Aeronautics and astronautics – Aircraft structure – Ice prevention
Reexamination Certificate
2001-06-12
2002-08-06
Jordan, Charles T. (Department: 3644)
Aeronautics and astronautics
Aircraft structure
Ice prevention
C244S13400A
Reexamination Certificate
active
06427946
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to methods and apparatus for modifying ice adhesion strength between ice and selected materials. More particularly, the invention relates to systems and methods which apply electrical energy to the interface between ice and such materials so as to either increase or decrease the ice adhesion strength to facilitate desired results.
BACKGROUND
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 aircraft!
The above-referenced problems generally derive from the propensity of ice to stick and form onto 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.
It is, accordingly, an object of the invention to provide systems and methods which modify ice adhesion strength beneficially.
A further object of the invention is to provide systems for reducing ice adhesion on vehicle surfaces such as aircraft wings, ship hulls and windshields to facilitate ice removal.
Still another object of the invention is to provide systems for increasing the coefficient of friction between ice-clad roads and automobile tires, and between ice and other objects such as shoe soles and cross-country skis.
These and other objects will become apparent in the description which follows.
SUMMARY OF THE INVENTION
Certain of above-referenced problems would be lessened if the ice adhesion strength were decreased between the ice and the surface upon which the ice forms. For example, if the adhesion strength between the ice and an aircraft wing were decreased sufficiently, wind pressure, buffeting or light manual brushing would remove the ice from the wing. Similarly, scraping an automobile windshield so as to be free of ice would be much less difficult if the ice adhesion strength between the ice and the windshield were lessened.
Other above-referenced problems would be lessened if the ice adhesion strength between ice and surfaces in contact with the ice were increased. For example, if the ice adhesion strength were increased between automobile tires and icy roadways, then there would be less slippage and fewer accidents.
Ice has certain physical properties which allow the present invention to selectively modify the adhesion of ice to conductive (and semi-conductive) 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. Hydrogen bonding occurs because the hydrogen atoms of water molecules in ice share their electrons with an oxygen atom. Thus, the nucleus of the water molecule—uniquely a single proton—remains available to bond with adjacent water molecules.
Similar to typical electron-based semiconductors, ice is electrically conductive. While this electrical conductivity is generally weak, the conductivity can be altered by adding chemical agents that donate or accept extra charge-carrying particles, i.e., protons in the case of ice.
Another physical property of ice is its evaporability. Evaporability of a substance is a function of vapor pressure at the substance surface. In most materials, vapor pressure drops rapidly at the liquid-to-solid interface. In ice, however, there is virtually no change in vapor pressure at the liquid-to-solid interface. The reason for this is that the surface of ice 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., and thus practically exists for most temperatures around the planet.
The LLL is also a major factor of ice adhesion strength. For example, if one brings the smooth surface of ice in contact with the smooth surface of an airplane wing, the actual area of contact between the two surfaces is on the order of one-thousandth of the total interface area between the two surfaces. The LLL functions as a wetting substance between the surfaces—the principal behind almost all adhesives—and substantially increases the effective contact area between the surfaces. This increase in contact area strongly affects ice adhesion.
The combination of the semiconductive properties of ice and the LLL allows one to selectively manipulate ice adhesion strength between ice and other surfaces. 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 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 between the ice and the surface.
In one aspect, the invention provides a power source connected to apply a DC voltage across the interface between ice and the surface upon which the ice forms. By way of example, the conductive surface can be an aircraft wing or a ship's hull (or even the paint applied to the structure). A first electrode connects 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. The surface area of the second electrode should be small as compared to th
Dinh T.
Lathrop & Gage L.C.
Trustees of Dartmouth College
Vock Curtis A.
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