Evaporation Mechanism Research Articles

Large eddy simulation of spray evaporation characteristics of alcohol-based fuels based on modified evaporation model with UNIFAC

An accurate description of spray atomization and evaporation behavior is an important prerequisite for studying fuel spray's combustion performance and emission characteristics, especially for multi-component blended fuels (e.g., alcohol-based fuels). To improve the simulation accuracy, the large eddy model combined with a modified evaporation model with UNIFAC is proposed to investigate the spray evaporation kinetics of the mixtures of alcohol and alkane under gasoline engine conditions. The model accuracy is verified from multiple perspectives, including bubble point pressure, bi-component droplet and spray evaporation experiments. Then the modified evaporation model with the UNIFAC coupled LES method is used to study the spray evaporation of alkane/ethanol mixtures. The conclusions are as follows: 1) Asymmetric vortex structures in the spray lead to circumferential inhomogeneous distribution of evaporation characteristics. 2) The vapor mass fractions are significantly higher than those of Raoult's law for small proportions of the bi-component mixtures E10 and E85. 3) The E10-NH spray evaporation rate and total evaporated mass were higher than E10. In conclusion, the modified evaporation model with the UNIFAC-coupled LES method captures the tiny turbulent vortex structures during spray atomization, which further reveals the evaporation mechanism of two-component alcohol-based fuels by spray atomization.

Entanglement entropy for the black 0-brane

We analyze the entanglement entropy between the black 0-brane solution to supergravity and its Hawking radiation. The black 0-brane admits a dual gauge theory description in terms of the matrix model for M-theory, named Banks Fischler Shenker Susskind (BFSS) theory, which is the theory of open strings on a collection of N D0-branes. Recent studies of the model have highlighted a mechanism of black hole evaporation for this system, based on the chaotic nature of the theory and the existence of flat directions. This paper further explores this idea, through the computation of the von Neumann entropy of Hawking radiation. In particular, we show that the expected Page curve is indeed reproduced, consistently with a complete recovery of information after the black hole has fully evaporated. A pivotal step in the computation is the definition of a Hilbert space that allows for a quantum mechanical description of partially evaporated black holes. We find that the entanglement entropy depends on the choice of a parameter, which can be interpreted as summarizing the geometric features of the black hole, such as the size of the resolved singularity and the size of the horizon. Published by the American Physical Society 2024

Protonated molecular clusters: promoting molecular complexity

Abstract Molecules identified in Space display a diversity greater than ever, yet the mechanisms responsible for this complexity remain largely unknown. The extreme conditions faced by these molecules under astrophysical conditions raise several questions about their persistence and evolution. In this work, we explore the role of gas-phase protonated molecular dimers, which act both as protectors of existing molecules and as promotors in the emergence of new species. Experiments were conducted using the DIAM irradiation device on four protonated dimers of astrophysical interest, namely the pyridine, methanol, glycine pure dimers and the diglycine-glycine mixed dimer. Analysis of the observed relaxation channels following an energy deposition mimicking cosmic radiation reveals three main mechanisms of evaporation, covalent bond breaking, and unimolecular reaction. Focusing on the latter, our experiments combined with quantum chemical calculations of the relevant pathways shed new light onto the role of the protonation site on the reactants.

The water vapor distribution profile in dry soil layer during evaporating with high spatial resolution monitored by distributed fibre-optic sensing technology

The dry soil layer (DSL) typically forms on the surface of sandy soils during the evaporation process, with water in the DSL moving solely as vapor. Understanding the DSL thickness and its water vapor distribution is crucial for accurately estimating soil water flux, improving evaporation mechanisms, and enhancing ecological conservation efforts. This study employed distributed fibre-optic sensing (DFOS) technology to achieve high spatial resolution measurements (up to 1 mm) of the water vapor distribution within the DSL. We measured soil water vapor profiles in a sand column subjected to evaporation over 24 days using a 60 cm long relative humidity sensing probe and an optical frequency domain reflection (OFDR) interrogator. We effectively captured the downward migration of the evaporating surface from the sand surface and quantified the inhibitory effect of DSL thickness on evaporation using a logarithmic function. Additionally, we identified a linear distribution of water vapor with depth in the DSL. Our findings offer novel insights into the role of DSL in the hydrological behaviour of unsaturated soils and demonstrate the potential of our approach for investigating dynamic changes in in-situ DSLs, particularly in arid and semi-arid regions.

