US2826395A - Atmospheric heat exchange apparatus and fan therefor - Google Patents

Description

March 11, 1958 M. PETTY 2,826,395

ATMOSPHERIC HEAT EXCHANGE APPARATUS AND FAN THEREFOR I Q r 6 SheetsSheet 1 Filed July 19, 1954 Mace/7 Fe f 2 INVENTOR.

March 11, 1958 M. PE4TTY 2,826,395

ATMOSPHERIC HEAT EXCHANGE APPARATUS AND FAN THEREFOR A Filed July 19', 1954 6 Sheets-Sheet 2 Macon Pe Hy INVENTOR.

' A TTDRNE Y3 March 11, 1958- I PETTY 2,826,395

ATMOSPHERIC HEAT EXCHANGE APP RATUS AND FAN THEREFOR Filed July 19, 1954 6 SheetsSheet 3 Jaw Mata/7 Fe z INVENTOR.

%Wi 7@ M k A TTORNE YJ Ma rch 11, 1958 M. PETTY ATMOSPHERIC HEAT EXCHANGE APPARATUS AND FAN THEREFOR 6 Sheet s-S heet 4 Filed July 19, 1954 Macon Pe INVENTOR March 11, 1958 I M. PETTY 2,326,395

ATMOSPHERIC HEAT EXCHANGE APPARATUS AND FAN THEREFOR Q 6 Sheets-Sheet 5 Filed July 19, 1954 Macon Fe f2 9/ IN VEN TOR.

ATTORNL-TYJ March 11, 1958 M. PETTY 2,8 6,3

ATMOSPHERIC HEAT EXCHAN'GEQAPPARATUS w FAN THEREFOR Filed July- 19,1954 6 Sheets-Sheet 6 IN VEN TOR.

Q1 Ma co/7 Pezzg v ATTORNEKS United States Patent ATMOSPHERIC HEAT EXCHANGE APPARATUS AND FAN THEREFQR Macon Petty, Houston, Tex., assignor to Hudson Engi nearing Corporation, Houston, Tex., a corporation of Texas Application July 19, 1954, Serial No. 444,271 4 laims. ((21. 257-4 improvements in variable pitch fans and controls therefor 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 either direct or 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 eifected in a number of ways including by-pass 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 through 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 installation, large volumes of air are usually passed through the heat exchange apparatus in order to effect the desired extent of heat exchange the medium being cooled; The cooling eifect of the air is dependent upon atmospheric conditions including hunudity and temperature and, since these conditions vary, it is ordinarily diffi'cult to produce exactly the 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 eftective in some instances, close control of the amount of heat exchange effected is diflicult. Also, with any of these various means, the amount of power consumed in causing air to how 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 effect 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 volume of air flowing.

While it might be considered that a workable solution to this problem of control would be to employ vari-.

able speed fans, such practice is commercially unaeceptwith able 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 constant speed in such heat exchange apparatus, and yet provides a simple means for controlling the amount of air passed through i the heat exchange apparatus responsive to a control variable to thereby accurately control the amount of heat exchanged in the apparatus with a minimum power consumption. A1so,'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 a eratein a substantially trouble-free manner and their use does not present any new control or maintenance problems to operators or to instrument mechanics.

The desired close control is very diflicult to obtain in conventional heat exchange equipment during cold weathof due to the limited need for cooling in addition to that obtained while the hot medium is exposed to the cold atmosphere in both the flow handling conduits and-in the heat exchanger with none or very little air flow.

The cold weather problem is particularly acute in heat exchangers in which air flows upwardly through the heat exchanger. For example, in a cooling tower the chimhey effect of the air heated by the water flowing through the tower is sufficient to cause flow of air through the tower when the fans are shutoff. The cooling effect of air thus caused to flow through the tower frequently may be equal to as much as 25 percent oi the efficiency of the tower during the summer months. Remembering that the cooling load is usually way down in cold weather the 25 percent cooling efiiciency may readily lower temperature of the water more than is desired.

A'further problem thatexists in cold weather is the icing of heat exchange apparatus, particularly cooling towers. In some instances, the inlet louvers of cooling towers will become iced over due to atmospheric conditions or to an accumulation of spray from the air outlet of the tower. The exterior walls of cooling towers are usually constructed to withstand high windconditions and the weight of the accumulated ice on the louvers is not ordinarily dangerous. There is, however, a. reduction in flow of air through the tower due to the reduced openings between the louvers which interferes with the normal operation of the tower. Another serious problem is encountered when ice forms in the interior of the tower. Cooling towers are conventionally provided with packing over which the water cascades in thin sheets in passing from the distribution system in the top of the tower to the sump in the bottom of the tower. When icing conditions prevail, cold air entering through the inlet in the base of the tower will tend to freeze the water passing over the lower section of packing. As ice builds up on the lower section of the packing, it reduces the temperature in the lower section of the tower and incoming air is warmed but slightly, if at all, in passing over the ice laden packing. This results in the cold air causing ice to form on a higher section of the packing. The ice moves progressively upward through the tower until the warming effect of the relatively warm incoming liquid halts progress of theice. The ice sometimes forms to such an extent in the tower that the packing system will collapse and the entire tower has been known to collapse under the weight of-ice.

Once a tower has become heavily iced, the mere shutting down of the fans is usually not sufficient to melt the ice as the chimney effect created by the warm air in the top of the tower will cause continuous flow ofair through the tower. Thus, the water will be cooled by the incoming air before it reaches the bottom of the tower and will not melt the ice in the bottom of the tower. This situation frequently is aggravated by wind conditions. It has been the practice in combating this problem. to cover the louvers or fan rings of cooling towers with tarpaulins to block flow of air or to employ a crew using hoses to hose off the ice. Either method is laborious and time consuming.

