Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SYSTEM AND METHOD FOR AN ELECTRICAL DE-ICING COATING
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to methods, systems and structures for modifying ice
adhesion strength between ice and selected objects. More particularly, the
invention
relates to methods, systems and structures that apply electrical energy to the
interface
between ice and objects so as to either increase or decrease the ice adhesion
strength to facilitate desired results.
2. Statement of the Problem
Ice adhesion to certain surfaces causes many problems. For example,
excessive ice accumulation on aircraft wings endangers the plane and its
passengers.
Ice on ship hulls creates navigational difficulties, the expenditure of
additional power
to navigate through water and ice, and certain unsafe conditions. The need to
scrape
ice that forms on automobile windshields is regarded by most adults as a
bothersome
and recurring chore; and any residual ice risks driver visibility and safety.
Icing and ice adhesion also causes problems with helicopter blades, and with
public roads. Billions of dollars are spent on ice and snow removal and
control. Ice
also adheres to metals, plastics, glasses and ceramics, creating other day-to-
day
difficulties. Icing on power lines is also problematic. Icing adds weight to
the power
lines which causes power outages, costing billions of dollars in direct and
indirect
costs.
In the prior art, methods for dealing with ice adhesion vary, though most
techniques involve some form of scraping, melting or breaking. For example,
the
aircraft industry utilizes a de-icing solution such as ethyl glycol to douse
aircraft wings
so as to melt the ice thereon. This process is both costly and environmentally
hazardous; however, the risk to passenger safety warrants its use. Other
aircraft
utilize a rubber tube aligned along the front of the aircraft wing, whereby
the tube is
periodically inflated to break any ice disposed thereon. Still other aircraft
redirect jet
engine heat onto the wing so as to melt the ice.
These prior art methods have limitations and difficulties. First, prop-
propelled
aircraft do not have jet engines. Secondly, rubber tubing on the front of
aircraft wings
is not aerodynamically efficient. Third, de-icing costs are extremely high, at
$2500-
$3500 per application; and it can be applied up to about ten times per day on
some
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aircraft. With respect to other types of objects, heating
ice and snow is common. But, heating of some objects is
technically impractical. Also, large energy expenditures
and complex heating apparati often make heating too
expensive.
The above-referenced problems generally derive
from the propensity of ice to form on and stick to surfaces.
However, ice also creates difficulties in that it has an
extremely low coefficient of friction. Each year, for
example, ice on the roadway causes numerous automobile
accidents, costing both human life and extensive property
damage. If automobile tires gripped ice more efficiently,
there would likely be fewer accidents.
U.S. Patent No. 6,027,075 discloses certain
embodiments of an invention in which electrical energy in
the form of a direct current ("DC") bias is applied to the
interface between ice and the object that the ice covers.
As a result, the ice adhesion strength of the ice to the
surface of the object is modified. Typically, the ice
adhesion strength is decreased, making it possible to remove
ice from the object by wind pressure, buffeting or light
manual brushing. In other applications, the ice adhesion
strength between ice and surfaces of objects in contact with
the ice are increased. For example, when the ice adhesion
strength is increased between automobile tires and icy
roadways, there is less slippage and fewer accidents. In
general, if a charge is generated at the interface of ice in
contact with an object, it is possible to selectively modify
the adhesion between the ice and the object.
In general, U.S. Patent No. 6,027,075 discloses a
power source connected to apply a DC voltage across the
interface between ice and the surface upon which the ice
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forms. By way of example, the object having the conductive
surface can be an aircraft wing or a ship's hull (or even the
paint applied to the structure). U.S. Patent No. 6,027,075
discloses a first electrode connected with the surface; a
nonconductive or electrically insulating material is applied
as a grid over the surface; and a second electrode is formed
by applying a conductive material, for example conductive
paint, over the insulating material, but without contacting
the surface. A practical problem, however, with the grid
electrode system disclosed in U.S. Patent No. 6,027,075 is
formation of the grid electrodes and associated insulating
layers. The individual components of the grid system,
including electrodes, wiring and insulators, are fabricated
on a small scale. Photolithographic techniques are capable
of fabricating
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such grid systems. Photolithography is used very effectively in integrated
circuit
fabrication. The use of photolithography to form a grid system for modifying
ice
adhesion, however, is less suitable. It involves a large number of patterning
and
etching steps. Applied to ice control technology, photolithography is
expensive,
complicated and unreliable.
SOLUTION
The present invention replaces the grid described in U.S. Patent No.
