US2040452A - Fan construction - Google Patents

Description

T. TROLLER May 12, 1936.

'FAN CONSTRUCTION s Sheets-Shet 1 Filed March 23, 1954" May 12, 1936. T. TROLLER FAN CONSTRUCTION Filed March 25, 1934 3 sheets-sheep 2 INVENTOR T. TROLLER FAN CONSTRUCTION May 12, 1936.

5 Sheets-Sheet 3 Filed March 25, 1934 INVENTOR Patented May 12, 1936 PATENT OFFICE 2,049,452- FAN ooNsmUc'rIoN Theodor Trollcr, Akron, Ohio Application March 23, 1934, Serial No. 717,000

This invention relates broadly to fan construction, and more particularly to fans designed for delivering fluid under pressure, and especially rotary fans for this purpose. The-invention has to do primarily with-increasing the efllcien'cy of such fans. 5

Rotary fans for delivering fluid under pressure, such, for example, as ventilating fans for mines, buildings, etc., are designed to deliver fluid in a desired direction, but, due'to various factors which cannot be. avoided, certain of which arise by reason of the rotational movement of the fan,

a tendency. is created to impartto the fluid a movement having a. component transverse of the desired direction of delivery. This causes cross currents in the delivered fluid and reduces the efilciency of the fan.

For example, in a. ventilating fan such as might be used for withdrawing air from a mine and which has a rotor or propeller for moving or delivering the air being withdrawn in a stream moving substantially in a straight line, as within a conduit having a substantially straight axis substantially coaxial with the propeller or rotor, the propeller blades have working faces designed to move the air in the delivery direction, but due to the shape of such blades, the rotational movement thereof and the friction between the air and blades the air is not actually delivered in a solid homogeneous unidirectional stream. The

- shape of the moving blades and the friction between the air and blades cause the air in addition to moving in the delivery direction to move also in a direction generally transversely of the delivery direction generally tangentially of the rotor. In other words, 'althoughthe-air has a major component of movement in the delivery direction, it'has a minor component,'but nevertheless a component 'ofsufflcient magnitude to materially reduce the efllciency of the fan, in a direction perpendicular to the desired delivery direction and, consequently, in the usual con-- sh'uction perpendicular to the axis of the rotor.

The movement of the air transversely of the delivery direction not only sets up cross currents,

'butalso,duetothefactthattheairhasmass,

results in centrifugal movement thereof. This, in turn, results in a condition in which the pressure builds up toward the periphery of the air stream and drops toward its center. The axial velocity of the air is likewise greatest adjacent theperiphery of the stream and decreases toward the center of the stream. The tangential velocity of the air, however, is greater near the center of the stream than at the periphery,

. air to move backwards or opposite the desired direction of delivery. The low efficiency of the fan under these conditions will readily be appreelated;

I provide for eliminating the undesirable conditions above referred to and greatly increasing 1 the efficiency of fans for delivering fluid under pressure. I provide for counteracting the tendency of the rotor to cause the fluid to have a component of movement transverse of the desired delivery direction. This is preferably done 15 by means cooperating with the rotor to control the fluid flow. I: prefer to use substantially stationary means and, in a fan of the type referred to above by way of example, to dispose the same substantially in axial. alignment with the pro- 20" peller. The invention in its broader aspects is not limited to any particular type of fan, but for purposes of illustration will be described as embodied in a fan for moving fluid forward in a conduit in a substantially straight line.

The desired results may be accomplished by using a series of circumferentially arranged vanes which deflect the fluid, preferably either just before or just after itpasses the rotor. The I vanes are preferably designed to impart to the fluid a movement roughly equal to its transverse component and opposite in direction so that the fluid is delivered generally along the conduit with a minimum of cross currents. Elimination of-the radial component of movement 'of a fluid delivered bya fan of the type specifically referred to above is particularly important and is efl'ectivelyaccomplished by my construction. The fluid is delivered with substantially uniform velocity throughout the cross section of the stream.

- other details, objects and advantages of the invention will become apparent as the following description of certain present preferred embodiments thereof proceeds.

