Fog Collection Research Articles

Waterdrop-assisted efficient fog collection on micro-fiber grids

Fog collectors can mitigate water scarcity by capturing droplets from fog streams. Previous research focuses on improving aerodynamic design and surface characteristics to enhance collection efficiency. However, limited attention has been given to micro-meter level fog-intercepting structures and the impact of waterdrop clogging. This study investigates the fog collection process on microfiber grids with varying fiber spacings and diameters. Waterdrops clog the grid openings with a pattern that small waterdrops satelliting large ones. Due to the small fiber diameter, the waterdrops are “visible” to incoming airflow and strongly affect fog droplet interception. The large waterdrops deflect incoming fog flow towards the small ones, and the small waterdrops efficiently capture the fog droplets. Consequently, the fog collectors based on microfiber grids demonstrated an exceptional water collection efficiency of up to 21.4%. The micro-fiber grids require minimal material usage and no special surface treatment, highlighting a great potential in fog water collection. Additionally, this work provides a novel design strategy of fog collector, i.e., reducing the size of the fog-intercepting structure to directly capture fog droplets by waterdrops.

Dual biomimetic surfaces with anisotropic wettability for multi-scale droplets manipulation

Droplets manipulation on functional biomimetic surfaces have been highly anticipated for their wide range of applications. However, preparing a metal platform for manipulating multi-scale droplets without external energy input remains a challenge. Herein, dual biomimetic surfaces (DBSs) were fabricated by twice laser and thiol modification. The unique interfacial behavior of the droplets can be realized under the synergistic effect of the special “millimeter-micrometer-nanometer” multi-hierarchical composite structure and chemical composition. The as-prepared DBSs can achieve multi-scale droplets manipulation, directional self-cleaning in various media, and efficient directional fog collection. Further, the mechanism of specific interface behavior is analyzed in depth. Nanoparticles endow DBSs with more capture points and condensation cores and micrometer mastoids realized the transmission and aggregation of microscopic droplets through the action of Laplace force. Based on resistance, energy barriers and three-phase contact line, influence of millimeter grooves on anisotropic wettability and directional transportation of the droplets is analyzed. Besides, the multi-hierarchical structure also endows DBSs with good droplets manipulation ability and stability. This work not only provides an advanced biomimetic platform, but also provides an important reference for metal-based lab-on-a-chip for multi-scale droplets manipulation.

Fog collection efficiency of superhydrophobic surfaces with different water adhesion prepared by laser grid texturing

Superhydrophobic surfaces are widely used in fog collection areas due to their water adhesion properties. Unfortunately, the relationship between the water adhesion and the fog collection efficiency of superhydrophobic surfaces has seldom been reported in the literature. Therefore, it is still a challenge to conduct scientific design of superhydrophobic surfaces for fog collection. In this work, superhydrophobic titanium alloy surfaces with different water adhesions were fabricated by laser grid texturing combined with silicone oil heat treatment. As the texturing interval increased from 50 µm to 500 µm, the adhesion force of the superhydrophobic surfaces correspondingly increased from 2.4 µN to 104.9 µN. The results show that the superhydrophobic surfaces with the texturing interval of 100 µm have the highest fog collection efficiency of 415.5 mg·cm−2·h−1. The reason is that an appropriate adhesion force (7.6 µN) of the superhydrophobic surface can effectively suppress the coalescence-induced droplets jumping. Furthermore, it can also facilitate the removal of condensed droplets by decreasing the critical size of droplets sliding.

