Water Film Research Articles

Modeling of fluence-dependent hole-burned spectra and hole-growth kinetics using multiple two-level system model.

Numerical formalism is presented that perfectly describes resonant low-temperature hole-burned spectra (including zero-phonon holes, ZPHs) and spectral hole-growth dynamics of Al-phthalocyanine tetrasulphonate embedded in hyperquenched glassy water films over more than seven orders of fluence magnitude (0.4 µJ/cm2-5.9 J/cm2). Frequency changes during spectral hole-burning (HB) are traditionally explained with the help of a single extrinsic two-level-system (TLSext) associated with impurity molecules. The new multiple two-level system (n-TLSext) models and data analysis presented in this work show that each chromophore in an amorphous medium can couple with multiple independent TLSext, which maintain perfect photo-memory, allowing a full return of the photoproduct to the initial ("preburn") state. Modeling reveals that the experimentally observed narrow photoproduct peak at higher energies, in close vicinity of the zero-phonon hole (ZPH), reflects a dynamical feature of the HB process populating so-called "terminal" states (states that do not interact with laser excitation). Within the n-TLSext model, each chromophore possesses multiple possibilities to create a photoproduct when in interaction with the burning laser, i.e., chromophores can interact with burning laser-light multiple times until reaching the terminal states. Due to phonon-assisted absorption, terminal states are typically at higher energies than the ZPH, in agreement with the hole burned spectra reported for many molecules embedded in various amorphous solids. However, many HB systems reveal both blue- (high-energy) and red-shifted (low-energy) antiholes (i.e., photoproducts). We suggest that future modeling of resonant holes in various proteins using our n-TLSext model will provide more insight on the complexity of the protein energy landscape.

Abrasive Wear Characteristics of 30MnB5 Steel for High-Speed Plough Tip of Agricultural Machinery in Southern Xinjiang Region

The high-speed plough tip is the core soil-touching component in southern Xinjiang field cultivation, but the interaction of the plough tip with the soil results in severe wear of the tip. The friction behaviour of sand and soil on plough tips was investigated with a homemade rotary abrasive wear tester in a one-factor multilevel test with three parameters: moisture content, velocity/rotational speed and friction distance. The objective was to study the friction behaviour of the sand soil and plough tip and analyse and characterise the wear amount, wear thickness and compressive stress distribution, three-dimensional wear morphology and microscopic wear morphology of the plough tips. The results show that with increasing speed, the wear amount changes more gently; with increasing soil water content, the soil adhesion force and lubricating water film increase so that the wear amount follows a second-order parabolic law; and with increasing friction distance, the wear amount gradually increases, and the wear rate also shows an upward trend when the plough tip is in the abrasive wear stage. The tip makes contact with the firmer soil with higher surface compressive stresses, causing the most wear. As the friction distance increases, sand particles become embedded in the contact surfaces, creating a groove effect along with spalling pits caused by fatigue wear. During the whole wear period, the groove effect is always accompanied by spalling pits appearing repeatedly. The analysis of the wear micromorphology of the plough tip shows that the number of flaking pits gradually decreases in the direction of soil movement, and the form of damage changes from impact wear to plough groove scratches. Abrasive wear interacts with corrosive wear to exacerbate plough tip wear.

Investigation of Water Film Dynamics on the Surface of an Airfoil in a High-Speed Flow and Subsequent Ligament Formation and Breakup from the Trailing Edge

Abstract In this work, the dynamics of a liquid film on the surface of NACA 0012 airfoil placed in a high-speed air flow is investigated. Experimental studies were carried out to assess the film thickness, droplet shedding, and the dynamics of the sheet. In the present work, air velocities up to 175 m/s were used with water films flowing between 1.4 and 2.6 cm2/s. The water was introduced on the airfoil via 26 holes each measuring of 0.5 mm holes separated by 1mm at 35 mm downstream of the leading edge of the vane. The results were obtained using four experimental tools. The first is a point measurement of the time-resolved film thickness using a confocal laser induced fluorescence method. Second is time averaged images of the film thickness on the entire vane surface. Third, high speed videos are obtained to study the accumulation and breakup of the liquid at the trailing edge of vane. Finally, laser diffraction and Phase Doppler interferometry were used to document the spray dynamics. The results illustrate that the average film thickness decreases with air velocity and increases with the water flow rate. Also, the dominant frequency of liquid film wave, ligament breakup length, drop size and spray concentration increase with the air velocity and is modestly affected by water flow rate. Finally, design tools are provided to predict the average film thickness and dominant frequencies of the film thickness, ligament breakup, spray concentration and droplet average size.

