CA1212363A - Axial and mixed flow fans and blowers - Google Patents
Axial and mixed flow fans and blowersInfo
- Publication number
- CA1212363A CA1212363A CA000391960A CA391960A CA1212363A CA 1212363 A CA1212363 A CA 1212363A CA 000391960 A CA000391960 A CA 000391960A CA 391960 A CA391960 A CA 391960A CA 1212363 A CA1212363 A CA 1212363A
- Authority
- CA
- Canada
- Prior art keywords
- casing
- axial
- mixed flow
- suction fan
- intermediate portion
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
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- Structures Of Non-Positive Displacement Pumps (AREA)
Abstract
ABSTRACT
An axial or mixed flow fan having an impeller including a hub and a plurality of radially extending blades, the impeller is surrounded by a casing which is preferably of circular cross sectional shape and is divided along its length into three portions. The first, inlet, portion is an inlet portion which terminates in a second, intermediate, portion which is of larger diameter than the minimum diameter of the first portion. The second portion terminates in a third, outlet, portion which is no larger in diameter than the minimum diameter of the first portion. The impeller is so positioned that the leading edge of the tip of each blade is positioned within the second portion while the trailing edge thereof is positioned within the third portion of the casing.
An axial or mixed flow fan having an impeller including a hub and a plurality of radially extending blades, the impeller is surrounded by a casing which is preferably of circular cross sectional shape and is divided along its length into three portions. The first, inlet, portion is an inlet portion which terminates in a second, intermediate, portion which is of larger diameter than the minimum diameter of the first portion. The second portion terminates in a third, outlet, portion which is no larger in diameter than the minimum diameter of the first portion. The impeller is so positioned that the leading edge of the tip of each blade is positioned within the second portion while the trailing edge thereof is positioned within the third portion of the casing.
Description
36~
The present invention relates to axial or mixed 1OrJl blowers or suction fans and more particularly to such blowers and fans which exhibit improved stability of operation.
It is known that conventional fans suffer from the problem of stalling when the gas flow past the fan blades breaks away from the surface of the blades and/or the housing surrounding the fan. The fans and blowers according to the present invention are designed to significantly reduce the liability of a stall con-dition occurring over a wide range of possible operating condi-tions.
Summary of the Invention The present invention consists in a high pressure axialor mixed flow blower or suction fan, comprising: an elongate tubular casing, an impeller disposed within said casing and having a hub rotatable about a longitudinal axis of the casing, and also having a plurality of impeller blades extending radially from said hub, each impeller blade having a tip with a leading edge and a trailing edge, a stationary center tube positioned within said casing upstream of the hub and carrying a plurality of guide vanes extending radially therefrom, the casing comprising a tubular inlet portion the cross sectional area of which is constant or is reduced gradually along its length and which extends at least from the guide vanes in a downstream direction until it terminates in a tubular intermediate portion of larger cross sectional area than the inlet portion at its point of termination, the intermediate portion in turn terminating in a tubular outlet portion which is no larger in cross sectional area than the inlet portion at its point of termination, the inlet portion and the intermediate por---` ~Z~LZ3~3 tion being connected by an imperforate and substantially annular first wall portion and the intermediate portion and the outlet portion being connected by an imperforate and substantially annular second wall portion, the impeller being so positioned that the leading edge of the tip of each blade is positioned within the intermediate portion while the trailing edge thereof is positioned within the outlet portion, characterised in that a plurality of fixed vanes are provided in, and are affixed to, the intermediate portion of the casing, each vane being connected to at least one of the wall portions.
The casing of the blower or fan is preferably circular in cross sectional shape. The inlet portion is preferably frusto-conical or cylindrical while the intermediate and outlet portions are preferably cylindrical. The diameter of the outlet portion is preferably slightly smaller than the minimum diameter of the inlet portion. As is conventional in such fans the diameter of the out-let portion should be only slightly larger than the diameter of the circle swept by the rotating blades of the impeller.
The diameter of the intermediate portion is larger than the diameter, or minimum diameter, of the inlet and outlet portions.
It is preferred that the diameter of the enlarged intermediate por-tion be from 1.1 to 1.5 times the diameter of the impeller and most preferably between 1.2 and l times that diameter.
The fixed vanes within the intermediate portion are pre-ferably disposed radially of the hub and axially of the casing. It is particularly preferred that these vanes narrow in a downstream direction.
