Abstract:
A system for modifying ice adhesion strength of ice adhered to an object comprises a composite coating containing wire electrodes covering the surface to be protected. In one embodiment, a composite coating contains electrode wires and insulator fibers. The composite coating is applied to the surface of an object on which the ice adhesion strength is to be modified. The electrode wires are connected to a dc bias source, and they function as cathodes and anodes alternately. The source generates a DC bias to an interface between the ice and the surface when the ice completes the circuit between anode and cathode wires. In another embodiment, a wire mesh is disposed on an electrically conductive surface of the object an opposing DC biases are applied to the mesh and the surface. In another embodiment, the coating has anode and cathode wires woven by insulator fibers as a composite cloth applied to the surface to protect the surface from ice.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    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.  
           [0003]    2. Statement of the Problem  
           [0004]    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.  
           [0005]    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.  
           [0006]    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 deicing 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.  
           [0007]    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. 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.  
           [0008]    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.  
           [0009]    U.S. Pat. No. 6,027,075, incorporated herein by reference, 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 a object, it is possible to selectively modify the adhesion between the ice and the object.  
           [0010]    In general, U.S. Pat. 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 forms. By way of example, the object having the conductive surface can be an aircraft wing or a ship&#39;s hull (or even the paint applied to the structure). U.S. Pat. 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. Pat. 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 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  
         [0011]    The present invention replaces the grid described in U.S. Pat. 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 μm, with the same range of open space between the electrode wires and insulator fibers. If ice forms in and over the composite coating, a dc 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.  
           [0012]    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.  
           [0013]    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.  
           [0014]    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.  
           [0015]    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  
       [0016]    A more complete understanding of the invention may be obtained by reference to the drawings, in which:  
         [0017]    [0017]FIG. 1 shows a deicing system incorporating an electrical coating to deice surfaces in accord with the invention;  
         [0018]    [0018]FIG. 2 shows an alternate deicing system incorporating an electrical coating to deice surfaces in accord with the invention;  
         [0019]    [0019]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;  
         [0020]    [0020]FIG. 4 depicts a composite coating in accordance with the invention in which the electrode wires have the same bias; and  
         [0021]    [0021]FIG. 5 depicts a wire mesh in accordance with the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]    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, refridgerator, road signs, ship overstructures, or other object subjected to cold, wet and ice conditions. More 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 50 μm within coating  12  (described in more detail below), approximately 20V is applied to coating  12  to provide 10 mA/cm{circumflex over ( )}2 current density through very pure atomospheric ice such as found on airplane wings.  
         [0023]    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 1-10 mA/cm{circumflex over ( )}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.  
         [0024]    [0024]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 be an 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.  
         [0025]    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.  
         [0026]    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 ). Typical current density applied to coating  42  is between about 1-10 mA/cm{circumflex over ( )}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.  
         [0027]    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 of the 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 dc bias, the ice adhesion strength between ice and the electrodes of coating, as well as between ice and surface, is modified.  
         [0028]    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.  
         [0029]    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.  
         [0030]    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 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.  
         [0031]    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.  
         [0032]    Electrolysis is an important factor. When a dc current flows through ice, gaseous hydrogen (H 2 ) and oxygen (O 2 ) 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.  
         [0033]    [0033]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 10-50 μm; typical spacings between wires  104  are also 10-50 μm. Wires  102 , 104  are for example made from gold, platinum plated titanium or niobium, or from metal with high resistance to electro-corrosion.  
         [0034]    [0034]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.  
         [0035]    [0035]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.  
         [0036]    A typical current density applied to coatings of the invention are from 1 to 10 mA/cm 2 . 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 μm, a bias of approximately 20 volts provides a current density of about 10 mA/cm 2  through very pure ice.  
         [0037]    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.  
         [0038]    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.  
         [0039]    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.  
         [0040]    In view of the foregoing, what is claimed is: