Environmental Engineering Reference
In-Depth Information
typical unit of 1600 m
2
of mesh produces an average of 12,000 liters (12 m
3
) of water a day
or roughly 7.5 L/m
2
/day, enough to sustain communities of 10,000 inhabitants or more.
Structures of PAFCs suitably treated have been able to achieve maximum outputs in ideal
conditions of 42 L/m
2
/day, and nearly a 6-fold increase. The variables affecting the efi-
ciency of harvesting are increased with the larger fog droplet size, during higher wind
speeds, and with narrower collection ibers/mesh widths. An analysis of wind speed,
wind direction, temperature, relative humidity, dew point, barometric pressure, solar
radiation, precipitation, and such atmospheric measurements will ultimately determine
the feasibility of PAFC use by accurately predicting the resulting potential amount of
water captured.
Today's most widely used material for atmospheric capture is polypropylene rafia, also
called “raschel,” which is a material classiied under a class of mosquito netting fabric
types (manufactured using Raschel knitting machines). This raschel can be coated with
different nanomaterial surfaces by using sol-gel techniques, which can either be furnished
by air gun, or controlled by immersion and subsequent forced drying.
The polypropylene itself is ultraviolet protected to avoid breakdown, allowing fur-
ther eficiency increases with smaller mesh sizes and iber widths. The application of
nanotechnology-coated screens for these new systems by using treated mesh showed
marked improvements in yields by nearly 30% in comparison to untreated screens [2].
With the results obtained by other researchers and the availability of optimal weather
condition sites in the ield, and with the combination of variable climate hosted in wind
tunnel chambers found in specialized laboratories, substantial progress toward optimiza-
tion of yields has been achieved. Applied research characterized by dedicated AWC har-
vesting methods has provided surprisingly rewarding results [3].
This research is not only being applied to raschel but also to a host of other substrates
that are better able to withstand harsh environmental conditions such as wind or snow,
in order to collect mist or fog and any form of water in the atmosphere, including haze,
drizzle rain, dew and even snow itself.
The careful consideration of the design of the materials used and the precise placement
of these fog fences, combined with their architecture, depend on the local weather condi-
tions. Maximizing the vertical capture as well as the horizontal capture is a key consider-
ation taken before their implementation (Figure 29.1).
Atmospheric water capture (AWC), as a general term for this technology, was irst coined
and adopted to distinguish it from the existing classiications for other types of water col-
lection methods, including surface, underground, continental, etc.
By limiting the ield to the water present in the atmosphere but has not yet precipitated
to the ground, great strides have been made and are now set for an important evolution.
Despite ongoing interest by dedicated researchers, the new and rapid advancements in
sail designs, including wind-driven turbines, and the latest developments in computer
modeling methods of the atmospheric conditions or luid dynamics coupled with and
optimized by material science in nanostructured coatings, improving such systems has
yet to be widely implemented. The purpose of this chapter is to place this new technology
into the hands of society, an especially important issue to those areas that suffer most from
the lack of geographic and economical incentives.
This refocused effort on materials and designs of structure has created a stronger case
of economics for atmospheric water harvesting. While we are still a considerable way from
applying the results developed to date, we have, in fact, opened up new possibilities on
obtaining the most water yields from the atmosphere with architectures that can be eco-
nomically built in order to provide water where it would not be economically feasible in
