Formation Of Water Film Research Articles

Numerical investigation on the thermal-flow performance of humid air-water in the interspace outside staggered tube bundles

A new model was established to investigate the thermal-flow performance of humid air-water in the interspace outside staggered tube bundles. The formation of spray water film, heat and mass transfer process between humid air and spray water including spray water droplets and film were considered in this model. The influence of structure parameters was analyzed for thermal-flow performance of humid air-water in the interspace outside staggered tube bundles. It can be found that to increase the longitudinal and transverse distance between tube bundles can improve the heat transfer performance between spray water and wall of tube bundles, and decrease the pressure drop of humid air-water. But the mass transfer between spray water and humid air will only decrease with the transverse distance between tube bundles. Meanwhile, the relative humidity of humid air is not fully utilized at the top of staggered tube bundles when the transverse distance is more than 20 mm. Otherwise, the spray water will be lost heavily at the 19–24th rows of staggered tube bundles. The row number of staggered tube bundles should be reasonably designed in term of the transverse distance. The new correlations of heat transfer and pressure drop are also obtained in term of the simulation results. The Parker's correlation will be also recommended to design the mass transfer performance of that.

Evaluation on the performance fluctuation after water ingestion for a turbofan engine compressor during flight descent

Turbofan engine compressor is most severely threatened by the entry of liquid water during flight descent. This study aims to deeply understand the fluctuations of compressor performance parameters caused by water ingestion through frequency spectrum analysis. The water content and droplet diameter distribution are determined based on the real heavy rain environment. Results reveal that most of the droplets actually entering the core compressor have a particle size of less than 100 μm. In addition, the formation and motion of water film plays a critical role in affecting the fluctuation characteristics. Water ingestion deteriorates the compression performance and aggravates the unsteady fluctuations of the fan. However, the performance of the core compressor is less affected by water ingestion, but their fluctuations are still exacerbated. For some important parameters, such as inlet mass flow rate, total pressure ratio, total temperature ratio, compression work and efficiency, their main frequency of fluctuation are switched from the original blade passing frequency to the rotor passing frequency, and their amplitudes are correspondingly amplified to varying degrees. These phenomena can be observed in both the fluctuations of the fan and core compressor. Moreover, the operating point of them will be in the long-period and large-amplitude fluctuations, which leads them experiences the non-optimal state for a long time and threatens their operating stability.

Effect of hydraulic and mechanical characteristics of sediment layers on water film formation in submarine landslides

Through two lab-scale experiments, we investigated the hydraulic and mechanical characteristics of sediment layers during water film formation, induced by elevated pore pressure—considered one of the triggers of submarine landslides. These involved (1) sandbox experiments to prove the effect of water films on mass movement in low slope gradients and (2) experiments to observe the effect of the tensile strength of semi-consolidated sediment layers on water film formation. Portland cement was used to mimic the degree of sediment cementation. We observed a clear relationship between the amount of cement and pore pressure during water film formation; pressure evolution and sediment deformation demonstrated the hydraulic and mechanical characteristics. Based on the results of these experiments, conditions of the sediment layers during water film formation are discussed in terms of pore pressure, permeability, tensile strength, overburden pressure, and tectonic stresses. The results indicate that the tensile strength of the sediment interface provides critical information on the lower limit of the water film formation depth, which is related to the scale of potential submarine landslides.

Residue-Assisted Water Layer Build-Up Under Transient Climatic Conditions and Failure Occurrences in Electronics

Electronic devices are exposed to a variety of climatic conditions worldwide. The day/night temperature fluctuations between the device interior and external conditions can lead to the formation of transient conditions within the enclosure that enhances the possibility of water layer build-up on the surface of printed circuit board assembly (PCBA). This article deals with the parametric investigation of the effects assisting the formation of water film on PCBA surfaces under transient climatic conditions, which alters the functionality of electronic devices. The investigated parameters include the external humidity level, PCBA cleanliness, temperature difference between ambient and the PCBA, and the rate of temperature/humidity change. The effect of residues commonly associated with the soldering operations-weak organic acids-on the water film formation was investigated at 25 °C/80%RH under isothermal and nonisothermal conditions. For nonisothermal conditions, the PCBA temperature was reduced to the level slightly above and below the dew point. The impact of external climate on the wetting time of the contaminated PCBA was demonstrated by its exposure to day/night cyclic conditions, and the overall effect on corrosion reliability of the electronic circuit was assessed. A combination of AC impedance and DC leakage current techniques was employed to determine the electrochemical changes of the PCBA surface resulting from the build-up of a conductive water film. The results show that the presence of hygroscopic flux residues increases the water vapor content above the surface, leading to moisture condensation under potentially noncondensing conditions, and results in the corrosion reliability issues.