THEORETICAL AND METHODOLOGICAL ASPECTS OF CLOUD WATER INTERCEPTION

Cloud water interception (CWI) occurs when water contained in fog and wind-driven rain collides with vegetation, merges into larger droplets, and precipitates to the ground. CWI has an important function as an additional source of water and its relationships with tropical cloud forests have often been emphasized. Despite its importance, there is no standardization of measurement methods, nor of the terms that designate the process in Portuguese. Therefore, a systematic analysis of research on CWI is necessary. To this end, the present study carried out a review of the theoretical and methodological aspects of CWI through description and analysis of terminology; history and chronology of studies on the topic; survey of the environmental conditions necessary for the CWI process to occur; analysis of methodological aspects relating to the measurement of CWI; and synthesis and discussion of magnitudes described in scientific literature. As a result, of the 31 publications reviewed, 14 different words were found, the most common being “Cloud Water Interception” (19.4%) and “Fog Drip” (16.1%). In general, CWI is more common in places such as continental edges and islands that are constantly subject to sea breezes. In most cases, the below-canopy measurement approach can be considered more accurate than those obtained by fog collectors. CWI is on average responsible for 42% of effective precipitation (n:41). The values listed show a large variation, between 0.5% and 462%, probably due to the different environmental characteristics of the sampled locations as well as variations in sample sizes.

High-effective fog collection on metal surfaces by temperature gradients

The acquisition of global freshwater resources has always been the direction of people's efforts. At present, metal materials based on special wettability and special structure have become an effective way to collect fog. However, it is still a bottleneck to further improve the water collection efficiency by carefully designing the wettability and special structure of materials. Therefore, we propose to use temperature gradient to enhance fog collection in metal surface. The mechanism of temperature gradient enhancement improves fog collection efficiency by 54 % and surface refresh rate by about 541 %. Further scattering measurements show that the capture time of fog particles at low cooling surface is shortened by about 40 %. Based on the theory of heat transfer and thermophoresis, the temperature gradient around the metal and the behavior of fog particles are analyzed, and it is concluded that the enhancement of fog collection performance on the metal surface can be caused by the temperature gradient caused by thermophoresis force. This work provides ideas for designing better fog collection equipment and materials.

Bionic Surfaces for Fog Collection: A Comprehensive Review of Natural Organisms and Bioinspired Strategies.

Water scarcity has become a critical global threat, particularly in arid and underdeveloped regions. However, certain insects and plants have evolved the capability to obtain water from fog under these arid conditions. Bionic fog collection, characterized by passive harvesting, minimal energy requirements, and low maintenance costs, has proven to be an efficient method for water harvesting, offering a sustainable water source. This review introduces two superwettable surfaces, namely, superhydrophilic and superhydrophobic surfaces, detailing their preparation methods and applications in fog collection. The fog collection mechanisms of three typical natural organisms, Namib Desert beetles, spider silk, and cactus, along with their bionic surfaces for fog collection devices, are discussed. Additionally, other biological surfaces exhibiting fog transport properties are presented. The main challenges regarding the fabrication and application of bionic fog collection are summarized. Furthermore, we firmly believe that environmentally friendly, low-cost, and stable fog collection materials or devices hold promising prospects for future applications.

Impact of varied fog collector designs on fog and rainwater harvesting under fluctuating wind speed and direction

Impact of varied fog collector designs on fog and rainwater harvesting under fluctuating wind speed and direction

Liquid-Assisted Bionic Conical Needle for In-Air and In-Oil-Water Droplet Ultrafast Unidirectional Transportation and Efficient Fog Harvesting.

Learning from nature, many bionic materials and surfaces have been developed for the directional transportation of water and fog collection. However, current research mainly focuses on the self-transportation behavior of droplets in air-phase environments, rarely concerning underoil environments. Herein, in this work, a liquid-assisted bionic copper needle was fabricated for the rapid self-transportation of water droplets in air and oil environments. The water droplet can be spontaneously transported on the as-prepared bionic copper needle from the tip to the base. More importantly, the water-prewetted bionic copper needle can achieve the ultrafast unidirectional transportation of a water droplet in an oil environment, showing a maximum transport velocity of 76.2 mm/s and a transport distance over 33 mm, which were ten times higher than those reported in the previous research. Additionally, the droplet transport mechanism was revealed. The effects of the apex angle and tilt angle of the as-prepared bionic needle and droplet volume on the self-transportation behavior of water droplets were systematically investigated. The results indicated that the transport velocity of the water droplet decreased with the increase of the apex angle of the conical needle, while it increased with the increase of the droplet volume and needle tilt angle. Furthermore, the as-prepared bionic copper needle exhibited excellent fog collection performance with a single copper needle fog collecting efficiency of up to 2220 mg/h, which was 9.7 times that of the original copper needle. In summary, this work provides a simple and novel method to fabricate bionic copper needles for the directional self-transportation of water droplets in air-phase and oil-phase environments as well as efficient fog collection. It shows great application potential in the fields of microfluidics, desalination, and freshwater collection.

