US3384165A - Heat exchanger - Google Patents

Description

May 21, 1968 R. T. MATHEWS HEAT EXCHANGER l1 Sheets-Sheet 1 Filed Feb. 5, 1966 INVENT OR RALPH T. MATHEWS Q/W Q .w Emm ATTQRNEY May 21, 1968 v R. 'r. MATHEWS HEAT EXCHANGER Filed Feb. 5. 1966 11 Sheets-Sheet 2 INVEN'IOR RALPH T. MAT HEWS ATTORNEY May 21, 1968 Filed Feb. 5, 1966 R. T. MATHEWS HEAT EXCHANGER ll Sheets-Sheet 3 INVEN 1 OR RALPH T. MATHEWS ATTORNEY y 1958 T. MATHEWS 3,384,165

HEAT EXCHANGER Filed Feb. 5, 1966 11 Sheets-Sheet 4 FIG.6

INVENTOR RALPH T. MATHEWS ATTORNEY R. T. MATHEWS HEAT EXCHANGER May 21, 1968 11 Sheets-Sheet 5 Filed Feb. 5, 1966 INVENT OR PH T. MATHEWS ATTORNEY HEAT EXCHANGER Filed Feb. 5, 1966 1,1 Sheets-Sheet 6 FIGS INVENTOR RALPH T. MATHEWS ATTORNEY R. T. MATHEWS HEAT EXCHANGEH May 21, 1968 ll Sheets-Sheet 7 Filed Feb. 5, 1966 INVENTOR RALPH T. MATHEWS ATTORNEY May 21, 1968 Filed Feb. 3, 1966 R. T. MATHEWS HEAT EXCHANGER ll Sheets-Sheet 8 FIG IO INVENTOR RALPH T. MATHEWS aw y-Mew ATTORNEY May 21, 1968 R. T. MATHEWS HEAT EXCHANGER ll Sheets-Sheet 3 Filed Feb. 5, 1966 INVENTOR RALPH T. MATHEWS ATTORNEY R. T. MATHEWS HEAT EXCHANGER ll Sheets-Sheet 10 Filed Feb. 5, 1966 FIG-15 FIG .19

INVENTOR RALPH T- MATHEWS Q BY Z-?)" FIG. I 7

ATTORNEY May 21, 1968 R. T. MATHEWS HEAT EXCHANGER 11 Sheets-Sheet 11 Filed Feb. 5. 1966 INVENTOR RALP H T. MATH EWS ATTORNEY United States Patent 3,384,165 HEAT EXCHANGER Ralph T. Mathews, Wallingford, Pa, assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a

corporation of Delaware Filed Feb. 3, 1966, Ser. No. 524,712 Claims. (Cl. 165-122) ABSTRACT OF THE DISCLOSURE An air type, finned tube heat exchanger having pairs of tube bundles disposed in upright V arrangement, in which the tubes have a length-to-diameter ratio above about 200 and are supported in generally horizontal planes, provided with means producing air flow generally transverse the tube bundles.

This invention relates to heat exchangers, and particularly to a V-type heat exchanger utilizing air flow past finned tubes through which process fluid is circulated in order to effect heat exchange.

Heat exchange on a large scale is an exceedingly serious problem for a wide range of industries, including, for example, power utilities, chemical manufacture, oil refining, and heating and ventilating generally, the problem being particularly severe in hot regions and those having water scarcities or water supplies so loaded with salts or the like as to require expensive pretreatment. However, air type heat exchangers have proved equally useful in cool climates and, in fact, even where there exist plentiful water supplies, because excessive heating or cooling of natural waters is objectionable from the water pollution standpoint, and this has led to a growing utilization of air as one component of the heat exchange pair.

A serious disadvantage of conventional air type heat exchangers has been the excessive space requirements necessary for their accommodation, plus the fact that large size air-moving equipment of heavy power consumption is necessary to maintain the high-magnitude air flows through the apparatus. Moreover, conventional units are not well-suited to the utilization of auxiliary water sprays, which are necessary, as hereinafter detailed, in order to take care of heat loads where the ambient temperature of the atmosphere might be temporarily well above usual levels, or where process overloads are encountered exceeding substantially the dry air design limit of the equipment.

The V-type heat exchanger of this invention cures the foregoing problems, while affording enhanced efliciency in heat exchange, the manner in which this is accomplished being set forth in the following detailed description and the drawings, in which:

FIG. 1 is a somewhat schematic, broken-away perspective view of a preferred embodiment of heat exchanger according to this invention utilizing three air propulsion units in parallel arrangement to move air past tube bundles spanning the air paths of all three units,

FIG. 2 is an end elevation view of FIG. 1 taken on line 22 thereof, details of fan assembly support and inlet and outlet connections with the tube bundles being omitted in order to simplify the showing, but one type of associated water spray auxiliary being added,

FIG. 3 is a partially broken-away view of a short length of finned tube employed in the apparatus of FIGS. 1 and 2,

FIG. 4 is a side elevation view in section showing the moderate temperature chamber housings for the fans of FIGS. 1 and 2,

FIG. 5 is a sectional side-elevation view detailing the construction and operative mounting of a preferred design of louvers optionally employed with the apparatus of FIGS. 1 and 2,

FIG. 6 is a schematic portrayal of a pair of louvers of the type shown in FIG. 5, provided with a balanced force diagram representative of the forces acting on water droplets entrained in the air intake to the exchangers,

