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A comparative study of two large radiative dew water condensers
Abstract
In order to improve the yield of dew condensation from atmospheric vapor, two large (30m2 in area) insulated plane radiative condensers, inclined at 30°, were installed in Ajaccio (Corsica island, France; latitude 41°55′N, longitude 8°48′E). Prototype P1 was elevated such that the underside was open and exposed. Prototype P2, however, was enclosed on all sides and closer to the ground. Both used a special radiative foil that enhances dew formation. The period of observation for P1 was July 22, 2000–November 11, 2001, and for P2 was December 10, 2001–December 10, 2003. All data were compared with respect to the same horizontal calibration plate of polymethylmethacrylate (Plexiglas) placed at 1m above the ground on a sensitive recording balance. Water yield of both prototypes were compared and correlated against meteorological data (cloud cover, relative humidity, wind speed, condenser temperature and air temperature). Both prototypes exhibit improved performances when compared with the calibration plate: more dew days (+16% and +15% for P1 and P2, respectively); decrease of the humidity threshold (−3% and −4.4% for P1 and P2); increase of dew yields for wind speeds up to 3ms−1. A model of the mass and thermal exchanges with the ambient air was used. Two adjustable parameters (heat and mass transfer coefficients) are used in the model. The values of these parameters were found larger than the values obtained in continental sites where dew forms with weak wind, thus emphasizing the peculiarities of dew formation in windy islands. When data are reduced with the calibration PMMA data, prototype P1 provided average water yields slightly larger than the enclosed prototype P2, a result that can be attributed to the influence of surface thermal radiation.
... Néanmoins, dans le cas d'un transfert radiatif prépondérant, permettant une production de froid suffisante pour abaisser la température de surface du macro-échangeur en dessous de la température de rosée, un troisième potentiel d'application consisterait à produire de l'eau par condensation de l'humidité de l'air [60,61]. En effet, de nombreux travaux de recherches [58,[62][63][64] ont montré expérimentalement qu'il était possible d'obtenir des quantités d'eau jusqu'à 0,7 L/m²/nuit [63]. On précise à nouveau que dans le cas de cette application, le transfert convectif aura tendance à limiter cette production d'eau en réchauffant la surface. ...
... Néanmoins, dans le cas d'un transfert radiatif prépondérant, permettant une production de froid suffisante pour abaisser la température de surface du macro-échangeur en dessous de la température de rosée, un troisième potentiel d'application consisterait à produire de l'eau par condensation de l'humidité de l'air [60,61]. En effet, de nombreux travaux de recherches [58,[62][63][64] ont montré expérimentalement qu'il était possible d'obtenir des quantités d'eau jusqu'à 0,7 L/m²/nuit [63]. On précise à nouveau que dans le cas de cette application, le transfert convectif aura tendance à limiter cette production d'eau en réchauffant la surface. ...
... Polymères Polyéthylène (PE) 0,9 [63,69,117,118] Polyéthylène pigmentée avec du ZnS, ZnSe, TiO2, ZrO2 et ZnO [119,120] Polyéthylène dopé avec des microsphères de TiO2 et de BaSO4 (foil) 0,89 [58,62] Films mince semi-conducteur (PbS et PbSe) sur feuilles de polyéthylène 0,1-0,3 [119] Polyméthylméthacrylate PMMA (Plexiglas) 0,94 [58,63,118,121] Résine de polyphenylenoxide (PPO) [122] Polycarbonate (PC) [117] Polytétrafluoroéthylène PTFE (Téflon) 0,85 [58,63] Polytéréphtalate d'éthylène (Mylar) [117] Polyimide (Kapton) [117] Ethényle (Vinyle) [117] Fluorure de polyvinyle (Tedlar) [117,121] Polypropylène (PP) [117] Peintures Acier peint en noir + polyéthylène [70] Cuivre peint en noir [123] Aluminium peint en blanc [71] Dépôts plasma Nitrure de silicium (SiN0,35) ~ 0,9 [72] Couches successives de SiO2 et HfO2 sur substrat de silicium ~ 0,65 [107] Autres ...
Industrial concentrated solar power plants consume 4 m3/MWh of water to cool down their thermodynamic cycle. In arid area, it could induce conflicts of use on a more fundamental resource than electricity. This fact highlights the need to develop alternatives dry cooling technologies but equally effective. The solar field represents 50% of the investment cost of a CSP plant to be used only daily for the heat production needed for the thermodynamic cycle. The approach of the project is to use this huge area as macro-heat exchanger with its surrounding environment through a coupled heat transfer with the ambient air (convective) and with outer space at 3K (radiative). After validating the compatibility of solar field materials for a such application, these research works has shown experimentally that in addition to extract the waste heat of the thermodynamic cycle, it could also produce cold by night radiative cooling. An innovative alternative solution for cooling CSP plants offering two new features to their already existing solar field for the benefit of its paying off.
... Despite so many attempts, there are only very few numerical models that simulate dew on passive surfaces. The most straightforward approaches applied to compute dew are based on: (i) correlating dew with meteorological variables such as relative humidity, wind and solar radiation among others (Nilsson, 1996;Muselli et al., 2002Muselli et al., , 2006bMuselli et al., , 2009Beysens et al., 2005;Sharan et al., 2007;Maestre-Valero et al., 2011), (ii) solving a surface energy balance on the condensing surface (Pedro and Gillespie, 1982;Nilsson, 1996;Jacobs et al., 2008;Maestre-Valero et al., 2012), and (iii) using neural networks (Lekouch et al., 2012). ...
... Most research published on dew collection or modeling is commonly based on the performance of manufactured surfaces that can be installed on fields (Muselli et al., 2006b(Muselli et al., , 2009 or sometimes on roofs (Sharan et al., 2007;Clus et al., 2013). However, to our knowledge no or few investigations have been focused on dew formation on water surfaces. ...
... Moreover, huge differences were found in the dew yield sensitivity to DT (a 1 ¼ 0.068 ± 0.042 mm C À1 for the RDC and a 1 ¼ 0.036 ± 0.019 C À1 for the pan; Table 2). The dew yield sensitivity for RDC was between the values found by Muselli et al. (2006bMuselli et al. ( , 2009, whereas in the case of the pan it was notably lower. ...
Dew is the result of water condensing from the atmospheric humidity on a surface sufficiently radiatively cooled by its own emission of radiation. This chapter presents the optical basis for the dew formation and a description of three passive dew condensers: a radiative dew condenser (RDC), an experimental pan, and an agricultural pond. It focuses on the presentation of the results of study for dew collection. Muselli et al. studied the dew yield at the Dalmatian Coast with two 1 m² RDCs concluding that it could be worthwhile to rehabilitate the numerous deserted rain collectors existing in the region for the objective of dew harvesting. Finally, the chapter shows two cases for dew modeling: one based on the correlation with climatic variables and other based on the mass transfer equation.
... The cooling source can be a refrigerator system or an off-grid radiative cooler. [45,81] The cooling temperature is defined as the ambient air temperature minus the temperature of the radiative emitter. In the radiative cooling technology, the cooling temperature is affected by external factors including atmosphere conditions (e.g., air temperature, humidity, cloud, etc.), solar irradiation, and wind speed. ...
... [185] After optimized the slope's tilt angle as a 20°-30° to minimize natural convection effect and maximize the dew drop recovery by gravity, [45] a year-round study reported in 2006 demonstrated a dew condensation achieved in humid condition (RH80-90) by polyethylene (PE) foil-base condensing slopes. [81] These PE-based setups harvested more dew than its referenced PMMA-based setting and showed better performance in higher relative humidity environment and winter season (Figure 23b). In another report by the same research group, condensation highly depended on weather conditions, with a maximum daily dew condensation of less than Figure 22. a) Schematic of current ISSG systems with a solid SSA assisted by wick for water transport, and a new ISSG system with a porous SSA that has self-contained water channels. ...
... Figure 24 is plotted on a daily basis for easy comparing sorbent-based condensers that work in cyclic-working mode with radiative condensers in a relatively continuous working state. The daily condensing rate of the nighttime condenser and MOF-condenser are both from literature, [40,81] while the daily condensing rate of the daytime condenser is a rough estimation from the reported hourly Figure 23. Schematics of various AWH devices. ...
Renewable energy harvesting from the sun and outer space have aroused significant interest over the past decades due to their great potential in addressing the energy crisis. Furthermore, the harvested renewable energy has benefited another global challenge, water scarcity. Both solar steam generation and passive radiative cooling‐enabled atmospheric water harvesting are promising technologies that produce freshwater in green and sustainable ways. Spectral control is extremely important to achieve high efficiency in the two complementary systems based on absorbing/emitting light in a specific wavelength range. For this reason, a broad variety of solar absorbers and IR emitters with great spectral selectivity have been developed. Although operating in different spectral regions, solar selective absorbers and IR selective emitters share similar design strategies. At this stage, it is urgent and necessary to review their progress and figure out their common optical characteristics. Herein, the fundamental mechanisms and recent progress in solar selective absorbers and IR selective emitters are summarized, and their applications in water production are reported. This review aims to identify the importance of selective absorbers/emitters and inspire more research works on selective absorbers/emitters through the summary of advances and the establishment of the connection between solar absorbers and IR emitters.
... Il est possible de s'affranchir des effets du vent par une architecture de condenseur adaptée, comme un cône, ou d'implanter le condenseur à l'abri du vent (arbres, haies, etc.). Pratiquement, il est difficile d'obtenir un bon rendement de rosée pour des vents supérieurs à 4 m · s -1 à 10 m du sol [7] [8]. ...
... Le même type de condenseur a été construit au sol, pour diminuer son coût. Le rendement n'en est que légèrement diminué [8]. ...
... Utiliser des structures porteuses pour soutenir de grands condenseurs aériens n'est pas envisageable compte tenu des coûts élevés. Une comparaison entre des condenseurs aériens (sur structure porteuse) et au sol a déjà été effectuée à Ajaccio (France) [8] montrant seulement une faible réduction des rendements entre les deux structures. Des expériences ont été implémentées à Kothara (région côtière du Kutch en Inde) pour déterminer si des rendements en rosée satisfaisants pouvaient être obtenus à partir de condenseurs construits au sol. ...
