CA2015521C - Shroud assembly for axial flow fans - Google Patents
Shroud assembly for axial flow fansInfo
- Publication number
- CA2015521C CA2015521C CA002015521A CA2015521A CA2015521C CA 2015521 C CA2015521 C CA 2015521C CA 002015521 A CA002015521 A CA 002015521A CA 2015521 A CA2015521 A CA 2015521A CA 2015521 C CA2015521 C CA 2015521C
- Authority
- CA
- Canada
- Prior art keywords
- blades
- fan
- orifice
- diameter
- band
- 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 - Fee Related
Links
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
- 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
- F04D29/547—Ducts having a special shape in order to influence fluid flow
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S415/00—Rotary kinetic fluid motors or pumps
- Y10S415/914—Device to control boundary layer
Abstract
ABSTRACT OF THE DISCLOSURE
An axial fan is disclosed that includes a hub supported for rotation around the longitudinal axis of the fan, a plurality of impeller blades attached to the hub and extending radially from the axis of rotation, a shroud assembly including a band encircling the blades and spaced from the tips of the blades a sufficient distance to provide ample clearance to avoid contact between the blades and the band during shipment and operation of the fan, the shroud further including an orifice positioned upstream of the blades for preventing air from flowing between the orifice and the band, the orifice having a downstream end located adjacent to but spaced from the impeller blades and having a diameter such that the impeller blades extend outwardly from the hub beyond the orifice so that the flow of air over the tips of the impeller blades is substantially reduced, which increases the efficiency of the fan.
An axial fan is disclosed that includes a hub supported for rotation around the longitudinal axis of the fan, a plurality of impeller blades attached to the hub and extending radially from the axis of rotation, a shroud assembly including a band encircling the blades and spaced from the tips of the blades a sufficient distance to provide ample clearance to avoid contact between the blades and the band during shipment and operation of the fan, the shroud further including an orifice positioned upstream of the blades for preventing air from flowing between the orifice and the band, the orifice having a downstream end located adjacent to but spaced from the impeller blades and having a diameter such that the impeller blades extend outwardly from the hub beyond the orifice so that the flow of air over the tips of the impeller blades is substantially reduced, which increases the efficiency of the fan.
Description
201~21 SHROUD ASSBMBLY FOR AXIAL FLOW FANS
This invention relates to axial flow fans, generally, - -and in particular to an improved shroud assembly for such -fans. --As the impeller blade of a fan moves through a fluid, such as air, pressures on opposite sides of the blade are different. This pressure differential will cause the fluid to flow over the tip of the blade from the discharge or high pressure side of the blade to the intake side or low pressure side of the blade thus forming a vortex. This reduces the efficiency of the fan. The conventional approach to reducing -or preventinq this flow of air, is to provide some sort of seal between the blade tip and the shroud, which usually involves reducing the clearance between the blade tip and the shroud to a minimum. For example, see Langenkamp et al U.S.
Patent No. 2,030,993 and Robb et al U.S. Patent No.
4,406,581. Also see Figure 7, where the importance of reducing tip clearance to improve fan efficiency is demonstrated.
The problem, however, is that it is very difficult to manufaature, ship, install, and operate satisfactorily a fan having a small clearance between the blades and the shroud, ~ince it requires an almost perfect balancing of the rotating ' :.
2015~21 hub and blades, almost perfect centering of the rotating hub and blades in the shroud, and an almost perfectly round opening in the shroud. Therefore, as a practical matter, commercial fans are provided with enough tip clearance to operate even though the hub and blades are not perfectly balanced, the blades are not all the exact same length, the hub is not perfectly centered, and the opening in the shroud is not perfectly round. This compromise does, of course, -~
reduce the efficiency of the fan. --It is an object of this invention to provide an axial fan having the efficiency of a low fan tip clearance fan without the problems describPd above. ~ -~
It is a further object of this invention to provide an ---axial fan in which there is substantially no pressure differ- ~
ential between opposite sides of the blades adjacent the - -blade tips thereby substantially eliminating the flow of air -over the blade tips and the forming of a vortex. -It is a further object of this invention to provide such -~
an axial fan where the tips of the fan blades travel in a -space where there is little or no movement of air thereby reducing substantially the effect of tip clearance on fan efficiency. i~
It is a further object of this invention to provide an axial fan having a shroud assembly that includes a cylindrical section or band that encircles the fan blades and is spaced therefrom and an orifice section having its downstream edge adjacent to but spaced from the impeller blades, which extend outwardly beyond the downstream edge of , .. ,' ' 2~1~521 the orifice into a zone of non-moving air. The air moves out of the way of the blade tips, of course, but does not move much relative to the space through which the blade tips move.
United States Patent No. 4,515,071, which issued to Elmer S. Zach on May 7, 1985 and is entitled "Ventilation Air Control Unit" discloses an axial fan having a shroud assembly that includes a cylindrical section or band that encircles the fan blades and is spaced therefrom and an orifice section having its downstream edge adjacent to but spaced from the impeller, which extend outwardly beyond the downstream edge of the orifice into a zone of non-moving air. This structural arrangement resulted when Zach replaced a twelve inch ventilating fan with a fourteen inch fan for forcing air into a grain drying and storing bin for drying and -~
ventilating the grain in the bin.
Zach teaches use of a flange or orifice having an inner -diameter less than the overall span of the fan blade for redirecting the flow of air away from the tips of the fan blade and toward its center (claim 4, lines 18 et seq.).
It i8 an object of this invention to provide an axial -fan with an orifice, fan blade, and a band or cylindrical section encircling the fan blade and orifice, the diameters of which have a fixed relationship within a range and that substantially eliminates the flow of air over the tips of the fan blades which substantially reduces the effect of tip clearance on the efficiency of the fan, thereby allowing the tips of the fan blades to be spaced from the band '', ~'''".'' "
2~15521 sufficiently to avoid the manufacturing, shipping, installation, and operating problems described above.