FIG. 7 is a plan view of an assembled manifold type tube bundle prior to V mounting in the apparatus of FIGS. 1 and 2,

FIG. 8 is a section taken on line 88, FIG. 7,

FIG. 9A is a fragmentary end view of the tube bundle of FIGS. 7 and 8,

FIG. 9B is a fragmentary cross-sectional end view of a tube bundle such as that shown in FIG. 9A, except that this bundle is provided with box headers,

FIG. 10 is a cross-sectional side elevation of a box header provided with individual end plug access to individual tubes,

FIG. 11 is a cross-sectional side elevation of an alternate design of box header provided with a removable cover plate for access to all tubes simultaneously,

FIG. 12 is a fragmentary transverse cross-section of a tube bundle showing details of a preferred support strap construction and the assembly with respect to the finned tubes supported thereby,

FIG. 13 is a fragmentary perspective view showing a convenient way of assembling the tube bundles of this invention,

FIG. 14 is a fragmentary perspective view of an alternate design of tube support strap adapted to longitudinal tension assembly within the tube framework,

FIG. 15 is an end view taken on line 1515, FIG. 14,

FIG. 16 is a side elevation view of a special design of strap employed as a temporary aid in the assembly of finned tubes within bundles,

FIG. 17 is a plan view of a horseshoe type individual tube support member shown in assembled relationship with the tube support strap of FIG. 16,

FIGS. 18 and 19 illustrate a finned tube assembly technique readily performed with the aid of the tube support strap of FIG. 16, and

FIG. 20 is a schematic representation of a control system adapted to the automatic control of heat exchangers according to this invention.

Generally, the heat exchanger of this invention comprises a pair of tube bundles disposed in upright V arrangement, each tube bundle being made up of a multiplicity of finned tubes having a length-to-diameter ratio above about 200, the tubes being disposed in generally horizontal superposed planes, an inlet header provided with a process fluid supply line connected in open communication with a first preselected group of terminal ends of the tubes, an outlet header provided with a process fluid removal line connected in open communication with a second preselected group of terminal ends of the tubes, support means carrying substantially the full weight of the tubes individually disposed longitudinally between the inlet header and the outlet header substantially transverse rows of the tubes lying in a common horizontal plane within the tube bundles, and powered'means impelling air flow generally transverse the tube bundles.

By way of example solely, there is hereinafter described a heat exchanger according to this invention utilized for the cooling of a chemical process fluid, because this application presents special problems which have not been hitherto solved by apparatus and methods of the prior art.

As is well known, the chemical industry usually requires special materials of construction for the fabrication of its vessels, piping and other equipment to minimize corrosion difficulties and, frequently, operations have to be conducted at relatively high pressures and temperatures, so that heavy stainless steel and, often, even more expensive materials are employed, which represents a heavy capital investment. It is thus of the litmost importance that there be extreme compactness in design, with a minimum weight utilization of expensive materials of construction, not only as regards lengths of connecting pipe lines but also for the tube bundles of heat exchangers and other apparatus.

Compactness is achieved with the heat exchangers of this invention by utilization of an upright V design for the tube bundles, which results in a lateral space saving of approximately 40% over conventional horizontal flat bundle exchangers, and by utilizing multiple unit installations mounted closely adjacent one another, conveniently at overhead locations which represent the only above ground space available in already congested chemical plant manufacturing areas.

Referring to FIGS. 1 and 2, there is shown a typical triple air propulsion unit design which, collectively, services two tube bundles, indicated generally at and 11, running the full length of the assembly. The apparatus can be conveniently erected on a structural steel framework, indicated generally at 12, on a cubical modular basis, each of the identical bays A, B and C housing onethird of the apparatus, and each being provided at the top with a transition fitting 14 within which is mounted an induction fan 15 drawing the cooling air through the unit. Adjacent units are normally closed off from their neighbors by air-impermeable side walls 16; however, the design of FIG. 1 is special as hereinafter described, in that the two interior side walls are eliminated on the exteriors of the V arrangement to permit side-directed air flow as shown by the directional arrows.

The heat exchangers are mounted on elevating legs, not shown in FIG. 1 but denoted at 17, FIG. 2, presenting the base ends to free air flow from the bottom of the construction. Optionally, the base ends are closed off by adjustable louvers 20, which are advantageous as control mechanims but which can have a dual function as spray drop collectors, as hereinafter set forth.

FIG. 2 depicts the upright V construction for the tube bundles 10 and 11, the included angle of which can vary from about 40 to about 65, with the 60 angle shown being especially preferred. The cooling air flow in this instance is, as denoted by the arrows, up from the base of the apparatus, past louvers 20, through the tube bundles in substantially transverse flow with respect to the tubes, as shown for the cut-away portion at the upper end of tube bundle 10, thence out through transition fitting 14 under the induced draft of fan 15, with discharge through stack opening 22.

Since the cooling air is elevated rapidly in temperature when used dry, as in the usual case, it is essential that the direct drive for fan 15 be protected from heat exposure. This is conveniently accomplished (see FIG. 4) by employing structural steel members (not shown) from which depend thermally-insulated ducts 26 which carry air to the fan drive motor 27 and its direct-connected gear box 28 disposed in vertical orientation within an axially disposed draft tube 29 open at the top end. Thus, fan 15, during rotation, simultaneously draws clean, cool air from the outside surroundings radially inward through struts 26 and annularly around motor 27 and gear box 28, thereby affording ventilation at all times during operation. If desired, an externally mounted auxiliary blower (not shown) can be provided outside transition fitting 14 to force cooling air through the duct structure to continue cooling even when motor 27 is shut down for repairs or servicing. However, frequently, natural draft produces enough cooling air circulation through struts 26 to keep the motor and gear box cool even when fan operating ower is. switched oif.

