Abstract:
A fan blade assembly is provided. The fan blade assembly may include; a fan blade having an airfoil shaped section, formed by being run lengthwise though a die and a flap portion integral with the airfoil section also run lengthwise through the die, the fan blade having a hub end and a tip end, a tapering trailing edge on a trailing edge of the fan blade defined by removing a portion of the trailing edge of the fan blade after it has been run through the die, the tapering trailing edge defining the fan blade to be narrower moving from the hub end toward the tip end, and a flared portion interrupting the tapering trailing edge near the tip end, the flared portion defining the fan blade to become wider from the beginning of the flared portion to the tip end. A method for making a fan blade may also be provided.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to a fan blade. More particularly, the present invention relates to a protruded or extruded fan blade having a geometry to achieve high efficiency. 
       BACKGROUND OF THE INVENTION 
       [0002]    It is generally understood in axial fan design, that a factor relevant to high efficiency operation is to distribute the exiting air velocity as evenly as possible over the entire length of the fan blade. This is typically accomplished in fan blade design by variation of the airfoil chord and angle along the length of the blade, with the widest chords and highest angles near the slower moving hub end of the blade, and narrower chords and lower angles near the faster moving tip of the blade. 
         [0003]    Fans used in cooling towers and air-cooled heat exchangers are generally placed inside of a shroud to improve their efficiency. While the use of a shroud does improve fan performance there are still losses due to aerodynamic drag along the surface of the shroud and air recirculation between the end of the blade and the surface of the shroud. Overcoming these losses through careful design of the fan blade can further improve the operating efficiency of the fan. Fast and inexpensive fabrication of such a fan blade would be a welcome development. 
         [0004]    Accordingly, it is desirable to provide a method and apparatus that in some embodiments provide a relatively inexpensive fan blade that is capable of efficient operation. 
       SUMMARY OF THE INVENTION 
       [0005]    The foregoing needs are met, to a great extent, by the present invention, wherein in one aspect an apparatus is provided that in some embodiments a relatively efficient fan blade that can be economically produced.          present contribution to the art may be better appreciated. There are, of course, additional embodiments of the invention that will be described below and which will form the subject matter of the claims appended hereto. 
         [0006]    In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of embodiments in addition to those described and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purpose of description and should not be regarded as limiting. 
         [0007]    As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a side view illustrating a cooling tower using a fan blade according to a preferred embodiment of the invention. 
           [0009]      FIG. 2  is a cutaway side view of a fan blade in accordance with the invention. 
           [0010]      FIG. 3  is a side view of a fan in accordance with an embodiment of the invention. 
           [0011]      FIG. 4  is a graph illustrating performance of the fan blade of the fan of  FIG. 3 . 
           [0012]      FIG. 5  is a side view of another fan in accordance with an embodiment of the invention. 
           [0013]      FIG. 6  is a graph illustrating performance of the fan blade of the fan of  FIG. 5 . 
           [0014]      FIG. 7  is a side view of another fan in accordance with an embodiment of the invention. 
           [0015]      FIG. 8  is a graph illustrating performance of the fan blade of the fan of  FIG. 7 . 
           [0016]      FIG. 9  is a side view of another fan in accordance with an embodiment of the invention. 
           [0017]      FIG. 10  is a graph illustrating performance of the fan blade of the fan of  FIG. 9 . 
           [0018]      FIG. 11  is a top view of a fan blade according to the fan shown in  FIG. 9 . 
           [0019]      FIG. 12  is a cross-section view of the fan blade shown in  FIG. 11 . 
           [0020]      FIG. 13  is an exploded view of a fan blade according to an embodiment of the invention. 
           [0021]      FIG. 14  is a side, cross-section view of a fan blade according to the fan of  FIG. 13 . 
           [0022]      FIG. 15  is a top view of a fan blade in accordance with the fan blade of  FIG. 13 . 
           [0023]      FIG. 16 . is an exploded view of a fan blade and a hub assembly. 
           [0024]      FIG. 17  is a front view of a fan blade and hub assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]    An economical, corrosion resistant, light-weight, hollow fan blade for use in cooling towers and air-cooled heat exchangers can be produced by means of extruding a metal, such as aluminum, through a die. Similar hollow profiles may be produced using composite materials by pultruding fiberglass wetted with resin through a die. Fan blades produced by either the extrusion or pultrusion method will initially have a constant chord and constant angle over their entire length. To improve the static pressure capability of these fan blades, it is common to form these blades with an integral trailing edge extension, or flap, that may be flat or upwardly curved. 
