Water Collection Rate Research Articles

Boosting Droplet Transport for Fog Harvest.

Wedge-shaped superhydrophilic tracks have been considered as one of the most effective ways to transport droplets for diverse cutting-edge applications, e.g., energy harvesting and lab-on-a-chip devices. Although significant progress, such as serial wedge-shaped tracks with curved edges, has evolved to advance the liquid transport, the ultrafast and long-distance transporting of drop-shaped liquid remains challenging. Here, inspired by the cactus spine that enables fast droplet transport and the serial spindle knot of spider silk, which is capable of collecting condensate from a wide range of distances, we created serial wedge-shaped superhydrophilic patterns and optimized their side edges with a convex brachistochrone curve to boost the acceleration. The junctions of the serial patterns were meanwhile reformed into concave brachistochrone curves to lower the energy barrier for sustained transport. For transporting the liquid in drop shapes to the long distance at high velocity, the wedge-shaped tracks were slenderized to the greatest extent to suppress the liquid spreading and thus prevent the degradation of the Laplace driving force. Moreover, the junction that determines the energy barrier of droplet striding was carefully designed based on the principle of minimizing momentum loss. The exquisite architecture design pushed the droplet transport to a maximum instantaneous velocity of 207.7 mm·s-1 and an outermost transport distance of 120.5 mm, exceeding most wettability or geometric gradient based reports. The transported volume of the droplets can be readily regulated by simply scaling the created architectures. The enhanced droplet transport facilitates the motion and departure of the cohered droplets, enabling a 1.9-fold rise of the water collection rate and 12-fold increase of the heat transfer coefficient during the fog harvest test. This scalable, controllable, and easily fabricatable surface design provides an essential pathway in realizing high-performance manipulation of droplets and possibly pioneers substantial innovative applications in multidisciplinary fields. Those include but are not limited to energy harvesting, lab-on-a-chip devices, and MEMS systems.

Spontaneous continuous multiple jump of condensate droplets on superhydrophobic surface with hierarchical micro-nano structures

When two or more droplets coalesce on a superhydrophobic surface, the released surface energy will partially convert into kinetic energy, resulting in droplet jump from substrate surface. In this paper, a kind of superhydrophobic surface with hierarchical papillary micro-nano structures was fabricated to facilitate droplets coalescence-induced jump. The surface is easy to prepare without complex process. Different from single jump, a kind of spontaneous continuous multiple jump was observed on this kind of superhydrophobic surface. The influences of continuous multiple jump on condensation nucleation rate and water collection rate are investigated and a theoretical model is adopted to determine energy conversion efficiency of continuous multiple jump. The results find that continuous multiple jump makes large droplets to move spontaneously, and improves performance of superhydrophobic surface to maintain dropwise condensation even under a high subcooling. With condensing, the continuous multiple jump becomes more frequent. The average condensation nucleation rate is 303 % higher than those of surfaces without hierarchical micro-nano structures. The water collection rate on superhydrophobic surface is 2 times higher than those without hierarchical micro-nano structures. The energy conversion efficiency of continuous multiple jump is two times higher than that of single jump. This study provides a potential direction for heat transfer enhancement of condensation and self-cleaning.

Poly(l-lactic acid) Janus Shape Memory Membranes with Uniform Vertically Penetrative Channels and Slit Pores for Enhanced Fog Collection: Synergistic Effect of Transport through Membranes and Sequential Sliding Behaviors of Water Droplets.

In this work, poly(l-lactic acid) (PLLA) Janus shape memory membranes with uniform vertically penetrative channels (SMEUVs) with slit pores have been fabricated with the help of template-assisting spray-coating and uniaxial tension at high temperature. During fog collection, superhydrophobic and hydrophilic surfaces act as the front (fog-facing) side and back side, respectively, in which the structural characteristics play essential roles. On one hand, the vertically penetrative channels in SMEUVs and the special pore geometry contribute to lower resistance, accelerating the transport of captured water through membranes (from the superhydrophobic side to the hydrophilic side). On the other hand, the movement of water droplets along the back side has been guided by the oriented structures of slit pores, promoting the detachment of droplets from the hydrophilic surface. Their synergistic effect removes captured water in a timely manner and provides fresh sites for the subsequent nucleation of water, enhancing fog collection performance. As a result, the optimal specimen (Janus SMEUVs with a draw ratio of 2.5, placed in the parallel direction) exhibits a much higher water collection rate (∼6×) relative to references (superhydrophobic and hydrophilic membranes). Our results are significant for sustainable development in view of both fog collection in arid regions and the biodegradability of PLLA.