Specifically, it is a further object and feature of this invention to provide an axial fan having an orifice, a fan blade, and a band wherein the diameter of the fan blade is about 103~ of the diameter of the orifice ana the diameter of ~-the band is about 106~ of the diameter of the orifice, which substantially eliminates the effect of tip clearance or fan efficiency and provides ample clearance between the tip of the fan blade and the band to substantially eliminate damage - P--to the fan blade as a result of a reduction of such clearance - ~ `
in an effort to improve fan efficiency. -These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached drawings and appended claims. `-In The Drawings: -:.
Figure 1 is a view of the discharge side of a fan constructed in accordance with the preferred embodiment of this invention.
Figure 2 is a sectional view taken along line 2--2 of Figure 1.
Figure 3 is a view of the intake side of the fan of Figure 1.
Figure 4 is a partial sectional view of an alternate embodiment of the invention.
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201~21 Figure 5 is a graph of the performance data of three fans, and ---Figures 6A, 6B, and 6C show the arrangement of the fans and the shrouds that produced curves A, B, and C of Figure 5, ~ -Figure 6C being the fan that embodies this invention.
Figure 7 is a graph showing the effect of tip clearance on fan efficiency.
The fan of Figures 1, 2, and 3 include~ hub 10 to which four impeller blades 12 are attached. Preferably, the blades are curved along their transverse axes to provide concave surfaces facing the discharge side of the fan, as shown in Figure 2. Hub 10 is mounted on shaft 14. The shaft is supported for rotation around its longitudinal axis by bearings 16 and 18 that are mounted on end plates 20 and 22 --of bearing housing 24. The hub, the shaft, the bearings, and bearing housing are supported in the center of rectangular fan casing 26 by support v~nes 28 that extend between the -bearing housing and the fan casing. Sheave 30 mounted on shaft 14 on the outside of bearing housing 24 is rotated by ~-belt 32 which in turn rotates hub 10 and the impeller blades.
Belt 32 is driven by an electric motor that is usually mounted on the fan casing. The motor is not shown.
In accordance with this invention, the fan is provided with shroud assembly 34 that includes cylindrical section or band 36 and orifice section 38. The cylindrical section is attached to and supported by orifice section 38. The orifice section in turn is connected to rectangular fan casing 26.
In the embodiment shown, the orifice section is an integral ' ',.: ' ::
part of the front wall of the fan casing. It curves toward the center of the fan casing and rearwardly toward impeller blades 12, as shown, to provide a nozzle shaped guide for the air flowing through the fan. Although it need not do so, the orifice section shown straightens out and becomes cylindrical as it approaches the impeller blades to provide a section of --uniform diameter through which the air flows before reaching - -the impeller blades.
In accordance with this invention, the impeller blades -extend outwardly beyond the orifice section with the tips of ~ -the blades adjacent to but spaced from the cylindrical -_ section of the shroud, as shown in Figure 2. This --arrangement provides annular space 40 between the orifice section and the cylindrical section in which the air does not move substantially. Consequently, there is little pressure --differential between the sides of the impeller tips which -results in substantially no radial flow of air over the tips of the blades. Therefore, there is no need for the tips of ~-the blades to be close to the shroud to obtain the greatest ~ -efficiency for the fan. This is shown by the results of comparative tests on three fans, one of which being ;
constructed in accordance with this invention.
The best method to use in evaluation of the improved performance of the fan of this invention tfan C), shown in curves "C" of the attached curve sheet, is the use of "system .. ..
re~istance" curves to make the performance of present technology ~curves "A" and "B") equal the performance of the :,:
',.,'-',''.~' .'' .: '.' '' '':' ~r~
7 201~
improved fan (curves "C"). Each fan had an orifice that was 25" in diameter.
As shown in Figures 6A, 6B, and 6C, the impeller blades of fan A are located inside the orifice with the blade tips spaced 0.341 inches from the orifice. Fan B also has its - -blades located inside the orifice, but the blade tips are -much closer to the orifice, i.e., about 0.171 inches. Fan C
has its shroud and blades positioned in accordance with this invention with the end of the orifice spaced about 0.75 -inches from the cylindrical section, i.e., the cylindrical section has a diameter that is 106~ of the diameter of the orifice. The fan blades extend beyond the orifice about -0.375 inches, i.e., the diameter of the blades is about 103%
of the diameter of the orifice. The forward edge of each blade is about 0.25 inches from the end of the orifice.
Obviously, substantial clearance is provided between the stationary and moving parts of the fan.
"System resistance" is the resistance to air flow when a fan or blower i~ attached to a fixed duct system. Changes in performance are then made by application of "fan laws". The -"system resistance curves" in this instance are parabolic curves with the origin at zero for CFM and static pressure (P9) . . :. :
Table I below shows four different performances of fan C
at four different static pressures (Ps). The static -pressures were 0.000", 0.125", 0.250", and 0.375".
Gonerally, 809~ of commercial fan sales are for performances . .
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~
201~21 at static pressures (Ps) of 0.125" and 0.250", and 20% would be static pressures (Ps) of 0.000" (Free Air) and 0.375".
T~BLE I
Performance of Improved Fan (Curve "C") CFM: 6629 6050 5400 4600 RPM: 1150 1150 1150 1150 - -~
Ps: 0.000" 0.125" 0.250" 0.375" --BHP: 0.422 0.48 0.531 0.575 Static Eff: 0.0% 24.8% 40.0% 47.2% - -Each of the four static pressures of fan C has a different "system resistance curve". These "system ; .~ .
resistance" curves can be calculated by the following ~ -equation:
cfm = constant ~ (1) : :
or .
cfm = constant (2) \/ Ps '''.' '.' :''.`'~,''''''' For curve "C", the constants are:
Ps: 0.000 0.125" 0.250" 0.375" ---Constant: 0 17112 10800 7512 ,. .:
cfm is in cubic feet per minute Ps (static pressure) is in inches of water - :
'.' ''' .'~ "
Three of these "system re~istance curves" for Ps =
0.125", 0.250", and 0.375" are plotted in dashed lines in Figure 5~
"'''. , ,"',,'' - g The "system resistance curve" for Ps = 0.000" (~ree Air) is a special case because Ps = O. Therefore, the constant in the above equation is also equal to 0. Then:
CFM of curve "C" @ Ps = O
= K
CFM of curve "A" or "B" @ Ps = O
Kl x 1150 = new RPM for curve "A" or "B"
(Kl)2 x 0.000" = new Ps for curve "A" or "B" = O
(Kl)3 x BHP for curve "A" or "B" - new BHP for curve --"A" or "B" @ New RPM
Figure 5 shows curves for Volume (CFM) vs Static Pressure (PS), Volume (CFM) vs Horsepower (B~P), and Static Efficiency vs Volume (CFM) for the fans of present ~echnology - -(Curves "A" and "B") and the improved fan (Curve "C").