The commencement and termination of the intermediate
The present invention relates to axial or mixed 1OrJl blowers or suction fans and more particularly to such blowers and fans which exhibit improved stability of operation.
It is known that conventional fans suffer from the problem of stalling when the gas flow past the fan blades breaks away from the surface of the blades and/or the housing surrounding the fan. The fans and blowers according to the present invention are designed to significantly reduce the liability of a stall con-dition occurring over a wide range of possible operating condi-tions.
Summary of the Invention The present invention consists in a high pressure axialor mixed flow blower or suction fan, comprising: an elongate tubular casing, an impeller disposed within said casing and having a hub rotatable about a longitudinal axis of the casing, and also having a plurality of impeller blades extending radially from said hub, each impeller blade having a tip with a leading edge and a trailing edge, a stationary center tube positioned within said casing upstream of the hub and carrying a plurality of guide vanes extending radially therefrom, the casing comprising a tubular inlet portion the cross sectional area of which is constant or is reduced gradually along its length and which extends at least from the guide vanes in a downstream direction until it terminates in a tubular intermediate portion of larger cross sectional area than the inlet portion at its point of termination, the intermediate portion in turn terminating in a tubular outlet portion which is no larger in cross sectional area than the inlet portion at its point of termination, the inlet portion and the intermediate por---` ~Z~LZ3~3 tion being connected by an imperforate and substantially annular first wall portion and the intermediate portion and the outlet portion being connected by an imperforate and substantially annular second wall portion, the impeller being so positioned that the leading edge of the tip of each blade is positioned within the intermediate portion while the trailing edge thereof is positioned within the outlet portion, characterised in that a plurality of fixed vanes are provided in, and are affixed to, the intermediate portion of the casing, each vane being connected to at least one of the wall portions.
The casing of the blower or fan is preferably circular in cross sectional shape. The inlet portion is preferably frusto-conical or cylindrical while the intermediate and outlet portions are preferably cylindrical. The diameter of the outlet portion is preferably slightly smaller than the minimum diameter of the inlet portion. As is conventional in such fans the diameter of the out-let portion should be only slightly larger than the diameter of the circle swept by the rotating blades of the impeller.
The diameter of the intermediate portion is larger than the diameter, or minimum diameter, of the inlet and outlet portions.
It is preferred that the diameter of the enlarged intermediate por-tion be from 1.1 to 1.5 times the diameter of the impeller and most preferably between 1.2 and l times that diameter.
The fixed vanes within the intermediate portion are pre-ferably disposed radially of the hub and axially of the casing. It is particularly preferred that these vanes narrow in a downstream direction.
The commencement and termination of the intermediate
2 -portion are preferably both abrupt with the intermediate portion being joined to the inlet or outlet portion by an annular wall por-tion which lies in a plane at right angles to the longitudinal axis of the Ean or blower casing. While it is not essential that the intermediate portion terminates abruptly in a downstream direction, it is essential that this termination takes place, in an axial direction, between the leading and trailing edges of the impeller blades.
The arrangement according to this invention may be used with equal advantage in fixed or variable pitch fans and blowers.
In certain cases it is desirable to provide in the inlet portion a plurality of radially directed guide vanes which are each rotatable about its own longitudinal axis. These guide vanes pre-ferably extend between the wall of the inlet portion and a cylin-drical stator disposed coaxially with the casing. These guide vanes are preferably used in axial flow fans and blowers in which the blades of the impeller are not themselves rotatable about their own longitudinal axes. These variable pitch guide vanes may be positioned at angles relative to the longitudinal axis of the fan of from + 45 to - 90. The angle is considered to be positive if the - 2a -",, 12~3~;3 vanes cause the incoming gas stream to be moved so as to increase the angle through which the direction of movement of the gas stream is changed by the impeller; it is considered negative when that angle is reduced. A similar convention is used when considering the fixed vanes in the intermediate portion. In fans and blowers where the impeller blades are of variable pitch such guide vanes are not generally required.
The minimum diameter of the inlet portion is preferably slightly larger than the impeller diameter. The most preferred minimum diameter of the inlet portion is from 1.01 to 1.1 times the impeller diameter. The stability of the fan for any given minimum diameter of the inlet portion increases as the axial distance between the leading edge of the impeller and the terminal edge of the inlet portions increases. This increased stability is however associated with a slight loss of efficiency.
Best Mode of Carrying Out the Invention Hereinafter given by way of example only are details of a variety of embodiments of the invention described with reference to the accompanying drawings in which :-Fig. 1 is a diagrammatic longitudinal sectional viewthrough `one embodiment of a mixed flow fan according to this invention.
Fig. 2 is a pressure/volume diagram for the mixed flow fan of Fig. 1.
Fig. 3 is a diagrammatic longitudinal sectional view through another embodiment of a mixed flow fan according to this invention.
Fig. 4 is a pressure/volume diagram for the mixed flow fan of Fig. 3.
Fig. 5 is a diagrammatic longitudinal sectional view through a further embodiment of a mixed flow fan according to this i.lvention.
Fig. 6 is a diagrammatic longitudinal sectional view through a still further embodiment of a mixed flow fan ~21~3~:i3 according to this invention.
Fig. 7 is a pressure/volume diagram for the mixed flow fans of Figs. 5 and 6.
In describing the various embodiments of this invention the same numeral will be used to describe the same integers in the different embodiments of the invention.
As is seen in Figs. 1, 3, 5 and 6 the fan 10 comprises a casing 11 or circular cross sectional shape which surrounds and is coaxial with an impeller 12 which comprises a hub 13 and a plurality of radially directed blades 14. The cylindrical casing 11 is divided into three principal parts.
A frusto-conical inlet part 15 terminates in a cylindrical imtermediate part 16 of enlarged diameter which in turn terminates in a cylindrical outlet part 17. The intermediate part 16 terminates and the outlet part commences intermediate the leading and trailing edge of the impeller blades 14.
Upstream of the impeller 12, and coaxial therewith is a centre tube 18. A plurality of radially directed guide vanes 19, each mounted on a spindle 20, are positioned about the centre tube 18. Each vane 19 extends radially outwardly to the inside surface of the inlet port 15 of the casing 11 and is rotatable about its spindle 20 such that the angle of the vane to the longitudinal axis of the fan may be varied.
The intermediate part 16 may include an array of fixed vanes 21 which may be axially of the fan as in Figs 3 and 5 or at an angle to that axis as in Fig. 1.
In the arrangement shown in Fig. 1 the minimum diameter of the inlet part 15 is equal to the diameter of the outlet part 17, i.e. approximately equal to the diameter of the impeller 12.
The intermediate portion includes a number of fixed vanes 21 each of which extends at 45 to the axis of the casing and is radially directed relative to the impeller.
The inlet portion 15 is extended rearwardly as cylindrical wall 22 which continues the minimum diameter of 12~23~3 inlet portion 15 and is connected to the radially inner edges of the vanes 21.
Figure 2 is a pressure/volume diagram for the fan shown in Fig. 1. Each solid line represents the measured P/V
relationship for the angular setting of moveable guide vanes indicated. The dotted lines represent contours of equal efficiency with the point of maximum efficiency marked with a cross. It can be seen from Fig. 2 that the fan of Fig. 1 showed a smooth P/V curve for all vane angles tested showing that the fan was not stalling at any point throughout its full operating ranges.
Figure 3 shows another embodiment of the invention in which the intermediate portion includes a number of fixed vanes which extend axially of the casing and radially relative to the impeller. The inlet portion 15 is extended with the frusto conical wall 22 defining the minimum diameter of the inlet portion.
In this arragnement an aperture was left in the fixed vanes adjacent the leading edge of the intermediate portion to increase interaction of circulating flow between each pair of fixed stabilising vanes.
In can be seen from Fig. 4 that the above embodiment is free from stall characteristics.
Figures 5 and 6 show further embodiments of the invention.
Figure 5 shows an arrangement in which axially and radially disposed vanes 21 are provided in the intermediate portion. Figure 6 shows a very similar arrangement but without the vanes. In each of these situations the inlet portion stops abruptly at the start of the intermediate portion.
Figure 7 compares the P/V performance of the fans of Fig. 5 and 6 with the Fig. 5 fan results shown in dashed lines and the Fig. 6 fan in solid lines. It can be seen that while the removal of the fixed guide vanes has not induced iZ123Ç~
stalling in the fan, it has substantially reduced pressures at low volumes.
The arrangement according to this invention may be used with equal advantage in fixed or variable pitch fans and blowers.
