US2027745A - Ventilator - Google Patents

Description

Jan. 14, 1936. W, J, MONTGOMERY 2,027,745

Filed Spt. 13, 1953 2 Sheets-Shea?l l 3Q if ATT Y Jam 149.1936. w. J. MoNTGoMERY 2,027,745

VENTILATOR Filed Sept. 13, 1933 2 Sheets-Sheet 2 u l ATT'Y Patented Jan. 14, 1936 vEN'rmAToR William J. Montgomery, Upper Arlington, Ohio,

assignor. to The Jeffrey ManufacturinglComw pany, a corporation of Ohio Application September 13, 1933, Serial No. 689,293 6 cl s. (01.230-120i i By invention relates to ventilators of th rotary fan type and one of its objects is to provide improved and eiiicient mechanism for directing the now of air without contraction of now and to make the full cross-sectional area of themas-- sageway eii'ective in a more eilcient manner.

Another object of the invention is the provision of an annular inlet and an annular outlet respectively diverging to and converging from the 10 plane of rotation of the fan, with an inwardly projecting lip or annulus adjacent to the tips of the ian blades between such inlet and outlet.

A further object of the `invention is the provis on of aeroioil blade sections for a rotary fan in which the pitch angle of each aerofoil section varies for each* increment along the length of the blade section in accordance with a constant pitch diameter ratio. More particularly it is the object of the present invention to increase the 2o eillciency of a rotary fan by combining means for controlling the flow of the air through'the fanwith aerofoil sections each of which has compression and suction surfaces of gradually decreasing area radially outward and in which the pitch angles vary for each increment of space radially along the length of each section in accordance with a predetermined pitch-diameterratio so as to produce a uniform pressure over the-entire area of the opening through the ventilator to effect a I uniform flow of air .volume over such area.

Other objects of the invention will appear hereinafter, the novel features and combinations being set forth in the appended claims. i

i In the accompanying drawings Fig. lis an elevational view of a ventilator embodying my improvements;

. Fig. 2 is a sectional elevation taken on the line 2---2 of Fig. 1 looking in the direction of the arrows; l

40 i Fig. 3 is afsectional elevation taken on the line 3 3 of Figui looking in the direction of the arrows, with a pulley added; t

Fig. 4 is a detail of a portion of Fig. 3; Fig. .5 is'an elevational viewl of one of the removable aerofoil propeller blade sections;

Figs; 6A to 6H, inclusive, show by means of sec- 1 tions'taken on the lines A to H, respectively, of

Fig. 5, the shapes and contours of both`sides oi the aerofoil sections shown in Fig. 5; and

Fig. 7 is a sectional plan view of the lo 7er portion of one of the hollow deflectors at the` central vportion of the fan structure shown in Figs. 1 and 3.

The'fan casing I Il is mounted on nthe spacedapart plates II, II which are bolted at I2, I2

'55 to the concrete foundation I3. 'Ihe casinglll may be provided with annular nanges I4, I4 at its periphery to facilitate mounting in the arc- .shaped recesses in the upright plates II, II and v the securing of the casing4 I0 to the mouth of the duct .I5 of a mine. Such duct may bebf con vcretein the form of a tunnel connected to the usual Ventilating passageways in a coal mine al-v though I wish it be understood that my improve' ments may have a general application.

To 'form the rotary fan I have found by ex- 10 periment that the selection of approximately two thirds of the outer portions of the aeroplane propeller blades extending from the outermost tips toward the axis of rotation and the mounting of such aerofoil ksections IB, I6 as shown in the accompanying drawings, greatly increases the efciency over that obtained in other Ventilating fan structures in use for ventilation of coal mines. Bu't to obtain maximum eillciency each aerofoill section-is warped to give it a predetermined pitch 20 angle at various cross-sections or increments along the length of the blade radially outward.

