US2739655A - Variable pitch fan - Google Patents

Description

March 27, 1956 Filed Dec. 1'7, 1951 M. PETTY VARIABLE PITCH FAN 3 Sheets-Sheet l Iii [5AM Macon Pezfy INVENTOR. M

ATTORNEYS March 27, 1956 M. PETTY 2,739,655

VARIABLE PITCH FAN Filed Dec. 17, 1951 3 Sheets-Sheet 2 M0 0 0/? Fe Hy INVENTOR.

A TTOHNE Y5 March 27, 1956 M. PETTY 2,739,655

VARIABLE PITCH FAN Fil ed Dec. 17, 1951 5 Sheets-Sheet 3 f l 30 [/8 1s 1' W 62 q 5o Mac on Fe 2 fy INVENTOR.

United States Patent 9 VARIABLE Prrcr-r FAN Macon Petty, Houston, Tex, assignor to Hudson Engineeriug Corporation, Houston, Tern, a corporation of Texas Application December 17, 1951, Serial No. 262,078

6 Claims. (Cl. 170-16it32) This invention relates to improvements in heat exchange apparatus wherein air is used as one heat exchange medium to cool or heat another heat exchange medium in indirect heat exchange relationship therewith. In one of its aspects, this invention relates to improvements in variable pitch fans for use in such type of apparatus.

Air cooled heat exchangers have been used in many processing industries to cool a product or stream of material by indirect heat exchange with the atmosphere which is caused to flow through the heat exchange apparatus by a power driven fan. Usually such apparatus is sized to accommodate the maximum heat exchange load which is anticipated to be placed thereon and the fan blades are set at a constant pitch and revolved at a constant speed so that a substantially constant amount of air is drawn or pushed through the heat exchange apparatus. Control of the amount of heat exchange occurring in the heat exchange apparatus has been effected in a number of ways including bypass arrangements for shunting a portion of the medium to be cooled around the heat exchange apparatus, shutters or louvers to control the amount of air passing over the apparatus and, in some instances, by shutting down one or more fans in a group of the same serving a common installation.

In such type of installations, large volumes of air are usually passed through the heat exchange apparatus in order to efiect the desired extent of heat exchange with the medium being cooled. The cooling efiect of the air is dependent upon atmospheric conditions including humidity and temperature and, since these conditions vary, it is ordinarily diflicult to produce exactly desired amount of cooling even on a day to day basis. It becomes increasingly diflicult to do this when the heat exchange load itself is variable independently of the atmospheric conditions so that not only must the quantity of air be controlled in accordance with atmospheric conditions but also in accordance with the heat exchange load. While the various means outlined above for controlling the amount of heat exchange have been somewhat eifective in some instances, close control of the amount of heat exchange effected is difiicult. Also, with any of these various means, the amount of power consumed in causing air to flow through the heat exchange apparatus cannot be accurately maintained at the minimum required to move the exact volume of air across the heat exchange apparatus to eifect the desired heat exchange because there is no means provided to exactly regulate the flow of air while causing power consumption to vary in accordance with the column of air flowing.

While it might be considered that a workable solution to this problem of control would be to employ variable speed fans, such practice is commerically unacceptable not only because variable speed drivers are expensive compared to constant speed drivers but also because variable speed motors are relatively ineflicient and expensive to operate. The present invention permits the desirable use of constant speed motors to drive fans at a ice constant speed in such heat exchange apparatus, and yet provides a simple means for controlling the amount of air passed over the heat exchange elements responsive to a control variable to thereby accurately control the amount of heat exchanged in the apparatus with a minimum power consumption. Also, the apparatus is particularly adapted to be used in conjunction with conventional control instruments employing instrument air commonly found in many processing industries. These control instruments have been highly developed to operate in a substantially trouble free manner and their use does not present any new control or maintenance problems to operators or to instrument mechanics.

It is an object of this invention to provide in a heat exchange apparatus power driven means for causing air to flow across heat exchange elements responsive to the heat exchange load existing at any particular time whereby the power consumed to cause said air flow can be maintained at a minimum consistent with the heat exchange load and yet wherein the power driven means can operate at a constant speed.