A preferred design of finned tube 33 useful in this invention is that shown in FIG. 3, this comprising an inner conventional round cross-section process tube 32, which is fabricated from an appropriate material of construction (e.g., stainless steel) resistant to corrosion by the process fluid passed through it and of the necessary strength, heat resistance and other characteristics to accommodate the process fluid from the chemical manufacturing standpoint. The fin assembly indicated generally at 34 is of unitary construction tightly forced on or otherwise intimately bonded over the full inside periphery coaxially with process tube 32, making the construction as nearly integral as practicable. Aluminum has proved to be a good material of construction for fin assembly 34, due to its light weight, ease of working, good resistance to plant atmosphere corrosion and its high heat conductivity.

As shown, the external fin 34a is a continuous extruded helical screw having an outside diameter of, typically, 2.25" with a pitch providing seven to nine fins per inch of tube length for a process tube 32 of 1" outside diameter. The fin tube can typically be approximately 0.040" wall thickness, while individual fins can have a crest thickness of 0.018 and a root thickness of 0.065" where water sprays are used.

FIG. 7 is a plan view of a high pressure service manifold type tube bundle, shown in section along line 88 in FIG. 8. The manifold design utilizes, in this instance, four-pass serpentine flow from process fluid inlet header 38, through the finned tubes 33, to process fluid outlet header 39.

As will become clearer from description to follow, tube bundles K10 and 11 are built up from parallelly disposed individual finned tube 33 sub-assemblies, the straight length ends of which are connected in process fluid flow continuation by U-bends 40, welded or otherwise fixedly attached thereto at joints 4'1. Connection is made to headers 38 and 39 via enlargements 42 at the tube ends, which are weld-attached in open communication with the headers, disposed parallel one to another but transverse the tube bundle. Since the finned tube assemblies 3 3 can be relatively long (e.g., 36 for the three-unit assembly shown in FIG. 1), it is imperative that the weight of the tubes be supported at frequent intervals along their lengths with retention of full freedom to expand or contract with variation in temperature of the process fluid, particularly when the tubes are full of a liquid phase process fluid, as this adds appreciably to the gross weight. Otherwise the tube bundles will sag in random fashion, thereby preventing all uniformity in air flow passage through the bundle as well as any uniform ingress of cooling liquid sprayed on the outside of the fin assembly 34. Moreover, since individual finned tubes 33 sometimes require that maintenance work be done on them, tube weight supporting means should preferably be readily demountable to permit access to any point in the interior of the tube bundle by temporarily displacing adjacent tubes laterally, so as to expose any particular one for repair without the necessity to first remove any more tubes from the bundle than is absolutely essential.

Tube support in this invention is provided by demountable support straps 46-, shown in plan in FIG. 8 and in side elevation in FIG. 9A, the details of which are hereinafter described. First, however, it is believed essential to orderly description to treat of the external framework for the individual tube bundles. This framework is fabricated from conventional structural steel shapes consisting of longitudinal channels 47 bolt-attached to heavy end transverse I-beams 48. To provide lateral stiffening at intervals along the length of the bundle, additional, somewhat lighter transverse I-beams 49 have been incorporated, these being provided with fixedly-attached end plates 49a for bolt attachment to the webs of channels 47. Channels 50, which constitute the support members receiving the ends of support straps 46, are fixedly attached to the inwardly disposed lengths of I-beams 49.

The weight of headers 38 and 39 is carried in yoke plates 51 mounted with yoke openings 51a disposed parallel to but outboard of longitudinal channels 47, plates 51 being welded or otherwise joined to the webs of channels 47.

Referring to FIGS. 1 and 9B, the right-hand end of the tube bundle is the top end of the bundle in the upright V final assembled position. Stiffening plates 54 are weldattached across the channel 47 flanges at appropriate intervals to stiffen and strengthen the construction, whereas triangular-shaped pieces 55 securely welded or otherwise attached to the web at the ends of channels 47 constitute the corner attachment points to the upper ends of the upright frame pieces defining bays A, B and C of FIG. 1, whereas pad pieces 56 constitute base supports for the framework denoted generally at 57 to which transition fittings 14 are attached.

Tube bundles 10 and -11 are supported in upright V arrangement upon longitudinal pedestal strip 23 (FIG. 2), the central portion of which is closed off for its full length to bar by-pass air flow. It is most convenient, as hereinafter described, to assemble all of the tubes within framework 12 while the latter is laid flat and thereafter lift the fully assembled tube bundle pairs into place on opposite sides of pedestal strip 23. Since the tube bundles are relatively heavy, this final assembling is most readily accomplished with the aid of a power crane and it is preferred to provide drilled holes, such as hole 24 in triangular pieces 55 (FIG. 912) for ready insertion of the crane lift hook.

In the interests of weight saving, channels 50 are preferably aluminum, although they can equally well be aluminized steel to reduce possible electrolytic interaction with aluminum support straps 46. Where aluminum channels 50 are employed, they are preferably isolated from direct contact with l-beams 49 by interposition therebetween of a micarta strip, not shown.