As shown in Figs. 6A tov 6H, inclusive, the

" warping of the flatter side I l of each aerofoil Sectio I6 varies from 12 at the tip A to 33 1 at the section H near the hub extension I8. Intermediate 'these extremes the pitch angles vary as shown by Figs. 6B to 6G, inclusive these being sectional views on the corresponding section lines of Fig. 5. 30

'I'he formula for determination of the pitch angles for each increment of blade used in the rotary fan is obtained by letting P=pitch` in inches for each blade; that is, the distance through which the air is forced by the blade parallel to thel axis of rotation for each complete rotation of the blade.

R=radius in inches of each increment; that is,

the radius from the axis of rotation of the fan` to the cross-section lines indif cated in Fig. 5.' f

9=pitch angle for each increment.

'I'hen The pitchfdiameter ratio 'is desired to be constant at approximamy 64% for various sizes bf rotary fans.

v'As/determined `by experiment the following table is that for fans of maximum efficiency-'in which each blade is so warped that its pitch noted formula:

piameter Pitch 11% 1' 11" .639 2' 1" .sie spit," .642 i, 12 :gig Average .643. 5 2" .646 5' 10" 648 e' s" .s4

The diameter D above mentioned is the diameter of the fan; that is, they diameter of the circle circumscribed by the tips of the blades thereof A during a complete revolution. It is therefore a constant for any given fan. The pitch of any given fan is also a constant. For example, as seen from the above table, the pitch for a three foot (3') fan is constant at approximately one foot and eleven inches (111"), and the pitch for a ten foot (10') ian is constant at approximately six feet five inches (65) On that side I9 of the aerofoiLsection I6 opposite the warped side I1 the surface I9 is provided at each increment with a definite and predetermined' curvature as shown in Fig. 6, so

as to provide increased thickness of material to the right of the radial -line 20, a short distance back from the leading edge 2| of the propeller blade. The radii of the. curvatures at the leading edge 2| decrease radially outward as shown in Fig. 6. Thetrailing edge 22 is relatively thin.

It should be understood that when the aerofoil sections are mounted in a fan structure they are `rotated in the direction of the arrow 23 of Fig. 5 for greatest efficiency in a suction fan or in ,a blower.

As shown in Fig. 3 the aerofoil sections I6 are secured by means of bolts 24 to the disc`"25, the,l hub 26 of which is keyed to the shaft 21. A pulley 21' may be operatively connected to the shaft 21.' V The shaft 21 is journaled in the bearings 30, 3| mounted on bar/ cross-beams 32, 33 the ends of which are secured at 34,'35 to the casing I0 ,by bolts 34', 35". Pipe pedestals 36, 31 have their lower ends secured at 38, 39 to the lower portion of the casing I3 and their upper ends to the lower sides of the bar cross-beams 32, 33, intermediate the endsof the latter by means of the rings 32', 33'.v As shown in Figs. 1 and 3 the vertical pedestals 36 and 31 are directly under the journal bearings 3|) and 3|.

' As shown at 40, 4| the journal bearings 30, 3| are detachable from the upper sides ofthe bars 32, 33 so that theV entire fan structure` including all of the aerofoil sections shown in Fig. 1 is removable for repair, or for reversal from the full line position to the dotted line position.4

shown in Fig. 3. If the shaft 21 is rotated anticlockwise as viewed in the direction ofthe arrow sa of Fig. 3, so that. the fan maries move in the direction of the arrow 42 of Fig. '1, the flow of a`ir will be inward as indicated by the arrow 68 ture is connected.

in Fig; 3, the fanthen operating as a blower to force air'into the duct .to which the fan structhermore, by the use of such asymmetrical disc the 'individual blades may be reversed in their positions on the disc '25 when the fan is to be changed from a suction fan to a blower or vice versa. 'Ihe holes 60 in the hub end I8 of the blade section I6 enable the bolts 24 to" secure the sections detachabiy to either sideprthe disc 25. The leading edges 2| should all be arranged so as to move in the desired direction of rotation. For instance, vwhen the blades I6 are mounted as shown in Fig. 3 the direction of rotation is anti-clockwise as viewed in the direction of the arrow 58. l

Although the fan unit'comprising the hub 26, the disc 25 and the blades |6, may be reversed by detaching the inner framework from the casing I0 and sliding the hub 26 off the shaft 21 and then afterreversal replacing the hub on the key 59,-I prefer to reverse the blades individually because of the ease with which this may be done after an installation has been made. By referring to Fig. 3 it can readily be seen that when the blades are reversed by bolting to the opposite side of the disc 25 the tips of the blades relative to the lip 62 may be adjusted by loosening the set screws 6|, sliding the hub 26 to proper position and re-tightening the set screws.