... Les nombreuses mesures physiques menées sur les sites d'Ajaccio (France ; M uselli et al., 2001, 2002a, 2006b) ; Zadar, Komiza et Biševo (Croatie ; M ileta et al., 2006) ; Kothara (Inde ; Sharan et al., 2007a) ont été déjà corrélées par rapport à l'humidité relative RH ou plus précisément la grandeur directement proportionnelle (T d -T a ) = f(RH), grandeur discriminante dans l'étude d'un gisement de rosée. Prenons l'exemple des données expérimentales collectées sur les sites de Biševo ( Figure (Beysens et al., 2005b ;M uselli et al., 2006b ;M ileta et al., 2006 ;Sharan et al., 2007a). ...
... f F s'exprime en fonction de V à 10 m. Pour une vitesse de vent V i , le facteur de forme f F (V i ) est égal au gain en température (Beysens et al., 2003a ;M uselli et al., 2006b) et suit l' Eq. I.(4) : ...
... De nombreuses mesures sur sites (M uselli et al., 2002a ;Beysens et al., 2003ab ;Mileta et al., 2004 ;M uselli et al., 2006b) confirment que la composante vitesse du vent f(V) est un facteur limitant dans la production d'eau par refroidissement radiatif. Par exemple, à Ajaccio, Beysens et al. (2005b), n'observent plus aucun événement de condensation pour V 10 > 2,2 m s -1 et même pour des valeurs plus faibles sur Grenoble et Bordeaux (lorsque V 10 > 0,5 m s -1 ). ...
Renewable sources (solar, wind, atmospheric vapour) represent interesting alternative solutions to meet the needs of isolated populations in water stress (less than 15 L per day) and without electricity . Radiative condensers of atmospheric humidity can produce potable fresh water thanks to a passive natural phenomenon (radiative cooling) that does not require conventional energy. Since year 2000, the University of Corsica, CEA and CNRS have officially agreed to develop the tools to carry out the transition between laboratory prototypes and real systems. In order to approach the maximum theoretical yield (0.8 L m-2), large planar prototypes of 30 m² were built and several protocols of measurement have been elaborated. A numeric digital code (CFD) was developed to determine the performances of complex systems on a large scale (several hundreds of m²) before their installation. New radiative materials for condensation being the subject of a patent deposited, selective in wavelength, were formulated to answer both the constraints of passive air-conditioning of constructions in diurnal cycle and water production in the night cycle. With the help of the OPUR association (www.opur.u-bordeaux.fr), a demonstration roof of 15.1 m² in Biševo-Croatia (annual average yield: 0.18 mm) and a dew production plant of 850 m² (15000 m² planned) was set up. They confirm the potential of technology since the expected plant production will be able to reach 5 m3 of water per day. In similar terms, the solar and wind resources, in a hybrid system of decentralized energy production (coupled with a fossil or hydrogen standard auxiliary source) can mitigate the absence of electrification in certain areas. In this manuscript, computer codes were worked out for physical and economic optimization, concerning either the electrification of isolated sites or the massive production of electricity by connection to a distribution network, for various applications (continue production or voltage drops limitation). The obtained results make it possible to consider the use of a coupling EnR-H2. For this reason, our research team obtained the financing of a PV-H2 power plant on the site of the laboratory: 3.6 MW coupled to an electrolyser and a fuel cell of power of more than 100 kW.
... Par la suite d'autres publications s'ajoutent pour modéliser le phénomène sur des géométries plus simples, en particulier des surfaces planes. On peut notamment citer Nikolayev et al. (1995) [80], Pedro et Gillespie (1981) [84], Gandhidasan et Abualhamayel (2004) [46], Wahlgren (2001) [98], [76]. Certains de ces modèles font l'hypothèse que le ux de chaleur échangé par conduction avec la surface de condensation est négligeable devant les autres ux. ...
... Il est aussi possible d'envisager le problème point de vue des températures, ce qui se traduit par T s < T d . Des mesures sur des dispositifs extérieurs montrent que T d − T s est de l'ordre de 0.5K [14] [65] [76]. ...
Ce travail est une contribution à l’amélioration de la condensation et de la collecte passive de l’eau de rosée. Dans une première partie, une surface traitée par sablage est utilisée pour la condensation en laboratoire. Sur cette surface rugueuse, refroidie par contact, les gouttes condensées se détachent plus vite que sur la surface non-traitée, et la collecte passive par gravité des gouttes est augmentée. Les expériences montrent que la combinaison du sablage et des effets de bord peut augmenter considérablement la collecte passive par gravité à partir d'un substrat. Des gains d'environ 30% par rapport au même support lisse sont obtenus. Dans une deuxième partie, un dispositif original de refroidissement radiatif en laboratoire est développé, qui réalise des échanges radiatifs entre un objet de petite taille et une source froide. Ce dispositif permet d’étudier de manière contrôlée l’influence des propriétés radiatives des matériaux sur les performances des condenseurs passifs de rosée. En environnement humide, la condensation est obtenue sur des objets de géométries variées, y compris des géométries peu compactes et/ou de faibles conductivités thermiques pour lesquelles le refroidissement par contact est peu efficace. Un résultat important a été obtenu par cette technique : l’émissivité de la surface de condensation ne joue un rôle important qu'au début de la condensation, puis la surface se couvre de gouttes condensées qui déterminent son émissivité globale. Un modèle simple des échanges radiatifs entre une goutte posée sur une surface plane et son environnement est proposé afin d'établir une expression de l'émissivité moyenne d'une surface couverte de gouttes.
... The relative humidity is highly correlated to dew water yields. In a study comparing two large (30 m 2 in area) passive dew condensers in Ajaccio, France, Muselli et al. (2006) found that the limiting value of humidity below which dew did not form was 80.7 and 79.3 % for both condensers. Similarly in southwest Morocco, Lekouch et al. (2012) found that water mostly condensed when the relative humidity was between 74 and 92 %. ...
... For example, a study comparing an uphill site with a downhill site showed that the yield from the latter was 40 % lower than that of the uphill site (Kidron 2000). In addition, Muselli et al. (2006) showed that a condenser exposed from the sides had a higher yield (mean dew yield: 0.118 L/day) than one that was enclosed and closer to the ground (mean dew yield: 0.111 L/day). ...
Dew water refers to the atmospheric vapor that condenses during the evening or early morning on exposed surfaces. In arid or insular areas, dew water collection systems nave been explored as a means of providing water for human and agricultural consumption. In order to utilize dew water for irrigation, there are two possible options: using a small passive condenser that allows for the irrigation of a small number of trees, or using a large dew water irrigation system that allows for the irrigation of large areas. The main goal of this paper is to highlight the possibility of using dew water for irrigation in arid and semi-arid regions through a review of various factors that affect dew water collection, and of the possibilities in terms of the condenser type and the system design.
... The relative humidity is highly correlated to dew water yields. In a study comparing two large (30 m 2 in area) passive dew condensers in Ajaccio, France, Muselli et al. (2006) found that the limiting value of humidity below which dew did not form was 80.7 and 79.3 % for both condensers. Similarly in southwest Morocco, Lekouch et al. (2012) found that water mostly condensed when the relative humidity was between 74 and 92 %. ...
... For example, a study comparing an uphill site with a downhill site showed that the yield from the latter was 40 % lower than that of the uphill site (Kidron 2000). In addition, Muselli et al. (2006) showed that a condenser exposed from the sides had a higher yield (mean dew yield: 0.118 L/day) than one that was enclosed and closer to the ground (mean dew yield: 0.111 L/day). ...
Dew water is water droplets formed due to condensation of atmospheric water vapor on surfaces of temperature below its dew point temperature. Dew water can be seen as a nonconventional source of water and may be exploited in regions where weather conditions favor dew formation and inadequate supply and quality of water is a prevalent problem. There are two main types of dew condenser, the apparatus used to collect dew water, namely radiative (also called passive) and active condensers. Radiative passive collectors rely on exploiting the physical processes responsible for dew formation to collect dew water without any additional energy input. Previous studies indicate that a 1 m2 radiative condenser yields between 0.3 and 0.6 L/day of dew water in arid and semi-arid regions. Active condensers have been designed as an alternative method of collection that produces higher yields by using additional energy inputs. Several designs of active condensers have been patented for which the yield can reach 20 L/day for portable devices, and up to 200,000 L/day for larger agricultural water devices. Active condensers are also known as atmospheric water generators, dehumidifiers, and air to water devices. Most of the active condensers are based on a regenerative desiccant that attracts and holds large volumes of water from the air or on a means of cooling the condensing surface below the dew point temperature (refrigeration circuit). The larger yields and wider range of environmental conditions in which dew can be collected make active condensers a promising option as an alternative or supplemental source of water in water scarce regions. The aim of this paper was to provide a comprehensive review of radiative and active condensers, including dew formation processes, methods of dew collection, and parameters that influence the dew collection. Subsequently, patents of active condensers were reviewed to ascertain how they ca
n be integrated with different types of renewable energy and to assess the potential use of such integrated systems as a sustainable source of water in regions that suffer water scarcity and/or as a sustainable source of water for agriculture.
... Humidity direct condensation units are based on principle of surface cooling below the dewpoint of the ambient air. This can be achieved passively by radiative cooling (Beysens et al., 2003;Muselli et al., 2006;Guan et al., 2014) or actively by compressor chiller (Gido et al., 2016;Habeebullah, 2019). This technology is suitable for humid climates where dew point of ambient air is sufficiently high (Bagheri, 2018). ...
An experimental system for extraction of water from ambient air has been proposed for hot and dry desert conditions. The energetically autonomous system is based on sorption unit with nominal flow 2000 m³/h of process air and 1000 m³/h for regeneration air, PV modules (20 m²), unglazed photovoltaic-thermal collectors (77 m²) for electricity production and night radiative cooling and solar thermal collectors (22 m²) for heat production. Water storage tanks (3 x 1 m³) of heat and cold are complemented by batteries (30 kWh) to balance electric production and load. The system has been designed and built as two containers: production container with sorption unit and energy container with storage of energy harvested by solar roof to establish an autonomous operation with no need for external inputs. Autonomous operation of the system produces about 100 l/day in extreme desert conditions in yearly average according to simulations. The experimental system is being tested and monitored in Sweihan (UAE) in desert conditions to get knowledge on system operation in real environment.
