Evaporation Kinetics Research Articles

On evaporation kinetics of multicomponent aerosols: Characteristic times and implications for volatility measurements

On evaporation kinetics of multicomponent aerosols: Characteristic times and implications for volatility measurements

Beam-shaping in laser-based powder bed fusion of metals: A computational analysis of point-ring intensity profiles

Laser-based powder bed fusion has the potential to enable manufacturing of local material properties and locally varying alloys. One promising approach under research is shaping of the applied laser beam. The current commercial standard using a Gaussian laser beam profile is associated with a high energy intensity peak and strong gradients. A potential alternative beam shape is the point-ring profile where laser energy is distributed between a central spot and an outer ring. We conduct a numerical study of beam shape impact on melt-pool shapes, surface temperatures, evaporation and flow dynamics of single-melt-tracks. To that end, we apply a Weakly Compressible Smoothed Particle Hydrodynamics solver coupled with a ray-tracing laser scheme. A point-ring profile is compared to a standard Gaussian profile. The profiles are studied at two different beam sizes to find the influence of beam size on the shape effect. We find good agreement between numerical results and experimental data for both narrow and deep, as well as wide and shallow melt-tracks. The simulation results show that beam size and thus energy density influence the effect beam-shaping has on the melt-pool dynamics. Both the distribution of evaporation and surface tension forces over the melt-pool surface are found to depend on the used beam shape. The study highlights the importance of distinguishing between size and shape effects when investigating laser beam shapes. Both energy density and its distribution need to be tuned for the desired melt-pool behavior.

Physical Vapor Deposition of Indium-Doped GeTe: Analyzing the Evaporation Process and Kinetics

Chalcogenide glasses have broad applications in the mid-infrared optoelectronics field and as phase-change materials (PCMs) due to their unique properties. Chalcogenide glasses can have crystalline and amorphous phases, making them suitable as PCMs for reversible optical or electrical recording. This study provides an in-depth analysis of the evaporation kinetics of indium-doped chalcogenides, GeTe4 and GeTe5, using the physical vapor deposition technique on glass substrates. Our approach involved a detailed examination of the evaporation process under controlled temperature conditions, allowing precise measurement of rate changes and energy dynamics. This study revealed a significant and exponential increase in the evaporation rate of GeTe4 and GeTe5 with the introduction of indium, which was particularly noticeable at higher temperatures. This increase in evaporation rate with indium doping suggests a more complex interplay of materials at the molecular level than previously understood. Furthermore, our findings indicate that the addition of indium affects the evaporation rate and elevates the energy requirements for the evaporation process, providing new insights into the thermal dynamics of these materials. This study’s outcomes contribute significantly to understanding deposition processes, paving the way for optimized manufacturing techniques that could lead to more efficient and higher-performing optoelectronic devices and memory storage solutions.

Cellulose–derived carbon scaffolds with bidirectional gradient Fe3O4 distribution: Integration of green EMI shielding and thermal management

Cellulose papers (CPs) possess a pore structure, rendering them ideal precursors for carbon scaffolds because of their renewability. However, achieving a tradeoff between high electromagnetic shielding effectiveness and low reflection coefficient poses a tremendous challenge for CP-based carbon scaffolds. To meet the challenge, leveraging the synergistic effect of gravity and evaporation dynamics, laminar CP-based carbon scaffolds with a bidirectional gradient distribution of Fe3O4 nanoparticles were fabricated via immersion, drying, and carbonization processes. The resulting carbon scaffold, owing to the bidirectional gradient structure of magnetic nanoparticles and unique laminar arrangement, exhibited excellent in-plane electrical conductivity (96.3 S/m), superior electromagnetic shielding efficiency (1805.9 dB/cm2 g), low reflection coefficients (0.23), and a high green index (gs, 3.38), suggesting its green shielding capabilities. Furthermore, the laminar structure conferred upon the resultant carbon scaffold a surprisingly anisotropic thermal conductivity, with an in-plane thermal conductivity of 1.73 W/m K compared to a through-plane value of only 0.07 W/m K, confirming the integration of thermal insulation and thermal management functionalities. These green electromagnetic interference shielding materials, coupled with thermal insulation and thermal management properties, hold promising prospects for applications in sensitive devices.