Another object of this invention is to provide a heat exchange apparatus including a simple yet rugged variable pitch constant speed fan for causing air to flow across the heat exchange elements in an amount correlated to the heat exchange load and which is particularly adapted to be controlled by commercially available control instru ments which are commonly existent in petroleum refineries, gasoline plants, chemical plants, compressor stations and the like.

Another object of this invention is to provide a heat exchange apparatus in which air is employed as one heat exchange medium and is caused to flow across heat exchange elements by a power driven fan having variable pitch fan blades and pneumatic means for varying the pitch thereof responsive to a control variable, said control means being adapted to employ conventional instrument air at pressures commonly existing in commercial installations, the fan being provided with stop parts to limit the pitch change in said blades.

Another object of this invention is to provide in such heat exchange apparatus stop parts that are so situated that one set of such parts will limit the maximum positive pitch angle of the fan blades to be such as to load the driver for the fan a predetermined maximum amount and that another setof stop parts are situated to limit the pitch of the fan blades to be such that the fan will prevent natural draft through or across the heat exchange apparatus.

Another object of this invention is to provide a heat exchange apparatus in which air is employed as a heat exchange medium and is caused to flow across the heat exchange surfaces by a constant speed fan having variable pitch fan blades controlled by fluid pressure exerted through a conduit connected to the fan hub on the side thereof opposite to the hubs connection to a motor for driving the same.

Another object of this invention is to provide a variable pitch fan having a simple mechanism for varying the pitch of the fan blades including a fluid pressure responsive means, such as a diaphragm, adapted to respond over the desired control range to conventional control instruments.

Another object of this invention is to provide a fan having a plurality of variable pitch fan blades adapted to have their pitch controlled by a flexible diaphragm acting on a spring biased piston connected to the fan blades, the diaphragm being subject to pneumatic fluid introduced into the fan hub from the end thereof opposite the drive connection for the fan.

Another object of this invention is to provide a fan hub adapted to have a plurality of fan blades journaled therein and having a drive connection to one of its ends for turning the same, a piston reciprocally mounted in the hub and having. means for connecting it to the fan blades so that movement of the piston will cause the pitch angle of the blades to change, and further having a flexible diaphragm acting to move the piston under the influence of pneumatic pressure exerted on the diaphragmthrough a conduit connected to the hub on the side opposite the drive therefor and including a rotary union.

Other objects, advantages and features of this invention will be apparent to one skilled in the art upon a consideration of the written specification, the appende claims, and the attached drawings wherein:

Fig. 1 illustrates a preferred embodiment of the apparatus of this invention in a typical installation thereof;

Fig. 2 is a lateral cross-sectional view of the fan hub of this invention;

Fig. 3 is a longitudinal cross-sectional view of the fan hub taken on the line 3-3 of Fig. 2;

Fig. 4 is a partial cross-sectional view taken on line 4-4 of Fig. 2 and shows the relationship of the piston and stop parts of the fan hub of this invention;

Fig. 5 is a View taken on the line 5--5 of Fig. 2; and i' Fig. 6 is an isometric view of a pin adapted to be connected to the end of a fan blade for coacting with the piston to vary the pitch of the blade.

Like characters of reference are used throughout the and can comprise, for example, internal combustion engine jacket cooling water, various hydrocarbon process streams, compressed gases which are desired'to be cooled, or any other medium from which it is desired to extract or add heat from the atmosphere. It is to be understood that the apparatus of this invention can be used to cool or heat a medium passing through the tube bundle by indirect heat exchange with the atmosphere dependent upon the relationship of the temperature of such medium to that of the atmosphere.

Disposed around tube bundle 10 isa housing compris r ing hood 16 surmounted by fan ring 17', which together arev adapted to guide air in a stream acrosstubes 13 for cooling or heating the medium passing therethrough. In. the installation shown, a fan including a hub 18 and a plurality of fan blades 19 is disposed to have the hub coaxial with fan ring 17 and is driven by motor 20 via speed changer 21 and drive shaft 22.

