and air-assisted conditions were experimentally studied by measuring droplet size distributions and droplet velocities using a Spraytec Fraunhofer type particle sizer and Laser-Doppler Anemometry. A computational fluid dynamics code was applied to calculate the flow field and the droplet trajectories. The measured and calculated film thickness distributions on the substrate were compared. The experimental and simulation results provided the necessary information for understanding the painting process using airless and air-assisted systems and for improving the performance of these atomizers.

Diagrams for Analysis of Film Units

Diagrams are proposed for determination of film-flow regimes of water along pipe walls, and for calculation of film thickness and pressure losses during ascent of a parallel-current flow. The question concerning the driving force for absorption in parallel- and counter-current flow regimes is examined.

Binder distribution model for asphalt mixtures based on packing of the primary structure

Film thickness describes the coating around aggregate particles on asphalt mixtures. The standard method of calculating film thickness has proven to present several limitations, such as assuming an average thickness independent of particle size, being completely independent to the porosity of the mixture and considering only one mineral type. In this paper, a binder distribution model is developed for aggregates according to size and role in the structure. The aggregates are separated into two different structures: primary structure, the load bearing one, and secondary structure, smaller material that provides stability to the skeleton. A coating thickness for these two structures is calculated from a geometrical consideration that includes the packing arrangement of particles and the effect of overlapping as the film grows. The results were compared with known rutting performance of field mixtures and moisture conditioned laboratory mixtures, showing a good correlation between film thickness and resistance to failure.

Oscillatory and steady shear viscosity: The Cox–Merz rule, superposition, and application to EHL friction

The new quantitative approach to elastohydrodynamic lubrication requires a description of the steady shear dependent viscosity for calculations of film thickness and friction. This property can be obtained from measurements in pressurized thin-film Couette viscometers. However, frequency dependent viscosity can be obtained from a torsionally vibrating quartz crystal viscometer at high pressure or a relatively simple ambient pressure measurement with a shear impedance spectrometer. Here it is shown for squalane and for a cyclic hydrocarbon and for a diester that both the steady shear dependent viscosity and the frequency dependent viscosity obey time-temperature-pressure superposition with the simplest shifting rule over the range of conditions investigated. Flow curves shift along a constant steady stress path or a constant complex modulus path. The Cox–Merz rule has been confirmed only for squalane and then only near the transition. The EHL friction for squalane at low pressure may be predicted with fair accuracy from the frequency dependent viscosity measured at ambient pressure. It appears that the Cox–Merz rule only applies to low-molecular-weight liquids when the molecule is composed of a long chain.

Measurement of Oil Film Pressure on Running Continuously Variable Transmission Pulley - Part 2: Oil Film Thickness Calculation Based on EHL Theory

Measurement of Oil Film Pressure on Running Continuously Variable Transmission Pulley - Part 2: Oil Film Thickness Calculation Based on EHL Theory