All-day freshwater harvesting enabled by designing benzoxazine molecule with intrinsic photothermal conversion and radiation cooling ability

The importance of clean water resources for human health and economic development cannot be overlooked. Providing a way for fully passive all-day freshwater harvesting presents a significant challenge. Herein, we propose a strategy for all-day freshwater harvesting passively through a freestanding Janus film which combining solar-driven interfacial desalination during day time and dew water generation driven by passive radiative cooling at night. Specifically, the core of the strategy was a new bio-based benzoxazine which containing high-infrared emittance in the atmospheric window and the resultant cured black freestanding film owns a steady high light absorbance in the whole range of the solar irradiation wavelength. The home-made device made by the Janus film achieved a drinkable freshwater collection efficiency of 90.9 % when desalinating seawater under 1 sun illumination and achieved a dew water collection rate of 68.36 g m−2 day−1 at night. Moreover, the film has an excellent antibacterial effect, which ensures the quality of water collection and enhances the service life. Combining the advantages of bio-based raw materials, a simple fabrication process and scalability of the film, the all-day freshwater collection system makes a promising solution to alleviate freshwater shortage in many arid regions, islands and even boats sailing on the sea.

Water collection through a directional leaf vein pattern by fast laser marker ablation of stainless-steel

Inspired by the natural water harvesting mechanisms of desert beetles, cactus thorns, and leaf veins, we designed a heterogeneous wettability surface with superhydrophilic pattern integrating leaf vein as the directional water transport main channel, attached capillary triangles as auxiliary channel plus a deep rough desorption channel on an overall superhydrophobic surface for an efficient water collection. A superhydrophilic surface was initially fabricated on the stainless steel disc by laser marker ablation allowing 1 μL droplet to spread completely to 0° within 0.12 seconds, followed by fluorine-containing coating transforming superhydrophilic surface to superhydrophobic one. Directional water transport patterns were then etched on the superhydrophobic surfaces by the secondary laser marker. The surface energy gradient and Laplace pressure induced by the pattern facilitated directional fast transport and efficient desorption of droplets, thus improving water collection efficiency. The enhancement mechanism of the water harvesting behavior for such surfaces was analyzed, with one focus on enhancing collection in hydrophobic regions with capillaries to reduce bouncing off loss and the other on improving balanced cycling of the collection process. At a fog flow rate of 1500ml/h and 20cm away from the fog outlet, the directional leaf vein-patterned 19.625cm2 sized surface demonstrated a fog water collection rate (WCR) of 5.6 Kg·m-2·h-1 and first drop collection at the 49th s, an impressively short time rarely reported. Compared to the superhydrophobic, superhydrophilic samples, and the reference, WCR increased by 180%, 62%, and 59%, respectively, and the first droplet collection time decreased by 73%, 46%, and 62%, respectively. This efficient water collection method has huge potential in arid regions.

Solar-Driven Evaporator With "Starburst Turbine" Design Featuring Directional Salt Crystallization, Antibacterial, and Catalytic Multifunctionality for Efficient Water Purification.

Facing the global challenge of water scarcity, solar-driven desalination is considered a sustainable technology for obtaining freshwater from seawater. However, issues such as uncontrolled salt crystallization and bacterial contamination limit its efficiency and practicality. This study proposes an innovative solar-driven evaporator designed to address these challenges using optimized shape design and advanced photothermal materials. Based on finite element analyses, cylindrical evaporators with a "Starburst Turbine" shape are designed and fabricated, achieving directional salt crystallization and a record-breaking water collection rate of 3.56kg m-2 h-1 and an evaporation rate of 4.57kg m-2 h-1 under one sun illumination. During continuous 60-h illumination tests, the evaporator maintained a stable evaporation rate, attributed to its excellent directional salt crystallization capability. Additionally, the evaporator demonstrates superior photodynamic antibacterial performance and photocatalytic degradation of organic pollutants. Under one sun illumination for 1 h, it achieves 100% sterilization of S. aureus and E. coli, and a 95.4% degradation of methylene blue (MB), demonstrating its potential to purify various wastewater types. These findings underscore the significant scientific and practical value of integrating antibacterial and photocatalytic functions into solar water purification materials, providing a sustainable solution to global water scarcity challenges and environmental protection.