Calculated values of CFM and PS where the "system resistance curves~ intersect the performance curves of "A"
and "B" can be determined by applying constants of Curve "C"
in equation (2). By consulting Figure 5, the values of BHP :
are manually read from the Volume ~CFM) vs Horsepower (BHP) - ~
curve, of Figure 5, at the CFM calculated for the ~ -intersection of "system resistance curve" and Curves "A'i and -"B". -: :
Curve "A" Performance Data at the Intersection of "System Resistance Curves" of Curve "C"
': . '. ' PS 0.000" 0.087" 0.180" 0.282" ~:
BHP 0.360 0.4B5 0.43 0.443 ~;
201~5~1 -- ~.o ..
Curve "B" Performance Data at the Intersection of the "System Resistance Curves" of Curve "C"
PS 0.000" 0.099" 0.206" 0.333" .
BHP 0.369 0.405 0.446 0.481 -There are certain well recognized engineering laws derived from engineering fundamentals that apply to all centrifugal and axial flow machinery performance. These are - -called "Fan laws" by those skilled in the art. -The "fan laws" are now employed to compare the perfor-mances of fans "A" and "B" (curves A and B) to the - ..
performance of fan C (curve "C") for the four static pres-sures shown in Table I.
The "fan laws" are in this instance~
, ...
Ratio of changes in RPM or Cfm = Kl Ratio of changes in Static pressure = (K
Ratio of changes in BHP - (K1)3 The comparison is made by moving data from curve "A" and .
curve "B" along "system resistance curves" to curve "C" by use of the "fan laws" as follows: :
:
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;' ', 201~.~21 TABLE II
Performance Data for Curve "A' and Upgraded to Curve "C"
CFM: 5462 5047 4582 3989 RPM: 1150 1150 1150 1150 Ps: 0.000" 0.087" 0.180" 0.282"
BHP: 0.360 0.405 0.43 0.443 Static Eff: 0.0% 17.1% 30.2% 40.0~ -CFM&RPM-Kl:~6629~=1.2137 ~65)=1.1987 ~540~=1.1785 ~46~=1.1517 1~5462J ~5047~ ~4582~/ ~3989/
~6629~2 1 4730 ~65~2=1 4370~54~2=1.3889 p ~2=1.3298 \~546-2J ~50471 ~4582J ~3989~ - -~6629~ 1 7877 ~5~3=1 7225~54oo~3=l.6369~ ~3=1.5355 ~5462~ ~5047l ~458~ 3989~ - -CFM: 6629 6060 5400 4600 RPM:(+21.3~)1396 (+19.8%) 1378 (+17.8%)1355 (+15.2%)1326 Ps: 0.000" 0.125" 0.25" 0.375"
BHP:(+52.4%)0.643 (+45.4%) 0.698 (+32.5%)0.704 (+18.1%)0.679 Static Eff: 0.0% (-31.2%) 17.1% (-24.5%)30.2% (-8.5%) 40.0%
Evaluation of Table II shows that fan A at 0.000" (Free ~-Air) had increased RPM by 21.3% and required more power E~HP
, by 52.4%. Similar but lower increases were shown for the -other static pressures: 0.125" 0.250" and 0.375". The loss -in static efficiency was 31.2% at 0.125" static pressure 24.5% at 0.250" static pressure and 8.5% at 0.375" static - -pressure.
Table III shows the result when data from curve "B" is moved to equal the performance of curve "C".
S ~
201~21 TABLE III
Performance Data From Curve "B" and Upgraded to Curve "C"
CFM: 5769 5384 4902 4335 RPM: 1150 1150 1150 1150 Ps: 0.000" 0.099" 0.206" 0.333"
BHP: 0.369 0.405 .446 .481 Static Eff: 0.096 20.796 35.7996 47.2%
~6629~=1 1491 ~605 ~ =1.1237 ~ ~ =1.1016 ~5769/ 5084/ ~4902~ ~4335J
Ps: ~629~2=l.32o4 ~2=1.26~7~54~2=1 2135~600~2 1 12 5769l 5384/ ~4902/ ~4335/ ~`
BHP:~ 6629~ 1 5172 /65~3=1 4189/>~54~3=1.3368~ ~3 1.1948 ~,5769/ 1~ ,4902/ \,4335/
CFM: 6629 6050 5400 4600 RPM:(+14.9%)1321 (+12.3%) 1292 ~+10.2%)1269 (+6.1%) 1220 Ps: 0.000" 0.125" 0.250" 0.375" -- -B~P:(+32.7%)0.560 (+19.896) 0.575 (+7.2%) 0.596 0.575 Static Eff: 0.0% (-16.5~) 20.7% (-10.7%)35.79% 47.2%
Evaluation of Table III shows that fan "B" at 0.000" ; ~
(Free Air) had increased RPM by 14.996 and required 32.7% more ; `
power, BHP. Similar but lower increases were shown for static pressures of 0.125" and 0.250". At the 0.375" static pressure, however, only the RPM increased by 6.1%. Increased RPM will increase the noise level.
Tables II and III show clearly that reduction in tip clearance of the present technology will bring increased eficiencies, but this also brings on a problem of how to effectively manufacture such equipment and ship to the ultimate user.
