Патент USA US2107897код для вставки
Feb. 8, 1.938. - K.‘ n. MCMAHAN 2,107,897 FAN Filed July 24, 1935 200 6004” Plow 0 600 700 670 w Cub/'c' 2 Sheets-Sheet l 000 sw~ 1000 ti. “\ Qlw3unQz5?u.Lkx z u A a a. u PQ 4. . 7 [M 2” ' 3W‘ ' 4W 5” Flow- Cubic feet per' min. m 900 we InventoP: 1 Kenton D.MCM,Q|"1OT1, bL-J His Atto?neg. Feb. 8,1938. K. D‘. MQMAHAN 2,107,897 ‘ FAN Filed July’ 24, 1935 o awy” // 200 4W 600 " m - 6, 2 Sheets-Sheet 2 ‘M642. I000 I200 14” I609 MW Flow - Cub/c féet per min. M 400 600 E00 7000 rpl. £200 I400 1600 1500 W. wn hm: eD.,cA 11.1 km m9G9 m m o 2,107,897 Patented Feb. s, 1938 UNITED STATES PATENT OFFICE 3.107.897 ran . Kenton n. Mommas; Schenectady, Np!" ‘u signor to General Electric Company, a cor poration of New York Application July :4, 1m. Serial No. 32.850 '1 Claims. (cl. 280-127) select a fan which will operate on the portion of My. invention relates to fans and more particu larly to fans of the centrifugal type enclosed in the curve. past the knee. This means that, for a scroll or housing. . ' example, referring to the solid 'line curve of Fig. The object of my invention'is to provide an im 5 ' proved fan adapted to move a large quantity of air against a high back pressure. What I consider to be novel and my invention will be better understood by reference to the fol lowing speciilcation and appended claims when 10 considered'in connection with the accompanying drawings in which Fig. 1 is a side‘ view broken away in part of my improved fan; Fig. '2 is‘ a sec tional view along the lines 2-2 of Fig. 1; Figs. - 3 and 4 are curves illustrating the performance 15 of the fan°with di?erent widths of scrolls; Fig. 5 is a side view of a double inlet fan; Fig. 6 is a sectional view of the fan‘in Fig. 5 along the line 6-6, and Figs. 7 and 8 are curves illustrating the performance of the double inlet fan with di?er g0 ent widths of scroll. v - Referring to Figs. 1 and 2 of the drawings, I0 ‘ indicates a scroll or housing in which a centrifu gal fan II is mounted. Tan H consists of a number of curved blades 12 mounted parallel to 25 the axis of rotation of the fan and spaced uni-' formly about the axis. Blades I! are secured at 4. the fan of which this curve was made should be operated in a system in which the back pres- 5 sure is less than 1.1 inches of water so that upon any slight variation in pressure there will not be a greatvariation in flow. It would not be sat isfactory to operate this .fan against a much higher back pressure because then the fan would 10 be operating on the portion of the curve which is substantially horizontal. when operating on this portion of the curve the fan would tend to be unstable because a slight variation in the pres sure would cause a very- wide variation in ?ow. 15 Of course if the fan is to operate in a system in which the pressure varies widely. it would be nec essary to operate the _fan very' much further down on the steep slope of this. curve. vI have found that with a- given length of blade and 20 diameter fan the operating characteristics , of the fan may be altered by varying the width of the scroll. I have found that if this width is too small the flow which can, be producedby the fan ‘I against a given pressure is reduced and if thisv scroll is too wide then the maximum pressure; one end to a disc II and at the other end to a ring a against is, reduced. whichInthe Fig.fan 2, will I have operate indicated satisfactorily; the ef l4. Disc i3-is connected to a hub Iii. Huh. I! is secured on the end of a shaft l6 which is adapted fective length of blade by the, letter b, the clear 30' to be connected to a source of power such as- an ance within the scroll at each end of the blade 30 electric motor or the like for driving the fan. by the letter 0, and the overall width of the scroll ‘ Scroll Ill is provided with an inlet ‘opening H by the iletter 's. I have °found that when the in which is mounted a curved orifice I8. An ratio of the clearance c at each side of the blade outlet I8 is provided for the housing ‘ill from to the effective blade length b is .3, the perform ance of the fanis the most desirable. In other. 5 which the air passes from the scroll it. In op eration the-centrifugal fans serve to convert. a words for a most satisfactory ‘operation the scroll velocity head of air to a pressure head so that a width s should be approximately 1.6 times the certain volume of air may be passed through-a effective blade length b... The difference in per formance of the‘ fan with a lesser and greater duct, machine or other apparatus against apres 40 sure inherent'in the systemthrough which the clearance ,is indicated in Figs. 3 and 4. The ‘0 ‘ air is passed.