Thermoresponsive nanofiber yarns for water harvesting enhanced by harp system

The escalating global water crisis necessitates innovative approaches to developing sustainable water resources. Fog water collectors with variable surface wettability offer controlled fog harvesting in water-scarce regions. This study develops thermoresponsive fog collecting materials by electrospinning poly(N-isopropylacrylamide)-polyvinylidene fluoride (PNIPAm-PVDF) into yarns that are transformed into harp-like structures for enhanced water harvesting rate. Both meshes and harps using electrospun membranes exhibit the remarkable ability to transition between hydrophilic and hydrophobic wetting states at temperatures below the lower critical solution temperature (LCST). Hydrophilic and hydrophobic surfaces play distinct roles in fog water collection. Hydrophilic surfaces have a high affinity for water and enables droplet capture. Hydrophobic surfaces help the removal of aggregated water droplet and fog water collection. The highest water collection rate obtained with the electrospun PNIPAm-PVDF harp was 1415 ± 7.0 mg·cm−2 h−1. The water harvesting system based on the electrospun PNIPAm-PVDF harps exhibits a 485 % increase in water collection compared to the standard meshes made from the same material, emphasizing their potential for significantly improving the overall rate in fog water harvesting applications.

High-performance solar water purification enabled by controlled water convection in integrated porous aerogel multistage distiller

The employment of solar multistage distillers possessing thermal localization and energy cycle properties for saltwater desalination exhibits significant potential in fulfilling the increasing worldwide need for freshwater. In order to prevent salt crystallization on evaporators, most evaporators, however, excessively boost brine exchanging in distiller while ignoring heat loss during water convection. Here, we introduce an interesting porous aerogel-based multistage distiller (PAMS) that effectively suppresses heat loss during saltwater exchanging by controlling the water absorption rate through pore structure devising. This allows us to optimize the balance between evaporation, water transport, and salt-crystallization resistance. Finally, PAMS can reach a remarkable evaporation rate of 5.93 kg m−2h−1 and a high water-collection rate of 4.03 kg m−2h−1 under one solar irradiation thanks to the adjustable balance. Besides, PAMS exhibits impressive long-term stable antibacterial properties, which enhances the anti-biofouling and increases its reliability as a source of freshwater for ocean farm.

Nanoscale Drag Reduction Effect Enables Efficient Fog Harvesting

AbstractSurfaces with macro‐scale hydrophilic/hydrophobic regions (conventional Janus mode) are often considered as prime candidates for fog harvesting. However, the water collection efficiency of such surfaces frequently fails to meet the requirements of practical applications due to the occurrence of surface flooding caused by water droplet pinning. Here, an in situ molecular confined modification strategy is proposed to construct upgraded Janus mode for achieving nanoscale drag reduction effect, thereby improving the fog collection efficiency. Specifically, nanoscale hydrophilic sites are designed to effectively reduce the critical volume size required for water droplets to slide off, thus avoiding the surface flooding. Fibers with upgraded Janus mode (PAN‐TO) realize a water collection rate of 4035 mg cm−2 h−1, markedly exceeding that of most materials with conventional Janus mode. Moreover, the high interface bonding strength between hydrophilic sites and the material surface can withstand the impact of water and sand flushing, ensuring the long‐term usability of the material. The applications of PAN‐TO fibers in irrigation and dyeing are demonstrated. This work shows a nanoscale surface engineering proposal for building a next‐generation fibrous fog harvesting device.