A Simulation and Experiment on the Optimization Design of an Air Outlet Structure for an Air-Assisted Sprayer

In response to the issues of low-velocity zones and non-uniform jet velocity distribution in the airflow field of traditional air-assisted orchard sprayers, an arc-shaped air outlet suitable for axial-flow air-assisted systems is designed. This article employs the method of CFD numerical simulation and experimental verification to compare and analyze the internal flow field of the air-assisted system and validates the reliability of the numerical simulation results through calculation error and chi-square test. The wind speed of the cross-section is measured at different distances from the outlet, and the distribution characteristics of the outflow field wind speed before and after the structural optimization of the air-assisted system are compared. The horizontal distribution of fog droplets is collected using a fog collection chamber. The experimental results show that the design of the arc-shaped outlet increases the average wind speed of the annular outlet from 14.95 m/s to 18.20 m/s and reduces the proportion of low-speed area from 20.83% to 0.71%. When the rounded corner radius of the air outlet is 50 mm, optimal parameters are attained. The maximum error between the simulated and experimental values is 9.52%. At a significance level of 0.05, the χ2 value is 0.252, indicating that the simulated values follow the distribution of the actual measurement values. On the cross-sections located at distances of 0.5, 0.75, 1, 1.25, and 1.5 m from the air outlet, the wind speed distribution with no arc-shaped air outlets exhibits a “low left and high right” type, tending to shift towards the right as a whole. Fog droplets also display a drift tendency towards the right side. The wind speed distribution with arc-shaped air outlets shows a symmetric “high in the middle and low on the sides” type. Fog droplets concentrate in the central position. The optimized air-assisted system can reduce the air field’s low-flow area, increase the airflow distribution uniformity, improve the average wind speed at the outlet, and decrease fog droplet drift. This provides a reference for the structural design of air-assisted systems in current orchard sprayers of the same type.

Tetradecanoate in situ reaction prepares a stable and efficient 3D framework for fog collection

Slippery liquid-infused porous surface (SLIPS) strategy has recently attracted significant attention in the field of foggy water collection. However, the surface on which the lubricant is injected is often unstable, losing control of fog capture and droplet movement. The 3D frame structure combined with the nano-needle-like structure produces a strong oil locking ability to provide more stable Slippery liquid-infused porous surface. In this work, copper myristate flower-like clusters were directly grown on the walls of porous copper foam wires by in situ reactions, resulting in a superhydrophobic skeleton directly, and a 3D skeleton of the injected lubricant was obtained after lubricant injection. The framework also features excellent droplet capture, droplet coalescent growth, and droplet removal, as well as significant anti-ice and anti-fouling properties. This work simplifies the preparation process and it is easy to meet the reaction conditions. The prepared lubricant injected skeleton has excellent atomized collection properties (98.7% higher than the original sample) and has the potential for mass fabrication. It provides a new idea for the efficient and rapid preparation of the liquid infusion fog collection structure.

Review of directional liquid transport on surfaces with different structures

Directional liquid transport has many cutting-edge applications, such as fog collection, agricultural drip irrigation, biochemical microreactors, water harvesting, non-powered micro-drug delivery, thin-film lubrication etc. There are many surfaces or linear structures in the natural systems can occur directional transport of water. In this paper, two bionic structures inspired by natural structures and two artificially fabricated surface structures are presented and their flow laws and mechanical mechanisms are described. Thereby, it is analysed that surface-driven external forces, such as the gradient of surface energy and the gradient of Laplace pressure, and surface pinning in other directions are the key points to drive the directional flow of liquids.