~ In the application-ofa centrifugal curves of Figs. 3 and 4 were made for a fan‘hav ‘fan to a ' particular system the back pressure ing an effective blade length b of 3% inches and against which the fan‘ must operate is determined adiameter of 71/2 inches. The dotted line curve by ~the- characteristics of the system. ‘The 5 amount of -,air which it is desired to pass through the. system is also determined, by-characteristics ‘ ofv Figs. 3 and 4 represent the performance‘ of the fan with a scroll width 3‘ of 5% inches in which case the .clearance c on each side is- ‘V. inchgand the ratio of the clearance .c to the Referring to‘the curves of Fig.4, it will be seen -' blade length -.is- .234. The solid line curves of of.~=the system. - ~ ' the-tithe ?ow produced-by a particular fan- de 59 pendsupon the static-pressure against which it is “operated. Inv most- systems-the pressure of the Figs. 3 and .4 represent the performance of the ' system :will vary slightly and in other systems and so the ratio of the clearance c to the effective blade length b is .3. The dash and dot. line in which for example a .damper is located the pressure against which the fan isoperating may, . vary quite widely. Therefore, it is necessary to fan with a scroll width s‘ of. 6 inches in which the clearance c each side of the fan is 1% inches curves§of Figs. 3 and 4 arev thev performance . curves for the fan with a scroll width so! 8% 2 12,107,897 inches in which the clearances c are 1% inches or the ratio of clearance c to the effective blade length I) is .368. From reference to Fig. 3 it may be seen that the e?iciency of vthe fan with the wider scroll is substantially the same as the effi ciency of the fan with the intermediate scroll width. However, the e?iciency ‘curvefor the fan with the smallest clearance or smallest scroll width falls off more rapidly from the peak value. By reference to Fig. 4 it may be .seen that the curve of performance of the fan with the inter mediate width of the three scroll widths for varies between 1.5 and 1.7 times the blade length. However, for the most satisfactory performance the scroll width should be approximately 1.6 times the effective blade length. In Fig. 1 it may be seen that a cut-off 20 is provided with an inclined edge 2| at an angle a: to a radial line extending from the axis of the fan. Thecut-oif 20 serves to prevent eddies at this point in the outlet opening I9. The in 5 clined edge 2| also serves to reduce the noise of 10 the fan by compensating in part for deviations in the inclination of the‘ blade l2. If a sharp which the curves were taken shows a higher flow , edge were provided at this point, the variations throughout the operating‘ range of the fan than in the position of the blade would cause one jet of air to pass on one side of the edge and another 15 15 the corresponding curve for the 'fan with a small er scroll width. Also, the fan with the interme diate width operates satisfactorily against va higher back pressure than the fan with the great er scroll width. Taking a speci?c example for jet of air from the following blade to pass on the other side of the edge. This produces a pul-_ sation which is proportional to the rate of'pas sage of the blades l2 by this point. vThese pulsa 20 a ?ow of 500 cubic feet per minute the fans are tions sometimes cause a vibration of the blades operating near their maximum e?iciency but the pressure against which the intermediate scroll width will operate is approximately ..1 inch of water higher than either of the other two fans with the lesser or greater scroll width. How ever, the fan with the greater scroll width can when their frequency approaches the natural pe riod of vibration of the blades and thereby pro duce considerable noise. This inclined edge therefore serves to compensate‘ for slight devia tions in the inclination of the blades and so elim inates these pulsations and the resultant noise. not satisfactorily operate at thatwpoint because I have found that an angle at of about 15° at a slight variation in the back pressure would cause a wide variation in the flow produced by 30 the fan. Similarly for a flow of 600 cubic feet per minute the fan with the intermediate width would operate satisfactorily against a back pres sure greater than .9 inch of water, whereas the fan with the lesser width would not produce so 35 great a flow against'this back pressure or would '_ f'only produce this ?ow against a back pressure "40 of .8 inch of water. The fan with the