Abstract:
A mixed flow fan wheel has a convex hub, an axially-spaced away concave annular shroud, and a plurality of angularly distributed blades extending between and interconnecting the hub and shroud, all which cooperatively define a plurality of inter-blade flow channels. Each has a pressure surface and spaced suction surface extending not only between spaced inlet and discharge edges but also, crosswise thereto, spaced hub-side and shroud-side edges. Each discharge edge is convex relative a center of geometry of the blade therefor. Each inter-blade flow channel originates in a generally rectangular shape between flanking inlet edges and terminates in another generally rectangular shape between flanking discharge edges, with a procession of gradations of generally rectangular shapes forming a progressive transition therebetween. Moreover, each inter-blade flow channel twists or corkscrews from inlet thereof to the discharge.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of U.S. patent application Ser. No. 11/431,403, filed May 10, 2006 now abandoned, which claims the benefit of U.S. Provisional Application No. 60/682,306, filed May 18, 2005. The foregoing disclosures are incorporated herein by this reference thereto. 
    
    
     BACKGROUND AND SUMMARY OF THE INVENTION 
     The invention relates to mixed flow roof exhaust fans. A number of additional features and objects will be apparent in connection with the following discussion of the drawings and preferred embodiment(s) and example(s). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       There are shown in the drawings certain exemplary embodiments of the invention as presently preferred. It should be understood that the invention is not limited to the embodiments disclosed as examples, and is capable of variation within the scope of the appended claims. In the drawings, 
         FIG. 1  is a perspective view of roof exhaust fan in accordance with the invention, comprising an upblast embodiment thereof; 
         FIG. 2  is an enlarged scale partial sectional view taken along line II-II in  FIG. 1 ; 
         FIG. 3  is a bottom perspective view of the fan wheel in  FIG. 2 ; 
         FIG. 4  is a bottom plan view thereof; 
         FIG. 5  is a top plan view thereof; 
         FIG. 6  is a side elevational view thereof; 
         FIG. 7  is a sectional view taken along line VII-VII in  FIG. 5  except all the blades of the wheel but two are removed from view for convenience for showing the mating of the shroud and hub edges thereof to the shroud and hub respectively; 
         FIG. 8  is a blade plan view of the left blade in  FIG. 7 , and rotated clockwise from its orientation in  FIG. 7  by about a quarter of a turn, it being typical of all the other blades of the wheel; 
         FIG. 9  is a blade elevational view taken in the direction of arrows IX-IX in  FIG. 8 ; 
         FIG. 10  is a sectional view taken along line X-X in  FIG. 8 ; 
         FIG. 11  is a sectional view taken along line XI-XI in  FIG. 8 ; and 
         FIG. 12  is a partial sectional view comparable to  FIG. 2  except showing a downblast embodiment in accordance with the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIGS. 1 and 2  show a roof exhaust fan  20  in accordance with the invention. This particular embodiment is arranged for upblast service. One aspect of the invention comprises its modularity. In this aspect, the fan  20  comprises a core package  22 , a top cylinder and cap  24  and  26 , and an outer band  28 . 
     During installation, preferably the core package  22  is mounted on the roof independent of and earlier than attachment of the top cylinder and cap  24  and  26  and outer band  28 . After the core package  22  is seated and mounted, then preferably the top cylinder and cap  24  and  26  and outer band  28  are attached to it. One advantage of this modularity is shown by contrasting  FIG. 2  against  FIG. 12 . To turn ahead to  FIG. 12 , it shows another embodiment of a roof exhaust fan  120  in accordance with the invention except arranged for downblast service. In  FIG. 12 , the core package  22  is the same as utilized in  FIGS. 1 and 2 . The distinguishing aspect of  FIG. 12  is that the up-exhausting outer band  28  of  FIG. 2  has been replaced with a down-exhausting outer band  128  as shown. Hence the same core package  22  is convertible for utilization in various fan arrangements, including without limitation upblast and downblast service. 
     In consequence, it is an aspect of the invention that the factory&#39;s production of the core package  22  is uniform regardless of whether the end-use is either upblast, downblast or other. The place and time where a particular end-use is determined for the core package  22  is when the other modular components of the fan are attached on the installation site. Indeed, this modular fan  20 / 120  accepts being converted from a preceding mode to a succeeding mode (eg., as from upblast mode to downblast mode) even after an extended service life in the preceding mode. As long as the core package  22  is functional, it allows conversion at any date. 
     Returning to  FIG. 2 , it shows that the core package  22  includes a stationary base  32  and baffle  34 . The base  32  props up a stationary motor support plate  36  (motor not shown) by means of multiple posts  38  (only two shown). Suspended off the motor shaft (again, motor is not shown, neither is the shaft) is a rotational fan wheel  40 . 