In tube bundle heat exchangers it is customary to waste to atmosphere'the air warmed by passing through the exchangers. These exchangers are frequently found in processing plants where this warmed air could be advantageously used to warm at least a portion of the plant during cold weather.

In the use of the fan assembly shown in application Serial No. 262,078 referred to above, it has been found that the workmen who are not familiar with the details of construction of the fan hub have diificulty in setting the limit stops to obtain the desired range of pitch angle. The biased piston has also required that a source of pressure fluid be available to permit adjustment of the stops due to the necessity for overcoming the force exerted by the spring in order to adjust one of the stop elements. It has further been found that some means should be provided for adjusting force exerted by the spring urging the blades toward one extreme pitch angle if a single spring is to be used in a number of installations. This is true because heat exchangers on which the fan assemblies are installed vary considerably in design and therefore considerable difference in back pressure will be found between different heat exchangers. Also the number or size of tube bundles, or number and design of cooling tower packing may be varied in the same basic design, changing the back pressure of the design. Thus, a spring under a compression or tension sufficient to move the blades to a desired angle of pitch in one case may be too strong or too weak for use in another case.

It is an object of this invention to provide in a heat exchange apparatus power driven means for causing air to flow through the apparatus responsive to the heat exchange load existing at any particular time whereby the power consumed to cause said air to 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 through the heat exchange apparatus in an amount correlated to the heat exchange load and which is particularly adapted to be controlled by commercially available control instruments 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 through the heat exchange apparatus 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 commonly existing in commercial installations, the fan being provided with stop parts to limit the pitch change in said blades.

Another object is to provide in heat exchange apparatus a variable pitch fan and control therefor which will prevent flow of air through the apparatus due to natural draft when conditions are such as to make such fiow undesirable.

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 set of 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 is to provide in a variable pitch fan adjustable limit stops in which the adjustable stop parts are external of the hub and are mechanically and operationally simple.

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 through the heat exchange apparatus 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 in an air-cooled heat exchange apparatus having a variable pitch fan, a pneumatic control system which will automatically vary the fan blade pitch angle in a predetermined range in response to a process variable, and which will selectively reverse the pitch of the fan blades to a negative pitch sufiicient to cause reverse flow of air through the heat exchanger to utilize the heat available in the fluid to be cooled for heating an area or de-icing.

Another object is to provide a method of de-icing a heat exchanger in which air warmed by heat exchange with the medium to be cooled is used to melt ice.

Another object is to provide a biased variable pitch fan assembly in which the biasing means is outside the portion of the hub which carries the fan blades and may be removed without disassembling the fan, and the blades, with the biasing means removed, are freely rotatable to permit setting of the limit stops without a source of power available to overcome the biasing means.

Another object is to provide a fan assembly of the type disclosed in said application, Serial No. 262,078, in which the biasing means is positioned outside of the portion of the hub carrying the fan blades and means is provided for varying the force exerted by the biasing means.

Another object is to provide a fan assembly of the type disclosed in said application, Serial No. 262,078, in which the biasing means is positioned externally of the hub and transmits a biasing force to the blades by biasing the diaphragm, and the biasing force and the pressure fluid to operate the diaphragm are both introduced into the chamber through a single opening.

Another object is to provide in a pressure operated variable pitch fan assembly having an external means for biasing the fan blades and in which pressure fluid is fed to the assembly through the nose of the hub, a flexible connection in the pressure conduit which will give long service and which will permit slight orbital and oscillatory movement of the assembly.

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 appended claims, and the attached drawings wherein:

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

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 33 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 55 of Fig. 2;

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;

i Fig. 7 illustrates the use of this invention in a typical which is shown;-v

Fig. 8 is a diagrammatic view of a 16-tan cooling tower equipped with fans and controls according to this invention in which the fans are arranged in batteries responsive" to a single control;

Fig.9 is a diagrammatic illustration of a heat exchanger equipped with de-icing controls;

Fig. 10 is a view in elevation of a modified form of fan assembly with parts brokenaway to illustrate certain details of the assembly;

Fig. 11 is a fragmentary view along the line 11-11 of Fig. 10 illustrating the blade holder set screws and retainer clamp employed in the Fig. 10-modification; and

Fig. 12 is a view partly in elevation and partly in vertical cross section of a still furthermodified form of fan assembly.

Like characters. of reference are used throughout the several views to designate like parts.

Referring, now to Fig. 1 in particular, there is illustrateda typical installation of the apparatus of this invention'. The installation comprises a tube bundle designated generally bythe numeral 10 whichincludes inlet and outlet headers 11 and 12, respectively, and connected for fluid flow therebetween by a pluralityof parallel tubes 13. The medium to be cooled is passed internally through direct heat exchanger or cooling tower, only a portioniof V the tube bundle from conduit 14 to conduit 15 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 thisinvention 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 mediumto thatof the atmosphere.

Disposed around tube bundle 10 is a housing comprising hood 16 surmounted by fan ring 17, which. together are adapted to guide. air in a stream across tubes 13 for cooling or heating the'medium passing there- 'through. In the installation shown, a fan including a hub 18 and'a plurality of fan blades 19'is disposed to have the hub coaxialwithfan 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 liquidbut 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 O to 15 lbs. or more 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 instrument is set. Such a control instrument is shown schematically in Fig. l 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 set-point of the instrument. The process variable can be measured by a suitable sensitive element, such as temperature sensitive element 24 situated in eflluent conduit 15 of tube bundle 10, and this element will cause instrument 23 to vary the instrument air pressure in accordance with changes in the process variable. Thus, for example,

should the temperature of the effluent liquid in conduit 15 ,rise above theset-point of instrument 23, sensitive element 24' can cause instrument to decrease the air pressure in conduit 25Yand thereby increase the pitchot the fan blades 19 to cause an increasedflow of air across the tube bundle. This will reduce the temperature of the fluid in conduit-15 backto the control point.