Channels 50 are assembled with their webs inwardly disposed from the inner flanges of transverse I-beams 49, thereby forming oppose-d enclosed box constructions 59 adapted to receive the opposite ends of support straps 46 through slots 6% spaced at regular intervals along the channel length.

There exist a number of ways in which channels 50 can be attached to I-beams 49, so as to form a unit construction therewith, one of which (FIG. 13) constitutes the use of angle clips 61 adapted to be attached in opposition to the two sides of the I-bearns by a common through-bolt 62 with lower legs wedged tightly beneath the adjacent flanges of the I-beams, micarta isolation strips (not shown) being again used to isolate aluminum components from steel.

As seen particularly in FIGS. 9A, 9B, 12 and 13, support straps 46 are stiff but springy pieces (typically 2" x 12% x thick aluminum) having their central lengths bent in a regular repetitive undulatory pattern to form individual concave recesses formed on a circular arc conforming quite closely to approximately 60 of the lowermost peripheral expanse of finned tubes 33. The rigorous development of a preferred design of strap 46 is shown schematically in.FIG. 12. Here the longitudinal center lines of the strap ends are drawn in in broken line representation and a construction line drawn from the center line at the left-hand side, where the strap is first bent arcuately, to the center line at the right-hand side, where the straight strap end recurs again. This construction line makes angles of 150 measured counterclockwise as seen in FIG. 12 with respect to both left-hand and right-hand strap end center lines. The pitch of the undulations is such that neighboring finned tubes 33 in any given row are spaced one from another on equal pitches of, typically, 2 /2 for the specific tubes of 2% outside diameter hereinbefore mentioned, thus leaving a longitudinal A air passage clearance between adjacent tubes of any given horizontal row. A small clearance of typically is provided between the tops of the finned tubes 33 and the undersides of the support straps for the next succeeding row thereabove, which accommodates some lack of straightness in adjacent tubes, however, tubes 33 are brought up snugly into fixed spotted relationship one with another by the springiness of individual tubes, locking the tubes in a tight uniform tube center-to-tube center equilateral triangular pattern g, FIG. 12, throughout. At the same time, essentially the full weight of each row of the tubes is carried exclusively by the support straps 46 and transmitted in turn to channels 50, I-beams 49 and the bundle framework generally. Thus, there is no sagging of the finned tubes, provided that support straps 46 are employed at relatively short spacings (e.g., every four feet) of unsupported tube length extending between the extreme ends of the tube bundle.

The support strap hereinabove described is the subject of my patent application Ser. No. 524,811 of common assignment filed of even date herewith.

The convenience in assembly of the foregoing construction is portrayed in FIG. 13, which illustrates how successive tube layers can be readily built up in sequence between pairs of adjacent support straps 46.

It is usually preferred to assemble the tubes in a bundle by bringing them into place from the top, and this is most easily done by laying the bundle framework flat before attachment thereto of the uppermost I-beam 49, channel 50 sub-assembly, denoted generally at F in FIG. 13. The lower ends of straps 46 are then inserted in order from right to left in slots of the bottom channel 50' successive finned tubes 33 being next placed one above the other in each row, cradled within the opposed undulations of adjacent straps, after which the next rows in horizontal progression to the left are built up in turn. As shown in FIG. 13, the extreme right-hand strap denoted 46 is actually only a half-strap, retained at its end abut ting channel 47 by a welded clip 67, the purpose being to utilize to the utmost all available cross-sectional area within the bundle framework for the accommodation of heat exchange tubes. Any unused open area remaining is closed off by spring-clipped panels 68 (FIG. 9A), which thus prevents by-pass of air through the unit.

Usually, the weights of tubes 33 bias straps 46 right- Ward'ly as seen in FIG. 13, so that there is automatic alignment of the straps in their proper final positions; however, if desired, a rake tooth retainer (not shown) can be used to temporarily secure the straps against lateral displacement one from another.

An exceptionally convenient temporary retainer is that detailed in FIG. 13, straps 46 being in this instance provided with slots 66 at their upper ends deep enough for full reception of tension bar 69, which is advanced in notch-by-notch progression from right to left. The lefthand end of bar 69 is formed into a hook 70 adapted to overlie the bottom of slot 66 in the left-most strap 46 and thereby lock all tube rows to the right against any shifting during the time that the tube bundle is being assembled.

The top edge of tension bar 69 is provided with a succession of equally spaced notches 71 located distances apart equal to the final desired spacing of individual straps 46 one from another. A slot 72 large enough to slidably receive tension bar 69 is cut in longitudinal channel 47 at the points where support straps 46 are employed, and there is slipped over the right-hand free end of the bar a freely slidable slotted keeper piece 73 which drops by force of gravity into successive notches 71 on bar 69 during its advance to the left, securely locking all straps in place until another notch advance is desired. When all finned tubes 33 have been assembled within the bundle, sub-assembly F can be lowered into place to an extent where the upper ends of straps 46 just enter top slots 60, which position can be preserved by using temporary locking dowels inserted through holes 75 drilled in the web of channel 47. Then tension bar 69 can be rocked slightly to disengage book 70 and the bar withdrawn completely through slot 72, after which the sub-assembly F is lowered to final position with upper ends of straps 46 fully inserted within slots 60. Finally, sub-assembly F is bolted securely at both ends to the longitudinal channels 47 and the tube bundle assembly is complete.

