Drop Evaporation Research Articles

Calculation of steam drop mixture flows with boiling explosion mechanism using a multidimensional nodal method of characteristics

A hyperbolic model of a vapor-drop mixture is presented which takes into account the evaporation of drops by highlighting an explosive mechanism. The model is developed on the basis of the generalized-equilibrium model of a mixture previously proposed by the author. In this early model, the equations were hyperbolized by adding interfractional-interaction forces, and the liquid fraction was assumed to be incompressible. In the model proposed here, we assume that the phase transition at intense droplet evaporation occurs in an overheated state, when the fluid temperature exceeds the saturation temperature. A characteristic analysis of the model equations is carried out and their hyperbolicity is shown. An analytical formula is obtained for calculating the speed of sound in a vapor-drop mixture. It is noted that the speed of sound in the mixture in the presence of phase transformations turns out to be somewhat lower than that given by wood's formula. The multidimensional nodal method of characteristics for integrating hyperbolic systems, which is based on splitting the original system of equations into a number of one-dimensional subsystems, is described. Differential relations that hold true along the characteristic directions for each of the subsystems are derived. When calculating one-dimensional problems, an iterative algorithm of the inverse method of characteristics is applied. The computational method has been tested on a number of problems with self-similar solutions. Using the described method of integrating a multidimensional system of equations, the flow of a vapor-droplet flow near the disk was studied. It is shown that, in a number of cases, the explosive boiling of liquid droplets should be taken into account because it can significantly change the pattern of the flow around a disk.

Investigation on Single Drop Evaporation Characteristics of Two-Component Fatty Acid Methyl Esters at High Temperature

Investigation on Single Drop Evaporation Characteristics of Two-Component Fatty Acid Methyl Esters at High Temperature

Water Drop Evaporation on the Rough Surface: The Experiments and Modelling

Water Drop Evaporation on the Rough Surface: The Experiments and Modelling

Toxicology of insecticides — theory, implemented in practice

Goal. Ecological and toxicological substantiation of improving the chemical protection of agricultural crops and perennial plantations from harmful arthropods based on the updated assortment of insectoacaricides, the properties of chemicals and the characteristics of harmful insect and mite species in the technology of growing strategic crops.
 Methods. The sensitivity of phytophages was investigated on natural populations collectedё on crops of certain crops and determined by various methods of poisoning adopted in toxicology. The coefficient of selectivity of the insecticide in the phytophage — entomophage system was calculated by the ratio CK50 , % a.v. for phytophage to SC50 , % a.v. for an entomophage. The effect of urea on the properties of working solutions of chemical and microbiological preparations was studied in their mixture using special techniques.
 Results. Studies have shown different susceptibility of natural arthropod populations to modern insecticides, which have different selective effects on entomophages. The selectivity factor ranged from 15 to 560. Improved anti-resistance system to protect crops from harmful arthropods. The information on the possibilities of joint application of insecticides of different nature with Urea in a single technological process is generalized, which leads to a significant reduction in the evaporation of drops of solution from the treated surface.
 Conclusions. Expansion of the range of pesticides, especially those with a different mechanism of toxic action, makes it possible to prevent or slow down the development of resistance in arthropods to insecticides. An improved anti-resistance system for protecting agricultural crops from harmful arthropods provides a decrease in the toxic load on the agrocenosis and a reversal of resistance to the initial parameters. Urea is an active anti-evaporation agent for working solutions of insecticides of various nature.

