Evaporation Rate Research Articles

Highly efficient solar steam evaporation via elastic polymer covalent organic frameworks monolith

Three-dimensional solar steam evaporators with efficient water purification performance have received increasing attention recently. Herein, elastic polymer covalent organic frameworks (PP-PEG) containing PEG chains with intriguing adaptability to guests are prepared by forming porphyrin rings. PP-PEG foams demonstrate full spectrum absorbance and excellent photothermal conversion properties. Through well-designed thermal management and optimization of the hydrophilicity and PEG chain length, we obtain a highly efficient solar evaporator with an evaporation rate of 4.89 kg m−2 h−1 under 1 sun in self-contained mode. The optimized solar evaporation rate is increased to 18.88 kg m−2 h−1 under 1 sun with a facile truncated cone reflector, exceeding all known solar steam evaporators. This innovative design holds immense promise for desalination and water purification owing to its simple preparation, high efficiency and durability.

Pagoda solar evaporators with an alternating hot-cold pattern for rapid, scaling-free desalination of hypersaline brines

Solar-driven evaporation holds significant potential for desalinating hypersaline brines, which pose challenges for traditional reverse osmosis. However, achieving both rapid evaporation and scaling prevention remains a key obstacle. In this study, we introduce a pagoda-like solar evaporator designed to optimize heat and mass transfer during the evaporation process of hypersaline brines. The interconnected multi-layer structure creates an alternating hot–cold pattern that integrates solar and environmental evaporation, enhancing the overall evaporation rate. This pattern also induces thermal Marangoni convection within the evaporator, mitigating local ion accumulation and providing durable scaling resistance. The pagoda evaporator sustains an evaporation rate of approximately 1.70 kg·m−2·h−1 over 8 h with a 20 wt% NaCl solution and produces 7.78 L·m−2·day−1 of fresh water without surface scaling in outdoor experiments. This innovative and facile design marks a significant advancement in the sustainable and efficient desalination of highly saline brines.

Enhancing the sustainability of interfacial evaporation to mitigate solar intermittency via phase change thermal storage

Solar-driven interfacial water evaporation is a low-carbon footprint strategy for addressing global water scarcity. However, the operation of the evaporator requires continuity of solar radiation. Herein, the key to overcoming the intermittency of sunlight lies in utilizing the heat storage/release cycle of phase change materials. Additionally, the synergistic effect of high thermal conductivity materials and increased heat transfer area addresses the nonuniform spatial temperature within the heat storage device caused by the low thermal conductivity of molten paraffin. Although the heat transferred to the paraffin reduces the evaporation rate under illumination, the thermal storage/release capacity of paraffin increases the evaporation mass by 171.5% in darkness. Ultimately, after one light–dark cycle, the total evaporation mass over the entire period increased by 11.5%. Finally, although paraffin undergoes sensible and latent heat absorption and release across various temperature ranges during multiple light–dark cycles and prolonged operation, the phase change delays at different internal locations still ensure stable dark-state evaporation compensation for the evaporator, thereby enhancing the sustainability of the evaporation process.

Surface patterned polyvinyl alcohol/CNT hydrogels for sustained solar powered high concentration brine desalination and salt harvesting

Solar-driven interfacial evaporation is an attractive way to achieve water purification. However, high water evaporation rates often result in the precipitation of salt crystals on the surface of the evaporator leading to decay of the evaporation efficiency over time, which makes it difficult to balance high water evaporation rates with salt resistance. Herein, an anisotropic polyvinyl alcohol/CNT hydrogel is constructed by directional freezing and surface patterning. The polymer backbone formed by the polyvinyl alcohol chains interacts with the water clusters to reduce the evaporation enthalpy of water and the absorbed water can be released by squeezing the hydrogels due to the micron-sized vertically aligned pores. More importantly, by designing the structure of the hydrogels surface, the gas–liquid interface of the evaporators can be increased while the growth direction of the salt crystals can be controlled. As a result, the water evaporation rate can be increased from 3.26 kg m-2h−1 to 3.69 kg m-2h−1 under one sun irradiation through surface patterning. After 50 h of continuous operation in 10 wt% NaCl solution under one sun irradiation, the water evaporation rate gradually increases and a large amount of salt collection is collected, which proves its satisfactory salt resistance.