Disposedin conduit 25 is a rotary union 26which provides a fluidpassage between stationary conduit 25 and revolving hub 18. Such. a rotary union iswell'known to those skilled in the art.

Referring now to Figs. 2 to 6, there is shown in detail the construction of hub IS and'itsattendant parts. Dispose d'within hub 18 is a cylinder 30' adapted toreceive a piston 31 reciprocal therein. Piston 31 is preferably mounted to have its longitudinal axis coaxial with the longitudinal axis of .hublS andisthus adapted to move longitudinally withinthe hub. The pistonis provided with ameans for biasingit 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 itsends bearing against a shoulder 34 adjacent one end ofthe 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 thelatter can .be connected to shaft 22 of Fig. 1 to transmit power from motor 20 to revolve hub 18. Drive shaft 36 is bolted :tohub 18 by plurality ofstuds 37.

Disposed. within hub. 18 is a pressure extensible means in the form cfa flexible diaphragm 38.forming one wall of a pneumatic pressure chamber 39, the other. Walls being formcd'by a partof the hub.- Such part of the hub can comprise an upper cover or flange plate 40.. This flange plateis 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 thetwo flange plates is attached to the lowerportion of the hub by means of studs 43..

Disposedon theend of piston 31. adjacent diaphragm 38 is a diaphragm back-up member 4-4 having a face 45 extending over amajor portion of the'central area of the diaphragm. Thebackaup memberv is connected to piston 31. by reduced diameter portions 46 and 47 situated in correspondingly shaped openingsin 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 40 so as to have its longitudinal axis coaxialwiththe longitudinal axis of hub 18;. Disposed in the length of conduit 48 is rotary union 26 comprising a stationary part 26a.and a revolving part 26b so th-atpneumatic fluid passing through stationary conduit 25 can be-transmitted to. chamber39 even while the hub is rotating.

From the foregoing, it will be apparent that there is provided. means which is biased in onev direction by. a biasing means. and movablev in the other direction under theinfluence of a fluid pressure applied thereto. This fluid' 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. It will also be apparent that the fan hub is driven through a connection'at one of itsends. and that the fluid pressure supply conduit is connected to the hub atits opposite end,.the drive shaftandat least that part of the supply conduit containing the rotary union being coaxial with the hub so that these elements canbe rotated together about a common axis. One advantage of this construction isthat 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 thehub. Thus fan blade portions 1% can be threaded into ferrules 50 whichin turn are journaled into the hub. Ferrules S6 havean annular outwardly extending shoulder 51 and are received in a eounterbore 52 radially disposed in the fan hub. Disposed between shoulder 53 of the counterbore 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 counterbore 52 by a retainer ring 60 attached to hub 18 with studs 61.

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

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 640 adapted to be received in groove 63, can be attached to the end of the ferrule by means of a cap screw 65. Pin 6 is situated eceentrically 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 3% 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 3t) 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 bearing 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 G-rings 86 carried between retainer ring 66 and blade ferrule 51' 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 29 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 it} and out conduit 15 for contact with temperature sensitive element 24. Control instrument 23 can be set to maintain a desired temperature for the efiluent medium. Upon a variation of the temperature of the efiluent medium from this set point, as for example, should the temperature of the eliluent 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 efiluent 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 etfiuent medium from tube bundle 143 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 23 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 efiiciency 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 Ill 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 angnlarly disposed with respect to the pitch angle of the fan blades so that movement of piston 31 towards the 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 sufficiently into the hub so that when end wall 72 of groove contacts the end of the stud, the fan blades will be at their maximum pitch angle and such maximum pitch angle will be suflicient to load motor 2t) to its designload. Stud-74 is adjusted, so thatwhen end wallil of groove 70 contacts the end thereof, .the fan bladeswill. be at the minimum desired pitch angle. In a preferred, form of this invention, this pitch angle is such asto be slightly negative, that is, the rotationot the fan with the blades at this negative pitch angle will 'tendltocause air.to How in a direction opposite that in which'it normally flows. in thismanner, and with suitable adjustment. of this negative pitch angle, any natural draftwhich would occur through housing 16 and fan ring 17 due to heating of they air by tube bundle can be counteracted and a complete stoppage of air flow across the tube bundle can 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 angleand movement toward the diaphragm end of the hub (with decreased pneumatic pressure) will decrease the fan blade pitch angle.

Figs. 7 and 8 illustrate the application of the variable pitch fan apparatus and control system of this invention to a cooling tower wherein water is cooled by directcontact with air drawn through thetowerby the fans. The control system shown is responsive tochangesinthe temperature of the etlluent water to vary thepitch of the fan blades, and thus the amount of power consumed, to maintain the efiluent water at the desired temperature. Itwil] be apparent to those skilled in the art that the system may be controlled by changes in temperature, pressure, level, etc., of any variable in the process with which the tower, is being used.