         [0026]    For fan blades without a trailing edge flap, or for blades with a trailing edge flap that is not modified after extrusion, the chord and angle of the blade will likely remain constant. The exit air velocity for constant chord, untwisted blades often have a highly uneven distribution with very low air velocity near the fan hub, and much higher air velocity near the tip of the blade. As is common for fans operating within a shroud, there are significant losses due to drag and recirculation near the shroud, 
         [0027]    A method used to simulate twisted and tapered fan blades with an extruded or pultruded profile is to cut a portion of the trailing edge flap diagonally, leaving the widest chord near the hub and the narrowest chord at the tip end of the blade. The amount of taper can have a dramatic effect on the exiting air velocity distribution, and therefore, the efficiency of the fan in operation. As was seen with the constant chord blades, however, there is still a significant reduction in velocity near the tip end due to drag and recirculation losses at the shroud. 
         [0028]    To overcome many of the losses at the tip end of the blade, a new variation in fan blade design has been developed. A “flare-tip” is created by tapering the trailing edge flap over most of the length of the blade, but increasing the chord width near the tip. The flare tip design overcomes drag and recirculation losses at the tip of the blade, providing a more even velocity distribution and, thus, higher operating efficiencies. Various embodiments of the invention will now be described with reference to the drawing figures, in which like reference numerals refer to like parts throughout. Various spacial terms such as front, back, top, bottom, upward, rearward, and other relative terms are intended to provide a reference with respect to the views shown in the drawings and are not intended to be limiting. 
         [0029]    An embodiment in accordance with the present invention provides a fan having multiple fan blades having some of the features described herein. 
         [0030]      FIG. 1  shows a partly cut away side view of a cooling tower  10 . The cooling tower  10  includes a fan  12  located in a shroud  14 . The fan  12  is comprised of fan blades  26  supported by blade shanks  16  that attach to a hub  18 . The hub  18  is attached to a vertical shaft  20  of gear box  21  that is mechanically attached to a drive shaft  22 . The drive shaft  22  is operatively connected to a motor  24 . The motor  24  turns the drive shaft  22 , which turns the vertical shaft  20  of gear box  21 , which turns the hub  18 , which turns the blade shanks  16 , which turn the fan blades  26 . 
         [0031]      FIG. 2  shows a cross-section of a fan blade  26  in accordance with an embodiment of the invention. The fan blade  26  has a hollow air foil section  28  and a trailing edge extension  30 . The geometry of the trailing edge extension  30  (also referred to as flap  30 ) in combination with the other features of the fan blade  26  provides some of the benefits in terms of efficiency. 
         [0032]    The fan blade  26  is supported and attached to the hub  18  by a blade shank  16  extending through at least part of the hollow section  28 . Struts  32  and  34  extend vertically through the hollow section  28  between the upper surface  36  and lower surface  38  to provide support and rigidity to the fan blade  12 . 
         [0033]      FIGS. 3 ,  5 ,  7 , and  9  show fans  12  having four fan blades  26  having various geometries. Other embodiments may use more or fewer blades  26 .  FIGS. 4 ,  6 ,  8 , and  10  show graphs indicating the performance of the fan blade  26  shown in the FIG. immediately preceding the graph. One of ordinary skill in the art may select a fan blade  26  with a geometry having a performance desired for a particular installation. After reviewing this disclosure, one of ordinarily skill in the art may modify and interpolate the data shown in the graphs to arrive at a geometry that will provide an estimated desired performance. 
         [0034]      FIGS. 3 ,  5 ,  7 , and  9  show fans  12  having fan blades  26  attached to a hub  18 . The fan blade  26  includes an upper surface  36  and lower surface  38  and a trailing edge profile  40 . As shown in the trailing edge profiles  40  and the corresponding performance graphs of  FIGS. 3-10 , varying the trailing edge profile  40  may significantly alter performance. 
         [0035]      FIG. 9  shows a fan blade  26  having a tip extension  46  that interrupts the narrowing of the fan blade  26  defined by the sloping of the trailing edge profile  40 . The tip extension  46  causes the width of the fan blade  26  to become longer as the trailing edge profile extends toward the end of the fan blade  26 . 
         [0036]      FIG. 11  shows a fan blade  26  in accordance with an embodiment of the invention. The fan blade  26  has a hub end  42  that is near the hub  18  (not shown in  FIG. 11 ) when the fan blade  26  is attached to a hub  18 . The fan blade  26  has a tip end  44  that is on an opposite end than the hub end  42 . A tip extension  46  may be attached to the tip end  44  of the fan blade  26 . 
