Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D19/00—Axial-flow pumps
  • F04D19/002—Axial flow fans
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/08—Sealings
  • F04D29/16—Sealings between pressure and suction sides
  • F04D29/161—Sealings between pressure and suction sides especially adapted for elastic fluid pumps
  • F04D29/164—Sealings between pressure and suction sides especially adapted for elastic fluid pumps of an axial flow wheel
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04D—NON-POSITIVE-DISPLACEMENT PUMPS
  • F04D29/00—Details, component parts, or accessories
  • F04D29/40—Casings; Connections of working fluid
  • F04D29/52—Casings; Connections of working fluid for axial pumps
  • F04D29/54—Fluid-guiding means, e.g. diffusers
  • F04D29/541—Specially adapted for elastic fluid pumps
  • F04D29/545—Ducts

Definitions

• banded axial-flow fan to describe a fan having a hub that rotates on an axis and has blades extending in an outwardly direction (for example, generally radially) from the hub to a circular band that connects the blade tips. Blade rotation tends to force air in the general direction of the fan axis.
• fan and housing combination to describe such axial flow fans in combination with a housing (e.g., a shroud or a duct) that guides airflow entering and/or leaving the fan.
• shroud we mean an airflow guide shaped and positioned to guide airflow moving between the fan and a heat exchanger.
• An example of a banded shrouded fan that moves air through a heat exchanger is disclosed in Gray U.S. Patent, 4,548,548, which is hereby incorporated by reference.
• duct we mean an elongated flow path such a those used in heat, ventilation, and air conditioning systems.
• Airflow recirculation can be explained as follows.
• the fan generates a pressure difference between the upstream side of the fan (the side from which air is drawn) and the downstream side of the fan (the side of the fan which exhausts the airflow) — i.e., pressure is higher on the downstream side than on the upstream side.
• Airflow recirculation is the undesired flow of air from the downstream to the upstream side of the fan, resulting from this pressure difference.
• the recirculating airflow passes through the running clearance between the housing and the band.
• One way to reduce recirculation is to reduce the fan-to-housing clearance.
• Another way to reduce recirculation is to incorporate labyrinth seals between the fan and the housing. In some cases these methods may present difficulties in economic manufacture.
• the invention features certain configurations for banded, axial-flow fan and housing combinations that provide a surprising combination of efficiency, low noise, and manufacturability.
• the invention generally features fan and housing combinations which include stationary flow control vanes (e.g. thin members) positioned to encounter and redirect recirculating airflow. A portion of the housing is positioned outward of the fan band, and there are running clearances between the band and the housing such that recirculating airflow moves in a pathway between the fan and the housing.
• the stationary flow control vanes are attached to the housing.
• the invention provides a combination of efficiency, manufacturability and low noise. Without wishing to bind our to a particular theory, such benefits may be explained at least in part as follows.
• Recirculating airflow generally has a swirling (rotational) component of velocity imparted either by the fan blading or by vicious effects in the recirculation passage.
• this swirl causes the fan blades to operate locally at an angle of attack different from that of the main flow.
• Swirl also may increase inflow turbulence, which causes broadband noise, and it may lead to flow non-uniformities causing undesirable tones.
• the invention is particularly suited for shrouded fans that draw airflow through an upstream heat exchanger, but the invention also can be applied to fans that blow air through a downstream heat exchanger. It is also particularly suited for ducted fans.
• the first configuration features placement of the vanes generally within the space between the fan band and the housing, although embodiments in which the vanes continue downstream of the fan band are also included within the first configuration.
• This configuration is best suited for applications in which there are axial packaging constraints, such as automotive applications in which a shrouded fan draws air through a heat exchanger immediately adjacent (usually upstream of) the fan.
• the second configuration features placement of the vanes such that they are at least partially (or even entirely) upstream of the fan band from the perspective of the primary airflow.
• Such configurations are particularly suited for ducted fans, such as those in airhandlers for heating, ventilating and/or cooling buildings, where axial space is less constrained.
• the housing and vanes are a single injection molded plastic unit.
• the vanes may be injection molded as part of an array that is assembled with the housing.
• Preferred embodiments are also characterized by a fan-to-housing (usually a shroud) running clearance of at least 0.25% of the fan diameter.