... The trace amounts of water play an essential role in various interfacial phenomena, such as adsorption [3], corrosion [4,5], friction [6], etc. In addition, the condensation process is critical for a wide range of industrial applications, such as refrigeration cycles [7], power plants [8], and water harvesting [9]. ...
Water condensation on solid surfaces is a universal phenomenon that plays an essential role in many interfacial phenomena, such as friction, corrosion, adsorption, etc. Thus far, the initial states of water condensation on surfaces with varying chemical properties have yet to be fully explained at the nanoscale. In this study, we performed a real-time characterization of water condensation on self-assembled monolayers (SAMs) with different functional groups using quartz crystal microbalance with energy dissipation monitoring (QCM-D). We found that the kinetics of water condensatison is critically dependent on the head group chemistries. We discovered that the condensed water’s viscoelasticity cannot be predicted from macroscopic water contact angles, but they were shown to be consistent with the predictions of molecular simulations instead. In addition, we also found a highly viscous interfacial water layer on hydrophilic protein-resistant SAMs. In contrast, the interfacial water layer/droplet on either hydrophilic protein-adsorbing or hydrophobic SAMs exhibited lower viscosity. Combining our and previous findings, we discuss the influence of interfacial hydration on the viscoelasticity of condensed water.
... Inclined plane condensing panel is another commonly used dew condenser. 28,87,88 Large-area prototypes of foil panel, 89,90 and even dew plants (see Figure 4b), 91−93 have already been implemented to validate the feasibility of nocturnal dew generation promoted by radiative cooling, even under wind speeds as large as 4.5 m s −1 . 28 Compared with an ordinary condensing panel, the yield of dew water obtained from the improved one was indeed increased by up to 20%. ...
In the context of global water scarcity, water vapor available in air is a non-negligible supplementary fresh water resource. Current and potential energetically passive procedures for improving atmospheric water harvesting (AWH) capabilities involve different strategies and dedicated materials, which are reviewed in this paper, from the perspective of morphology and wettability optimization, substrate cooling, and sorbent assistance. The advantages and limitations of different AWH strategies are respectively discussed, as well as their water harvesting performance. The various applications based on advanced AWH technologies are also demonstrated. A prospective concept of multifunctional water vapor harvesting panel based on promising cooling material, inspired by silicon-based solar energy panels, is finally proposed with a brief outlook of its advantages and challenges.
... Indeed, in the study carried out by [76], hilltops and sun-shaded areas exhibits higher dew formation and duration in comparison to downhills. Furthermore, an installation with an open structure has shown to collect more dew in comparison with an enclosed sides installation [79]. This has been explained by the fact that, when the surface is close to the ground is more likely to experience more heating effect from the ground ( Table 2). ...
Soiling is a crucial problem for solar energy power plants particularly in regions that have high soiling rates, dust storms, water scarcity and a great solar energy potential. Moreover, in areas with high humidity, the cementation of dust particles seems to be highly impacted by dew condensation on the front surface of solar panels. This impact can have a positive or negative effect depending on the climatic conditions and the surface properties. This review presents a critical investigation of studies regarding the effect of dew on soiling with a focus on the existing solutions to mitigate soiling by dew. Through this work, the papers have been studied and classified whether dew was the main topic of the paper or it is just mentioned as influencing factor on soiling. Furthermore, the dew effect was investigated whether it is experimentally found or just expected. Two kinds of solutions relying on either the enhancement of dew water or its mitigation have been highlighted in this review. About 61% of papers dealt with dew-soiling nexus have given a great interest to the enhancement of dew water formation ensuring solar panels self-cleaning, thus increasing their performance, while 39% of papers have recommended dew suppression. From a sustainability point of view, this work shows that instead of using conventional water resources that are limited, dew as a nonconventional water source may significantly be exploited to mitigate soiling losses in solar energy power plants.
... Therefore, the maximum theoretical dew collection can be calculated around 0.1 L/m 2 per hour and depends on the number of condensing hours, which can be determined for one night (i.e., for 8 h equal to 0.8 mm per night) [114]. However, the maximum obtained dew in the previous case studies was nearly half, and 0.38 mm per night [115]. ...
Conventional green roofs, although having numerous advantages, could place water resources under pressure in dry periods due to irrigation requirements. Moreover, the thermal efficiency of green roofs could decrease without irrigation, and the plants could get damaged. Therefore, this study aims to improve the efficiency of conventional green roofs by proposing a new multipurpose green roof combined with fog and dew harvesting systems. The analysis determined that the average water use of green roofs in the summer (in humid regions) is about 3.7 L/m2/day, in the Mediterranean regions about 4.5 L/m2/day, and in arid regions about 2.7 L/m2/day. During the dry season, the average fog potential in humid regions is 1.2 to 15.6 L/m2/day, Mediterranean regions between 1.6 and 4.6 L/m2/day, and arid regions between 1.8 and 11.8 L/m2/day. The average dew potential during the dry season in humid regions is 0.1 to 0.3 L/m2/day, in the Mediterranean regions is 0.2 to 0.3 L/m2/day, and in the arid regions is 0.5 to 0.7 L/m2/day. The analysis of the suggested multipurpose green roof combined with fog/dew harvesting systems, in the summer, in three different climates, show that fog harvesting could provide the total water requirement of the green roofs, and that dew harvesting by PV (photo-voltaic) panels could provide 15 to 26% of the water requirements. Moreover, it could show a higher thermal impact on the building, higher efficiency in stormwater management, less dependence on the urban water network, and greater efficiency in decreasing urban air, water, and noise pollution. Finally, the novel green roof system could consume less water due to the shaded area by mesh and solar PVs and maximize the utilization of the roof area, as solar panels could be applied on the same green roof.
... Hence, the condensation process is limited by the rate of heat loss from the surface, which is necessary to keep its temperature below the dew point. The process of radiative cooling toward the night sky drives natural atmospheric moisture extraction via the formation of dew on surfaces (Muselli et al. 2006;Nikolayev et al. 1996;Sharan 2013). The maximum expected yield of radiative dew harvesting is ∼0.8 L/(m 2 d) (Beysens et al. 2013) but empirical studies of passive dew capturing reveal much lower and varying water yield (Beysens et al. 2005;Guan et al. 2014;Jacobs et al. 2002Jacobs et al. , 2008Nilsson 1996). ...
Water scarcity is the first and most challenging crisis worldwide. Atmospheric water, also known as air humidity, is one of the most accessible resources and therefore could be used as a sustainable resource for water harvesting. There are some mechanisms for atmospheric water harvesting, including the following methods: vapor condensing, active cooling of the ambient air, and fog harvesting. The use of the Moisture Harvesting Index (MHI) for estimating water production and its energy requirements are demonstrated. Due to varying daily and seasonal meteorological conditions, the MHI shows considerable variability. There are different systems with specific functions to harvest water based on the methods and used materials in the process of atmospheric water generator (AWG) systems. AWGs are nowadays more effective as relative humidity and air temperature are increasing due to climate change.
... The gas and aerosol mixture aloft and throughout the atmosphere, which dissolve into rain, are likely different from the mixture near the surface, and dew and frost originate from the surface. The factors influencing dew composition include 1) dry depositional material on the surface of dew formation (gases and aerosols); 2) soluble trace gases; and 3) the direct exchange of material from plants (Wisniewski, 1982;Muselli et al., 2002Muselli et al., , 2006Beysens et al., 2006;Singh et al., 2006;Lekouch et al., 2010). As a result, dew is considered to be an important mechanism for wet pollutant deposition (Wagner and Steele, 1992;Rubio et al., 2002;Polkowska et al., 2008). ...
... La production de rosée varie suivant les effets conjoints des paramètres météorologiques climatiques (échelle de la couche limite atmosphérique, voir de l'atmosphère) et microclimatiques (échelle de l'ordre de la centaine de mètres ; Guyot, 1999 (Beysens et al., 2005a ;M uselli et al., 2006a ;M ileta et al., 2006 ;Sharan et al., 2007). La droite h M représente le rendement maximal que l'on peut attendre pour un RH déterminé, elle s'écrit selon l'Eq. ...
La vapeur d'eau atmosphérique est une ressource en eau sous exploitée. Les matériaux à forte émissivité infrarouge (rayonnement thermique) sont utilisés en climatisation passive de jour. De nuit, ils se refroidissent et sont une technologie bon marché, robuste et efficace pour condenser cette ressource renouvelable avec des rendements mesurés supérieurs à 0,6 L m-2 par nuit. L'enjeu de ces travaux de recherches était d'avancer la compréhension de ces systèmes, de mettre au point les outils et de développer les techniques permettant la réalisation de condenseurs de grandes dimensions.
Des matériaux (films polymères et peintures) originaux et innovants ont été développés pour ces applications : ils conjuguent une grande émissivité IR et un état de surface optimisé pour un coût inférieur à 1 € m-². Des simulations numériques CFD (Phoenics) ont été programmées dans le but d'optimiser la mise en œuvre des condenseurs de rosée sur des systèmes réels complexes et de grande superficie. De nouvelles méthodes d'estimation (mesure de volume ou estimation indirecte) de la ressource potentielle en eau de rosée sont discutées en fonction de l'influence des paramètres météorologiques pour les îles de Biševo (Croatie), Tahiti et Tikehau (P. Française) et les sites de Panandhro et Yellagiri Hills (Inde).
Enfin, deux systèmes réels novateurs ont été réalisés : une toiture pérenne de démonstration de
15,1 m² installée à Biševo (rendements moyens de 0,181 mm pour un maximum de 0,526 mm). Le second est la première usine à rosée, réalisée avec l'IIMA, dans l'état du Gujarat (Inde). La surface actuelle est de 850 m² et sera étendue à 15 000 m² pour produire jusqu'à 5 m3 d'eau pure par nuit.