Numerical Analyses of Ultrasonic Atomization Utilizing Acoustic Effects of a Beam Diaphragm

To study mechanisms of jet atomization, a novel method of experimentation utilizing the resonation of diaphragms made from thin steel plates has been previously developed. In the experiments, a diaphragm covered by a film of water emitted acoustic sounds, and jet atomization from the water film was observed. Experiments using diaphragms composed of different materials and fast Fourier transformation analysis of the acoustic sound revealed that jet atomization occurred under limited surface conditions of the diaphragm and a specific range of frequency. In this article, the dynamics of a resonating body composed of the diaphragm and water film were analyzed using the finite element method with a combination of theoretical analyses of surface waves of water, such as the well-known Lang’s equation. The present FEA results, from harmonic response analyses with consideration of viscous damping effect due to interaction between the diaphragm and water film, precisely confirmed the results of FFT analysis previously obtained by the experiment. Specifically, the peak frequency of the frequency response agreed well with the FFT results, and the shift of the peak frequency and attenuation due to the interaction in the analyses corresponded with the difference in surface conditions between the hydrophilic and hydrophobic materials of the diaphragm in the experiments. Our interpretation of the mechanism of jet atomization is expanded by the present numerical results.

Unsteady numerical simulations of aircraft icing based on the dynamic grid method

In this study, an unsteady numerical simulation method based on dynamic grids was established to solve unsteady aircraft icing processes. The dual-time step method was used to achieve the time advancement of the transient airflow and droplets fields. The droplets trajectory was calculated using the Euler method, which incorporates a supercooled large droplets model. The transient evolution of the water film and ice layer on the substrate surface was considered in the icing thermodynamic model. The accuracy of the unsteady method for ice-shape prediction was verified via comparison and analysis of numerical examples. Additionally, the rime and glaze ice formation processes were explored, and the coupling effects of ice horn growth and the air convective heat transfer coefficient, water collection coefficient, and water film flow on the substrate surface were studied. The ice shapes calculated by unsteady and quasi-steady methods were compared. The results indicated that the latter predicts a larger icing range than the former. Moreover, there may be more obvious distinctions between these two methods in predicting glaze ice.

Effect of the temperature control device on the emission character of condensable particulate matter from industrial heating plant

Condensable particulate matter (CPM) is one of the major emissions of primary particles in coal combustion. The removal efficiency of CPM using the temperature control device (TCD) based on the concept of a heat exchanger application with lower capital cost was investigated in an industrial heating plant. TCD operates without water and flue gas interactions and ensures efficient control of CPM emissions, and it also minimizes the potential ion accumulation in recycled WESP water, which could otherwise hinder the removal of CPM. The total mass and chemical speciation were determined by EPA method 202. The total mass of CPM was removed by 25.7–60.6% after the TCD. The CPM captured by CPM filters (CPMspa) was down to around 15–21% and the FPM also was reduced by around 11–26%. The occurrence of vapor gradient forces and thermophoresis forces could enhance the contact between CPM and water film, which was built up on the surface of the cooling tubes during the process of TCD. Then, part of the CPM was removed with a water film. The low capital and operating cost of TCD can be installed in the industrial heating plant or be set up after the WESP in the coal-fired power plant to enhance the CPM removal efficiency.

Model of the influences of fiber diameter and content on flowability of basalt fiber reinforced phosphorus building gypsum composite slurry

Water film thickness (WFT) is a primary factor influencing the flowability of cement mortar and gypsum slurry. However, conventional WFT calculation models have overlooked the impact of fiber surface properties on flowability. This study addresses this issue by introducing a parameter called the residual moisture distribution coefficient into the residual moisture distribution coefficient (RMDC) and the WFT calculation model. Thirty-six groups of basalt fiber-Phosphogypsum composite slurry with varied mix proportions were designed and assessed for their flowability and packing density. The RMDC and WFT were derived from fitting with the improved model. Finally, a basalt fiber-Phosphogypsum composite slurry flowability prediction model based on WFT was established, laying a foundation for the design and further application of fiber-gypsum composite flowability.

Trimetallic Phosphide Nanostructures Derived from In Situ Coated ZIF-L Film for Overall Water Splitting

Trimetallic Phosphide Nanostructures Derived from In Situ Coated ZIF-L Film for Overall Water Splitting

Numerical Analysis of the Influence of Preadsorbed Water on Methane Transport in Crushed Shale

Summary Methane migration in shale is affected by preadsorbed water. To understand this effect, we examined several key parameters, including the effective pore diameter Le, the pore volume distribution of Le, the effective porosity ϕe, the equivalent particle diameter da, and the water film thickness h. Using these parameters, we established an equivalent relationship linking the particle packing da and the Le and the ϕe of the capillary pores within a unit-length cuboid of particles. Based on this relationship, a conceptual model was developed to simulate methane adsorption and transport in partially saturated crushed shale, incorporating parameter estimation for the tangential momentum adjustment factor δ and methane desorption rate coefficient kd, where δ characterizes the slip flow intensity and kd is related to the Langmuir adsorption constant. The finite element method was used to calculate the methane permeability ke, Knudsen diffusion coefficient Dke, surface diffusion coefficient Ds, and adsorption phase transition rate Rm, which are all affected by adsorbed water. The model’s numerical results were validated through comparison with the results from adsorption experiments. These results revealed three distinct regions in the trend of the variation in δ with Le: a rapid increase in Region I (Le < 10 nm), a slowing increase in Region II (10 ≤ Le ≤ 100 nm), and a gradual increase in Region III (Le > 100 nm). In addition, kd is positively correlated with da. kd is also correlated with water saturation S; specifically, kd decreases when S ≤ 12%, increases when S = 12% to 45.8%, and decreases again when S exceeds 45.8%. The results also reveal overall negative correlations between h and ke, Dke, Ds and Rm. Furthermore, the rates of change in ke, Dke, Ds and Rm with increasing ε (ε is the bending coefficient associated with adsorbed water) range from 7.5% to 49.4%. Similarly, ke, Dke, and Ds increase by factors of 0.73–7.19 with increasing χ (χ is the coverage rate of the adsorbed water film). Additionally, as the adsorption time t increases, Ds initially increases rapidly, followed by a gradual increase. Between t = 500 seconds and 1,500 seconds, the rate of change in Ds decreases by 20%. Rm shows a three-stage relationship with t, namely, a rapid decrease from t = 0 seconds to 500 seconds, a steady decrease from 500 seconds to 1,000 seconds, and a stabilization from 1,000 seconds to 1,500 seconds, with Rm ranging from 1.10×10-11 mol/(m3·s) to 9.45×10-11 mol/(m3·s) overall. Ds increases with the adsorption amount ratio Ed (Ed is the ratio of the adsorption amount at t to the equilibrium adsorption amount). As Ed ranges from 0.2 to 0.6, the rate of change in Ds increases by 87% to 100%. Furthermore, Rm is negatively linearly correlated with Ed.

Premelting Theory‐Based Mechanism for Water Freezing in Saline Soil

AbstractThe unfrozen water content constitutes a pivotal parameter in freezing soil, significantly impacting its thermal‐mechanical and deformation behavior. This study delves into the alterations in soil attributes as unfrozen water content varies. It examines the influences of impurities, van der Waals forces, and Coulomb forces on the water film, employing the premelting theory as a foundation. A critical state curve quantifying the ratio of the surface charge density to impurity concentration is parameterized for various soil types. Subsequently, combining the theory of effective solution concentration, we have provided calculation methods for the particle surface parameters of pore solutions as ideal and non‐ideal dilute solutions, respectively. This has determined the key variables in the model. Additionally, through the integration of equivalent particle sizes, packing structure, and water film thickness, a calculation model is devised and verified for determining the unfrozen water content and residual water content within in freezing soil. The findings indicate that fluctuation in the unfrozen water content primarily stem from impurities. In soils with equivalent saline content, impurity levels exhibit proportionality to the equivalent particle sizes. The residual unfrozen water is predominantly present within the absorbed water layer.

