Radial flow fan with impeller having blade configuration for noise reduction

Information

  • Patent Grant
  • 6514036
  • Patent Number
    6,514,036
  • Date Filed
    Friday, April 27, 2001
    23 years ago
  • Date Issued
    Tuesday, February 4, 2003
    21 years ago
Abstract
A debris blower with a radial flow fan having an impeller that includes a set of impeller blades that are spaced about a rotary axis of the impeller in a predetermined manner such that at least two spacing angles are used to space the impeller blades circumferentially apart from one another. The use of a plurality of spacing angles operates to distribute the noise that is generated by the rotating impeller blades over several tones or frequencies.
Description




FIELD OF THE INVENTION




The present invention generally relates to radial flow fans and more particularly to a debris blower including a radial flow fan having an impeller with a noise reducing blade configuration.




BACKGROUND OF THE INVENTION




Debris blowers are known in which an impeller or a fan driven by a motor creates an air stream which is directed into a duct. The air stream discharged from the open end of the duct is employed to blow debris off walks, driveways and lawns. Known higher performance blowers employ a radial flow fan in order to efficiently generate the pressure and volumetric flow rate required for the application. These devices tend to be relatively noisy such that their use is often unpleasant for the user and those in the vicinity of the blower.




The scale of the impeller, the practical speeds at which it can be driven, and a practical number of blades results in blade passing frequencies that create tonal noise emission. Tonal emission at the blade passing frequency typically falls within the frequency range over which the human ear is sensitive and creates an unpleasant sound quality. Further, as the impeller blades of these devices are typically spaced apart evenly around the circumference of the impeller, the noise emission contains one or more discrete tones at frequencies related to the blade passing rate. It is this concentration of noise at one or more particular frequencies, rather than the overall amplitude of the noise, that most people find unpleasant.




Given the design criteria of modern high performance debris blowers, along with issues relating to its overall size, weight and cost, changes to the size of the impeller, its rotational speed and/or the number of impeller blades to change the frequency of the noise that is generated by the passing impeller blades to a frequency that is outside the sensitive range of human hearing have not been practicable.




It is therefore an object of the present invention to provide a radial flow fan having an impeller with a blade configuration that spreads the blade passing noise out over several frequencies to improve the quality of the noise that is generated during the operation of the radial flow fan.




SUMMARY OF THE INVENTION




In one preferred form, the present invention provides a radial flow fan having a housing having at least one inlet, an outlet and an impeller cavity in fluid connection with the inlet and the outlet, and an impeller. The impeller is rotatably supported in the impeller cavity on a rotary axis and includes an annular flange member and a plurality of impeller blades that are fixedly coupled to the annular flange member such that each of the impeller blades is adjacent another of the impeller blades in a predetermined circumferential direction. Each adjacent pair of the impeller blades defines a spacing angle. The impeller is configured such that a first predetermined quantity of the impeller blades are spaced apart from an associated adjacent impeller blade with a first predetermined spacing angle and a second predetermined quantity of the impeller blades are spaced apart from an associated adjacent impeller blade with a second predetermined spacing angle that is not equal to the first predetermined spacing angle. The plurality of first impeller blades are configured to intake a compressible fluid in a first direction generally parallel the rotary axis and to expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity. The use of a plurality of spacing angles operates to distribute the noise that is generated by the rotating impeller blades over several tones or frequencies.




Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.











BRIEF DESCRIPTION OF THE DRAWINGS




Additional advantages and features of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings, wherein:





FIG. 1

is a side view of a blower constructed in accordance with the teachings of the present invention;





FIG. 2

is a sectional view of the blower of

FIG. 1

taken along its longitudinal axis;





FIG. 3

is an end view of a portion of the blower of

FIG. 1

, illustrating the set of first impeller blades in greater detail;





FIG. 4

is an end view of the impeller illustrating the set of second impeller blades in greater detail;





FIG. 5

is a perspective view of the impeller illustrating the set of first impeller blades; and





FIG. 6

is a perspective view of the impeller illustrating the set of second impeller blades.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS




With reference to

FIGS. 1 and 2

of the drawings, a blower constructed in accordance with the teachings of the present invention is generally indicated by reference numeral


