Constant Evaporation Rate Research Articles

Experimental and Statistical Determination of Convective Heat and Mass Transfer Coefficients for Eucalyptus nitens Sawn Wood Drying

This study aimed to develop a model using experimentally obtained convective heat and mass transfer coefficients to predict the effect of temperature, humidity, and drying rate on wood drying. Tangential wood samples of Eucalyptus nitens (H. Deane & Maiden) were used in the investigation. The experimental design consisted of two temperature levels (40 °C and 55 °C), two relative humidity levels (55% and 75%), and two air velocity settings (2 m·s−1 and 3 m·s−1). The experiments were conducted under a constant evaporation rate, spanning the maximum and critical moisture content in the wood. A statistical model using multivariate regression was created to predict the convective heat and mass transfer coefficients. The results indicated that the experimental data and empirical correlations exhibited an error margin of 37.77% and 37.86%, respectively. A significant positive correlation was found between the convective heat transfer coefficient and air velocity, temperature, and relative humidity, while the convective mass transfer coefficient showed a significant positive correlation only with air velocity and temperature. The model predicted the convective heat and mass transfer coefficients with high accuracy and statistical significance. Using the proposed method, we successfully obtained both convective coefficients, which enable accurate description of heat and mass flow during the convective drying of Eucalyptus nitens wood.

The doomsday of black hole evaporation

Abstract By assuming simultaneously the unitarity of the Hawking evaporation and the universality of Bekenstein entropy bound as well as the validity of cosmic censorship conjecture, we find that the black hole evaporation rate could evolve from the usual inverse square law in black hole mass into a constant evaporation rate near the end of the Hawking evaporation before quantum gravity could come into play, inferring a slightly longer lifetime for lighter black holes.

Evaporation and wetting behavior of water on the laser-textured silicon substrate

It is important to elucidate the impact of surface micromorphology on the evaporation mechanism and behavior to design rational micromorphologies for enhancing/regulating evaporation. In this study, we investigated the wetting and evaporation behaviors of water droplets on monocrystalline silicon surfaces with concentric circular textures etched using a laser engraving system at varying spacing intervals. Only when the texture spacing overlapped did it exhibit a significantly increased apparent surface energy and evaporation rate. The droplet volume decreased consistently at a constant evaporation rate at different temperatures, and the process involved two stages: constant contact radius (CCR) and constant contact angle (CCA). Laser etching increases the thickness of the oxide film from 10 to 377 nm, resulting in enhanced hydrophilicity. For millimeter-sized droplets, microscopic capillary phenomena in the vicinity of the triple line dominated the evaporation behavior rather than liquid/gas interface evaporation.

A Self-Adaptive and Regenerable Hydrogel Interfacial Evaporator with Adjustable Evaporation Area for Solar Water Purification.

Solar-driven interfacial evaporation is a potential water purification solution. Here, a novel regenerable hydrogel interfacial evaporator is designed with tunable water production. Such an evaporator is fabricated by readily mixing hydroxypropyl chitosan (HPCS) and dibenzaldehyde-functional poly(ethylene glycol) (DF-PEG) at ambient conditions. Dynamic Schiff base bonds bestow on the HPCS/DF-PEG hydrogel (HDH) evaporator self-adaptivity and pH responsiveness. The as-prepared HDH is enabled to spontaneously change shape to adapt to different molds, endowing the evaporator with adjustable evaporation area. The water production performance of the intelligent evaporator is first evaluated using tunable evaporation index (TEI, the tunable evaporated water mass per hour), which can be altered from 0kg h-1 to 3.21kg h-1 under one sun. Besides, the large-scale evaporator can be expediently fabricated by virtue of the self-adaptivity. Benefiting from the pH responsiveness, the HDH evaporator is successfully regenerated with the removal of organic dye by the liquefaction-dialysis-regeneration operations. Meanwhile, the re-created evaporator maintains the self-adaptive characteristic and almost constant water evaporation rate compared to that of the initial evaporator. Therefore, this distinctive concept provides a facile strategy to develop smart and recyclable solar-driven interfacial evaporators for flexible water purification.