A solar-electric dual-driven microporous hydrogel evaporator for all-weather highly efficient water purification

Solar-driven interfacial water evaporation technology holds significant potential for addressing global water scarcity. However, the variable nature of solar intensity in natural environments limits its reliability for all-weather highly efficient water purification. Herein, we develop a novel solar-electric dual-driven water purification evaporator featuring an electrically heated mesh within a microporous hydrogel composed of carbon nanotubes (CNTs) and polyacrylamide (PAAm). The synergistic photothermal and electrothermal effect of the microporous hydrogel enables the dual-driven evaporator to achieve an ultrafast evaporation rate of 16.35 kg m−2 h−1 under one sun irradiation with 3 A current input, demonstrating remarkable superiority to other dual-driven evaporators. Even under dark conditions, the evaporator maintains robust performance, achieving an impressive evaporation rate of 6.45 kg m−2 h−1, which surpasses existing photothermal-driven systems. Significantly, the integration of the solar-electric dual-driven evaporator with solar panels and a mobile power source creates a water purification system that can achieve closed-loop solar energy utilization. A five consecutive rainy day outdoor validation demonstrates that such a system exhibits an excellent average water collection rate of 3.1 kg m−2 d−1. This work provides a convenient and efficient approach to enhance the accessibility of purified water under varying environmental conditions.

Innovative 3D-printed surfaces for efficient water harvesting from air

PurposeThe purpose of this study is to develop nature-inspired 3D surfaces for atmospheric water harvesting.Design/methodology/approachInitially, cylindrical-shaped protrusions were produced utilizing a 3D printer to obtain a surface with a high surface area. Subsequently, an electrospraying technique was employed to coat the tips of these hydrophobic protrusions with hydrophilic nano-scale particles and fibers, utilizing polyamide 6 (PA6) or PA6/chitosan (CH) blends. In the next stage of the study, the impact of protrusion shape was investigated by fabricating surfaces with cylindrical, conical and tree-shaped protrusions. Following the production of 3D surfaces, PA6 was electrosprayed onto the protrusions to achieve varied wettability patterns on the 3D surface. Finally, the water collection rates and capacities of the surfaces were evaluated.FindingsWater collection tests demonstrated that PA6-coated surfaces exhibited greater water collection capacity compared to untreated surfaces. Furthermore, the addition of CH enhanced the water collecting efficiency of the 3D surface. It was found that the shape of the protrusions significantly influenced water collection capacity. Particularly, cone-shaped protrusions exhibited the highest water collecting capability among the different shapes tested.Originality/valueIn this study, 3D printing and electrospraying techniques were combined to create 3D surfaces characterized by high surface area, along with hydrophilic and hydrophobic regions to produce superior surfaces for atmospheric water harvesting.

Transforming waste polystyrene foam to carbon on zeolite for efficient solar water desalination

Solar-driven water evaporation was well-proven to be a sustainable technique for seawater desalination by using renewable energy. In this technology, carbon material is preferably chosen as a photothermal conversion material due to its excellent stability and corrosion resistance. However, the applicability of carbon-based materials was constrained by their poor mechanical strength and the high cost. In this paper, carbon coated sands and zeolites were prepared by using waste polystyrene foam (white pollution) as carbon source and this waste utilization method greatly reduces material costs. The solar-driven water evaporation device was fabricated by confining these carbon-coated composites in the PVA hydrogel. Owing to the superior light absorption (over 96 %) and good hydrophilicity for water transfer, the carbon-coated sand and zeolite exhibited maximum evaporation rate of 1.51 and 1.24 kg m−2h−1 under 1 sun illumination, respectively. In outdoor test, the maximum water collection rate was 0.92 kg m−2 h−1. It is possible to create an effective and environmentally beneficial solar interfacial water evaporation system with this approach.

ANSYS Fluent-CFD analysis of a continuous single-slope single-basin type solar still

The present study endeavours to substantially contribute towards alleviating the global water scarcity problem. The task entailed designing a computational model of a renewable energy-based evaporator. Using ANSYS Fluent, the CFD simulations of a three-dimensional conventional continuous single slope, single basin solar still were carried out in summer at 23.79°N, 86.43°E coordinates. With the optimized inclination condensation angle of 29° and water depth at 1 cm, the solar still recorded the highest hourly drinking water, about 1.5 kg m−2, at 11:00 h. The continuous production resulted in a water collection rate of 8.6 kg m−2 day −1, encompassing the production of all previous models. Additionally, compared with the literature correlation for solar still simulated mass, the Power model calculation was the closest, with a 12.4% variation. Furthermore, the study showcases that CFD is an economical, efficient, and easily diagnosable technique for designing solar stills.

An Atmospheric Water-Harvester with Ultrahigh Uptake-Release Efficiency at Low Humidity.