A New model of gas-water two-phase seepage based on Newton's law of motion

The pore throat size, structure distribution, and lithology of porous media in gas reservoirs are varied, and the gas-water two-phase seepage law is complex, making it difficult to describe the seepage model. Newton's law of motion is a basic law of motion in classical mechanics, and its application in gas-water two-phase seepage modeling is an innovative practice of classical mechanics in seepage mechanics systems. Based on Newton's three laws of motion, a gas-water two-phase seepage model was established from the force analysis of fluid, and the relationship between velocity and pressure difference, pipe radius, water film thickness, viscosity, etc. was derived under the condition that the model reached a stable state, i.e., force balance. The relationship is referred to as the steady-state model. Subsequently. the equivalent permeability representation model was derived based on the steady-state model to calculate the permeability of rock samples with different channel distribution characteristics. The results were consistent with the measured values, and there is a good correspondence between channel distribution characteristics and permeability. The relative permeability calculation method was established based on the steady-state model and capillary pressure curve. The obtained relative permeability curve aligned with the two-phase seepage law and coincides with the relative permeability curve obtained by Poiseuille's law. Finally, a new productivity equation was derived based on the steady-state model, and the Inflow Performance Relationship (IPR) curve calculated by the gas well example was consistent with the traditional equation. The research results were based on the force analysis of fluid in porous media and fundamentally explored the law of fluid flow. The derived seepage model can be used to calculate reservoir permeability, the gas-water relative permeability curve, and gas well productivity analysis and to effectively guide gas reservoir development. The study was a successful application of the basic theory of mechanics in gas-water two-phase seepage in gas reservoirs.

Acoustics of wet porous media with evaporation/condensation

This paper investigates acoustic wave propagation in wet rigid-frame porous media accounting for evaporation and condensation. At equilibrium, the solid walls are covered by a thin water film, and water vapor in the air is at its temperature-dependent saturation pressure. Small acoustic perturbations cause water to vaporize or condense, which together with the reversibility of the phase change, lead to a linear problem where the usual local poro-acoustics physics is enriched with the (i) Clapeyron relation linking liquid-wall temperature, vapor pressure, and latent heat of vaporization, (ii) latent heat transfer in the solid frame, (iii) diffusion equation for water vapor in air, and (iv) water vapor's equation of state. The equilibrium temperature highly influences the vapor concentration and the physical parameters of saturated moist air. Using the two-scale asymptotic homogenization method, it is shown that the dynamic permeability is determined similarly to classical porous media, while the effective compressibility is modified by evaporation/condensation and the equilibrium temperature. This modification is influenced by vapor mass and heat flows associated with phase changes through a local fully coupled heat transfer and water vapor diffusion problem, with specific boundary conditions at the gas–water interface. The analysis identifies dimensionless parameters and characteristic frequencies defining the upscaled model's features. Depending on equilibrium temperature, the theory qualitatively and quantitatively determines the characteristics of acoustic waves propagating through the media. The results are illustrated and discussed with analytically developed models.

Dynamic water gating facilitated the formation of micro-nano water films for rapid solar-driven evaporation

Dynamic water gating facilitated the formation of micro-nano water films for rapid solar-driven evaporation

Functionalized super-hydrophobic nanocomposite surface integrating with anti-icing and drag reduction properties

Anti-icing and drag reduction are two significant issues for aircraft, but functional surfaces integrating both properties are rarely reported. Here, we propose a functional super-hydrophobic nanocomposite surface with sharkskin-like groove structures, which achieves the combination of anti-icing and drag reduction properties. The nanocomposite surface was prepared by stripping polydimethylsiloxane doped with carbon nanotubes from a laser-prepared sharkskin-like structure mold and then spraying a layer of polytetrafluoroethylene hydrophobic coating. The microstructures and nanoparticles with low surface energy provide the surface with hydrophobicity and icephobicity, enabling droplet transitions between Cassie and Wenzel states during icing-melting process. Carbon nanotubes enhance the Joule heating performance when voltage is applied. Ice at interface melts into water film, significantly reducing adhesion and enabling efficient anti-icing. Under the influence of the bionic sharkskin riblet structure, the vortices are lifted and pinned above the riblet tips, which reduces the near-wall velocity gradient and total wall shear stress, ultimately leading to lower drag. In addition, the flexible surface undergoes adaptive deformation to more effectively conform to the fluid flow during motion. The riblet protrusions increase the contact area between the flexible surface and the fluid, thereby enabling the absorption of more turbulent energy and fluctuations, further reduces drag. This study presents a new method for manufacturing functional surfaces for practical anti-icing and drag reduction applications.

