A Pragmatic Device Based on a Double‐Sided Functional Structure for Efficient Water Harvesting

Abstract

Water collection from fog has received much attention to meet the challenges of scarcity of clean drinking water in desert and arid regions. Currently, solar‐thermal technology is being used as an efficient, sustainable, and low‐cost method for water desalination to produce clean water. To collect the clean water, in recent years, most researchers have designed the structure of water collection surfaces. However, the heat released during the liquefaction process of droplets has an adverse effect on the condensation of droplets, and thus affecting the water collection efficiency. Here, in order to improve water collection efficiency, a radiative cooling layer is introduced on the back of the collection surface to dissipate the heat released during droplet liquefaction. The radiative cooling layer, consisting of poly(vinylidene fluoride‐co‐hexafluoropropene) embedded with SiO2 and CaMoO4 nanoparticles, can theoretically cool 18.1 °C below the ambient temperature in the daytime. With the addition of cooling coating on the back of the water collection surface, the water harvesting efficiency can be increased by 43–52%. The developed water harvesting device may provide a new pathway to the efficient collection of fresh water.

Accurately Quantifying Clear-Sky Radiative Cooling Potentials: A Temperature Correction to the Transmittance-Based Approximation

“…Models that yield the level of detail needed for such calculations are comparatively rare [1,5,13]. One model, which has achieved almost universal use in recent radiative cooling literature, is the transmittance-based cosine approximation [1,[14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29], which was first used as part of a more comprehensive model by Granqvist in 1981 [1]. This model assumes that the irradiance of the atmosphere originates from greenhouse gases, including water vapor, carbon dioxide and ozone, and calculates the spectral, angular sky irradiance based on an effective spectral angular emittance as follows:…”

“…Since the irradiance from ozone and absorptance/emittance of SiO films have little overlap and the SiO film has a narrowband emittance, such a choice is justifiable in that context. However, the approximation has since been used to calculate the radiative cooling potentials of ideal emitters and cooling powers of radiative coolers with different spectral emittances, leading to both a systematic underestimation of cooling potential and a related overestimation of performance [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29]. The MODTRAN hemispherical emittance, which is more accurate, should ideally be used instead.…”

Heat-shedding with photonic structures: radiative cooling and its potential

“…(h) Schematic of water harvesting with a radiative cooling coating on the back of the water collection surface. Reproduced with permission 172. Copyright r 2020.…”

“…(i) SEM images of the electrochemically etched Al sheet for 11 min. Reproduced with permission 172. Copyright r 2020.…”

Highly Efficient Multiscale Fog Collector Inspired by Sarracenia Trichome Hierarchical Structure

“…[15][16][17] Their conical structures can directionally transport condensed water from the tip to the bottom, releasing the tip surface area for further fog condensation. [18][19][20][21][22] Conical structures are usually combined with fog harps to construct fog collectors for highly efficient fog harvesting. [23][24][25][26][27][28] However, the velocity of directional water transport on these conical structures remains of ≈0.5 mm s −1 , which limits further enhancement of fog harvesting by fog collectors.Fortunately, a more efficient fog harvesting and transport mode was discovered on Sarracenia trichomes that has a unique hierarchical microchannel structure around the needle-shaped trichomes (Figure 1a).…”