• running clearance we use the term running clearance to designate the spacing between the fan band and portions of the housing that extend around the fan band.
• the housing is characterized by a reduction in radius at a location rearward of the trailing edge of the fan band.
• the pathway of recirculating airflow can include an inlet formed between the trailing edge of the fan band and the portion of the housing at the reduced radius.
• the trailing edge of the fan band is the rearward-most portion of the band.
• the band includes a lip that extends rearward of the blade trailing edge.
• at least a portion of the vanes is positioned radially outward of the inlet to the recirculation pathway.
• the above-described housing radius reduction can reduce the housing radius R r (see Fig. 2A) to a value approximately equal to, or even less than, the outer radius of the trailing edge of the fan band (R b , see Fig. 2A, described below) .
• approximately equal in this context means a radius that would risk interference if the portion of the housing with the reduced radius were not offset axially from the fan band.
• the two radii may differ by less than standard or nominal radial running clearance "C" (see Fig. 2A) .
• an inlet to the recirculation pathway is formed between the housing and the trailing edge of the band; the housing comprises a rearward portion which extends first rearwardly and then inwardly and forwardly, forming a pocket axially rearward of the inlet of the recirculation flow path.
• Such pockets may have a rounded back or a straight back.
• a portion of the vanes may extend into the pocket, and at least a portion of the vanes is axially rearward of the trailing edge of the band.
• the vanes may be characterized by a reduction in radius at a position axially rearward of the trailing edge of the fan band.
• the recirculating airflow pathway includes an outlet formed between the housing and an outwardly flaring segment of the leading edge of the fan band.
• Advantages may be achieved according to the invention with other geometries that do not include this detail, however.
• the vanes may be straight (radial or non-radial) taken in a section in a plane normal to the fan axis. Alternatively, the vanes may be curved taken in a section in a plane normal to the fan axis. II. Vanes Upstream Of The Fan Band
• the space through which airflow recirculates comprises a restriction upstream (from the perspective of recirculating airflow) of the vanes.
• the restriction causes the airflow to jet into the spaces between the vanes, rather than to be deflected radially or tangentially.
• the band comprises a lip flaring outwardly to establish the above described restriction.
• the vanes may be part of a single injection molded plastic piece.
• the vanes may be arranged in an array whose inward tips are connected by an inner ring.
• the inner ring gives structural rigidity to the vane assembly, which allows the housing to be formed around the vane assembly.
• the vanes may be molded in various configurations that better match the direction of incoming recirculating airflow. These configurations may be particularly beneficial in fans producing a relatively low pressure rise at some segment of the duty cycle.
• the vanes may be molded so that the end faces of the vanes are beveled (preferably at least 20° and most preferably at least 30°) so that the high pressure side surfaces extend slightly further upstream (from the perspective of recirculation airflow) than the low pressure side surfaces.
• the sides of the vanes can also be hooked so that the high pressure side surfaces are concave near the upstream end of the vanes (e.g. so that the radius of the concave portion is between O.IS and l.OS, where S is the spacing between adjacent vanes).
• the vanes may be angled slightly from purely radial, with the radially inward tip being inclined towards recirculation flow impinging on the vanes.
• the vanes (or at least the high pressure side of the vanes, with the low pressure side being straight) may be curved in a planar section normal to the fan axis (e.g., the section may be cylindrical with a radius of curvature of between 0.15D and 0.3D).
• FIG. 1A is a side view in section of a fan and shroud according to the invention, including an upstream heat exchanger.
• Fig. IB shows a prior art fan.
• Figs. 2A-2D are views in section of portions of fan and shroud combinations according to the invention, showing alternative configurations of the shroud radius reduction.
• Figs. 3A and 3B are sections of fan and shroud combinations showing variations in shroud design upstream of the vanes.
• Figs. 4A-4C are diagrammatic representations of arrays of vanes according to the invention in circumferential view.
• Figs. 5A and 5B are side views, in section, of other fan/shroud combinations according to the invention, in which a heat exchanger is downstream of the fan.
• Fig. 6 is a diagrammatic representation of a fan and duct combination according to the invention.
