Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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WATER CONSERVATION USING FLOATING OPTICALLY-REFLECTIVE DEVICES
Cross References to Related Applications
This application claims priority from U.S. Provisional Patent Application
Serial No.
62/081,544, entitled "Water conservation using floating reflectors", filed on
November 18, 2014,
which is hereby incorporated by reference as if set forth in full in this
application for all
purposes.
Background
Conservation of water is a matter of great concern and interest, especially at
times of
ongoing or anticipated drought. Issues of potential environmental damage,
human displacement,
and overall costs are serious disincentives to infrastructural approaches such
as constructing or
expanding reservoirs or building dams. Evaporation due to absorption of
incident sunlight by the
water in existing reservoirs makes up a significant fraction of potentially
avoidable water loss.
Simple surface covers, as currently used to prevent water loss in small ponds
or swimming pools
by physically blocking evaporation, can reduce gas exchange, block incident
light and increase
underlying water temperature, so even if such covers could be scaled up to
reservoir-size, they
would have very negative consequences to the ecosystem of the reservoir.
Covering the water surface using surface films of oils and hydrocarbon-based
materials
has also been proposed. This has the additional disadvantage of adding a non-
aqueous liquid, and
potential pollutant, to the reservoirs.
It is therefore desirable to provide a scalable method of reducing absorption
of incident
sunlight that allows adequate atmospheric gas exchange. The ability to keep
underlying water
temperature within a predetermined range, and to avoid permanently shading any
particular
region without introducing potential pollutants would be additional desirable
features.
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Summary
The present invention includes a method for conserving water in a reservoir.
In one
embodiment, the method comprises deploying onto the upper surface of water in
a reservoir a
floatable device with a wettable lower surface, wherein the device comprises a
first element and
a second element, the first element providing the device with a high albedo
upper surface. In
one embodiment, the first element comprises a plurality of highly reflective
particles and the
second element comprises a binder configured to hold the reflective particles
together. In one
embodiment the reflective particles comprise hollow glass spheres and the
binder comprises a
biodegradable bioplastic.
Brief Description of the Drawings
Figure 1 is a cross section view illustrating a floatable high albedo device
with a wettable
lower surface according to one embodiment.
Figure 2 is a top-down view illustrating a floatable high albedo wettable
device according
to another embodiment.
Figure 3 is a flowchart illustrating the steps of a method for using a
floatable high albedo
device with a wettable lower surface to conserve water according to one
embodiment.
Figure 4 is a flowchart illustrating the steps of a method for forming a
floatable high
albedo device with a wettable lower surface according to one embodiment.
Figure 5 is a flowchart illustrating the steps of a method for using a
floatable high albedo
device with a wettable lower surface to cool a body containing water trapped
in the form of ice,
snow, or permafrost, according to one embodiment.
Detailed Description
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The manner in which the present invention provides its advantages can be more
easily
understood with reference to Figures 1 and 2.
Figure 1 shows a device with a high albedo upper surface 106. The device
comprises a
first element 102, which in the shown embodiment takes the form of a plurality
of highly
reflective particles, which provide the high albedo upper surface. In some
embodiments the
particles may be hollow glass particles, which may be spherical. In other
embodiments, the
particles may be porous and/or non-spherical. The lower surface of the device
is wettable, such
that when the device is positioned on the upper surface of a body of water,
the water makes good
contact with the device's lower surface, wetting it. The device further
comprises a second
element 104, which acts as a binder to hold the particles of the first element
together. In some
embodiments the second element may also be responsible for providing the
device with a highly
wettable lower surface 108. In these cases, the second element may be chosen
in part for its
ability to bind the particles together by making strong bonds to the
particles' surfaces, and in part
for characteristics enabling the resulting composite of particles and binder
to exhibit high
wettability. In other embodiments, the first element may be responsible for
providing the device
with a highly wettable lower surface.
In some embodiments, the wettability may be provided by a third element, not
shown in
Figure 1, rather than by the second element.
Wettability offers several advantages to the device. One is that it helps the
device "cling"
to the water surface, so that it will be less likely to be lifted off or blown
away in windy or
stormy conditions. Another is that the underlying water can be drawn into the
thickness of the
device, penetrating to the upper surface, where gas exchange may occur with
the overlying
atmosphere. In some embodiments the device may comprise an element having high
porosity,
facilitating the water penetration and gas exchange. In some embodiments the
high porosity
element may be the same element as the second element
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In some embodiments, the entire lower surface of the device may be wettable.
In some
cases, adequate cling and gas exchange may be achieved with a fraction of the
lower surface
significantly less than 100% being wettable.
In some embodiments, the binding material may be dispensed with altogether,
and the
particles of the first element may be enclosed within a container such as a
mesh bag. The shape
and relative volume of the container with respect to the volume of the
contained particles may be
chosen such that when the device is allowed to float on a water surface, there
are sufficient
spaces between the particles to allow gas exchange to occur. Wettability may
not be a relevant
parameter in these embodiments.
In some embodiments, whether or not a binder is used, a container used to
restrict the
area over which the reflective particles spread may be a boom, such as those
used to contain oil
spills, rather than a more completely enclosing structure such as a mesh bag.
Figure 2 is a top-down view illustrating one embodiment 200 including floating
reflective particles 202 whose spread over the surface of a body of water,
indicated by dashed
lines, is confined to a limited area by a floating boom 210.
It should be noted that the density and dimensions of the particles relative
to the surfaces
and dimensions of device 100 are not shown to scale in Figures 1 and 2.