, 'I hat is to say, after being individually reversed lthe blades I6 may be brought into the desired longitudinal movement of the hub along the key 69. The fan structure may be secured in adjusted position by means of the key set screws 6|, 6|.

The two frames comprising the bars 32, 33 and pipe pedestals 36, 31 are eac detachably secured to the casing I0. The lower en s of the pipes may be removably secured to the sockets 38 and' 39 by means of set screws 38 and 36', and the sockets themselves may be detachably secured to the casing 'I0 by means of the bolts 36', 31'.

Covering the bearings 30 and 3| are hollow shells or deectors 43, 44 each of about the diameter of -the disc 25 and shaped so as to direct the flow of air along curved paths from the center of the deector facing the current of air to the annular passageway in the plane of rotation of the fan. The shape of each deflector issuch that when the flow of air is against the same it Areduces the tendency of the air current to con-v tract when-in the plane of rotation of the fan. `Whether the fan acts as a blower to force yair into the coalA mine or as a suction fan to take air out of the coal mine the flow of air through the casing I0 will be with maximum efliciency since the full cross-sectional area`of the annular passageway is effective.

When the flow of' the air is into the coall mine the inner deilector 43 prevents back flow of the air and when the ilow is out of the coal mine the' outer deflector 44 acts to prevent back currents.

of air, It will thus be seen 4that the shells 43 and 44 each serves a double purpose in that each prevents back ilow ofair and moreover each acts when the flow of air is against it to eiliciently direct the flow of air intov the plane of voperation of the rotary` fan.

As shown'in Fig. 7, which is a sectional plan view of the lower half of thel deilector 44, the latter is provided with a slot 43.' to flt over the vertical pipe 36, and alsowith slots 45 and 46 for fitting over the bar cross-beam 32.

The lower portion of the shell 44. is provided in Fig. 2 which is a section taken on the line 2,--2

looking in the direction of the arrows.` By means of screws 49 the lateral extensions 41, 48 may be detachably secured to the) cross-beam 32. In a similar manner the defiector 43 may be detachably secured to the-cross-beam 33.

It should be particularly noted that the upper, lower and forward sides of the extensions 41, 48 are curved as shown at 50, 50', 5I and that the exposed edge of the fiat bar 32 is flush with the adjacent surfaces of the extension 48 as shown at 52 in Fig. 2. The bar 32 is i'lat and relatively thin and the extension is arranged as shown in Figs. 1 and 2.to reduce interference with the flow of air into the fan casing. 'I'he ends of the screws 49 are arranged to be ush'with the surfaces 50, 50'.

In co-operation with the curved surfaces of the defiector 43, 44 I have provided surfaces 54 and 55 at theinlet and outlet respectively, each sur face having the shape of a frustum of a cone. The surfaces at 54, 55 are preferably so shaped as to have such a path as to be in co-operation with thepath afforded by the shells 43, 44, to form approximately a Venturi duct.

In this manner the annular inlet port converges to the plane of operationof the fan blades and the outlet port diverges from such plane. By providing such annular ports with the walls thus shaped the stream of air flows through the an nular passageway with uniform density and the friction along the inlet and outlet surfaces is reduced to a minimum. In other 'wordsf the ow of air isso effectively directed and controlled that Awhile passing through the casing it is acted upon with maximum efiiciency by .the fan blade sections. I

However, since the tips of the fan blade sections must be spaced from the fan casing an appreciable leakage takes place from. the inlet surface to the outlet surface 54 as viewed in Flg. 3.

