Thin Water Film Research Articles

Cleaning of Conveyor Belt Materials Using Ultrasound in a Thin Layer of Water

Cleaning of conveyor belts in the food industry is imperative for preventing the buildup of microorganisms that can contaminate food. New technologies for decreasing water and energy consumption of cleaning systems are desired. Ultrasound can be used for cleaning a wide range of materials. Most commonly, baths containing fairly large amounts of water are used. One possibility to reduce water consumption is to use ultrasonic cavitation in a thin water film on a flat surface, like a conveyor belt. In order to test this possibility, a model system was set up, consisting of an ultrasound transducer/probe with a 70-mm-diameter flat bottom, operating at 19.8 kHz, and contaminated conveyor belt materials in the form of coupons covered with a thin layer of water or water with detergent. Ultrasound was then applied on the water surface at different power levels (from 46 to 260 W), exposure times (10 and 20 s), and distances (2 to 20 mm). The model was used to test two different belt materials with various contamination types, such as biofilms formed by bacteria in carbohydrate- or protein-fat-based soils, dried microorganisms (bacteria, yeasts, and mold spores), and allergens. Ultrasound treatment increased the reduction of bacteria and yeast by 1 to 2 log CFU under the most favorable conditions compared with water or water-detergent controls. The effect was dependent on the type of belt material, the power applied, the exposure time, and the distance between the probe and the belt coupon. Generally, dried microorganisms were more easily removed than biofilms. The effect on mold spores was variable and appeared to be species and material dependent. Spiked allergens were also efficiently removed by using ultrasound. The results in this study pave the way for new cleaning designs for flat conveyor belts, with possibilities for savings of water, detergent, and energy consumption.

Numerical investigation for the effect of the liquid film volume on thermocapillary flow direction in a thin circular liquid film

NASA Astronaut Dr. Pettit carried out a thermocapillary flow experiment onboard the International Space Station in 2003. In this experiment a thin water film containing milk powder was formed in a stainless-steel wire ring. Heating a section of the ring by a soldering iron induced in the water film a thermocapillary flow towards the heated section of the ring (outward flow: cold to hot). This flow was in the opposite direction of the usually observed thermocapillary flows (inward flow: hot to cold). To shed light on this interesting phenomenon observed in the space experiment, we have conducted a three-dimensional numerical simulation study. Simulation results showed that the film geometry of the water film is a key factor determining flow direction and flow strength. When the liquid film free surfaces are convex, i.e., the water film volume is larger than that when the free surfaces are flat, an outward flow develops in the film as observed in the space experiment. However, when the free surfaces are concave, the simulation predicts an inward flow.

Experimental evidence for cm propagation lengths of long-range guided terahertz radiation by thin layers of water

Terahertz waves can be guided with low losses along thin layers of a strongly absorbing medium embedded in a dielectric. By means of end-fire coupling experiments, we demonstrate the polarization dependent excitation, propagation, and detection of this loss-guided mode, demonstrating long propagation lengths for terahertz radiation along thin water films. Broadband frequency and time resolved analysis using transmission terahertz time domain spectroscopy are performed. A theoretical model is used to isolate the coupled mode from co-propagating spurious modes. Hereby, experimental propagation lengths in the cm range are demonstrated, 2–3 orders of magnitude above the intrinsic propagation length in bulk water.

Methane combustion in hydrate systems: Water-methane and water-methane-isopropanol

Kinetics of dissociation of synthetic and natural methane gas hydrates, and also double isopropanol-methane hydrate is investigated. Thermal fields of the sample surfaces are measured by means of thermal imaging in combustion of released methane with clathrate dissociation. The dissociation rates of natural hydrate and double hydrate with isopropanol are many times lower than those of synthetic methane hydrate. Methane combustion is accompanied by formation of a thin water film on the powder surface, which has a strong effect on the heat and mass transfer mechanisms. The experiments demonstrated partial self-preservation for methane hydrate and the absence of self-preservation for double isopropanol-methane hydrate. The experimentally observed dissociation rate of double isopropanol-methane hydrate is considerably lower than that of methane hydrate.