Experimental investigation of hydrodynamics and heat transport during horizontal coalescence of two drops impinging a hot wall

This paper presents an experimental study on hydrodynamics and heat transport during the horizontal coalescence of two drops impinging a hot wall. The study addresses the influence of distance between impact locations, the time interval between drop impact, and wall superheat on the transport processes. The experiments were conducted under a pure vapor atmosphere with the refrigerant FC-72 at a saturation temperature of 54°C, corresponding to a system pressure of 0.94 bar. The drops were generated with a constant diameter and a constant impact velocity. The temperature field at the surface of the heater was measured by an infrared camera with a high spatial and temporal resolution. The local heat flux distribution was derived from the temperature field by solving the transient three-dimensional heat conduction equation within the substrate. The total heat flow was evaluated by integrating the local heat fluxes over the footprint of the drop. The impact parameters (drop size and impact velocity), the time interval between drop impact, and the distance between impact locations were evaluated through post-processing of the black-and-white images captured employing a high-speed camera. The results for simultaneous drop impingement reveal that the heat transported from the wall to the fluid is not affected by the presence of neighboring drop as long as the drops do not contact each other. In the case of horizontal coalescence of drops, the heat flow is reduced both during the spreading and receding phases and during the sessile drop evaporation phase. This can be explained by the reduction of solid–liquid interface and of three-phase contact line length after the coalescence. An increase in wall superheat leads to reducing the footprint of the drop and increasing of heat flow. Asymmetric behavior of the drop hydrodynamics and heat flux is observed during the non-simultaneous drop impingement.

Can a liquid drop on a substrate be in equilibrium with saturated vapor?

It is well known that liquid and saturated vapor, separated by a flat interface in an unbounded space, are in equilibrium. One would similarly expect a liquid drop, sitting on a flat substrate, to be in equilibrium with the vapor surrounding it. Yet, it is not: as shown in this work, the drop evaporates. Mathematically, this conclusion is deduced using the diffuse-interface model, but it is also reformulated in terms of the maximum-entropy principle, suggesting model independence. Physically, evaporation of drops is due to the so-called Kelvin effect, which gives rise to a liquid-to-vapor mass flux if the boundary of the liquid phase is convex.

Influence of nanofiber coating thickness and drop volume on spreading, imbibition, and evaporation

It is known that heat transfer resulting from the drop impact onto a hot substrate can be enhanced with the use of nanostructured coatings, such as nanofiber mats, on the substrate surface. One heat transfer enhancement mechanism is related to liquid imbibition into the porous structure and subsequent evaporation. The detailed mechanisms of liquid spreading, imbibition into the porous structure, and evaporation are still not understood. In this work, the influence of nanofiber coating thickness and drop volume on the kinetics of ethanol drop spreading, liquid imbibition and evaporation on a substrate without additional heating are studied. The initial phase of drop spreading as well as the overall processes are studied simultaneously which allows a direct comparison of influencing factors on the different wetting stages or subprocesses. Four different mat thicknesses in the range of 4−42 μm were investigated, and the results for the drop spreading and evaporation were compared with the bare silicon surface. The results show that, for a mat thickness of 14 μm and higher, the maximal imbibed area as well as the drying time depend only on the drop volume and are nearly independent of mat thickness. However, for the thinnest mat tested, the imbibed area was significantly smaller and the drying time was longer than for thicker coatings.

Evaluating Subtle Field Imprints in Water by Droplet Evaporation Method

Abstract
 Background: Even though water is regarded as something long understood and explained by conventional science – many open-minded researchers know that it still hides many mysteries (water clusters, coherent domains, so-called memory, etc.). Many of these mysteries come to fore in ultra-high dilution (UHD) experiments and practices, where usually not even one molecule of the originating substances is left. Mostly, they can be tackled only by using the droplet evaporation method (DEM).1 
 Aim: One of the hypotheses of water memory suggests that through UHD (dilutions, shaking) the field of a substance is stably impressed into water. If this is true than we should be able to imprint also a field itself - not originating from a certain substance, but from other sources. Such imprint should be revealed by an appropriate research method.
 Method: The DEM consists of monitoring dried water drops by dark field microscopy. It was discovered in the previous century by Ruth Kübler, a German artist, and further developed by Bernd-Helmut Kröplin, Minnie Hein, Berthold Heusel M. A. and Georg Schröcker. It has also been used to research the still controversial special characteristics of ultra-high diluted aqueous solutions.2 It has been proved capable of demonstrating differences in subtle influences of an UHD (around 10-47 M, practically “pure” water) of As2O3 on common wheat seeds. This method is therefore, capable of transferring certain, not yet fully understood or generally accepted subtle physical characteristicsof the solution to the remnant patterns after drop evaporation.3, 4
 We used DEM to evaluate experiments on impressing the subtle field of five bioenergy healers and two so called “informed” objects (a glass and an “energy” card) into mineral or spring water with well-known characteristics. In all these experiments we also used control water that was of the same origin, but placed in a separate room. The DEM images were analyzed by special computer programs and statistically evaluated. No mother tincture of any kind was used.
 Results: The results demonstrate that even such subtle fields can leave stable and reproducible imprints in water - made visually accessible by the remnant patterns after drop evaporation. The irradiated water samples were statistically different from the control. This difference can usually be observed even by a naked eye.
 