Radio-frequency controlled crystalline phase transformation of MoS2 thin film fabricated by unique vapour-plasma mixing technique

Successful fabrication of molybdenum disulfide thin films on silicon substrates by a unique vapour-plasma mixing technique at a relatively low temperature of 300 °C is reported. This mixing technique involves simultaneous sputtering of a molybdenum target and thermal evaporation of sulphur flakes to form MoS2 molecules. Raman studies confirm the formation of MoS2 with characteristic E12g and A1g modes observed at ∼384 and ∼408 cm−1. The effects of radio frequency (RF) power on the physical properties of MoS2 film at a constant sulphur evaporation rate are investigated. The Raman and X-Ray photon spectroscopy reveal that a controlled crystalline phase transition between metallic tetragonal (1 T-MoS2) and semiconducting hexagonal (2H–MoS2) has been successfully achieved upon variation of the RF power. Furthermore in X-Ray diffraction analysis, Scherrer's, Williamson-Hall and Size-Strain Plot methods are used to extract relevant correlations between structural properties (viz. Crystallite sizes, strains) and the thin film growth controlling parameters.

An interface-resolved phase-change model based on velocity decomposition

An interface-resolved phase-change model is proposed in the interface-capturing framework based on the coupled level-set and volume of fluid (CLSVOF) method. A velocity decomposition method is employed to ensure the numerical stability and accuracy of interface propagation. Specifically, the velocity u is decomposed into the potential part u˜ associated with the phase change and the remaining rotational part u¯. The potential velocity u˜ is computed by solving a Poisson equation. A modified momentum equation is derived to solve the rotational-part velocity u¯, which is divergence-free. The momentum equation is solved using the Computational Air-Sea Tank (CAS-Tank) developed previously by Yang et al. [1]. To evolve the interface and ensure the mass conservation, a continuous interfacial velocity uΓ is constructed by adding the velocity uˆ associated with the volume change of liquid (or gas) to u¯, where uˆ is computed by solving a Poisson equation with constant coefficient. The proposed method is verified in the context of the two-dimensional (2D) droplet with constant evaporation rate, one-dimensional (1D) Stefan and sucking problems, 2D droplet evaporation at saturation temperature, 2D droplet evaporation below saturation temperature, and a three-dimensional (3D) evaporating droplet falling under the gravity. The results show that the proposed method is accurate and stable. The numerical method is also validated by simulating an evaporating droplet falling under the gravity and the numerical results are found to be in agreement with the results in the literature. The interaction of two evaporating droplets is also simulated in a 3D domain to show the capability of the proposed method in solving 3D problems.

Self-cleaning solar water evaporation device based on polyaniline/TiO2/natural cellulose fibers for contaminant water

Wastewater accounts for a large part of the water body on the earth. Solar water evaporation is an effective way to produce fresh water from seawater or polluted water. However, the co-evaporation or deposition of contaminants may reduce the efficiency and freshwater quality during water evaporation. In this work, a self-cleaning solar water evaporator is developed based on the natural lignocellulose fibers (NCF), polyaniline (PANI), and TiO2, which shows great advantages of wide-range light absorption, super hydrophilicity, and low thermal conductivity. Nanofibrous PANI is polymerized on the surface of NCF to form a mesoporous network by adding the NCF to the polymerization solution. P25 TiO2 nanoparticles as photocatalysts are dispersed into the above reaction to form the hybrid PANI/TiO2/NCF composite disc by simply filtration. Owing to the synergistic effect between the photothermal PANI and the photocatalytic degradation of TiO2 nanoparticles in the solar water evaporator device, the water evaporation rate can reach 2.36 kg m−2 h−1 (under 1 sun irradiation), and the contaminant (100 ppm tetracycline) can be efficiently degraded. Interestingly, the solar water evaporator device still maintains a constant solar evaporation rate after working for 10 h, and no contaminant is accumulated. The bifunctional solar water evaporation device, which combines photocatalytic and photothermal effects, has great potential application in organic contaminant water with a self-cleaning effect.