Referringfirst to Fig.7, cooling towertt'i. is provided with louvers 38 through which air is drawn into.v the tower. Air passes upwardly, through the .tower indirect heat exchange relation with water passing through the tower. The water is cooled inularge-part.by evaporation, and the saturated air is exhausted through fanrings 89 on top of the tower. ,Water. to becooled isintroduced into tower 87 through inlet 90, distributed horizontally throughout the tower and cascadedover packing distributedthroughout the tower. ,tobreak the water. into droplets and insure intimate ,contacthof, the .;wate1:'.with air passing throughthe tower, as will ,be ,readily undere stood bythose skilled in, the -art. Cooled water is collected in, sump,91, from whence it flows by conduit 92 into pump room93find, {the water is pumped. out of et t ou h, outlet (94.

The pitch of the. fansinot shown) in thefan rings89 may be varied by the mechanismhereinbeforedescribed; with instrument air supplied, to thefan assembliesthrough supply conduit 95.

The pressure exerted by the instrument air at. the :fan assemblies is regulated by a control system responsive to changes in temperature of the elfiuentwater fromtower 87. As in the case of the type of heatexchange apparatus shown in Fig. 1,,this'controlsysteml is made up of conventional, pneumatic control instruments and: may take any desired form. It is particularly important that a pneumatic system ,be .used with cooling towers as such instruments are not particularly susceptible to damage by moisture which is always present inand about a cooling tower. The system illustrated includes a pnematie controller 96 Which'operates a relay, regulator 97 in response'to, changes in a temperature sensitive element 98 located in the pathhof the efflu'ent stream of water in pump room 93.. When'temperature sensitive element 98 registers a temperature above thesetpoint ofcontroller,96, thecontroller will cause relay regulator 98 to change ,the ,pneumatic pressure in supply .line 95 downstream of the regulatorto increase the pitch of the fan blades Conversely'when temperature of efliuent 10 water ,fallsbelow theset point, relay regulator 97 ,will change thepneumatic', pressure in supply -.line 1downstream of the regulatorto decrease the pitchofi the fan blades;

Controller 96 is preferably operated by, instrument air and may be connected to instrument air supply. line 95 at aipoint upstream ofiregu1ator97' by a branch line 99. Controller96' governs the actiontof-regulator 97 by regulating the pressureain a conduit'100 which interconnectsthe controller 96 and the regulator-97., Where only one or perhaps two fans -arecontrolled by, thelsystem, controller 96 may beconnectedrin the,supply line.95 in, placeof regulator 97, but where a largemumb'er of fans are controlled ,Ibythis system, a,relay. .regulator is preferredas it'can deliver a .large volume of, pressure fluid in a short time and rapidly efiect the changes called for bythe element98l.

The temperature sensitive element 98.is ,ofi the. type utilizing a .temperatureusensitivet expansible..;fluid -.and

laction of, controller, 96 is responsive to the pressure exerted by I the. expansible fluid through a conduit 103. The pressure exerted by the expansible fluid is,-.of, course, responsive to the :,temperature of ,thewater in pump room ,93 and to.changes ,in temperature of the water in the pump room.

Pressure gauges .104 are provided in line 95 upstream and downstream of relay. regulator; 97 to assist in adjusting the several instruments whichamake up the control system."

Preferably, filter regulators 10'1.and'1021 are provided inlines 95,and 99, respectively, atpoints upstream of' relay ;regulator 97 :and controllerv 96, respectively, but downstream of theconnection between. these two lines. Filter regulators. 10.0and101 filter instrument air passing therethroughitoremove debris fromthecontrol system and provide a pressurewreduction in the lines Conventionalainstrument air pressure varies from-plant to plant, but will usually be much higher than is required toioperate, the control system.v Regulators 101 and-102 are preferably, adjustable and-.are set to deliver only the pressure .needed too-perate the system.. For instance, the instrument air supply, may be under a pressure of from 50.to .250. pounds; Regulator -111 the'supply line 95 may be set to .deliver 30 to -35 poundsto relay regulator -97,. and .regulator v100 .in branch line' 99 set to deliver 20. to 25,,pounds to'the pneumatic controller 96. It, will beunderstood that the amount of pressure reduction will,,depend .uponv :thepressure required to move the-diaphragm: to oneextreme position against-thedorce exerted by the spring of theifansassembly, and will also depend upon theparticular control instruments employed.

In Fig. ,8 there vis.,illustrated a cooling towerhaving a large numberof fans and the manner in which the pneumatic controlsystem may be adapted to-control a large number of fans. .The fans are divided into two groups and instrument air supply conduit .95 'provides air .pressure for one group; and conduit 95a provides air pressure for the other group. Conduit 95 is provided with control instruments as explained'above and-conduit 95a is provideduwitha filterregulator 101a, a relay regulator 97a, and gauges, 104a identicalwith those-providedfor conduit 95.1 Conduit 100mis .connectedto relay regulator 97a as well; as relay regulator-'99 and-changes in the pressure inconduit- 100, willycontrol both regulators to changethe pitch of the fan blades in both banks of fans. The controller 96 and. relay regulators 97 and 9711 may be physically positioned closely adjacent each other so that the addition ofthe. second relay regulator to the system will not substantially affect the sensitivity of the y tem.

