Abstract:
A method for deicing a rotor blade having a blade root, a blade tip, and a leading edge in which the rotor blade is operably coupled to a hub of a turbine includes circulating heated air through an outflow channel from the blade root towards the blade tip, recirculating the heated air via a return channel from the blade tip to the blade root, whereupon the recirculated heated air becomes returned air, and reheating the returned air for further circulation.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to wind turbines, and more specifically to methods and apparatus for increasing the efficiency of wind turbines.  
         [0002]     Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient.  
         [0003]     Generally, a wind turbine includes a rotor having one or more blades. The rotor is mounted on a housing or nacelle, which is positioned on top of a truss or tubular tower. The turbine&#39;s blades transform wind energy into a rotational torque or force that drives one or more generators, rotationally coupled to the rotor through a gearbox. The gearbox steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid. Gearless direct drive turbines also exist.  
         [0004]     Under some atmospheric conditions, the rotor blades become covered with ice. Ice buildup typically occurs on the leading edge of the airfoil and causes a reduced lifting capability. As the ice layer becomes increasingly thick, weight is added to the airfoil so that the lifting airfoil surface becomes modified. For air turbines, this modification can result in diminished aerodynamic rotor blade performance. (For airfoils on airplanes, a similar loss in performance can result in a crash.)  
         [0005]     Airfoils or rotor blades can be difficult to service due to their operating environment. Installing resistive heating wires or other electrical conductors onto the leading edge of an airfoil can provide a conduit for lightning that renders the airfoil useless. In at least one known technique for reducing icing, an inflatable air bladder has been bonded to the leading edge of airfoils. However, inflation of the air bladder alters the aerodynamics of the airfoil or rotor blade, and the air bladder itself may be or become subject to fatigue and failure in at least some environments.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0006]     There is therefore provided, in some aspects of the present invention, a method for deicing a rotor blade having a blade root, a blade tip, and a leading edge. The rotor blade is operably coupled to a hub of a turbine. The method includes circulating heated air through an outflow channel from the blade root towards the blade tip, recirculating the heated air via a return channel from the blade tip to the blade root, whereupon the recirculated heated air becomes returned air, and reheating the returned air for further circulation.  
         [0007]     In other aspects of the present invention, there is provided a deicing apparatus that includes a turbine or engine having a hub, a rotor blade operably coupled to the turbine or engine and having blade root, a leading edge, a tip, an outflow channel therein from the blade root to the blade tip, and a return channel from the blade tip to the blade root. The return channel is configured to recirculate air flowing through the outflow channel back the to blade root. The deicing apparatus also includes a heater configured to direct heated air through the outflow channel and to reheat the recirculated air.  
         [0008]     In another aspect, the present invention provides a wind turbine having a rotor. The rotor has at least one blade. The wind turbine also has a thermal camera system including a thermal camera that is configured to detect thermal radiation from a leading edge of the rotor blade to determine whether icing exists on the leading edge of the rotor blade.  
         [0009]     It will be appreciated that configurations of the present invention provide effective detection of ice on rotor blades and/or effective deicing of rotor blades.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1  is a drawing of an exemplary wind turbine in which a configuration of the present invention may be utilized.  
         [0011]      FIG. 2  is a diagrammatic view of a wind turbine rotor blade representative of various configurations of the present invention, showing air circulation channels.  
         [0012]      FIG. 3  is a cut-away view of the wind turbine rotor blade of  FIG. 2  along line  3 - 3  showing the air circulation channels and insulation present in some configurations in greater detail.  
         [0013]      FIG. 4  is another view of the wind turbine rotor blade of  FIG. 3 .  