Weather-related changes in the dehydration of respiratory droplets on surfaces bolster bacterial endurance

HypothesisThe study shows for the first time a fivefold difference in the survivability of the bacterium Pseudomonas Aeruginosa (PA) in a realistic respiratory fluid droplet on fomites undergoing drying at different environmental conditions. For instance, in 2023, the annual average outdoor relative humidity (RH) and temperature in London (UK) is 71 % and 11 °C, whereas in New Delhi (India), it is 45 % and 26 °C, showing that disease spread from fomites could have a demographic dependence. Respiratory fluid droplet ejections containing pathogens on inanimate surfaces are crucial in disease spread, especially in nosocomial settings. However, the interplay between evaporation dynamics, internal fluid flow and precipitation and their collective influence on the distribution and survivability of pathogens at different environmental conditions are less known. ExperimentsShadowgraphy imaging is employed to study evaporation, and optical microscopy imaging is used for precipitation dynamics. Micro-particle image velocimetry (MicroPIV) measurements reveal the internal flow dynamics. Confocal imaging of fluorescently labelled PA elucidates the bacterial distribution within the deposits. FindingsThe study finds that the evaporation rate is drastically impeded during drying at elevated solutal concentrations, particularly at high RH and low temperature conditions. MicroPIV shows reduced internal flow under high RH and low temperature (low evaporation rate) conditions. Evaporation rate influences crystal growth, with delayed efflorescence and extending crystallization times. PA forms denser peripheral arrangements under high evaporation rates and shows a fivefold increase in survivability under low evaporation rates. These findings highlight the critical impact of environmental conditions on pathogen persistence and disease spread from inanimate surfaces.

Enhanced insights into paired droplet evaporation dynamics on heated substrates: Unveiling the role of convection and diffusion

This study aims to examine the evaporation characteristics of single and multiple droplets on a heated substrate. By utilizing a multi-syringe pump, deionized water droplets were precisely deposited on a copper substrate, ensuring uniformity and accuracy in the experimental setup. The shadowgraph technique was instrumental in determining the droplet contact angle and volume with exceptional clarity and precision. This work numerically predicted the vapor distribution and local evaporation flux across the liquid-air interface. A critical assessment of the role of natural convection at varying substrate temperatures was performed by contrasting diffusion-only cases with those incorporating both diffusion and convection. The findings reveal that the droplet pinning motion remains unchanged across different distances between droplets and various substrate temperatures, indicating that neither vapor accumulation nor substrate temperature significantly influences the behavior of the contact line. Notably, the study identifies a reduction in the evaporation rate of closely positioned paired droplets, related to a shielding effect. However, with increasing substrate temperature, the role of natural convection was found to become more pronounced, effectively reducing the overall evaporation time for both single and paired droplets, thus facilitating a quicker evaporation process.

TO HIGHLY PRODUCTIVE SYNTHESIS OF ALUMINUM NANOPARTICLES IN PLASMA FLOW AT ATMOSPHERIC PRESSURE

Purpose. To study the highly productive evaporation of aluminum micron powder in an atmospheric pressure plasma jet for the synthesis of nanoaluminum. Using special plasma technology, nanoparticles can be produced by rapid melting and evaporation of the initial micrometer particles and their subsequent re-nucleation. Research methods. Methods of mathematical and computer modeling of subsonic plasma turbulent jets at atmospheric pressure and experimental studies of two-phase processes during thermal plasma treatment using an arc plasma torch. Results. Based on computer modeling, a special reactor system was designed and developed, which includes a plasma-jet reactor with an electric arc plasma torch for the synthesis of aluminum nanoparticles. Numerical modeling makes it possible to determine the position of the melting point, evaporation and crushing of a molten particle, the evolution of the fractional composition of the dispersed phase, and find the speed and temperature of the particle in the area from its melting point to the crushing point. An experimental test of the operation of the reactor system was carried out using arc plasma torches with a power of 30 and 150 kW. It has been shown that intensifying the fragmentation of dispersed raw materials in a plasma jet can be useful in technologies for producing nanomaterials. The consequence of the fragmentation process is the redistribution of the fractional composition of the powder along the plasma jet and the accompanying changes in the dynamics of movement, heating and evaporation of particles. It has been determined that when the temperature of the largest aluminum particles reaches 2500 C, the total amount of evaporated mass is theoretically equal to 100%. The main parameters influencing the behavior of particles in a plasma jet are particle diameter, powder injection rate, flow rate, temperature and composition of the plasma gas. Taking these parameters into account will allow the process to operate at increased productivity. Scientific novelty. A mathematical description of the process of fragmentation a polydisperse powder, based on a continuum approach, has been obtained, which makes it possible to determine the position of the crushing point of a molten particle, the fractional composition of the dispersed phase, and find the speed and temperature of the particle in the area from its melting point to the point of crushing and evaporation. It was shown for the first time that it is possible to carry out a process in which complete evaporation of a molten drop is achieved due to the high enthalpy of the plasma before the end of mixing with steam. Practical value. A special reactor system has been designed and developed, which includes a plasma-jet reactor with an electric arc plasmatron for the synthesis of aluminum nanoparticles. The operating parameters of the reactor system have been determined, which will allow the synthesis of aluminum nanoparticles to be carried out with high productivity.