Fig.9 illustrates the modification of the control system to provide for ,de-icing of a cooling. tower. Generally, the de-icing isaccomplished by reversing the flow of air throughthe tower. so, as to utilized the heatpicked up by .air in contact with the relatively warmer .wateras it comes into the tower and to pass such warmed air in 'reverse direction through the tower so that this heat may be used to melt any ice formed in the normal upstream air section of the tower. While the reverse flow of air through the tower might be accomplished by other means as will readily suggest themselves to those skilled in the art, the pneumatically controlled variable pitch fan lends itself very readily to a very simple method of reversing flow of air through the tower. This is accomplished essentially by setting the physical limit stops within the fan assembly to permit the fan blades to be rotated into a substantial negative pitch angle which upon rotation of the fan will cause reverse flow of air through the tower. It is preferred that during the normal operation of the tower the blades rotate in a range between the positive pitch angle which will load the prime mover for the blades the desired amount and the low pitch angle which will substantially oppose the chimney effect of the tower and this is accomplished by limiting the pressure which may be supplied by the control system during normal operation to that pressure which will move the blades into the desired low pitch angle. Thus, the control system will accomplish the function of the negative pitch limit stop which has now been moved to a position permitting a greater negative pitch than required to oppose the chimney eifect. The control system pressure may be limited to the desired amount by adjustment of filter regulator 101 so that it will only permit a pressure within line 95 downstream from regulator 101 sufiicient to move the fan blades to the desired low pitch. On the other hand, controller 96 may be pre-set so that it will not cause relay regulator 97 to supply a pressure fiuid to the fan assemblies sufiicient to move the fan blades beyond the desired low pitch. The term low pitch when used herein is intended to include a neutral pitch and a negative pitch as well as a low positive pitch inasmuch as the low pitch limit stops may be set at any of these three positions.

With the fan blade assembly designed to operate between a predetermined high and low pitch angles during normal operation, such operating being accomplished by a given range of fluid pressure, the de-icing is accomplished by exposing the fan assemblies to a pressure outside such range which will InOVe the fan blades into a greater negative pitch angle and efiect reverse flow. When the fan blade assemblies are designed to move from positive to negative pitch with an increase in pressure as shown herein, the fan blades may be moved into the desired negative pitch angle which will reverse flow of air through the tower by overriding or by-passing the normal control instruments 96 and 97 and supplying to the fan blade assemblies a pressure suflicient to move the blades into the desired negative pitch angle. In reverse flow there will be a tendency to entrain water in the air stream if excessive velocity is employed and for this reason the fan blades should be limited by the low pitch stop to a position which will provide low velocity reverse flow.

It is usually desirable to continue normal operation of the tower while the de ving is being effected and for this reason it is preferable to provide for de-icing the tower a cell at a time. This may be accomplished by connecting the fans of the tower to conduit 95 by branch conduits 95b and 95c, each of which leads to a pair of fans which it is desired to de-ice separately from the remainder of the tower. The increased pressure necessary to accomplish the de-icing is provided by a conduit 1115 connected to the instrument air supply conduit upstream of regulator 1531 of the control system and connected to each of branch conduits 95b and 950 by threeway valves 106 and 106a, respectively. When it is desired to de-ice the cell of the tower serviced by conduit 95b, valve 106 is moved to a position at which line 105 will communicate with branch line 951) (as shown in the drawings) and the fan assemblies will be exposed to til) the pressure within line 105. The instrument air supply pressure upstream of regulator 101 is usually more than it is desirable to subject the diaphragm of the fan assembly to, and for this reason a pressure regulator 107 is placed in line 105 to reduce the pressure within this line to a value just sufficient to move the fans into the desired negative pitch. In this manner, the diaphragm will be protected against the full instrument air pressure. After de-icing is complete in the cell serviced by conduit 95b, valve 106 is turned to connect lines 95 and 95b and normal control is resumed. Valve 106a may then be turned to de-ice position to de-ice the cell serviced by conduit 95c. As many branch conduits as necessary may be provided to service all of the fans of a tower with each of the branch conduits servicing one or more fans as desired. Valves 106 and 106a may be located on a control panel at ground level if desired so that they will be very simple to reach and to operate. While a by-pass system is preferred as it permits the de-icing of the tower one cell at a time, it will be understood that the normal control system might be provided with means for overriding the controller and supplying a fluid under suflicient pressure through conduit 95 to accomplish full reversal of the fan blades.

When a tower employing the defrost system is first installed, regulator 101 should be set to deliver as a maximum that pressure which will move the fan blades into a slight negative pitch and give static air conditions within the tower. When such pressure has been determined, gauge 104 between regulator 101 and relay regulator 97 may have marked thereon the pressure at which the chimney etfect is opposed. This mark will serve as a reference line in the event it becomes necessary to change regulator 101. Regulator 107 should be set for a somewhat higher pressure which is suflicient to move the blades into the desired negative pitch which will give slight reverse floW of air through the tower. By way of example in a tower in which blades revolving at a minus 11 or 12 degree pitch angle will oppose the chimney effect of the tower and maintain static conditions in the tower, further reversal of the blade pitch angle to a negative pitch of from 15 to 18 degrees will give the slight reverse flow desired to de-ice the tower. A slightly greater negative pitch can be employed to increase the air flow if desired.

Fig. 10 shows a modified form of fan assembly in which the biasing means is outside of the portion of the hub which carries the fan blade holders so that the size of the spring may vary without effecting the size of the hub and additionally so that the compression of the spring may be varied. It was originally thought that a uniform spring under a predetermined compression would be usable in a large number of designs. It has been found, however, that as the back pressure of the heat exchangers varied the spring compression need also be varied to maintain the force required to overcome the spring within the desired limits. The back pressure of heat exchangers will vary with differences in design from heat exchanger to heat exchanger, with the number of tube bundles in an indirect heat exchanger and with the amount of packing in a direct heat exchanger. Thus, if a basic hub is to be used in a large number of designs, it is desirable to be able to vary the force exerted by the spring so that the number of tube bundles or the amount of packing, as the case may be, may be varied from design to design. It is also advantageous to be able to vary the number of tube bundles or the amount of packing from time to time in a given heat exchanger.

