Thin Water Film Research Articles

Experimental and CFD simulation of interactions between water droplets with different surface features to understand water droplet erosion

Water droplet erosion (WDE) has received considerable attention in recent years. Different approaches have been proposed to understand WDE and find lasting solutions. Among them is understanding the interaction between the droplet impacts and the target surface, especially at the erosion initiation stage. For this reason, we studied the interactions between water droplets and different surface features to understand WDE. These surface features included flat smooth surfaces and grooved and porous samples. For the grooved samples, depths of 1.0 and 0.5 mm were studied and their WDE performance was evaluated. The 0.5 mm groove showed a longer incubation period than the flat reference sample. This work suggested that a thin water film is formed in the groove, which aids in dampening the impacts of subsequent water droplets. However, the maximum erosion rate is not affected by introducing these grooves. The WDE performance of the porous samples is better than that of the solid material. This is because the porous structure dissipates the impact energy of the water droplets. The simulation results were in agreement with the experimental observations in this work. Furthermore, the simulation showed that the water droplet impacting patterns on different surface features are attributed to the effect of radial and axial airflows.

Pore-scale modelling of elastic properties in hydrate-bearing sediments using 4-D synchrotron radiation imaging

Gas hydrate contains abundant methane gas, which is considered to be a promising energy resource to mitigate the influence of climate change in the future. Understanding the effect of fluids-solid-hydrate spatial distribution on elastic properties of hydrate-bearing sediments benefits the well-log interpretation. We constructed 4-D hydrate-bearing models covering a wide hydrate saturation range based on high-resolution digital images obtained by Synchrotron Radiation X-Rays Computed Tomography (SRXCT). We analysed the elastic moduli and elastic wave velocities of these models by the static Finite Element Method (FEM). The results demonstrated that the dominant hydrate morphology transits from pore-filling to load-bearing when hydrate saturation increases. At low hydrate saturations, the hydrate formed around some gas bubbles blocks local pore space. Therefore a great enhancement in compressional wave velocity was observed at low hydrate saturations. While the shear wave velocity was less affected due to the presence of thin water films. Based on the simulated results, an empirical model was developed to compute the compressional and shear wave velocities considering the free gas phase. The comparison with some experimental measurements validated the applicability of the model.

A new species, Cricotopus cataractaenostocicola, living in a cyanobacterial colony on vertical rocky substrates with trickling water film in Japan (Diptera: Chironomidae).

Trickling water on nearly vertical rocky substrates is a common feature of mountainous regions of Japan. The thin water film is inhabited by discoid colonies of the cyanobacteria Nostoc. This species resembles the North American Nostoc parmelioides Ktzing, which forms ear-like colonies in stream beds and is inhabited by symbiotic chironomid larvae. The Nostoc colony in Japan was inhabited by a chironomid larva inside a ring-shaped burrow in the colony. Morphological analyses suggested that these individuals belong to a new species closely related to Cricotopus spp. symbiotic with Nostoc parmelioides. Here, we described the chironomid species Cricotopus cataractaenostocicola sp. nov. The species was distinguished from other congeneric species mainly by the morphology of male hypopygia. It has an anal point and long setae on the outside of the gonocoxite, and does not have setae near the apex of the inner lobe in the gonocoxite. Almost all the Nostoc colonies contained one large larva or pupa. The outer layer of the chironomid-symbiotic Nostoc colony had an elastic hardness. The 3D computer tomography (3DCT) scan showed a connected network of internal passages that are sufficiently wide to be traversed by the larvae, suggesting that cavities are present for the larvae to pass through. Future studies should investigate the formation of cavities and their purpose. As pioneers in the observation of living organisms using 3DCT, we provided the CT data to the Natural History Museum in Vienna.

Archaeal lipids in soils and sediments: Water impact and consequences for microbial carbon sequestration