 Conclusion
 These results have several implications. They confirm as follows:
 a) water memory – the main background of UHD effects,
 b) the possibility to imprint the fields into water,
 c) the existence of subtle fields not yet generally recognized by physical community and
 d) the capability of DEM to express the imprints.

A year of attenuation data from a commercial dual-polarized duplex microwave link with concurrent disdrometer, rain gauge, and weather observations

Abstract. Commercial microwave links (CMLs) in telecommunication networks can provide relevant information for remote sensing of precipitation and other environmental variables, such as path-averaged drop size distribution, evaporation, or humidity. The CoMMon field experiment (COmmercial Microwave links for urban rainfall MONitoring) mainly focused on the rainfall observations by monitoring a 38 GHz dual-polarized CML of 1.85 km path length at a high temporal resolution (4 s), as well as a co-located array of five disdrometers and three rain gauges over 1 year. The dataset is complemented with observations from five nearby weather stations. Raw and pre-processed data, which can be explored with a custom static HTML viewer, are available at https://doi.org/10.5281/zenodo.4923125 (Špačková et al., 2021). The data quality is generally satisfactory for further analysis, and potentially problematic measurements are flagged to help the analyst identify relevant periods for specific study purposes. Finally, we encourage potential applications and discuss open issues regarding future remote sensing with CMLs.

An analytical model for the evaporation of multi-component spheroidal drops based on Stefan–Maxwell equations

An analytical evaporation model for multi-component spherical and spheroidal drops, based on the analytical solution of the Stefan–Maxwell equations is proposed to study the multi-component steady diffusion in the gas phase. A comparison with the ‘classical’ approach based on the Fick’s law is reported for three families of liquid mixtures, namely alkanes, alcohols and water solutions of alcohols under a wide range of operating conditions. The local vapour fluxes of each vaporising species on the drop surface are correlated with the local Gaussian curvature. The effects of drop shape and of the modelling of constitutive equations on the evaporation rates are discussed. Comparison of the present model with experimental measurements of different compositions of tetradecane–hexadecane drops vaporising in stagnant air shows a rather satisfactory agreement.

Characterizing the Occurrence and Spatial Heterogeneity of Liquid, Ice, and Mixed Phase Low‐Level Clouds Over the Southern Ocean Using in Situ Observations Acquired During SOCRATES

AbstractSupercooled liquid water (SLW) and mixed phase clouds containing SLW and ice over the Southern Ocean (SO) are poorly represented in global climate and numerical weather prediction models. Observed SLW exists at lower temperatures than threshold values used to characterize its detrainment from convection in model parameterizations, and processes controlling its formation and removal are poorly understood. High‐resolution observations are needed to better characterize SLW over the SO. This study characterizes the frequency and spatial distribution of different cloud phases (liquid, ice, and mixed) using in situ observations acquired during the Southern Ocean Clouds, Radiation, Aerosol Transport Experiment Study. Cloud particle phase is identified using multiple cloud probes. Results show occurrence frequencies of liquid phase samples up to 70% between −20°C and 0°C and of ice phase samples up to 10% between −5°C and 0°C. Cloud phase spatial heterogeneity is determined by relating the total number of 1 s samples from a given cloud to the number of segments whose neighboring samples are the same phase. Mixed phase conditions are the most spatially heterogeneous from −20°C to 0°C, whereas liquid phase conditions from −10°C to 0°C and ice phase conditions from −20°C to −10°C are the least spatially heterogeneous. Greater spatial heterogeneity is associated with broader distributions of vertical velocity. Decreasing droplet concentrations and increasing number‐weighted mean liquid diameters occur within mixed phase clouds as the liquid water fraction decreases, possibly suggesting preferential evaporation of smaller drops during the Wegener‐Bergeron‐Findeisen process.