10


. The blower


10


is shown to include a power source


12


, a switch assembly


14


for selectively controlling the power source, a housing


16


, an impeller


18


and a discharge tube assembly


20


. In the particular embodiment illustrated, the power source


12


is illustrated to include a motor assembly


30


having an electric motor


32


with a pair of terminals


34


and an output shaft


36


. The motor assembly


30


and switch assembly


14


are conventional in their construction and operation and need not be discussed in significant detail. Briefly, the switch assembly


14


is coupled to a source of electric power (e.g., via a power cord


40


) and via the terminals


34


, selectively provides the motor


32


with electricity in a predetermined manner that is related to the amount by which a trigger button


46


on the switch assembly


14


is depressed.




The housing


16


is illustrated to include a pair of housing shells


50


that collectively define a motor mounting portion


52


, a switch mounting portion


54


and a volute


58


having an impeller cavity


60


, a primary inlet


62


, a secondary inlet


64


and an outlet


68


. The motor and switch mounting portions


52


and


54


are conventional in their construction and operation, being employed to fixedly couple the motor assembly


30


and the switch assembly


14


, respectively, within the housing


16


. When the motor assembly


30


is coupled to the housing


16


by the motor mounting portion


52


, the distal end of the output shaft


36


extends rearwardly into the impeller cavity


60


.




The impeller cavity


60


extends radially around the output shaft


36


and is substantially enveloped on its forward and rearward sides by a pair of annular endwalls


70


and


72


, respectively, into which the secondary and primary inlets


62


and


64


, respectively, are formed. A plurality of vent apertures


76


that are skewed to the rotary axis


80


of the output shaft


36


are formed through the housing


16


forwardly of the endwall


70


. A plurality of circumferentially extending inlet apertures


86


are spaced around the housing


16


rearwardly of the endwall


72


. The circumference of the portion of the housing


16


into which the inlet apertures


86


are formed is illustrated to be larger than the diameter of the primary inlet


62


. The outlet


68


intersects the impeller cavity


60


generally tangent to the outer diameter of the impeller cavity


60


in a manner that is conventionally known. However, the outlet


68


turns forwardly after this intersection and extends along an axis that is offset both vertically and horizontally from the rotary axis


80


of the output shaft


36


. The outlet


68


terminates at a coupling portion


90


that is configured to releasably engage a mating coupling portion


92


on the proximal end


94


of the discharge tube assembly


20


.




With reference to

FIGS. 2 through 6

, the impeller


18


is illustrated to include a mounting hub


100


, a flange member


102


, a set of first impeller blades


104


and a set of second impeller blades


106


. The mounting hub


100


is generally cylindrical and includes a mounting aperture


110


, which is sized to engage the distal end of the output shaft


36


in a press-fit manner to thereby couple the impeller


18


to the motor assembly


30


for rotation about the rotary axis


80


. Those skilled in the art will readily understand that although press-fitting is employed to fix the impeller


18


for rotation with the output shaft


36


, any appropriate coupling means may be utilized for this purpose. The flange member


102


is coupled to the mounting hub


100


and extends radially outwardly therefrom in a continuous manner to thereby completely segregate the sets of first and second impeller blades


104


and


106


from one another.




During the operation of the blower


10


, the impeller


18


rotates within the impeller cavity


60


. Rotation of the set of first impeller blades


104


imparts momentum to the air that is disposed between each adjacent pair of first impeller blades


104


, slinging the air radially outwardly toward the outlet


68


. The air exiting the outlet


68


as a result of the momentum imparted by the set of first impeller blades


104


creates a negative pressure differential that generates a primary air flow


120


that enters the housing


16


through the inlet apertures


86


and is directed into the set of first impeller blades


104


by the primary inlet


62


in a direction generally parallel the rotary axis


80


.




Similarly, rotation of the set of second impeller blades


106


imparts momentum to the air that is disposed between each adjacent pair of second impeller blades


106


, slinging the air radially outwardly toward the outlet


68


. The air exiting the outlet


68


as a result of the momentum imparted by the set of second impeller blades


106


creates a negative pressure differential that generates a secondary air flow


122


that enters the housing


16


through the vent apertures


76


. The housing


16


is constructed such that the motor


32


rejects heat to the secondary air flow


122


before it travels through the secondary inlet


64


. The secondary inlet


64


directs the secondary flow


122


into the set of second impeller blades


106


in a direction generally parallel the rotary axis


80


and opposite the primary air flow


120


.