An alternate, somewhat simplified design for retention of support straps 46 is detailed in FIGS. 14 and 15, this having the advantage that straps 46 can be assembled under predetermined longitudinal tensions, which can be particularly desirable in installations where there exists considerable transmitted vibrational stress from adjacent plant equipment, such as reciprocatory compressors or the like. In this case, an exceptionally tight tube assembly is desirable to insure that invariant air passages are maintained throughout the tube bundles.

The alternate design dispenses with channels 50 and substitutes I-beams 49 which are slotted on the inboard flanges at 78 to receive the ends of the straps, again provided with longtiudinal slots 66, which then overlie the web portions 49' of the I-beams. The outer edges of the slotted ends of the straps are cut away to form notches 79 which receive oppositely disposed C-profile spring clamps 80, brought into tight abutment at the top edges against the underside of the inboard flanges of I-beams 49 and at the bottom edges against the lower ends of notches 79 by tightening the nuts 81 on bolts 82 threaded at both ends and passed through drilled holes in web 49'. It will be understood that an identical construction is employed on the other ends of straps 46, making it possible to effect tension adjustment at will from either side of the tube bundles.

Regardless of which design is employed, straps 46 apparently cross brace finned tubes 33 in tight rigidity, which enables tilting of the assembled tube bundles into any plane without change of tube position.

It is sometimes desirable, as an aid in the assembly, to support individual tubes in temporary position at preselected points farther apart than the 4 span intervals hereinbefore described, and the apparatus shown in FIGS. 17-19 has been devised for this purpose. Here a strap 46" identical in all respects with straps 46 hereinbefore described, except with the modifications now to be detailed, is employed solely for assembly purposes.

Strap 46" is notched along both edges as indicated at 85 in the root portions of the undulations so as to receive U-piece-s 86, which are proportioned to just abut the crests of the opposed undulations on the strap 46 disposed to the right, thereby affording a temporary base for support of the finned tube 33 thereabove. It is contemplated that straps 46" and their U-pieces 86 will be employed at alternate intervals of, for example, every 8' apart over the tube bundle length, thereby affording support and location to individual tubes while they are being rolled in or otherwise attached to their headers. Thereafter, when the final straps 45 are put into place, these are first assembled in the alternate vacant positions existing between straps 46". Then the latter are pulled and replaced by regular straps 46, bringing the assembly to completion.

For purposes of the description, a tension bar as is shown in FIG. 18 in conjunction with notched end straps 46 and 46".

While, as hereinbefore mentioned, louvers 20 are optional, their use is especially advantageous where critical heat exchange control is to be maintained, or where water sprays are employed as cooling aids; however, louvers possess advantages even in dry air operation, and where manual control is relied upon, so that their general use is preferred.

Referring to FIGS. 2, and 6, the louvers are mounted within a squat, square cross-section breeching 88 located beneath the upright V tube bundle assembly and athwart the lowermost air passage of the unit, which is provided with a multiplicity of longitudinal members 87, upon which are pivotally mounted the co-parallel individual louvers 20. These louvers are typically approximately 8 long, measured tip-to -tip, and are spaced at uniform distances apart of about 4", so that they overlap when closed, as will be apparent from the right-hand broken-line representation of one louver shown in closed position.

It will be noted that the left-hand louver 20' is of shortened construction, so that it presents no interference troubles in the course of closure.

Louvers 20 are formed with reverse curvatures as regards the blade portions 20a and blade portions 2%, both being formed, typically, on 5" radii. Blade portions 20b are provided with oppositely disposed U cross-section water collection gutters 89 and 99, respectively, each serving an individual side of a louver 20 on which it is mounted. It is contemplated that louvers 20 will be mounted at a slight slope inwardly toward the center of the unit, so as to obtain ready gravitational drainage of water collected thereon into a central sump 91 (FIG. 2) from which it can be recycled as spray water by centrifugal pump 92, where sprays are used as hereinafter described, or run to waste if the water is wash water or otherwise contaminated.

Louvers 20 are operated in unison through bar connector 93, which is provided with upstanding finger portions 94 fixedly attached to the ends of all blade portions 2%, and actuating crank 95 pinned to bar connector 93 at the right-hand end of the sub-assembly. In order to coordinate the actuation of the abbreviated righthand louver with its neighbors, there is provided a short connector bar 96 securely attached through finger portions 97 to the tip ends of the two rightmost louvers shown in FIG. 5.

The foregoing design of louver was evolved in order to entrap and conserve virtually all droplet water draining from the tube bundles in their upright V mounting, since the resultant of forces (gravitational and air supply velocity) acting on water drops, as shown schematically in FIG. 6, is a component of force x directed against louvers 20 for the full range of settings of the louvers. Accordingly, the water droplets impinge on the louvers and drain via gutters 89 and 90 into sump 91. This is an important function of the louvers which, besides their streamlined direction of cooling air over the entire crosssection of the apparatus, are simultaneously adapted to collect and retrieve any cooling water, or cleansing water used to wash down finned tubes 33 from time to time.

A preferred auxiliary water spray arrangement is depicted in FIG. 2 and comprises manifolded spray nozzles 190 mounted, typically, in multiples of four across the width of a tube bundle 72" wide, the nozzles oriented with openings generally parallel to the outboard faces of the tube bundles at spacings therefrom of about 12''. Typically, the nozzles can discharge 1-10 gals/hr., depending upon the heat removal requirements of the particular installation. As will be clear from description to follow, both the location and the spacing of the sprays longitudinally of the bundles can be varied widely to obtain predetermined cooling patterns. Spray water is supplied to nozzles 100 by one or more pumps 92 via supply lines 101 and 102, with gravitational drainage return effected via collection gutters 103 and drain pipes 104 discharging into sump 91.