Atmospheric water harvesting is a practical strategy that is achieved by removing materials from air moisture to relieve global water scarcity. Here we design a water-harvester (i.e., MOF-303/thiolated polymer composite (MTC)) by using a metal-organic framework (MOF-303) and thiolated chitosan (TC) skeleton. Intermolecular hydrogen bonding between TC and MOF-303 facilitates porous structures with enlarged air-polymer interfaces for long cycling life and high capacity at low relative humidity. Benefiting from synergetic effects on porosity and anchorage for accelerating the uptake-release of moisture, MTC exhibits a rapid water uptake capacity of 0.135 g/g in 60 min under 12.5 RH% and ultrafast water desorption kinetics of 0.003 g/g/min at 8.5 RH%, which is superior to the as-reported MOF-303 based adsorbents. At low heat (∼40 °C), the water desorption and collection rate, respectively, are 0.0195 and 0.0168 g/g/min within 210 min, showing ultrahigh harvesting efficiency. These results highlight the enormous potential as promising materials for solving the world's water scarcity crisis. This study offers an insight into the design of AWH materials, which can be extended into applications in some realms, e.g., freshwater development for industry in arid areas, water engineering-related devices and systems, etc.

Recent advances in water collection based on solar evaporation

Solar evaporation attracted lots of attention due to its environment-friendly and high efficiency, which is a potential approach to collecting fresh water. Many efforts have been made to improve the evaporation rate in the open space. While the actual water collection rate is far less than the evaporation rate, especially in passive water collection, limiting its practical and scalable applications. In this review, we focus on freshwater collection based on solar evaporation. Firstly, heat and mass transfer behaviors on the evaporation side were summarized to improve evaporation performance, including heat transfer processes in thermal radiation, convection, and conduction; mass transfer processes in water supply, evaporation enthalpy, and salt rejection. Sequentially, subcooling, wettability, and geometry of the condensation side were discussed to improve water collection performance, which should be designed collaboratively with the evaporation side in a confined space. Finally, thermal recovery and electricity generation beyond water collection were also introduced, and some challenges still need to improve in the further for scalable and practical applications, including passive water collection rate, integrated system, and long-term issues.

Different wettability surfaces composited by polydopamine-based SiO2/TiO2 coatings for efficient water collection and anti-corrosion application

Designing hybrid surfaces with superhydrophilic and superhydrophobic properties represents a promising approach for fog collection. Inspired by the adhesive properties of mussel proteins, a polydopamine (PDA) film was firmly attached to a brass surface through a combination of chemical etching and spontaneous dopamine polymerization. By harnessing the exceptional characteristics of PDA as a "double-sided adhesive," a hybrid surface with mixed wettability was created using a facile and cost-effective method involving SiO2 and TiO2 nanoparticles (NPs). The TiO2 NPs served as the hydrophilic sites for water capture, while the SiO2 NPs acted as the hydrophobic region to induce water droplet rolling. The resulting hybrid surface exhibited a significant improvement in water collection rate, measuring approximately 1.182 g/cm2/h, which was 1.84 times higher than that of the bare brass surface. This demonstrated a remarkable enhancement in fog collection capacity. Moreover, the hybrid surface demonstrated commendable corrosion resistance and remarkable durability, indicating its great potential for widespread application in practical scenarios.

Solar-Driven Multistage Device Integrating Dropwise Condensation and Guided Water Transport for Efficient Freshwater and Salt Collection.

Interfacial solar vapor generation (ISVG) is an emerging technology to alleviate the global freshwater crisis. However, high-cost, low freshwater collection rate, and salt-blockage issues significantly hinder the practical application of solar-driven desalination devices based on ISVG. Herein, with a low-cost copper plate (CP), nonwoven fabric (NWF), and insulating ethylene-vinyl acetate foam (EVA foam), a multistage device is elaborately fabricated for highly efficient simultaneous freshwater and salt collection. In the designed solar-driven device, a superhydrophobic copper plate (SH-CP) serves as the condensation layer, facilitating rapid mass and heat transfer through dropwise condensation. Moreover, the hydrophilic NWF is designed with rational hydrophobic zones and specific high-salinity solution outlets (Design-NWF) to act as the water evaporation layer and facilitate directional salt collection. As a result, the multistage evaporator with eight stages exhibits a high water collection rate of 2.25 kg m-2 h-1 under 1 sun irradiation. In addition, the desalination device based on the eight-stage evaporator obtains a water collection rate of 13.44 kg m-2 and a salt collection rate of 1.77 kg m-2 per day under natural irradiation. More importantly, it can maintain a steady production for 15 days without obvious performance decay. This bifunctional multistage device provides a feasible and efficient approach for simultaneous desalination and solute collection.