Features of Urea influence on physicochemical properties of working solutions of insecticides

Goal. To study the effect of Urea on the properties of working solutions of emulsions and suspensions of chemical and microbiological drugs in plant protection against pests.
 Methods. Information-analytical analysis of the effectiveness of joint use of insecticides with Urea. Laboratory experiments on the effect of Urea on: evaporation of droplets from the treated surface; surface tension; reaction of the medium of suspensions and emulsions of working solutions of chemical and microbiological preparations. To do this, in aqueous solutions of insecticides and biological products in concentrations recommended for use in field crops, was added 0.2% aqueous solution of Urea. After a certain period of time, the characteristics of the solutions were determined. An analytical generalization of the change in the properties of working solutions under the influence of urea is carried out.
 Results. The information on the possibilities of joint use of insecticides and microbiological preparations with Urea in a single technological process is generalized. Their combination leads to a significant reduction in the evaporation of solution droplets from the treated surface, but does not affect the surface tension and reaction of the solutions.
 Conclusions. Urea is an active anti-evaporator of working solutions of insecticides of various nature. Adding it to the solutions of evaporation of drops from the treated surface reduces more than 1.5 times. It does not significantly affect the surface tension and reaction of the solution. This characteristic of the solutions is maintained for 24 hours after preparation.

Vapor Flux on Bumpy Surfaces: Condensation and Transpiration on Leaves

Drop condensation and evaporation as a result of the gradient in vapor concentration are important in both engineering and natural systems. One of the interesting natural examples is transpiration on plant leaves. Most of the water in the inner space of the leaves escapes through stomata, whose rate depends on the surface topography and a difference in vapor concentrations inside and just outside of the leaves. Previous research on the vapor flux on various surfaces has focused on numerically solving the vapor diffusion equation or using scaling arguments based on a simple solution with a flat surface. In this present work, we present and discuss simple analytical solutions on various 2D surface shapes (e.g., semicylinder, semiellipse, hair). The method of solving the diffusion equation is to use the complex potential theory, which provides analytical solutions for vapor concentration and flux. We find that a high mass flux of vapor is formed near the top of the microstructures while a low mass flux is developed near the stomata at the leaf surface. Such a low vapor flux near the stomata may affect transpiration in two ways. First, condensed droplets on the stomata will not grow due to a low mass flux of vapor, which will not inhibit the gas exchange through the stomatal opening. Second, the low mass flux from the atmosphere will facilitate the release of highly concentrated vapor from the substomatal space.

Further Insights into Patterns from Drying Particle Laden Sessile Drops.