Effect of temperature and surfactants on evaporation and contact line dynamics of sessile drops

Researches on droplet evaporation has a vast range of applications in different fields. The mechanisms of droplets evaporation have been a topic of investigation for decades. The droplet after spreading on the substrate exhibits constant evaporation rate for a constant base diameter and decreasing contact angle; followed by another evaporation mode with constant contact angle and decreasing base diameter; and finally, evaporation with decreasing of both contact angle and base diameter. In the present study, the evaporation rate and mechanisms influenced by surfactant and temperature effects are analysed. The evaporation was demonstrated to be related to the dynamics of the sessile droplet spreading ability and the depinning event. It remains complex to predict the evaporation of the sessile droplet due to the continuous change in surfactant local concentration. Moreover, the temperature change modifies the surface tension and the induced inner flows. These two questions find answers in the triple line dynamic which controls the evaporation rate. The forces controlling the depinning with surfactant was quantified. A clear constant force was found following depinning. Such dynamic equilibrium demonstrates also the effect of the friction, surface roughness and moreover the limit of surfactant concentration in the triple line direct vicinity. The evaporation rate shows two particularities: one is the classical decrease of the evaporation rate after depinning; the second in case of surfactant, there is an enhancement appearing at later droplet lifetime, which could be a consequence of film evaporation contributing to the evaporation near the triple line. The local evaporation does not change significantly despite the change in the contact angle with respect to surfactant concentration. The substrate temperature enhances evaporation rate. The coupled temperature and surfactant effect show a local evaporation rate decreasing with surfactant concentration increase at ambient temperature (around 20 °C) and enhancement with surfactant concentration at higher temperature.

Evaporation Dynamics of Sessile Saline Microdroplets in Oil.

The occurrence of concentration and temperature gradients in saline microdroplets evaporating directly in air makes them unsuitable for nucleation studies where homogeneous composition is required. This can be addressed by immersing the droplet in oil under regulated humidity and reducing the volume to the picoliter range. However, the evaporation dynamics of such a system is not well understood. In this work, we present evaporation models applicable for arrays of sessile microdroplets with dissolved solute submerged in a thin layer of oil. Our model accounts for the variable diffusion distance due to the presence of the oil film separating the droplet and air, the variation of the solution density and water activity due to the evolving solute concentration, and the diffusive interaction between neighboring droplets. Our model shows excellent agreement with experimental data for both pure water and NaCl solution. With this model, we demonstrate that assuming a constant evaporation rate and neglecting the diffusive interactions can lead to severe inaccuracies in the measurement of droplet concentration, particularly during nucleation experiments. Given the significance of droplet evaporation in a wide array of scientific and industrial applications, the models and insights presented herein would be of great value to many fields of interest.

Seepage-evaporation controlled depletion of initially water-filled reservoirs on Earth and Mars: Analytic versus HYDRUS modeling

Analytical solutions are obtained for water extinction from an axisymmetric crater, filled at t < 0 and depleted by evaporation and transient infiltration into a Gardner or capillarity-free homogeneous soil during the time interval 0 ≤ t ≤ Te. The extinction time Te is found for crater beds, the shapes of which are shallow cones, spherical, spheroidal, and paraboloidal caps. An instantaneous seepage flow rate, Q(t), is approximated by truncated two-term formulae of Wooding for a zero-depth disk in Gardner's soil or Hunt for paraboloidal craters (soils with no capillarity). The instantaneous evaporation losses are the product of a constant A-pan evaporation rate and the shrinking area of a flat horizontal disk of the free water, which dwindles in the crater. In HYDRUS simulations of a van Genuchten soil, the Reservoir Boundary Condition is used for a falling water level in the ponded depressions. Cones and paraboloids are selected as craters, initially fully or partially filled with free water at t = 0, and infiltrating until extinction. The results are presented as drawdown curves and – for shallow craters - attest a good match between analytical approximations and HYDRUS numerical simulations. Experiments with the extinction of water from small axisymmetric ponds in dune sand are also carried out. They allow blitz-evaluation of hydraulic parameters of the subjacent sand. Hydrological implications for commingling surface-subsurface (pore) water entities in terrestrial and Martian environments are discussed.

