US2936948A - Axial blower with cone-shaped hub - Google Patents

Description

May 17, 1960 B. c. ECK

AXIAL BLOWER WITH coumsm sn HUB 2 Sheets-Sheet 1 Filed July 8, 1955 INVENTOR Bruno CT EA- 3/ MQJ.

Ritaldag-,f,

May 17, 1960 B. c. ECK 2,936,948

AXIAL BLOWER WITH CONE-SHAPED HUB Filed July 8, 1955 2 Sheets-Sheet 2 FIG. 3

/NVFNTOR ,Brunv (T Bk V 7 2,936,948 AxIAL BLowEn wrrn' CONE-SHAPED HUB Bruno Christian Eek; Kolin-lflettenherg'; Germany Application July s, 1955, Serial Nb. siesta Claimspriority, application Germany October-'15; 1954* 7 Claims (Cl. 230-120) The present" invention relates to blowers and, mdrepartic'ularly, to an axial blower with a; done-shaped hub, Axial blowers having a meridian cross" sectionwhich decreases in the direction of flow of the fluidid'elive'red thereby have been knownfor a long time; Such blowers whichusually are called riieridianaccelerated axialblow ers are obtained by making the hub graduallytbificr'ease or by drawing in the outer mantle or'by both. Thisft'y'p'e has the great advantage that Without profiling, i.e. by providing simple sheet metal blades, pressures" can be obtained which approach thevalu'es obtained with radial blowers. Non-profiled" blowers are necessary if, for" instance strongly corrosive dust particles are 'included in the fluid to-be delivered. ular type of blowers has been employedespecially when suctionblowers were required. These meridian accelerated axial blowers are not to be confused with axial blowers in which due to the noticeable change in' density the meridian cross sections have tobe changed (axial compressors). Blowers of this type with a considerably high degree of efliciencyabove 80%-have been known. These heretofore known blowers, however, have the drawback that they yielda rather unfavorable characteristic of' which practically a smalfv range only is satisfactory whichbrings about the necessity of designing. such blower very precisely. T is fact enhances great drawbacks and makes necessary later corrections if; as is often the:case; pressure and quantity were not precisely known at the time the blower was designed. Another drawback consists in that in spite of alletforts, the high-maximum degrees of efiiciency possible nowadays with normal axial blowers could not be obtained heretofore. v Still another drawbackof the heretofore known axial blowers consists in that, when the blower. works in the neighborhood-f the steeply declining section of the characteristicswhich declines with decreasing delivery, strong noises occur which have a rather disturbing efiiect;

Whereas with normal axial blowers, the influence of the hub is determined only'by the ratio ofthe hubdiamcter to theouter diameter, with meridian acceleratedaxial blowers a'plurality of structural features may: be varied which features are: e

(a) The ratio of the rear diameter of the hub'to-the outer diameter.

(b) The ratio of the free meridianentrance annular or ring surface tothe free meridian-exit ring surface. 0 p

(c) The merging linesorcontour of thehubt In this connection the difference between anincrease along. a cone or a more or less curved design-is to be considered.-

(d) A possible outer change in the contour ofthe mantle line for instance by drawing in them'antleor by enlarging the same.

In addition to the above, similar to normal axial blowers, the various blade features may be varied, i.e. the number of blades, the curvature of the blades, twist, etc.

United States Patent '0 2,935,948 Patented May 17, 1960 2. and brewers, riieoptimun design of Suc meridian ac :lerate'd axial, never is considerably more difii'culft than.

the dimensiohifigof a normal axial blower. In addition law is availableby thereto, with nsm arann blowers a i I means of which nowadayslalriiostall questions in connection with the ridrrflal axial blower can be solved by pure theoretical means. The, application of this law to merime ers has up to date been unsuccenter. This failure-1s due to the fact that the Baursfeld law' as basis of said" thbfy is not applicable to meridian ascertained b er Thus, when designing a meridian accele'fated' axia b diver, the de grief is'iath'er helpless and has" to" do dnsid'e rablei guesswork. The experience eemfirugn mn s is" of littlevalue in this connection because due' t o'cavitatiomthefblades of centrifugal pumps laid: olit difi'ereritlyland would not yield optimum results with meridian accelerated axial blowers.

It is, therefore, an object of the piserit' invention to provide a meridian accelerated axial. blower which will overcome the above mentioned drawbacks. I

It is another object ofthi'sf invention to provide a meridian aceelernen axialblower with specific-structural features which have to be followed in order" to obtain improved efficicncy. y

It is a still further object of this invention to provide amieridian accelerated axial blower which-is of relatively simple construction and high efficiency.

These and;other objects andadvantages of the inventionwill appear more clearly from the followingspecification-in connectio with the accompanying drawings, in which: i i

Fig.- 1* is a perspectiye view, partly in' section of a meridian accelerated 'axial'blower.