The evaporation of colloidal dispersions is an elegant and straightforward route to controlled self-assembly of particles on a solid surface. In particular, the evaporation of particle laden drops placed on solid substrates has received considerable attention for more than two decades. Such particle filled drops upon complete evaporation of the solvent leave behind a residue, commonly called particulate deposit pattern. In these patterns, typically, more particles accumulate at the edge compared to the interior, a feature observed when coffee drops evaporate. Consequently, such evaporative patterns are called coffee stains. In this article, the focus is on the evaporation of highly dilute suspension drops containing particles of larger diameters ranging from 3 to 10 μm drying on solid substrates. This helps us to investigate the combined role of gravity-driven settling of particles and capillary flow-driven particle transport on pattern formation in drying drops. In the highly dilute concentration limit, the evaporative patterns are found to show a transition, from a monolayer deposit that consists of a single layer of particles, to a multilayer deposit as a function of particle diameter and initial concentration of particles in the drying drop. Moreover, the spatial distribution of particles as well as the ordering of particles in the deposit patterns are found to be particle size dependent. It is also seen that the order-disorder transition, a feature associated with the organization of particles at the edge of the deposit, observed typically at moderate particle concentrations, disappears at the highly dilute concentrations considered here. The evaporation of drops containing particles of 10 μm diameter, where the effect of gravity on the particle becomes significant, leads to uniform deposition of particles, i.e, suppression of the coffee-stain effect and to the formation of two-dimensional percolating networks.

Experimental Studies of the Evaporation of Pure Liquid Droplets in a Single-Axis Non-Resonant Levitator

Though a simple daily observation, evaporation of drops is still poorly understood due to the complex nature that involves hydrodynamic effects in the bulk fluids and transport phenomena at the liquid-vapor interface. This paper reports on the evaporation of single component droplets (water, ethanol, acetone, and glycerol) levitated in a single-axis non-resonant levitator. It was observed that the acetone and ethanol evaporated faster than water, although the acetone is the most volatile. The estimated lifetime of acetone is less than 5min, which is much shorter as compared to 56min for ethanol or about 90min for water droplets. On the other hand, glycerol showed no tendency to evaporate. With increasing the evaporation time, the ratio of large and small semi-axis decreases and tends to 1 corresponding to changes in drops shape from oblate ellipsoid to a sphere. Based on the classical D2-law, the surface regression rates have been estimated.

Nanopore-Mediated Spontaneous Dilution of Droplets: When Evaporation Turns to a Dilutor.

Droplet evaporation on surfaces is ubiquitous and affects areas as diverse as climate, microbiology, the chemical industry, and materials science. While solute concentration is the universally taken-for-granted behavior in drop evaporation, the present work shows that saline droplets evaporating on nanoporous thin-film surfaces can get diluted rather than concentrated. The driving mechanism of this phenomenon is attributed to the flow drawn from the drop through the nanopores by an annular peripheral evaporation. This fluid transport can continuously collect the salt solution from a concentrated region of the droplet, which is induced by radial microflows during drop evaporation. The coupling of these processes leads to the overall drop dilution effect. The influence of substrate temperature and drop volume was also investigated. This study opens up new perspectives on many natural phenomena and offers alternatives for physicochemical applications in small dimensions as well as for water desalination technologies.

Effect of contact angle hysteresis and sensitivity of gas-liquid interfacial tension to temperature of a sessile-drop on evaporation dynamics

The evaporation process of drops on a solid surface is widely applied to daily life and industrial fields. Both contact angle hysteresis and the sensitivity of gas-liquid interfacial tension to temperature are important factors affecting the drop evaporation reflected in the contact line and contact angle. To investigate the internal mechanism, according to the lubrication theory and slip boundary conditions, we establish a mathematical model of the drop evaporation on a uniformly heated solid wall with considering the effect of contact angle hysteresis. This model is numerically solved by using a coordinate transformation method and Freefem++14.3, a highly efficient solver. The accuracy of the numerical calculation method is verified by comparing the numerical results with experimental results, and the grid independence is validated. The effect of contact angle hysteresis on the dynamics of evaporating drops is discussed, and the evaporation characteristics of drops with different tension sensitivities of the air-liquid interface to temperature are further investigated. The results show that the contact angle hysteresis has an apparent influence on the drop evaporation process which includes drop spreading stage, contact line pinning stage, and depinning stage. In the drop spreading stage, the increase in the hysteresis angle shortens the spreading time, and reduces the spreading velocity and radius, while in the contact line pinning stage, the pinning time is prolonged and the reduction of drop mass is significantly increased with hysteresis angle increasing. In the contact line depinning stage, the contact angle hysteresis reduces the contact angle, and a flatter shape emerges, thereby enhancing the ability to transfer heat and accelerating evaporation as well as shortening the depinning time. In addition, the large hysteresis angle leads to a large advancing contact angle and a small receding contact angle. The reduction in receding contact angle is more notable than the increment of advancing contact angle. The temperature sensitivity coefficient of the gas-liquid interfacial tension can be increased by reducing the receding contact angle, thereby improving the wettability of the drops on the wall enhancing the heat transfer and accelerating the evaporation. Regulating the contact angle hysteresis and the sensitivity of the interfacial tension to temperature can realize the manipulation of the drop movement, thus controlling the evaporation process.