         [0014]      FIG. 5  is a perspective view of a wind turbine configuration that uses a thermal camera to detect icing on a leading edge of an airfoil. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]     In some configurations and referring to  FIGS. 1, 2 , and  4 , the present invention employs blade heating to deice airfoils or rotor blade(s)  10  of a wind turbine  100 . Nacelle  102  of wind turbine  100  may be mounted on a tall tower  104 , only a portion of which is shown in  FIG. 1 . A resistive heating unit  12  coupled with a blower  14  is mounted in a hub  16  of a wind turbine  100  or near a blade root  20 . Heated air  22  is directed through a outflow channel  24  from blade root  20  towards blade tip  26  and then recirculated  28  via a return channel  30  from blade tip  26  to blade root  20 , whereupon heating unit  12  reheats the return air  28 . In this manner, warm return air  28  insulates outgoing hot air  22  and heat is dissipated primarily into the leading edge  32  of rotor blade  10 . In some configurations and referring to  FIG. 3 , Insulation  34  can be added to an outside wall  36  of return channel  30  to optimize heat transfer to leading edge  32 . Electrical power is provided to resistive heating unit  12  and blower  14  via a slipring (not shown), so that rotation of hub  16  (and hence, rotor blades  10 ) is not impeded.  
         [0016]     Thus, in some configurations, a rotor blade deicing system  10  comprises at least one heater element  12  located near either a rotor blade root  20  or hub  16 . Heater element  12  is coupled to a blower or fan  14  to circulate heated air  22  from heater element or elements  12 . Heated air  22  is then directed into a “c” channel  24  installed along leading edge  32  of rotor blade  10 . The “c” channel  24  is located inside rotor blade  10 . Further, “c” channel  24  forms a tube because it is bonded or otherwise attached to the inside of leading edge  32  of rotor blade  10 . Therefore, in some configurations, heated air  22  flows from heating unit  12  along leading edge  32  of rotor blade  10  inside a contained tube  24 . Heated air  22  flows from root  20  of rotor blade  10  towards tip  26 . When heated air  22  reaches tip  26  or a point near tip  26 , its flow direction is reversed by directing the flow through a return tube  30  which forms a “C” shell of “c” channel  24 . Thus, in some configurations, the effect is effectively similar to a tube inside a tube or a shelled tube with the hottest air on the inside and the cooler, return air on the outside. Advantageously, heated air  28  from return path  30  partially insulates heated air  22  in outgoing path  24  and the return heated air  28  is re-heated, i.e., the air being heated is in a closed or nearly closed circuit.  
         [0017]     In some configurations, “c” channel  24  forms a tube because it is bonded to the inside surface of leading edge  32  of rotor blade  10 . Also, as used herein, a lower case “c” refers to an interior tube  24  containing the hottest heat-unit  12  discharge air  22 , whereas an upper case “C” refers to the shell or exterior tube  30  enclosing a return path and containing relatively cooler air  28 . Outer “C” shell  30  is insulated  34  in some configurations to reduce thermal losses to the inside of rotor blade  10 . The “c” or “C” shape used in many configurations of the present invention advantageously increases or optimizes heat transfer to leading edge  32  of rotor blade  10 .  
         [0018]     A higher temperature and/or a greater volume of heated air may be required to melt blade ice under some atmospheric conditions. Therefore, heater  12  and/or blower  14  are adjustable in some configurations to adjust either or both of the volume of heated air or the temperature of the heated air in accordance with ambient atmospheric conditions to melt ice.  
         [0019]     In some other configurations of the present invention and referring to  FIG. 5 , ice is detected using a thermal camera system  40  including a thermal camera that is aimed at a leading edge  32  of rotor blade  10  and configured to detect thermal radiation from leading edge  32 . The system is configured to utilize sensors (not shown) to detect or otherwise estimate or infer physical parameters that may include of thermal output, airflow rate, thermal conductivity, and/or atmospheric conditions (such as temperature and/or wind speed). These estimates or measurements of thermal parameters are used by thermal camera system  40  along with detected radiation  44  to determine icing on leading edge(s)  32  of rotor blade(s)  10 . Paint  42  (e.g., black paint) applied to leading edges  32  of rotor blades  10  in some configurations allows icing to be detected with thermal camera  40  without having to pre-heat blades  10 .  
         [0020]     In some configurations, specific leading-edge zones of a rotor blade are heated. For example, in some configurations, a linear or rotational actuator is provided for the interior “c” tube or tubes. Hot discharge air that flows outward through the shell is returned via a selected path by using the actuator to rotate or move the interior “c” tube to align with a selected duct slot.  
         [0021]     It will thus be appreciated that various configurations of the present invention are effective for deicing and/or detecting icing on rotor blades and airfoils, and are particularly useful in conjunction with wind turbines.  
         [0022]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.