Unsteady-state entropy generation analysis of the counter-flow dew-point evaporative coolers

The surging demand for air conditioning, especially in hot climates, underscores the urgency of strategies aimed at curbing fossil fuel reliance and fostering energy saving strategy. Despite the longstanding utility and advantages of the conventional mechanical vapor compression refrigeration system, sustainability hurdles persist owing to its pronounced electricity demand. While evaporative cooling, harnessing water evaporation, emerges as a more efficient alternative, its efficacy is contingent upon environmental conditions. Addressing this, dew-point evaporative cooling (DPEC) presents an innovative direction, showcasing superior efficiency by directing supply air into a wet channel. This study delves into the thermodynamic losses within a counter-flow configured DPEC system, employing a transient entropy generation model rooted in the second law of thermodynamics to provide a comprehensive analysis of DPEC’s performance. Key findings that emerged from this study reveal that (1) the transient entropy generation is intricately distributed across different layers of the dew point evaporative cooling (DPEC) system, including dry air, wet air, the channel plate, and the water film; (2) Parametric analyses highlight the significant impact of factors on entropy generation, inlet air temperature has a minimal effect on system efficiency, but higher temperatures increase thermal losses. Excessive humidity limits evaporative potential, while low humidity significantly increases entropy generation. The system performs optimally at a working ratio of 0.3 and lower air velocities (within the inlet air velocity range of 0.6 to 2.2 m/s). Channel length has little impact, while the system is more sensitive to channel height, with a height of 2.5–3.5 mm being conducive to better performance. Experimental validation demonstrates the model’s accuracy in predicting system performance. The research contributes to a deeper understanding of DPEC systems, offering insights for achieving optimal operating conditions and enhancing overall efficiency in the pursuit of sustainable development.

Performance of air source heat pump units with different wettability evaporators

The air source heat pumps (ASHPs) for winter heating have the advantages of high efficiency and environmental protection. However, the outside evaporator’s frosting negatively impacts the performance of heat pump systems in low-temperature and high-humidity environments. In this paper, we fabricated the superhydrophobic evaporator and mounted it on a commercial ASHP unit, expanding the use of superhydrophobic surface modification technology from heat exchangers in the laboratory to the ASHP units. Then we investigated the operating characteristics of two ASHP units equipped with hydrophilic and superhydrophobic evaporators respectively under six distinct outdoor and indoor environmental conditions experimentally. In the non-frosting conditions, film condensation formed on the surface of the hydrophilic evaporator and the evaporation temperature decreased with the formation of water film, resulting in a decrease in heat production and COP. In the frosting conditions, the time of forming the frost layers with the same thickness on the superhydrophobic surface was more than 4 times longer than that on the hydrophilic surface. The COP of the superhydrophobic evaporator unit was improved by 2.9% to 8.2% under the non-frosting conditions, by 11.5% under the continuous heating conditions and by 14.28% when the hydrophilic unit performed two defrosting cycles, respectively. During the period in which the hydrophilic evaporator unit completed two frosting/defrosting cycles, the energy loss coefficient caused by the defrosting process was 31.65% compared to the superhydrophobic evaporator unit. This work extended the experimental method of superhydrophobic heat exchanger, contributing to the application of superhydrophobic finned-tube evaporators in ASHP units.

Concentrated solar thermoelectric power generator equipped with a novel ultrathin wet porous membrane cooling technique; experimental study