     The fan wheel  40  comprises an outlet-side hub  42 , an inlet-side shroud  44 , and a cascade of angularly-paced blades  46  that extend between and interconnect the shroud  44  with the hub  42 . 
     The hub  42  has sort of a dish structure while the shroud  44  has a ring or band structure. To turn ahead to  FIG. 7 , it shows better that both the hub  42  and shroud  44  have slant surfaces in the form of, in more technical language, frustums of right circular cones. The hub  42  has a slant angle that is flatter or shallower than that of the shroud  44 . The hub  42  and shroud  44  alike have major and minor bases (ie., the base with the larger diameter and the other with the smaller diameter, respectively). The hub  42 &#39;s major base&#39;s diameter is smaller than that of the shroud  44 &#39;s major base. Given the foregoing, the hub  42  and shroud  44  cooperatively determine the lateral boundaries of the flow passage through the wheel  40 . Indeed, more particularly, the flow passage through the wheel  40  is furthermore chopped up by the cascade of blades  46 , which define an angularly-spaced cascade of passageways, there being one such passageway between each adjacent pair of blades  46 . 
     With the foregoing in mind,  FIG. 2  (as well as  FIG. 12 ) shows another aspect of the invention, and it concerns an outlet diffuser  48 . This outlet diffuser  48  is produced directly in the motor support plate  36  in the form of a chamfer around the cylindrical bottom rim thereof. In the same technical language as used above, it is preferred if this outlet diffuser  48  is shaped as a frustum of a right circular cone. Whereas one non-limiting example of how to construct this diffuser  48  is shown as producing it directly in the lower margin of the motor support plate  36 , other suitable ways are readily recognizable to ordinarily skilled persons in the art. 
     It is additionally preferred if the outlet diffuser  48  is shaped to have the same slant angle as the hub  42 . It is more preferential still if the outlet diffuser  48 &#39;s minor base is comparably the same size as and arranged to form nearly a seamless continuation of the hub  42 &#39;s major base. That way, the outlet diffuser  48  forms nearly a seamless geometric continuation of transition from the geometry of the hub  42 , except that instead of being rotating like the hub  42  the outlet diffuser  48  is stationary. It is believed that this outlet diffuser  48  in accordance with the invention reduces momentum losses with the air outputted by the wheel  40 . It is not known if this loss-savings is obtained by reducing friction losses, expansion losses or whatever. 
     Referencing now  FIGS. 3 through 11 , these series views show various inventive aspects of the mixed flow fan wheel  40  in accordance with the invention. By way of background, mixed flow fans have impellers (in the instance here, it has a wheel construction) whose output is somewhere between being centrifugal outputted and axially outputted. 
     This distinction can be reckoned another way. Here, this mixed flow impeller  40  in accordance with the invention has the wheel construction as shown, comprising the hub  42 , the axially-spaced away shroud  44 , and the cascade of angularly-spaced blades  46  distributed between and interconnecting the shroud  44  and hub  42 . If the wheel  40  were inverted from how it is illustrated in  FIG. 3  or  6 , then the geometry of the hub  42  could be reckoned as an inverted dish, and the geometry of the shroud  44  as a lampshade situated relatively above and surrounding the hub  42 . The shroud  44 &#39;s open neck defines the inlet or intake for the wheel  40 . Engineers, among others, are interested in rating such wheels  40  of mixed flow fans by various performance and/or geometry metrics. One such geometry metric that interests engineers is the ratio of the outer diameters of the hub  42  and shroud  44  respectively. Generally the ratio of hub to shroud diameter is less than 100%. Indeed, if the ratio approaches 100% (unity), then it is more accurate to say that the result is a centrifugal-flow impeller. Conversely, if the ratio approaches 0% (zero), then it is more accurate to say that the result is an axial-flow impeller (eg., a prop). Therefore, a mixed flow impeller has a hub to shroud size-ratio that is situated between those two extremes.  FIG. 7  illustrates an example hub to shroud geometry that is preferred in accordance with the invention. 
     With reference to  FIG. 4 , the wheel  40  is designed to rotate in the clockwise direction. Hence the blades  46  can approximately be classified as a variety of backwardly curved blades. But only approximately, because the blades  46  have an inventive configuration all their own as will be more particularly described below. There are eleven (11) symmetrically-distributed blades  46  in this preferred embodiment of the wheel  40 . 
     The blades  46  are all substantial copies of each other. For convenience of production, the blades  46  are formed into shape from flat sheet stock. However, it is believed it would be preferred better if the blades  46  were formed into airfoils (not illustrated). The hub  42 , shroud  44  and blades  46  may all be produced out of a common metal—such as and without limitation aluminum or stainless steel—and then welded together into a solid unit to obtain the rigid wheel  40  as shown. 