... Beysens et al. [27] have critically assessed the work of Kogan and Trahtman [26] and stated that their assumptions were incorrect and the passive dew collector as proposed could not generate as much water as it was claimed. In order to increase the dew condensation from atmospheric air, Muselli et al. [28] constructed and installed two large inclined insulated plane radiative condensers in Corsica Island, France. The performance of the two passive collectors was compared with a horizontal plane, used as a reference. ...
... L/m 2 . These studies included regions with different environments and climate: Kungsbacka (Sweden); Dodoma (Tanzania); Brive-la-Gaillarde, Bordeaux, and Ajaccio (France); Osaka (Japan); Jerusalem (Israel); Komiza and Zadar (Croatia); Central Netherlands; Tahiti; Tikehau; South-West Morocco; and Wrocław and Sudetes (Poland) [14,17,18,25,[47][48][49][50][51][52][53][54][55][56][57]. ...
Since water shortage has been a serious challenge in Iran, long-term investigations of alternative water resources are vital. In this study, we performed long-term (1979–2018) model simulation at seven locations (costal, desert, mountain, and urban conditions) in Iran to investigate temporal and spatial variation of dew formation. The model was developed to simulate the dew formation (water and ice) based on the heat and mass balance equation with ECMWF-ERA-Interim (European Centre for Medium-Range Weather Forecasts–Re-Analysis) meteorological data as input. According to the model simulation, the maximum mean yearly cumulative dew yield (~65 L/m2) was observed in the mountain region in the north part of Iran with a yearly mean cumulative dew yield was ~36 L/m2. The dew yield showed a clear seasonal variation at all selected locations with maximum yields in winter (mean monthly cumulative 3–8 L/m2 depending on the location). Here we showed that dew formation is frequent in northern Iran. In other areas, where there was suffering from water-stress (southern and central parts of Iran), dew can be a utilized as an alternative source of water. The dew yield during 2001–2014 was lower than the overall mean during the past 40 years a result of climate change in Iran.
... Dew, rain and fog events occurred approximately 100 days in 2018, but water collection occurred only 51 days because not all droplets formed on the condenser slid to the collection container. Similar results were reported in other studies as well [8,10,11,25]. The dew events were observed when the relative humidity was at least 80% or more as shown in Figure 5. Similarly, a study in the southwest Morocco showed that when the relative humidity was between 74%, and 92%, water condensed on the condenser surface [10]. ...
Dew condensers collect dew via thermal radiation and cooling affect without the use of external energy. The aim of this project was to design the 1m x 1m with 30° angle square funnel dew, fog and rainwater collector to calculate the dew yield in Abu Dhabi urban area. In addition, studies were conducted to determine whether the collected dew quantity is significant for practical use and to verify the cooling effect in condenser surface using temperature sensors. Aluminum was chosen as dew collector material due to its high emissivity. Square funnel was chosen as condenser shape due to easiness of the assembly and feasibility of its design. The quantity of the collected water depended on the weather condition. The average collected water was 0.016 ml/day (0.016 mm/m ² /day). Temperature sensor analysis showed that there was a 3.5 °C temperature difference between condenser top and bottom indicating the cooling effect of square funnel shape.
... Therefore, for example, if we had used a 100 W/m 2 radiative emitter in similar ambient conditions, with no parasitic losses, we would expect about 1.8L/m 2 /day. We note that 73% relative humidity is at or below the threshold of dew collection for previous ra-diatively cooled systems [9,22]. So, not only did the system greatly exceed the maximum yield, it did it at a relative humidity at which other systems wouldn't collect any dew at all. ...
Based on advances in deep radiative cooling (i.e., radiative cooling very far below ambient temperature), and by separating the roles of the radiative emitter and dew collector, we derive new theoretical dew collection limits. We verified the theory using a thermoelectric cooling system (TEC) that replicates an ideal radiative emitter. The system employed a passive, gravity-driven airflow design. Assuming 100 W/m2 radiative cooling power, we measured the equivalent of ? 1.8L/m2/day with an average relative humidity of only 73%, which greatly exceeds previous theoretical upper bounds and is in good agreement with our theoretical predictions. These ideas not only point to dramatically improved dew collection yields, but that dew can be collected 24 hours per day even at low relative humidity.
... The gas and aerosol mixture aloft and throughout the atmosphere, which dissolve into rain, are likely different from the mixture near the surface, and dew and frost originate from the surface. The factors influencing dew composition include 1) dry depositional material on the surface of dew formation (gases and aerosols); 2) soluble trace gases; and 3) the direct exchange of material from plants (Wisniewski, 1982;Muselli et al., 2002Muselli et al., , 2006Beysens et al., 2006;Singh et al., 2006;Lekouch et al., 2010). As a result, dew is considered to be an important mechanism for wet pollutant deposition (Wagner and Steele, 1992;Rubio et al., 2002;Polkowska et al., 2008). ...
... Research works on radiative sky cooling dew condensers can be traced back to the 1960s. 311 Efforts have been devoted to analyze climate and weather conditions, 312,313 to develop radiative cooling surface materials, 171,314 to design dew collectors, 169 and to study operating conditions that affect the water production rate. 46,[315][316][317] The dilemma for the radiative sky cooling dew harvester is that the local atmosphere should have a large amount of water vapor (i.e., high humidity) that can be condensed, while the presence of a large amount of water vapor inevitably limits the radiative cooling power due to the infrared absorption of water. ...
Radiative sky cooling cools an object on the earth by emitting thermal infrared radiation to the cold universe through the atmospheric window (8–13 μm). It consumes no electricity and has great potential to be explored for cooling of buildings, vehicles, solar cells, and even thermal power plants. Radiative sky cooling has been explored in the past few decades but limited to nighttime use only. Very recently, owing to the progress in nanophotonics and metamaterials, daytime radiative sky cooling to achieve subambient temperatures under direct sunlight has been experimentally demonstrated. More excitingly, the manufacturing of the daytime radiative sky cooling material by the roll-to-roll process makes large-scale deployment of the technology possible. This work reviews the fundamental principles of radiative sky cooling as well as the recent advances, from both materials and systems point of view. Potential applications in different scenarios are reviewed with special attention to technology viability and benefits. As the energy situation and environmental issues become more and more severe in the 21st century, radiative sky cooling can be explored for energy saving in buildings and vehicles, mitigating the urban heat island effect, resolving water and environmental issues, achieving more efficient power generation, and even fighting against the global warming problem.
... Hence, the condensation process is limited by the rate of heat loss from the surface, which is necessary to keep its temperature bellow the dew point. Radiative cooling towards the night sky drives natural atmospheric moisture extraction via the formation of dew on surfaces (Muselli et al., 2006;Nikolayev et al., 1996;Sharan, 2013). The maximum expected yield of radiative dew harvesting is~0.8 ...
The enormous amount of water vapor present in the atmosphere may serve as a potential water resource. An index is proposed for assessing the feasibility and energy requirements of atmospheric moisture harvesting by a direct cooling process. A climate-based analysis of different locations reveals the global potential of this process. We demonstrate that the Moisture Harvesting Index (MHI) can be used for assessing the energy requirements of atmospheric moisture harvesting. The efficiency of atmospheric moisture harvesting is highly weather and climate dependent, with the smallest estimated energy requirement found at the tropical regions of the Philippines (0.23 kW/L). Less favorable locations have much higher energy demands for the operation of an atmospheric moisture harvesting device. In such locations, using the MHI to select the optimal operation time periods (during the day and the year) can reduce the specific energy requirements of the process dramatically. Still, using current technology the energy requirement of atmospheric moisture harvesting by a direct air cooling process is significantly higher than of desalination by reverse osmosis.
... Hence, the condensation process is limited by the rate of heat loss from the surface, which is necessary to keep its temperature bellow the dew point. Radiative cooling towards the night sky drives natural atmospheric moisture extraction via the formation of dew on surfaces (Muselli et al., 2006;Nikolayev et al., 1996;Sharan, 2013). The maximum expected yield of radiative dew harvesting is~0.8 ...
The enormous amount of water vapor present in the atmosphere may serve as a potential water resource. An index is proposed for assessing the feasibility and energy requirements of atmospheric moisture harvesting by a direct cooling process. A climate-based analysis of different locations reveals the global potential of this process. We demonstrate that the Moisture Harvesting Index (MHI) can be used for assessing the energy requirements of atmospheric moisture harvesting. The efficiency of atmospheric moisture harvesting is highly weather and climate dependent, with the smallest estimated energy requirement found at the tropical regions of the Philippines (0.23 kW/L). Less favorable locations have much higher energy demands for the operation of an atmospheric moisture harvesting device. In such locations, using the MHI to select the optimal operation time periods (during the day and the year) can reduce the specific energy requirements of the process dramatically. Still, using current technology the energy requirement of atmospheric moisture harvesting by a direct air cooling process is significantly higher than of desalination by reverse osmosis.
... Their model suggested collection rates between 3 and 7 L/m 2 per night and indicated that collection rates are heavily influenced by both ambient temperature and relative humidity. Muselli et al. [25] measured yields of 0.05-0.4 L/m 2 per night on Corsica Island, France, with two prototypes covered with a polyethylene sheet embedded with TiO 2 foil and BaSO 4 microspheres to promote condensation. ...