Evaporation Dynamics of Deionized Water Droplets on Rough Substrates: The Coupling of Stick-Jump Motion And Evaporation

Abstract Substrate roughness can greatly affect the evaporation of sessile droplets, thus determining the efficiency of applications, such as ink-jet printing and coating. Here, we conduct experiments on the evaporation of deionized water droplets on glass substrates with roughness in the range 0.1 - 0.2 µm to investigate its effect on the dynamics of the contact angle and radius, as well the heat and mass transfer during evaporation. We discover a “stick-jump” phenomenon as part of a five-stage process that is determined by the evolution characteristics of the contact angle and radius, and includes the volume expansion, first stick, second stick, jump and final stages. Moreover, we find that the evaporation mode of the droplets is not affected by the increase of substrate roughness, whereas the heat and mass transfer processes intensify with the increase of substrate roughness in the presence of non-uniform evaporation effects. Also, the pinning-depinning mechanism of the “stick-jump” phenomenon during evaporation is carefully analyzed in terms of the Gibbs free energy, thus establishing a relation among Gibbs and excess Gibbs free energies and substrate roughness, which predicts the evaporation dynamics of the droplet. We anticipate that this study unravels key aspects of the droplet evaporation-mechanisms on rough substates toward optimizing and advancing relevant technology applications.

A mesoscopic approach for nanoscale evaporation heat transfer characteristics

We propose a mesoscopic approach for investigating steady/transient nanoscale evaporation heat transfer characteristics, whose kinetic nature makes it an ideal tool to model the evaporation kinetics at the liquid-vapor interface and the microscopic wall-fluid interactions. Simulation of the evaporation of a flat nanoscale thin liquid film demonstrates its capability of resolving kinetically limited evaporation and liquid film adsorption. For the simulation of an evaporating meniscus in a nanochannel, our proposed mesoscopic approach considers the conservation of mass, momentum and energy of both liquid and vapor phases, thereby naturally incorporating both the multi-dimensional heat transfer effect and vapor transport resistance in nano-confined space. We demonstrate that solid-fluid interaction plays dominant roles on the interfacial transport during nanoscale evaporation, and vapor transport resistance has nonnegligible influences on the evaporation heat/mass transport in nano-confined spaces. By handling statistical behavior of molecule ensembles, this mesoscopic approach not only preserves microscopic physics but also has high computational efficiencies, enabling the simulation of space and time domains on the practical application level. This work paves the way for quantitative investigations of steady/transient nanoscale evaporation heat transfer characteristics using mesoscopic approach.

Evaporation Dynamics on a Lithium Niobate Surface.

Manipulating the water evaporation dynamics is a prerequisite in various modern-day applications like DNA stretching, rapid disease diagnostics, and inkjet printing. One method to affect the evaporation dynamics of droplets is to externally apply electric fields. However, surfaces that bear an intrinsic surface charge have not yet been investigated with respect to their evaporation behavior. In this study, we investigate water droplet evaporation on lithium niobate (LN), a ferroelectric material with a very high spontaneous polarization of 0.7 . Our results show that a droplet deposited on an LN surface evaporates in three stages: (i) constant contact radius (ii) mixed phase (iii) stick-slip, which is likely originating from the intrinsic surface charge. The influence of the polarization direction of the LN surface as well as the relative humidity of the environment on various evaporation characteristics were studied. The results suggest that the specific adsorption layers forming on charged surfaces, e. g. from the humidity of the surrounding air, play a key role in the evaporation process. Furthermore, compared to other materials with similar contact angles, LN demonstrated a significantly large evaporation rate. This property might also be attributed to the intrinsic surface charge and could be exploited in heat transfer applications.