greater width would still ,be operating on an unsatisfac tory portion of the curve. For a ?ow of- ‘700 cubic feet per minute the fan with the wider scroll would operate the most satisfactorily, but the difference between it and the fan with the intermediate width is not very great. However, it is obvious that the fan with the greater width 45 does not operate satisfactorily over as wide a range as the fan with the intermediate width. At this point the ‘fan with the lesser width cannot produce the ?ow against, a back pressure more than two thirds of the pressure against which 50 the other two fans will operate satisfactorily. It is to be noted that the difference in the per formance of this fan is relatively great when it is considered that the scroll width has been changed'from the one with the most satisfactory operation by only 1 inch in total width or 1A inch 'in clearance on each side of the fan. Thus it may be seen that when the ratio of the clear ance c to the effective blade length I) is reduced from .3 to .234 or increased from .3 to .368 the which the edge'2l is inclined is satisfactory, how ever, it is not critical but must not be so great as to causetoo large an obstruction in the passage 30 of air from the opening l9. Referring to Figs. 5 and 6, a double inlet cen trifugal fan is shown. This type of fan with a double inlet is generally provided where the space requirements limit the diameter of fan or 35 where other considerations such as the flow re quired would otherwise make it necessary to use two single inlet fans for which one double inlet fan may be substituted. ' . ~ Referring to Figs. 5 and 6, 22 indicates a scroll 40 .in which are located two centrifugal fans 23 and 24. Fans 23 and 24 are provided respective ly with curved blades 25 and 26 mounted parallel and spaced from the central axis of the fan. Fan blades 25 and 26 are secured respectively to ~discs 21 and 28 which are mounted on a hub 29. Hub ‘29 is mounted on a shaft 30 which is con nected to a source of power such as an electric motortfor driving the fan. Scroll 22 is provided. with two inlet openings 3| and 32 in which are located curved orifices 33 and 34 respectively. A 50 single outlet opening 35 ‘is provided. A cut-off 36 is provided in the opening 35 having an in— clined edge3'l. The cut-off 36 with its inclined edge 31 performs the same functions as the cut off 20 with its inclined edge 2l_ of the single in let fan illustrated in Figs. 1 and 2. In single inlet fans the fan diameter is usually about twice the blade length and in double in let fans the blade length is approximately equal 60 operation of the fan is greatly altered. ' However, in general practice this clearance has been much to the fan diameter. I have found that by divid 60 less than thatrepresented by the dotted curves ing the blades of a double inlet fan in half and of Figs. 3 and 4. It is an almost universal prac- ' spacing them as though two single inlet fans tice to provide a clearance which is approximate were being used the performance of the fan can ly .1 of the blade length. This means that the be made substantially the same as though two 65 overall scroll width is generally made about 1.2 single inlet fans of ' the same diameter were 65 times the blade length whereas the curves of used. The lengths of blades 25 and 26 are in-. Figs. 3 and 4 represent a variation from approxi dicated by letters in and b: respectively. The mately 1.5 times the blade length to 1.7 times clearance on each side of In is indicated by the the blade length. Thus by comparison" with letter or. _ Similarly, the blade length of blades 70 present practice-any one of the curves of Figs. 3 26 is indicated by b: and theclearance on each 70 and 4 represents an improvement in perform side by oz. The total scroll-'~"-’width is indicated ance of the fan \over previous practice. There by letter St. The ratio of or tofu and 0: to b: is .3. fore, when other factors a?'ect the dimensions of In other words, the width of the scroll St equals the scroll such as the available space, it may be 1.6 times b1+bz. To indicate the difference in found satisfactory to use a scroll width which the performance of the fan with the fan blades 75 . 2,107,097 formed as a single fan with the spacing at each side of the blades the same as would be provided for a single inlet fan of the same diameter as . compared with a fan with the blades divided in two and spaced apart so that the total clearance is equal to twice the clearance of a single inlet fan, curves of Figs. 