US2303832A - Axial blower - Google Patents

Description

Dec. 1, 1942. J. M. FUNK l 2,303,832

AXIAL BLOWER Filed Jan. 17, 1941 2 Sheets-Sheet 1 K ,v x /r/ I Dec. 1, 1942."

med aan. i7. 1941 Patented Dec. 1, 1942 UNITED STATES PATENT OFFICE 2,303,832 AXIAL BLOWER n v James M. Funk, Ottawa, Ill.

Application January 17, 1941, Serial No. 374,911

(ci. 23m-12o) l 4Claims.

This invention relates to a new and improved axial blower.

The principal object of my invention is to provide an axial blower unit providing pressure resisting characteristics obtainable heretofore only with larger diameter centrifugal blower types of fans, the blower of my invention having the further advantage, of particular importance in furnace installations, of operating much more quietly and with smaller power consumption than any centrifugal blower of equivalent capacity with which I am familiar.

More specifically stated, the blower of my invention embodies an improved fan hub, fan inlet, and fan tip shrouding structure which obtains with a smaller diameter fan the results heretofore obtainable only with larger diameter fans.

The invention is illustrated in the accompanying drawings, in which- Figure 1 is a view partly in vertical section and partly in front elevation of a furnace having a blower unit made in accordance with my invention;

Fig. 2 is a section through the blower unit on a larger scale;

Fig. 3 is a plan view of Fig. 2 looking down on the blower unit from the motor end;

Fig. 4 is a sectional detail of the rubber cushioned fan hub construction, and

Figs. 5 to 9 are blade sections taken at different radii, as indicated by the correspondingly numbered lines in Fig. 3.

The same reference numerals are applied to corresponding parts throughout these views.

Referring rst to Fig. 1, the reference-.numeral IU designates generally the axial blower unit of my invention and II a hot air' furnace wherein the same is installed. The blower unit I comprises a shroud ring I2, suction fan I3, and electric motor I4 for driving the fan, the motor being mounted on arms I secured at their opposite ends to the motor housing and shroud ring, as indicated at I6 and I l. The ring I2 may be formed integral with a horizontal partition wall I8 but is preferably removably mounted by means of its annular flange I9 on the wall I8 in an opening 20 provided in said wall at the center thereof. The unit is disposed with the axis of rotation of the fan I3 and armature shaft 2| of the motor substantially vertical, with the motor I4 uppermost and spaced from the bottom of the combustion chamber 22 of the furnace in which liquid, gaseous,l or other fuel is burned. The door, indicated at 23 on the outer casing 24 of the furnace, afords access to the chamber' 22.

The casing 24 has one or more cold air inlets 25 provided in the bottom thereof under a dust collector wor filter 26 disposed horizontally in the lower portion of the casing, below the partition I8 as shown. The cold air-inlet may open directly tothe basement as shown, 2l indicating the basement floor, or there may be one or more fresh air conduits opening to the outside of the building. At 28 are indicated hot air outlet conduits.

' In the operation of the unit I0, the cold air is drawn in through the dust collector 26 and is discharged upwardly so as to scrub the hot walls of the combustion chamber 22 and be heated thereby, the air thus heated being discharged through the hot air conduits 28 to the various rooms to be heated. In other words, 29 is a suction chamber on one side of Vthe partition wall I8 and 30 is a pressure chamber on the other side. The air flow through the furnace keeps the motor I4 as well as the Walls of the combustion chamber 22 from reaching excessive temperatures. The motor would otherwise be incapable of operating for any length of time in a zoneat such temperatures. The general direction of air flow is indicated by the arrows in Fig. 1, these arrows indicating the resultant angle of force vectors acting in and upon the airstream when the resistance to the flow of air through the furnace approximates the usual working pressures. The resultant direction of flow changes from axial to radial with increase in downstream resistance to flow. That is to say,

the iiow of air is more in an axial direction as,

the quantity of air ow is increased and in a radial direction as the iow is decreased to a minimum, at which point all of the energy imy parted by the fan to the air is converted to stat-ic pressure. Since the downstream resistance to flow in the average furnace installation does not vary appreciably and is usually of a low value, it follows therefore that in the operation of the unit I0 the substantially axial flow of air up-` wardly will produce an efficient heat exchangev the blades is to permit air now in an axial direc-Y tion past the back plate and to increase the flow rate and the air handling capacity of the fan. The exact diameter of back plate required in relation to blade tip diameter is governed by the static pressure which it is desired to build up in the furnace or other cabinet in connection with which the blower unit is used to overcome resistance to air flow through the cabinet. The diameter of the back plate 32 is increased for higher static pressure in the cabinet, that is the back plate is extended out to a larger diameter in the circle swept out by the blades 33 until a point is reached where the peripheral velocity converted to pressure, in accordance with well known fan laws, equals the required operating pressure in the cabinet. The location of the motor I4 in the immediate downstream area of the fan I3 has been found to be very important from the standpoint of eicien-t performance, because there is no air now directed to the space occupied by the motor and in the absence of the d motor there would be eddy currents at this point and accordingly a marked loss in efl'ciency by reason of the energyin. thestream being partly expended in the void behind the fan.. The filling of the voidA by the motor I4, which provides more or less streamlined surfaces for air flow past the same, results in, a.v fan performance nearer to centrifugal blower performance, and the operation is, moreover, quiet because of the. absence of eddy currents and consequent shock noise. The diameter ofthe inlet opening 34`v inV the shroud ring I2 in relation tothe diameter of the fan I3, and the closeness of the fan I3.- to the inside surface 35 of the shroud ring I2, also the radius of curvature of the inlet flange 36, 'and having the upstream end of the inlet flange 3.8. ofv smaller diameter than the downstream end, all in combination and in the relationship shown have been found to give the best performance. The blades 33 are set at a back angle inV relation tothe direction of rotation,` as indicated at 31 and38in Fig. 3, 31 showing the angularity of the leading edges 39 and 38 showing the angularity of the trailing edges 4e. The angles` at 31 and 38 are approximately 31.". Experiment has indicated that if. the leading edges- 39. are given a. forward sweep, greater energy is imparted to the air than where a back angle is employed, assuming of course the same R.P.M. However, the back angle or backward sweep has been employed here because it makes for quietk operation. while still obtaining the eciency desired. The tips of the blades, as indicated at 4 I and 42, are also rounded to reduce noise. Figs. 5-9 show the cross sections of the blades at different radii as indicated by the lines 5-5 to E-Sin Fig. 3. Due to the fact that it is desired to have the air. move axially, the pitches of the sections are formed as shown in Figs. 5 to 9, the sectionsbeing formed on expanding radius lines so as to obtain a desired stream expansion for passage around the combustion from the leading edges 39 to approximately .4 of the chord, at which point the kinetic energy generated by the blades 33 equals the downstream surrounding pressure. The diameter of the inlet opening 34 in the shroud ring in relation to the fan diameter is also very important, the opening having a radius of approximately .77 of the radius of the fan. A slight variation in the diameter of the inlet opening was found to affect the fans capacity appreciably, the shroud ring being a very important factor in the performance of this fan unit. At 43 are indicated radial webs joining the inner edges of the blades 33 to the back plate 32 on the working face thereof. These webs also vact tol prevent back flow of air radially between the blades. Small openings 44 are provided in circumferentially spaced relation in the back plate 32 in close proximity to the hub 3| to alchamber 22, as indicated by the arrows in Fig. l.

Six impeller` blades 33 are shown, but it must be understood that the number of blades andthe axial length thereofY are subject to change, depending upon the fan capacity'desired, in accordance with well known fan laws.