As will be explained in greater detail below, the pitch of fan blades 19 is controlled by the application of fluid pressure to a variable pitch control mechanism. It is an important feature of this invention that such fluid pressure can be controlled by conventional control instruments available on the market today. The fluid can 'be a liquid but is preferably gaseous, such as air, because of the greater availability of air and also because any leakage of air is not critical. Instruments employing either hydraulic or pneumatic fluids are well-known to those skilled in the art. The pneumatic instruments commonly apply a controlled air pressure, variable within the range of 0 to 15 lbs. per square inch gauge, to the apparatus to be controlled, in this instance the variable pitch control mechanism, in accordance with the variation of a process variable from the set-point or desired condition of the variable at which the'i'nstrument isset. Such a control instrument is shown schematically in Fig.

1 at 23 and is adapted to feed air from conduit 24a into instrument air conduit 25 at a pressure within the range of 0 to 15 lbs. per square inch gauge, the exact pressure determining the amount of pitch of the fan blades and being dependent upon the pitch required to cause suflicient air flow to maintain the process variable at the setpoint of the instrument. The process variable can be measured by a suitable sensitive element, such as temperature sensitive element 24 situated in efliuent conduit 15 of tube bundle 10, and this element will cause instru ment 23 to vary the instrument air pressure in accordance with changes in the process variable. Thus, for example, should the temperature of the effluen-t liquid-in conduit 15 rise above the set point of instrument 23, sensitive element 24 can cause instrument 23' to decrease the air pressure in conduit 25 and thereby increase the pitch of the fan blades 19 to cause an increased flow of air across the tube bundle. This will reduce the temperature or" the fluid in conduit 15 back to the control point.

Disposed in conduit 25 is a rotary union 26 which provides a fluid passage between stationary conduit 25 and revolving hub 18. Such a rotary union is well known to those skilled in the art.

Referring now to Figs. 2 to 6, there is shown in detail the construction of hub 18 and its attendant parts. Dis posed within hub 18 is a cylinder 30 adapted to receivea piston 31 reciprocal therein. Piston 31 is preferably mounted to have its longitudinal axis coaxial with the longitudinal axis of hub 18 and is thus adapted to move longitudinally within the hub. The piston is provided with a means for biasing it in one direction and this means can comprise a spring 32 situated in a hollowed. out portion 33 of the piston so as to have one of its ends bearing against a shoulder 34- adjacent one end of the piston and its other end against a spring retainer ring 35. This ring is carried in an annular groove in the end of the connecting drive shaft 36. It will be understood that the latter can be connected to shaft 22 of Fig. 1 to transmit power from motor 20 to revolve hub 18. Drive shaft 36 is bolted to hub 18 by a plurality of studs 37.

Disposed within hub 18 is a pressure extensible means in the form of a flexible diaphragm 38 forming one wall of a pneumatic pressure chamber 39, the other walls being formed by a part of the hub. Such part of the hub can comprise an upper cover or flange plate 40. This flange plate is joined to a lower flange plate 41, also a part of the hub by means of suitable flange bolts 42. The entire diaphragm assembly comprising a diaphragm and the two flange plates is attached to the lower portion of the hub by means of. studs 43.

Disposed on the end of piston 31 adjacent diaphragm 38 is a diaphragm back up member 44 having a face 45 extending over a major portion of the central area of the diaphragm. The back up member is connected to piston 31 by reduced diameter portions 46 and 47 situated in correspondingly shaped openings in the end of piston 31.

In communication with pneumatic pressure chamber 39 and diaphragm 38 is a pneumatic pressure supply conduit 48 which is connected to flange plate so as to have its longitudinal axis coaxial with the longitudinal axis of hub 18. Disposed in the length of conduit 48 is rotary union I 26 comprisingv a stationary part 26a and a revolving part 26b so that pneumatic fluid passing through stationary conduit 25 can be transmitted to chamber 39 even while the hub is rotating.

From the foregoing, it will 'be apparent that there is provided means which is biased in one direction by a bias ing means and movable in the other direction under the influence of a fluid pressure applied thereto. Thisfiuid pressure can be hydraulic in nature but is preferably pneumatic because not only of the greater availability of the latter'but also because leakage is not an important factor.

supply conduit is connected to the hub at its opposite end,

greases the drive shaft and at least that part of the supply conduit containing the rotary union being coaxial with the hub so that these elements can be rotated together about a common axis. One advantage of this construction is that there is no necessity for thrust bearings and thrust rods in the fan pitch change mechanism.