Treatment of 4-chlorobenzoic acid by plasma-based advanced oxidation processes

Studies show that oxidation resistant pollutants are present after conventional water treatment systems. Nowadays a new class of oxidation processes is studied: advanced oxidation processes. Our process is based on the use of an electrical discharge (Glidarc and DBD) to produce HO, which is generated on the surface of a thin film of water. The first results show that the DBD is more efficient than the Glidarc with a degradation efficiency of the target pollutant (4-chlorobenzoic acid (pCBA)) of about 0.87gkWh−1 for DBD and 0.16gkWh−1 for gliding arc discharge. However, it appears that secondary reactions due to corrosion of the metallic micro-structured plate cause slower degradation of the pollutant. Moreover, the presence of nitrates in solution after treatment indicates the formation of NOx in the discharge and the possible formation of nitrogenous oxidation by-products.

Water Vapor Adsorption on Goethite

Goethite (α-FeOOH) is an important mineral contributing to processes of atmospheric and terrestrial importance. Their interactions with water vapor are particularly relevant in these contexts. In this work, molecular details of water vapor (0.0-19.0 Torr; 0-96% relative humidity at 25 °C) adsorption at surfaces of synthetic goethite nanoparticles reacted with and without HCl and NaCl were resolved using vibrational spectroscopy. This technique probed interactions between surface (hydr)oxo groups and liquid water-like films. Molecular dynamics showed that structures and orientations adopted by these waters are comparable to those adopted at the interface with liquid water. Particle surfaces reacted with HCl accumulated less water than acid-free surfaces due to disruptions in hydrogen bond networks by chemisorbed waters and chloride. Particles reacted with NaCl had lower loadings below ∼10 Torr water vapor but greater loadings above this value than salt-free surfaces. Water adsorption reactions were here affected by competitive hydration of coexisting salt-free surface regions, adsorbed chloride and sodium, as well as precipitated NaCl. Collectively, the findings presented in this study add further insight into the initial mechanisms of thin water film formation at goethite surfaces subjected to variations in water vapor pressure that are relevant to natural systems.

Detection of water with high sensitivity to study polymer electrolyte fuel cell membranes using cold neutrons at high spatial resolution

Thermal neutron imaging is a powerful non-invasive diagnostic technique to study water management within a proton exchange membrane (PEM) fuel cell. To isolate the hydration behavior of membrane, significant increase in detecting thin water films is needed. A humidity cell is developed to study hydration of a PEM using cold neutron imaging. Spatial and temporal changes of PEM water uptake are quantified. Water film as small as 1 μm thick and corresponding to a volume containing 10 ng of liquid water at high spatial resolution is detected. This represents an order of magnitude improvement in water detection efficiency achievable at thermal neutron imaging facilities.

A mechanistic model for pipeline steel corrosion in supercritical CO2–SO2–O2–H2O environments

A mechanistic model was established to predict uniform corrosion rate and investigate the corrosion mechanisms of pipeline steel in supercritical CO2–SO2–O2–H2O environments. A six-region division (SIWDES: Supercritical CO2, Interface, Water film, Deposition, Electrodic, and Solid) was applied to mathematically describe the model. The modified three-characteristic-parameter correlation model was used to calculate the ion activity coefficients, which calculates the activity coefficients of ions in thin water film with high ionic strength. The model can reasonably predict the corrosion rate of pipeline steel for the primary variables, determine the concentration distribution of each component in the water and product films, and also reflect the impact of corrosion product film on corrosion rate. A comparative analysis between the model and the experimental results showed that the model reasonably predicted the effects of the main factors on corrosion rate.

Photoactivated ${\rm TiO}_{2}$ Gas Chromatograph Detector for Diverse Chemical Compounds Sensing at Room Temperature

A photoactivated gas detector operated at room temperature is microfabricated using a simple TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> sol-gel process. Prior to ultraviolet (UV) illumination, water-soluble compounds (short-chain alcohols) are dissociated in the thin water film on the TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> surface and are detected. However, less water-soluble compounds were not detected because of these water layers. With the increase of the photoinduced oxygen ions by UV illumination, it is first reported that less water-soluble organic compounds (e.g., ethyl acetate and 1, 4-dioxane) are detected with the photoactivated gas detector. The proposed detector greatly extends the detection range of metal-oxide-based sensors for use in gas chromatographs.