Nozzles 100 can be of either the atomizing type or can be relatively coarse sprays, the latter being ordinarily preferred for exteriorly mounted nozzles because the fins of tubes 33 are then well-wetted, which produces the maximum cooling action. Water atomized into the air stream lowers the air temperature, thus reducing the mean temperature diiference (abbreviated MTD in the literature) between the cooling air and the process fluid in transit through finned tubes 33 without, however, extensively wetting the tubes. Atomized water spraying is sometimes advantageous to reduce the temperature of the ejected air at the hot side (inboard faces) of the tube bundles and thus is preferably applied by sprays which are disposed interiorly of the tube bundles, as by omitting one row of finned tubes 33 of a given bundle and directing the spray atomizers in opposition, or at right angles, to the air flow through the bundles.

I have found that intermittent spraying of finned tubes 33 is particularly efficient in the utilization of cooling water, this type spraying being effected by reciprocallymounted nozzle assemblies (not shown) adapted to traverse the tube bundles longitudinally, with return timed to occur prior to drying of water on the tube fins, thereby minimizing the build up of heat-insulating deposits on the fins.

It is essential that clean water be employed as the spray liquid, and the use of filters, sedimentation removal of solids within sump 91 and even treatment of the water with wetting agents and/or soluble corrosion inhibitors are all worthwhile procedures. Moreover, the water should be of low sedimentation characteristics on drying.

The upright V tube bundle arrangement according to this invention has proved exceptionally advantageous when auxiliary spray water is utilized, it being found that the enetration of water droplets from nozzles 100 occurs to an appreciable extent throughout practically the entire transverse extent of the air path of a 4-6 tube bank size heat exchanger.

A problem with horizontally disposed prior art heat exchangers has been that spray water collected between tubes unpredictably until such severe flooding occurred that random extensive areas would actually dump large amounts of water at different times impossible to anticipate. The cooling water was thus wastefully employed and oftentimes did as much harm as good, since it blocked air flow past the heat exchange tubes over relatively large areas and, in addition, unbalanced the air passage so that some areas of the exchanger preferentially funneled air through at exceedingly high velocities whereas, in others, there existed substantially zero flow.

In comparison, the V tube bundle arrangement preserves an exceedingly even stratified air flow throughout the entire construction, as has been verified by smoke tests, especially when side walls 16 are employed, with or without louvers 20. Moreover, there is no localized water flooding of the tubes, any excess fin-wetting water draining downwardly from one tube layer to its next-lower neighbors and thence into gutters 103 with speedy return to sump 91 via drains 104. This latter is an important advantage, not only from the standpoint of conserving high cost spraying water but also because it eliminates spray drift, which is a nuisance to plant personnel and a potential hazard to electrical and other process equipment located anywhere in the vicinity.

Referring to FIG. 1, the usual operation of heat exchange units according to this invention is that represented by the discharge air flow directional arrows drawn for the two outside units. That is, with louvers 20 opened at the bottom, air is impelled through the units, generally transversely inwardly past the tubes of the bundle pairs in V arrangement, and thence past the blades of induction fans 15, with discharge of the heated air through stacks 22.

The typical V heat exchanger design hereinbefore detailed dimensionally by way of example, which allows for A" clearance between adjacent fin peripheries, has proved to be especially effective in maintaining constant air velocities through the units. Thus, with air supplied, through louvers 20 at a velocity of approximately 1200'/ min. there is, of course, throttling in passage past the tubes of bundles and 11, which accelerates the air flow. However, since the discharge from both bundles is thereafter combined inside the V, the final discharge velocity maintained is again at about the original 1200/ min. supply level.

I have found that, throughout practically the entire extent of the United States, one can rely on dry air cooling without any auxiliary water spray utilization for at least of the time for most chemical plant cooling processes. However, it is highly desirable to make provision for at least limited water spray cooling sup lementation in locations where exceedingly high dry bulb temperatures are encountered over protracted periods of time. In addition, spray supplementation should, of course, be provided where an adjustable range of process fluid cooling is necessary incident to the manufacturing operation for which the heat exchange is being conducted. Finally, spray supplementation has a distinct economic advantage in many instances, because the air volumes to be handled are sharply reduced when Water sprays are available as cooling aids, reducing fan power costs and permitting certain fans to be shut off entirely in order to effect repairs or general maintenance.

The heat removal advantage of spray supplementation is so marked in most instances that a 300-400% increase in heat removal capability on the air side is often very quickly obtained after water spraying of the tinned tubes 33 is commenced. The reason for this is evidently that maintenance of a water film on fins 34a and their support tubing increases greatly evaporation of water from the fins and the temperature differential between the hot fluid passing through tubes 32 and the fins. So etfective is this action, that I have found that I can easily obtain condensation of process fluids with my exchangers, and even a measure of appreciable process liquid sub-cooling, all as taught with reference to FIG. 20.

Atomizing sprays as hereinbefore described are generally less effective; however, they do increase the mean temperature difference by lowering the air temperature appreciably by the heat take-up ascribable to cooling water evaporation and are definitely worthwhile, either alone or in conjunction with coarse s rays.