Ambient energy sources, including ambient air, ground and night sky, have potential for space cooling. The night sky offers the lowest temperature and, therefore, the greatest potential across most of the US. Compared to a previous analysis that considered only the sensible cooling load, the objective of this new project was to evaluate the potential of night-sky radiation (NSR) to also serve the latent cooling load. ASHRAE standard 55 was used to establish the comfort limits (22°C for room temperature and 60% relative humidity). Condensation was evaluated as the mechanism for humidity reduction, thus the dew-point temperature, 13.9°C, corresponding to the ASHRAE limits was the maximum target temperature for night-sky cooling. Typical meteorological year (TMY3) weather data was used for eleven locations representing ASHRAE climate zones. Building heat gain, infiltration/ventilation requirements and night-sky radiator size were characterized by a load-to-radiator ratio LRR defined as the infiltration/ventilation volume flow rate times the ratio of building floor area to radiator area. Three values of LRR were evaluated: 0.35, 3.5 and 35 m/hr. Three thermal storage cases were considered: 1. Annual NSR cooling potential (seasonal storage), 2. Diurnal storage, and 3. The minimum storage capacity to serve the entire annual load, as well as the effects of capacity less than the minimum. To evaluate the effect of night-sky radiator temperature on storage capacity, six NSR temperatures Trad = 13.9 to −26.1°C were tested. Results showed that even in Miami, FL (the most challenging climate evaluated), annual NSR potential exceeded the total sensible and latent cooling load, at least for the lowest LRR and highest Trad. For diurnal storage, NSR could serve less than 20% of the load in the hot and humid southeast, but the entire load in the mountain west. The minimum storage capacity to meet the entire annual load corresponds to the capacity required to bridge the span of time without NSR availability during which the largest cooling load occurs. This capacity decreases with decreasing LRR and decreasing Trad. For the southeast, large capacity is required, but for Louisville, for instance, sufficient capacity is provided by the equivalent of as little as 0.05 m of water over the floor area of the building for LRR = 0.35 m/hr. These results demonstrate that for much of the US, night-sky radiation has the potential to serve the entire annual sensible and latent cooling load.
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... Dew collection has been known over 140 years where water vapor in air is condensed on a given surface [30]. During the last decade, passive dew collection has become of increasing interest [31,32] because of its potential to be used for drinking and domestic purposes. This is of special importance to developing countries situated within arid to sub-tropical regions where there is limited access to clean water. ...
The condensation phenomenon plays an important role in the heat transfer process in the chemical and power industry, including nuclear power plants. Condensers that are based on natural forces are called passive condensers and they do not require pumps or blower to move fluid. Examples of passive condensers include passive condenser systems in nuclear reactor safety systems, closed loop heat pipes, passive condenser for harvesting dew from surrounding humid air and passive refrigeration systems. In nuclear reactors, there is a greater emphasis on replacing the active systems with passive systems in order to improve the reliability of operation and safety. Heat pipes with passive condensers have been developed to transport high heat flux from electronic devices. In practical operations of the passive condensers, small amounts of non-condensable gas may exist in working vapors due to characteristics of the system or dissolution of working vapors. It is well known that the presence of non-condensable gases in a vapor can greatly reduce the performance of condensers. This is because of the fact that the presence of non-condensable gas lowers the partial pressure of the vapor, thus reducing the saturation temperature at which condensation occurs. In this chapter, state-of-the art in passive condensers topics are covered including various types of passive condensers designs and their applications. The theory of passive condensation, condensation models, and experimental work on the passive condensers is presented. Practical heat transfer relations applicable to various passive condensers are presented and discussed.
... Neste sentido, a desumidificação do ar poderá ser uma alternativa, pois mesmo em regiões secas há disponibilidade de umidade relativa de 15 g.kg -1 .O desafio de outros pesquisadores explorou o aumento da área superficial do trocador de calor capaz de gerar 30 L.m -2 .dia -1 com placas de alumínio com temperatura de 0ºC(MUSELLI et al., 2006).Habeebullah(2009)empregou bobinas de refrigeração semelhantes às empregadas em aparelhos de climatização. Para umidade relativa típica da região da Arábia Saudita (entre 30 e 70%) foram obtidos 17,6 kg.m -2 .dia ...
The state of Rio Grande do Sul, Brazil, has an average rainfall between 1200-2400 mm per year. However, climate change is concentrating these rains in the south and east of the state. As a consequence, since the last 10 years there are situations of extreme water stress for water potability in the western and northern regions. However, these regions maintain minimum relative humidity levels above 60%. Therefore, this study investigated the use of Peltier system in compact configuration with photo disinfection to obtain drinking water. The module consisted of a box of expanded polystyrene, Peltier chip, aluminum heatsinks, fans, plastic container and funnel. The storage unit was comprised of a water quartz tube (60×700 mm) with the passage of UV radiation (germicidal lamp of 8 W) and the hydraulic pump responsible for removal of all water from the storage system. The condensation induced with relative humidity of 80% generated up to 2.6 L.m−2·h−1 and the energy consumption was about 7.92 kWh per liter of water collected. © 2014, ABES - Associacao Brasileira de Engenharia Sanitaria e Ambiental. All rights reserved.
... One of such examples is an attempt to get potable water by condensation of dew from ambient air. In recent years pilot studies were conducted in this field (Muselli et al., 2002Muselli et al., , 2006a Beysens et al., 2007; Clus et al., 2007a; Sharan et al., 2007a). In India and Morocco, these experiments were carried out on a large scale (Clus et al., 2007b; Sharan et al., 2007b; Clus et al., 2010; OPUR, 2011). ...
The measurements of dew formation efficiency and chemistry were performed in Poland in September 2009, as a part of a longer, two-year sampling campaign. Pairs of sites, representing centers of major Polish cities and rural conditions in three different regions, were compared. With the aim to get more detailed landuse-oriented characteristics of dew, two additional sites were set close to Wroclaw. Collection of dew at each site was made by means of flat, insulated, passive radiative condenser, 1 m2 in area. The analysis has included a number of physico-chemical variables, i.e.: dew water volume, pH, conductivity (σ), concentration of some major anions: F−, Cl−, , , , and cations: Na+, K+, Mg2+, Ca2+, The dew formation efficiency at the rural stations is about two times higher than in the nearby city centres and such regularity is complex in its origin. The results show generally low contamination of dew (16.8–132.6 μS cm−1) in comparison to literature examples, but definitely more acidic (pH ∼5.0). The urban dew is characterized about two times higher contamination than nearby rural and independently of the place of collection the dominant ions are , and Ca2+, all anthropogenic in origin. The sources of dew pollution have mostly regional character or alternatively urban emissions effectively contaminate dew even several tens of kilometers away. The urban dew pH is higher than rural, but dew is potentially acidic and corrosive at the level of urban canopy.
... A simplification in Eq. (3) can be made by assuming that dew starts to form at the dew point temperature (this is strictly true only for hydrophilic substrates or on geometrical or chemical surface defects, see Beysens, 2006). Measurements (Museli et al., 2002(Museli et al., , 2006Beysens et al., 2005;Lekouch et al., 2012) indicate that T a − T d rarely exceeds 1 K. Then Eq. (3) can be rewritten as ...
There is a general need to determine dew yield in any place of the world. However, its determination requires systematic measurements that are not available everywhere. In addition, it depends on the particularities of the dew collector. A simple analytical formula valid for planar dew collectors is elaborated here. It is based on laboratory experiments where it is established that heat loss with surrounding air is the dominant parameter that limits dew condensation. A simple analytical formulation is then derived, which only needs cloud coverage, wind velocity, air and dew point temperature data to be collected, at least once in a day before sunrise. The formulation is tested in several places in the world with different climates. Agreement within typically 30% is found with dew measurements. Such an analytical relationship can thus provide a useful tool to obtain a worldwide estimation of the dew potential.
... In contrast to rain and fog, which are atmospheric precipitations, dew forms on a surface and thus the yield of dew water is very dependent on the nature and environment of this surface. Dew yield can be much improved by a careful choice of both condensing substrate materials and condenser design (Nilsson et al., 1994;Nilsson, 1996;Muselli et al., 2002;Beysens et al., 2003;Muselli et al., 2006a;Beysens et al., 2006;Gandhidasan and Abualhamayel, 2005;Sharan et al., 2006). ...
... Recently, systematic investigation were performed of adapted condensing architecture using high yield radiative materials with hydrophilic properties (complete wetting case) that enhance dew water nucleation (see Beysens, 2006) and dew drop gravity recovery. The influence of local meteorological parameters such as wind speed and relative humidity was systematically studied (Nilsson, 1996;Vargas et al., 1998;Muselli et al., 2002;Muselli et al., 2006a;Beysens et al., 2003Beysens et al., , 2005Jacobs et al., 2008;Sharan et al., 2007). Water quality was also investigated Muselli et al., 2006b). ...
... La production de rosée varie suivant les effets conjoints des paramètres météorologiques climatiques (échelle de la couche limite atmosphérique, voir de l'atmosphère) et microclimatiques (échelle de l'ordre de la centaine de mètres ; Guyot, 1999 (Beysens et al., 2005a ;M uselli et al., 2006a ;M ileta et al., 2006 ;Sharan et al., 2007). La droite h M représente le rendement maximal que l'on peut attendre pour un RH déterminé, elle s'écrit selon l'Eq. ...
Atmospheric water vapor is an alternative water resource that could be more exploited. Highly infrared emissive materials are already used for diurnal passive cooling and air-conditioning. During the night, they have proved to cool their surface and to be an efficient and cheap technology for condensing artificial dew with common rates reaching 0.6 L m-² per night. The aim of this work was to enhance the knowledge and to develop the tools and the technology for transposing this application from experiment to complex and large scale real systems. New cheap polymeric materials (films and paints) presenting high IR emissivity and selected surface wetting properties have been formulated for dew harvesting.
CFD numerical simulations have been programmed as tools for enhancing the efficiency of new implemented condensers if built with complex shapes and on large surfaces. New methods (volume measurements or roundabout estimation) are discussed for evaluating dew potential on the islands of Biševo (Croatia), Tahiti and Tikehau (French Polynesia) and both Indian sites Panandhro and Yellagiri Hills.
Two real systems have been implemented: The first is a 15.1 m² perennial show roof on Biševo Island (Croatia). Average dew yield was 0,181 mm for a maximum record of 0.526 mm. The second implementation (with IIMA, in Gujarat State, India), is the first dew plant, that already develops 850 m² and will soon be extended to 15 000 m² to produce maximum 5 m3 of water a night.