Numerical investigation of evaporation-induced flow around sessile droplets using a sharp-interface algebraic VOF approach

In this study, we numerically investigate the external gaseous flow around an evaporating sessile droplet, especially the interaction between different transport mechanisms of the evaporation-induced flow and evaporation dynamics. A sharp-interface algebraic volume-of-fluid (SA-VOF) solver which incorporates the Boussinesq approximation to deal with thermal and solutal buoyancy has been developed for direct numerical simulation of evaporating droplets in natural convection. Evaporation of a heptane droplet is first simulated to validate the developed solver, and the predicted evaporation rates show good agreement with experimental data. An evaporating sessile droplet on a heated substrate is then simulated through three distinct models to account for contributions from different transport mechanisms of the evaporation-induced flow, i.e. diffusion, the Stefan flow and natural convection. Extensive cases have been simulated at different gravity levels and environmental conditions to clarify the separate role of each mechanism. Results show that the convective flow can enhance evaporation of sessile droplets considerably at elevated substrate temperatures, accounting for up to 40.4% of total evaporation at the substrate temperature of 60 °C and the humidity of 36%. The contribution of the Stefan flow or natural convection in the evaporation process increases with the substrate temperature while stays almost independent of the environmental humidity. Additionally, minute details of the evaporation-induced flow at zero and normal gravity, including flow field, gas mixture density, vapor fraction and temperature distribution, are comparatively studied to reveal the complex characteristics of momentum, mass and heat transfer associated with droplet evaporation in natural convection.

Integrating phase change materials and spontaneous emulsification: In-situ particle formation at oil–water interfaces

The properties of interfaces between two immiscible fluids, as engineered by interfacial materials, are crucial in various processes, including printing, coating, and multiphase flow in porous media. Interfacial materials, such as surface-active molecules and particles can be adsorbed from the bulk fluid phases to the interface or formed in-situ at the interface. In this study, we develop a methodology to form stiff silica-based particles in situ at the oil–water interface through coupling of phase change materials and spontaneous emulsification. This process is demonstrated by introducing a heptane micellar solution that spontaneously generates a microemulsion phase when in contact with an aqueous phase. Micron-sized droplets, consisting of an aqueous silicate precursor mixture, undergo a sol–gel reaction, leading to the generation of colloidal-sized particles. SEM micrographs and confocal images of dried samples, taken from the aqueous-heptane interface, reveal the formation of particles post-gelation. The in-situ formation of stiff particles can be characterized through the dynamics of evaporation, where a significant reduction in the heptane evaporation rate is observed. This particle generation method, utilizing phase change materials and emulsion templates, is spontaneous, energy-efficient, and enables particle formation at the interface at a predetermined time. Our findings offer valuable insights for the fabrication of interfacial materials with tailored properties and controlled timing.

Dynamics of Condensation and Evaporation of Liquid Nitrogen in a Closed Vessel Pressurized with Helium, Nitrogen, and Their Mixture

Dynamics of Condensation and Evaporation of Liquid Nitrogen in a Closed Vessel Pressurized with Helium, Nitrogen, and Their Mixture

Lake depth, a key parameter regulating evaporation in semi‐arid regions: A case study from Dali Lake, China

AbstractAs climate change intensifies, understanding the dynamics of lake evaporation is imperative, especially in semi‐arid regions where water resources are already scarce. This study examines the regulatory role of lake depth on evaporation rates, focusing on a terminal lake in a semi‐arid region: Dali Lake in China. Using the Complementary Relationship Lake Evaporation model, we simulated the heat and temperature lag time of Dali Lake, an 8 m deep lake, due to its heat storage capacity. This approach was validated through moderate‐resolution imaging spectroradiometer (MODIS)‐based surface temperatures of Dali Lake and adjacent Ganggenor Lake. Dali Lake, by storing heat during the warmer months, maintains lower surface temperatures compared with the shallower Ganggenor Lake. Under the same climatic conditions, Dali Lake has an annual evaporation of 980 mm, which is 45 mm less than that of Ganggenor Lake, which has an annual evaporation of 1024 mm. To further study the impact of lake depth, we simulated the heat storage and evaporation of Dali Lake during the Holocene, when the lake reached up to 34 m average depth, representative of the maximum depth reached by Dali Lake. During the Holocene, under constant climate conditions, the annual evaporation would be 44 mm/year less than the average evaporation from 1984 to 2016. Average annual evaporation decreased with increasing depth, showing a significant reduction during warmer months, while the release of heat during the ice‐cover period did not result in additional evaporation. Our results highlight the important relationship between lake depth and evaporation under climate change, emphasizing the necessity for depth‐specific water management strategies in semi‐arid regions.

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.