The primary and secondary air flows


120


and


122


combine in the outlet


68


and are discharged through the coupling portion


90


into the discharge tube assembly


20


. In the example provided, the height of the first impeller blades


104


is substantially larger than that of the second impeller blades


106


and as such, the mass flow rate of the primary air flow


120


will be substantially larger than the mass flow rate of the secondary air flow


122


. As the flange member


102


is continuous, the primary and secondary flows


120


and


122


cannot travel in an axial direction beyond the flange member


102


until they have been slung radially outwardly of the impeller


18


.




The set of first impeller blades


104


is fixedly coupled to a first side


150


of the flange member


102


such that each pair of the first impeller blades


104


(e.g., first impeller blades


104




a


and


104




b


) is separated by a predetermined spacing angle


152


, wherein one of the pair of first impeller blades


104


(e.g., first impeller blade


104




b


) is spaced apart from the other one of the pair of first impeller blades


104


(e.g., first impeller blade


104




a


) in a predetermined circumferential direction by the spacing angle


152


. The set of first impeller blades


104


are spaced about the flange member


102


such that spacing angles


152


having at least two different magnitudes are employed to space the first impeller blades


104


apart. Preferably, the set of first impeller blades


104


are spaced apart with a spacing angles


152


having a multiplicity of magnitudes, wherein the spacing angles


152


are distributed in a predetermined pattern that is repeated around the circumference of the impeller


18


.




Similarly, the set of second impeller blades


106


is fixedly coupled to a second side


160


of the flange member


102


such that each pair of the second impeller blades


106


(e.g., second impeller blades


106




a


and


106




b


) is separated by a predetermined spacing angle


162


, wherein one of the pair of second impeller blades


106


(e.g., second impeller blade


106




b


) is spaced apart from the other one of the pair of second impeller blades


106


(e.g., second impeller blade


106




a


) in a predetermined circumferential direction by the spacing angle


162


. The set of second impeller blades


106


are also spaced about the flange member


102


such that spacing angles


162


having at least two different magnitudes are employed to space the second impeller blades


106


apart. As with the set of first impeller blades


104


, the set of second impeller blades


106


are preferably spaced apart with spacing angles


162


having a multiplicity of magnitudes, wherein the spacing angles


162


are distributed in a predetermined pattern that is repeated around the circumference of the impeller


18


. Also preferably, the magnitudes and pattern of spacing angles


162


for the set of second impeller blades


106


is different from the magnitudes and pattern of the spacing angles


152


for the set of first impeller blades


104


.




In the particular embodiment illustrated, the pattern of spacing angles


152


that is employed for the set of first impeller blades


104


is configured such that a first one of the first impeller blades


104


(e.g., first impeller blade


104




b


) is adjacent a first one of the other first impeller blades (e.g., first impeller blade


104




a


) and cooperates to define a first area


170


on the flange member


102


therebetween, and each of the first impeller blades


104


(e.g., first impeller blade


104




b


) is also adjacent a second one of the other first impeller blades (e.g., first impeller blade


104




c


) and cooperates to define a second area


172


on the flange member


102


therebetween. The spacing of the first impeller blades


104


is such that none of the first and second areas


170


and


172


that are adjacent any one of the first impeller blades


104


is equal in magnitude.




Each of the first impeller blades


104


is shown to begin at an inward point


174


and terminate at an outward point


176


. Each of the first impeller blades


104


(e.g., first impeller blade


104




b


) is configured such that its inward point


174


is radially inward of the outward point


176


of the first one of the other first impeller blades


104


(e.g., first impeller blade


104




a


) and its outward point


176


is radially outward of the inward point


174


of the second one of the other first impeller blades


104


(e.g., first impeller blade


104




c


). Accordingly, a first straight line passes through the mounting aperture


110


through the inward point


174


of the first impeller blade


104




b


and the outward point


176


of the first impeller blade


104




a


and a second straight line passes through the mounting aperture


110


through the inward point


174


of the first impeller blade


104




c


and the outward point


176


of the first impeller blade


104




b.