Evaporative self-assembly of soft colloidal monolayers: the role of particle softness.

We investigate the sessile drop evaporation aided self-assembly of microgel particles by varying their softness. Evaporation of sessile drops containing amphiphilic microgel particles at suitable concentrations results in uniform monolayer deposits that span the entire drop area. At lower concentrations, the deposits are in the form of monolayer coffee rings whose width scales with particle concentration. Using softer microgels synthesised with a lower quantity of crosslinker, we show that the monolayer coffee rings do not form at low particle concentrations. The microgels adsorbed at the interface deform, and the extent of deformation depends on the softness of the microgels as well as their concentration at the interface. Upon complete evaporation of the solvent, the microgel-laden interface is transferred to the substrate. The final deposit shows hexagonal particle arrays where the interparticle separation increases with increasing microgel softness and decreases with particle concentration in the drop. Further insight into the role of microgel softness in the microstructure of the particulate deposits is obtained by measuring the viscoelasticity of the particle-laden interface. Interestingly, the interface loaded with lesser crosslinked microgels exhibits viscoelastic nature even at lower particle concentrations, whereas the higher crosslinked microgels show viscous behaviour.

Drop vaporization frequency response: an approximate analytical solution for mixed injection regimes

This work is devoted to a theoretical analysis of evaporating mass frequency response to pressure oscillations of a spray of repetitively injected drops into a combustion chamber. A single stationary spherical droplet continuously fed with the same liquid fuel, so that its volume remains constant in spite of the evaporation, the so-called ‘mean droplet' in the Heidmann analogy, represents this vaporizing spray of droplets. The feeding is realized with a liquid-liquid heat transfer coefficient by using a source point placed at the mean droplet centre, in such a way that only radial thermal convection and conduction effects are allowed inside the droplet during the process. This feeding procedure is now viewed as a proper boundary condition that is a mixed or a generalized feeding regime controlling the whole process of liquid fuel injection into the combustion chamber. Drawing upon a linear analysis based on the Rayleigh criterion, the evaporating mass response factor is evaluated. Effects due to the variation of the heat transfer coefficient and of the process characteristic times are analysed. Especially, an abrupt increase in the response function is related to the influence of the value of a particular fuel thermodynamic coefficient.

Sessile volatile drop evaporation under microgravity

The evaporation of sessile drops of various volatile and non-volatile liquids, and their internal flow patterns with or without instabilities have been the subject of many investigations. The current experiment is a preparatory one for a space experiment planned to be installed in the European Drawer Rack 2 (EDR-2) of the International Space Station (ISS), to investigate drop evaporation in weightlessness. In this work, we concentrate on preliminary experimental results for the evaporation of hydrofluoroether (HFE-7100) sessile drops in a sounding rocket that has been performed in the frame of the MASER-14 Sounding Rocket Campaign, providing the science team with the opportunity to test the module and perform the experiment in microgravity for six consecutive minutes. The focus is on the evaporation rate, experimentally observed thermo-capillary instabilities, and the de-pinning process. The experimental results provide evidence for the relationship between thermo-capillary instabilities and the measured critical height of the sessile drop interface. There is also evidence of the effects of microgravity and Earth conditions on the sessile drop evaporation rate, and the shape of the sessile drop interface and its influence on the de-pinning process.