The mineral protection of microbial necromass is critical for soil carbon stabilization. The water impact on the interactions between minerals and microbial necromass, however, remains unclear due to a lack of proper methods to quantify the mineral-protected microbial necromass. Here, we used offline hydrous pyrolysis to release the archaeal necromass—isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) bound to clay minerals by heating samples at increasing temperatures (150, 200, 250, 300, and 350 °C) under argon atmosphere. The content of extractable isoGDGTs in soils reached the maximum at 200–250 °C, indicating the release of bound isoGDGTs. By investigating the free and bound isoGDGTs along a soil transect with increasing soil water content (SWC), we found that the portion of bound isoGDGTs reached up to 97% of total isoGDGTs in dry soils, and decreased with increased SWC, suggesting that SWC controls isoGDGT stabilization on clay minerals. This relationship was confirmed in the soils from the Northeast China Transect, where the proportion of bound isoGDGTs decreased with increased mean annual precipitation from 160 to 814 mm. Such a connection was further supported by the water-saturated samples of the lake and marine sediments, which have a much lower proportion of bound lipids than the soils. The decrease of bound lipid portion with increasing water content is related to the lower attachment of microbial cells to minerals in wetter soils. Microbial cells are more strongly attached to the mineral phase under drier conditions due to the thin water film on the mineral surfaces. In addition, microorganisms secrete more extracellular polymeric substances under drier conditions, which reinforces the interactions between microbial-derived organic matter and minerals. The increased microbe-mineral interactions under drier conditions offer more stable microbial legacies and stabilize organic matter in the (semi)arid regions.

The forgotten world of subaerial desmids (Zygnematophyceae) in the Atlantic Forest, southeast Brazil

Although desmids (Zygnematophyceae) are widely distributed, their diversity in subaerial environments remains little known and explored. Subaerial algae live above the soil in a thin water film, directly exposed to the air. Desmids possess specific strategies to face environmental stress, such as mucilaginous sheaths that enable them to adhere to the substrate and protect the cells against desiccation. Also, zygospore production may be a strategy to survive. We conducted a taxonomic survey of the subaerial desmids in the Atlantic Forest biome (Rio de Janeiro city and other municipalities in the state of Rio de Janeiro). Briefly, we analyzed their strategies to resist sudden environmental changes, especially desiccation, a common condition in this environment. From 2006 through 2008, 100 samples were taken from natural and artificial vertical wet surfaces and tree bark. The material collected was identified based on morphological and metric characteristics of the vegetative and reproductive phases of the life cycle. We identified 57 species, varieties, and taxonomic formae, distributed in 12 genera, 2 orders, and 4 families. The study revealed that most subaerial algae were previously reported for Europe and North and South America. From the total taxa, 12% are reported for the first time for Brazil and 14% for South America. Even though subaerial environments are subject to stressful conditions, only three of the 57 taxa showed adaptive structures such as thick mucilage envelopes, spores, or zygospores.

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.

Molecular simulation on CO2 adsorption in partially water-saturated kaolinite nanopores in relation to carbon geological sequestration

CO2 geological sequestration in depleted gas/oil reservoirs is regarded as a promising strategy to mitigate CO2 emission thanks to the well-developed nanoscale pore structures providing substantial adsorption spaces. Therefore, the fundamental understanding of CO2 adsorption in shale nanopores can provide important insights into geological CO2 sequestration. In this work, we use molecular dynamics (MD) and Grand canonical Monte Carlo (GCMC) simulations to investigate CO2 adsorption in kaolinite nanopores with two different basal surfaces and study moisture effect. In the absence of water, CO2 presents stronger adsorption in gibbsite nanopores than siloxane nanopores. In gibbsite pores, water tends to spread over the surfaces forming thin water films. While CO2 is driven to the middle of the pore, an enrichment of CO2 is observed at the water-CO2 interface. On the other hand, water bridges form in siloxane pores. In siloxane mesopores, the shape of water clusters gradually turns to be spherical ones as pressure increases suggesting a more CO2-wet surface, while the deformation of water clusters in micropores is not obvious due to stronger confinement effects. The CO2 distributions in siloxane mesopores can be divided into six zones. The highest CO2 density appears in the three-phase contact areas, while CO2 has a high tendency to accumulate in two-phase contact areas. In general, the presence of water results in the reduction of CO2 adsorption in both gibbsite and siloxane pores. Overall, water has a more detrimental influence on CO2 adsorption in gibbsite pores than siloxane pores. Our work should provide important insights into CO2 adsorption in kaolinite nanopores and reveal CO2 adsorption mechanisms in the presence of water.