A plurality of fan blades are journaled in the hub so as to have their longitudinal axes radial to and substantially perpendicular to the longitudinal axis of the hub. Thus fan blade portions 1% can be threaded into ferrules which in turn are journaled into the hub. Ferrules 50 have an annular outwardly extending shoulder 51 and are received in a counter-bore 52 radially disposed in the fan hub. Disposed between shoulder 53 of the counter-bore and shoulder 51 of the ferrule is an anti-friction bearing 54. A second bearing 55 is disposed on the opposite side of shoulder 51 and the entire bearing-fan blade assembly is maintained in place in counter-bore 52 by a retainer ring attached to hub 18 with studs 61.

As shown most clearly in Fig. 3, a set screw 62 can be screwed through ferrule 50 to abut against the end of blade portion 19a to prevent the same from becoming unscrewed from the ferrule.

Thus it will be seen that fan blades 19 are journaled into hub 18 and can be turned about their own longitudinal axes.

Referring now more particularly to Figs. 2 and 5 the end of each of the ferrules 50 is provided with a groove 63 extending across the face of the end. A pin 64, including a rectangular base portion 64a adapted to be received in groove 63, can be attached to the end of the ferrule by means of a cap screw 65. Pin 64 is situated eccentrically of the longitudinal axis of the ferrule and of the fan blade. Each of the pins of the plurality of ferrules provides a connection between the fan blades and piston 31 such that longitudinal movement of the piston turns the fan blades about their axes. Thus, the pins can extend into an annular groove 66 cut in piston 31 and is slidable transversely of piston 31 within this groove as the piston is moved back and forth in its cylinder. Since pin 62 is eccentric of the axis about which fan blades 19 turn, movement of the piston will cause pin 64 to slide in the groove and thereby revolve the fan blades about their axes to cause a change in their pitch angle.

Thus it will be seen there is provided a biased piston or member adapted to be moved responsive to pneumatic pressure to change the pitch angle of a plurality of fan blades carried by a hub, means being provided for connecting the piston and fan blades.

In accordance with one feature of this invention, stop parts are provided to limit the movement of the piston and thereby limit the change in pitch angle of the fan blades. As shown most clearly in Figs. 3 and 4, piston 31 is provided with an annular groove 70 therearound which preferably has sloping end walls 71 and 72. Tapped through the Wall of hub 18 are a pair of studs 73 and 74 having sloping end faces 75 and 76 adapted to abut against end walls '72 and 71, respectively. Studs 73 and 74 are adjustable inwardly and outwardly with respect to the cylinder wall 30 to vary the length thereof extending into groove 70 and thereby vary the distance piston 31 can move before end wall 72 contacts end 75 of stud 73 or before end wall 71 contacts end 76 of stud 74. Surrounding the outer ends of studs 73 and 74 are lock nuts 77 and 78 which have an inner threaded portion 79 adapted to screw over the threads of studs so that upon rotation of the lock nut, the studs can be locked in adjusted position. A suitable wrench-hold 80 can be disposed in the outer ends of the studs and is accessible by removing plug 81 from the ends of the stop nuts and inserting a suitable tool into the stop nut to turn the studs and thereby adjust their position.

It will thus be seen that there is provided a first set of stop parts carried by hub 18 and piston 31 which are situated to limit longitudinal movement of the piston in one direction and a second set of stop parts carried by the hub and piston to limit the latters longitudinal movement in another direction. In this manner means are provided for determining the maximum and minimum pitch angle of the fan blades capable of being effected, the means being adjustable by simple mechanical manipulation without dismantling of the hub and Without changing any of the components thereof except the extent to which studs 73 and 74 are screwed into groove 70.

In a preferred form of the invention, a closed lubricant-containing zone is maintained within the hub to afford proper lubrication of the piston, pins 64, and the bearings surrounding the blade ferrules. This chamber can be provided by suitable sealing means between the hub and the piston and between the hub and the blade ferrules to confine grease or lubricant within the hub. The seals can be provided by suitable O-rings 85 carried between the hub and the piston and O-rings 86 carried between retainer ring 60 and blade ferrule 50. With these sealing means in place, the interior of the hub wherein there is contained the movable parts requiring lubrication can be filled with a suitable lubricant for constantly bathing the working parts therewith.