Integrating atmospheric water harvester with hydrovoltaics: Simultaneous freshwater production and power generation

Integrating an atmospheric water harvester (AWH) with hydrovoltaic (HV) technology pokes a new technology and notification to the arid region people to harvest freshwater and electricity simultaneously from the humid atmosphere even in the non-water region. In this work, we have fabricated a composite material by attaching the sulfonic groups to the graphitic oxide substrate (SGhO) through a one-step reflux method. The material delivers an excellent water absorbing ability of 0.3 g g−1h−1and 2 g g−1in 19 h under a 40–60 % humid environment. The electrical experiments show during moisture absorption, a specific voltage and current are generated indicating the dissociation of sulfonic groups in the graphitic structure creates a drift movement of H+ions through the composite. Our device delivers a voltage of 0.25 V and a high current of 160 µA from a single device during moisture movements through the structure under the relative humidity of 60–65 %. The rapid enhancement of the interfacial temperature from 31 °C to 44 °C within a minute due to the presence of graphitic oxide shows excellent photothermal capacity for the light-induced evaporation mechanism and collecting the condensed water as freshwater. The composite can evaporate all absorbed water within 0.5 h in one sun illumination (1 kW/m2) under the ambient relative humidity (RH) of 40–60 %. Several trials of washing treatments were done to ensure the chemical bonding of sulfonic groups into the graphitic structure. Therefore, it was confirmed the excellent stability, and repeatability for repeatable practical applications. Furthermore, the purity of the collected water is conducted with various analyses such as pH, TDS, and UV–Vis absorption studies and confirmed the excellent purified water which highly meets the global drinking water standards. Therefore, this work demonstrates a single way to achieve dual goals such as water harvesting as well as power generation for a better tomorrow.

Theoretical insights into laser-assisted field evaporation of ionic compounds

This study addresses the kinetic process of field evaporation of MgO assisted by ultrafast laser pulses combining density functional theory and molecular dynamics. A quantitative model is presented to describe the competitive evaporation of Mg and O ions under various conditions by comparing the activation barriers. The coordination number has a significant impact on the evaporation kinetics. The evaporation ratio of Mg to O rises with increasing DC field strength and laser intensity. Moreover, the energetics of evaporation is in correlation with photo-induced field ionization, revealing distinct mechanisms of evaporation for Mg and O. While Mg undergoes further ionization and field evaporation simultaneously, the evaporation of O is coupled with the relaxation of excited carriers. The final charge state of evaporated O is determined by the DC field strength rather than the laser intensity. Our findings provide insights into laser–matter interactions in ionic compounds and contribute to the development of atom probe techniques.

Evaporation characteristics of single free-falling liquefied natural gas droplet under different ambient conditions based on the VOF method

The evaporation characteristics of droplets is a fundamental issue for accurate depictions of moving liquefied natural gas (LNG) droplets and constantly changing ambient environment owing to intense heat, mass transfer, and momentum exchanges. In this study, a modified droplet evaporation model is developed to investigate the evaporation behavior of a single free-falling LNG droplet under various ambient conditions. The proposed model captures the droplet interface and calculates the mass transfer rate through the vapor concentration gradient using the volume of fluid method integrated with a smooth function. Evaporation experiments were conducted on a single free-falling LNG droplet to capture the evaporation process. The results indicate that it is acceptable to ignore the effect of the Stefan flow of a single free-falling LNG droplet. This study also examined the impact of different ambient conditions on evaporation characteristics. The results indicate that the evolution of the droplet diameter is mainly influenced by the ambient temperature because it affects the thermal properties of the surrounding gas and the distribution of the boundary layer. The temporal characteristics of the Nu and Sh numbers generally stabilize after a period of rapid decline. This study provides a theoretical basis for understanding the evaporation mechanisms of LNG droplets.