Thermodynamic Properties of Bridging Clusters in Thin Films of Water between Hydrophobic Surfaces Assessed from Surface Force Isotherms

In the course of a long-term effort to cope with surface force data for thin films of water between hydrophobic surfaces, we have applied the bridging-cluster model (Eriksson, J. C.; Henriksson, U. Bridging-cluster model for hydrophobic attraction . Langmuir 2007, 23, 10026 - 10033) to the recently published surface force isotherms for water films between hexadecylthiolated gold surfaces in the thickness range of 20-100 nm and temperature range of 10-40 °C (Wang, J.; Yoon, R.-H.; Eriksson, J. C. Excess thermodynamic properties of thin water films confined between hydrophobized gold surfaces. J. Colloid Interface Sci. 2011, 364, 257 - 263). We show that these isotherms can be faithfully reproduced on the basis of the bridging-cluster model. The thermodynamic excess properties (ΔGc , ΔHc , and TΔSc) of linear clusters that are assumed to bridge the core of the films were calculated from the experimental surface force isotherms. A crucial step taken was to infer two-dimensional ideal mixing of the clusters with the surrounding film water. We find that ΔHc and TΔSc are both negative quantities, with the latter being larger than the former, which implies a positive excess Gibbs energy of a cluster, ΔGc = ΔHc - TΔSc. Typically, for temperatures between 10 and 40 °C, these cluster properties are of the order of some kBT units, corresponding to 10(-4)-10(-3)kBT per water molecule entailed. Our analysis yields support of the notion that elongated aggregates can arise in thin films of water between hydrophobic surfaces driven by entropy of mixing.

Assessment of penetration through vacuum cleaners and recommendation of wet cyclone technology

In many commercial vacuum cleaners, the captured aerosol particles contained in the dust collector may accidentally release from the exhaust filtration owing to leakage or penetration. Vacuum cleaners may cause dust to become airborne by exhausting air that is not completely filtered. This may cause the operator to inhale dust, in turn causing health problems. This study aimed to investigate the dust penetration rates from three commercial vacuum cleaners and suggest the best technique for completely filtering exhaust air using a combination of cyclonic separation and water filtration. The commercial vacuum cleaners were tested inside a custom-built hood, and the exhausted particles were monitored using a sampling probe in conjunction with an aerosol particle sizer. Quartzose mineral dusts were added to each vacuum cleaner through the dust transport line. A 2400 L/min wet cyclone was employed as the proposed vacuum cleaner. It was designed using Stokes scaling, and its collection characteristics were evaluated using polystyrene latex beads. Surprisingly, the conventional vacuum cleaners failed to capture an overall average of ˜14% of the particles in the given size range. However, only ˜3.8% of the collected particles escaped from the vacuum cleaner that used the wet cyclone technology. Thus, the proposed vacuum cleaner should potentially be an effective method for vacuuming household dust. Implications: The successful investigation of conventional vacuum cleaners is useful for both manufacturers and users. As an effective vacuum cleaning mechanism, household dust is able to migrate along the thin water film that forms on the inner walls of the cyclone vacuum cleaner. It collects dust in a small water inflow (3 mL/min), which allows it to capture a higher percentage of contaminants than most of the currently available vacuum cleaners. The significantly low accidental exposure rates achieved by this new vacuum cleaner enable healthy conditions in various environments, including indoors.

Insights into silicate carbonation processes in water-bearing supercritical CO2 fluids

Subsurface injection of CO2 is commonplace in certain industries, yet deployment at the scale required for emission reduction is unprecedented and therefore requires a high degree of predictability. Accurate modeling of subsurface geochemical processes related to geologic carbon sequestration requires experimentally derived data for mineral reactions. Most work in this area has focused on aqueous-dominated systems in which dissolved CO2 reacts to form crystalline carbonate minerals. Comparatively little laboratory research has been conducted on reactions occurring between minerals in the host rock and the wet supercritical fluid phase. We studied the carbonation of wollastonite [CaSiO3] exposed to variably hydrated supercritical CO2 (scCO2) at 50, 55 and 70°C and 90, 120 and 160bar. Reactions were followed by three novel in situ high pressure techniques, which demonstrated increased dissolved water concentrations in the scCO2 resulted in increased wollastonite carbonation approaching ∼50wt.%. Overall, the X-ray diffraction and infrared and magic angle nuclear magnetic resonance spectroscopies experiments conducted in this study allow detailed examination of mechanisms impacting carbonation rates. These include the development of amorphous passivating layers, thin liquid water films, and amorphous hydrated carbonate phases. Collectively, these results emphasize the importance of understanding geochemical processes occurring in wet scCO2 fluids.