The improved fan of this invention allows for acceptable manufacturing tolerances without 108s of performance.
' '' ',.
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2 ~ 2 1 SUMMARY
Tables IV and V shown below are summaries of all per-centage changes in performance when curves "A" and "B" are made equal in performance to curve "C".
TABLE IV
Percentage Change to Make Curve "A" Equal Curve "C"
For Curve "A":
Static pressure : -of Curve "C" 0.000" 0.125" 0.250"0.37"
CFM +21.37% +19.87% +17.85%+15.17%
RPM ~21.37~ +19.87% +17.85%+15.17%
Ps +47.30~ +43.7% +38.89%+32.99% : -BHP +52.4% +45.4% +32.5%+18.1% - -Static Eff. none -31.1% -24.5%- 8.5% :~
TABLE V
. . , Percentage Change to Make Curve "B" Equal Curve "C" ~ -For Curve "B": ~ ;
Static pressure : -of Curve "C" 0.000" 0.125" 0.250"0.375" - :
CFM +14.:91% +12.37~ +10.16%+6.11~
RPM +14.91% +12.37~ +10.16%+6.11% : -Ps l32.04~ +26.27% +31.35%+12.6%
BHP +32.7% +19.8% +7.2% none -Static Eff. none -16.5% -10.7% none Figure 4 is an alternate embodiment of this invention. ~.
Structurally, it is the same as the embodiment in Figures 1, 2, and 3 with the addition of annular bracket 42 to support :
and connect the rearward edge of the orifice section to the cylindrical section. This embodiment does not perform as well as the preferred embodiment, but better than fans A and 3. : :
From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects -~
;' '..' :~:'' 201~21 hereinabove set orth, together with other advantages which -are obvious and which are inh~rent to the apparatus and structure.
It will be understood that certain features and subcom-binations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. -Because many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all mattex herein set forth or shown in -the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
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This invention relates to axial flow fans, generally, - -and in particular to an improved shroud assembly for such -fans. --As the impeller blade of a fan moves through a fluid, such as air, pressures on opposite sides of the blade are different. This pressure differential will cause the fluid to flow over the tip of the blade from the discharge or high pressure side of the blade to the intake side or low pressure side of the blade thus forming a vortex. This reduces the efficiency of the fan. The conventional approach to reducing -or preventinq this flow of air, is to provide some sort of seal between the blade tip and the shroud, which usually involves reducing the clearance between the blade tip and the shroud to a minimum. For example, see Langenkamp et al U.S.
Patent No. 2,030,993 and Robb et al U.S. Patent No.
4,406,581. Also see Figure 7, where the importance of reducing tip clearance to improve fan efficiency is demonstrated.
The problem, however, is that it is very difficult to manufaature, ship, install, and operate satisfactorily a fan having a small clearance between the blades and the shroud, ~ince it requires an almost perfect balancing of the rotating ' :.
2015~21 hub and blades, almost perfect centering of the rotating hub and blades in the shroud, and an almost perfectly round opening in the shroud. Therefore, as a practical matter, commercial fans are provided with enough tip clearance to operate even though the hub and blades are not perfectly balanced, the blades are not all the exact same length, the hub is not perfectly centered, and the opening in the shroud is not perfectly round. This compromise does, of course, -~
reduce the efficiency of the fan. --It is an object of this invention to provide an axial fan having the efficiency of a low fan tip clearance fan without the problems describPd above. ~ -~
It is a further object of this invention to provide an ---axial fan in which there is substantially no pressure differ- ~
ential between opposite sides of the blades adjacent the - -blade tips thereby substantially eliminating the flow of air -over the blade tips and the forming of a vortex. -It is a further object of this invention to provide such -~
an axial fan where the tips of the fan blades travel in a -space where there is little or no movement of air thereby reducing substantially the effect of tip clearance on fan efficiency. i~
It is a further object of this invention to provide an axial fan having a shroud assembly that includes a cylindrical section or band that encircles the fan blades and is spaced therefrom and an orifice section having its downstream edge adjacent to but spaced from the impeller blades, which extend outwardly beyond the downstream edge of , .. ,' ' 2~1~521 the orifice into a zone of non-moving air. The air moves out of the way of the blade tips, of course, but does not move much relative to the space through which the blade tips move.
United States Patent No. 4,515,071, which issued to Elmer S. Zach on May 7, 1985 and is entitled "Ventilation Air Control Unit" discloses an axial fan having a shroud assembly that includes a cylindrical section or band that encircles the fan blades and is spaced therefrom and an orifice section having its downstream edge adjacent to but spaced from the impeller, which extend outwardly beyond the downstream edge of the orifice into a zone of non-moving air. This structural arrangement resulted when Zach replaced a twelve inch ventilating fan with a fourteen inch fan for forcing air into a grain drying and storing bin for drying and -~
ventilating the grain in the bin.
Zach teaches use of a flange or orifice having an inner -diameter less than the overall span of the fan blade for redirecting the flow of air away from the tips of the fan blade and toward its center (claim 4, lines 18 et seq.).
It i8 an object of this invention to provide an axial -fan with an orifice, fan blade, and a band or cylindrical section encircling the fan blade and orifice, the diameters of which have a fixed relationship within a range and that substantially eliminates the flow of air over the tips of the fan blades which substantially reduces the effect of tip clearance on the efficiency of the fan, thereby allowing the tips of the fan blades to be spaced from the band '', ~'''".'' "
2~15521 sufficiently to avoid the manufacturing, shipping, installation, and operating problems described above.
Specifically, it is a further object and feature of this invention to provide an axial fan having an orifice, a fan blade, and a band wherein the diameter of the fan blade is about 103~ of the diameter of the orifice ana the diameter of ~-the band is about 106~ of the diameter of the orifice, which substantially eliminates the effect of tip clearance or fan efficiency and provides ample clearance between the tip of the fan blade and the band to substantially eliminate damage - P--to the fan blade as a result of a reduction of such clearance - ~ `
in an effort to improve fan efficiency. -These and other objects, advantages, and features of this invention will be apparent to those skilled in the art from a consideration of this specification, including the attached drawings and appended claims. `-In The Drawings: -:.