' Fig. 2 illustrates" on a scale somewhat-larger than the scale of Fig; 1-" theimpeller with cone-shaped hub shown in Fig; 1

.FigLQB is a diagrammatic representation of an impeller Fig. 4 is aview of-animpellerwith blade'adjustment; f

In order tolo'vercome-g; the above outlined drawbacks and to rnateriali'zethe objectsset forthabove, investigationshavebeen-carriedon over a number of years and have beenverified bynumerous tests as a result of which it has been found according to'the present invention that with axial blowers having a cone-shaped hub and in which the outer mantle is cylindrical? or nearly cylindrical, the ratio of the diameter of the rear portion of the hub to the oiite'r'blade diameter must] bele'ss than two third s" and iiustbFg'r'e'ater than one-half; whereas at the'same time the'hllb is' to'befiesigned'fas coiie-shaped 'or approximately cone shaped mantlewith' a"gnei:ating agle 7 between 10 and 20 while the ratio of the free meridian entrance annular or ring surface to the free meridian exit annular motor l-mountedona base 2 and d'rivingly connected I It will be evident that in-view of the numerous pos: 7

' sibilities of variations possible with meridian accelerated tionvll being designedas" difiuser mantle. The cyan:

through a'shaft3 with the cone-shaped impeller" 6; The cone-shaped impeller-'6 is provided with impeller blades Sand atits intake side isconnwted toshaft 3 by means ota- -head 7 thecontourof which has been designed'in conformity with the' general -factors governing the flow I I of 'a fluid' alonig surfaces. Behind th'e impeller 6" there isprovided the guiding wheel 8-which carries" the guiding blades+"9:- This "guide wheel'-=8 si'multaneously serves as bearing for shaft 3 and' furthermore 'c'arriesthe diffuser core ltk" The=blower propenis surrounded by a cylin drical mantle i -which at it's intake end merges "with i an intake elbow "section -1'1sand atitsdischarg end merges with a discharge connection "12, said discharge mime drical blower mantle 4 andthe diffuser mantle 12 are supported by supports 13.

The impeller 6 shown by itself on a larger scale in Fig. 2 has its cone-shaped hub arranged on shaft 3. The head 7 which connects the cone-shaped hub 6 of the impeller 6 with shaft 3 at the intake end, is designed in connection with principles governing the flow of fluid along surfaces. Half of the conical angle of the coneshaped hub 6' is designated with the letter 7 as illustrated in Fig. 2 of the drawings. I

The various relative dimensions or diameters critical for a blower according to the present invention and shown in connection with Fig. 2 are as follows: the letter d designates the pitch diameter of the impeller blades, whereas the outer diameter of the impeller blades is designated with the letter d The front diameter of the hub 6' is designated el, and the diameter of the rear portion of the hub is designated with the letters d The diameter ol of the front portion of the'hub and the outer diameter d; of the blades determine the free meridian entrance ring surface The diameter d of the rear portion of the hub and the v Fig. 2a shows the contour of a blade the length of which is designated with the letter I.

Fig. 3 diagrammatically illustrates an impeller blade as seen from the top. In this diagrammatic illustration, the impeller is designated with the reference numeral 5, whereas the impeller axis shown as a dot dash line is designated with the reference numeral 3'. It has been found that the rear hub diameter d i must be less than approximately two-thirds of the outer diameter d; of the blades. Preferably the outer mantle is cylindrical or approximately cylindrical, whereas the hub should have a cone shape or an approximate cone shape. Half the conical angle 7 should be from 10 to The coneshaped hub of the impeller 6 may sharply or in a somewhat rounded manner merge into an approximately cylindrical discharge or intake. This merging portion may be located within or outside the arrange of the blades or outside thereof as is shownin Fig. 2. The ratio of the free meridian entrance ring surface Tina-d2.)

to the corresponding surface at the impeller exit, should be within the limits of 1.15 to 1.35. By corresponding surface at the impeller exit is meant the corresponding annular or ring surface at the exit side of the impeller which The curvature of the blades is of importance. If thus the mean radius of curvature of the blades 5-is designated with R-by profiling is meant the radius of the mean skeleton line i.e. that line which is obtained if the profile of the profiled blades is halved at a plurality of portions and the thus found points are interconnected by a curve the ratio of this radius of curvature to the outer blade diameter at the respective point should be less than about 1.1. This requirement should preferably be met'along the entire length of the blade. The term mean radius has been employed because, when using a relatively thick sheet metal, the radii of curvatures of the inner and outer contour may differ somewhat from each other. It is necessary to find the curvature in an unequivocal manner. To this end, the central portions of the profile are connected by a curve- 'This curve will then have the so-called mean radius. The ratio of the respective blade chord to the respective diameter should preferably be 4 within the limits of 0.3 to 0.75 whereas the blade chord should decrease from the outside la toward the inside li. This is all the more remarkable as with normal axial blowers this feature would reduce the degree of efiiciency while simultaneously increasing the pressure. The twist of the blades as expressed by the difference in angle of the blade chord at thehub and at the outside (angle 6 in Fig. 3) should be smaller than 25, whereas the outer entrance angle of the blades ,B measured with regard to the circumference should be less than 35. The last mentioned feature which is known per se will in connection with the other above mentioned features bring about a further improvement of the degree of cfficiency of the blower. I

As to the blades, again numerous investigations and tests have been conducted in order to find the arrangement which will assure the most favorable degree of eficiency. It has been found that the most favorable degree of efficiency will be obtained with a blade number ranging from, four to six.