6,027,075.
An embodiment of the present invention provides a composite coating comprising
separate, closely spaced wire electrodes separated by insulator fibers. The
wire
electrodes and insulator fibers are typically woven together using known and
reliable
industrial technologies. The wire electrodes are connected alternately to a DC
power
source in such a manner to function as cathodes and anodes. The composite
coating
is durable and flexible, and is typically applied to the surface to be
protected using
conventional adhesives. The metal wires may be gold, platinum-plated titanium
or
niobium, or other material with high resistance to electro-corrosion. As
dielectric
insulator fibers, nylon, glass or other dielectric material may be used. The
dielectric
fibers keep the metal electrodes apart, while providing coating integrity. In
addition,
the dielectric insulator fibers electrically insulate the wire electrodes from
the surface
on which the composite coating is applied. Typical wire diameters are in the
range of
from 10 to 100 gym, with the same range of open space between the electrode
wires
and insulator fibers. If ice forms in and over the composite coating, a do
bias is
applied to the electrodes. As a result, the ice adhesion strength at the
interface of the
ice and the surface of the object being protected is modified.
In another embodiment of the invention, the wire electrodes of a composite
coating are connected to a DC bias source so that they have the same DC bias.
The
surface on which the composite coating is applied is electrically conductive
and has
an opposite DC bias. Ice formed in the spaces of the composite coating close
the
electrical circuit.
In another embodiment of the invention, a wire mesh comprising electrically
conductive wires is formed. The wire mesh is disposed on an electrically
conductive
surface, with an insulating layer interposed between the wire mesh and the
surface.
A DC bias is applied to the wire mesh and an opposite DC bias is applied to
the
surface. Ice that is formed in the spaces of the wire mesh closes the
electrical circuit.
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Those skilled in the art should appreciate that
the above-described system can be applied to surfaces of
many objects where it is desired to reduce ice adhesion
strength, such as on car windshields, airplane wings, ship
hulls and power lines. When the invention takes the form of
a composite cloth, it contains both the functional anodes
and cathodes necessary for the system to work. Therefore,
it is not important whether the surface of the object to be
protected is electrically conductive or nonconductive.
The invention may be summarized according to one
aspect as a system for modifying ice adhesion strength of
ice adhered to an electrically conductive surface,
comprising: a composite coating having a wire mesh covering
the surface, the coating including electrically conductive
wires; an electrically nonconductive insulating layer
between the coating and the surface; and a DC power source
for applying a DC bias between the mesh and the surface via
a circuit formed with the ice, wherein application of the DC
bias causes electrolysis of the ice.
According to another aspect the invention provides
a system for modifying ice adhesion strength of ice adhered
to an electrically conductive surface, comprising: a
composite coating covering the surface, the coating having a
plurality of electrically conductive electrode wires and a
plurality of electrically insulating insulator fibers, the
insulator fibers separating each of the electrode wires from
one other and insulating the electrode wires from the
surface; a DC power source for applying a DC bias between
the electrode wires and the surface via a circuit formed
with the ice, wherein application of the DC bias causes
electrolysis of the ice.
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According to another aspect the invention provides
a system for modifying ice adhesion strength of ice adhered
to a surface, comprising: a composite coating covering the
surface, the coating having a plurality of cathode wires, a
plurality of anode wires, and electrically insulating
insulator fibers, the insulator fibers insulating the
cathode wires from the anode wires; a DC power source for
applying a DC bias between the cathode and anode wires via a
circuit formed with the ice.
The invention is next described further in
connection with preferred embodiments, and it will become
apparent that various additions, subtractions, and
modifications can be made by those skilled in the art
without departing from the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the invention may
be obtained by reference to the drawings, in which:
FIG. 1 shows a deicing system incorporating an
electrical coating to deice surfaces in accord with the
invention;
FIG. 2 shows an alternate deicing system
incorporating an electrical coating to deice surfaces in
accord with the invention;
FIG. 3 depicts a composite coating having cathode
wires and anode wires in accordance with the invention that
operates to modify the adhesion of ice formed on a surface;
FIG. 4 depicts a composite coating in accordance
with the invention in which the electrode wires have the
same bias; and
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FIG. 5 depicts a wire mesh in accordance with the
invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention includes methods, systems and
structures which modify ice adhesion strength to objects
such as metals and semiconductors by application of a DC
bias to the interface between the ice and the objects.