Influence of potassium bromide on the growth of succinic acid crystals

Succinic acid doped with KBr crystals with attractive optical property like non linearity was grown by proper synthesis. The crystal was grown by utilizing slow evaporation technique from the solution taking water as solvent. At room temperature the growth of crystal arises maintain constant rate of evaporation results in a formation of transparent crystals with high optical quality. Non volatile devices with high memory fabricated with ferroelectric materials observers the concentration of the researchers. Actually the ferroelectric materials have sufficient capability function as an actuator with high permittivity, good piezoelectric behaviour to create new NLO device. The following investigations were carried out to confirm the grown crystals. Single crystal and Powder X-ray diffraction studies were carried out to confirm the crystal structure, UV–Visible studies for transparency and TGA/DSC for thermal stability. Finally the NLO property was determined by SHG efficiency.

Growth and Characterization of Potassium succinate crystal

Potassium succinate single crystals with attractive optical property like non linearity were grown by proper synthesis. The crystal was grown by utilizing slow evaporation technique from the solution taking water as solvent. At room temperature the growth of crystal arises maintain constant rate of evaporation results in a formation of transparent crystals with high optical quality. Non volatile devices with high memory fabricated with ferroelectric materials observers the concentration of the researchers. Actually the ferroelectric materials have sufficient capability function as an actuator with high permittivity, good piezoelectric behaviour to create new NLO device. The following investigations were carried out to confirm the grown crystals. Single crystal and Powder X-ray diffraction studies were carried out to confirm the crystal structure, Uv-Visible studies for transparency and TGA/DSC for thermal stability. Finally the NLO property was determined by SHG efficiency.

Effect of diatomite on soil evaporation characteristics

The soil evaporation property which can cause dry–wet cycle has an important impact on soil cracking and salinization. This study focuses on the effect of diatomite, which has an inner porosity structures, on soil evaporation. The results show that the whole process of evaporation can be divided to three stages by two turning points for both homogeneous soil and the mixed soil. However, the durations of constant evaporation rate stage and falling rate stage become longer with the increasing of incorporation mass ratio of diatomite. The volumetric water contents are same and about 0.1 when the evaporation process enters the residual stage for the diatomite, the calcined diatomite and the loess even though the initial saturated volumetric water contents of these soils are different. When the mixing proportion of diatomite is less than 30%, the higher the mixing ratio, the more water that the mixture can maintain. On the contrary, the increase of the mixing ratio has no obvious effect on the volumetric water content during evaporation. For the calcined diatomite, when the mixing proportion is about 3–10%, the increase of the mixing ratio has no obvious influence on the results. The volumetric water content range of the mixture of calcined diatomite at turning point I is 0.124–0.164, the value is about 10% larger than that of the mixture of diatomite. At the turning point II, the volumetric water content range of the mixture of calcined diatomite is 0.004–0.04, and it is smaller than that of the mixture of diatomite. The layered soil results show that the first stage of mixed soil becomes longer as the thickness of cover layer increases, and the layer sequence has increasing effect on evaporation which the duration of the overall evaporation of mixed soil becomes longer when the diatomite lays underneath.