• Figs. 7-9 are side views in section of other fan and housing combinations. II. Vanes Upstream Of The Fan Band
• Fig. 10 is a side view in section of a fan and duct showing vanes upstream of the fan band.
• Figs. 11 is a side view in section of a ducted, banded fan being used with a dual-ring vane assembly.
• Fig. 12 is an end view of the vanes taken along 12-12 of Fig. 11, showing only a portion of the vanes.
• Fig. 13A. is a close-up of the circled portion of Fig. 12.
• Figs. 13B and 13C are similar views of alternative configurations.
• Fig. 14A is a sectional view taken along 14A-14A of Fig. 12 showing square leading edge details for a pair of vanes.
• Fig. 14B is a section of an alternative vane configuration.
• Fig. 15 is perspective view of one particular vane embodiment according to the invention.
• FIG. 1A fan 20 is positioned in shroud 26 to pull air through heat exchanger 21.
• Axis A is the fan's rotational axis.
• Fan 20 has a band 24 connecting the outer tips of blades 22. Band 24 terminates at its upstream edge in a lip 30.
• Vanes 28 are attached to shroud 26.
• Figs. 4A-4C are sectional views (perpendicular to the fan axis) of arrays of vanes 28, showing the alternative configurations of the vanes. The sections are taken looking rearwardly along the fan axis, and the direction of fan rotation is clockwise.
• vanes 28E are radial.
• vanes 28F are straight, and they are angled from the radial direction.
• vanes 28G are curved to receive airflow having a rotational component in the direction of fan rotation.
• the design of vanes 28 and shroud 26 permits the entire shroud and the vanes to be injection molded as a single unit.
• the spacing between vanes 28 is selected to remove swirl without excessively blocking airflow. In typical applications there will be more than 10 and less than 1000 (e.g., 30-200) of these vanes, although there may be fewer or more in specific applications.
• Fan 20 and shroud 26 are designed with running clearances to avoid interference between band 24 and shroud 26.
• Shroud 26 has a radius reduction rearward of band 24 (formed by shroud segments 27 and 29) , which reduces the shroud radius (R r ) to less than the outer radius (R b )of band 24 at its trailing edge, plus clearance "C".
• Fig. 2A illustrates R r , R b and R c on a fan and housing similar to that shown in Fig. 1A.
• Shroud 26 is mounted to radiator 21 by mounts 23.
• Fig. IB is a figure reproduced from Gray, U.S. 4,548,548.
• the recirculation flow path between the shroud and the band does not include vanes.
• the radius of the shroud is relatively constant rearward of the lip of the band, at a value that must provide clearance between the band and the shroud.
• the radius of the fan band R b , the radius of the shroud after the reduction R r , and clearance "C" are shown in Fig. 2A, discussed below.
• the operation of the invention can be described as follows. Recirculating airflow enters the inlet between band 24 and the shroud radius reduction formed by segments 27 and 29. The airflow turns to travel in space 32 and encounters vanes 28 whereby rotational velocity is reduced. The airflow exits the recirculation path through outlet 36, which is formed between the upstream edge of lip 30 and shroud 26.
• the widths of inlet 34 and outlet 36 are as narrow as manufacturing processes permit to minimize leakage and resulting lost energy.
• Figs. 2A-2D are diagrammatic representations of details of fan/shroud combinations that are similar to the one shown in Fig. 1A, with differing inlets to the recirculation flow path space. In each of those figures, fan blades terminate in a similar band. Vanes are included in the space between the fan band and the shroud. The shroud includes a radius reduction rearward of the trailing edge of the fan band.
• Figs. 2A-2D The specific designs of the shrouds differ in these radius reductions, thus providing different inlets to the recirculation flow path.
• the embodiments of Figs. 2A-2D will only be described to highlight the differences among those embodiments.
• Features in Figs. 2A-2D are numbered with numbers corresponding to those used in Figs. 1A.
• the shroud radius reduction segments 27A and 29A are rearward of the trailing edge of band 24A.
• the inner radius of segment 29A is less than the outer radius of the trailing edge of band 24A.
• shroud segment 29B has an inner radius slightly larger than the outer radius of the trailing edge of band 24B.