Atmospheric implications of hydrogen bonding between methanesulfonic acid and 12 kinds of N-containing compounds

The hydrogen bonding interactions between methanesulfonic acid (MSA) and NHx compounds, such as ammonia (A), alkylamines (aNHx), and cyclic amino compounds (cNHx), were investigated using density functional theory, atoms in molecules, localized molecular orbitals-based energy decomposition analysis, and atmospheric clusters dynamic code methods. The results revealed that these dimers exhibit hydrogen bonds by SOH⋯N interactions. MSA–cNHx dimers showed higher binding energies compared to MSA–aNHx/A dimers. Topological analysis using AIM confirmed the presence of hydrogen bonding in these dimers by ρ(r) and ∇2ρ(r). The results of IRI indicate that there are different strength types of hydrogen bonding interactions in these dimers. LMO–EDA highlighted electrostatic interactions as the main attractive force, particularly in MSA–cNHx dimers. ACDC results showed a low evaporation rate for MSA–cNHx dimers compared to others. These findings suggest that MSA plays a crucial role in NPF events, and MSA–cNHx clusters could potentially act as nucleation nuclei in the atmosphere.

A 3D-Printed Bionic Membrane with Autonomously Passive Unidirectional Liquid Transfer Capability for Water Condensation, Collection, and Purification.

Interfacial solar vapor generation is a promising technology for alleviating the current global water crisis, and the evaporation rate and efficiency have approached the theoretical limit. In a practical interfacial evaporation water purification system, the collection rate of purified water is typically lower than the evaporation rate. Passive collection devices based on gravity are susceptible to environmental influences and exhibit low collection efficiency, while active collection devices consuming external energy suffer from complex device systems and extra energy consumption. Given that both collection devices are nonselective and unable to distinguish contaminants mixed in the vapor, bionic membranes with autonomously passive and unidirectional water transfer capacity are developed through 3D printing for efficient water collection. More importantly, the bionic membranes are capable of high-speed water transportation without the need for external energy or gravity drive and liquid-selective transportation for separating oily pollutants from the collected products. The directional transport property facilitates the modular assembly of the bionic membrane, extending its application to practical large-scale solar-driven seawater desalination systems.

Accumulation of road salt in a calcareous fen: Kampoosa Bog, western Massachusetts.

Road salt poses a threat to the quality of soils and water resources. Wetlands located in salt contaminated areas are at risk of experiencing lower plant and animal species diversity. Therefore, it is critical to understand how modifications to salt application rates and hydrological events impact wetland water quality. Here, we use chloride mass flux, discharge, groundwater chloride concentration, meteorological, and salt application data from 2012-2020 to estimate chloride accumulation and outflux rates in the Kampoosa Bog subwatersheds, located in Stockbridge and Lee, Massachusetts, and bordered by major highways (Interstate-90 and U.S. Route 7). We also investigate the correlation between wetland size and chloride retention rate. During the 2018-2019 period, mean annual chloride application rates in the major watershed increased from 363000 kg/year (2012-2017) to 479000 kg/year. This led to a net chloride accumulation (KB100 subwatershed: 339000 kg; KB150 subwatershed: 188000 kg) and increased groundwater chloride concentrations in the fen. Chloride outflux from these subwatersheds was primarily driven by discharge. We found that the relationship between wetland percent cover and chloride retention is complex. Although the percent wetland cover is greater in the KB100 main wetland region compared to the KB150 subwatershed, high precipitation in 2018 resulted in similar chloride retention efficiencies (~26%). During the drier year (2019), chloride retention was higher in the wetland region due to its gentle slopes which promote water accumulation and consequently higher evaporation rates which lowers discharge and chloride outfluxes. The chloride steady-state concentration analysis also suggests that there is potential for chloride accumulation to continue because the watershed has not yet reached steady-state chloride concentrations. Without major modifications to salting practices, chloride concentrations will continue increasing and potentially promote the re-growth of invasives (Phragmites) and continued growth of salt tolerant species (Typha angustifolia/xglauca) that diminish plant diversity.