Integrated effects of rainfall regime and canopy structure on interception loss: A comparative modelling analysis for an artificial larch forest

AbstractModel optimization is essential for accurately simulating rainfall interception loss (I) in artificial forests and for quantifying the influence of canopy structure, rainfall regime, and meteorological variables on I. Herein, the revised Gash (addressing physical mechanisms) and Wang (addressing canopy structural impacts) models were used for comparative I simulations using a larch plantation in NW China. We used throughfall (Tf) and stemflow (Sf) measurements from the growing seasons of three consecutive years and found that from the total rainfall measured (1371.6 mm) in 59 selected rain events, Tf, Sf, and I accounted for 80.8%, 1.6%, and 17.6%, respectively. Surprisingly, the two tested models showed similar behaviours in their I simulations, with their performances classified as “very good,” exhibiting 5% and 2.3% cumulative I relative errors for the revised Gash and Wang models, respectively. We noted that, although I was well simulated for light–moderate rain events (&lt;25 mm), absolute errors increased significantly as rainfall amount and duration increased, owing to the constant evaporation rate applied in the models. Leaf area index (LAI) explained 40% of the water detention variation in the canopy, rather than I, which only reflected canopy storage capacity dynamics during the growing season. Collectively, our results revealed that models only addressing the independent impact of wet evaporation or structural dynamics are inadequate for accurately simulating I during heavy rain events (&gt;25 mm). Therefore, future models should account for the potential errors arising from evaporation estimation and consider the effects of LAI.

Does sunlight always accelerate water droplet evaporation?

We investigate droplet evaporation, which is a natural phenomenon but the mechanism is not well understood. We are surprised to find that sunlight irradiation does not always enhance droplet evaporation, which is against the common sense that “Sun accelerates water evaporation.” This is true at least for short-time evaporation. A whole droplet lifetime consists of two regimes of evaporation: a light induced deterioration regime and an acceleration regime. The deterioration regime is explained by the decreased temperature difference from the droplet bottom to apex, weakening Marangoni flow to hinder conduction heat transfer from the substrate to the droplet. The enhanced regime is explained by the reduced light energy reflection via the droplet surface. The substrate conduction heat transfer and radiation heat transfer of light are coupled to dominate evaporation. The two mechanisms create opposite contributions, resulting in a constant evaporation rate for sunlight irradiation on a droplet. However, natural light decreases the evaporation rate vs time. Hence, evaporation rates with and without sunlight irradiation cross at a specific time. Our work enhances the fundamental understanding of droplet evaporation and provides a useful guideline for efficient solar energy utilization.

Extrem climate engineering geology: Soil engineering properties response to drought climate and measures for disaster mitigation