FIG. 1 shows one system 10 incorporating an electrical
deicing coating 12 to affect ice 14 that might adhere to
surface 16. Surface 16 may for example be an airplane wing,
helicopter blade, jet inlet, heat exchanger for kitchen and
industrial equipment, refrigerator, road signs, ship
overstructures, or other object subjected to cold, wet and
ice conditions. More
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specifically, coating 12 is applied over surface 16 to protect surface 16 from
ice 14.
Coating 12 is preferably flexible so as to physically conform to the shape of
surface
16. In operation, a voltage is applied to coating 12 by power supply 18.
Typically this
voltage is over two volts and generally between two and one hundred volts,
with
higher voltages being applied for lower temperatures. By way of example, for a
temperature of -10C and an anode-to-cathode spacing of 50Nm within coating 12
(described in more detail below), approximately 20V is applied to coating 12
to provide
lOmA/cm~2 current density through very pure atmospheric ice such as found on
airplane wings.
When voltage is applied, ice 14 decomposes into gaseous oxygen and
hydrogen through electrolysis. Further, gases form within ice 14 generating
high-
pressure bubbles that exfoliate ice 14 from coating 12 (and hence from surface
16).
Typical current density applied to coating 12 is between about 1-10mA/cm~2. If
desired, voltage regulator subsystem 20 is connected in feedback with power
supply
18, and hence with the circuit formed by coating 12 and ice 14, so as to
increase or
decrease DC voltage applied to coating 12 according to optimum conditions.
FIG. 2 shows one system 40 incorporating an electrical deicing coating 42 to
affect ice 44 that might adhere to conductive surface 46.Conductive surface 46
may
for example bean airplane wing, helicopter blade, jet inlet, heat exchanger
for kitchen
and industrial equipment, refridgerator, road signs ship overstructures, or
other object
subjected to cold, wet and ice conditions. More specifically, coating 42 is
applied over
surface 46 to protect surface 46 from ice 44. Coating 42 is preferably
flexible so as
to physically conform to the shape of surface 46. In operation, a voltage is
applied
between coating 42 and surface 46 by power supply 48. The bias voltage applied
to
coating 42 may be equal and opposite to the bias voltage applied to surface
46. If
desired, an insulator 45 may be disposed between coating 42 and surface 46;
insulator 45 preferably comprises a dielectric mesh configuration described
below.
Typically the voltage between coating 42 and surface 46 is over two volts and
generally between two and one hundred volts, with higher voltages being
applied for
lower temperatures.
When voltage is applied, ice 44 decomposes into gaseous oxygen and
hydrogen through electrolysis. Further, gases form within ice 44 generating
high-
pressure bubbles that exfoliate ice 44 from coating 42 (and hence from surface
46).
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Typical current density applied to coating 42 is between about 1-10mA/cm~2. If
desired, voltage regulator subsystem 50 is connected in feedback with power
supply
48, and hence with the circuit formed by coating 42, surface 46, and ice 44,
so as to
increase or decrease DC voltage applied to coating 42 according to optimum
conditions.
Systems 10, 40 thus modify the electrostatic interactions which form the
bonding between ice and metals. These interactions are effectively changed
(either
reduced or enhanced) by application ofthe small DC (direct current) bias
between ice
and the metals. As described below, the composite coating comprises metal
electrode wires separated by dielectric insulator fibers in a flexible format
so as to be
applied to surface 16 needing protection from ice. By applying a do bias, the
ice
adhesion strength between ice and the electrodes of coating, as well as
between ice
and surface, is modified.
Ice has certain physical properties which allow the present invention to
selectively modify the adhesion of ice to conductive (and semi-conductive)
surfaces.
If a charge is generated on the surface coming on contact with ice, it is
possible to
selectively modify the adhesion between the two surfaces. First, ice is a
protonic
semiconductor, a small class of semiconductors whose charge carriers are
protons
rather than electrons. This phenomenon results from hydrogen bonding within
the
ice. Similar to typical electron-based semiconductors, ice is electrically
conductive,
although this electrical conductivity is generally weak.
Another physical property of ice is that its surface is covered with a liquid-
like
layer ("LLL"). The LLL has important physical characteristics. First, the LLL
is only
nanometers thick. Second, it ranges in viscosity from almost water-like, at
temperatures at or near to freezing, to very viscous at lower temperatures.
Further,
the LLL exists at temperatures as low as -100 C.