With the apparatus assembled as shown in Figs. 2 and 3, the fan hub and its attendant parts are mounted in the fan ring 17 so that the longitudinal axis of the hub is coaxial with the axis of the fan ring. Then shaft 22 is suitably connected to drive shaft 36 to provide a drive connection between motor 20 and the fan hub through the speed changer 21. Then with the piping arranged as in Fig. 1, motor 20 can be started and medium to be cooled or heated passed through conduit 14, tube bundle 10 and out conduit 15 for contact with temperature sensitive element 24. Control instrument 23 can be set to maintain a desired temperature for the effluent medium. Upon a variation of the temperature of the eflluent medium from this set point, as for example, should the temperature of the efiluent medium rise, control instrument 23 will effect a change in pneumatic pressure in chamber 39 to thereby increase the pitch of the fan blades and accordingly draw more air across the tube bundle to additionally cool the medium being passed therethrough. Should atmospheric conditions change, as for example, a drop in temperature thereof, this change in conditions will be reflected by a drop in temperature of the effluent medium in conduit 15 which will cause instrument 23 to decrease the pitch of the fan blades and thereby decrease the amount of air passing over the tube bundle 10. With this control arrangement, a uniform outlet temperature of the efiluent medium from tube bundle 10 can be maintained even though the inlet temperature thereto or atmospheric conditions rapidly change.

During any load condition or any change therein, the fan will be running at a constant speed and will be merely drawing enough air through the apparatus to effect the proper cooling or heating of the medium inside of the tube bundle. As a result, motor 20 will be loaded only sufficiently to cause this amount of air to pass over the tube bundle and in many instances the motor will be running well under its rated load so that power consumption is at a minimum consistent with the heat exchange load of the apparatus. Further, the fan will operate with a minimum required static pressure differential and therefore at the maximum fan efficiency possible for the existing heat exchange load. Still further, the load on the speed changer will be at a minimum.

It will be appreciated that instrument 23 can be made sensitive to any process variable which in turn is sensitive to or determined by the amount of air flowing across tube bundle 10 Whether that process variable be a condition of the medium in conduit 15 or not.

In the preferred form of the apparatus, pins 64 are angularly disposed with respect to the pitch angle of the fan blades so that movement of piston 31 towards the 7 diaphragm end of the fan hub will cause the pitch angle of the blades to increase and movement of the piston in a direction towards the driver end of the fan hub will cause the pitch angle of the blades to decrease. Thus should the instrument air or control instrument fail so that pressure within chamber 39 decreases to atmospheric, the fan blades will assume a position of maximum pitch and thereby prevent a complete stoppage of heat exchange service. With such an arrangement, stud 73 is screwed sufiiciently into the hub so that when end wall 72 of groove 70 contacts the end of the stud, the fan blades will be at their minimum pitch angle and such minimum pitch angle will be sufiicient to load motor 20 to its design load. Stud 74 is adjusted so that when end wall 71 of groove 70 contacts the end thereof, the fan blades will be at the minimum desired pitch angle. in a preferred form of this invention, this pitch angle is such as to be slightly negative, that is, the rotation of the fan with the blades at this negative pitch angle will tend to cause air to flow in a direction opposite that in which it normally flows. In this manner, and with suitable adjustment of this negative pitch angle, any natural draft which would occur through housing 16 and fan ring 17 due to heating of the air by tube bundle 10 can be counteracted and a complete stoppage of air flow across the tube bundle can I be effected.

However, it is contemplated that the action of the pneumatic pressure can be opposite that just described. Thus, by moving pins 64 to a position in groove 53 radially opposite that shown in the drawings, that is at the threaded hole 65a, movement of piston 31 away from the diaphragm end of the hub (by increased pneumatic pressure) will increase the fan blade pitch angle and movement toward the diaphragm end of the hub (with decreased pneumatic pressure) will decrease the fan blade pitch angle.