<p indent="0mm">Due to global climate change, extreme climate events occur in increasing frequency and intensity and act on earth surface in various ways, inducing a series of engineering geological disasters, which seriously affect the sustainable economic and social development, and bring many new challenges to current engineering geology research. There is an urgent need to strengthen the basic research on extreme climate engineering and disaster prevention and mitigation. It has important strategic and practical significance for improving China’s defense and decision-making capabilities when major projects are subjected to climate change and extreme climate events, and for improving China’s comprehensive prevention and control capabilities of natural disasters. It is also an important mission and development direction of modern engineering geology. This paper focuses on how the extreme climate affects geological bodies and major projects, and how to induce disasters from the perspective of engineering geology. In addition, this paper systematically summarizes the research advances of drought climate-induced soil engineering property response processes and catastrophic mechanisms, especially the processes and mechanisms of soil evaporation, shrinkage, and desiccation cracking. Generally, the evaporation process of soil water occurs in three fairly distinct stages: constant rate stage, falling rate stage and residual stage. The constant rate stage occurs when the soil is still fully saturated. The moisture transfer is dominated by liquid flow and mainly controlled by capillary force. The change of soil from saturated to unsaturated state results in the evaporation transition from constant rate stage to falling rate stage. In this stage, the moisture transfers in both liquid and vapor forms and the later one gradually dominates the evaporation process. The evaporation reaches residual stage when the pore water is dominated by absorbed water, and the moisture transfers in vapor form only. The volumetric shrinkage soil is mainly attributed to suction-induced pore size reduction. Based on soil shrinkage characteristic curve, three shrinkage stages can be distinguished: normal shrinkage, residual shrinkage and zero shrinkage. Most of the volumetric shrinkage occurs before the air-entry point while the soil is still fully saturated. The shrinkage direction of soil shows obvious anisotropy, which can be quantified by shrinkage geometry factor. At low degree of compaction, the radial shrinkage strain is higher than axial shrinkage strain, and the shrinkage geometry factor is larger than 3, while it is contrary at high degree of compaction. The reversibility of shrinkage deformation depends on soil suction. Shrinkage deformation is reversible when suction is higher than <sc>113 MPa.</sc> Drying-induced soil desiccation cracking process takes place in three typical stages (i.e., primary cracks initiate, sub-cracks initiate and crack network stabilization), and presents evident time-order characteristics. New cracks always start perpendicularly from the existing cracks. Generally, the initiation and propagation of desiccation cracks show evident dynamic characteristics and significantly depend on soil water evaporation rate, stress state and shrinkage potential. The cracks initiate at constant evaporation rate stage where soil is still fully saturated. The cracking water content can be much higher than liquid limit. Cracking is likely to occur if the tensile stress, which is induced by soil suction or shrinkage constraint, reaches the tensile strength of soil. It is believed that soil suction and tensile strength are the two key mechanical parameters that control the cracking behavior. From a perspective of soil structure, cracking is the result of pore shrinkage and microstructure re-arrangement. The mechanical effect and shrinkage potential are proposed as the two prerequisite factors for crack initiation. Quantitative characterization of crack patterns plays a very important role in understanding the cracking dynamic and mechanism. Image processing technique has been proved as a powerful, efficient and high-accurate tool for quantitative description of crack patterns. In the past decades, systematic research methods for soil cracking have been well established, including testing, monitoring, quantifying, data processing etc. These achievements make up for the research blanks of drought climate disasters in the field of engineering geology, and provide scientific basis for guiding engineering geological practice and disaster prevention and mitigation in arid regions. In the future, in addition to strengthening basic research on climate change and atmosphere-geological body interaction, the related technical research should also be strengthened, such as distributed optical fiber sensing technology, microbial geological engineering technology on nature-based solutions, big data and cloud computing technology, artificial intelligence technology, so as to prevent and mitigate disasters in engineering geology by providing advanced theoretical and technical support.

A comprehensive comparison between substrate heating and light heating induced nanofluid droplet evaporations

A comprehensive comparison between substrate heating and light plasmonic heating induced nanofluid droplet evaporations is presented. The substrate temperature was kept as 36.5 °C for substrate heating, but a 1400 W/m2 irradiation flux emitted by a xenon lamp was used for light heating. Both two heating modes yield constant contact diameter evaporation. Because light irradiation reorganizes nanoparticles to generate dynamically varied heat source in nanoscale due to the plasmonic effect, the two heating modes are found to display three differences. First, droplet surface temperature decreases monotonically from contact line to apex for substrate heating, but for light irradiation, droplet surface temperature displays nonmonotonic variation including a contact line region CLR and a bulk volume region BVR. Temperature gradient is significant in CLR but does not exist in BVR. Second, the substrate heating generates both radial flow and Marangoni flow in the whole droplet. Thus, coffee-ring and dispersed nanoparticles are observed on substrate. On the other hand, for light heating, the Marangoni flow is only confined in CLR due to the local temperature gradient there, creating most of nanoparticles deposition near the contact line. Third, because the droplet surface area decreases versus time, the evaporation rate reduces to behave the non-linear variation of droplet volume for substrate heating. The situation is changed for light heating induced droplet evaporation. The enhanced plasmonic heating in CLR due to nanoparticles deposition there offsets the effect of droplet surface area decreasing. Thus, light heating would give rise to the constant droplet evaporation rate, which is distinct to substrate heating. This work enhances the fundamental understanding of the droplet evaporation dynamics under the condition of light heating induced plasmonic heating effect.