Effect of Droplet-Laden Fibers on Aerodynamics of Fog Collection on Vertical Fiber Arrays.

Growing population, along with rapid urbanization, has led to severe water scarcity, necessitating development of novel techniques to mitigate this looming problem. Fog contains water in the form of liquid droplets suspended in air, which can be collected on a porous structure placed in the path of the fog flow. We first develop an artificial fog-generating system using the thermodynamic principle of mixing of air streams followed by condensation, which closely mimics the liquid water content and droplet size distribution of natural fog. We then investigate how collected fog droplets growing on fiber surfaces alter the aerodynamics of fog flow across vertical fiber arrays, called harps, thus affecting their fog collection efficiency. As deposited droplets grow on the fiber surface, they increase the area occluded by droplet-laden fibers, thus increasing the effective shade coefficient (SCact), which increases with time from its initial geometric value (SCgeo), eventually reaching a quasi-steady state, as droplet shedding due to gravity and droplet growth due to fog collection balance each other. We find that this difference in the SCgeo and SCact is governed by local fiber geometry and its physico-chemical morphology; the process dynamics is captured by a nondimensional number, SC*, which increases with the length scale corresponding to the critical volume of droplet shedding relative to the fiber diameter, V*. Thus, there is a significantly greater increase in the effective shade coefficient for thin fibers having larger values of V* as compared to fibers with larger diameters which have lower V* values. On hydrophobic fibers, the quasi-steady state is achieved faster, and the time-averaged SCact is lower as compared to hydrophilic fibers due to the lower critical volume of droplet shedding. The shape of droplets growing on harp fibers affects the aerodynamics of fog flow, its inertial capture mechanism, and efficiency, which can guide design considerations for fog harps toward achieving optimal fog collection performance.

Laser-Textured Hybrid Brass Pattern Array Surface for High-Efficiency Fog Collection.

Fog collection holds promise for addressing water shortage. However, the conventional fabrication of fog collection devices, normally chemical methods, suffers many challenges, such as complicated preparation and environmental issues. Herein, we proposed a green fabrication strategy to construct superhydrophobic/hydrophilic surfaces on the brass substrate via the combination of laser fabrication and heat treatment. The wettability of brass is directly dictated by the laser process parameters. The different superhydrophobic/hydrophilic hybrid pattern surface with a rectangular/triangular array was designed for an optimal fog collection performance. The maximum water collection efficiency of the prepared surface is measured up to 427.36 mg h-1 cm-2, which is 97% higher than that of the control sample. Furthermore, the surface can be folded into different forms to realize a flexible collector. We envision that our work provides a green fabrication strategy to construct a superwetting surface for highly efficient fog collection.

Dual liquid-assisted single-layered Janus mesh membrane with controllable and efficient directional water transport for multiple applications

Janus porous membranes with anisotropic interfaces exhibiting directional liquid transport properties have emerged as important tools for addressing real-world issues, such as oil-spill cleanup and fog collection. Here, a single-layered Janus mesh membrane with asymmetric wettability and a well-tuned hydrophilization depth is prepared using an ethanol-assisted floating method. Consequently, the well-regulated hydrophilization depth combined with a water-assisted strategy achieves controllable and efficient directional water transport properties, which also gives rise to a high anisotropic critical breakthrough pressure. In addition, the water-assisted controllability can form an on–off gate capable of allowing or blocking water to pass through upon request. Moreover, we theoretically and experimentally determine the changeable contact area as important in directional water transport properties. Controllable directional water transport behavior with a high pressure difference has been demonstrated in on-demand oil–water separation and intravenous infusion, whereas the efficient directional water transport properties have potential applications in fog collection. Overall, this work provides a new idea for the preparation of a single-layered multifunctional Janus mesh membrane with a high anisotropic critical breakthrough pressure and opens an avenue for controllable and efficient directional water transport properties for diverse applications.