Plasmonic wooden flower for highly efficient solar vapor generation

Abstract Solar vapor generation has become a promising water purification technology owing to its eco-friendly and energy-saving features. However, it remains as a big challenge to further improve the solar-driven evaporation performance, especially to further increase the efficiency of solar energy utilization. Here, a novel plasmonic wooden flower is fabricated, in which Ag-polydopamine (PDA) core-shell structured nanoparticles (Ag@PDA NPs) are loaded on the wooden flower. The superior structural characteristics of the porous wooden flower and the Ag@PDA NPs provide a synergetic effect. Thus, it exhibits a high light-harvesting absorption of 98.65%. Moreover, the hydrophilic Ag@PDA NPs promote the formation of water films on both sides of the flower petal. Meanwhile, the abundant capillary channels and pinholes in the wood further enhance the heat convection and solar-driven evaporation of the water films on both sides of the petal. With the excellent thermal management performance, the plasmonic wooden flower device has a high vapor generation rate of 2.08 kg m−2 h−1 and an ultrahigh solar-to-vapor efficiency of 97.0% under 1 sun illumination, among the best values reported in the literature. It is promising for future water treatment applications in large scale including recovery of metal ions, brine desalination and sewage purification.

Effect of particle concentration on the tribological properties of NBR sealing pairs under contaminated water lubrication conditions

The abrasive wear behavior of elastomers has attracted a lot of attention and interest in order to better comprehend its effect on the service performance of the fluid sealing pairs. The objective of this work was to study the tribological performance of the fluid sealing pairs under various abrasive concentration conditions. Therefore, this study developed an abrasive wear test experiment for an acrylonitrile–butadiene rubber (NBR) cylinder against 316L stainless steel plate tribo-pairs to evaluate reciprocating sliding tests under different particle concentrations.Results demonstrate that the abrasives feature strong aggressivity, which impedes the formation of a good friction-reduction water film, results in weak lubrication, changes the friction coefficient and wear rate, and deteriorates the tribological performance of the tribo-pairs. The friction coefficients of the low abrasive concentration are relatively small, and the friction coefficient increases with increasing abrasive concentration.At different abrasive concentrations and sizes, the rubber matrix is attacked in various forms by the hard particles, which appear as pinning, particle agglomeration embedment, and abrasive flow erosion. Particle concentration affects the damage behavior of the tribo-pairs, and the particles easily enter the interface of the tribo-pairs when their concentration is high.

Monitoring analysis of two pavement sections of highway BR-448/RS included in the Asphalt Thematic Network Project

Highways are the mode of transport used for the transportation of the majority of loads and passengers in Brazil; however, the lack of conservation of pavements has caused several economical losses to the country. Only through suitable pavement management the rehabilitation measures taken might ensure a satisfactory level of service. The present research aimed at evaluating the performance of two pavement sections of the federal highway BR-448/RS, in southern Brazil. For three years, the evolution of the pavement structural capacity and functional condition were followed in order to propose performance trends. Deflections, permanent deformations, and surface defects surveys scarcely varied and were quite low due to the thick asphalt layers used (19 cm). On the other hand, segregation of the asphalt mixture was observed when the final layer was laid. That segregation affected pavement texture, reduced tire-road friction, and caused the formation of surface water films; thus, reducing the road safety. In general, the proposed trend lines predicted quite accurately the pavement performance throughout the period evaluated and will be used in the MeDiNa software database for the creation of a new Brazilian pavement design method.

Numerical simulation of the effect of rain on aerodynamic performance and aeroacoustic mechanism of an airfoil via a two-phase flow approach

In the present study, two complex physical phenomena have been completely simulated and discussed in detail to predict the aerodynamic degradation and aeroacoustic mechanism of a NACA 0012 airfoil in both dry and heavy rain conditions. For this purpose, a CFD-based multiphase model was adopted to numerically investigate the process of formation of the water film layer on the airfoil surface by coupling the Lagrangian Discrete Phase Model (DPM) and the Eulerian Volume of Fluid (VOF) models. The Ffowcs Williams–Hawkings (FW–H) method was used to predict the aerodynamic noise of the airfoil in a heavy rain condition. The results showed that there were significant degradations of the airfoil aerodynamic performance because of water film formation especially at lower angles of attack. The maximum value of lift-to-drag ratio degradation was 56% at the angle of attack of 2°. Also, the Sound Pressure Level (SPL) increased due to the rain condition. The SPL was sensitive to the raindrop impact on airfoil surface and caused to increase SPL especially in the frequency region less than 2000 Hz. By increasing the angle of attack, the SPL increased especially in the high-frequency region higher than 2500 Hz in rain condition.