Short term evaporation estimation in a natural semiarid environment: New perspective of the Craig – Gordon isotopic model

Evaporation is one of the most important processes in the hydrologic cycle and is considered as one of the lead factors governing climate in terrestrial environments, particularly in arid areas. In natural open systems, evaporation should be considered as a time dependent function and a cumulative process. We applied and compared Craig-Gordon isotopic model with the Penman-Monteith physical evaporation model, after a biannual hydrologic cycle characterization in a natural semi-arid environment to determine annually reliable balance budgets and estimations. Our results show that isotopic evaporation rates reflect a sinusoidal behavior during isotopic fractioning rather than a lineal and constant evaporation rate. This sinusoidal behavior exhibits the influence of solar radiation and other meteorological variables that have not yet been considered in the C-G isotopic mass balance model. The estimation of isotopic evaporation in natural environments are reliable during the dry season while estimations of isotopic loss fraction (f) in the wet season behave as an isotopic mixing model of evaporated water-precipitation-runoff. Physical and isotopic methodologies are difficult to relate due to basic fundamentals and development conceptualizations: accordingly, further work is required to enhance the Craig-Gordon and Gonfiantini evaporation model and its relationship with physical methodologies in order to improve the estimation of evaporation in natural semiarid environments.

Drying Mediated Aggregation Pattern of CdTe QDs towards the Fabrication of Molecular Devices

Drying mediated self-aggregation patterns of CdTe colloidal QDs through simple evaporation method was reported. Thioglycolic acid (TGA) capped CdTe QDs were prepared in aqueous phase through colloidal route and their structural, optical and morphological behaviors were studied. The drying patterns of CdTe QDs were fabricated under a constant evaporation rate. The coffee ring effect and the drying pattern formations were studied for the TGA capped CdTe colloidal QDs suspension in an aqueous medium. The structural behavior of the CdTe QDs and the drying patterns were revealed by the X-ray diffraction analysis. The size-tunable optical properties of the prepared CdTe QDs were studied by the optical absorption and emission spectroscopy. The capping effects of TGA on CdTe QDs were confirmed by the FT-IR analysis. The surface morphology of the TGA capped CdTe QDs and the drying mediated aggregation patterns of CdTe colloidal suspension were studied by the scanning electron microscopy analysis. The drying mediated patterns from the evaporation technique were suggested as a simple technique for the fabrication of molecular devices.

Evaporation of ethanol-water sessile droplet of different compositions at an elevated substrate temperature

We experimentally investigate the evaporation dynamics of sessile droplets with different compositions of ethanol-water binary mixture at different substrate temperatures. At room temperature, a binary droplet undergoes two distinct evaporation stages unlike only the pinned stage evaporation for pure droplets. In the binary droplets, the more volatile ethanol evaporates faster leading to a nonlinear trend in the evaporation process. At elevated substrate temperature, we observed an early spreading stage, an intermediate pinned stage and a late receding stage of evaporation. Increasing the substrate temperature decreases the lifetime of binary droplets rapidly. At high substrate temperature, we found that the lifetime of the droplet exhibits a non-monotonic trend with the increase in ethanol concentration in the binary mixture, which can be attributed to the non-ideal behaviour of water-ethanol binary mixtures. Interestingly, the evaporation dynamics for different compositions at high substrate temperature exhibits a self-similar trend showing a constant normalised volumetric evaporation rate for the entire evaporation process. This indicates that the evaporation dynamics of a binary droplet of a given composition at high substrate temperature is equivalent to that of another pure fluid with a higher volatility at room temperature. The evaporation rates of pure and binary droplets at different substrate temperatures are compared against a theoretical model developed for pure and binary mixture droplets. The model predictions are found to be quite satisfactory for the steady evaporation phase of the droplet lifetimes.