In the accompanying drawings I have shown certain present preferred embodimentsof the- V invention, in which I I Figure 1 is a longitudinal vertical central crosssectional viewthrouglr a fan construction; i a Figure 2 an elevationalview looking from left to right in Figure 1;

Figure 3 is an elevational view looking from ht tole ftinFigure 1;

Figure {iis a fragmentary'diasrammaticelevational view showing the shape of the conduit or outer fairing;

Figure 5 is a side view of one of the vanes;

.Figure 6 is an end view of the vane shown in Figure .5;

Figure '7 is a view of the vane looking downwardly in Figures 5 and 6, Figure '7 being to enlarged scale;

Figure 8 is a view similar to Figure 1, but relatively diagrammatic and to reduced scale, showing a modified construction;

Figure 9 is a cross section through a.- vane of the type having appreciable thickness; and

Figure 10 is a diagrammatic fragmentary view showing how the angle am is measured.

Referring more particularly to Figure 1, reference numeral 2 designates a mine shaft or entry extending generally horizontally and opening at the right-hand side of the figure. To assist in ventilating the mine it is desired to withdraw the spent air outwardly through the shaft 2. At the mouth of the shaft there is provided a conduit or outer fairing, designated generally by reference numeral 3, which has a substantially square or rectangular inner extremity 4 closely fitting the shaft and a substantially square or rectangular outer extremity 5 terminating in a flared discharge portion 6. Intermediate the ends of the outer fairing or conduit 3 is a section I of circular cross section, which section is connected with the extremities-of the conduit by sections 8 and 9, respectively, which are smooth transformation sections whose cross section changes gradually from a circle to a square or rectangle. The transformation is illustrated by the diagrammatic showing of Figure 4.

There is provided a base ill having uprights ll extending within the conduit, which uprights support bearings I 2 in which is journalled for rotation a driving shaft I3 extending longitudinally of the mineshaft and disposed at or near its transverse center. Connected with the shaft l3 at its left-hand extremity, and in radial alignment with:' the section 1 of the outer fairing, is a rotor comprising two propellers ll each having two blades l5 extending in radially opposite directions, such propellers being mounted hub to hub with their blades extending substantially at right angles to one another, as shown in Figure 1, so as, in effect, to rotate as a single 4-bladed propeller. The propeller blades are so designed that when the propeller rotates in the counterclockwise direction, viewing Figure 2, or the clockwise direction, viewing Figure 3 (such directionsbeing indicated by arrows) it withdraws air from the mine shaft 2 and delivers it in a gen-' erally outward direction, or toward the right viewing Figure 1.

Keyed to the shaft I 3 intermediate the bearings I2 is a pulley l6 through which the shaft I3 is driven by a belt II which extends out of the conduit and within tubular guards ll therein, such guards being of generally streamlined cross section, as shown in Figure 1, so as to reduce the resistance offered thereby to the airbeing delivered by the fan. The belt I1 is driven by any suitable source of power, as by an electric motor positioned in a room or building. adjacent the. shaft. I

There is provided aninner fairing designated generally by reference numeral IQ and which comprises a central generally cylindrical portion 20 substantially surrounding and enclosingi'the bearings, shaft and and Stmported by the 2| and 22 are to promote gradual lateral deflection of the air at the center of the shaft so as to avoid undue resistance to the air by the portion 20.

There are provided three vanes 23 equally spaced circumferentially and, which are positioned immediately upstream from the rotor comprising the two propellers. The purpose of the vanes is to cooperate with the rotor to control the air flow so that the air will be delivered generally longitudinally of the conduit with a minimum of cross currents. As above stated, the rotational movement of the rotor tends to impart to the air a movement having a component 7 transverse of the desired'delivery direction, and

I design the vanes so as to counteract to at least a substantial extent this tendency of the rotor. The vanes deflect the air in such manner as to impart thereto a movement roughly equal to the transverse component of the movement imparted by the rotor and opposite in direction.

Design of the vanes to accomplish above referred to is a nice problem, as these vanes should give the desired effect but should not the results cause any appreciable reduction of the eiliciency of the whole fan system by losses through friction on the vanes or by eddies and turbulence in the moving fluid caused by the vanes. I have solved such problempartly by. theoretical considerations and partly by experiment, correlating the results to produce a fan construction approaching very closely a theoretically perfect fan. I shall now proceed to describe how the vanes are designed.