The LLL is also a major factor of ice adhesion strength. The combination of
the semiconductive properties of ice and the LLL allows one to selectively
manipulate
ice adhesion strength between ice and other objects. Generally, water
molecules
within a piece of ice are randomly oriented. On the surface, however, the
molecules
are substantially oriented in the same direction, either outward or inward. As
a result,
all their protons, and hence the positive charges, either face outward or
inward. While
the exact mechanism is unknown, it is likely that the randomness of water
molecules
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transitions to an ordered orientation within the LLL. However, the practical
result of
the ordering is that a high density of electrical charges, either positive or
negative,
occurs at the surface. Accordingly, if a charge is generated on the surface
coming
on contact with ice, it is possible to selectively modify the adhesion between
the two
surfaces. As like charges repel and opposites attract, an externally applied
electrical
bias at the interface of the ice and the other surface either reduces or
enhances the
adhesion of the ice to the other object.
Ice includes polar water molecules that strongly interact with any solid
substrate which has dielectric permittivity different from that of ice. In
addition, there
is theoretical and experimental evidence for the existence of a surface charge
in ice.
This surface charge can also interact with the substrate.
Electrolysis is an important factor. When a do current flows through ice,
gaseous hydrogen (HZ) and oxygen (OZ) accumulate at the ice interfaces in the
form
of small bubbles, due to ice electrolysis. These bubbles play a role in the
development of interfacial cracks, reducing the ice adhesion strength.
FIG. 3 depicts a composite coating 100 having cathode wires 102 and anode
wires 104, in accordance with the invention. Dielectric wires 106 form an
insulating
weave about wires 102, 104 to prevent shorting. Wires 102, 104 for example
connect
to power supply 18 (or supply 48) such that appropriate current density
affects ice
adhering to coating 100. Typically, the current density is made to decrease
adhesion
strength between ice and coating 100, such that coating 100 operates to
protect
surfaces, such as surface 16, from ice. Typical spacings between wires 102 are
10-
50pm; typical spacings between wires 104 are also 10-50pm. Wires 102, 104 are
for
example made from gold, platinum plated titanium or niobium, orfrom metal with
high
resistance to electro-corrosion.
FIG. 4 depicts a composite coating 120 in accordance with the invention.
Coating 120 has alternating electrode wires 122, each with equal bias from the
connected power supply. Coating 120 may for example be applied to surface 46
of
FIG. 2, where surface 46 is conductive; a voltage potential exists between
surface 46
and wires 122. An insulating mesh 124 prevents wires 122 from shorting, and
further
prevents shorting between wires 122 and surface 46. Ice 44 completes the
circuit
between wires 122 and surface 46 to invoke the ice adhesion modifications of
the
invention.
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FIG. 5 depicts a wire mesh coating 150 constructed in accordance with the
invention. Mesh coating 150 is generally conductive, with both wires 152 and
weave
components 154 being conductive. Mesh coating 150 is thus applied to
conductive
surface 46 with an insulator 45 disposed therebetween. Insulator 45 is
constructed
so as to protect surface 46 when ice 44 completes the circuit between mesh
coating
150 and surface 46. A voltage potential between mesh coating 150 and surface
46
modifies the adhesion strength of ice 44 as desired.
A typical current density applied to coatings of the invention are from 1 to
10
mA/cm2. Operating voltages are typically in the range of from 2 to about 100
volts,
depending on ice temperature and spacing between wires. The lower the
temperature, the higher the voltage required. The larger the interwire
spacing, the
higher the voltage required. For a typical temperature of -10°C and a
spacing of 50
,um, a bias of approximately 20 volts provides a current density of about 10
mA/cmz
through very pure ice.
It is important that anode wires 104, FIG. 3) have a very high resistance to
anodic corrosion. For that, they may be coated with thin layers of platinum or
gold or
amorphous carbon. Other alloys may also be applied. Cathode wires 102 should
also be impenetrable to hydrogen. Examples of good cathode material include
gold,
copper, brass, bronze, and silver.
A composite coating or wire mesh in accordance with the invention is flexible.
It can protect a wide variety of surface materials and shapes, including, as
examples:
airplane wings, helicopter blades, protective grids on jet engine inlets, heat
exchangers of kitchen and industrial refrigerators, road signs, and ship
superstructures.
The wire meshes and composite coatings described herein can be fabricated
using conventional methods used in industry. An inventive mesh or composite
coating can be applied to a surface by simply stretching it over the surface
of with a
thin layer of adhesive placed between the composite coating or mesh and the
surface.
In view of the foregoing, what is claimed is:
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