In most parts, the fan hub assembly has not been altered and reference is made to the disclosure of the Fig. 1 to Fig. 6 embodiment for the general construction and operation of the Fig. 10 assembly.

Referring now in detail to the modified assembly, piston 108, which corresponds to piston 31 of Fig. 3, is provided with a threaded bore 109 in its end adjacent to diaphragm 110. Diaphragm 110 is provided with a bore is s (not shown) in register with bore 109. Athreaded bolt 111 extends through the bore in diaphragm 110 and has one of its ends threadedly received in piston 108. A

but 112 is threadedly received about bolt '111 on the side of the diaphragm opposite the piston and secures the diaphragm 110 to piston 108. Bolt 111 extends through an opening 113 in the upper cover or flange plate 114 of the diaphragm housing. A spring 115 is received about bolt 111 and rests upon an abutment insert 116 which is received in an annular seat 117 surrounding bore 113. A washer 118 is received over the end of bolt 111 remote from diaphragm 110 and rests upon the end of spring 115. A nut 119 is then threaded to the same end of bolt 115 and by varying the position of nut 119 along the length of bolt 111 the compression of spring 115 may be readily varied. The force exerted by 'the spring under compression will be transmitted to bolt 111 and through the connection provided by piston 108, the spring will bias the'fan blades toward one extreme pitch angle. i

in this modification bolt 111 is a part of the low pitch stop and is provided with an enlargement which abuts against insert 116 to arrest or limit downward movement of diaphragm 110. Preferably, this abutment is a nut 120 threadedly received on bolt 111 and the low pitch angle of the fan blades may be varied by moving nut 120 toward or away from the diaphragm along. bolt 111.

The high pitch limit stop is provided by a stop member carried by cover plate 114 ofthe diaphragm housing in a position to be engaged by diaphragm 110 as it is flexed upwardly. This stop may be provided by a plurality of dogs 121 which depend from cover 114 and are spaced about bolt 111 in a position to engage the diaphragm closely adjacent its connection with bolt 111. As diaphragm 110 is flexed upwardly under the influence of spring 115, the diaphragm will abut stops 121 to limit.

further movement of the diaphragm in an upwardly direction. Stops 120 and 121 are herein referred to as low and high pitch limit stops, respectively. While this relationship is preferred, it will be understood that their relationship could. be reversed by rotation of the fan blades in the blade holders 180 degrees as hereinabove explained.

Preferably, some means is provided for external ad- I justment of the high pitch of the fan blades. Referring to Fig. l1, it will beseen that there is provided an internally threaded-blade holder or ferrule 122 which may be journaled in the hub in a similar manner to ferrule 50' and eccentrically connected to piston 108 in the same manner as ferrule 50 is connected to piston 31. One or more set screws 124 are carried by blade holder 122 adjacent the outer end thereof. These set screws are adapted to engage the outer periphery of shank 123 of the fan blade and hold the blade holder and blades in a desired relative rotative relation. It will be notedthat the blade holder is provided with a counterbore 122a at its outer end, and that set screws 124 extend into this counterbore. As the threaded section of the ferrule begins inwardly from the counterbore and hence the set screw 124, any distortion of the threaded shank 123 by set screws 124 will not interfere with the threaded connection between ferrule and blade shank. The set screws 124, when in engagement with blade shank 123, are of such length-that the head of the set screw will extend a short distance above the outer peripheral surface of blade holder 122. An annular set screw retainer clamp 125 is received about the blade holder 122 and overlies the heads of set screws 124. This retainer clamp is a squeeze ring provided with a take-up bolt 126 to squeeze the retainer clamp tightly about the blade holder and lock the set screws against rotation. With this arrangement 'it will readily be seen that while high pitch limit stops which the high pitch limit of the blades may be readily and easily varied. It will also be apparent that the manner of operation of these stops is readily ascertainable from the exterior of the hub assembly and a person i not familiar with the particular design will quickly understand the operation of the stops and be able to change the pitch of the fan blades.

The adjustment and set-up of the fan assembly is as follows: The portion of the hub carrying the blade holders may be assembled as is apparent from the views of the embodiment shown in Figs. 1 through 5. Piston 108 is firmly secured to diaphragm 110 by means of b'olt 111 and nut 112. Insert 116 is inserted over bolt 111 and the low. pitch limit stop 120 is threaded onto bolt 111. The high pitch limit stop should be set first and in order to insure that diaphragm 110 is firmly abutted against stops 121 the spring 115 may be temporarily positioned about bolt 111 and placed under slight compression. Each individual fan blade is then rotated in its respective blade holder 122 to the desired angle of maximum pitch. This operation is readily accomplished using a spirit level device to determine the angle-of inclination of the blades. After the blades are locked into position, the prime moveris started up and by testing the load imposed upon the motor it may determine if the correct blade angle has been selected. This determination may be made measuring the horsepower being delivered to the fan, by measuring the current passing through the motor in the case of an electric motor, or any other known means of determining the load imposed upon a prime mover. In making this test spring 115 should be under a compression which will maintain the diaphragm in abutment with high pitch limit stops 121 to maintain the blades in full high pitch.

After the high pitchlimit stop has been adjusted, spring- 115 is removed and the blades rotated to the desired low pitch. Low pitch stop 12tl is then moved along bolt 111. until it abuts insert 116. It will be notedthat by provid-- ing a removable spring carried outside the portion of thehub carrying the fan blade holders that the low pitch able to overcome the spring force and permit rotation of the blades to low pitch.

The low pitch limit stop may be set in difierent posi tions depending upon the control system used and upon the heat exchanger with which the assembly is to be used.