There is `also a tendency for the centrifugal forces exerted-by the fan blade sections to produce local eddy currents at the fan blade tips thereby causing back flow of the air instead of useful forward flow toward the outlet. l In order to reduce toa minimum the losses at the tips of the aerofoil Vsections I have provided' an annular inwardly projecting lip or baille plate 82 between the inlet and outlet surfaces 54, 55 as shown in Figs. 3 and 4. I have also squared the tips of the blades at 53 as have edges at right angles to axial line 2li.l I have found by experiment that the annular lip 62 must be located at the rear of the tips ofthe blades in order to obtain maximum eiliciency of operation of the'fan as a unit. For instance, when the fanis rotating in such a direction as to force the air in the direction of the arrow` 58 of Fig. 3 the annular lip will be located relative to the blade tips as shown in full lines in this view. It is therefore important to reverse the fan blade unit to the dotted line position shown in Fig. 3 when the ow of the air isto be in the direction of the dotted line.

arrow 58'.' I if It has also been found by experiment that to obtain maximum efficiency the overlapping of the approximately square tips of the blades rela'- tive to the annular 1ip'82 should be varied when the size of the fan is varied. For instance, the overlapping measured radially in fans up to six feet in diameter should be l/2"; for fans seven or eightfeet in diameter-.such overlapping shouldbe %1'; and for fans nine or ten feet in diameter the overlapping should be 1/1".

It can readily be seen by referring to the parts shown in full lines in Fig. 3 that when the air ow is in the direction of the arrow 58 the annular plate 62 acts as a defiector of the air flowing along th surface of the inlet 54 to counteract the tendency of the blade sections to produce a centrifugal action on the air and at the same time such annular plate acts as an abutment or baiile to v prevent back ow thereby counteracting the tendency of the blade tips to produce eddy currents. 'I'he squaring of the blade tips as shown at 53 in Fig. 5 increases the area of gripping action on the.

air between the blades and front surface-of the lip 62. The latter is therefore effective in cooperation vwith the blade sections with its pitch angles as shown in Fig. 6 and as predetermined according to the formula above set forth, to re- 'duce to a minimum thelosses at the blade tips by maintaining uniform volume and velocity over the entire area of the passageway through the fan casing.

By referring to Figs. 5 and 6A to 6H, inclusive, it will be understood that the .efficiency of operation of the ventilator depends uponv the shape of the aerofoil sections and the positions of the various surfaces at the cross-section increments illustrated in Figs. 6A to 6H, inclusive. Assumingthe blade to be rotating in the direction of the arrow 23 in Fig. 5, the impelling surface I1 has the maximum pitch angle (33 12') where the circle ofrotation is the smallestand the minimum pitch angle (12) at the tip of the blade where the circle of rotation is the greatest.

The air impinging or propelling surface I1 is warped or spiraled as shown in Figs. 6A to 6H,

inclusive, in accordance with the increasing lengths of the circles through which the various radial portions of the blade travels. Furthermore, the outer portion of each blade is tapered toward the tip in the plane of rotation of the fany as' viewed in Fig. 3 and is also tapered toward the tip relative to the direction of movement of the air through the ventilator as indicated by the arrow 58.

The leading edge portions of each blade is of y decreasing thickness radially outward as shown I1 and the suction surface l 9 are consequently distributed radially outward to produce a uniform pressure over the entire area of the opening through the ventilator to effect a uniform flow of air volume over such area in the direction of the arrow 58parallel to the axis of notation of the fan unit.

In other words the ai;` impelling action and the air suction action each varies in accordance with the lengthsof circles of rotation with the result that in cooperation with the inlet and outlet surf faces 54 and 55 and the central circular supporting structure, the blower action on the'air will be uniformly distributed as to pressure and volume over the entire annularv area ofthe opening through the ventilator, thereby greatly increasing the efliciency of the ventilator..