Muzzle bubble dynamics characterization of underwater launching

To comprehensively understand the dynamic behavior of muzzle bubbles during underwater launching, an emptying process aligned with the muzzle flow characteristics is established and an evaporative condensation mechanism is modeled according to the high temperature and pressure properties of the propellant gas. Utilizing the spherical bubble theory, which comprises the inflation process and evaporative condensation effects, the dynamics of muzzle bubbles and their corresponding pressure waves are investigated. The numerical simulation results well agree with the experimental observations in terms of bubble radius and near-field pressure waves. Furthermore, the influence of two key factors on the bubble dynamics is examined: underwater launching depth and initial muzzle pressures. The results illustrate that the inflation process needs to be accurately described for precise pressure wave predictions. Using the evaporation condensation model, the bubble radius and frequency can be accurately characterized. Moreover, the launching depth influences the free expansion radius and oscillation frequency mostly due to the increase in hydrostatic pressure, which decreases by 33% and increases by 150% in the 1–20 m range, respectively. The initial muzzle pressure affects the initial expansion velocity and initial shock wave mainly due to the increase in the mass flow rate, which increase by 56% and 82% in the 35–65 MPa range, respectively.

A hurricane trigger in desalted ocean water

For forming a hurricane, two things are needed: a strong thunderstorm and warm water of the ocean surface. The first thing accumulates the desalted seawater as a working medium of hurricane, and the second one “feeds” the hurricane engine by this medium. The thin mechanisms of evaporation of the desalted ocean water are considered in this article. It is shown that the local oxidation of seawater under the eye wall can change the power and motion-direction of hurricane.

Modelling the evaporative cooling effect from methanol injection in the intake of internal combustion engines

Renewable methanol is one of the most promising alternative fuels for internal combustion engines. However, its much higher latent heat of vaporization compared to traditional fossil-based hydrocarbon fuels poses new challenges. On both spark-ignition (SI) engines and dual-fuel (DF) engines, methanol can be introduced through injectors installed in the intake path, with its evaporation then causing a cooling effect to the intake air flow. While this is beneficial in mitigating knock with both SI and DF operations, it could potentially lead to cold-starting issues in SI engines and incomplete combustion in DF engines. To properly model the in-cylinder behaviour, the mixture temperature after methanol injection needs to be accurately predicted. A simple yet effective methanol evaporation model based on the liquid droplet and film evaporation mechanisms is thus proposed here to quantify the evaporative cooling effect from methanol injection. The model first treats the methanol spray as a group of droplets with identical size, and after reaching the wall the model assumes that the remaining methanol forms a thin liquid film. The evaporation rates and the consequent temperature drops of these two modes are calculated separately. The calculation results indicate that only a negligible amount of methanol evaporates as droplets, with the predicted temperature drops agreeing well with the validation datasets when taking only the film evaporation into account. The key factor for this good agreement is that the balance between the heat and mass transfer needs to considered when evaluating the surface temperature of a liquid methanol film. The proposed model also suggests that the droplet evaporation can be greatly improved with an injection angle nearly parallel to the air flow, or a finer initial droplet size. Both measures are more effective than increasing the air temperature before injection.

Solvent Cavitation during Ambient Pressure Drying of Silica Aerogels.