The meridian accelerated axial blower according to the invention may be controlled by an arrangement according to Fig. 4. Impeller blades with. adjustable pitch have been known heretofore, however, with these known arrangements, the blades were adjusted over their entire width with the result that the ends of the blades near the lower blade edge cause considerable disturbances in the flow when the edges extending into the flow, as well as the protruding edges of the holding bolt caused rather inconvenient disturbances in the flow. These drawbacks have been avoided according to the present invention by an arrangement which makes it possible to adjust the blades over a certain width only of said blades. Thus, for instance, each impeller blade may be sub-divided into two blade sections. In this instance either the blade section on the intake side is stationary and the other blade section is adjustable or vice versa. According to the embodiment shown in Fig. 4, the blade sections 5a are stationary at the intake side. The blade sections 5b which are located on the exit side are turnable about the holding bolt or pivot 14 which is rotatably journalled in the conical hub of the impeller 6. The upper portion of Fig. 4 shows in full lines an impeller blade in normal position, whereas the lower portion of Fig. 4 shows an impeller blade in adjusted position indicated by broken lines. The adjusting mechanism itself does not form a part of the present invention and any standard adjusting mechanism known for adjusting the blades of an impeller of a blower may be employed in this connection. The control eifect obtained by such a design is not much inferior to the control effect obtained when the blades are adjusted over their entire width. However, the drawbacks which as outlined above are inherent to the heretofore known arrangement with the adjustment of the blades over their entire width are not present with the control arrangement according to the invention.

It is, of course, understood that the present invention is,'by no means, limited to the particular construction shown in the drawings but also comprises any modifications within the scope of the appended claims.

What I claim is:

1. In combination in an axial blower: a hollow at least approximately cylindrical member, and an impeller rotatably arranged within said cylindrical member and having a substantially cone-shaped hub provided with blades thereon and having a generating angle of from 10 to 20, the ratio of the hub diameter at the rear end of the rear hubd -to the outer diameter of the bladesd being less than 2:3 and greater than 1:2, and the ratio of the free annular meridian entrance surface {t a-dz.)

to the free annular meridian exit surface {ea-d2.)

than 1.1:1.

3. In combination in an axial blower: a hollow at least approximately cylindrical member, and an impeller rotatably arranged within said cylindrical member and having a substantially cone-shaped hub provided with blades thereon and having a generating and 'y of from to 20, the blades being so designed that the blade chordsedecrease from the outer diameter of the blades to the inner diameter thereof, the ratio of the rear hub diameter to the outer blade diameter being less than 2:3 and greater than 1:2, and the ratio of the free annular meridian entrance surface to the'free annular meridian exit surface being within the limits of from 1.15:1 to 1.35:1. 1 l

4. In combination in an axial blower: a hollow at least approximately cylindrical member, and an impeller rotatably arranged within said cylindrical member and provided with blades thereon and having a generating angle of from 10 to 20, the ratio of the respective blade chords to the respective blade diameters pertaining thereto being from 0.3:1 to 0.75:1, the ratio of the rear hub diameter to the outer blade diameter being less than 2:3 and greater than 1:2, and the ratio of the free annular meridian entrance surface to the-free annular meridian exit surface being within the limits of from 1.15:1 to 1.35:1.

5. In combination in an axial blower: a hollow at 'least approximately cylindrical member, and an impeller rotatably arranged within said cylindrical memberand provided with twisted blades thereon and having a generating angle of from 10 to 20, the twist 6 of said blades expressed by the difierence in angle of the blade chord at the hub and at the outer periphery of the respective blade being less than 25, the ratio of the rear hub diameter to the outer blade diameter being less than i 2:3 and greater than 1:2, and the ratio of the free annular meridian entrance surface to the free annular meridian exit surface being within the limits of from 1.15:1 to 1.35:1.

6. In combination in an axial blower: a hollow at least approximately cylindrical member, and an impeller rotatably arranged within said cylindrical member and having a substantially cone-shaped hub provided with blades thereon and having a generating angle of from 10 to 20, the entrance outer angle fi of the blading being less than 35, the ratio of the rear hub diameter to the outer blade diameter being less than 2:3 and greater than 1:2, and the ratio of the freeannular meridian entrance surface to the free annular meridian exit surface being within the limits of from 1.15 :1. to 1.35:1.

7. In combination in an axial blower: a hollow at least approximately cylindrical member, and an impeller rotatably arranged within said cylindrical member and having a substantially cone-shaped hub provided with fromfour to six blades thereon and having a generating angle of from 10 to 20, the ratio of the rear hub diameter to the outer blade diameter being less than 2:3

and greater-than 1:2, and the ratio of the free annular meridian entrance surface to the free annular meridian exit surface being within the limits of from 1.15:1 to 1.35:1.

Van Ornum et a1. Sept. 4, 1956

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