... This value is related to the 10-year series of measurements carried out in a grass area in the northern part of Poland, but conducted with the use of different methodology (wet-cloth method), therefore it cannot be quantitatively compared. On the other hand, our results refer well to those obtained around the world Muselli et al., 2006a;Jacobs et al., 2008) with the use of nearly the same way of collection. The measurements conducted simultaneously at several other sites in Poland representing different landuses show that the very similar formation efficiency of dew and hoarfrost is rather a rule (Fig. 2). ...
Arid regions are classified on the basis of severe lack of available water which further affects the growth as well as the development of flora, fauna, and human life. The idea of recovering water from atmosphere has remained quite a problem in arid regions. AWH defined as atmospheric water harvesting, is a prominent way to overcome water scarcity. It is considered as an alternative source of fresh water regardless of the physical conditions prevailing in a certain area. Various techniques are used to harvest atmospheric water that comprises adsorption-based technology, fog collector, atmospheric water generator and few other models in other to harvest atmospheric water. In this chapter, our focus will mainly be based on potential behind harvesting atmospheric water in arid regions and we will be going through different case studies to have in-depth knowledge and information regarding it.
Freshwater scarcity will be one of the most challenging issues in the coming time. Atmospheric water harvesting could be a solution to such a problem in semi-arid and arid regions. This could help to fill the thirst as well as improve irrigation. There are several methods available to retrieve water vapour from the air but research is needed for a cost-effective and efficient method with optimized parameters. The methods proposed in this study utilize the Peltier device for water condensation, and in-depth experimental analysis has been done to investigate the optimal conditions for maximum water production from atmospheric moisture. The experimental setup was designed in such a way that during the condensation process, the online monitoring of water condensate was recorded for more than 10–12 h each day using a digital electronic weighing balance with an accuracy of 1 × 10–5 kg. The water produced in this study was tested for the physico-chemical parameters, and the results were discussed with a comparison to the American Public Health Association (APHA) standards. The rate of produced condensed water from humid air was achieved as 19 L.m−2.day−1. This study will help us to develop applications in the field of alternative water resources near the coastal areas, such as Gujrat state in India for potability.
Freshwater scarcity will be one of the most challenging issues in the coming time. Atmospheric water harvesting could be a solution to such a problem in semi-arid and arid regions. This could help to fill the thirst as well as, improve irrigation. There are several methods available retrieve water vapour but research is needed for a cost-effective and efficient method with optimized parameters. This method utilizes the Peltier device for water condensation and in-depth experimental analysis has been done to investigate the optimal conditions for maximum water production from atmospheric moisture. The experimental setup was designed in such a way that during the condensation process, the online monitoring of water condensate was recorded for more than 10-12 hours each day using a digital electronic weighing balance with an accuracy of 0.01 gram. The produced water was tested for the physico-chemical parameters of condensed water, and the results were discussed with a comparison to the standard results. The rate of produced condensed water from humid air was achieved as 19 L/m ² -day. This study will help us to develop applications in the field of alternative water resources near the coastal areas for potability.
Thirty-one percent of the primary energy consumed in the United States comes from the burning of natural gas, 70–90% of which is composed of methane (CH₄). Natural gas is recovered from onshore and offshore natural gas and oil wells and from coal beds. Currently, the United States has enough supply of dry natural gas to sustain current consumption for 92 years. Meanwhile, California consumes 2.14 MMcf (43.2 million tons) of natural gas per year, over a quarter of which is used to generate electric power and which provides approximately 40% of the electrical energy in the state. Because an extensive nationwide storage and distribution network already exists for natural gas, the development of renewable CH₄ could enable rapid and widespread distribution of zero-carbon energy services. Thus, for California to meet its renewable portfolio standard, that is, 60% renewable energy for electricity generation by 2030, and to conserve a limited resource, it is imperative to assess how to develop and deploy technologies for renewable generation of CH₄ in the next decade.
Sub-ambient radiative cooling has been achieved recently by applying advanced nanofabrication technologies, which attracts extensive research attention due to its passive cooling characteristic. Water condensation is an important application of radiative cooling, which is also an unconventional technology for gaining fresh water without consuming energy. However, limited efforts have been devoted to improving the water harvesting using the state-of-the-art radiative cooling materials. To efficiently accomplish dew condensation by radiative cooling, we first take a theoretical approach to analyze the weather conditions for effective dew condensation. Then, we propose the durable enhance specular reflector-metal by 3 M Company (DESR-M) as an efficient material for dew condensation and further improve its dew condensation performance through a simple hydrophilic coating. The dew condensation performance shows significant enhancement over the previously used polytetrafluororoethylene (PTFE) radiative condenser. On-site experiment result shows that the hydrophilic DESR-M can achieve lowest cooling temperature among all the three samples. The dew yield improves by 72.7% and 88.1% compared to DESR-M and PTFE, respectively.
In this study, we performed model simulations to investigate the spatial, seasonal, and annual dew yield during 40 years (1979-2018) at ten locations reflecting the variation of climate and environmental conditions in Jordan. In accordance with the climate zones in Jordan, the dew formation had distinguished characteristics features with respect to the yield, seasonal variation, and spatial variation. The highest water dew yield (an overall annual mean cumulative dew yield as high as 88 mm) was obtained for the Mountains Heights Plateau, which has a Mediterranean climate. The least dew yield (as low as 19 mm) was obtained in Badia, which has an arid climate. The dew yield had a decreasing trend in the past 40 years due to climate change impacts such as increased desertification and the potential of sand and dust storms in the region. In addition, increased anthropogenic air pollution slows down the conversion of vapor to liquid phase change, which also impacts the potential of dew formation. The dew yield showed three distinguished seasonal patterns reflecting the three climates in Jordan. The Mountains Heights Plateau (Mediterranean climate) has the highest potential for dew harvesting (especially during the summer) than Badia (semi-arid climate).
The current review focuses on the contribution of non‐rainfall water (NRW) to arid and semi arid regions (with a focus on the Negev), where NRW may provide a constant source of water that may facilitate the survival of different organisms, especially microorganisms. Factors that determine the amounts of NRW and the contribution of NRW to plants and organisms are discussed. Nevertheless, although important, significant variation exists regarding the amounts of NRW, which may stem from improper use or inherent drawbacks of some of the measurement devices. This may lead to erroneous conclusions regarding the possible role played by NRW. For instance, with prokaryotes (bacteria, cyanobacteria) requiring liquid water (≥ 0.1 mm) for growth, small inaccuracies in NRW around this threshold may either lead to the conclusion that NRW is sufficiently high to facilitate their growth, or rather, is too low to facilitate their growth. Arguing that some of the devices used to measure NRW may greatly overestimate the amounts, the possible contribution of NRW to soil bacteria and cyanobacterial biocrusts is analyzed. We suggest that while NRW may assist the growth and survival of mosses and some types of lichens (mostly non‐crustose), no conclusive findings were thus far reported regarding the use of dew for cyanobacteria growth. The use of dew by cyanobacterial crust for growth should be critically examined, and the possibility that NRW may even result in a negative carbon balance for cyanobacterial crusts should be considered.
The potential of sky radiation (SR) to serve the latent space cooling loads was evaluated. Using ASHRAE standard 55 comfort limits (room temperature 22 °C, relative humidity 60%, and dew-point temperature 13.9 °C), condensation was the chosen mechanism for humidity reduction. Typical meteorological year (TMY3) weather data were used for eleven ASHRAE climate zones. Three values of load-to-radiator ratio (LRR) (infiltration/ventilation volume flow rate times the ratio of building floor area to radiator area) were evaluated: 0.35, 3.5, and 35 m/h. Three thermal storage cases were considered: 1. Annual cooling potential, 2. Diurnal storage, and 3. Minimum storage capacity to serve the entire annual load. Six SR temperatures Trad = 13.9 to '26.1 °C were tested. Even in the most challenging climates, annual SR potential exceeded the total sensible and latent cooling load, at least for the lowest LRR and the highest Trad. For diurnal storage, SR served less than 20% of the load in the hot and humid southeast, but the entire load in the mountain west. The minimum storage capacity to meet the entire annual load decreased with decreasing LRR and decreasing Trad. For the southeast, large capacity was required, but for Louisville, for instance, sufficient capacity was provided by 0.05 m3 of water per m2 of floor area for LRR = 0.35 m/h. These results demonstrate that for much of the U.S., sky radiation has the potential to serve the entire annual sensible and latent cooling load.
Dew harvesting can be a supplementary source of freshwater in semiarid and arid areas. Several experiments on small-scale dew condensers (usually of 1 m²) have been carried out in many places in the world; however, few experiments have been conducted on large-scale collectors integrated into buildings. This work aims to assess one year of dew water harvesting in Combarbalá (Chile) using a painted galvanised steel roof as collecting surface. The roof (36 m²) was coated with a high-infrared-emissivity paint containing aluminosilicate minerals (OPUR, France). Dew measurements were conducted daily from September 2014 to August 2015. The dew yield and its relationship with meteorological variables were analysed. The results show that despite the low nocturnal relative humidity throughout the year (average: 48%), dew collection occurred on 56.1% of the recorded days. The daily average collection rate was 1.9 L d¹, with a maximum of 15 L d¹. The maximum daily dew yield is correlated strongly with relative humidity and correlated weakly with air temperature and wind speed. Considering the same rooftop can collect dew and rain, it was estimated that over one year dew water could contribute to roughly 8.2% of the total water collected, considering both sources.
An innovative atmospheric moisture harvesting system is proposed, where water vapor is separated from the air prior to cooling and condensation. The system was studied using a model that simulates its three interconnected cycles (air, desiccant, and water) over a range of ambient conditions, and optimal configurations are reported for different operation conditions. Model results were compared to specifications of commercial atmospheric moisture harvesting systems and found to represent saving of 5-65% of the electrical energy requirements due to the vapor separation process. We show that the liquid desiccant separation stage that is integrated into atmospheric moisture harvesting systems can work under a wide range of environmental conditions using low grade or solar heating as a supplementary energy source, and that the performance of the combined system is superior.