Each first impeller blade


104


is arcuately shaped from its inward point


174


to its outward point


176


. Each first impeller blade


104


tapers outwardly away from the flange member


102


from its inward point


174


to an intermediate point


178


between the inward and outward points


174


and


176


.




Similarly, the pattern of spacing angles


162


that is employed for the set of second impeller blades


106


is configured such that each of the second impeller blades


106


(e.g., second impeller blade


106




b


) is adjacent a first one of the other second impeller blades (e.g., second impeller blade


106




a


) and cooperates to define a third area


180


on the flange member


102


therebetween, and each of the second impeller blades


106


(e.g., second impeller blade


106




b


) is also adjacent a second one of the other second impeller blades (e.g., second impeller blade


106




c


) and cooperates to define a fourth area


182


on the flange member


102


therebetween. The spacing of the second impeller blades


106


is such that none of the third and fourth areas


180


and


182


that are adjacent any one of the second impeller blades


106


is equal in magnitude.




Each of the second impeller blades


106


begins at an inward point


184


and terminates at an outward point


186


. Each of the second impeller blades


106


(e.g., second impeller blade


106




b


) is configured such that its outward point


186


is radially outward of the inward point


184


of the first one of the other second impeller blades


106


(e.g., second impeller blade


106




a


) and its inward point


184


is radially inward of the outward point


186


of the second one of the other second impeller blades


106


(e.g., second impeller blade


106




c


). Each second impeller blade


106


is arcuately shaped from its inward point


184


to its outward point


186


. Accordingly, a first straight line passes through the mounting aperture


110


through the inward point


184


of the first impeller blade


106




b


and the outward point


186


of the first impeller blade


106




c


and a second straight line passes through the mounting aperture


110


through the inward point


184


of the first impeller blade


106




a


and the outward point


186


of the first impeller blade


106




b.


Each second impeller blade


106


tapers outwardly away from the flange member


102


from its inward point


184


to an intermediate point


188


between the inward and outward points


184


and


186


.




Preferably, the spacing between any adjacent pair of impeller blades is not equal to any other spacing between an adjacent pair of any of the other first and second impeller blades


104


and


106


to thereby distribute the noise energy over a maximum number of frequencies. Construction in this manner, however, is extremely difficult, particularly where the impeller


18


is formed in a molding process, due to the unsymmetrical distribution of material in the impeller


18


. The unsymmetrical distribution of material tends to facilitate distortion in the molded impeller


18


as it cools, as well as offsets its rotational center of gravity about its axis of rotation so that it vibrates when it is rotated.




In view of these difficulties, the set of first impeller blades


104


are instead divided into a plurality of identically configured first blade groups


200


, wherein each of the first blade groups


200


includes an identical quantity of the first impeller blades


104


which are spaced apart in a predetermined first blade spacing pattern. In the example provided, each of the first blade groups


200


includes a total of four (4) of the first impeller blades


104




a,




104




b,




104




c


and


104




d,


with the first impeller blade


104




a


being spaced apart from predetermined reference point (e.g. the first impeller blade


104




d


in another first blade group


200


) by an angle of 57°, the first impeller blades


104




a


and


104




b


being spaced apart with a spacing angle


152


of 41°, the first impeller blades


104




b


and


104




c


being spaced apart with a spacing angle


152


of 49° and the first impeller blades


104




c


and


104




d


being spaced apart with a spacing angle


152


of 33°. The first blade groups


200


are fixed to the first side


150


of the flange member


102


such that they are offset from one another by a predetermined angular spacing (e.g., 57°).




Similarly, the set of second impeller blades


106


are divided into a plurality of identically configured second blade groups


220


, wherein each of the second blade groups


220


includes an identical quantity of the second impeller blades


106


which are spaced apart in a predetermined second blade spacing pattern. In the example provided, each of the second blade groups


220


includes a total of three (3) of the second impeller blades


106




a,




106




b


and


106




c,


with the second impeller blade


106




a


being spaced apart from predetermined reference point (e.g. the second impeller blade


106




c


in another second blade group


220


) by an angle of 40°, the second impeller blades


106




a


and


106




b


being spaced apart with a spacing angle


162


of 32° and the second impeller blades


106




b


and


106




c


being spaced apart with a spacing angle


162


of 48°. The second blade groups


220


are fixed to the second side


170


of the flange member


102


such that they are offset from one another by a predetermined angular spacing (e.g., 40°).