Figure 1 is a view of the discharge side of a fan constructed in accordance with the preferred embodiment of this invention.
Figure 2 is a sectional view taken along line 2--2 of Figure 1.
Figure 3 is a view of the intake side of the fan of Figure 1.
Figure 4 is a partial sectional view of an alternate embodiment of the invention.
.', . . .
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201~21 Figure 5 is a graph of the performance data of three fans, and ---Figures 6A, 6B, and 6C show the arrangement of the fans and the shrouds that produced curves A, B, and C of Figure 5, ~ -Figure 6C being the fan that embodies this invention.
Figure 7 is a graph showing the effect of tip clearance on fan efficiency.
The fan of Figures 1, 2, and 3 include~ hub 10 to which four impeller blades 12 are attached. Preferably, the blades are curved along their transverse axes to provide concave surfaces facing the discharge side of the fan, as shown in Figure 2. Hub 10 is mounted on shaft 14. The shaft is supported for rotation around its longitudinal axis by bearings 16 and 18 that are mounted on end plates 20 and 22 --of bearing housing 24. The hub, the shaft, the bearings, and bearing housing are supported in the center of rectangular fan casing 26 by support v~nes 28 that extend between the -bearing housing and the fan casing. Sheave 30 mounted on shaft 14 on the outside of bearing housing 24 is rotated by ~-belt 32 which in turn rotates hub 10 and the impeller blades.
Belt 32 is driven by an electric motor that is usually mounted on the fan casing. The motor is not shown.
In accordance with this invention, the fan is provided with shroud assembly 34 that includes cylindrical section or band 36 and orifice section 38. The cylindrical section is attached to and supported by orifice section 38. The orifice section in turn is connected to rectangular fan casing 26.
In the embodiment shown, the orifice section is an integral ' ',.: ' ::
part of the front wall of the fan casing. It curves toward the center of the fan casing and rearwardly toward impeller blades 12, as shown, to provide a nozzle shaped guide for the air flowing through the fan. Although it need not do so, the orifice section shown straightens out and becomes cylindrical as it approaches the impeller blades to provide a section of --uniform diameter through which the air flows before reaching - -the impeller blades.
In accordance with this invention, the impeller blades -extend outwardly beyond the orifice section with the tips of ~ -the blades adjacent to but spaced from the cylindrical -_ section of the shroud, as shown in Figure 2. This --arrangement provides annular space 40 between the orifice section and the cylindrical section in which the air does not move substantially. Consequently, there is little pressure --differential between the sides of the impeller tips which -results in substantially no radial flow of air over the tips of the blades. Therefore, there is no need for the tips of ~-the blades to be close to the shroud to obtain the greatest ~ -efficiency for the fan. This is shown by the results of comparative tests on three fans, one of which being ;
constructed in accordance with this invention.
The best method to use in evaluation of the improved performance of the fan of this invention tfan C), shown in curves "C" of the attached curve sheet, is the use of "system .. ..
re~istance" curves to make the performance of present technology ~curves "A" and "B") equal the performance of the :,:
',.,'-',''.~' .'' .: '.' '' '':' ~r~
7 201~
improved fan (curves "C"). Each fan had an orifice that was 25" in diameter.
As shown in Figures 6A, 6B, and 6C, the impeller blades of fan A are located inside the orifice with the blade tips spaced 0.341 inches from the orifice. Fan B also has its - -blades located inside the orifice, but the blade tips are -much closer to the orifice, i.e., about 0.171 inches. Fan C
has its shroud and blades positioned in accordance with this invention with the end of the orifice spaced about 0.75 -inches from the cylindrical section, i.e., the cylindrical section has a diameter that is 106~ of the diameter of the orifice. The fan blades extend beyond the orifice about -0.375 inches, i.e., the diameter of the blades is about 103%
of the diameter of the orifice. The forward edge of each blade is about 0.25 inches from the end of the orifice.
Obviously, substantial clearance is provided between the stationary and moving parts of the fan.
"System resistance" is the resistance to air flow when a fan or blower i~ attached to a fixed duct system. Changes in performance are then made by application of "fan laws". The -"system resistance curves" in this instance are parabolic curves with the origin at zero for CFM and static pressure (P9) . . :. :
Table I below shows four different performances of fan C
at four different static pressures (Ps). The static -pressures were 0.000", 0.125", 0.250", and 0.375".
Gonerally, 809~ of commercial fan sales are for performances . .
':"~'; '. . ' :,' :,. . .
~
201~21 at static pressures (Ps) of 0.125" and 0.250", and 20% would be static pressures (Ps) of 0.000" (Free Air) and 0.375".
T~BLE I
Performance of Improved Fan (Curve "C") CFM: 6629 6050 5400 4600 RPM: 1150 1150 1150 1150 - -~
Ps: 0.000" 0.125" 0.250" 0.375" --BHP: 0.422 0.48 0.531 0.575 Static Eff: 0.0% 24.8% 40.0% 47.2% - -Each of the four static pressures of fan C has a different "system resistance curve". These "system ; .~ .
resistance" curves can be calculated by the following ~ -equation:
cfm = constant ~ (1) : :
or .
cfm = constant (2) \/ Ps '''.' '.' :''.`'~,''''''' For curve "C", the constants are:
Ps: 0.000 0.125" 0.250" 0.375" ---Constant: 0 17112 10800 7512 ,. .:
cfm is in cubic feet per minute Ps (static pressure) is in inches of water - :
'.' ''' .'~ "
Three of these "system re~istance curves" for Ps =
0.125", 0.250", and 0.375" are plotted in dashed lines in Figure 5~
"'''. , ,"',,'' - g The "system resistance curve" for Ps = 0.000" (~ree Air) is a special case because Ps = O. Therefore, the constant in the above equation is also equal to 0. Then:
CFM of curve "C" @ Ps = O
= K
CFM of curve "A" or "B" @ Ps = O
Kl x 1150 = new RPM for curve "A" or "B"
(Kl)2 x 0.000" = new Ps for curve "A" or "B" = O
(Kl)3 x BHP for curve "A" or "B" - new BHP for curve --"A" or "B" @ New RPM
Figure 5 shows curves for Volume (CFM) vs Static Pressure (PS), Volume (CFM) vs Horsepower (B~P), and Static Efficiency vs Volume (CFM) for the fans of present ~echnology - -(Curves "A" and "B") and the improved fan (Curve "C").