Numerical Investigation on the Effect of Dry and Wet Compression on a Linear Low Speed Compressor Cascade

Several techniques are implemented to reduce the temperature rise in multistage compressors, which leads to the noticeable improvement in specific power output of a gas turbine. The objective of the present investigation intends to understand the effect of incidence angles on the aerodynamic performance of the compressor cascade under wet compression. Using large eddy simulations (LES) the effects of wet compression on compressor flow separation and wake formation are investigated. Experimental investigation was performed to validate the numerical results. The study reveals notable flow modifications in the separated flow region under the influence of wet compression and the total loss coefficient reduces significantly at the downstream side of the compressor for positive incidence angles. On the other hand, for negative incidence angles the wet compression enhances the total pressure losses inside the blade passage. Also, in the present investigation, particular emphasis has been given to understand the water film formation at negative and positive incidence angles.

Experimental study on the mixing characteristics inside an inner preheating transpiring-wall reactor for supercritical water oxidation

The mixing characteristics between bulk flows and transpiring water are critical to feed degradation and water film formation inside a transpiring-wall reactor (TWR). In this study, a supercritical water oxidation system with an inner preheating TWR is established, and special experiments are designed by adding organic matter (glycerol) to the transpiring water to evaluate the mixing degree between the bulk flows and transpiring water in the hydrothermal flame zone. Although the chemical oxygen demand concentration of the reactor effluent increases significantly due to the addition of glycerol to the transpiring water, a certain amount of glycerol is entrapped into the flame zone and degraded. The increase in jet velocity with increased heat source flow or temperature is favorable for mixing and enhances jet entrainment. Moreover, increasing the transpiring coefficient and transpiring water temperature can increase the radial velocity of transpiring water, which also benefits mixing. Possible applications utilizing the mixing characteristics are further proposed.

Numerically Simulating the Formation and Motion of Water Films and Erosion-Hazardous Droplets in Flow-Through Parts of Steam Turbines

A model for the process of coarse liquid particle formation in the flow-through parts of steam turbines is considered. A numerical approach is proposed to describe the formation and development of a water film on the surface of the interblade channels, and the main factors affecting the distribution of the film parameters along the curvilinear walls of the blades are presented. It is assumed that the only source of the water film is represented by liquid-phase particles deposited on the blade surfaces. The process of film detachment from the exit edge of the blade together with its subsequent destruction and the formation of large erosion-hazardous droplets is considered. The developed model has been integrated into the earlier proposed numerical approach to the description of the motion of liquid-phase particles and their interaction with solid surfaces. At the same time, an amendment has been introduced therein taking into account the presence of a water film when a liquid phase particle collides with a solid wall. The developed numerical method makes it possible to describe all the main gas-dynamic processes occurring in the course of motion for erosion-hazardous droplets in the interblade channels. This method has been tested using experimental studies on streaming wet-steam flow in a flat nozzle grating at different initial humidity of the working medium. Using the laser flux diagnostics system, velocities and sizes inherent in droplets beyond the grating along its spacing have been determined. The developed model provides a good agreement of these parameters with the experimental data in the places of the maximum concentration of coarse droplets. However, there is a significant discrepancy for some areas of the flow in the obtained results concerning the velocity distribution. The effect that the initial steam moisture exert on the characteristics of the water film on the blade surface is considered. It is established that the film thickness significantly affects the interaction between the droplets and the blade surface in the areas wherein the collision energy is small. These areas are characterized by a large angle between the velocity vector of the projectile droplet and that normal to the surface at the collision site.

Transport, retention, and release of Escherichia coli and Rhodococcus erythropolis through dry natural soils as affected by water repellency

Microbial transport in soil affects pathogen retention, colonization, and innoculant delivery in bioremediating agricultural soils. Various bacteria strains residing in the fluid phases of soils are potential contaminants affecting human health. We measured the transport of hydrophilic Escherichia coli (E. coli) and hydrophobic Rhodococcus erythropolis (R. erythropolis) bacteria through initially air-dried wettable or water-repellent soil columns to understand the effect of water repellency and the hydrophobicity of the organism on its retention, release, and transport properties. Bacteria suspensions infiltrated the top of the columns under saturated (0 cm) and unsaturated (−5 cm) flows in the air-dried (pulse 1) and rewetting (pulse 2) conditions. Cells were recovered from the leachates and the soil extracts by the viable counts. Wettable soil efficiently retained both hydrophobic and hydrophilic bacteria (>80%) in initial air-dried conditions (pulse 1). Even after rewetting, and the formation and expansion of water films and corresponding reduction of the air-water interfacial area (pulse 2), few bacteria were released (maximum 31.5% and 10.1% for saturated and unsaturated flows, respectively), whereas more cells were released from the water-repellent counterpart (more that 72%). The smaller size of hydrophobic R. erythropolis made cell transport possible within the thinner water films of both soils compared to hydrophilic E. coli through pulses 1 and 2. The shape of each strain's retention profiles was uniform and exponential as influenced by soil, strain, and water flow conditions. The results suggest that hydrophobic bacteria will disperse readily when leached into initially dry soil, while hydrophilic bacteria are more susceptible to leaching, posing a risk of pathogen contamination. Clearly the wettability of soil and organisms affects fate and transport.

Effect of sulfate ions on oil detachment from calcite surface: experiments and molecular dynamics simulations

To investigate the influence of sulfate ions in low-salinity waterflooding of carbonate reservoirs, we combined the physical experiments and molecular dynamic simulations. Contact angle experiments results showed that there is an optional salinity during the low-salinity waterflooding of carbonate reservoirs. Moreover, the sulfate ions have a significant effect on core wettability. Based on the experiments results, we conducted molecular dynamic simulations to explore the reaction mechanism in molecular scale. Results showed that under the dispersion force and the electrostatic interaction, the oil molecules migrate to the calcite surface and array in two layers, and form the oil-wet surface. The detachment of oil from calcite surface can be divided into two steps: the formation of water channel under electrostatic interaction; the formation of water film under H-bonding interaction. As a result, the calcite surface will alter from oil-wet to water-wet. Results shows that the sulfate ions participate in the electrostatic interaction and H-bonding interaction, accelerate the formation of water channel and water film, and accelerate the oil detachment from calcite surface.

Shale gas transport in wedged nanopores with water films

With the consideration of a mobile high-viscosity water film and a bulk water layer, an analytical model is proposed to predict gas flow behaviors and gas apparent permeability in nanopores. Physical molecular forces are analyzed to determine the properties and formation of the high-viscosity water film and the bulk water layer. Boundary conditions at a solid-liquid interface and a liquid-gas interface are modified to account for water slippage and gas slip. How mobile bulk water molecules influence gas transport capability in pores of different geometry is investigated with different pore sizes and pressure for the whole range of water saturation, which has been validated with experimental data and simulation results. Besides, the effect of a wedged pore structure on multiphase flow behaviors is also investigated to figure out the influences of pore shape.

Thin water films covering oxide nanomaterials: Stability issues and influences on materials processing

Abstract

Effect of Surface Hydrophilicity on the Desulfurization Performance of ZnO/SiO2 Composite

Two kinds of ZnO/SiO2 composite (labled as SZ-1 and SZ-2) were synthesized by sol–gel method and characterized by X-ray diffraction (XRD) patterns, XPS (X-ray photoelectron spectroscopy) spectra and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectra. Water adsorption on the prepared sample was studied by in situ DRIFT. The as-synthesized SZ-1 and SZ-2 sample have different surface property due to the various aging methods in the sample preparation processes, thus showing different results of water adsorption. The adsorption sites (Si atom in Si–O–Si bond) on the surface of SZ-2 for water molecule are occupied by the –OCH3 group and the hydrophilicity of SZ-2 is weaker, in comparison to SZ-1, which inhibits the formation of water film and ultimately decreases desulfurization performance of SZ-2. So, the desulfurization performance can be changed by altering the hydrophilicity of sorbent.

An experimental investigation of dynamic ice accretion process on a wind turbine airfoil model considering various icing conditions

In the present study, the dynamic ice accretion process over a typical wind turbine airfoil model (i.e., DU96-W-180 airfoil) was experimentally investigated under various icing conditions. The experimental study was conducted in the Icing Research Tunnel of Iowa State University (i.e., ISU-IRT). Different icing conditions (i.e., rime, mixed and glaze) that wind turbine may experience in winter were reproduced by manipulating the airflow temperature, velocity, and liquid water content (LWC) in ISU-IRT. While a high-speed imaging system was used to reveal the dynamic ice accretion process over the surface of the test model, an infrared (IR) thermal imaging system was used to map the corresponding temperature distributions over the ice accreting airfoil surface. Time variations of the ice thickness accreted along the leading edge (LE) of the test model were extracted based on the acquired high-resolution images of the ice accretion process under different test conditions. It was found that, due to the obvious runback of the impacted water (i.e., formation of water film and rivulets) over the airfoil surface, the growth rate of the ice layer accreted along the airfoil leading edge was much slower under the glaze icing condition, in comparison with those under the rime and mixed icing conditions. Such surface water transport behavior was also found to expand the ice influencing region. From the temperature evolutions during the dynamic icing processes, the transient processes of droplet impingement, water film/rivulets formation, and ice roughness growth were temporally resolved, providing comprehensive details of the unsteady heat transfer during the dynamic icing process. While the surface temperature increment due to the direct droplet impingement was found to decrease monotonously along the chord in rime case, a stream-wise ‘plateau’ region was observed in the glaze and mixed icing cases due to the complex multiphase mass/heat transfer associated with the surface water transport behaviors.

Optimization of structural parameters of an inner preheating transpiring-wall SCWO reactor

A computational fluid dynamics model of an inner preheating transpiring wall reactor for supercritical water oxidation was proposed to optimize the structural parameters. Results showed that higher feed degradation efficiencies and lower inner surface temperatures of the porous wall were obtained at higher reactor diameters. Although the increase in reactor length promoted feed degradation, the increased inner surface temperatures of the porous wall were unsuitable for water film formation. A pyknic-type reactor with a lower length/diameter (H/D) value at a constant volume was more beneficial for water film formation and feed degradation. A higher feed concentration or feed flow required a lower H/D value to ensure an ideal water film formation and feed degradation. We proposed the use of sectional heat load as a new parameter for reactor design based on the similarity between the boiler furnace and the transpiring wall reactor. The sectional heat load in a certain range was calculated to serve as guide in the design of transpiring wall reactors.

Method and numerical simulation for evaluating the effects of water film on the performance of low-speed axial compressor

Numerical simulations for a low-speed axial compressor under water ingestion are performed to evaluate the aerodynamic performance degradation due to the formation of water film. The water film thickness on a blade surface is calculated by a self-compiled program developed by the authors. In addition, the blade surface is divided into several regions, which can be roughened separately, to elucidate the characteristics of the nonuniform water film. The equivalent sand roughness corresponding to the root-mean-square water film thickness are specified for the blade surface to simulate the aerodynamic losses of the blade row caused by water deposition. The results show that the water film thickness is positively correlated with the water content, and negatively correlated with the compressor outlet pressure. The overall compression performance presents a downtrend after water ingestion. When the water content increased from 0.37% to 4.02%, the compression efficiency deteriorated by 1%–3% compared with the dry condition. The distribution of the static pressure coefficient on the blade surface is also changed, wherein the deviation degree at the tip region is greater than that at the hub region. Unfortunately, considering the limitations of the current water film models and computational methods, the water film formed on the tip region cannot be simulated. Therefore, the calculated results near the stall point are different from the experimental results. However, rough surface treatment can still be considered as a feasible method for evaluating the effects of water film on compressor performance.

Effect of Solder Mask Surface Chemistry and Morphology on the Water Layer Formation Under Humid Conditions

This paper investigates the water film buildup on solder masked printed circuit board assembly (PCBA) laminates under humid conditions. The effects of solder mask surface chemistry, morphology, and roughness were investigated using different commercial laminates coated with solder mask. Chemical composition of the materials was analyzed using Fourier transform infrared spectroscopy. Microstructure and surface morphology were investigated using scanning electron microscopy, whereas the wettability was assessed using static contact angle technique, and correlated with the morphological observations. Solder mask surface waviness was characterized and quantified using a mechanical stylus profilometer. The formation of water film on a PCBA surface was monitored in situ by optical microscopy and electrochemical impedance spectroscopy and correlated with the observations of surface features. The results show that the solder mask surface chemistry and morphology significantly influence the water film formation, which is important for corrosion reliability of electronics exposed to humid conditions.