Deconstructing plasma fog collection technology: an experimental study on factors impacting collection efficiency

Water scarcity is a global challenge that hinders human development. In recent years, electrostatic fog collection technology has emerged as a promising technology to alleviate this issue. Although electrostatic fog collectors based on a variety of electrode structures have been developed previously, there has been less research into other factors affecting the efficiency of electrostatic fog collection (e.g. electrical factors, environmental factors, etc), which has delayed the commercial application of the technology. In this paper, we experimentally investigate the effects of power supply polarity, voltage, airflow direction, airflow velocity, fog concentration and temperature on collection efficiency using a typical wire-mesh electrode fog collector as an example. The results show that both electrical and environmental factors influence the collection efficiency by changing the charge and the electric field force of the droplets. Negative polarity corona and high voltage are more favorable for fog collection. High velocity airflow and high fog concentration increase the amount of water collected due to the ability to bring more droplets into the electric field. However, the collection efficiency is reduced by the weakening of the corona discharge. High temperature accelerates the evaporation of fog droplets, which is not favorable for fog collection. In conclusion, this work will not only contribute to revealing the underlying mechanisms of the electrostatic fog collection but also will guide the development of highly efficient fog collectors.

Bio‐Inspired Fog Harvesting Meshes: A Review

AbstractFreshwater scarcity has become a critical global challenge affecting some of the most vulnerable populations. In response, significant effort has focused on ways to increase access to this precious resource. Within the context of geographical, cultural, political, and technological factors governing freshwater availability, atmospheric water harvesting (AWH) has demonstrated tremendous promise to help address these shortages. Specifically, mesh‐based fog harvesters have received considerable attention for their passive qualities compared with their energy‐dependent technological siblings (sorbents, condensation, etc.), yet their specific water yield (SY) has developed only modestly in recent decades. While the plant and animal kingdom provide diverse examples of passive fog collection, and science has developed a remarkable understanding of these processes, much of this knowledge has yet to be translated practically at scale. This is partially due to challenges in mass‐producing complex (often micro‐scale) structures observed in nature. Fortunately, manufacturing technology is catching up with scientific understanding, especially at the scale of mesh design. To this end, the review begins by surveying bioinspired research in fog harvesting. Afterward, this study identifies milestones in developing bioinspired fog harvesting meshes, concluding in a discussion of future mesh research opportunities connecting bioinspiration and emerging advanced manufacturing techniques.

Evaluating Mesh Geometry and Shade Coefficient for Fog Harvesting Collectors

The most valuable resource for sustaining life on earth is water. In dry and semi-arid areas, the problem of water scarcity can be resolved with the aid of fog collection techniques employing fog collectors. Fog collection is greatly influenced by a variety of factors. Some are design parameters, while others depend on ambient circumstances. Geometry and the mesh’s shade coefficient are important design factors that can be modified and have an impact on the rate at which fog collects in fog collectors. The shape of the mesh holes and the process used to create the mesh serve to identify geometry and measure the shade coefficient. In this paper, a straightforward mathematical technique is proposed to make it easier to calculate the shade coefficient of various mesh shapes used in fog harvesting and to provide an approximation of the mesh volume and cost. Five alternative geometries were used: the rectangular mesh, square mesh, Raschel mesh, triangular mesh, and hexagonal mesh. The current simple method will facilitate the design of the fog mesh collector and can assist in achieving the ideal shade coefficient and most effective mesh geometry for fog harvesting. Rectangular meshes were solely used as an example to evaluate the results. Stainless steel rectangular meshes with various shade coefficients were tested for fog collection, and the amount of water collected by each mesh varied. It was concluded that the optimum shade coefficient ranged 50–60% for fog collection.