Calculated values of CFM and PS where the "system resistance curves~ intersect the performance curves of "A"
and "B" can be determined by applying constants of Curve "C"
in equation (2). By consulting Figure 5, the values of BHP :
are manually read from the Volume ~CFM) vs Horsepower (BHP) - ~
curve, of Figure 5, at the CFM calculated for the ~ -intersection of "system resistance curve" and Curves "A'i and -"B". -: :
Curve "A" Performance Data at the Intersection of "System Resistance Curves" of Curve "C"
': . '. ' PS 0.000" 0.087" 0.180" 0.282" ~:
BHP 0.360 0.4B5 0.43 0.443 ~;
201~5~1 -- ~.o ..
Curve "B" Performance Data at the Intersection of the "System Resistance Curves" of Curve "C"
PS 0.000" 0.099" 0.206" 0.333" .
BHP 0.369 0.405 0.446 0.481 -There are certain well recognized engineering laws derived from engineering fundamentals that apply to all centrifugal and axial flow machinery performance. These are - -called "Fan laws" by those skilled in the art. -The "fan laws" are now employed to compare the perfor-mances of fans "A" and "B" (curves A and B) to the - ..
performance of fan C (curve "C") for the four static pres-sures shown in Table I.
The "fan laws" are in this instance~
, ...
Ratio of changes in RPM or Cfm = Kl Ratio of changes in Static pressure = (K
Ratio of changes in BHP - (K1)3 The comparison is made by moving data from curve "A" and .
curve "B" along "system resistance curves" to curve "C" by use of the "fan laws" as follows: :
:
' ' '':~ ' '. .
~ ' " ''', .'' ,'' ~'~
;' ', 201~.~21 TABLE II
Performance Data for Curve "A' and Upgraded to Curve "C"
CFM: 5462 5047 4582 3989 RPM: 1150 1150 1150 1150 Ps: 0.000" 0.087" 0.180" 0.282"
BHP: 0.360 0.405 0.43 0.443 Static Eff: 0.0% 17.1% 30.2% 40.0~ -CFM&RPM-Kl:~6629~=1.2137 ~65)=1.1987 ~540~=1.1785 ~46~=1.1517 1~5462J ~5047~ ~4582~/ ~3989/
~6629~2 1 4730 ~65~2=1 4370~54~2=1.3889 p ~2=1.3298 \~546-2J ~50471 ~4582J ~3989~ - -~6629~ 1 7877 ~5~3=1 7225~54oo~3=l.6369~ ~3=1.5355 ~5462~ ~5047l ~458~ 3989~ - -CFM: 6629 6060 5400 4600 RPM:(+21.3~)1396 (+19.8%) 1378 (+17.8%)1355 (+15.2%)1326 Ps: 0.000" 0.125" 0.25" 0.375"
BHP:(+52.4%)0.643 (+45.4%) 0.698 (+32.5%)0.704 (+18.1%)0.679 Static Eff: 0.0% (-31.2%) 17.1% (-24.5%)30.2% (-8.5%) 40.0%
Evaluation of Table II shows that fan A at 0.000" (Free ~-Air) had increased RPM by 21.3% and required more power E~HP
, by 52.4%. Similar but lower increases were shown for the -other static pressures: 0.125" 0.250" and 0.375". The loss -in static efficiency was 31.2% at 0.125" static pressure 24.5% at 0.250" static pressure and 8.5% at 0.375" static - -pressure.
Table III shows the result when data from curve "B" is moved to equal the performance of curve "C".
S ~
201~21 TABLE III
Performance Data From Curve "B" and Upgraded to Curve "C"
CFM: 5769 5384 4902 4335 RPM: 1150 1150 1150 1150 Ps: 0.000" 0.099" 0.206" 0.333"
BHP: 0.369 0.405 .446 .481 Static Eff: 0.096 20.796 35.7996 47.2%
~6629~=1 1491 ~605 ~ =1.1237 ~ ~ =1.1016 ~5769/ 5084/ ~4902~ ~4335J
Ps: ~629~2=l.32o4 ~2=1.26~7~54~2=1 2135~600~2 1 12 5769l 5384/ ~4902/ ~4335/ ~`
BHP:~ 6629~ 1 5172 /65~3=1 4189/>~54~3=1.3368~ ~3 1.1948 ~,5769/ 1~ ,4902/ \,4335/
CFM: 6629 6050 5400 4600 RPM:(+14.9%)1321 (+12.3%) 1292 ~+10.2%)1269 (+6.1%) 1220 Ps: 0.000" 0.125" 0.250" 0.375" -- -B~P:(+32.7%)0.560 (+19.896) 0.575 (+7.2%) 0.596 0.575 Static Eff: 0.0% (-16.5~) 20.7% (-10.7%)35.79% 47.2%
Evaluation of Table III shows that fan "B" at 0.000" ; ~
(Free Air) had increased RPM by 14.996 and required 32.7% more ; `
power, BHP. Similar but lower increases were shown for static pressures of 0.125" and 0.250". At the 0.375" static pressure, however, only the RPM increased by 6.1%. Increased RPM will increase the noise level.
Tables II and III show clearly that reduction in tip clearance of the present technology will bring increased eficiencies, but this also brings on a problem of how to effectively manufacture such equipment and ship to the ultimate user.
The improved fan of this invention allows for acceptable manufacturing tolerances without 108s of performance.
' '' ',.