One side of any thermoelectric power generator (TEG) is hot while the other side should always stay cold. The higher the temperature difference, the greater the power generation. This paper offers a particular ultrathin wet porous membrane (UWPM) as a new cooling method for a solar thermoelectric power generator. According to the graphical abstract, the membrane has a capillary-wicking feature on one side, making it possible to be soaked spontaneously and create a steady thin water film on the ceramic layer of the thermoelectric, thereby serving as an energy-free, enthalpy of vaporization-based cooling method (surface vaporization). Interestingly, water is replenished spontaneously as long as the water exists in the tank. The suggested mechanism is tested under two weather conditions: one hot, dry day (ambient air around 40 °C) and one moderate day (ambient air around 30 °C), with different air speeds between 1.5 and 4.5 m/s to simulate different wind speeds in real applications. Power, cold side surface temperature, maximum conversion efficiency, etc., are measured, evaluated, discussed, and compared with the common fin-pin heatsink/fan thermal management tool. Notably, the implementation of the UWPM demonstrates a substantial enhancement in thermoelectric generator performance. It is noted that the lowest temperature that can be obtained through vaporization can be colder than ambient air temperature, approaching the wet-bulb temperature. The UWPM keeps the cold side temperature up to 10 degrees colder than that achieved in the heatsink method. This is why the generated power by the TEG is around 2.5 times higher when utilizing the UWPM. Furthermore, unlike the fin-pin heatsink (FPH) thermal management tool, warmer weather conditions do not diminish the cooling quality of the UWPM method. Indeed, the cold side temperature on a hot, dry day is almost the same as that on a moderate day using the UWPM technique. This is because hot ambient temperature induces greater and easier vaporization, leading to a higher cooling effect.

Determining Consumptive Water Use for Corn Cultivation at High Altitudes: A Comparative Study of Three Methods

A desirable water supply in agriculture requires quantitative methods to determine crop requirements. De-termination of hydric request of maize Var INIAP 102 is promising, mainly at altitudes over 2000 meters above sea level. This study analyzed three methods (lysimeter, evaporimeter tank, and empiric formula FAO) to determine Chimborazo province's hydric requirements for Var INIAP 102. Vegetative and yield variables were recorded, and the effect of different water films on the vegetative growth of maize was de-termined. When water was more available in the soil, the vegetative growth, yield, and pod weight per plant of maize Var INIAP 102 were higher. This study is of great importance because determining the hydric requirement of maize Var INIAP 102 was done for the first time in Chimborazo province and will support farmers in better water use for irrigation. Keywords: irrigation sheet, lysimeter, sweet corn, water requirements, evaporation tank

Determining Consumptive Water Use for Corn Cultivation at High Altitudes: A Comparative Study of Three Methods.

A desirable water supply in agriculture requires quantitative methods to determine crop requirements. De-termination of hydric request of maize Var INIAP 102 is promising, mainly at altitudes over 2000 meters above sea level. This study analyzed three methods (lysimeter, evaporimeter tank, and empiric formula FAO) to determine Chimborazo province's hydric requirements for Var INIAP 102. Vegetative and yield variables were recorded, and the effect of different water films on the vegetative growth of maize was de-termined. When water was more available in the soil, the vegetative growth, yield, and pod weight per plant of maize Var INIAP 102 were higher. This study is of great importance because determining the hydric requirement of maize Var INIAP 102 was done for the first time in Chimborazo province and will support farmers in better water use for irrigation. Keywords: irrigation sheet, lysimeter, sweet corn, water requirements, evaporation tank

Impact of organic acid molecular length and structure on rock oil-wetting rapidity and stability

The oil-wetting properties of organic acids play a crucial role in various industrial applications, including enhanced oil recovery, oil spill remediation, surface modification, and so on. This study investigated the impact of organic acid molecular length and structure on oil-wetting rapidity and stability on sandstone and carbonate. Model oils prepared by dissolving organic acids in n-decane, and crude oil, were used as the oil phase. Their oil-wetting behavior was evaluated by contact angle values. The maximum molecular length of each organic acid was approximated based on its molecular structure. Our results indicate that organic acids change wettability much faster in carbonate rock than in sandstone. Longer organic acid molecules exhibit enhanced oil-wetting potential due to increased hydrophobic interactions with oil phases. Water film does not have a long-term impact on the oil-wetting process by organic acid on Indiana limestone. However, the existence of a water film largely inhibited the oil-wetting process for Indiana limestone in crude oil, and for Berea sandstone in crude and model oil. Furthermore, molecular structure, such as the presence of functional groups, significantly influences oil-wetting properties. Organic acids with an aromatic ring demonstrated a more stable oil-wetness against wettability alteration induced by surfactant treatment. Gemini surfactants with benzene ring(s) in the spacer removed aromatic organic acid more efficiently than surfactants without benzene ring. Overall, this study provides insights into the design and optimization of organic acids for applications requiring effective oil-wetting and oil-wetness stability, as well as the designing of surfactant structures with higher oil removal efficiency.