Figure 3 is a flowchart of the steps of a method 300 for using a device of the
type shown
in Figure 1 to conserve water in a reservoir. In step 302, a floatable device
comprising a first
element and a second element is obtained, the device having a wettable lower
surface and a high
albedo upper surface, the high albedo upper surface being provided by the
first element. In step
304, the device is deployed onto the top surface of water in the reservoir.
Figure 4 is a flowchart of the steps of a method 400 for making a device of
the type
shown in Figure 1. At step 402, a first element with high reflectivity is
obtained. At step 404, a
second binding element is obtained. At step 406, the first and second elements
are mixed
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together, and shaped as desired. At step 408, the shaped mixture is exposed to
an elevated
temperature for a time sufficient to allow good binding to occur. At step 410,
the resulting heated
mixture is allowed to cool to room temperature, forming the desired device. In
some
embodiments, a temperature of 325 degrees Fahrenheit for 10 minutes has been
found to be
suitable for an experimental mixture involving hollow glass spheres and PLA -
Polylactic acid or
polylactide, a compostable thermoplastic aliphatic polyester derived from
corn. In this particular
mixture, the glass spheres provide high reflectivity and wettability, while
the PLA is attractive
for its excellent binding properties, its non-toxicity, its biological
derivation and compostability,
and its brightness. Glass is also a very good choice for its innocuousness in
the natural
environment.
Examples of glass-based commercially available products that may be considered
for the
particles of the first element include perlite, an amorphous volcanic glass,
3MTM Glass Bubbles
Kl, and Poraver beads formed from post-consumer recycled glass.
In the water conservation applications of most interest to the present
invention, it is
envisaged that a plurality of devices such as the one shown in Figure 1 may be
deployed to float
on the upper surface of the body of water of interest. It may be desirable to
limit the fraction of
the water surface area covered by these devices to well under 100%, in order
to maintain
adequate levels of gas exchange between the water and the overlying
atmosphere. In one
embodiment, the number of devices deployed may be chosen such that no more
than 30% of the
total water surface would be covered.
In some embodiments, each device may be formed to include one or more through
holes
that extend through the thickness to facilitate gas exchange between the
underlying water and the
overlying atmosphere.
It some embodiments, each deployed device may be allowed to float freely over
the water
surface. However, there may be advantages to constraining the motion of the
device to some
extent. Prevailing wind and currents may act to drive all the devices towards
one end of the
reservoir, maybe even piling them up against the banks, so reducing coverage
to below the
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desired levels. Even if the devices remain separate, so that the total covered
volume remains
constant, there may be negative consequences to aquatic life if one portion of
the water surface is
continuously kept shaded. Another problem is the practical consideration of
how difficult it may
be to gather up a large number of freely floating devices when desired, for
example, prior to
removing and/or replacing them.
These problems may be addressed by designing the floatable device to include a
central
member that can be attached to a restraining or anchoring device that in turn
is attached either to
the bed of the reservoir, or the shore, or a dock. The attachment may be fully
rigid, hinged or
pivoting, or even flexible, for example with some sort of rubbery connecting
member. Portions
of the floatable device other than the central member may themselves be
attached to the central
member by rigid, hinged, pivoting, or flexible means. In all these cases, the
resulting constrained
area of movement will enable the devices to be relatively easily accessed for
removal or
replacement, and will avoid the potential weather-driven concentration of
devices at one portion
of the reservoir. In some embodiments where non-rigid attachments as discussed
above are used,
there will be the additional advantage that small movements of the high albedo
surface
responsive to wind and currents can occur and will typically "average out" the
shading of the
underlying water.
The methods and apparatus described herein may also be advantageous in
applications
other than the water conservation of immediate interest as described. One
example is to help
stabilize permafrost, with a possible side benefit of preventing release of
methane (a powerful
greenhouse gas). Other possibilities include snow stabilization, avalanche
prevention,
maintaining lower temperatures in glacial melt ponds, and in flood control.
The materials used
must be carefully selected for appropriate levels of safety, to humans and the
environment as a
whole, in any and all such deployment locations.
Figure 5 is a flowchart of the steps of a method 500 for using a device of the
type shown
in Figure 1 to cool a body containing water trapped in the form of ice, snow,
or permafrost. In
step 502, a floatable device comprising a first element and a second element
is obtained, the
device having a wettable lower surface and a high albedo upper surface, the
high albedo upper
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surface being provided by the first element. In step 304, the device is
deployed onto the top
surface of the body.
The term "reservoir" is used in this application to refer to any body of water
with an
upper surface exposed to incident sunlight. As such, it includes man-made
reservoirs and
naturally occurring lakes and other similar bodies that could be considered to
be water sources
for human use.
The term "wettable" as a characteristic of a material surface is used in this
application to
mean hydrophilic or able to be easily and thoroughly wetted by water. The
contact angle between
water and a wettable surface is less than 90 degrees, possibly even 0 degrees.
The terms "highly reflective" and "high albedo" are used in this application
to mean
having a reflectivity over the visible spectrum greater than15% (which is
higher than the average
reflectivity of an exposed water surface to incident sunlight) and preferably
greater than 90%.
Values in these reflectivity ranges are significantly greater than the average
reflectivity of water
to incident sunlight.
Embodiments of the present invention thus enable the environmentally benign
generation
and deployment of high albedo devices to areas in which the resulting cooling
of the surface (e.g.
water, permafrost, snow, ice etc) in the vicinity of the deployment may be
highly beneficial.
The above-described embodiments should be considered as examples of the
present
invention, rather than as limiting the scope of the invention. Various
modifications of the above-
described embodiments of the present invention will become apparent to those
skilled in the art
from the foregoing description and accompanying drawings. Accordingly, the
present invention
is to be limited solely by the scope of the following claims.
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