Thus, there has been provided a variable pitch fan assembly comprising a hub rotatable by a coaxial driving connection at one end thereof, a fluid pressure responsive means carried by the hub with means connecting it to a plurality of variable pitch fan blades journaled in the hub and means for introducing fluid pressure to the fluid pressure responsive means from the end of the hub opposite the driving connection including a conduit having a portion coaxial with the hub and a rotary union in that portion of the conduit. Also such an assembly is provided in combination with a heat exchange apparatus employing air for indirect heat exchange with a medium to be cooled or heated, the pitch of the fan blades being made responsive to a variable process condition by a suitable fluid pressure control instrument having a fluid connection to the fiuid pressure responsive means of said hub.

From the foregoing it will be seen that this invention is one well adapted to attain all of the ends and objects hereinabove set forth, together with other advantages which are obvious and which are inherent to the structure.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is without the scope of the claims.

As many possible embodiments may be made of the invention Without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be inter preted as illustrative and not in a limiting sense.

The invention having been described, what is claimed 1. in a variable pitch fan the combination comprising a symmetrical hub with a central cylindrical bore therethrough, the hub formed with openings extending radial- 1y from said bore with fan blades journaled therein, a substantially cylindrical member reciprocally mounted within the bore, means between the cylindrical member and fan blades for varying the pitch of the blades upon reciprocation of the member, a housing connected to one end of the hub and being coaxial with the bore, a diaphragm member within said housing operatively connected to said cylindrical member to urge it in a direction away from said housing, a drive shaft connected to the end of the hub opposite the housing, and concentric with the bore, means for supplying pressure fluid to the housing including a conduit connected to the end of the housing remote from the drive shaft connection and having a portion coaxial with the cylindrical member with a rotary coupling in said portion, a resilient element within the cylindrical member having one end connected to the cylindrical member and the other connected to the drive shaft to thereby urge the cylindrical member to ward the diaphragm member, and stop means operatively connected with the cylindrical member to limit reciprocal motion.

2. In a variable pitch fan the combination comprising a symmetrical hub with a central cylindrical bore therethrough, the hub formed with openings extending radial- 1y from said bore with fan blade holders journaled therein, a substantially cylindrical member reciprocally mounted within the bore, means between the cylindrical member and fan blade holders to turn them in their journals for pitch changing purposes upon reciprocation of the cylindrical member, a housing connected to one end of the hub and being coaxial with the bore, a diaphragm member within said housing operatively connected to said cylindrical member to urge it in a direction away from said housing, a resilient element having a free end connected to the cylindrical member and the other end supported against movement, the hub having a fitting upon its side opposite the housing adapting the hub for mounting upon a drive shaft, means for supplying pressure fluid to the housing including a conduit connected to the end of the housing remote from the drive shaft fitting and having a portion coaxial with the cylindrical member with a rotary coupling in said portion, and stop means operatively connected with the cylindrical member to limit reciprocal motion.

3. The arrangement of claim 2 wherein the fan blades aremounted for pitch variation between a slightly negative pitch and a predetermined positive pitch.

4. The arrangement of claim 2 wherein the wall of the hub which forms the bore itself provides the bearing for the cylindrical member.

5. The arrangement of claim 2 wherein seal means are provided between each blade holder and the hub surrounding the blade holder radially of the journal, seal means between the cylindrical member and the hub, one on each side of the blade holder openings, and a lubricant confined in the hub by the seal means.

6. The arrangement of claim 2 wherein the pitch changing means includes a cam groove in the periphery of the cylindrical member and eccentric means on the blade holders engageable in said groove.

References Cited in the file of this patent UNITED STATES PATENTS 1,384,672 Murray July 12, 1921 1,649,246 Morrisey Nov. 15, 1927 2,135,190 Martin Nov. 1, 1938 2,278,376 Young Mar. 31, 1942 2,358,973 Hartwig Sept. 26, 1944 2,392,341 Squier Jan. 8, 1946 2,398,106 McCollum Apr. 9, 1946 2,438,542 Cushrnan Mar. 30, 1948 2,457,609 Smith-Pert et al Dec. 28, 1948 2,473,697 Annesley June 21, 1949 2,514,097 Sharp July 4, 1950 2,539,339 Stepanoft Jan. 23, 1951. 2,553,214 Sanders May 15, 195i FOREIGN PATENTS 569,867 Great Britain June 12, 1945.

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