.': .
2 ~ 2 1 SUMMARY
Tables IV and V shown below are summaries of all per-centage changes in performance when curves "A" and "B" are made equal in performance to curve "C".
TABLE IV
Percentage Change to Make Curve "A" Equal Curve "C"
For Curve "A":
Static pressure : -of Curve "C" 0.000" 0.125" 0.250"0.37"
CFM +21.37% +19.87% +17.85%+15.17%
RPM ~21.37~ +19.87% +17.85%+15.17%
Ps +47.30~ +43.7% +38.89%+32.99% : -BHP +52.4% +45.4% +32.5%+18.1% - -Static Eff. none -31.1% -24.5%- 8.5% :~
TABLE V
. . , Percentage Change to Make Curve "B" Equal Curve "C" ~ -For Curve "B": ~ ;
Static pressure : -of Curve "C" 0.000" 0.125" 0.250"0.375" - :
CFM +14.:91% +12.37~ +10.16%+6.11~
RPM +14.91% +12.37~ +10.16%+6.11% : -Ps l32.04~ +26.27% +31.35%+12.6%
BHP +32.7% +19.8% +7.2% none -Static Eff. none -16.5% -10.7% none Figure 4 is an alternate embodiment of this invention. ~.
Structurally, it is the same as the embodiment in Figures 1, 2, and 3 with the addition of annular bracket 42 to support :
and connect the rearward edge of the orifice section to the cylindrical section. This embodiment does not perform as well as the preferred embodiment, but better than fans A and 3. : :
From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects -~
;' '..' :~:'' 201~21 hereinabove set orth, together with other advantages which -are obvious and which are inh~rent to the apparatus and structure.
It will be understood that certain features and subcom-binations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims. -Because many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all mattex herein set forth or shown in -the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.
~-..
,, -.~
-:
.: :
~' ' '' ~; - .
:'','' ;''' '" ' , ' .
~ f~
Claims (3)
1. An axial fan comprising a hub, means supporting the hub for rotation around the longitudinal axis of the fan, a plurality of impeller blades attached to the hub and extending radially from the axis of rotation, a shroud assembly including a band encircling the blades and spaced from the tips of the blades a sufficient distance to provide ample clearance to avoid contact between the blades and the band during shipment and operation of the fan, said shroud further including an orifice positioned upstream of the blades, said band having a diameter that is about 106% of the diameter of the orifice means for preventing air from flowing between the orifice and the band, said orifice having a downstream end located adjacent to but spaced from the impeller blades, said impeller blades having a diameter that is about 103% of the diameter of the orifice so that the impeller blades extend outwardly from the hub beyond the orifice to reduce the flow of air over the tips of the impeller blades substantially while providing ample clearance between the tips of the impeller blades and the band.
2. An axial fan comprising, a rotatable fan hub, a plurality of impeller blades carried by the hub, a fan casing for supporting the hub and blades, said casing further supporting a fan blade shroud assembly including a cylindrical band that extends from the casing over the blades and an orifice that decreases to a diameter less than the diameter of the circular path of the tips of the blades and extends to a position adjacent to but spaced from the blades to combine with the band to provide an annular space having little or no air movement in which the tips of the blades move as the blades are rotated to thereby reduce substantially the radial flow of air over the tips of the impeller blades and thereby increase the efficiency of the fan, the diameter of the band being about 106% of the diameter of the orifice and the diameter of the blades being about 103% of the diameter of the orifice.
3. The axial fan of claim 2 in which the impeller blades are spaced from the end of the orifice about .250 inches.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US07/430,185 | 1989-11-01 | ||
| US07/430,185 US4927328A (en) | 1989-03-02 | 1989-11-01 | Shroud assembly for axial flow fans |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2015521A1 CA2015521A1 (en) | 1991-05-01 |
| CA2015521C true CA2015521C (en) | 1994-03-08 |
Family
ID=23706408
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002015521A Expired - Fee Related CA2015521C (en) | 1989-11-01 | 1990-04-26 | Shroud assembly for axial flow fans |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4927328A (en) |
| EP (1) | EP0499604B1 (en) |
| AU (1) | AU649612B2 (en) |
| CA (1) | CA2015521C (en) |
| DE (1) | DE69024820T2 (en) |
| WO (1) | WO1991006779A1 (en) |
Families Citing this family (30)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO1991005169A1 (en) * | 1989-09-29 | 1991-04-18 | Micronel Ag | Miniature fan |
| US5248224A (en) * | 1990-12-14 | 1993-09-28 | Carrier Corporation | Orificed shroud for axial flow fan |
| US5215438A (en) * | 1991-11-07 | 1993-06-01 | Carrier Corporation | Fan housing |
| US5215437A (en) * | 1991-12-19 | 1993-06-01 | Carrier Corporation | Inlet orifice and centrifugal flow fan assembly |
| US5423660A (en) * | 1993-06-17 | 1995-06-13 | Airflow Research And Manufacturing Corporation | Fan inlet with curved lip and cylindrical member forming labyrinth seal |
| EP0645543A1 (en) * | 1993-08-31 | 1995-03-29 | Caterpillar Inc. | Low noise cooling system |