Gas Flows near Solids Coated with Thin Water Films

We determined the tangential momentum accommodation coefficient (TMAC) of nitrogen gas at glass surfaces that were coated in thin water films produced by controlling the humidity. The accommodation coefficients were determined by measuring the damping of a spherical particle which was separated from a flat plate by a distance of 10 nm to 10 μm. We examined two solids: hydrophilic glass terminated in hydroxyl groups and hydrophobic glass terminated in methyl groups. At the same relative humidity, thicker films of water form on the hydroxyl-terminated films than on the methyl-terminated films, consistent with formation of hydrogen bonds on the hydroxyl-terminated solid and not on the methyl-terminated solid. The TMACs are surprisingly interesting functions of the humidity. For the hydroxyl-terminated silica, the TMAC is 0.5 at 0% relative humidity and increases almost to 1 when the humidity increases to a few percent. The TMAC decreases to 0.25 at around 87% humidity before rising to 0.9 at 100% humidity. W...

Anti-charging process for electron beam observation and lithography

Electron beam (e-beam) exposure of insulating material gives rise to charge accumulation which degrades pattern resolution and position during lithography and observation. In this paper we propose a process which reduces significantly the artifacts due to charging effects by using a charge dissipater based on a bi-layer deposited on top of the insulating substrate. The first layer is an inorganic thin film and soluble in water at room temperature, while the second layer is a metallic thin film. We reported the results of this process during e-beam lithography and observation of insulating samples.

Chemical evolution of dissolved inorganic carbon species flowing in thin water films and its implications for (rapid) degassing of CO2 during speleothem growth

Rapid degassing of CO2 from a thin film of drip water on the surface of stalagmites is often considered to have a large effect on both speleothem growth and stable isotope values and is offered as an explanation for higher δ13C and δ18O values than expected under conditions of stable isotope equilibrium. However, the time constant for degassing of CO2 from the solution only depends on film thickness and the coefficient of molecular diffusion for CO2. Thus, for thin films, the time for degassing of CO2 is much shorter than the time for subsequent equilibration of the dissolved carbon species and precipitation of CaCO3. In this context, degassing of CO2 is always fast.Here we present three experiments that enable the determination of the time constants for degassing of CO2, τdeg, subsequent equilibration to a new pCO2, τeq, and precipitation of CaCO3, τpr, in a thin film of an H2O–CO2–CaCO3 solution flowing on a calcite surface. The experiments are performed under cave-analogue conditions.At a temperature of 20°C and for a film thickness of δ≈0.01cm, τdeg≈2s. τeq≈13s and, thus, one order of magnitude larger. Finally, τpr≈400s for δ≈0.01cm, again one order of magnitude larger. The experimentally determined values for τdeg, τeqτpr are in good agreement with the theoretical predictions.Our results confirm that the chemical evolution of the drip water proceeds in three subsequent major steps. During the first step of degassing of CO2, pH and Ca2+ concentration remain almost constant. During equilibration to the lower pCO2 of the solution, pH increases to about 8 whereas the Ca2+ concentration still remains constant. Finally, during precipitation of calcite, pCO2 remains at its low level and pH decreases slightly.These results suggest that the drip rate may have an important influence on the stable isotope signals recorded in speleothems. Stalagmites growing beneath drip sites with stable, intermediate drip rates (i.e., in the range of τeq) may be best suited for palaeoclimate reconstruction.

Correlation between microstructure and salt-water durability of Ag thin films deposited by magnetron sputtering

The effect of nitrogen addition to the sputter gas during Ag deposition on the salt-water durability of the Ag thin films was investigated. The Ag thin films deposited in sufficient nitrogen exhibited better salt-water durability and almost the same reflectance as the Ag thin films deposited in argon only. Additionally, it was found that the haze growth observed after soaking the thin films in salt water was prevented by using a ZnO under layer. From the microstructure analysis, it was found that the improvement in the salt-water durability was attributable to the small crystallite of the Ag and the strong adhesion between the substrate and each layer.