         [0037]    The tip end of the fan blade  26  may be equipped with an end cap  47 . The end cap  47  may be made of an injection molded plastic or any other suitable material. The end cap  47  may be attached to the fan blade  26  by rivets  48 . Other suitable attaching means or fasteners may also be used. The end cap  47  may be formed to have a desired geometry for the tip of the fan blade  26  that may be difficult to achieve by extrusion or protrusion of the fan blade  26 . 
         [0038]    A hub cap  50  may be located on the hub end  42  of the fan blade  26 . The hub cap  50  may be attached to the fan blade  26  by rivets  52  or any other suitable means or fasteners. The hub cap  50  may serve to close the hollow airfoil portion  28  of the fan blade  26  and reduce the likelihood of foreign matter from entering the fan blade  26 . Removal of the hubcap  50  may provide access to the interior of the fan blade  26  for inspection and/or maintenance. 
         [0039]    The holes  54  in the fan blade are to allow bolts or other fasteners to attach the fan blade  26  to the blade shanks  16  (not shown in  FIG. 11 ). 
         [0040]    Point  56  represents where the rotational center of the fan  12  to which the fan blade  26  is associated with.  FIG. 11  shows various dimension lines expressing example lengths and locations of various features expressed as functions of R (the radius of the assembled fan as measured from the rotational center  56  as shown in  FIG. 11 ) and C (the chord or the width of the fan blade as shown in  FIG. 12 ). 
         [0041]      FIG. 12  shows a cross-section of a fan blade  26  having a hollow airfoil section  28  and a trailing edge extension or flap  30 . Dimension lines are shown expressing example lengths and locations of various features expressed as functions of C (the cord or the width of the fan blade  26  as shown in  FIG. 12 ). 
         [0042]      FIG. 13 , shows an exploded view of a fan blade  26  in accordance with an embodiment of the invention.  FIG. 13  shows how the fan blade  26  attaches to the blade shank  16  via bolts  58  having threads  59 . The fan blade  26  attaches using bolts  58 , washers  60  and nuts  62 . The bolts  58  extend through the holes  54 . The blade shank  16  extends through the hub cap  50  into the hollow airfoil section  28 . Rivets  52  connect the hubcap  50  to the fan blade  26 . The tip cap  47  attaches to the fan blade  26  via rivets  48 . There are weights  64  attached inside the tip of the blade  26  using bolts  58 , washers  60  and nuts  62  to balance the assembly. 
         [0043]      FIG. 14  shows a cross-section of a fan blade  26  taken along the line  14 - 14  of  FIG. 15 . The fan blade  26  shown in  FIG. 14  is shown attached to the blade shank  16 . 
         [0044]      FIG. 15  shows the fan blade  26  assembly of  FIG. 13  in an assembled form.  FIG. 15  is partially cut away to show part of the connection  61  between the weights  64  and the fan blade  26 . 
         [0045]      FIG. 16  is a partially exploded view of the fan blade  26  and hub  18 . The fan blade  26  attaches to the hub  18  with U bolts  66  engaging the blade shank  16  of the fan blade  26  and the hub  18 . The U bolts  66  attach to the hub  18  with washers  60  and nuts  62 . The blade shank  16  is seated in a cradle  68 . The U bolts  66  extend through holes  70  in the hub  18 . 
         [0046]      FIG. 17  shows the fan blade  26  attached to the hub  18  in the manner described above. 
         [0047]    According to some embodiments of the invention, the fan blade  26  may be fabricated by being extruding a metal such as aluminum through a die. Alternatively, a material such as fiberglass and resin may be protruded through a die to fabricate the fan blade. Once the fan blade has been extruded or protruded, the specific shape may be further refined by trimming or machining the fan blade. For example, the trailing edge profile may be cut into the fan blade by milling the fan blade. Other machining or cutting techniques may also be used. Other features such as holes and the like may be cut or punched into the fan blade. Other components such as the hub cap, the blade shank and the tip end cap may be attached to the fan blade. 
         [0048]    It should be understood that specific hardware and methods used to assemble and attach the various components are provides as examples only and are not limiting the invention to the specific examples set forth. 
         [0049]    The many features and advantages of the invention are apparent from the detailed specification, and thus, it is intended by the appended claims to cover all such features and advantages of the invention which fall within the true spirit and scope of the invention. Further, since numerous modifications and variations will readily occur to those skilled in the art, it is not desired to limit the invention to the exact construction and operation illustrated and described, and accordingly, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.