Over the last 20 years, dew harvesting has evolved to fruition due to a better understanding of its physics, thermodynamics, and the radiative cooling process of condensing substrates. Although resultant yields are relatively small, dew positions itself as a viable water resources supplement because it occurs naturally and frequently in many locations globally, particularly in the absence of precipitation or when more traditional water sources are subject to depletion. Moreover, dew water is generally potable, especially in rural locations, where it is most beneficial. This review summarizes dew harvesting research achievements to date including formation processes, collection in various environments, prediction models, water quality, and applications. The paper concludes with outlining existing gaps and future research needs to improve the understanding and performance of dew harvesting in the context of adaptation to climate change.
Prix de l'Université Ibn Zohr, 7ème édition 2009-2010
Main topic of this study is evaluation of the contribution of deposited precipitation (DP) to the falling precipitation (FP) amount. An automatic device for DP weight measurement developed and produced at the Institute of Atmospheric Physics was used. The tipping bucket rain gauges were used for the FP measurement. Present paper summarizes the results of measurements of deposited and falling precipitation in three localities: Suchdol, Prague (capital of the Czech Republic), Poledník (Bohemian Forest), and Smĕdava (the Jizerské hory Mts.). Two later introduced stations are situated in the mountainous part of the Czech Republic. For each of mentioned stations the daily averages of the DP totals were determined by the values 0.074 mm for Suchdol, 0.112 mm for Poledník, and 0.103 mm for Smĕdava. Further the mean daily DP sums were evaluated for the days with the occurrence of this precipitation only by the values 0.136 mm, 0.276 mm, and 0.289 mm for the stations Suchdol, Poledník, and Smĕdava, respectively. Obtained results were compared with the findings published in the literature. In each of the stations the ratio between the deposited and falling precipitation was determined as well. For the Suchdol this ratio reached 95.2% in December 2013.
The recovery of clean water from dew has remained a fascinating problem in the arid regions of the globe. The stone heaps near the city of Feodosia in the Crimean peninsula were considered for many years to be artificial dew-catching constructions for obtaining drinking water. Several attempts to reconstruct these systems have been made but they have been considered unsuccessful because of low yield. This has caused some doubts and negative estimations regarding the role of the Crimean stone heaps as water collectors. The opinion that there were no dew-catching constructions in Crimea still dominates today.In this discussion we shall consider the role of the Crimean stone heaps as water con-densers and a model of Nikolayevet al. (1996) of this process. Some conclusions will be put forward showing why this model does not correspond with the system under consideration, hence concluding that the above-mentioned negative opinion, which is based on the model, is a rather hasty conclusion.The traditional model of the Crimean water collector will be modified by the consideration of the role of the draught in the process of condensation. Qualitative and quantitative analysis of the process and of draught outbreak will be proposed. The efficiency of the collector will be estimated.
We report on the development of an inexpensive radiative condenser for collecting atmospheric vapor. Based on the experience gained using a small working model in Grenoble (France), a prototype of 10×3 m2 was established in Ajaccio (Corsica, France). The condensing surface is a rectangular foil made of TiO2 and BaSO4 microspheres embedded in polyethylene and has an angle of 30° with respect to horizontal. The hollow part of the device, thermally isolated, faces the direction of the dominant nocturnal wind. Dew measurements were correlated with meteorological data and compared to dew condensed on a horizontal polymethylmethacrylate (PMMA, Plexiglas) reference plate. The plate served as a reference standard unit and was located nearby. Between July 22, 2000 and November 11, 2001 (478 days), there were 145 dew days for the reference plate (30%), but 214 dew days for the condenser (45%). This yield corresponds to 767 l (3.6 l, on average, per dew day). The maximum yield in the period was 11.4 l/day. Dew mass can be fitted to a simple model that predicts dew production from simple meteorological data (temperature, humidity, wind velocity, cloud cover). Chemical analyses of the water collected from the plate were performed from October 16, 1999 to July 16, 2000 and from the condenser, from July 17, 2000 to March 17, 2001. The following parameters were investigated: suspended solids, pH, concentration of SO42−, Cl−, K+, Ca2+ ions. Only Cl− and SO42− ions were sometimes found significant. Wind direction analyses revealed that Cl− is due to the sea spray and SO42− to the combustion of fuel by an electrical plant located in the Ajaccio Gulf. Except for a weak acidity (average pH≈6) and high concentration of suspended solids, dew water fits the requirements for potable water in France with reference to the above ions.
In the dew model, the contribution of the fluxes of infrared radiation, sensible and latent heat to the energy balance of a dew plate are parametarised according to detailed micrometeorological measurements of Holtslag and De Bruin. The model is tested with measurements of dew on the glass surface of an automatic sequential dew sampler. Results of model calculations and measurements of dew occurrence show a fairly close correspondence. Taking the hours of rain into account, it appears that about 75% of the time a surface is wet during the nocturnal hours because of dew or rain. This may be important for the dry deposition of easily soluble air pollutants. -from Authors
PREFACE TO THE SECOND EDITION LIST OF SYMBOLS 1. SCOPE OF ENVIRONMENTAL PHYSICS 2. GAS LAWS Pressure, volume and temperature Specific heats Lapse rate Water and water vapour Other gases 3. TRANSPORT LAWS General transfer equation Molecular transfer processes Diffusion coefficients Radiation laws 4. RADIATION ENVIRONMENT Solar radiation Terrestrial radiation Net radiation 5. MICROCLIMATOLOGY OF RADIATION (i) Interception Direct solar radiation Diffuse radiation Radiation in crop canopies 6. MICROCLIMATOLOGY OF RADIATION (ii) Absorption and reflection Radiative properties of natural materials Net radiation 7. MOMENTUM TRANSFER Boundary layers Wind profiles and drag on uniform surfaces Lodging and windthrow 8. HEAT TRANSFER Convection Non-dimensional groups Measurements of convection Conduction Insulation of animals 9. MASS TRANSFER (i) Gases and water vapour Non-dimensional groups Measurement of mass transfer Ventilation Mass transfer through pores Coats and clothing 10.MASS TRANSFER (ii) Particles Steady motion 11.STEADY STATE HEAT BALANCE (i) Water surfaces and vegetation Heat balance equation Heat balance of thermometers Heat balance of surfaces Developments from the Penman Equation 12.STEADY STATE HEAT BALANCE (ii) Animals Heat balance components The thermo-neutral diagram Specification of the environment Case studies 13.TRANSIENT HEAT BALANCE Time constant General cases Heat flow in soil 14.CROP MICROMETEOROLOGY (i) Profiles and fluxes Profiles Profile equations and stability Measurement of flux above the canopy 15.CROP MICROMETEOROLOGY (ii) Interpretation of measurements Resistance analogues Case studies: Water vapour and transpiration Carbon dioxide and growth Sulphur dioxide and pollutant fluxes to crops Transport within canopies APPENDIX BIBLIOGRAPHY REFERENCES INDEX
This paper describes an energy budget approach which allows the estimation of dew duration (DD) from standard weather station measurements of air temperature, dew point temperature, wind speed and cloud cover. Differences between observed and estimated values of DD were, on average, ⩽1 h for an exposed leaf and ⩽1.5 h for a shaded leaf.
Two methods of the evaluation of the amount of the atmospheric humidity condensed naturally are proposed. The comparison of these two methods is done from climatological considerations. The results in a hot and humid climate are very close; but in a hot and dry climate there is gap of 4% between the two methods.Experiments were conducted in three different climates; the results are similar to those of the theory. But the dew collected represents about 40% of which must be obtained.This paper describes the study and presents the results.
In this paper, a new dew model is presented which is easy to apply and requires only a very limited amount of synoptic data, viz., cloud cover, relative humidity, air temperature and wind velocity. In the dew model, the contribution of the fluxes of infrared radiation, sensible and latent heat to the energy balance of a dew plate are parametarised according to detailed micrometeorological measurements of Holtslag and De Bruin. The model is tested with measurements of dew on the glass surface of an automatic sequential dew sampler. Results of model calculations and measurements of dew occurrence show a fairly close correspondence. The frequency and duration of dew deposition over a year, for 3 places in the Netherlands, have been calculated with the model, using only synoptic data. The numbers of dewy nights and dewy hours were calculated for the year 1987. This resulted in about 220 dewy nights and 1600 dewy hours. Taking the hours of rain into account, it appears that about 75% of the time a surface is wet during the nocturnal hours because of dew or rain. This fact may be important for the quantification of the dry deposition of easily soluble air pollutants and for the effect of air pollutants on vegetation.
Dew formation on short grass has been studied with a balance, recording weight of condensation, and with filter papers to absorb moisture. Three regimes are distinguished: in the first, daytime evaporation continues and the grass remains dry; in the second, the surface continues to lose weight but the grass becomes wet owing to the partial condensation of water vapour evaporating from the soil; in the third, this loss of weight ceases or there is an increase in weight attributed to condensation of atmospheric water vapour. A distinction is therefore made between ‘distillation’ of water vapour from soil to grass (1–2 mg cm−2hr−1) occurring on very calm nights through a laminar layer with a transfer coefficient approaching the molecular value; and ‘dewfall,’ the turbulent transfer of water vapour from the atmosphere, negligible when the wind at 2 m falls below 0.5 m/sec but reaching 3–4 mg cm−2hr−1 with stronger winds. This distinction is supported by analysis of the surface heat-budget. On windless nights, since heat flux from the soil and net radiative loss were almost equal, the transfers of sensible and latent heat from the atmosphere were negligible and distillation was of much greater importance than dewfall. Implications for taller crops and warmer climates are briefly considered.
Two energy balance (EB) analyses, based on two different methods to estimate the downward long wave radiation, were used to model dew duration. Model I utilized cloud cover and cloud altitude to calculate sky temperatures whereas model II was based only on cloud cover to estimate sky apparent emissivity. The models were validated with hourly data from on-site weather station instrumentation for nights with and without occurrence of dew and cloud data from airport weather records, and compared with an empirical model, the CART/SLD model. The accuracy of predicting hourly dew occurrence with the EB models was greater than with the CART/SLD model. EB models I and II correctly predicted dew occurrence in 91 and 88% of hours, respectively, compared with 75% for the CART/SLD model. The majority of CART/SLD errors were due to late estimation of dew onset. It is proposed that an EB model can be used more effectively than the current CART/SLD model without a need for increased environmental observations in most localities.