Inclined solar interface evaporation system with downward steam generation for efficient desalination and salt crystallization positioning

Solar-driven Interfacial Vapor Generation (SIVG) has been recognized as a potentially effective method of converting seawater into potable freshwater resources. In this work, we employed a straightforward approach to cultivate CuS and polypyrrole on copper foam as an solar absorber, while sterilized face towels served as water an evaporation interface and water transport sites. An inclined steam blocking evaporator with a salt-out part that attracts salt aggregation was ingeniously designed to improve the salt-resistant performance. Even in 15 wt% brine, the evaporation equipment maintained a stable and high evaporation rate, with an average evaporation rate of about 1.588 kg m−2 h−1 under 1 solar illumination. More particularly, in order to improve the water collection rate, a beveled condensers placed at the bottom of the steam blocking evaporator was customized, so as to shorten the steam condensation path and achieve internal water collection. Therefore, the water collection rate of the evaporator is as high as 2.238 kg m−2 h−1 and water collection efficiency is 85.90 %. Additionally, the evaporation device can effectively purify heavy metal ions and organic matter. This study can provide a new idea for the design and performance improvement of solar interfacial vapor generation and water collection device.

Durable superhydrophobic coating based on halloysite nanotubes for versatile oil/water separation and reusable water collection

Fog water collection gains increasing attention for harvesting atmospheric water to solve the water resource crisis in arid or semi-arid areas. In this work, a durable superhydrophobic coating based on halloysite nanotubes (HNT) for water collection is fabricated by introducing 1H,1H,2H,2H-perfluorodecyl trimethoxysilane (PFTS) modified HNT into a hydrophobic polydimethylsiloxane (PDMS) coating to construct a rough and superhydrophobic surface. The dip-coating method is employed to apply the coatings onto various substrates. The surface wettability, water collection rate, mechanical stability, and durability, oil/water separation efficiency and flux, and oil absorption capacity are investigated in detail. When the content of fluorinated modified HNT (F-HNT) is 15 %, superhydrophobic F-HNT@PDMS coated fabrics with a high water contact angle (157.3°) as well as a low sliding angle (3.7°) are obtained, and the treated fabrics show excellent self-cleaning ability. After 100 mechanical wear cycles, the coated fabrics remain superhydrophobicity, and the oil/water separation efficiency is maintained above 99.5 %. Furthermore, different substrates dip-coated with F-HNT@PDMS exhibit high-efficiency water collection rates of 952.25–1058.5 mg∙cm−2∙h−1. Therefore, this work provides a feasible strategy for preparing a durable superhydrophobic coating with a high-efficiency water collection rate and is expected to be applied in fog water harvesting in scarce areas.

Improved Water Collection from Short-Term Fog on a Patterned Surface with Interconnected Microchannels.

Fog harvesting is considered a promising freshwater collection strategy for overcoming water scarcity, because of its environmental friendliness and strong sustainability. Typically, fogging occurs briefly at night and in the early morning in most arid and semiarid regions. However, studies on water collection from short-term fog are scarce. Herein, we developed a patterned surface with highly hydrophilic interconnected microchannels on a superhydrophobic surface to improve droplet convergence driven by the Young-Laplace pressure difference. With a rationally designed surface structure, the optimized water collection rate from mild fog could reach up to 67.31 g m-2 h-1 (6.731 mg cm-2 h-1) in 6 h; this value was over 130% higher than that observed on the pristine surface. The patterned surface with interconnected microchannels significantly shortened the startup time, which was counted from the fog contact to the first droplet falling from the fog-harvesting surface. The patterned surface was also facilely prepared via a controllable strategy combining laser ablation and chemical vapor deposition. The results obtained in outdoor environments indicate that the rationally designed surface has the potential for short-term fog harvesting. This work can be considered as a meaningful attempt to address the practical issues encountered in fog-harvesting research.