Ambient-pressure drying of silica gels stands out as an economical and accessible process for producing monolithic silica aerogels. Gels experience significant deformations during drying due to the capillary pressure generated at the liquid-vapor interface in submicron pores. Proper control of the gel properties and the drying rate is essential to enable reversible drying shrinkage without mechanical failure. Recent in operando microcomputed X-ray tomography (μCT) imaging revealed the kinetics of the phase composition during drying and spring-back. However, to fully explain the underlying mechanisms, spatial resolution is required. Here we show evidence of evaporation by hexane cavitation during the ambient-pressure drying of silylated silica gels by spatially resolved quantitative analysis of μCT data supported by wide-angle X-ray scattering measurements. Cavitation consists of the rupture of the pore liquid put under tension by capillary pressure, creating vapor bubbles within the gels. We found the presence of a homogeneously distributed vapor-air phase in the gels well ahead of the maximum shrinkage. The onset of this vapor/air phase corresponded to a pore volume shrinkage of ca. 50 vol % that was attributed to a critical stiffening of the silica skeleton enabling cavitation. Our results provide new aspects of the relation between the shape changes of silica gels during drying and the evaporation mechanisms. We conclude that stress release by cavitation may be at the origin of the resistance of the silica skeleton to drying stresses. This opens the path toward producing larger monolithic silica aerogels by fine-tuning the drying conditions to exploit cavitation.

Evaporation mechanisms during droplet levitation and coalescence based on molecular dynamics

Droplet levitation and coalescence mechanisms have consistently been a focal point in scientific research. From the perspective of molecular interactions, we investigated the influence of vapor pressure on the levitation and coalescence of droplets. The evaporation of nanodroplets and liquid pools under different initial environments was simulated by nonequilibrium molecular dynamics. The study analyzed the effects of evaporation during the processes of droplet levitation and coalescence and determined the existence of the Knudsen layer. Knudsen layers consisting of water molecules rather than clusters are generated during the evaporation. The definition, properties, and mechanisms of the layers were investigated.

Hypergolic Ignition by Off-Center Binary Collision of Monoethanolamine-NaBH4 and Hydrogen Peroxide Droplets

Hypergolic ignition of H2O2 and MEA-NaBH4 by off-center collision of their droplets was experimentally studied, focusing on the characteristics and mechanism of droplet mixing, droplet heating and evaporation, and gas-phase ignition. The whole collision ignition process was divided into five stages, which were compared, respectively, with that of head-on collision. Under the condition of a slightly off-center collision (for cases where B < 0.35), H2O2 droplets penetrate MEA-NaBH4 droplets after the collision and coalesce with it, but the internal H2O2 drop inside the MEA-NaBH4 droplet does not form a stable sphere. Instead, it rotates and expands inside the mixed droplet. With B increasing to 0.59, the droplets no longer coalesce after collision but separate away, forming satellite droplets. In such cases, multi-ignition mode is observed. When B increases to a certain extent, specifically, 0.85, a grazing collision is observed such that no mass transfer exists during the interaction of droplets, which leads to ignition failure. A theoretical model quantifying droplet swelling rate was established to calculate the volume change of the droplet. It was found that the swelling can be attributed to the flash boiling of superheated internal H2O2 fluid. Meanwhile, the ignition delay time was found to linearly decrease with B at various Wes until the extent where the chemical reaction takes over control, leading to an almost constant time delay defined as RDT. Additionally, the regime of ignition modes corresponding to different droplet mixing features is summarized in the We-B parametric space.

Dynamic evaporation characteristics of liquefied natural gas droplets

To delve into the intricate evaporation and dispersion mechanisms of dense droplets formed in the vicinity of liquefied natural gas (LNG) accidental releases, it is imperative to first examine the evaporation dynamics of individual moving LNG droplets. This paper presents a visual experimental setup designed to scrutinize the temporal evolution of diameter and displacement of single free-falling LNG droplets. Additionally, eight typical drag force models used for droplet motion state calculations were assessed. The optimal drag force models were selected to accurately predict the displacement of LNG droplets in the wide range of 100 < Re < 10 000. Moreover, eight typical gas phase models applied to predict heat and mass transfer were evaluated, revealing that none accurately capture the dynamic evaporation of free-falling LNG droplets. Subsequently, a new gas phase model suitable for predicting LNG droplet evaporation behavior is proposed. Furthermore, the periodic oscillation behavior of LNG droplet shape during the falling process is uncovered. The oscillation amplitude and dominant frequency of droplets are quantitatively investigated using the aspect ratio of droplets. Finally, an in-house program is developed to comprehensively analyze the evaporation characteristics of LNG droplets under different initial droplet diameters, velocities, and ambient temperatures. Based on gray relational analysis, the relative importance of three impacting factors on the evaporation coefficient is ranked.