• segment 29C has a radius approximately equal to that of the fan band. Segment 26C flares outwardly, to optimize performance in some applications. The thickness of the shroud may decrease with rearward extent, so that the outer shroud diameter in this segment flares less or is generally cylindrical. In Fig. 2D, segment 29D is rounded to form a pocket 48D. This geometry allows a large amount of flare to be used on an injection moldable part. Vanes 28D extend into the pocket.
• Figs 3A and 3B are sections of fan and housing combinations that are similar to the fan of Fig 1A, except in the configuration of shroud 26' and 26" upstream of the fan.
• fan blade 22 terminates in a band 24.
• Vanes 28 are positioned in the recirculation flow path.
• Motor supports 37 extend from a downstream extension of the shroud.
• a restriction is not formed between the band 24' and shroud 26'.
• the radius of shroud segment 26" is essentially constant, and a restriction is formed between band 24 and shroud 26". Both configurations are within the spirit of the invention.
• Figs. 5A and 5B show two alternative fan and housing configurations in which the fan is upstream of the heat exchanger, and the shroud guides airflow (shown generally with an arrow) from the fan into the heat exchanger.
• fan blade 54 has a band 55 with a lip 56 that forms an inlet to the fan. Airflow recirculation takes place through inlet 67 into space 57 between the shroud 58 and the band 55, and exits outlet 68. Vanes 59 are positioned in space 57 to encounter recirculating airflow and reduce swirl in the recirculating airflow.
• Fan motor 65 is positioned between the fan and the heat exchanger 62.
• Shroud 58 includes a segment 60 to which motor supports 61 are attached.
• Fig. 5B fan 70 blows air into downstream heat exchanger 82.
• motor 71 of the assembly of Fig. 5B is upstream of the fan.
• the fan band 75 has a lip 76 on the downstream side, and the inlet to the fan is formed by a shroud segment 80 which curves inwardly and back toward heat exchanger 82.
• the motor 71 is attached to support 81. Recirculating airflow moves through inlet 83 to space 77 between band 75 and shroud 78, and exits outlet 84. Vanes 79 are positioned in space 77 to encounter that recirculating airflow and to reduce swirl in it. In this configuration, the inlet restriction upstream of the vanes and the vane shaping referenced below may be beneficial.
• Fig. 6 is a section showing a variation of the invention useful in ducted fans.
• the vanes 44 are provided as a separately molded part having a flared rear face 49 which terminates in an edge 50 that forms the inlet 52 for the recirculation flow path.
• the blades 48, the band 46 and the duct 51 are similar to those described below.
• Fig. 7 shows a fan 640 housed in a shroud 642 which guides airflow through a radiator (not shown) upstream of the fan.
• Vanes 644 are L-shaped in this view and radial in a plane perpendicular to the fan axis.
• Lip 646 forms a restriction inlet 648 with lip 647.
• the vanes are spaced from 1/8 to 1/2 of an inch apart around the circumference, with the smaller spacing being used in very small fans.
• the fan and housing combination of Fig. 7 can also be used (with some modification) as a ducted fan.
• the width of the recirculation outlet is at least twice the width of the recirculation inlet. Increasing the width of outlet reduces the velocity of the leakage flow thus reducing flow disruption as the recirculation flow enters the main flow.
• fan 780 has a band 782 with an upstream edge that turns back axially to form lip 784.
• Shroud 786 includes vanes 788.
• a lip 790 on shroud 786 forms a restriction 792 in the recirculation path, which feeds the airflow to vanes 788 and from there to outlet 794.
• the outlet to the recirculation path is at least twice as wide as the restriction.
• band 800 of fan 801 has a trailing lip 802 which forms restriction 803 with shroud 804.
• Leakage vanes 805 extend from shroud 804.
• Bell mouth 807 together with the axially forward edge of band 800 form outlet 806 to the recirculation path.
• Fig. 10 depicts a fan 90 in which the housing 92 is a duct or shroud having vanes 94 upstream of band 96.
• Inlet 91 is formed between the upstream edge of band 96 and duct 92.
• This inlet (“X") is on the order of 0.005D- 0.02D. Recirculation airflow is entrained into vanes 94 and leaves through the open sides 98 of the slots between vanes 94.
• the array of vanes is provided by a dual ring structure 217 which fits within the duct 212 just upstream of the fan 214.
• the vane assembly may be made from molded plastic, hard plastic foam, or any suitable material which may be fashioned into the requisite geometry. As shown in Fig. 11, the assembly consists of an outer ring 216, an inner ring 218, and a plurality of vanes 220 disposed generally radially between the two rings 216, 218.
• the ring 218 gives structural rigidity to the assembly. This is beneficial if it is desired to form the housing by wrapping sheet metal, or some other flexible material, around the perimeter of the outer ring 216 to form the duct.
• the inner ring 218 also divides the duct into separate flow passageways, an inner primary passageway 222 through which the primary flow passes, and an outer, annular recirculation passageway 224 through which the recirculation flow passes.
• the inner ring 218 helps to inhibit radial flow, where it exists, from reentering the fan.
• a banded fan 214 in which the band 226 terminates in a curved lip 228.
• the curved lip 228 forms a restriction 230 in the recirculation passageway 224.
• the vanes 220 may be substantially flat, non-shaped vanes. Such vanes generally may provide adequate performance. As explained below, however, for other applications (e.g., low pressure rise fans or fans that are designed both for high and low pressure rise) additional vane shaping can improve performance.
• Tangential deflection of airflow is reduced by bevelling the end face 234 of each of the vanes 220, as shown in Fig. 14B.
• the end face 234 is beveled such that the high pressure side surface 236 of the vane projects further upstream (taken from the perspective of the recirculation flow) than the low pressure side surface 238.
• the bevel angle, ,9 can be at least 20°, and is preferably 30° or more. Deflection of flow in the inward radial direction is reduced by incorporating additional detailed vane shaping in two respects. First, as shown in Fig.
• the high pressure side surface 236 is made concave by the addition of a cylindrical region 242 at the leading edge 250, i.e., the juncture of the high pressure side surface 236 and end face 234.
• the radius of curvature r of the cylindrical region 242 can be on the same order as 1/2 of the spacing between vanes.
• the vanes can be non-radial in a section perpendicular to a plane normal to the fan axis.
• the innermost tips 250 of the vanes 220 are inclined into the impinging recirculation flow.
• the lean angle, ⁇ should preferably be between 3° and 10° from radial.
• vanes (or at least the high pressure side of the vanes) of some embodiments are slightly cylindrical in a plane normal to the fan axis.
• the center of curvature is parallel with the fan centerline and is placed on a tangent to the outside periphery of the vane.
• the radius of curvature is approximately 20% of the fan diameter.
• the vanes are radial at the outer periphery of the device, and are more inclined toward the flow as radius decreases.
• Fig. 15 is a perspective view of a portion of a dual ring structure 217 looking axially toward the rear face 232 of vanes 240. As described above, the leading edge 242 of vanes 220 is beveled, and the high pressure side face 236 is shaped. The vanes are slightly cylindrical in a plane normal to the fan axis.
• vanes can be used with fan/shroud combinations that blow air through a downstream heat exchanger.
• they can be used with the fan/shroud combinations as generally described in a commonly owned U.S. Patent Application titled Fan Inlet With Curved Lip And Cylindrical Member Forming Labyrinth Seal, filed on June 17, 1993, by Michael Sortor, and given serial number 08/079,317. That application is hereby incorporated by reference. What is claimed is:

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Structures Of Non-Positive Displacement Pumps (AREA)
• Exhaust Gas After Treatment (AREA)
• Filling Or Discharging Of Gas Storage Vessels (AREA)

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• 1994
  • 1994-08-30 WO PCT/US1994/009782 patent/WO1995006822A1/fr active IP Right Grant
  • 1994-08-30 AT AT94926638T patent/ATE216757T1/de not_active IP Right Cessation
  • 1994-08-30 DE DE69430488T patent/DE69430488T2/de not_active Expired - Lifetime
  • 1994-08-30 ES ES94926638T patent/ES2173121T3/es not_active Expired - Lifetime
  • 1994-08-30 JP JP7508228A patent/JPH09505375A/ja active Pending
  • 1994-08-30 EP EP94926638A patent/EP0746689B1/fr not_active Expired - Lifetime

Patent Citations (7)

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