Evaporation, spreading, and possible uptake of droplets on sorghum (Sorghum bicolor) and cowpea (Vigna unguiculata) leaves using an imaging-based technology.

Sprayed agrochemical droplets have a dynamic evolution on the leaf surface, undergoing changes in shape and volume due to spreading, evaporation, and adsorption. To better understand these processes, an accessible imaging-based experimental methodology is presented to precisely measure droplet spreading, evaporation, and potential uptake by a leaf within a controlled relative humidity environment. Laboratory experiments were conducted to determine the effect of hydrocarbon surfactants, accelerators (light mineral oil), and humectants (high fructose corn syrup) on droplet spread, evaporation, and potential uptake when applied to sorghum (Sorghum bicolor 'Tricker') and cowpea (Vigna unguiculata) leaves. Experiments on cowpea leaves showed uniform spreading and no change in evaporation compared to the predicted rate. In contrast, on sorghum leaves, results suggest that the volume loss rate exceeds the predicted evaporation rate (up to 23%), indicating a potential uptake by the leaves. Some accelerated dynamics on sorghum can be attributed to the lateral spreading observed on hairy leaves along the veins, increasing the contact area by an average of 65%. However, samples containing light mineral oil, typically considered an accelerant to aid in uptake, demonstrated the highest rate but exhibited minimal spreading. The study demonstrates how droplet composition affects droplet dynamics on waxy and hairy leaves by using an imaging-based methodology to measure evaporation rates, volume loss, contact angle, wetted area, and spreading behavior. The findings highlight some of the complex coupling between the crop protection product composition and droplet life cycle on a leaf. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

TEOS-10 and the climatic relevance of ocean–atmosphere interaction

Abstract. Unpredicted observations in the climate system, such as recent excessive ocean warming, are often lacking immediate causal explanations and are challenging numerical models. As a highly advanced mathematical tool, the Thermodynamic Equation of Seawater – 2010 (TEOS-10) was established by international bodies as an interdisciplinary standard and is recommended for use in geophysics, such as, and in particular, in climate research. From its very beginning, the development of TEOS-10 was supported by Ocean Science through publishing successive stages and results. Here, the history and properties of TEOS-10 are briefly reviewed. With focus on the air–sea interface, selected current problems of climate research are discussed, and tutorial examples for the possible use of TEOS-10 in the associated context are presented, such as topics related to ocean heat content, latent heat, and the rate of marine evaporation; properties of sea spray aerosol; or climatic effects of low-level clouds. Appended to this article, a list of publications and their metrics is provided for illustrating the uptake of TEOS-10 by the scientific community, along with some continued activities, addressing still pending, connected issues such as uniform standard definitions of uncertainties of relative humidity, seawater salinity, or pH. This article is dedicated to the jubilee celebrating 20 years of Ocean Science. This article is also dedicated to the memory of Wolfgang Wagner, who sadly and unexpectedly passed away on 12 August 2024. His contributions to TEOS-10 are truly indispensable constituents; Wolfgang was an essential co-author of various related documents and articles. He will be deeply missed. All the rivers run into the sea; yet the sea is not full; unto the place from whence the rivers come, thither they return again. The King James Bible: Ecclesiastes, 450–150 BCE He wraps up the waters in his clouds, yet the clouds do not burst under their weight. Holy Bible: New International Version, Job 26:8 Of the air, the part receiving heat is rising higher. So, evaporated water is lifted above the lower air. Leonardo da Vinci: Primo libro delle acque, Codex Arundel, ca. 1508 Two-thirds of the Sun's energy falling on the Earth's surface is needed to vaporize … water … as a heat source for a gigantic steam engine. Heinrich Hertz: Energiehaushalt der Erde, 1885 The sea-surface interaction is obviously a highly significant quantity in simulating climate. Andrew Gilchrist and Klaus Hasselmann: Climate Modelling, 1986 The climate of the Earth is ultimately determined by the temperatures of the oceans. Donald Rapp: Assessing Climate Change, 2014