Evaporation rate and kinetic mechanism of noble antimony under vacuum

Herein, a novel mathematical and statistical method is applied to the kinetic study of vacuum gasification of noble-antimony alloys. The evaporation rates of pure and noble antimony in a unit time at 823–1023 K and 5–600 Pa are determined using a vacuum differential gravimetric furnace, and their respective evaporation mechanisms under vacuum are analyzed in detail in conjunction with their triple point. Results show that the actual evaporation rates of pure and noble antimony are consistent with those obtained using a nonlinear logistic model (ω=A2+(A1-A2)/[1+P/P0a); the goodness of fit (R2) is > 0.9965 at all temperatures. The critical pressure values of pure and noble antimony at 823–1023 K are obtained, which are linearly dependent on the temperature. According to the theoretical and actual maximum evaporation rates of pure and noble antimony, the evaporation coefficient is corrected and the relation between the actual evaporation rate and temperature (lgω=AT+B) is further obtained, which can be used to calculate and predict the evaporation rates of noble antimony at different temperatures. By studying the evaporation rate of pure and noble antimony, this study provides the kinetic parameters for vacuum gasification of noble antimony and simultaneously enriches the kinetic database, which develops and improves the theory and practice of vacuum gasification of noble-metal alloys.

Evaporation Mechanisms and Heat Transfer in Porous Media of Mixed Wettabilities with a Simulated Solar Flux and Forced Convection Through the Media

Abstract An experimental apparatus was designed to study the impacts of wettability on evaporation of water for: 1) a 5.7-cm-thick layer of hydrophilic Ottawa sand; 2) a 5.7-cm-thick layer with 12% hydrophobic content, consisting of a 0.7-cm-layer of n-Octyltriethoxysilane-coated hydrophobic sand buried 1.8 cm below the surface of hydrophilic sand; and 3) a 5.7-cm-thick layer with mixed wettabilities, consisting of 12% n-Octyltriethoxysilane-coated hydrophobic sand mixed into hydrophilic sand. The sand-water mixtures experienced forced convection above and through the sand layer, while a simulated solar flux (i.e., 112 ± 20 W/m2) was applied. Evaporation from homogeneous porous media is classified into the constant-rate, falling-rate, and slow-rate periods. Wettability affected the observed evaporation mechanisms, including the transition from constant-rate to falling-rate periods. Evaporation entered the falling-rate period at 12%, 20%, and 24% saturations for the all hydrophilic sand, hydrophobic layer, and hydrophobic mixture, respectively. Wettability affected the duration of the experiments, as the all hydrophilic sand, hydrophobic layer, and hydrophobic mixture lasted 17, 20, and 26 trials, respectively. Both experiments with hydrophobic particles lasted longer than the all hydrophilic experiment and had shorter constant-rate evaporation periods, suggesting hydrophobic material interrupts capillary action of water to the soil surface and reduces evaporation. Evaporation fluxes were up to 12× higher than the vapor diffusion flux due to enhanced vapor diffusion and forced convection.

Selective recovery of Sm from Sm-Co magnet scrap by vacuum distillation

Sm-Co rare earth permanent magnet materials are widely used in special fields such as new energy and electronic information. Sm-Co permanent magnet scraps are generated during the preparation and the use of end-of-life permanent magnets, which need to be recycled for the sustainable development. It is proposed to selectively recover Sm from the Sm-Co permanent magnet scraps by vacuum distillation. The experimental investigations were carried out in a vacuum furnace with double temperature zones for the efficient condensation of Sm vapor based on the thermodynamic and kinetic calculations. The recycling feasibility of the recovery of rare earth and the evaporation mechanism of Sm were also demonstrated in this work. The results show that Sm with the purity over 99% was obtained by the molybdenum condenser used as a condensing collectors at given conditions, providing a reference for the pyrometallurgical recovery of rare earth secondary resources.