Both the blades and the vanes are preferably "equally spaced circumferentially to avoid unbalance. The number of vanes is preferably unequalto the number of blades of the rotor so as to avoid impulses in the air stream which would be brought about when the respective blades which may be defined by the following formulae:

a. Q 'tan a,

( .=-;-L ta pr.

in which L is the length of each vane in a direction parallel to the axis of the propeller;

' ha is the average width of each propeller blade;

1 Gm is the angle between the thickness center 7 line of a section of each propeller blade in a plane perpendicular to the length of the blade at the center, in the direction of the length of the blade, of its effective portion and the plane of rotation of any point on the blade;

Zp is the number of propeller blades;

:zvisthe number of vanes;

pr is the angle between a tangent at the edge of 'each vane nearer the propeller to the thickness center line of a section of the vane which .lies in a first plane perpendicular to a second plane containing the axis of the propeller and the edge of the vane remote from the propeller, which edge extends substantially perpendicular to the axis of the propeller, which first plane is at a radial distance r from the axis of the propeller, and a line through the point of tangency parallel to the axis of the propeller; and

b: is the width of each vane at a radial distance r from the axis of the propeller'in a plane perpendicular'to the axis of the propeller in a direction perpendicular to the edge of the vane remote from the propeller.

The various terms used in the formulae are indicated in the more or less diagrammatic show-' ings of Figures 5, 6, 7 and 10. -It is believed that with the above explanations as to the various terms andthe showings of the drawings application of the formulae will be self-evident.

In order to obtain the first value of the angle p: the known formula tan p, =7

radial distance r, the constant in formula (2) thereof nearer the rotor.

above may be calculated, and formula (2) may thereafter be used in calculating values of the angle pr corresponding to other radial distances 1.

The formulae which I have evolved define the shape of the vane so far as its length and breadth are concerned and give the direction in which the vane extends from any point along the edge This is given for simplicity by the direction of the tangent at the vane edge nearer the propeller to the thickness center line of eachvane section under consideration as the tangent has the same direction at thepoint of tangency as has the center line. Although the center line is somewhat curved, it closely approximates a straight line at the edge of the vane nearer the propeller so that the tangent for some distance from the vane edge very. closely approximates the section center line,

and in the practical working out of the shape of the vane the tangent itself may be used in place of the center line. Any error which might thus be introduced would be far less'than the allowable deviation, as will be pointed out below. As the opposite edge of the vane is a straight line perpendicular to the axis of the rotor, the shape of the vane is determined, as illustrated in Figure 7 by smoothly curving the respective section center lines so that they will assume superposed relation at their left-hand extremities. This is usual practice in aerodynamic design, and each of the section center lines may independently curve to the ultimate line C (see Figures 5 and 7) or the lines may assume superposed relation in groups before the line C is reached. In Figure 7 the two extreme lines are shown as assuming superposed relation at A and the three intermediate lines at B, the two composite lines thus produced becoming superposed at the line 0.

ultimate A few examples showing how my invention may be appliedmay be helpful in understanding it. As a first example let it be assumed that it 'is desired to deliver 150,000 cubic feet of air per minute against a pressure of 4" of water using a rotor having a diameter of 96" turning at a. speed of 1200 revolutions per minute. Good engineering practice would dictate that is. should be about 10", 5 vanes would probably be used as against 4 propeller blades and the angle on would be about 11. Using these figures, tan am (11)'=.195 and a1. mid, I L- 10 .195 -approxrrnately 2 0 V r p, tan p, by

As a second example let it be assumed that it is desired to deliver 16,500 cubic feet of air per minute against a pressure of 5" of water, using a rotor 24" in diameter turning at a speed of 3500 revolutions per minute. Under these circumstances a proper value for in. would be about 3.5", 4 propeller blades might be used as against 3 vanes, and the angle Gm should be about 16. Tan am would then equal .287 and 2 .287 If, however, considering a problem actually env countered in design, it should be desired to use follows:

r 1:, tan p, b,-

11. 9" 40. 0 s4 4. 2" 9" 48. 0 1. 11 5. 5" 0" 59. 0 1. to 8.5

If as a third example it should be desired to deliver 1250 cubic feet of air per minute against a' pressure of 2" of water with; a propeller 5.8" in diameter turning at a speed of 5000 revolutions per minute, tm should be approximately 2.2", the number of blades might be 4 as against 5 vanes, and the angle am should mately 28. 'Tan am would equal .532 and V all; i L- 2.2 .532 1.65