Severe Convection at Burgas Airport: Case Study 17 September 2022

Convection monitoring and forecasting are crucial for air traffic management as they can lead to the development of intense thunderstorms and hazards such as severe turbulence and icing, lightning activity, microbursts and hail that affect aviation safety. The airport of Burgas is located in southeast Bulgaria on the Black Sea coast and occurrences of intense thunderstorms are mainly observed in the warm season between May and September. This work presents an analysis of severe convection over southeast Bulgaria on 17 September 2022. In the late afternoon, a gust front was formed that reached the Burgas airport with a wind speed exceeding 45 m/s, the record for the past 50 years, damaging the instrument landing system of the airport. To analyse the severe weather conditions, we combine state-of-the-art observations from satellite and radar with the upper-air sounding and surface. The studied period was dominated by the presence of a very unstable air mass over southeast Bulgaria ahead of the atmospheric front. As convection developed and moved east towards Burgas, it had four characteristics of severe deep convection, including gravitational waves at the overshooting cloud top, a cold U-shape, a flanking line and a cloud top temperature below −70 °C. The positive integrated water vapour (IWV) rate of change preceded the lightning activity peak by 30 min. Analysis of integrated vapour transport (IVT) gives higher values by a factor of two compared to climatology associated with the atmospheric river covering the eastern Mediterranean sea.

Honeycomb-like Microthermal Traps on a Photothermal Surface for Highly Efficient Solar Evaporation.

Solar evaporation is an ecofriendly and practical method for seawater desalination. The photothermal layer, which absorbs solar energy and converts it to thermal energy, plays a crucial role in enhancing the efficiency of the evaporator. However, structural design methods for photothermal layers are often complex and energy-intensive. This work reports a simple and efficient strategy for fabricating a necklace-like beaded nanofiber self-organized honeycomb-structured photothermal material. The honeycomb-like cavities form numerous microscale thermal traps, achieving thermal localization while maintaining high energy utilization efficiency, which not only increases light absorption but also facilitates the diffusion and escape of steam. Besides, the hydrophobic honeycomb layer separates the photothermal layer and the interface water, which reduces considerable heat conduction loss and achieves an effective antisalting performance. These functional features endow the evaporator with an evaporation efficiency of 92.9%, and the evaporation rate reaches 2.11 kg m-2 h-1 at 1 sun irradiance, demonstrating its great potential for practical solar-driven seawater desalination under natural sunlight.

Analysis of group evaporation characteristics of droplet clusters in an evaporating spray

Droplet clustering in sprays refers to the dynamic evolution of highly concentrated regions due to the preferential accumulation of the polydisperse droplets in the turbulent airflow entrained by the spray. In the current study, we aim to experimentally investigate the collective vaporization of the droplets in droplet clusters in an air-assisted acetone spray characterized by the Group number, $G$ . The magnitude of $G$ depends on the cluster length scale and interdroplet spacing, and it indicates the vaporization mode that may vary from the isolated mode ( $G \ll 1$ ) to external group mode ( $G \gg 1$ ). The droplet measurements were obtained under atmospheric conditions at different axial and radial locations within the spray. Application of the Voronoi analysis to particle image velocimetry images of the spray droplets facilitated the identification and characterization of the droplet clusters, which allowed the measurement of $G$ for each cluster. The results highlighted that multiscale clustering of the evaporating droplets leads to multimode group evaporation of the clusters (characterized by a wide range of $G$ : 0.001–10). The trend of interdroplet spacing versus cluster area allowed the classification of the droplet clusters into small-scale clusters (which are of the order of the Kolmogorov length scale) and large-scale clusters (that scale with the large-scale turbulent eddies), that are found to exhibit distinct group evaporation behaviour. A theoretical model is invoked to correlate $G$ with the droplet evaporation rate for individual clusters, and some interesting observations are identified, which are explained in the paper.