While noise attenuation is primarily achieved through the configuration of the impeller


18


, the geometry of the housing


16


is also employed to aid in the attenuation of the noise that is generated during the operation of the blower


10


. In this regard, noise that results from the rotation of the impeller


18


is not discharged in a direct or straight-line manner from the housing


16


but rather is reflected off several various interior surfaces within the housing


16


as shown in FIG.


2


. For example, noise


250


that is directed rearwardly from the impeller


18


is reflected off the rearward wall


252


before it is reflected outwardly through the inlet apertures


86


. Similarly, noise


250


that is directed forwardly from the impeller


18


is reflected off the walls


254


of the outlet


68


before it is discharged through the outlet


68


. The reflecting of noise


250


off the various interior surfaces of the housing


16


permits the housing


16


to absorb some of the energy of the noise


250


to thereby attenuate the level of noise


250


that is transmitted out of the housing


16


.




While the invention has been described in the specification and illustrated in the drawings with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention as defined in the claims. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment illustrated by the drawings and described in the specification as the best mode presently contemplated for carrying out this invention, but that the invention will include any embodiments falling within the foregoing description and the appended claims.



Claims
  • 1. A radial flow fan comprising:a housing having at least one inlet, an outlet and an impeller cavity in fluid connection with the inlet and the outlet; and an impeller rotatably supported in the impeller cavity on a rotary axis, the impeller having an annular flange member and a plurality of impeller blades fixedly coupled to the annular flange member such that each of the impeller blades is adjacent another of the impeller blades in a predetermined circumferential direction, each adjacent pair of impeller blades defining a spacing angle, the impeller being configured such that a first predetermined quantity of the impeller blades are spaced apart from an associated adjacent impeller blade with a first predetermined angle and a second predetermined quantity of the impeller blades are spaced apart from an associated adjacent impeller blade with a second predetermined angle that is not equal to the first predetermined angle, the plurality of impeller blades being segregated into a plurality of identically configured first blade groups, each of the first blade groups having an equal number of impeller blades, the impeller blades within one of the first blade groups being spaced apart from one another with a predetermined pattern of spacing angles including at least one of the first predetermined angle and the second predetermined angle; wherein the plurality of impeller blades are configured to intake a compressible fluid in a first direction generally parallel the rotary axis and expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity.
  • 2. The portable debris blower of claim 1, wherein a spacing angle between a last impeller blades in a first one of the impeller blade groups and a first one of the impeller blades in a next one of the impeller blade groups is not equal to a spacing angle between each adjacent pair of impeller blades in the first one of the impeller blade groups.
  • 3. The portable debris blower of claim 2, wherein the predetermined pattern of spacing angles includes a plurality of non-equal spacing angles.
  • 4. The radial flow fan of claim 1, wherein the predetermined pattern of spacing angles includes a plurality of non-equal spacing angles.
  • 5. The radial flow fan of claim 1, further comprising a plurality of second impeller blades, the second impeller blades being fixedly coupled to the annular flange member such that each of the second impeller blades is adjacent another of the second impeller blades in a predetermined circumferential direction, each adjacent pair of second impeller blades defining a second spacing angle, the impeller being configured such that a first predetermined quantity of the second impeller blades are spaced apart from an associated adjacent second impeller blade with a third predetermined angle and a second predetermined quantity of the second impeller blades are spaced apart from an associated adjacent second impeller blade with a fourth predetermined angle that is not equal to the third predetermined angle;wherein the plurality of second impeller blades are configured to intake a compressible fluid in a second direction generally parallel the rotary axis and expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity.
  • 6. The radial flow fan of claim 5, wherein the plurality of second impeller blades are segregated into a plurality of identically configured second blade groups, each of the second blade groups having an equal number of the second impeller blades, the second impeller blades within one of the second blade groups being spaced apart from one another with a predetermined second pattern of spacing angles including at least one of the third predetermined angle and the fourth predetermined angle.
  • 7. The portable debris blower of claim 6, wherein a spacing angle between a last impeller blades in a first one of the second impeller blade groups and a first one of the impeller blades in a next one of the second impeller blade groups is not equal to a spacing angle between each adjacent pair of the second impeller blades in the first one of the second impeller blade groups.