For instance, it may .be set at a negative pitch substantially equal to the positive pitch of the blades and by rotation of the fan at this negative pitch angle the flow of air through the heat exchanger with which the assembly is used may be reversed. This is of particular value in tube'bundle exchangers which are associated with equipment it is' desired to keep warmer than ambient air during cold weather operation.

reducing the compression upon spring 115, the blades may be varied between neutral pitch and the predetermined negative pitch. during the cold months of the year to reverse the normal flow through the heat exchanger and thus move the air stream in reverse direction through the tube bundles exhausting the heated air into the plant with which the heat exchanger is used so that.

the heated air may warm the plant.

It is here pointed out that this reverse flow of air maybe utilized without using the control system hereinbefore disclosed. That is, the fan may be used during the warm months with the blades held in full positive pitch by spring and then a predetermined air pressure exerted on'thediaphragm during the cold months to completely reverse the blades to-the predetermined negative pitch to give the reverse flow air stream. This manner of opera tion may be used when it is desired to have reverse flow By increasing the instrument air pressure exerted upon the diaphragm, or by' of air but'not to vary the air stream to control the amount of air flowing through the heat exchanger.

Low pitch limit stop 120 may also be set at a position which will provide a slight negative angle on the fan blades to oppose the chimney eifect in a heat exchanger. A further setting for low pitch limit 120 is employed Where it is desired to use the de-icing feature explained hereinabove. When set for de-icing low pitch limit 120 will be set at a point which will allow the blades to move into a negative pitch suflicient to reverse flow of air through the heat exchanger in the desired amount, and the low pitch limit for normal operation will be provided by limiting the amount of air supplied to diaphragm 110 by some means in the control system.

After the limit stops have been adjusted, spring 115 is placed about bolt 111 and washer 118 together with nut 119 utilized to place the spring under the desired compression. The amount of compression of spring 115 should be just enough to move the fan blades into full high pitch when the diaphragm is exposed to the minimum amount of air pressure supplied by the control system. This minimum amount may be one atmosphere and, if so, the amount of compression may be readily tested without hooking up the control system. Otherwise, the control system should be hooked up and the minimum amount of pressure supplied to diaphragm 110 so that a test may be made to determine if the spring 115 is under a proper amount of compression. This test should be made with the fans rotating at full R. P. M. so that all forces acting on the fan blades may be taken into account. Conveniently the horsepower or current flowing through the motor, if electric, should be equal to the desired load to be imposed on the motor. In other Words, when such a load condition is reached, it is known by prior tests that diaphragm 110 is in abutment with limit stop 121. The spring tension should be no more than necessary to accomplish the desired objective as excessive spring tension will require a greater pressure to move the blades into abutment with the low pitch limit stop. By providing the externally accessible adjustment for the spring compression the amount of fluid pressure necessary to move the diaphragm into abutment with the low pitch limit stop will be approximately the same regardless of back pressure of the installation, thus simplifying and standardizing the control system. It is pointed out that the means for adjusting the compression of spring 115 is exterior of that portion of the hub which carries the fan blades and is quickly and easily accessible to change the compression of spring 115 either during initial installation or when the factors eifecting the back pressure of the heat exchanger are changed during the life of the heat exchanger.

After setting the high and low pitch limit stops and the compression on spring 115, a housing 127 is positioned about the spring and sealingly flanged to the cover plate 114 of the diaphragm housing. The housing has a cylindrical bore of a size to receive the spring and of a length to permit full throw of diaphragm 110 without the spring 1.15 or bolt 111 striking any portion of the housing.

A rotary union 128 is flanged to the free end of housing 127 in fluid communication with the interior of the housing. Preferably, one of the two rotatable parts of the rotary union is flanged directly to housing 127.

Closely adjacent the rotary union there is provided a support 1259 for the instrument air supply line. This sup port may be mounted on a crossbar 1% which is secured to the fan ring or other structure with which the fan assembly is associate By way of example in fan ring 89 of Fig. 7 crossbar 133 would extend across the upper lip of fan ring 89. instrument air supply conduit 131 is firmly anchored to support 129 and a length of flexible hose 131a interconnects the rotary union 128 and the supply conduit 131 at support 121 This flexible hose 131a forms a part of the instrument air supply line and should be of suificient length to allow slight orbital or oscillatory movement of rotary union l28. This is particularly important in the Fig. 10 embodiment inasmuch as the spring housing 127 necessitates the positioning of the rotary union some distance from the journals in which the fan assembly is mounted. The flexible conduit 131a should also be short enough that there will be no sharp bends in the flexible conduit adjacent its connections with the rigid portions of conduit 131 and rotary union 128 which might fatigue the conduit.

Referring to Fig. 12, there is shown a still further modified form of the fan assembly. This modification is substantially the same as the Fig. 10 modification except that there is provided an adjustable high pitch limit stop. In-

sert 116a which is carried by the outer cover 114 of the diaphragm housing is firmly secured to the outer'cover its by studs 132. Insert 116a is provided with a threaded bore 133 in which there is threadedly received an adjustable limit stop in the form of a sleeve 134. The nut 112 abuts against the lower end of sleeve 134 to provide the high pitch limit stop and low pitch limit stop nut 1' 9 abuts against the upper end of sleeve 134 to provide the low pitch limit stop. Inasmuch as sleeve 13 i is movable toward and away from diaphragm 119, it will be apparent that the sleeve 134 should first be adjusted to provide the desired maximum pitch angle and then the low pitch limit stop 1'20 adjusted to provide the desired low pitch angle. When the modification of Fig. 12 is used, the individual blades 123 must, as in the case of Fig. 10, be adjusted to the desired relative rotative relationship with their respective blade holders so that each of the blades will be at the same angle. However, in the 'Fig. 12 embodiment, it it is thereafter desired to vary the high pitch limit, it is only necessary to vary the single high pitch limit stop 34 to change the maximum high pitch to which the blades can be rotated.