Extensive operating experience has shown that V-type heat exchangers according to this invention are usually superior to conventional river water-cooled shell-andtube exchangers, and, in many cases, are also better than expensive cooling tower water-cooled installations.

FIGS. 10 and 11 show typical box header constructions which can be utilized for low pressure installations, FIG. 10 detailing a header having multiple plugs 35 in longitudinal alignment with finned tubes 33, so as to permit ready rod or hose cleaning. FIG. 11 shows a header closed by a common plate 36, provided with a gasket 37, preventing leakage.

Obviously, as is well known in the .art, a wide variety of process fluid flow patterns through preselected groups of tubes within the heat exchangers can be readily obtained by sub-dividing the box headers with transverse flow-routing partitions, and this is accordingly not further elaborated. Also, if desired, the process liquid can be cooled by dividing it into parallel flow through tube bundles 10 and 11 separately, or by routing it in series through first one bundle and then the other, or in various combination series-parallel flows best-suited to the requirements of the particular installation, the design affording a broad choice of alternatives in this regard.

Turning now to FIG. 20, there is shown in schematic cross-section a V-type heat exchanger according to this invention provided with automatic control facilities.

In this instance, the hot vaporous process fluid is introduced via line 109, which is divided into separate branches 109a and 10% leading to the inboard tubes of tube bundles 10 and 11, respectively. A box header construction, as shown in cross-section in FIG. 10, routes the flow into the plane of the figure for the first vaporous fluid pass, as indicated by the arrow representation within sections 10a and 11a, FIG. 20, whereas reverse flow as a second condensed liquid pass occurs in sections 10b and 11b. This produces a hot condensate product withdrawn from lines 110a and 110b, which latter are manifolded into line 111.

A portion of the condensate, determined by the liquid level maintained at the bottom of sections 10b and 11b, which are cross-tied by connections 110a and 11%, is retained in the sub-cooler sections consisting of first passes 10c, 11c and second passes 10d, 11d, the cold condensate discharged therefrom leaving via lines 115 and 116, respectively.

Hot condensate discharge line 111 is provided with a conventional air-operated flow control valve 117, and cold condensate discharge line 112 is provided with a similar automatic valve 118. These two flow control valves are connected in reverse-acting relationship, so that one opens when the other closes responsive to a signal transmitted to both valves via control line 119 running from conventional temperature controller 120. Temperature controller 120 operates on the basis of the temperature of the commingled hot and cold condensate mixture, sensed via line 123 at a point far enough removed downstream from the junction of lines 111 and 112 to insure that intimate mixture has been obtained.

Control of sub-cooler operation is achieved by interposing a set of automatically operated louvers 124 athwart the exit air passage from the sub-coolers 10c, 10d and 11c, 11d, these louvers being operated collectively as hereinbefore described with respect to FIG. by an air pressure actuation mechanism 125 responsive to a control signal transmitted from temperature controller 120 via line 126. In operation, it is usually satisfactory to confine the condensate flow control effected by valves 117 and 118 to the 310 lbs. part of the conventional 3-15 lbs. instrument air pressure range, reserving pressures above lbs. to effect progressive throttling closure of louvers 124, which otherwise remain full open.

Condensate is withdrawn from the system via line 128, into which lines 111 and 112 discharge, provided with air pressure-actuated flow control valve 129. This valve is responsive to a signal transmitted via line 130 from level controller 131 connected in parallel across the high and low level points of the first pass of the sub-cooler, denoted 10c.

It is usual, in chemical manufacturing practice, to maintain a quite constant pressure in the vapor input line 109, and conventional pressure controller 134 is provided to effect this, the ambient vapor pressure being sensed vi-a line 135 and control signals then generated which are passed via line 136 to control the pitch of variable pitch fan 15, or, via line 137, to conventional actuator 138 adjusting the position of louvers 20.

The supplementation water sprays are not detailed in FIG. 20, in order to simplify the showing, however, it will be understood that an arrangement such as that shown in FIG. 2 is suitable. This comprises a sump 91 with float-controlled fresh water make-up replenishment and water delivery throttling valve 140 interposed in line 101 running via filter 132., to the spray nozzles 100 (not shown in FIG. 20). Both the drive motor 141 for pump 92 and throttling valve 140 are controlled via signal line 142 provided with a thermal switch 143 disposed in the heat exchanger air intake passage. Thus, when the intake air attains a temperature too high for effective cooling, thermal switch 143 closes the power circuit to drive motor 141 and simultaneously opens valve 140 a suitable amount to commence supplementary water spraying. As the ambient air temperature increases, valve 140 opens wider, thus supplying additional spray water to meet the heat removal requirements.

I have found that the greatest economies in heat exchanger construction are obtained by employing relatively long finned tu'be assemblies 33 (e.g., of length-to-diameter ratios above about 200) and these are readily obtainable from the fabricators; however, there has hitherto been no method of assembling and supporting the long, naturally sagging lengths. Support straps 46 are effective for tubes of any conceivable length and, thus, tube length constitutes no limitation in the utilization of my invention.

Most often, air type heat exchangers are mounted at high, quite inaccessible locations, such as at rooftop levels, for example, so that they are subjected to gusting winds and full exposure to the weather. Side walls 16 are then especially important to the maintenance of uniform air flows. Additionally, arcuately recessed plates 30 slipped in piace over finned tubes 33 in prolongation of sidewalls 16 restrict air by-passing at the tube bundle ends.