Bioinspired Photothermal Metal-Organic Framework Cocrystal with Ultra-Fast Water Transporting Channels for Solar-Driven Interfacial Water Evaporation.

Herein, a bioinspired metal-organic framework (MOF) cocrystal produced from the co-assembly of a MOF [Ni3(hexaiminobenzene)2, Ni3(HIB)2] and p-chloranils (CHLs) is reported. Because of the 2D conjugation nature and the formation of persistent anion radicals, this cocrystal shows an excellent photothermal property, and is further used as an absorber in solar-driven interfacial water evaporation. The solar-driven interfacial water evaporation rate (4.04 kg m-2 h-1) is among the best compared with those of previously reported photothermal materials. Molecular dynamics simulation results suggested that the rotating of the CHL molecules relative to the MOF planes tuned the pore size to enable the ultra-fast water transporting, and thus ultra-high water transporting rates (1.11 × 1011 and 3.21 × 1011 H2O s-1 channel-1 at 298.2 and 323.0 K, respectively) for layered cocrystal structures, that are much higher than that of aquaporins (≈1.1 × 1010 H2O s-1 channel-1 at 298.2 K), are observed. The superior solar-driven water evaporation performance is thus attributed to the synergistic effect of the ultra-fast water transporting pores together with the excellent photothermal property of the cocrystal. This research provided a biomimetic strategy of rational design and production of charge transfer cocrystals to modulate their pores and photothermal properties for solar-driven interfacial water evaporation.

Dynamic Water Microskin Induced by Photothermally Responsive Interpenetrating Hydrogel Networks for High‐Performance Light‐Tracking Water Evaporation

AbstractSolar‐driven interfacial water evaporation is attracting increasing attention as a promising environmentally‐friendly solution to freshwater scarcity. It has been proven that a thin water layer on photothermal materials can prevent solar energy from invalidly heating the excess water to enhance the evaporation rate. However, the current water layers are usually formed on inelastic materials via confined capillarity, which are static and uncontrollable. Herein, we propose a flexible hydrogel‐based photothermal conversion material with thermal responsiveness by facile frontal polymerization, which can generate a unique dynamic water microskin (DWMS) during the solar evaporation process. The copolymerized hydrogel, introduced by the second polymeric poly(vinyl alcohol) network and thermally responsive poly(N‐isopropylacrylamide) (PNIPAM), exhibits reinforced mechanical strength and photothermally triggers reversible shrinking/swelling cycles that enable a thin water layer (≈32 µm) to balance the feedwater supply and photothermic energy input dynamically. As a result, a stable superior vaporization rate of 8.7 kg m−2 h−1 is achieved based on a cylindrical hydrogel with 6 cm height under 1 sun. Moreover, the simultaneous responsive bending allows efficient omnidirectional solar evaporation by light‐tracking to ensure maximum perpendicular solar absorption, which provides an alternative strategy for durable high‐efficiency solar evaporators for effective thermal management and solar utilization.

Towards Sustainable Energy Solutions: Evaluating the Impact of Floating PV Systems in Reducing Water Evaporation and Enhancing Energy Production in Northern Cyprus