Laser Analysis of the Evaporation Dynamics of Water Spin Isomers

Laser Analysis of the Evaporation Dynamics of Water Spin Isomers

Primordial black hole superradiance and evaporation in the string axiverse

In the string axiverse scenario, light primordial black holes may spin up due to the Hawking emission of a large number of light (sub-MeV) axions. We show that this may trigger superradiant instabilities associated with a heavier axion during the black holes’ evolution, and study the coupled dynamics of superradiance and evaporation. We find, in particular, that the present black hole mass-spin distribution should follow the superradiance threshold condition for black hole masses below the value at which the superradiant cloud forms, for a given heavy axion mass. Furthermore, we show that the decay of the heavy axions within the superradiant cloud into photon pairs may lead to a distinctive line in the black hole’s emission spectrum, superimposed on its electromagnetic Hawking emission.

Vacuum evaporation and condensation thermodynamics and evaporation kinetics of pure silver

A comprehensive analysis of the characteristics of vacuum evaporation and condensation of pure silver is crucial for advancing vacuum separation and purification technology for crude silver. This study analyzes the vacuum evaporation and condensation thermodynamics and evaporation kinetics of pure silver. The results reveal a substantial increase in the saturated vapor pressure and theoretical maximum evaporation rate of pure silver with increasing temperature. When the temperature is in the range of 1373 ∼ 1773 K and the pressure is in the range of 0.1 ∼ 10 Pa, the average molecular free path is between 0.514 ∼ 66.415 cm. Moreover, the mean molecular free path of silver increases with increasing temperature and decreasing pressure. Besides, the silver triple point occurs at a temperature of 1234.78 K and a pressure of 0.343 Pa. The average evaporation rate of pure silver demonstrates a linear relationship with temperature, and the relationship with pressure conforms to the Logistic model. Notably, the vacuum evaporation of pure silver is a first-order reaction. Furthermore, in this study, the kinetic equation of vacuum evaporation of pure silver is established. In the temperature range of 1473–1673 K, the gas phase mass transfer is the rate-controlling step rather than the mass transfer in the gas phase boundary layer. As the temperature increases, the rate-controlling step gradually changes into gas relative flow mass transfer and gas-liquid interface evaporation mass transfer.

Rate-limiting factors in thin-film evaporative heat transfer processes

In this paper, we present a theoretical study aimed at investigating the rate-limiting factors in thin-film evaporative heat transfer processes, considering the finite-rate evaporation kinetics. The problems of evaporation of a flat thin-film in either pure vapours or vapour-inert-gas mixtures are analysed based on the non-dimensionalised macroscopic transport equations for continuum fluids, coupled with out-of-equilibrium kinetic boundary conditions. Both the full numerical solutions and asymptotic analytical solutions at slow evaporation limit are provided and applied to analyse thin water film evaporation. Existing solutions, assuming negligible heat transfer in the gas domain, or negligible temperature jump across the non-equilibrium kinetic layer, or more boldly a thermodynamically equilibrial interface (i.e. its temperature is at the saturation temperature), can be fully recovered from the more general solutions presented here. Our results show that while these assumptions hold in special cases, they can lead to significant errors in many conditions, especially when the film thickness δ is reduced to a few micrometers or thinner. We show that the conventional views that the rate-limiting factors in thin-film evaporative heat transfer is either the heat diffusion through the liquid film or the mass transfer in the gas domain only apply to thick film (i.e. δ≫λ where λ is the mean free path in the vapour phase). As δ decreases to a few micrometer or smaller (more precisely when the Knudsen number Kn increases beyond O(1) in an pure vapour environment or when the kinetic Peclet number Pe is reduced below O(1) in inert gases), the interfacial thermal resistance due to the evaporation kinetics can be on the same orders of magnitude as the thermal resistance in the liquid film. The analysis also allow us to compare the heat transfer processes during the evaporation of a thin-film in pure vapours to those in inert gases, providing deeper insight into the effectiveness of various strategies for exploring the evaporation process in practical thermal management.

Drops of volatile binary mixtures on brush-covered substrates

We introduce a mesoscopic hydrodynamic model for drops of binary mixtures of volatile partially wetting liquids on brush-covered substrates, i.e., we model the coupled dynamics of spreading, evaporation, imbibition, diffusion and partial demixing of the two volatile components across the three phases—brush, drop and gas. The formulation of the model as gradient dynamics on an underlying free energy functional allows us to systematically account for cross-couplings between the six scalar fields needed to describe the dynamics of both components within each of the three phases. The energy accounts for concentration- and brush state-dependent capillarity and wettability, miscibility of the two components within drop and brush, and entropy in the gas. Finally, the usage of the model is illustrated by employing numerical time simulations to study the dynamics of a sessile drop.