The values of 1', pr, temp: and b1 would be as follows: a

r Pr tan Pr r be approxi-,

in; will in all cases 75 be exactly in accordance with my formulae. although I believe the formulae to define vanes of the most nearly perfect shape for accomplishing the desired results. For instance, in the second example given above I arbitrarily increased the length of the vanes from 8.2" to in order to increase the size and strength of the vanes sufficiently to adequately support the inner fairing. I find that satisfactory results are obtainable if the value of L is held within about 25 per. cent., more or less, of the theoretical value obtainable by application of formula (1) the value of the angle p; is held within about per cent., more or less, of the theoretical value obtainable by application of formula (2), and the value of biis held within about 10 per cent., more or less,

of the theoretical value obtainable by application of formula (3). These are usual engineering variations.

In Figure 8 there is shown a modified form of construction in which the vanes are positioned downstream with respect to the rotor, the vanes being used to support the portion of the inner ,fairing disposed downstream from the rotor.

The portion of the inner fairing upstream from the rotor would have to be supported otherwise in any appropriate way. In the construction diagrammatically illustrated in Figure 8 an electric motor 24 is mounted within the inner fairing, the rotor 25 being driven directly from the motor shaft 26. The wires for the motor could be led in in any appropriate manner, as through the nose of the inner fairing. The inner fairing in Figure 8 is substantially a conventional airship hull, as contradistinguished from the inner fairing of Figure 1, this being a matter of design and convenience. Such an airship hull offers less resistance to the airflow, but a construction such as shown in Figure '1 is cheaper to manufacture.

The vanes need not be of sheet metal as shown in Figures 1 and '8, but may be of appreciable thickness and may be constructed, for example, out of wood or metal forms covered 'with sheet metal, canvas, etc. When vanes of appreciable thickness are used they should have airfoilgsections, as shown at 23" in Figure 9, in which the nose or upstream extremity of the section is toward the right. My formulae contemplate the use of vanes of appreciable thickness, the angle 1):, as

above indicated, defining by the direction of its tangent at the vane edge nearer, the propeller the direction of each vane section center line. When vanes of appreciable thickness are used their surface contours as air foil sections are easily de-.

terminable by methods well known in the art. When. sheet metal vanes are used this is unnecessary due to the fact that for aerodynamic purposes the thickness of the sheet metal is negligible and its surface may be substantially conformed to the center lines as determined by my formulae.

While I have shown and described certain present preferred embodiments of the invention, it is to be distinctly understood that the same is not limited thereto but maybe otherwise variously embodies within the scope of the following claim.

I claim: I

In combination, a rotary propeller for moving fluid in a direction generally axially of the propeller and means cooperating with said propeller to control the fluid flow, said means being mounted substantially in axial alignment with the propeller and comprising a series of circumferentially arranged vanes, said propeller and vanes being designed, with usual engineering variations, in

accordance with the following formulae:

in which L is the length of each vane in a direction parallel to the axis of the propeller; in is the average width of each propeller blade; am is the angle between the thickness center line'of a section of each propeller blade in a plane perpendicular to thelength of the blade at the center, in the direction of the length of the blade, of its effective portion and the plane of rotation of any point on the blade; at is the number of propeller blades; 2v is the number of vanes; pr is the angle between a tangent'at the edge of each vane nearer the propeller to the thickness center line of a section of the vane which lies in a first plane perpendicularto a second plane containing the axis of the propeller and the edge of the vane remote from the propeller, which edge extends substantially perpendicular to the axis of the propeller, which first plane isat a radial distance r from the axis of the propeller, and a line through the point of tangency parallel to the axis of the propeller; and

b: is the width of each vane at aradial distance r from theaxisof the propeller in a planeper- I mote from the propeller.

TI-IEODOR TROLLER.

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