Hanging glacier avalanche (Raunthigad–Rishiganga) and debris flow disaster on 7 February 2021, Uttarakhand, India: a preliminary assessment

A catastrophic debris flow in the Rishiganga and Dhauliganga rivers in Uttarakhand, India, on 7 February 2021 left a trail of disaster. Around 100–150 people lost their lives according to Uttarakhand Chief Secretary statement given to ANI news portal, two hydropower projects were badly damaged and a bridge across the Rishiganga River was washed off in the event. Study shows that the debris flow is caused due to detachment of 0.59 km2 right lobe of a hanging glacier and resultant ice-rock avalanche. This right lobe of the glacier was located over a mountain slope having an average slope of 35° at 4700–5555 m a.s.l. and travelled 12.4 km before hitting the infrastructure projects. Role of precipitation, snow cover, land surface temperature, and permafrost processes were investigated for identifying causes of the event. Since 2012, monsoon precipitation and mean annual land surface temperature (LST) showed significant increasing trend. Snow cover during monsoon months showed increasing trend and September, October and November experienced decreasing trend at glacier elevations. Mean annual LST increased from − 0.3 °C in 2012 to a peak of 0.4 °C in 2016. Central lobe of the glacier advanced during this period and eventually fell off in 2016 suggesting that the LST warming forced reduction of frictional drag at the interface facilitating it advancement and eventual dislodgement. Permafrost modelling suggests warm permafrost below 50 m and conditions favourable for intense frost cracking up to 10–15 m. At ~ 40 m depth, the delayed response of 2012–2016 warming produced peak positive temperature conditions by December and probably facilitated the formation of thin film of water at the deeper layers acting as a lubricant for glacier sliding. It is also suggested that the increase in summer precipitation might have forced thickening of the accumulation area and thereby increasing the shear stress for sliding of the glacier. It is proposed that the recent change in the weather conditions in the region is primarily responsible for this event through geological, glaciological, and permafrost processes. Flood modelling study suggests a flood volume of ~ 10 MCM generating 24.5 m flow depth at the bridge site with 12.7 m/s flow velocity. The event highlighted the need for improved monitoring of the cryosphere areas of the Himalaya to capture the early warning signs for better preparedness.

Dynamics of electrostatic interaction and electrodiffusion in a charged thin film with nanoscale physicochemical heterogeneity: Implications for low-salinity waterflooding

The slow kinetics of wettability alteration toward a more water-wetting state by low-salinity waterflooding (LSWF) in oil-brine-rock (OBR) systems is conjectured to be pertinent to the electrokinetic phenomena in the thin brine film. We hypothesize that the nanoscale physicochemical heterogeneities such as surface roughness and surface charge heterogeneity at the rock/brine interface control further the dynamics of electrodiffusion and electrostatic disjoining pressure (Πel), thus the time-scale and the magnitude of the low salinity effect (LSE). In this regard, film-scale computational fluid dynamics (CFD) simulations were performed. The coupled Poisson-Nernst-Planck (PNP) equations were solved numerically in a thin water film confined between a solid surface and oil, both negatively charged. The solid surface is representative of sandstone (quartz/kaolinite) with patchwise physicochemical heterogeneity. The electrical properties of the oil are representative of a crude-oil sample. The OBR system was initially under chemical equilibrium with high salinity (HS) brine, then was exposed to low salinity (LS) brine. The time-scale of reaching chemical equilibrium under LS, and the spatio-temporal evolution of electric potential were investigated. We find that surface roughness (introduced by quartz patches on quartz surface) increases the diffusion time up to 3-fold due to increased tortuosity. However the effect of surface roughness and surface charge heterogeneity (introduced by kaolinite patches on quartz surface) on the effective diffusion coefficient (Deff) is minor. While surface roughness and surface charge heterogeneity affect the disjoining pressure (Πel) significantly, the influence of surface roughness on Πel is more pronounced under HS than LS condition. In contrast, the effect of surface charge heterogeneity is more appreciable under LS than HS. Our findings imply that the LS effect can be enhanced in rough, heterogeneously charged systems like clayey sandstone, although its magnitude depends on the charge density of the roughness and its variation with salinity. We introduce two scaling factors, namely the effective diffusion coefficient (Deff) and the retardation coefficient (ω), to upscale the nanoscale results to pore-scale and beyond.