Very satisfactory protection from rain water intrusion is obtained by providing stacks 22 with internal peripherally arranged collection gutters disposed just below the fan level, fans 15 quite effectively throwing the rain water outwardly by centrifugal action, whereupon it is drained off through a conventional storm water drainage system not detailed.

Also, it is sometimes helpful to vary the air throughput of selected heat exchange units in order to safeguard against freezing the process liquid being cooled. One example is the specific apparatus detailed in FIG. 1. Here provision is made for optional reverse air flow during cold weather through the middle heat exchange unit, housed in bay B, with discharge laterally through the cut away side walls 16 into the adjacent heat exchange units housed in bays A and C. This is readily accomplished by closing the louvers 20 on the bottom of bay B, and reversing the direction of fan 15 operation for the center unit. Under these circumstances, air is drawn in from the top of the center unit, contacting the hottest process fluid first in its reverse transit through the tube bundles, after which this heated air is discharged laterally into the air intakes of the adjacent units in bays A and C as indicated by the air flow directional arrows. This tempers the air intakes to the latter, and reduces the overall heat removal for the three-unit combination assembly to a level accommodating severe cold weather conditions. It will be understood that, in warm weather, the center unit is operated with louvers 20 open and the fan draw ing air inwardly, the same as its two neighboring units, the absence of the side partitions causing little or no difficulty.

A great variety of control facilities are available to the designer in the case of air type heat exchangers, especially convenient devices being variable pitch fans 15. Also, while the foregoing description has been directed to induction fans, solely by way of example, the substitution of propulsion blowers located at the intake ends of the units is, of course, entirely practicable; however, the induction fan design has the advantage that its housed protection as shown in FIG. 4 shields motors and gear boxes from water spray damage to perhaps the fullest extent.

Also, while the most extensive present use of the construction is for process fluid cooling, the units are equally well-adapted to heating service, if this is desired. Employment of the term fluid as descriptive of the material flowing through finned tubes 33 is intended to be comprehensive of both vapors and liquids and, while substantially horizontally disposed tubes 33 have been hereinbefore specifically taught, support straps 46 can be fabricated in slightly twisted edge-to-edge slopes, so as to furnish a slight progressive downward inclination throughout successive rows of tubes insuring gravitational liquid flow therethrough, if this is desirable. Accordingly, the term generally horizontal, as used in the claims, is intended to comprehend also tubes slanted enough to be self-draining.

It is convenient to provide walkways between neighboring batteries of heat exchangers constructed according to this invention, and this has proved completely practicable for the very light maintenance work which the units require. The only regular maintenance required is lubrication supply to the individual fan gear boxes 28, and this is readily achieved by using externally located oil supply-dip stick assemblies cut-in in parallel circuit with the counterparts integral with the conventional apparatus components.

A very important advantage of the construction is that support straps 46 are sufiiciently springy so that, when disengaged from slots 60 at one end, they can be deflected laterally a sufiicient amount to permit removal of a defective tube from anywhere within the tube bundles with the prior disengagement of only a few overlying tubes being necessary to open the way. This is made possible by the relatively shallow cradle portions of the straps abutting the finned tube peripheries, which readily free the tubes from restraint when straps 46 are temporarily bent aside.

From the foregoing it will be apparent that this invention can be modified in numerous respects without departure from its essential spirit, and it is accordingly intended to be limited only within the scope of the following claims.

What is claimed is:

1. A heat exchanger comprising, in combination:

(a) a pair of tube bundles disposed in upright V arrangement within a structure provided with air throughput passages at upper and lower ends but closed off from the exterior by substantially air-impermeable side walls,

(b) each tube bundle being made up of a multiplicity of finned tubes having a length-to-diameter ratio above about 200, said tubes being disposed on substantially triangular centers in generally horizontal superposed planes,

(c) an inlet header provided with a process fluid supply -line connected in open communication with a first preselected group of terminal ends of said tubes,

(d) an outlet header provided with a process fluid removal line connected in open communication with a second preselected group of terminal ends of said tubes,

(e) support means carrying substantially the full weight of said tubes individually disposed longitudinally between said inlet header and said outlet headcr generally transverse rows of said tubes lying in a common substantially horizontal plane within said tube bundles oriented in said V arrangement, and

(f) powered means impelling air flow generally transverse said tube bundles.

2. A heat exchanger according to claim 1 wherein said tube bundles are provided at preselected intervals with partitions extending across the full widths of said bundles interiorly of said V arrangement and said powered means impelling air flow generally transverse said tube bundles are disposed in parallel relationship one with another longitudinally of said tube bundles and on opposite sides of said partitions.

3. A heat exchanger according to claim 1 provided with adjustable louvers disposed in line with the air throughput course of said heat exchanger.

4. A heat exchanger according to claim 3 provided additionally with automatic control means adjusting the degree of opening of said louvers responsive to a sensed temperature which is a function of the current heat-exchanging capability of said heat exchanger.

5. A heat exchanger according to claim 1 provided with water sprays discharging water into said air flow genera-11y transverse said tube bundles.

References Cited UNITED STATES PATENTS 2,650,802 9/1953 Huet 165-176 2,680,603 6/1954 Taylor 261 3,148,516 9/1964 Kals 261-140 FOREIGN PATENTS 900,407 7/1962 Great Britain. 904,959 9/ 1962 Great Britain.

ROBERT A. OLEARY, Primary Examiner.

T. W. STRUELE, Assistant Examiner.

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