Real-Time Monitoring of the Evaporation and Fission of Electrospray-Ionized Polystyrene Beads and Bacterial Pellets at Elevated Temperatures.

This study uses real-time monitoring, at microsecond time scales, with a charge-sensing particle detector to investigate the evaporation and fission processes of methanol/micrometer-sized polystyrene beads (PS beads) droplets and bacterial particles droplets generated via electrospray ionization (ESI) under elevated temperatures. By incrementally raising capillary temperatures, the solvent, such as methanol on 0.75 μm PS beads, experiences partial evaporation. Further temperature increase induces fission, and methanol molecules continue to evaporate until PS ions are detected after this range. Similar partial evaporation is observed on 3 μm PS beads. However, the shorter period of the fission temperature range is necessary compared to 0.75 μm PS beads. For the spherical-shaped bacterium, Staphylococcus aureus, the desolvation process shows a similar fission period as compared to 0.75 μm PS beads. Comparably, the rod-shaped bacteria, Escherichia coli EC11303, and E. coli strain W have shorter fission periods than S. aureus. This research provides insights into the evaporation and fission mechanisms of ESI droplets containing different sizes and shapes of micrometer-sized particles, contributing to a better understanding of gaseous macroion formation.

Characteristic and mechanism of pollution by laser cleaning high-value vehicle parts with a complex structure in remanufacturing industry

Remanufacturing high-value vehicle parts is of substantial significance for the circular economy because it provides a second service life and reduces solid waste generation. Laser cleaning is a promising method in the remanufacturing industry owing to its high energy, precision, and efficiency. However, the pollution caused by laser cleaning remains unknown and has rarely been reported, limiting the application of this method. In this study, pollution removal and conversion using a high-energy laser were explored, and environmental life cycle and health risk assessments were conducted. The results showed that high-energy lasers might induce new organic pollutants, such as olefins, alkynes, and aldehydes. During laser cleaning, thermal elastic expansion and shock wave generation were the main mechanisms of rust removal, and evaporation and small-scope boiling were used for waste oil removal. The mean concentration of PM10 was above 7000 µg/m3 in laser rust removal, and the total concentration of volatile organic compounds (VOCs) was the highest in laser oil removal (∼ 2568 µg/m3). Particulate matter contained high amounts of Fe, Al, and Mn. An environmental life cycle assessment indicated that laser cleaning for stain removal significantly reduced the total environmental impact compared with that of traditional solvent-ultrasonic cleaning (∼ 40.0%) and sandblasting (∼ 83.3%). This study provides an environmental protection basis for increasing the use of laser cleaning in the remanufacturing industry.

Morphology Characteristics of the Liquid–Vapour Interface in Porous Media

The evolution of the liquid–vapour interface plays a crucial role in multiphase flow, heat and mass transfer, and fluid phase change in porous media. A thorough investigation of the interface under varying degrees of saturation is necessary and crucial to fully understanding the key mechanism of soil water evaporation. The pore voids and fluids are characterized using X-ray microtomography and image processing. Salt solutions usually replace pure water for better contrast and image development. Machine learning algorithms were employed to identify and extract the different phase and their interface accurately. Then, variations in the geometrical and topological features of the interface at varying saturation during evaporation were analysed to quantitatively describe the connectivity of the liquid phase and the morphological change in the liquid–vapour interface. Topological analysis reveals that normalized Euler characteristic numbers quantify the complementary connectivity of liquid and vapour phase. The curvatures of the liquid–vapour interface of the samples under various saturations classify the liquid–air interface curvature of samples under various saturations for quantitatively describing the migration progress and quantity distribution of typical interface along with drying.