A Study of Dew Water Yields on Galvanized Iron Roof in Kothara (North-West India)

In order to determine what amount of dew water can be collected without much investment during the dry season (October –May) in north - west India, a study was performed on plain, un-insulated, corrugated galvanized iron roofs that are common in this rural region. Between October 1, 2004 and May 31, 2005, the cumulative dew yield on a 18 m2 double - sloped (30�) test roof was 113.5 L. The west side gave 35 % higher water yield than the east side. The use of thermal insulation and more IR radiative materials would have increased this yield by 40 % (160 L). An analysis of dew events is made with meteorological data. It shows that the variable relative humidity is the most important parameter, which in turn is strongly correlated with the average wind direction with respect to monsoon direction. The cumulative dew water yield (6.3 mm) remains modest when compared with the average rain fall (300 mm). But dew occurs far more frequently than rain and it forms precisely during the dry season when water is most scarce.

Fog and Dew Collection Projects in Croatia

The present paper discusses the fog and dew water collection in Croatia. Zavizan, the highest meteorological station in Croatia(1594m) is chosen for collecting of fog water with a standard fog collector (SFC). The highest daily collection rate was 27.8 L / m2. The highest daily collection rate in days without rain was 19.1 l/m2. Dew is also a noticeable source of water, especially during the drier summer season. Dew condensers in Croatia have been installed on the Adriatic coast (Zadar) and islands Vis and Bisevo. We report and discuss the data collected since 2003. In the small Bisevo island, a special roof has been designed to improve the formation and collection of dew on a house. Data from April 2005 will be presented and discussed.Comment: accessible sur http://balwois.mpl.ird.fr/balwois/administration/full_paper/ffp-587.pd

Dew, fog, and rain as supplementary sources of water in south-western Morocco

International audienceThis study reports on one year (May 1, 2007 - April 30, 2008) of dew, fog and rain measurements carried out in the dryland area of Mirleft, Morocco in order to be used as alternative or supplemental sources of water. Four standard dew condensers and a passive fog net collector of 1 m² surfaces were used. Meteorological data were collected. 178 dew events (18.85 mm), 31 rain events (48.65 mm) and 7 significant fog episodes (1.41 mm) occurred, corresponding to almost 40% of the yearly rain contribution (48.65 mm, 31 events). Chemical and biological analyses were carried out. Dew and rain pH were neutral (close to 7) and the total mineralization was considerable (dew: 560 mg/L; rain: 230 mg/L). Ca²+, K+, SO42- and NO3- are found of continental origin; Cl-, Na+ and Mg2+ are of sea origin. The ions concentration agrees with the World Health Organization recommendations for potable water. The biological analysis shows harmless vegetal spores and little contamination by animal/human bacteria. A cost analysis shows that, with little investment, the population of the arid and semi-arid coastal areas of south-western north Africa could make dew water an interesting supplementary alternative water resource

Water recovery from dew

International audienceThe 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 Cent. to build artificial dew-catching constructions which were subsequently abandoned because of their low yield. The idea of dew collection is revised in the light 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

Dew condensation on desert beetle skin

Some tenebrionind beetles inhabiting the Namib desert are known for using their body to collect water droplets from wind-blown fogs. We aim to determine whether dew water collection is also possible for desert insects. For this purpose, we investigated the infra-red emissivity, and the wetting and structural properties, of the surface of the elytra of a preserved specimen of Physasterna cribripes (Tenebrionidæ) beetle, where the macro-structure appears as a series of “bumps”, with “valleys” between them. Dew formation experiments were carried out in a condensation chamber. The surface properties (infra-red emissivity, wetting properties) were dominated by the wax at the elytra surface and, to a lower extent, its micro-structure. We performed scanning electron microscope on histological sections and determined the infra-red emissivity using a scanning pyrometer. The emissivity measured (0.95 ± 0.07 between 8–14 μm) was close to the black body value. Dew formation occurred on the insect’s elytra, which can be explained by these surface properties. From the surface coverage of the condensed drops it was found that dew forms primarily in the valleys between the bumps. The difference in droplet nucleation rate between bumps and valleys can be attributed to the hexagonal microstructure on the surface of the valleys, whereas the surface of the bumps is smooth. The drops can slide when they reach a critical size, and be collected at the insect’s mouth

Condenseurs Radiatifs de Rosée.

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Roofs as dew collectors: III. Special Polyethylene foil on a school in Sayara (NW India)

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Dew Water Physical and Chemical Characteristics in Tropical Climate (French Polynesia).

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