Patent Application
20120003098
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.
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.
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.
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.
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.
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.
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.
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.
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,
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.
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.
An embodiment in accordance with the present invention provides a fan having multiple fan blades having some of the features described herein.
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.
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.
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.
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
Point 56 represents where the rotational center of the fan 12 to which the fan blade 26 is associated with.
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.
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.
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.