Water vapor interactions with FeOOH particle surfaces

Interactions between iron (oxyhydr)oxide particle surfaces and water are of fundamental importance to natural and technological processes. In this Letter, we probe the interactions between submicron-sized lepidocrocite (γ-FeOOH) surfaces and gaseous water using Fourier transform infrared spectroscopy. Formation of hydrogen bonds between different lepidocrocite surface OH functional groups and water was specifically monitored in the O–H stretching region. Molecular dynamics simulations of the dominant crystallographic terminations of these particles provided insights into interfacial water structures and hydrogen bonding networks. Theoretical power spectra were moreover used to validate interpretations of experimental spectra. This Letter constrains our understanding of incipient water adsorption reactions leading to thermodynamically stable and reversible thin water films at FeOOH particle surfaces. It also suggests that these water layers are structurally analogous precursors to those occurring at a FeOOH surfaces contacted with liquid water.

Experimental study of the performance of solar still using a reciprocating intermittent spray feeding system

One of the most important parameters in desalination using solar still is minimizing the flow rate of saline water feeding. Consequently, the saline water depth could decide the performance of the solar still. Some of the research works incorporated those parameters into consideration but in a limited scale. An experimental investigation on a stepped solar still with intermittent spray feeding system using flash evaporation was studied. That procedure was executed by feeding the saline water into the still through a controlled transverse reciprocating spray system on the form of fine droplets. This technique helps on the uniform spread of droplets on the top surface of a stepped-absorber solar still in an intermittent process. The thin film of the saline water has many significant advantages on the still performance due to its very low thermal inertia. The present approach has undergone a systematic study to optimize its performance. The still was tested at 250 rpm motor speed and at 15.606 l/h and 9.333 l/h rates of saline water spray flow. The spray frequency was 5, 4, 3, 2.5 spray per hour. Optimum operating conditions were identified. An accumulated productivity of 5.519 l/m2 over only 10 h with efficiency of 65.11% was obtained.

Les acides gras hydroxylés : agro-tensioactifs aux propriétés moussantes originales

Surfactants, which are molecules bearing a hydrophobic part and a hydrophilic part, are widely used in many daily life products (detergent, cosmetic, pharmaceutical...) because of their foaming properties. Indeed, they spontaneously go to the interface between air and water, which stabilizes the thin water films surrounding air bubbles to obtain foams. Currently, since the most used surfactants come from derivatives from petroleum-based products, their replacement by biomolecules is a major issue in the current context of sustainable development and green chemistry. This could promote the use of molecules from agricultural resources, such as hydroxyl fatty acids that can be extracted from oil or from the tegument of fruits and vegetables, as new agro-based surfactants. Here, we present recent research on the surfactant properties of the 12-hydroxy stearic acid coming from the castor oil. This fatty acid has very advantageous foaming properties compared to conventional synthetic surfactant systems: it enables the production of foams which are at the same time very abundant and, remarkably, stables over a span lasting more than 6 months. Moreover, these foams are thermoresponsive because the foam stability can be easily modulated by a simple modification of the temperature.

Crustacea in phytotelmata: a global overview

Phytotelmata, or plant-held water bodies, occur all over the world and include bromeliads, pitcher plants and tree holes. Largely ignored, these habitats can house surprisingly diverse aquatic invertebrate communities. To complement existing overviews of insect-dominated phytotelm inquilines, we assembled information on aquatic Crustacea in phytotelmata worldwide with records of over 100 species of freshwater crustaceans, illustrating the relatively common presence of crustaceans in these habitats. The records are patchily distributed and large geographic gaps remain, indicating the incompleteness of our knowledge. Copepoda (68 species) and Decapoda (16 species) are the dominant taxa in the list. Ostracoda (14 species) are the most typical inhabitants and the only ones that are observed using dispersal vectors (amphibians) on a local scale. Anomopoda (10 species) are the smallest group represented. The total richness in a metacommunity of phytotelmata is often low, with five species in bromeliads in a Honduran cloud forest and eight species in bromeliads in central Mexico being the highest richness recorded. Aspects of ecology and morphology indicate how there is a remarkable morphological similarity crustacean phytotelmata with several groups found in interstitial waters and as stygobionts. A substantial part of the recorded species, in particular Copepoda, normally live in the thin water film covering vegetation and soils, and probably occur in phytotelmata as occasional encounters.