Floating photovoltaic systems (FPVSs) are gaining popularity, especially in countries with high population density and abundant solar energy resources. FPVSs provide a variety of advantages, particularly in situations where land is limited. Therefore, the main objective of the study is to evaluate the solar energy potential and investigate the techno-economic perspective of FPVSs at 15 water reservoirs in Northern Cyprus for the first time. Due to the solar radiation variations, solar power generation is uncertain; therefore, precise characterization is required to manage the grid effectively. In this paper, four distribution functions (Johnson SB, pert, Phased Bi-Weibull, and Kumaraswamy) are newly introduced to analyze the characteristics of solar irradiation, expressed by global horizontal irradiation (GHI), at the selected sites. These distribution functions are compared with common distribution functions to assess their suitability. The results demonstrated that the proposed distribution functions, with the exception of Phased Bi-Weibull, outperform the common distribution regarding fitting GHI distribution. Moreover, this work aims to evaluate the effects of floating photovoltaic systems on water evaporation rates at 15 reservoirs. To this aim, five methods were used to estimate the rate of water evaporation based on weather data. Different scenarios of covering the reservoir’s surface with an FPVS were studied and discussed. The findings showed that annual savings at 100% coverage can reach 6.21 × 105 m3 compared to 0 m3 without PV panels. Finally, technical and economic assessment of FPVSs with various scales, floating assemblies, and PV technologies was conducted to determine the optimal system. The results revealed that a floating structure (North orientation-tilt 6°) and bifacial panels produced the maximum performance for the proposed FPVSs at the selected sites. Consequently, it is observed that the percentage of reduction in electricity production from fossil fuel can be varied from 10.19% to 47.21% at 75% FPV occupancy.

Solar powered integrated multi sensors to monitor inland lake water quality using statistical data fusion technique with Kalman filter

This study proposes a data-driven statistical model using multi sensor fusion and Kalman filtering for real-time water quality assessment in lakes. A recursive estimation technique, the Kalman Filter, is employed to handle uncertainties and enhance computational efficiency. The fusion process integrates data from sensors monitoring parameters like chlorophyll concentration, surface water elevation, temperature, and precipitation, producing Markov features to capture temporal transitions and environmental dynamics. Data synchronization and fusion are achieved through recursive KF methods, enabling real-time adaptive management in response to environmental fluctuations such as seasonal changes, precipitation (6–18%), and evaporation rates (1.2–11.9 mm/day). Over a 30-day evaluation period, the model accurately predicted chlorophyll concentrations, reaching 128 mg/m3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {mg}/\\hbox {m}^{3}$$\\end{document} in mid-level inflow regions (3.6 m water elevation) compared to 86 mg/m3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\hbox {mg}/\\hbox {m}^{3}$$\\end{document} in extreme inflow areas (5.5 m). The integration of Markov feature extraction and eigenvalue estimation enhanced prediction stability and sensitivity, with the KF maintaining computational efficiency at 7.8 ms per computation cycle. The model’s accuracy was validated by achieving a residual error of less than 0.05 with minimal noise interference. Overall, the system provides a resilient and precise framework for real-time lake water quality assessment, capable of handling multi-parameter uncertainties and dynamic environmental changes, thereby supporting informed decision-making for aquatic ecosystem management.

Polyurethane and fiber- based photothermal device for solar evaporation and crude oil adsorption

Photothermal materials exhibit significant potential for marine applications, yet their efficiency and durability require enhancement. This study presents a dual-layer photothermal device that integrates a polyurethane light absorption layer with a wood sponge layer, designed for water transport and thermal insulation. The wood sponge’s hydrophilicity and effective water transport properties improve water supply while minimizing heat loss. Under sunlight, the device achieves a surface temperature of 63.2°C and an evaporation rate of 1.86 kg/m2/h for seawater desalination. The porous design of both layers ensures salt resistance during extended desalination processes. Furthermore, the incorporation of disulfide bonds into the polyurethane enhances the material’s self-healing properties, enabling sustained performance even after prolonged use, thus extending its service life. Additionally, the device demonstrates effective crude oil adsorption capabilities attributed to its photothermal efficiency and porosity. This innovative design provides valuable insights for advancing solar-driven evaporation devices and crude oil adsorption systems in marine environments.