'Land 8 have been taken. The solid line curves of Figs. 7 and 8 are the per 3 fan blades mounted in parallel relation about a common axis, means to drive said fan blades, and a scroll having an inlet opening and an out let opening, the width of said scroll being be tween 1.5 and 1.7 times the eilfectivelengtn of said fan blades. 3. A centrifugal fan comprising a plurality of fan blades mounted in parallel relation about a formance curves for the fan as illustrated in ' common axis, means to drive said fan blades, and The dash-dot curves of Figs. '1 and 8 a scroll having an inlet opening and an outlet 10 -10 Fig. 6'. represent the performance of a fan with the same clearance between the blades and the sides 01' the scroll but with the blades abutting each other 15 20 25 30 35 45 50 opening, a clearance being provided on each side of the fan blades within the scroll equal to .3 times the e?ective length of ‘said fan blades. without any clearance between them and so the 4. A centrifugal fan comprising a plurality of total scroll width St is equal to 1.3 times bi+h. fan blades mounted in parallel relation about a From the curve of Fig. '7 it will be seen that the . common axis, means to drive said fan blades, peak of the efiiciency curve for the fan with the and a scroll having an inlet opening and an‘ lesser scroll width is reached at a lower ?ow ‘ outlet opening, a clearance being provided on than for the curve of the greater scroll width. each side of the fan within‘ the scroll between Also, the curves of Fig. 8 show that the flow of .24 and .35 times the effective length of said fan 20 the fan’ with the lesser scroll width is lower blades. against any given back pressure than the ?ow 5. A centrifugal fan comprising a plurality oi’. of the fan with the greater scroll width. By a fan blades mounted in parallel relation about a comparison of the solid line curve of Fig. 8 with ' common axis, means to drive said fan blades; the solid line curve of Fig. 4, it will be seen that and a scroll having an inlet opening and an out for any given back pressure the flow. of the let opening, the width of said scroll being ap double inlet fan is practically twice the ?ow of proximately equal to 1.6 times the effective length the single inlet fan. This indicates that the of said blades, and a cut-off located in said out double inlet fan of the same diameter with the let opening having an edge inclined at an angle clearance between the two halves of the fan of approximately 15° to a radial line intersect .30 being equal to twice the clearance between the ing the edge. fan and the scroll of the single inlet fan operates 6. A centrifugal fan comprising a plurality of as though it were two ‘single inlet fans or each fan blades mounted in parallel relation about a half of the fan operates independently of the common axis, means to drive said fan blades, and other half. Without this clearance there is in a scroll having two inlet openings and an outlet terference in the ?ow produced by the two fans opening, the-width of said scroll being approx and so a reduction in the total flow produced. imately equal to 1.6 times the effective length of From the foregoing it may be seen that an im said fan ‘blades, and a cut-off located in said proved centrifugal fan has been provided by the outlet opening having an edge inclined at an provision of a clearance between the fan blades angle of approximately 15° to a radial line inter 40 and scroll to produce the higher flow against a secting the edge. f higher back pressure. In addition, means have 7. A centrifugal fan comprising a plurality of been provided to reduce the noise of operation of fan blades mounted in two sets about a common the fan. axis with a spacing between thetwo sets equal What I claim as new and desire to secure by to .3 .times the combined length of the fan Letters Patent of the United States, is: . blades, means to drive said fan blades, and a. 45 1. A centrifugal fan comprising a plurality of scroll having two inlet openings and an outlet fan blades ‘mounted in parallel relation about a opening, clearances provided on each side of common axis, means to drive said fan blades, said fan blades being approximately equal to .15 and a scroll having an inlet opening and an times the'combined effective length of said fan outlet opening, the width of said scroll being ap blades, and a cut-oi! provided in said outlet 50 proximately equal to 1.6 times the effective length opening having ‘an edge inclined at ‘an acute of- said fan blades. ‘angle to a radial line intersecting the edge. 2. A centrifugal fan comprising a plurality of KENTON D. MGMAHAN.