     Each blade  46  has a pressure surface  50  opposite a suction surface  51  which are bounded by a hub edge  52 , a shroud edge  54 , a leading (intake-side) edge  56  and a trailing (outlet-side) edge  58 . In determining a design for each blade  46 , the warp of the surfaces  50  and  51  as well as the curvatures of the leading and trailing edges  56  and  58  are determined by aerodynamic and/or other performance considerations (eg., noise). The shapes of the hub and shroud edges  52  and  54  are determined by the necessity to conform with hub  42 &#39;s and shroud  44 &#39;s slant surfaces where they meet as shown. 
       FIGS. 7 and 8  afford more convenient study of a single blade  46  in isolation from the cascade of others in the wheel  40 . It is an aspect of the invention that the leading and/or trailing edges  56  and  58  are non-linear. The leading edge  56  is curved such that it recesses or arches into the center of geometry of the blade  46 . Conversely, the trailing edge  58  is curved such that it bulges or arches outward from the center of geometry of the blade  46 . 
       FIGS. 9 through 11  are a series of three views contrasting the warp across the span of the blade between the hub and shroud edges  52  and  54  thereof at three locations along the body axis of the blade  46  (eg., the axis progressing from leading edge  56  to trailing edge  58 ).  FIG. 9  shows best the warp in the span of the blade  46  at the leading edge  56 . Consider that the blade  46  divides space into two spaces, pressure-side space  64  (which as the blade is oriented in  FIG. 9  is above the blade) and suction-side space  66 . Hence the warp in the span of the blade  46  at the leading edge  56  is convex into the pressure-side space  64 . 
     The converse is true at the trailing edge  58  where, to skip ahead to  FIG. 11 , the warp in the span of the blade  46  at the trailing edge  58  is concave to the pressure-side space  66 . 
     The leading and trailing edges  56  and  58  are not flipped images of each other. Among other ways that they are not, they are not in these two respects. In a minor respect, the warp-curvatures of their apparent arcs are not coincident. The trailing edge  58  is apparently a bit more tightly warped or curled. The other and more significant respect is described next in rather difficult terms. That is, their respective warp-curvatures circumscribe respective apparent centers which are not contained in a common plane of symmetry. 
     To put that differently,  FIG. 9  shows that the leading edge  56 &#39;s warp circumscribes an apparent center that would be down and left in the view.  FIG. 11  shows that the trailing edge  58 &#39;s warp circumscribes an apparent center that would be up and—not right but—left in the view. If the apparent centers were contained in a common plane symmetry, then the trailing edge  58 &#39;s warp would (which it does not) circumscribe an apparent center which would be up and right at an equal angle of slant as the leading edge  56 &#39;s apparent center that is down and left. 
     But the foregoing is not the case with the blade  46 . Indeed, the apparent axes of symmetry for the blade  46  are corkscrewing counterclockwise in the progression along the body axis of the blade  46  from the leading to trailing edge  56  to  58 . To put that differently, consider the following.  FIG. 9  shows that the leading edge  56  might be reckoned as arranged about an apparent (eg., approximate) axis of symmetry that extends from the 1 o&#39;clock position to the 7 o&#39;clock position. In contrast,  FIG. 11  shows that the trailing edge  58  might be reckoned as arranged about an apparent (eg., approximate) axis of symmetry that extends from the 11 o&#39;clock position to the 5 o&#39;clock position. 
     Hence any imaginary surface containing a procession of (apparent) axes of symmetry for the blade  46  in the procession along the body axis from leading to trailing edges  56  to  58  thereof would be a corkscrewing surface, originating in the 1 o&#39;clock (to 7 o&#39;clock) position and terminating in the 11 o&#39;clock (to 5 o&#39;clock) position. 
       FIG. 10  shows yet a further asymmetry with the warp of the blade  46 . This one is involved. Consider the following. That is, the blade  46  could change from (i) being convex into pressure-side space  64  at the leading edge  56  to (ii) being concave to pressure-side space  64  at the trailing edge  58  by (iii) doing so ‘symmetrically’ about a corkscrewing surface of symmetry:—but apparently the blade  56  does not do this.  FIG. 10  is cross-section of the about midway-span of the blade  46 . The midway-span appears to contain an inflection point. That is, the hub-side half of the midway-span appears convex in pressure-side space  64  (eg., the left half of  FIG. 10 ) while the shroud-side half appears concave to pressure-side space  64  (eg., the right half of  FIG. 10 ). The change from convexity to concavity occurs at some intermediate inflection point, and  FIG. 10  shows that the midway-span apparently contains such an inflection point. 
     The invention having been disclosed in connection with the foregoing variations and examples, additional variations will now be apparent to persons skilled in the art. The invention is not intended to be limited to the variations specifically mentioned, and accordingly reference should be made to the appended claims rather than the foregoing discussion of preferred examples, to assess the scope of the invention in which exclusive rights are claimed.