Numerical Study on the Variable-Temperature Drying and Rehydration of Shiitake

Variable-temperature convective drying (VTCD) is a promising technology for obtaining high-quality dried mushrooms, particularly when considering rehydration capacity. However, accurate numerical models for variable-temperature convective drying and rehydration of shiitake mushrooms are lacking. This study addresses this gap by employing a model with thermo–hydro and mechanical bidirectional coupling to investigate five dehydration characteristics (moisture ratio, drying rate, temperature, evaporation rate, and volume shrinkage ratio) and a drying load characteristic (enthalpy difference) during VTCD. Additionally, a mathematical model combining drying and rehydration is proposed to analyze the effect of VTCD processes on the rehydration performance of shiitake mushrooms. The results demonstrate that, compared to constant-temperature drying, VTCD-dried mushrooms exhibit moderate shrinkage rates and drying time (16.89 h), along with reduced temperature variation and evaporation rate gradient (Max. 1.50 mol/(m3·s)). VTCD also improves enthalpy stability, reducing the maximum drying load by 58.84% compared to 338.15 K constant-temperature drying. Furthermore, drying time at medium temperatures (318.15–328.15 K) greatly influences rehydration performance. This study quantitatively highlights the superiority of variable-temperature convective drying, offering valuable insights for optimizing the shiitake mushroom drying processes.

Theoretical analysis of water-droplet condensation and evaporation in prescribed environment with radiation

Abstract A quasi-explicit algebraic solution of the problem of quasi-steady water droplet heat- and mass-transfer with condensation or evaporation in a prescribed environment including radiation has been obtained. The solution is based on the mass-fraction form of Fick’s law of species diffusive mass transport, which allows accounting for variation in gas density through the diffusion layer surrounding the droplet. A new term, the average vapor supersaturation through the diffusion layer, has been included that allows the model to be extended to environmental conditions significantly outside those for which it is theoretically derived (dilute or near-saturation), even to conditions of relatively high temperature, low relative humidity, and low pressure. The latter two have atmospheric significance because evaporative cooling can induce significant decrease in droplet temperature and possibly induce freezing. Basic modeling assumptions are confirmed by comparison with time-dependent temperature and evaporation-rate measurements of a laboratory laser-heated droplet. Accuracy of the new model is assessed by comparison with exact equations. For temperatures between −30 and 0°C and negligible radiation, relative-error magnitudes in droplet temperature and evaporation rate are less than 5%, even for relative humidity down to 10% and pressure down to 60 kPa. This represents an improvement in accuracy over the conventional model, in which property variations of density and supersaturation through the diffusion layer are not taken into account. Differences in predicted evaporation rates between the mass-fraction and the more common partial-density Fick’s laws, which can be significant (>10% above 70% relative humidity) in coupled, implicit equations, are shown to be made negligibly small (<0.5%) by linearizing about the saturation state.

Bifunctional Portable Powder for Freshwater Production With Moisture Harvesting and Undrinkable Water Purification.

Freshwater scarcity threatens human survival, particularly in extreme environments like deserts, oceans, and space. Compatible atmospheric water harvesting and undrinkable water purification offer an affordable approach to solving freshwater scarcity in these extreme environments. Nonetheless, developing composite sorbent to attain efficient atmospheric water harvesting and undrinkable water purification remains challenging. Hence, a portable hybrid hygroscopic powder (HLC powder) consisting of hydroxypropyl chitosan, dibenzaldehyde-functional poly(ethylene glycol), lithium chloride (LiCl), and nano carbon black is proposed. The HLC powder with optimized LiCl load can capture moisture from the air, showing a high water uptake of 1.76g g-1 at 34% relative humidity (RH) and appropriate over a wide humidity from 34% to 75% RH. pH-responsive sol-gel transition induced by Schiff base bonds transforms the HLC solution into hydrogel, inhibiting hydrated salt leakage. Meanwhile, to achieve efficient undrinkable water purification, the LiCl-free hybrid powder is utilized to convert the undrinkable water, including seawater, dye water, and human urine, to photothermal hydrogel evaporators with low evaporation enthalpies and high evaporation rates ranging from 1.81 to 2.05 kg m-2 h-1 under one sun. This strategy establishes a new path to conveniently obtaining freshwater, breaking hydrological restrictions.