Enhancing Dropwise Condensation through Bioinspired Wettability Patterning (original) (raw)
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Nature's moisture harvesters: a comparative review
Bioinspiration & Biomimetics, 2014
Nature has adapted different methods for surviving dry, arid, xeric conditions. It is the focus of this comparative review to pull together the relevant information gleaned from the literature that could be utilized to design moisture harvesting devices informed by biomimetics. Most water harvesting devices in current use are not informed by nature and those that do are usually based on a biomimetic principle that has been based on one species only. This review draws on the published literature to establish a list of species (animals (vertebrates/invertebrates) and plants) whose habitat is in mainly dry or arid regions and that are known to harvest airborne moisture. Key findings have been outlined and review comments and discussion set out. Following this, surface feature convergences have been identified, namely hexagonal microstructures, groove-like and cone-like geometries. This has been coupled with direction of water flow that is driven by surface energy. As far as the authors are aware, this convergent evolution has not been brought together in this manner before. In the future this information could be translated into an engineered device for collecting water from airborne sources.
Research Square (Research Square), 2021
The paper proposes an innovative improvement to the water collectors from atmospheric humidity condensation by introducing non-hydrophobic substances to speed up the water condensation and the dropping off process using simple technology, inexpensive and with high quality materials with the nality to favor sustainable irrigation in regions characterized by water resources scarcity favoring greening generally. The innovative collector' design and experimentation conduced con rm the possibility to collect water from air humidity in different regions with reduced rain days as semi desertic zones enhancing the gain of deserti cation process, harvesting water in urban landscape, in vertical greening and roof gardens. The rst principal innovative aspect of the novel design collector is the fast capacity of condensation caused from the method of design of the used materials and fast capacity of releasing water collected to contrast the undesired evaporations. The second innovative aspect is the reduced volume to permit a diffused and unexpensive implants which can be distribute suitably on the targeted landscape. Reduced costs and simplicity of fabrication announce real possibility of use in underdeveloped and poor countries to increase vegetation diffusion rstly and contributing on sustainable agriculture and architecture.
Bioinspired Plate-Based Fog Collectors
In a recent work, we explored the feeding mechanism of a shorebird to transport liquid drops by repeatedly opening and closing its beak. In this work, we apply the corresponding results to develop a new artificial fog collector. The collector includes two nonparallel plates. It has three advantages in comparison with existing artificial collectors: (i) easy fabrication, (ii) simple design to scale up, and (iii) active transport of condensed water drops. Two collectors have been built. A small one with dimensions of 4.2 × 2.1 × 0.05 cm 3 (length × width × thickness) was first built and tested to examine (i) the time evolution of condensed drop sizes and (ii) the collection processes and efficiencies on the glass, SiO 2 , and SU-8 plates. Under similar experimental conditions, the amount of water collected per unit area on the small collector is about 9.0, 4.7, and 3.7 times, respectively, as much as the ones reported for beetles, grasses, and metal wires, and the total amount of water collected is around 33, 18, and 15 times. On the basis of the understanding gained from the tests on the small collector, a large collector with dimensions of 26 × 10 × 0.2 cm 3 was further built and tested, which was capable of collecting 15.8 mL of water during a period of 36 min. The amount of water collected, when it is scaled from 36 to 120 min, is about 878, 479, or 405 times more than what was collected by individual beetles, grasses, or metal wires.
Effective directional self-gathering of drops on spine of cactus with splayed capillary arrays
Scientific reports, 2015
We report that the fast droplet transport without additional energy expenditure can be achieved on the spine of cactus (Gymnocalycium baldianum) with the assistance of its special surface structure: the cactus spine exhibits a cone-like structure covered with tilted scales. A single scale and the spine surface under it cooperatively construct a splayed capillary tube. The arrays of capillary tube formed by the overlapping scales build up the out layer of the spine. The serial drops would be driven by the asymmetric structure resulted from tilt-up scales-by-scales on the cone-shaped spine, and move directionally toward the bottom from top of spine, by means of the Laplace pressure in differences. In addition, after the past of the first droplet, thin liquid film of drop is trapped in the splayed capillary micro-tube on the surface of spine, which greatly reduces the friction of subsequential droplet transport in efficiency. This finding provides a new biological model which could be ...
Analysis of different condensing surfaces for dew harvesting
Water Supply, 2021
Due to water shortages in several places in the world, alternative water sources such as atmospheric water and greywater have been studied. Dew water harvesting by passive radiative cooling is an unconventional water source that is easy to use, install, and shows great potential in several places in the world. This paper aims to experimentally evaluate the dew yield through passive radiative cooling in Vicosa city, Minas Gerais, Brazil by using standard white plastic for dew harvesting, developed by the International Organization for Dew Utilization (OPUR), polypropylene plastic, black plastic, packaging tape, and anodized aluminum as condensing surfaces during two different periods. The polypropylene plastic and packing tape materials used in this present research have not been researched before in the literature. However, they have demonstrated potential for harvesting dew. As a result, the average water collected was, respectively, 0.151, 0.135, 0.140, 0.127, and 0.046 mm/night u...