Impact of rock morphology on the dominating enhanced oil recovery mechanisms by low salinity water flooding in carbonate rocks

Because of the complex nature of carbonate reservoirs, the required conditions for effective Low Salinity Water Flooding (LSWF) in these reservoirs need further and in depth investigation. In the present study, three calcite cores, i.e. Cal-1, Cal-2, and IL, with the same chemical composition are subjected to tertiary low salinity water flooding (LSWF), while the crude oil and composition of flooding brine kept the same. The experimental results show significant difference in the amount of enhanced oil recovery, as IL had the most additional oil recovery (20.8 % of IOIP), followed by Cal-2 (10.5 % of IOIP) and Cal-1 (3.9 % of IOIP). The results of contact angle, zeta potential, and effluent pH showed that the same geochemical reaction occurred for all three cores. High-resolution FE-SEM images demonstrate that the only difference in these three cases is the rock morphology. Dynamic contact angle measurements indicate that wettability alteration depends on the dominating mechanisms (diffusion/advection) that controls the replacement of high salinity thin water film (which is flanked by crude oil and rock) with the surrounding low salinity brine. The wide pore size distribution of Cal-1 compared to Cal-2 and IL results in a more diffusion-controlled oil recovery mechanisms, which is confirmed by the late-time and the gradual response of Cal-1 to tertiary LSWF. Also, a direct relation between effluent pH and the tertiary oil recovery of Cal-1 highlighted the role of the thickness of the water film in the diffusion rate. More homogenous Cal-2 has a high early oil recovery; however, the angular shape of its particles leads to a partial diffusion-controlled regime that causes a late-time recovery. Finally, the uniform and the rounded particles of IL drift the impact of diffusion away. The results of the present is study emphasizes the role of heterogeneity and angularity on the performance of tertiary LSWF.

Water film-driven Mn (oxy)(hydr)oxide nanocoating growth on rhodochrosite

Minerals exposed to moist air stabilize thin water films that drive a score of chemical reactions of great importance to water-unsaturated terrestrial environments. In this study, we identified Mn (oxy)(hydr)oxide nanocoatings formed by the dissolution, oxidation and precipitation of Mn in oxygenated water films grown on rhodochrosite (MnCO3) microparticles. Nanocoatings that could be identified by vibrational spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and (scanning and transmission) electron microscopy formed in water films containing the equivalent of at least 7 monolayers (∼84 H2O/nm2). These films were formed by exposing microparticles to moist air with at least 50% relative humidity (RH). Films of neutral pH reacted up to 14% of the MnII located in the topmost ∼5 nm region of the microparticles in atmospheres of up to 90% RH for 7 d. These reactions produced MnOOH, birnessite (MnO2) and hausmannite (Mn3O4) nanoparticles of low crystallinity, while exposure to atmospheric air for 1 yr. converted only 2% of MnII in this region to MnOOH. In contrast, reactions in alkaline water films converted up to ∼75% of the MnII but only after 16 d of reaction. These films produced MnOOH and MnO2 of low crystallinity, as well as crystalline hausmannite. Kinetic modeling of the time-resolved growth of the MnO stretching vibrational bands of these nanocoatings revealed two concurrent reaction processes. A 1rst-order process was assigned to nucleation events terminating only after a few hours, and a 0-order process was assigned to the sustained growth of nanocoatings from these nuclei over longer reaction time. By identifying nanocoatings formed by water film-driven reactions on rhodochrosite, our study adds new insight into mineralogical transformations relevant to anoxic–oxic boundaries in water-unsaturated environments.

Thermally Assisted Heterogeneous Cavitation through Gas Supersaturation.

We demonstrate that besides gaseous pockets also a gas supersaturated spot on a substrate can be a nucleus for cavitation. The supersaturation is achieved by either a formerly dissolved bubble or by heating locally the surface below the boiling temperature. The experiments are conducted in a thin film of water; one side of the water film is in contact with a gold coated substrate that is heated by a continuous laser through plasmonic heating. For nucleation of a bubble, the pressure at the heated spot is reduced by a transient rarefaction wave. The experimental findings suggest that the local gas supersaturation is responsible to nucleate cavitation and thus connects the phase transitions of cavitation and boiling. Additionally, the pressure waves in the liquid gap are studied numerically.

Tubular polypyrrole enhanced elastomeric biomass foam as a portable interfacial evaporator for efficient self-desalination