By reason of the tapering of the elongated aerofoil blades radially outward and the distribution of the impelling and suction surfaces- I1 and I8, and particularly due to the selection of a pitch-diameter ratio D of approximately 64 per cent, there is inherent in the rotary fan unit as determined by actual experiment a self-limitation featurelin thatwhen an electric motor is provided for normal operation under given conditions the fan head or resistance in the duct I5 may be increased or decreased within wide limits without overloading operate a Ventilating fan against the increase in pressure or resistance. However, by reason of the structure shown in the accompa ying drawings there will be sufficient slip of jth fan blades relative to the air acted on by such blades as to prevent overloading of the motor.

lIf a door in a break-through in a coal mine near the` intake opening should be left open accidentally, the air in the Ventilating passageways in the mine would'be short-circuited and the tendency of the motor would be to be overloaded by reason of the increased volume of air sent into the mine by the ventilator. But hereagain the self-limiting feature of the fan unit shown will also prevent overloading of the motor.

Heretofore an electric motor of sumcient horsepower to take care of such abnormal loads was required to operate mine Ventilating fans but by reason of the self-limiting feature of my improved fan structure a smaller motor may be used than is required otherwise. That is to say, my improved fan structure permits the use of a motor of substantially constant horsepower for a wide range of conditions which vary automatically and are beyond the control of the operator of the ventilator.

This application is a continuation in part of my co-pending application Ser. No. 569,460, filed October 17, 1931, for an Improvement in ventilators. v

Obviously those skilled in the art may make various changes in the details and arrangement of vparts without departing from the spirit and scope of the invention as defined by the claims hereto appended, and I wish therefore not to be restricted to the precise construction herein disclosed.

Having thus described and shown an embodiment of my invention, what I desire to secure by Letters Patent of the United States is:

l. In a ventilator, the combination with a casing having intake and outlet converging and diverging peripheral surfaces, of a rotary fan unit within said casing, comprising a radial aerofoil blade, and an inwardly `projecting annular lip between said intake andoutlet surfaces adjacent the blade tip of said fan unit and in radial overlapping relation with the tip of said blade.

2. In a ventilator, the combination with a casing having intake and outlet converging and diverging peripheral surfaces, of a rotary fan unit within said casing comprising an aerofoil blade, an inwardly projecting annular lip between said surfaces, and means for supporting said fan unit with the tip of said blade adjacent said lip and radially overlapping said lip on that side thereof adjacent to said intake surface.

3. In a ventilator, the combination with a casing having inner peripheral inlet and outlet surfaces, of an'inwardly projecting annular lip be. tween said surfaces, a fan unit within said casing comprising an aerofoil blade having a tip edge extending approximately along a. straight Apelling surface of gradually decreasing pitch angles radially outward tosecure uniform distributio'n of pressure and volume of air through lsaid casing, and means for mounting said fan unit with the tips on either side of said lip for rotation in such direction that the tips shall be in the angular space between the inlet surface land said lip.'

5. In a ventilator, the combination with a cas-,-

ing having converging and diverging inlet and outlet inner peripheral surfaces, of an annular lip vprojecting inwardly from said casing in aA yplane extending through the merger between said surfaces, a rotary fan unit comprising a plurality of aerofoil sections with squared tips,

casing with said tips on either side ofsaid lip in radial overlapping relation therewith, said tips being displaced therefrom anamount determined by thediameteryof the circle inscribed by the tips during rotation of said fan unit.

' 6. In a ventilator, the combination with a casing having converging and diverging inlet and outlet inner peripheral surfaces, of an annular vlip projecting inwardly from said casing in a plane extending through the merger between said surfaces, a rotary fan unit within said casing comprising a 'plurality of aerofoii propeller blades, a rotatably mounted support for the inner ends of said blades, each blade having an lmpelling and a non-impelling surface on the leading side, said impelling, surface being of decreasing pitch angles radially outward and terminating when the pitch angle increases to approximately 33 degrees; deecting means adjacent the support and Anon-impelling blade surface to direct fluid flow which, in cooperation with said casing' peripheral surfaces, effectively directs the fluid flow to the area swept by the impelling surface of the blades during rotation thereof, and means .for mounting said fan unit with the tips on either side of said lip for rotation in such direction that the tips shall be in the angular space between the inlet surface and said lip.

WnuAM J. lvIoN'rGl OMERY.

. line at a right angle to the radial axial line of fmeans for mounting said fan unit within said

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