The shroud ring I2, in accordance with the principal first disclosed in my Patent 1,993,158,

issued March 5, 1935, is provided to prevent backv lowf into the tips of the blades at the trailing edges 40. In the present case the ring is situated toprevent back' ow intol the tips when the fan is operating in an area of greater than atmospheric pressure. The ring shroud-.s the tip portion low a small outflow of air to cool the motor I4, the openings 44 being on a small enough radius in relation to the radius of the motor I4 to insure sufcient scrubbing action on the. walls .of the motor in its outow togive the desired cooling action, asy shown Vbythe arrow (Fig. 2).

The rubber cushioned hub construction shown in section in Fig. 4 makes for smooth and quiet operation, any noises originating in the fan being thereby isolated from the motor sol as not to be conducted into'the' surrounding. furnace' structure and accordingly magnified. A sleeve of. rubber formed by two bushings 45 and 4S serves to insulate the hub 3| of the fan from. the metal sleeve 41 on the armature shaft 2I. The sleeve 41 has an annular shoulder 48 on itsA inner end and has the projecting outer end threaded, as indicated at 49. The sleeveA 41 is'. keyed onA the shaft 2I, as shown at 50; The threads 49 are right handed so that the clockwise rotation. of the motor tends to tighten the nut 5I by means of which` the fan hub is retainedon the sleeve 41. The nut 5I compresses a split spring washer'52 so as to compress the rubberVv bushings 45 and 45 between the shoulder 48 and the nut 5I and accordingly mount the fan tightly on thek motor shaft. A cap screw t 53 threads in an axial hole 54 in the end ofthe shaft 2| toA hold the sleeve 41 against endwise movement relative to the shaft 2I. A washer 55 is providedv under the. head ofthe screw 53.

It is believed the` foregoing description conveys a good understanding of theY objects and advantages of my invention. The appended claims have been drawn to cover all legitimate modifications and adaptations.

I claim:

1. In' combination, ay suction fan comprising a substantially'circular' back plate having a substantiallycylindrical blade-carrying rim portion, said back plate` havingmeansat the center thereof for driving the same,.and impeller blades projecting radially fromthe cylindrical rim portion and in an axial direction from the upstream face of said back plate, a shroud ring defining a circular air inlet opening, the fan being disposed A on the downstream sid'eofsaid ringv in proximity the tip diameter'r of the blades, the air now induced by the fan through. the opening being generally in anaxial direction between the impeller blades past the rim'portion. of. the back plate,

the shroud ring being of a; fiormfextendin'g in- 75551 closely/spaced relaticnr to the tip' portions of the' blades on the upstream face thereof and also in close radially spaced relation to the tips of said blades part way to the downstream edges of the blades to prevent back flow of air into the tips of said blades.

2. In combination, a suction fan comprising a substantially circular back plate having a substantially cylindrical blade-carrying rim portion, said back plate having means at the center thereof for driving the same, and impeller blades projecting radially from the cylindrical rim portion and in an axial direction from the upstream face of said back plate, a shroud ring defining a circular air inlet opening, the fan being disposed on the downstream side of said ring in proximity to said opening With the upstream face toward the opening and in substantially coaxial relation thereto, the opening being of a diameter slightly larger than the diameter of the rim portion of said back plate but substantially smaller than the tip diameter of the blades, the air flow induced by the fan through the opening being generally in an axial direction between the impeller blades past the rim portion of the back plate, the radially outermost tips of the blades extending substantially parallel to the periphery of the cylindrical rim portion of the back plate, the shroud ring being of a substantially cylindrical form providing a front wall extending in closely spaced relation to the tip portions of the blades on the upstream face thereof and a cylindrical peripheral wall extending in close radially spaced relation to the radially outermost tips of said blades part way to the downstream edges of the blades to prevent back flow of air into the tips of said blades.

3. A structure as set forth in claim 1, wherein the suction fan includes radial webs joining the radially inner edges of the blades to the back plate on the upstream face thereof to prevent back iiow of air radially between the blades.

4. A structure as set forth in claim 2, wherein the suction fan includes radial webs joining the radially inner edges of the blades to the back plate on the upstream face thereof to prevent back flow of air radially between the blades.

, JAMES M. FUNK.

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