Cross-hatch textured cone enables Dual-Mode water transport and collection

Spontaneous droplet transport has broad application prospects in water collection, whereas droplet self-transport is still limited by slow transport velocity, short distance, and poor integrity. Here, a novel cross-hatch textured cone (CHTC) with gradient microchannels and circular grooves is proposed to realize ultrafast long-distance self-transport of multi-scale droplets, whose self-transport velocity is 1–4 orders of magnitude faster than natural or biomimetic structures with single curvature gradient. The CHTC triggers two modes of fluid transport: Droplet transport by Laplace pressure difference and capillary suction pressure-induced fluid transfer in microchannels on cone surfaces. The gradient microchannels connected by circular grooves ensure that the residual water layer and the water droplet detained on the CHTC can still be spontaneously transported to the base to eventually realize the entire droplet transport. A theoretical formula on the suction pressure is established to elucidate the driving force responsible for the self-transport of both detained water droplet and the residual water layer. The fog collection efficiency of the CHTC is about twice as high as the cone without microchannels. These findings will open the door to achieving ultrafast long-distance and lossless self-transport of droplets and will provide tremendous inspiration for the design of the water collection apparatus.

Fog Water Collection for Local Greenhouse Vegetable Production in the Atacama Desert

Agricultural production in the Atacama Desert is restricted by extreme aridity and poor soil quality. Between 18° S and 30° S, low stratocumulus clouds regularly cover the southeastern Pacific Ocean reaching the Coastal Cordillera. Thus, marine fog is constantly present in the coastal areas of the desert. Fog can be harvested using fog collectors. However, limited information is available with regards to the variability of fog presence throughout the year and along the coast of the desert. Combining fog water harvest with hydroponic production under greenhouse facilities presents an alternative for sustainable and local fresh food production. In this article, we analyze the potential of fog water collection in two sites (Alto Patache and Falda Verde) distant by about 1000 km within the Atacama Desert. Additionally, in both locations, the environmental conditions within greenhouse structures, the potential energy requirement for environmental conditioning (including the energy production from photovoltaic panels) and the water requirements of vegetable crops under greenhouse conditions were modeled. The annual average of fog water collection registered was 2.9 and 3.3 L per day per m2 in Alto Patache and Falda Verde, respectively. During the most demanding season for crop evapotranspiration, 2.13 m2 of fog collectors can supply the water required for 1 m2 of greenhouse crops. The energy required for water and air pumps in the hydroponic systems can be supplied with photovoltaic systems including eight PV modules and a battery storage capacity of 9.4 kWh. In conclusion, the present study sheds light on the possibilities of massive water collection from fog to be used in local and sustainable food production in the Atacama Desert.

Sorbent-coupled radiative cooling and solar heating to improve atmospheric water harvesting

Atmospheric water harvesting (AWH) technology is a promising technology for addressing global water shortages and contributing to social development. Current AWH technologies, including fog collection, dew collection, and sorption-based AWH mostly focus on a single water harvesting mechanism, and this can limit their working conditions and overall performance. In this work, a composite hydrogel with a low phase change enthalpy of water (1695 kJ kg−1) was coupled with radiative cooling and solar heating to improve passive AWH performance and working conditions. High thermal emittance ε¯LWIR = 0.98 and solar absorptance α¯solar = 0.93 were achieved for radiative cooling in the nighttime and solar heating in the daytime. During the night, radiative cooling could improve the water capture rate from 0.242 kg m-2h−1 (i.e., only sorbent) to 0.310 kg m-2h−1 (i.e., sorbent-coupled radiative cooling) in the outdoor experiment. In the daytime, solar interfacial evaporation improved the water release rate to 1.154 kg m-2h−1. Effects of meteorological parameters, such as relative humidity, ambient temperature, and solar intensity were also discussed theoretically and experimentally. It is indicated that the designed passive AWH device can work over a wide range of meteorological parameters. The outdoor all-day experiment indicated that the maximum water harvesting can be 2.04 kg m−2 in a cycle work. This demonstrates that sorbent-coupled radiative cooling and solar heating provide a potential approach for future solar-driven AWH systems.