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, and in combination with an apparatus employing air for direct heat exchange with a medium to be cooled, 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 fluid pressure responsive means of said hub.

There has also been provided a variable pitch fan assembly in which the force exerted by the biasing means may be selectively varied to make possible the use of a single assembly in a plurality of dilferent but comparable designs. The spring which provides the biasing means for the diaphragm, and hence the blades, has been located outside that portion of the hub which carries the fan blades. Thus, the basic hub design may be used with springs of varying size to suit the particular diameter blades being used. The compression adjusting means for this biasing spring as well as the high and low pitch limit stops are located exterior of the portion of the hub which carries the fan blades, are easily accessible, and their operation is easily understood by those not familiar with the complete design of the assembly. With the spring positioned exteriorly of the portion of the hub which carries the fan blades, it is possible to adjust both high and low pitch limit stops while the biasing spring is removed permitting the setting up and adjustment of the blades when a plant is being built and before a source of instrument air is available to operate the diaphragm.

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 apparatus.

It will be understood that certain features and subcombinations are of utility and may be employed without ref erence to other features and subcornbinations. This is contemplated by and is within 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 interpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

1. In a heat exchanger having means for contacting a medium to be cooled in heat exchange relation with air passing through the exchanger and a fan for circulating air upwardly through the heat exchanger, the combination therewith of a mechanism for varying the pitch of the blades of said fan between a selected positive pitch and a selected negative pitch, means responsive to a process variable, means responsive to said means controlling said mechanism to change the angle of pitch of said blades responsive to a change in the process variable, such control means so constructed and arranged as to effect a reduction in the amount of positive pitch and to move into a negative pitch of the blades in response to a reduction in the temperature of the stream, the maximum amount of said negative pitch being such that rotation of the fan will create a back pressure within the exchanger opposing the chimney elfect of the heated atmosphere within the exchanger to substantially prevent passage of air through the exchanger when the temperature of the stream reaches a predetermined low.

2. In a heat exchanger having means for passing a medium to be cooled in heat exchange relation with air passing through the heat exchanger, a variable pitch fan positioned to cause air to flow through the heat exchanger including mechanism for varying the pitch of the blades of said fan from a negative pitch suflicient to move air in a reverse flow direction to a positive pitch to move the maximum amount of air in the normal direction, pressure responsive means operating said mechanism, a control fluid supply conduit communicating with the pressure responsive means, fluid pressure control means controlling the control fluid supply conduit for varying within a predetermined range the pressure of the fluid supplied to the pressure responsive means through said conduit responsive to a process variable to change the pitch angle of the blades between selected limits as a function of a change in the process variable, and means selectively exposing the pressure responsive means to a pressure outside said range and causing movement of said blades into a negative pitch sufficient to cause a predetermined reverse flow of air through the heat exchanger, whereby the air is warmed and directed to the interior of the heat exchanger and forced out therefrom so that the heat may be utilized during periods of cold ambient air temperatures.

3. In a heat exchanger having means for passing a medium to be cooled therethrough in heat exchange relation with air passing through the heat exchanger, a variable pitch fan positioned to cause air to flow through the heat exchanger, a mechanism for varying the pitch of the blades of said fan from a negative pitch sufficient to move air in a reverse flow direction to a positive pitch to move the maximum desired" amount of air in the normal direction, means operating said mechanism, means controlling said operating means to vary the pitch of said blades within a predetermined range to vary the flow of cooling air through the exchanger during normal operation, means responsive to a process variable cooperable with the control means to change the pitch angle of the blades as a function of a change in the process variable, and means controlling said mechanism to selectively move said blades into a negative pitch outside said predetermined range sufficient to cause substantial reverse flow of air through the heat exchanger, whereby the air is warmed and directed to the interior of the heat exchanger and forced out therefrom so that the heat may be utilized during periods of cold ambient air temperatures.

4. In a heat exchanger having means for passing a medium to be cooled therethrough in heat exchange relation with air passing through the exchanger, a variable pitch fan positioned to cause air to flow through the exchanger, a mechanism for varying the pitch of the blades of said fan including means biasing the blades toward maximum positive pitch, pressure responsive means operating said mechanism, a control fluid supply conduit communicating with the pressure responsive means for supplying instrument air thereto, fluid pressure control means reducing the pressure in said conduit to a predetermined pressure and regulating movement of the pres sure responsive means with said reduced pressure responsive to a process variable to change the pitch angle of the blades as a function of a change in the process variable, the eifective pressure area of the pressure responsive means and the force exerted by the bias mechanism being so related that the full amount of said reduced pressure is required to move the blades into their normal minimum operating pitch angle, and means for selectively exposing the pressure responsive member to a pressure greater than said reduced pressure to move the fan blades into a substantial negative pitch and reverse the flow of air through the heat exchanger, whereby the air is warmed and directed to the interior of the heat exchanger and forced out therefrom so that the heat may be utilized during periods of cold ambient air temperatures.

References Cited in the file of this patent UNITED STATES PATENTS 2,169,121 Coy Aug. 8, 1939 2,225,209 Dewey Dec. 17, 1940 2,316,940 Dewey et al. Apr. 20, 1943 2,392,341 Squier Jan. 8, 1946 2,739,655 Petty Mar. 27, 1956

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