The recovery of clean water from dew has remained a longstanding challenge in many places all around the world. It is currently believed that the ancient Greeks succeeded in recovering atmospheric water vapour on a scale large enough to supply water to the city of Theodosia (presently Feodosia, Crimea, Ukraine). Several attempts were made in the early 20th century to build artificial dew-catching constructions which were subsequently abandoned because of their low yield. The idea of dew collection is revised in the fight of recent investigations of the basic physical phenomena involved in the formation of dew. A model for calculating condensation rates on real dew condensers is proposed. Some suggestions for the ‘ideal’ condenser are formulated.
Moisture in the air can be condensed as dew and used for drinking and irrigation. The radiative cooling properties of polymer foils can enhance the performance of dew collecting surfaces. The main restrictions in condensing water in warm and arid locations are climatic factors, the dew collector design, and the optically selective and adhesive properties of the condensing surface itself. This paper concerns observations of dew formation on radiatively cooled pigmented polyethylene foils. The experiments were carried out in Sweden and in arid Dodoma, Tanzania. The results are in agreement with thermodynamical calculations, though the variation is large in the daily measured dew water volumes. This variation is caused by the hourly and daily changes in wind-speed, cloud cover, dry bulb temperature, and dew point temperature. The results are compared with earlier outdoor observations in Tanzania.
An inexpensive radiative condenser for collecting atmospheric vapor (dew) was tested in Grenoble (France). The surface temperature measurements are correlated with meteorological data (wind velocity, air temperature) and compared to the corresponding surface temperature of a horizontal Polymethylmethacrylate (Plexiglas) reference plate located nearby. The condenser surface is a rectangular foil (1×0.3 m2) made of TiO2 and BaSO4 microspheres embedded in polyethylene. The foil has an angle θ with respect to horizontal. The under-side of the device, thermally isolated, faces the direction of the dominant nocturnal wind. Both a 2D numerical simulation of the air circulation around the foil and experimental measurements shows that the angle θ=30° is a good compromise between weak wind influence, large light-emission solid angle and easy drop collection. The study was conducted from November 25, 1999 to January 23, 2001. In comparison to the reference plate, it is found that water yield can be increased by up to 20% and water collection greatly facilitated.
Dew is the condensation into liquid droplets of water vapor on a substrate. The presence of a substrate is the origin of the peculiarities and richness of the phenomenon. We review the aspects related to heterogeneous nucleation and subsequent growth of water droplets. A key point is the drop interaction through drop fusion or coalescence, which leads to scaling in the growth and gives universality to the process. The effects of substrate heterogeneity and gravity effects are also considered. Coalescence events lead to temporal and spatio-temporal fluctuations in the substrate coverage, drop configuration, etc., which give rise to a very peculiar dynamics.When the substrate is a liquid or a liquid crystal, the drop pattern can exhibit special spatial orders, such as crystalline, hexatic phases and fractal contours. And condensation on a solid substrate near its melting point can make the drop jump.The applications of monitoring dew formation are manyfold. Examples can be found in nanoelectronics and optics (vapor deposition and thin films), medicine (sterilization process), agriculture (green houses). We here discuss in greater details the production of clean water by “atmospheric wells”.
Vacuum-evaporated aluminium films can show substantially different optical properties depending on the angle at which the vapour stream impinges on the substrates. Films deposited at 85° oblique incidence developed diffuse reflecting surfaces and showed greater absorption than those condensed at normal incidence. Electron micrographs of such films reveal chains of crystallites whose long axes are inclined to the substrate. The orientation of these crystallites gives rise to optical anisotropy and the optical transmission of the films strongly depends on the direction of the vapour beam. The surface density at which the films start to show surface roughness can be increased if the films are condensed in an argon atmosphere. These films were shown to have superior reflectivity and to exhibit very low absorption or scattering. Optical anisotropy in these films could hardly be observed.
We compare the characteristics of dew at nearly the same latitude (42–45°N) for the Mediterranean island of Corsica (Ajaccio, France) and two continental locations (Bordeaux, France, Atlantic coastal area; Grenoble, France, alpine valley). Dew amount was measured on a horizontal reference plate made of polymethylmethacrylate (PMMA) and placed at 1 m above the ground. Data are correlated with plate and air temperature, air relative humidity, wind speed and cloud cover during the period from 14-08-1999 to 15-01-2003.General features as well as particularities of the sampling sites are discussed. The average daily dew yield is higher for the island station at Ajaccio (0.070 mm) than the Bordeaux coastal area (0.046 mm) or the Grenoble valley (0.036 mm). However, the accumulated dew yield was highest for the coastal station (9.8 mm/year) as compared to the island (8.4 mm/year), and much larger than in the alpine valley (4 mm/year). The difference between cumulated and average dew yield stems from the greater number of dew days in the coastal area (58%) versus 33% for the island and 30% in the valley. The higher wind speeds at the island station (average wind during dew is 2 m/s) and lower relative humidity explain the smaller number of dew days. The dew rate seasonal variation is negligible in Bordeaux and exhibits during summer a maximum in Ajaccio and a minimum in Grenoble.A computer model that includes simple meteorological data (air temperature and relative humidity, wind speed, cloud cover) is used to determine the thermal balance and fit to dew mass evolution. Two parameters that account for heat and mass exchange can be adjusted. It was found that, within the uncertainties, these two numbers are the same for the two continental sites, thus allowing dew formation on plates to be evaluated from only simple meteorological measurements. Somewhat larger values are found for the island, due to limitations in the model, which are discussed.
The energy balance technique along with heat transfer theory for flat plates was used to develop a computer model to simulate the dew duration (DD) on a single leaf. The DD was inferred from a computation of the latent heat flux.Microclimatic data obtained in an apple orchard and in corn and soybean crops were used to verify the model. Estimates of DD were attempted for exposed and shaded leaves. On the average, the dew duration estimates were within 30 min of observed DD for exposed leaves and within 60 min for shaded leaves.
Incluye bibliografía e índice Reimpresion en 1986.
In a desert environment dew can serve as an important source of moisture for plants, biological crusts, insects and small animals. A measurement programme was carried out within a sand dune belt situated in the northwestern Negev desert, Israel, to measure daily amounts of dew deposition as well as micro-meteorological conditions during the dew formation and early-morning drying process. Dew quantities were measured by micro-lysimeters along a 200-m transect as well as by the eddy-correlation technique at a reference location. A simple physical model was constructed to simulate the dew deposition process as well as early-morning drying for the interdune area and the north- and south-facing dune slopes. Measurements carried out during September and October 1997 showed that the daily amounts of dew ranged between 0.1 mm/night and 0.3 mm/night within the interdune area. On the slopes, the amounts of dew were about 50% lower. Simulated results agreed well with the field data.
In order to understand how nocturnal net radiative loss affects dew formation, a shielding experiment was carried out in a rice field at the International Rice Research Institute during 16 nights in February, March, and April 1994. Four plots (with an area of 4×5m for each) in the field were used to measure the dew amount and duration in the rice crops. During each night, two of the four plots were covered using black plastic sheets from sunset (about 18:00) till 03:00 or 04:00 or 05:00 of the next day. The other two plots were used as a control (without cover). The results showed that in the dry season in the tropics, daily total dew duration on top leaves mainly depended on night time dew duration and the latent heat released by dew formation on the top leaves was about 20% of the nocturnal net radiative loss. The measurement error in nocturnal net radiative loss caused by dew formation on the dome of the net radiometer was typically about 7Wm−2, with 18Wm−2 as an extreme value in the dry season in the tropics during heavy dew nights. Both dew amount and dew duration on the top leaves could be reasonably predicted (r2=0.8) by a physically based simulation model, although a standard error remained of about 0.03mm for dew amount and 2.3h for dew duration, respectively. Measurement errors in weather variables, especially in net radiative loss and in water vapour pressure deficit, are probably the main causes of these deviations. Dew amount was more strongly affected by the nightly minimum value of water vapour pressure deficit than by its mean value. Guttation by the rice plants themselves supplied as much water to the leaf surface of the paddy rice crops as dewfall did. Unexpectedly, shielding from nocturnal net radiative loss provided a feasible method to measure guttation water intercepted by different layers inside the paddy rice crops.
Kogan and Trahtman [2003. The moisture from the air as water resource in arid region: hopes, doubts and facts. Journal of Arid Environments 53, 231¿240] analysed the functioning of a passive dew condenser built by F.I. Zibold in 1912 in Feodosia, and proposed a model to explain how thousands of litres of condensed water might be generated per day based on Zibold's design. In a previous publication, some of the present co-authors explained why it was not possible to obtain high water yields with Zibold-style dew condensers and that Zibold was apparently unaware that the stone heaps in Feodosia were in fact ancient Scythian and Greek tombs. Kogan and Trahtman [2003] take issue with our findings, thus the reason for this comment.
In a desert environment dew can serve as an important source of moisture for plants, biological crusts, insects and small animals. A measurement programme was carried out within a sand dune belt situated in the northwestern Negev desert, Israel, to measure daily amounts of dew deposition as well as micro-meteorological conditions during the dew formation and early-morning drying process. Dew quantities were measured by micro-lysimeters along a 200-m transect as well as by the eddy-correlation technique at a reference location. A simple physical model was constructed to simulate the dew deposition process as well as early-morning drying for the interdune area and the north- and south-facing dune slopes. Measurements carried out during September and October 1997 showed that the daily amounts of dew ranged between 0.1 mm/night and 0.3 mm/night within the interdune area. On the slopes, the amounts of dew were about 50% lower. Simulated results agreed well with the field data.
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Comment on the moisture from the air as water resource in arid region: hopes, doubts and facts Journal of Arid Environment accepted, subject to revision Measurement and modelling of dew in island coastal and alpine areas
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Proceedings of the inspection of the condenser, which was built in the Feodosia forest, 19.06.1915. French Translation: Rapport CEA-Saclay
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