| KR970010561B1 (en) * | 1994-04-18 | 1997-06-28 | 삼성전자 주식회사 | Constant noise air blower |
| US5762034A (en) * | 1996-01-16 | 1998-06-09 | Board Of Trustees Operating Michigan State University | Cooling fan shroud |
| GB2311562A (en) * | 1996-03-28 | 1997-10-01 | Rover Group | Fan cowl |
| US5749702A (en) * | 1996-10-15 | 1998-05-12 | Air Handling Engineering Ltd. | Fan for air handling system |
| US6302066B1 (en) | 1999-04-30 | 2001-10-16 | Caterpillar Inc. | Apparatus and method of cooling a work machine |
| KR100355827B1 (en) * | 2000-08-17 | 2002-11-07 | 엘지전자 주식회사 | Turbo fan of Window type Air conditioner |
| US6772606B2 (en) | 2002-07-15 | 2004-08-10 | Maytag Corporation | Method and apparatus for a plastic evaporator fan shroud assembly |
| US6676371B1 (en) * | 2002-08-22 | 2004-01-13 | Custom Molders, Inc. | Double barrel vehicle cooling fan shroud |
| US20040076514A1 (en) * | 2002-10-16 | 2004-04-22 | Sunonwealth Electric Machine Industry Co., Ltd. | Suspension type heat-dissipation fan |
| US11255332B2 (en) * | 2003-03-20 | 2022-02-22 | Nortek Air Solutions, Llc | Modular fan housing with multiple modular units having sound attenuation for a fan array for an air-handling system |
| NZ525693A (en) * | 2003-05-06 | 2006-01-27 | Jason Bregmen | Improvements relating to billboards |
| US7331758B2 (en) * | 2003-06-18 | 2008-02-19 | Mitsubishi Denki Kabushiki Kaisha | Blower |
| JP4444307B2 (en) * | 2003-06-18 | 2010-03-31 | 三菱電機株式会社 | Blower |
| US7238006B2 (en) | 2004-09-27 | 2007-07-03 | Studebaker Enterprises, Inc. | Multiple impeller fan for a shrouded floor drying fan |
| DE112005002765T5 (en) * | 2004-11-04 | 2007-09-06 | Mitsubishi Fuso Truck And Bus Corp. | Radiator cover structure |
| JP2008267176A (en) * | 2007-04-17 | 2008-11-06 | Sony Corp | Axial flow fan device, housing, and electronic equipment |
| US20090280008A1 (en) * | 2008-01-16 | 2009-11-12 | Brock Gerald E | Vorticity reducing cowling for a diffuser augmented wind turbine assembly |
| US9920653B2 (en) | 2012-12-20 | 2018-03-20 | United Technologies Corporation | Low pressure ratio fan engine having a dimensional relationship between inlet and fan size |
| US9932933B2 (en) | 2012-12-20 | 2018-04-03 | United Technologies Corporation | Low pressure ratio fan engine having a dimensional relationship between inlet and fan size |
| DE102014111767A1 (en) * | 2014-08-18 | 2016-02-18 | Ebm-Papst Mulfingen Gmbh & Co. Kg | Axial |
| JP6380222B2 (en) * | 2015-04-28 | 2018-08-29 | 株式会社デンソー | Air conditioner for vehicles |
| US10982863B2 (en) | 2018-04-10 | 2021-04-20 | Carrier Corporation | HVAC fan inlet |
| US10731889B2 (en) * | 2019-01-08 | 2020-08-04 | Regal Beloit America, Inc. | Motor controller for electric blowers |
| US11841022B2 (en) | 2020-01-06 | 2023-12-12 | Regal Beloit America, Inc. | Control system for electric fluid moving apparatus |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| GB118922A (en) * | 1917-10-12 | 1918-09-19 | Frederick John Brougham | Improvements in Apparatus for Automatically Controlling Temperature Regulators. |
| US1466472A (en) * | 1920-05-24 | 1923-08-28 | Elisha N Fales | Fan |
| GB355549A (en) * | 1929-10-14 | 1931-08-27 | Schmidt Sche Heissdampf | Improvements in and relating to fan-operated induced-draught installations |
| US2030993A (en) * | 1934-08-27 | 1936-02-18 | Internat Engineering Inc | Fan |
| DE1428273C3 (en) * | 1964-09-29 | 1973-01-04 | Siemens Ag, 1000 Berlin U. 8000 Muenchen | Impeller for a low-noise axial fan |
| US3832085A (en) * | 1972-10-04 | 1974-08-27 | Ford Motor Co | Automotive fan shroud |
| US3843277A (en) * | 1973-02-14 | 1974-10-22 | Gen Electric | Sound attenuating inlet duct |
| JPS56118593A (en) * | 1980-02-25 | 1981-09-17 | Hitachi Ltd | Blower |
| US4406581A (en) * | 1980-12-30 | 1983-09-27 | Hayes-Albion Corp. | Shrouded fan assembly |
| IT8353039V0 (en) * | 1982-03-15 | 1983-03-10 | Sueddeutsche Kuehler Behr | AXIAL FAN PARTICULARLY FOR WATER COOLED THERMAL ENGINE COOLING RADIATORS |
| US4515071A (en) * | 1982-04-05 | 1985-05-07 | Zach Elmer S | Ventilation air control unit |
| GB8334120D0 (en) * | 1983-12-21 | 1984-02-01 | Gerry U K | Diffusers |
| US4747275A (en) * | 1987-09-18 | 1988-05-31 | Carrier Corporation | Apparatus for controlling flow through a centrifugal impeller |
| DE3804217A1 (en) * | 1988-02-11 | 1989-08-24 | Bosch Gmbh Robert | AXIAL FAN |
-
1989
- 1989-11-01 US US07/430,185 patent/US4927328A/en not_active Expired - Lifetime
-
1990
- 1990-04-18 AU AU55320/90A patent/AU649612B2/en not_active Ceased
- 1990-04-18 WO PCT/US1990/002119 patent/WO1991006779A1/en active IP Right Grant
- 1990-04-18 EP EP90907996A patent/EP0499604B1/en not_active Expired - Lifetime
- 1990-04-18 DE DE69024820T patent/DE69024820T2/en not_active Expired - Fee Related
- 1990-04-26 CA CA002015521A patent/CA2015521C/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| EP0499604B1 (en) | 1996-01-10 |
| WO1991006779A1 (en) | 1991-05-16 |
| US4927328A (en) | 1990-05-22 |
| CA2015521A1 (en) | 1991-05-01 |
| AU5532090A (en) | 1991-05-31 |
| DE69024820T2 (en) | 1996-05-23 |
| DE69024820D1 (en) | 1996-02-22 |
| AU649612B2 (en) | 1994-06-02 |
| EP0499604A1 (en) | 1992-08-26 |
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| EEER | Examination request | ||
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