Three-dimensional (3D) materials that capture sunlight for desalination provide one promising solution to acquiring freshwater resources, but salt deposition and mechanical stability provide additional hurdles for continuous operation. Herein, this study presents a sustainable and elastic biomass evaporator (EC-PPy-MO) with the hierarchical micro-nano water transport channel and air cavities formed by hydrophilic tubular polypyrrole seamlessly integrated onto the external surface of biomass foam. The EC-PPy-MO foam exhibits high light absorption ability (∼91%) over a broad wavelength due to the waveguide effect of the polypyrrole with a slender tubular morphology and the hierarchical micro-nano structure in the biomass matrix. The EC-PPy-MO foam helps stabilize a thin water film to provide an efficient evaporative interface surface and ensure effective thermal insulation. As a result, the EC-PPy-MO foam evaporator parallel to the horizontal plane demonstrates a rapid evaporation rate of about 1.8 kg m-2h−1 under 1 sun irradiation. In parallel, the evaporator can maintain efficient evaporation without salt fouling in a solution with 7% NaCl salinity, while largely salt fouling appears when higher than 15% brine. However, EC-PPy-MO with melamine foam support floating in 25 wt% brine can be evaporated for 72 h without significant salt fouling accumulation, up to ∼ 2.8 kg m-2h−1. This is attributed to the fact that the exposed sides of the 3D EC-PPy-MO foam can eliminate the boundary Marangoni phenomenon resulting in the appearance of no significant salt fouling, while the exposed cold evaporation surface enhances the evaporation rate of the EC-PPy-MO foam. More importantly, EC-PPy-MO foam exhibits excellent mechanical stability, chemical stability, and elasticity, as well as remarkable water purification ability.

Molecular Dynamics Study on the Spontaneous Adsorption of Aromatic Carboxylic Acids to Methane Hydrate Surfaces: Implications for Hydrate Antiagglomeration

Spontaneous adsorption of aromatic carboxylic acids (phenylacetic acid, 2-napthylacetic acid, and 1-pyreneacetic acid) to the CH4 hydrate surface in both liquid hydrocarbon and aqueous phases has been investigated using molecular dynamics simulations, aiming to provide implications for hydrate antiagglomeration. Simulation results indicate that the liquid-phase environment, that is, the liquid hydrocarbon phase or aqueous phase, especially its hydrophilic/hydrophobic property, could profoundly affect the interfacial structures of CH4 hydrate and the adsorption behavior of aromatic carboxylic acids. In the hydrophobic hydrocarbon phase, with many CH4 molecules dissolved, more interfacial hydrate structures decompose and form a thin quasiliquid water film on the hydrate surface; aromatic carboxylic acids act as surfactants, that is, strongly adsorb to the hydrate/hydrocarbon interface and significantly lower the interfacial tension. Moreover, they adsorb to the interfacial water film on the hydrate surface with their carboxylic groups, which may destabilize the capillary liquid bridges formed among hydrate particles and then prevent hydrate coalescence. By contrast, fewer interfacial hydrate structures decompose in the aqueous phase, as CH4 molecules rarely dissolve in water but stay at the hydrate/water interface and stabilize the hydrate solid; only a few aromatic carboxylic acids adsorb to the hydrate/water interface by inserting their aromatic rings into the semicages on the hydrate surface, which may kinetically disturb the hydrate growth. Such adsorption is not very strong and mainly depends on the size matching between aromatic rings and semicages. Consequently, many more aromatic carboxylic acid molecules strongly adsorb to the hydrate surface in the hydrocarbon phase than in the aqueous phase, which can explain why antiagglomerants generally show a higher performance in the hydrocarbon phase and easily lose efficacy at high watercuts. Additionally, the molecular structures could also affect the adsorption behavior of aromatic carboxylic acids: with more aromatic rings, acid molecules can form stable aggregates via the π–π stacking interactions of the aromatic rings, adversely affecting the adsorption in the aqueous phase.

Optimization of nanoparticle yield for biomedical applications at femto-, pico- and nanosecond laser ablation of thin gold films in water

The paper considers the generation of colloidal gold nanoparticles by laser ablation of thin gold films of variable thickness in deionized water. The effect of laser fluence, pulsewidth, exposure, and film thickness on the generation of nanoparticles, its productivity and ergonomicity, particle dispersion and size is studied along with the related ablative mass loss from the films.

Surface Stability of Azobenzene‐Based Thin Films in Aqueous Environment: Light‐Controllable Underwater Blistering

AbstractAzobenzene‐based light‐responsive thin films are emerging as appealing candidates for smart cell‐culture substrates. Their attraction lies in the fact that they can be reversibly photo‐patterned, providing a route for dynamically mimicking the remodeling of the extracellular matrix. However, since the cells need to be cultured in aqueous environment, a key parameter in the layout of any biological application is the stability of the surface underwater. In this work, the authors perform a detailed investigation on the surface stability of azobenzene‐based thin films in water and in a biologically relevant aqueous medium in which surface blistering occurs, as a result of water–material interaction. The phenomenon arises due to film delamination, and it can be prevented by changing the underlying substrate, by an additional coating layer, or by photo‐induced control over the film permeability. It is also shown that the blister orientation can be controlled with polarized light. Furthermore, a simple model based on osmotic pressure is proposed to explain the blister formation. These findings provide a comprehensive overview of the interaction between water and the photo‐responsive film surface, pertinent for engineering biomaterials with enhanced dynamic control over the cell–material interface.

Sphere Falling Onto A Liquid Jet

Abstract The history of interfacial fluid dynamics is intertwined with the origins of flash photography from the 'Worthington Jet' of Aurthur Worthington [1] to the 'Milk drop coronets' of Harold Edgerton[2] , with this technique capturing ephemeral fluid impacts in their awe-inspiring beauty. Although camera technology has come far from the days of giant flash bulbs, this elegant technique still provides a uniquely focused window into the fleeting impact events that often seem chaotic in real time, but in the suspended reality of flash-photography are found to be surprisingly well patterned. We apply a similar technique with the help of a laser-controlled photo-receptor in a dark room at night with flashes going off when the light received by the photo-receptor is disturbed. The resultant sequential images of Figure 1 are achieved by the timed release of a 50 mm diameter steel sphere falling from 750 mm plunging through an upward moving Worthington Jet that was created by a 38 mm sphere dropped from 230 mm in line with the second sphere. The jet envelopes the sphere from all sides, with thin water films hugging and moving across the sphere surface continuously until they meet at the sphere apex creating beautiful fluid sheets and ligaments in Figure 2. This image not only captures the beauty of the impact but also reveals a novel mechanism of reducing the impact impulse force of falling objects. The sphere in this particular case experiences an almost 70% reduction in impact force compared to a quiescent pool impact [3, 4].

HYDRATION AND HEAT RELEASE OF CEMENT HARDENING IN THE COLD

The article provides a comprehensive coverage of the problem of the influence of negative temperatures on the properties and structure of concrete during its early freezing. Studies have established the regularity of the content of the liquid phase in the cement gel at low temperatures, as well as the strength gain of cement. Water under ordinary conditions freezes at 0 ° C, and it would seem to make no sense to talk about cement hydration, but the properties of thin films of water and the change in their physical properties allow cement hydration to occur. Such water freezes at more negative temperatures, and being in a liquid state can react with cement minerals

E-MPS法を用いた薄膜を有する壁面に対する水滴衝突による二次液滴の数値シミュレーション

The ice accretion on an aircraft threatens navigation safety because it causes deformation of the wing shapes and reduces the aerodynamics performance. In the glaze ice conditions, where the ambient temperature is about -10 to -3 ℃, impinged droplets do not freeze instantly, and they runback along the wing surface as a liquid film. In addition, splashing and rebounding occur, which generate secondary droplets, if supercooled large droplets (SLD) whose diameters are more than 40 μm impinge on an aircraft. Furthermore, liquid film on an aircraft wing at glaze ice conditions significantly affects these phenomena. The purpose of this study is to model the droplet impact behavior and the formation of secondary droplets on a wall with a thin water film in terms of SLD icing under glaze ice conditions by using the three-dimensional E-MPS method. In a vertical impact case, the crown is formed by the impingement, and no secondary droplet is generated by the finger jets. The crown height decreases with decreasing water temperature, which is attributed to the decrease in Weber number. In an oblique impact case, the total mass of secondary droplets increases as the impact angle decreases. The secondary droplet mass generation attains the maximum at about 39 degrees impact angle. Moreover, the secondary droplets do not appear as the impact angle decreases around 30 degrees, resulting from Kelvin-Helmholtz instability. The velocities of secondary droplets decrease as the secondary droplets are generated later.

Thin-water-film-enhanced TiO2-based catalyst for CO2 hydrogenation to formic acid.

Carbon dioxide (CO2) hydrogenation can not only mitigate global warming, but also produce value-added chemicals. Herein, we report a novel three-phase catalytic system with an in situ generated and dynamically updated thin water film covered on the noble-metal-free TiO2-based catalyst for highly efficient CO2 hydrogenation, realizing a four-time enhancement compared with that with the catalyst suspended in water. The water film plays dual roles by directly participating in the reaction and removing the produced oxygenates (mainly formic acid) from the catalyst surface by dissolution. These results demonstrate an effective design for CO2 hydrogenation, which will open a new door to three-phase catalysis.