In certain cases it is desirable to provide in the inlet portion a plurality of radially directed guide vanes which are each rotatable about its own longitudinal axis. These guide vanes pre-ferably extend between the wall of the inlet portion and a cylin-drical stator disposed coaxially with the casing. These guide vanes are preferably used in axial flow fans and blowers in which the blades of the impeller are not themselves rotatable about their own longitudinal axes. These variable pitch guide vanes may be positioned at angles relative to the longitudinal axis of the fan of from + 45 to - 90. The angle is considered to be positive if the - 2a -",, 12~3~;3 vanes cause the incoming gas stream to be moved so as to increase the angle through which the direction of movement of the gas stream is changed by the impeller; it is considered negative when that angle is reduced. A similar convention is used when considering the fixed vanes in the intermediate portion. In fans and blowers where the impeller blades are of variable pitch such guide vanes are not generally required.
The minimum diameter of the inlet portion is preferably slightly larger than the impeller diameter. The most preferred minimum diameter of the inlet portion is from 1.01 to 1.1 times the impeller diameter. The stability of the fan for any given minimum diameter of the inlet portion increases as the axial distance between the leading edge of the impeller and the terminal edge of the inlet portions increases. This increased stability is however associated with a slight loss of efficiency.
Best Mode of Carrying Out the Invention Hereinafter given by way of example only are details of a variety of embodiments of the invention described with reference to the accompanying drawings in which :-Fig. 1 is a diagrammatic longitudinal sectional viewthrough `one embodiment of a mixed flow fan according to this invention.
Fig. 2 is a pressure/volume diagram for the mixed flow fan of Fig. 1.
Fig. 3 is a diagrammatic longitudinal sectional view through another embodiment of a mixed flow fan according to this invention.
Fig. 4 is a pressure/volume diagram for the mixed flow fan of Fig. 3.
Fig. 5 is a diagrammatic longitudinal sectional view through a further embodiment of a mixed flow fan according to this i.lvention.
Fig. 6 is a diagrammatic longitudinal sectional view through a still further embodiment of a mixed flow fan ~21~3~:i3 according to this invention.
Fig. 7 is a pressure/volume diagram for the mixed flow fans of Figs. 5 and 6.
In describing the various embodiments of this invention the same numeral will be used to describe the same integers in the different embodiments of the invention.
As is seen in Figs. 1, 3, 5 and 6 the fan 10 comprises a casing 11 or circular cross sectional shape which surrounds and is coaxial with an impeller 12 which comprises a hub 13 and a plurality of radially directed blades 14. The cylindrical casing 11 is divided into three principal parts.
A frusto-conical inlet part 15 terminates in a cylindrical imtermediate part 16 of enlarged diameter which in turn terminates in a cylindrical outlet part 17. The intermediate part 16 terminates and the outlet part commences intermediate the leading and trailing edge of the impeller blades 14.
Upstream of the impeller 12, and coaxial therewith is a centre tube 18. A plurality of radially directed guide vanes 19, each mounted on a spindle 20, are positioned about the centre tube 18. Each vane 19 extends radially outwardly to the inside surface of the inlet port 15 of the casing 11 and is rotatable about its spindle 20 such that the angle of the vane to the longitudinal axis of the fan may be varied.
The intermediate part 16 may include an array of fixed vanes 21 which may be axially of the fan as in Figs 3 and 5 or at an angle to that axis as in Fig. 1.
In the arrangement shown in Fig. 1 the minimum diameter of the inlet part 15 is equal to the diameter of the outlet part 17, i.e. approximately equal to the diameter of the impeller 12.
The intermediate portion includes a number of fixed vanes 21 each of which extends at 45 to the axis of the casing and is radially directed relative to the impeller.
The inlet portion 15 is extended rearwardly as cylindrical wall 22 which continues the minimum diameter of 12~23~3 inlet portion 15 and is connected to the radially inner edges of the vanes 21.
Figure 2 is a pressure/volume diagram for the fan shown in Fig. 1. Each solid line represents the measured P/V
relationship for the angular setting of moveable guide vanes indicated. The dotted lines represent contours of equal efficiency with the point of maximum efficiency marked with a cross. It can be seen from Fig. 2 that the fan of Fig. 1 showed a smooth P/V curve for all vane angles tested showing that the fan was not stalling at any point throughout its full operating ranges.
Figure 3 shows another embodiment of the invention in which the intermediate portion includes a number of fixed vanes which extend axially of the casing and radially relative to the impeller. The inlet portion 15 is extended with the frusto conical wall 22 defining the minimum diameter of the inlet portion.