  • 8. The portable debris blower of claim 7, wherein the predetermined pattern of spacing angles includes a plurality of non-equal spacing angles.
  • 9. The portable debris blower of claim 6, wherein the predetermined pattern of spacing angles includes a plurality of non-equal spacing angles.
  • 10. The portable debris blower of claim 6, wherein each of the second impeller blades begins at an inward point and terminates at an outward point, each of the second impeller blades being configured such that its inward point is radially inward of the outward point of the first one of the outer second impeller blades and its outward point is radially outward of the inward point of the second one of the other second impeller blades.
  • 11. The portable debris blower of claim 10, wherein each of the second impeller blades is arcuately shaped from the inward point to the outward point.
  • 12. The portable debris blower of claim 10, wherein each of the second impeller blades tapers outwardly away from the flange member from the inward point to an intermediate point between the inward and outward points.
  • 13. The portable debris blower of claim 6, wherein the predetermined number of first blade groups is not, equal to the predetermined number of second blade groups.
  • 14. The portable debris blower of claim 13, wherein a quantity of the first impeller blades that form one of the first blade groups is not equal to a quantity of the second impeller blades that form one of the second blade groups.
  • 15. The portable debris blower of claim 1, wherein each of the impeller blades begins at an inward point and terminates at an outward point, each of the impeller blades being configured such that its inward point is radially inward of the outward point of the first one of the other impeller blades and its outward point is radially outward of the inward point of the second one of the other impeller blades.
  • 16. The portable debris blower of claim 15, wherein each of the impeller blades is arcuately shaped from the inward point to the outward point.
  • 17. The portable debris blower of claim 15, wherein each of the impeller blades tapers outwardly away from the flange member from the inward point to an intermediate point between the inward and outward points.
  • 18. A radial flow fan comprising:a housing having at least one inlet, an outlet and an impeller cavity in fluid connection with the inlet and the outlet; and an impeller rotatably supported in the impeller cavity on a rotary axis, the impeller including: an annular flange member; a plurality of first impeller blades fixedly coupled to the annular flange member such that each of the first impeller blades is adjacent another of the first impeller blades in a predetermined circumferential direction, each adjacent pair of first impeller blades defining a first spacing angle, the impeller being configured such that a first predetermined quantity of the first impeller blades are spaced apart from an associated adjacent first impeller blade with a first predetermined angle and a second predetermined quantity of the first impeller blades are spaced apart from an associated adjacent first impeller blade with a second predetermined angle that is not equal to the first predetermined angle, the plurality of first impeller blades being segregated into a plurality of identically configured first blade groups, each of the first blade groups having an equal number of first impeller blades, the first impeller blades within one of the first blade groups being spaced apart from one another with a predetermined pattern of spacing angles including at least one of the first predetermined angle and the second predetermined angle; a plurality of second impeller blades, the second impeller blades being fixedly coupled to the annular flange member such that each of the second impeller blades is adjacent another of the second impeller blades in a predetermined circumferential direction, each adjacent pair of second impeller blades defining a second spacing angle, the impeller being configured such that a first predetermined quantity of the second impeller blades are spaced apart from an associated adjacent second impeller blade with a third predetermined angle and a second predetermined quantity of the second impeller blades are spaced apart from an associated adjacent second impeller blade with a fourth predetermined angle that is not equal to the third predetermined angle, the plurality of second impeller blades being segregated into a plurality of identically configured second blade groups, each of the second blade groups having an equal number of the second impeller blades, the second impeller blades within one of the second blade groups being spaced apart from one another with a predetermined second pattern of spacing angles including at least one of the third predetermined angle and the fourth predetermined angle; wherein the plurality of first impeller blades are configured to intake a compressible fluid in a first direction generally parallel the rotary axis and expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity; and wherein the plurality of second impeller blades are configured to intake a compressible fluid in a second direction generally parallel the rotary axis and expel the compressible fluid to the outlet in a direction generally tangent the impeller cavity.
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