Patterned Nanobrush Nature Mimics with Unprecedented Water-Harvesting Efficiency
Advanced Materials Interfaces, 2018
This is due to the fact that at any given moment, the earth's atmosphere contains an astounding 37.5 million billion gallons of water as vapor, [2] and an efficient device to capture a fraction of this water vapor, in a cost-effective way would help solve the water crisis. Over the period of human existence, it has become apparent that biomimicking is the most efficient way to tackle such problems. When we look into nature, there are organisms, which in the course of evolution have acquired physical traits that enabled them to capture atmospheric water, even in the most arid corners of our planet. One such example is the Stenocara beetle of Namib Desert which capture water on its hardened forewings. [3] Electron microscopic images of these have revealed unique array of hydrophilic regions distributed on a superhydrophobic background, [4] creating a surface energy gradient, which facilitates efficient condensation and transportation of atmospheric water. Another such example is spider silk, which shows unique periodic spindle-knot structure when wetted and efficiently collects water from atmosphere through the combination of surface energy gradient and Laplace pressure difference. Other inspirations from nature are some cactaceae species which live in arid environments and are extremely drought-tolerant. [5] These species are shown to have structures with spines and trichomes which enable them to condense humidity efficiently from the atmosphere. Grasslands are also examples of natural atmospheric water harvesters. Hence, micro/nanostructuring of the water-collecting surface plays a critical role in determining the efficiency of water capture. With the advancement of nanotechnology, significant efforts have been directed toward fabricating surfaces with similar morphological features and chemical patterning to enable efficient water capture. [6,7] However, these natural and nature-mimicked surfaces collect atmospheric water in the form of dew/fog and require the temperature to drop below the dew point to cause condensation. For building a practical and round-the-clock operating atmospheric water generator, it is important to cool the condensing surfaces and the surrounding air efficiently, with minimum energy input. Heat transfer efficiency of the condensing surface material is as important as the water transfer efficiency for creating a viable radiative condenser. Although many biomimetic, patterned surfaces have been made for fog collection, inspired by active condensing Water scarcity is one of the most alarming problems of the planet. An ambient ion based method is developed to make hydrophilic-hydrophobic patterned silver nanowires (NWs) as humidity harvesters of unprecedented efficiency. Such water harvesters are developed by two-step surface modification of the as-synthesized NWs (known from a report earlier) using electrospray. These patterned NWs of ≈20 µm length and ≈200 nm width grown over a relatively large area (2 × 2 cm 2) exhibit atmospheric water capture (AWC) efficiency of 56.6 L m −2 d −1 , the highest reported so far. The whole fabrication process of the surface is performed under ambient conditions with a home-built nanoelectrospray ion source, without the help of any sophisticated instrumentation. The synthesized material combines and mimics two exciting examples of AWC in nature, which are cactae and Namib Desert beetles, which utilize AWC for their living. It is believed that the combination of the special features of the above two natural species helps to achieve the highest water capture efficiency reported till date. A working prototype using this surface for AWC is also fabricated.
Condensation of Moist Air on Mesh-like Surfaces
Asian Journal of Water, Environment and Pollution, 2020
Water scarcity is one of the crucial problems especially in hot, humid, arid and drought prone regions of the world. In these vulnerable regions, Earth's atmosphere water is the main source for getting potable water. In this work, a water harvesting device from moist air is designed and fabricated. The condensing substrate is mesh-like on which condensation of moist air is achieved by flowing cold water through the capillary tubes from solar based cooling unit. However, an outer surface of capillary tubes of mesh-like surface is coated with hydrophobic coating. From this device, water from atmospheric air is collected approximately 800 ml/m 2 in four hours at atmospheric temperature, relative humidity and degree of sub-cooling 32 °C, 80% and 5 °C respectively. This type of substrate is suitable to solve the water crisis for improving mass transfer rates and higher water yield during moist air condensation in the coastal, hot and humid area worldwide.
Biomimetics
The self-driving structure to orientate the water movement has attracted considerable attention. Inspired by the wedgelike structures of biological materials in nature, such as spider silks and cactus spines, anisotropic spreading can be realized by combining Laplace pressure gradient and hydrophilic surface. In this study, a series of groove patterns were fabricated by a combination of 3D printing and surface modification. PLA pattern was modified by the atmospheric pressure plasma, followed by grafting with hydrolyzed APTES. This work reports the anisotropic transport of water droplets on a series of designed dart-shaped groove patterns with specific angles in the main arrow and tail regions. This structure can induce capillary force to regulate droplets from the main cone to two wedgelike, whereas the droplets are hindered toward the opposite side is oat the vicinity of the groove’s tail. By means of the experiment, the mechanism of water transport in this pattern was revealed. T...
Biomimetics
Several flora and fauna species found in arid areas have adapted themselves to collect water by developing unique structures and to intake the collected moisture. Apart from the capture of the moisture and fog on the surface, water transport and collection both play an important part in fog-harvesting systems as it prevents the loss of captured water through evaporation and makes the surface available for the capture of water again. Here, we report the remarkable fog collection and water-channeling properties of Dryopteris marginata. The surface of D. marginata has developed an integrated system of multiscale channels so that the water spreads quickly and is transported via these channels very efficiently. These integrated multiscale channels have also been replicated using a facile soft lithography technique to prepare biomimetic surfaces and it has been proved that it is the surface architecture that plays a role in the water transport rather than the material’s properties (waxes ...