In this arragnement an aperture was left in the fixed vanes adjacent the leading edge of the intermediate portion to increase interaction of circulating flow between each pair of fixed stabilising vanes.
In can be seen from Fig. 4 that the above embodiment is free from stall characteristics.
Figures 5 and 6 show further embodiments of the invention.
Figure 5 shows an arrangement in which axially and radially disposed vanes 21 are provided in the intermediate portion. Figure 6 shows a very similar arrangement but without the vanes. In each of these situations the inlet portion stops abruptly at the start of the intermediate portion.
Figure 7 compares the P/V performance of the fans of Fig. 5 and 6 with the Fig. 5 fan results shown in dashed lines and the Fig. 6 fan in solid lines. It can be seen that while the removal of the fixed guide vanes has not induced iZ123Ç~
stalling in the fan, it has substantially reduced pressures at low volumes.
Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A high pressure axial or mixed flow blower or suction fan, comprising: an elongate tubular casing, an impeller disposed within said casing and having a hub rotatable about a longitudinal axis of the casing, and also having a plurality of impeller blades extending radially from said hub, each impeller blade having a tip with a leading edge and a trailing edge, a stationary center tube positioned within said casing upstream of the hub and carrying a plurality of guide vanes extending radially therefrom, the casing comprising a tubular inlet portion the cross sectional area of which is constant or is reduced gradually along its length and which extends at least from the guide vanes in a downstream direction until it terminates in a tubular intermediate portion of larger cross sectional area than the inlet portion at its point of termination, the intermediate portion in turn terminating in a tubular outlet portion which is no larger in cross sectional area than the inlet portion at its point of termination, the inlet portion and the intermediate portion being connected by an imperforate and substantially annular first wall portion and the intermediate portion and the outlet portion being connected by an imperforate and substantially annular second wall portion, the impeller being so positioned that the leading edge of the tip of each blade is positioned within the intermediate portion while the trailing edge thereof is positioned within the outlet portion, characterised in that a plurality of fixed vanes are provided in, and are affixed to, the intermediate portion of the casing, each vane being connected to at least one of the wall portions.
2. An axial or mixed flow blower or suction fan as claimed in claim 1, in which said casing is of circular cross section along its whole length.
3. An axial or mixed flow blower or suction fan as claimed in claim 2, in which the diameter of the intermediate portion is from 1.1 to 1.5 times the diameter of the impeller.
4. An axial or mixed flow blower or suction fan as claimed in any one of claims 1 to 3, in which each of the plurality of fixed vanes provided in the intermediate portion of the casing, extends substantially axially of the casing.
5. An axial or mixed flow blower or suction fan as claimed in any one of claims 1 to 3, in which each of the plurality of fixed vanes provided in the intermediate portion of the casing, extends substantially axially of the casing and substantially radially of the hub.
6. An axial or mixed flow blower or suction fan as claimed in any one of claims 1 to 3, in which each of the plurality of fixed vanes provided in the intermediate portion of the casing, extends substantially axially of the casing, each vane decreasing in depth in the direction of the outlet portion of the casing.
7. An axial or mixed flow blower or suction fan according to claim 1 in which the first annular wall portion lies in a plane at right angles to the longitudinal axis of the casing.
8. An axial or mixed flow blower or suction fan according to claim 1 in which the second annular wall portion lies in a plane at right angles to the longitudinal axis of the casing.
9. An axial or mixed flow blower or suction fan according to claim 1 in which the first and second annular wall portions both lie in a plane at right angles to the longitudinal axis of the casing.
10. An axial or mixed flow blower or suction fan according to claim 1 in which said hub has a maximum diameter which is more than half the total diameter of the blades.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000391960A CA1212363A (en) | 1981-12-10 | 1981-12-10 | Axial and mixed flow fans and blowers |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000391960A CA1212363A (en) | 1981-12-10 | 1981-12-10 | Axial and mixed flow fans and blowers |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1212363A true CA1212363A (en) | 1986-10-07 |
Family
ID=4121589
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000391960A Expired CA1212363A (en) | 1981-12-10 | 1981-12-10 | Axial and mixed flow fans and blowers |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1212363A (en) |
-
1981
- 1981-12-10 CA CA000391960A patent/CA1212363A/en not_active Expired
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |