US3083763A - Heat exchanger - Google Patents

Description

April 2, 1963 J. w. BROWN, JR

HEAT EXCHANGER Filed NOV. 18, 1959 2 Sheets-Sheet 1 HTIIIIIVI I I IN VEN TOR. JOHN w. Bko Wu, J]?- Beau/Md 11 4mm Hw awm (know-(l ATTORNEYS United States Patent Ofifice 3,933,763 Patented Apr. 2, 1963 3,933,763 HEAT EXQHANGER John W. Brown, .liz, Lakewood, (Elsie, assignor to llrown Fintnhe Company, Elyria, Ethic, a corporation of @hio Filed Nov. 18, 1959, Ser. No. 353,3(l8

8 iillairns. (Cl. 165--l59) This invention relates to heat exchangers. More particularly it relates to heat exchangers of the type embodying an outer shell of circular cross section within which is disposed a bundle of inner tubes having longitudinally extending external heat transfer fins. This application is a continuation-in-part of my copending application Serial No. 610,339 filed September 17, 1956, now abandoned.

In heat exchangers of this type, one of the heat exchange fluids flows longitudinally within the shell and outside of the finned tubes in the bundle, while the other heat exchange fluidflows within the tubes, the heat transfer fins being provided on the tubes to increase the rate of heat exchange between the fluids. The purpose of using a multiplicity of finned tubes is to obtain a large amount of heat exchange capacity in a limited space, which is particularly important in certain services. For example, heat exchangers of this type are often used as tank suction heaters or line heaters for heating heavy viscous liquids such as oil to reduce their viscosities sufficiently to enable them to be pumped from storage tanks or through pipe lines; in such service it is extremely important that the maximum heat exchange capacity be obtained in the space available, because of the dilrlculty of heating the viscous liquid and the troubles and costs of pumping it if its viscosity is not sufiiciently reduced.

Furthermore, in order to achieve maximum possible heat transfer between the fluid within the tubes and the fluid flowing along the tubes within the shell, the tubes must be positioned as close together in the bundle as possible without intermeshing of the fins on adjacent tubes. While positioning of the tubes in this manner minimizes the spaces between the tubes through which fluid might flow without coming into contact with or close to the fins at the same time it gives the bundle a generally polygonal shape transversely of the axes of the finned tubes and the shell. When for strength and economy of manufacture the shell is of circular cross section as is the almost universal practice, substantial spaces are necessarily left between the polygonal periphcry of the bundle and the circular interior of the shell. in the absence of the present invention, these wide peripheral spaces permit a substantial portion of the fluid flowing outside of the tubes to pass through the shell at such a distance from the fins on the tubes that little if any heat exchange can take place between such fluid and the fluid flowing within the tubes. This reduces the efficiency of the heat exchanger and increases the size and cost of a heat exchanger designed for a given duty. This undesirable bypassing or short circuiting of the spaces adjacent the fins where heat transfer is most effective is promoted by the surface resistance to fluid flow provided by the extended heat transfer surfaces of the fins. This factor is particularly important in heating highly viscous liquids in services of the kind described above; the resistances to fluid flow provided by the surfaces of the fins are accentuated by the high viscosity of the liquid which therefore has a pronounced tendency to seek the wider peripheral passages providing less resistance to flow; but because the liquid in such wider peripheral spaces is remote from the heat transfer fins it cannot be heated sufficiently to reduce its viscosity enough to permit easy flow. If in an attempt to avoid these problems the temperature of the fluid in the tubes is substantially increased with a view toward adding enough heat to reduce the viscosity of the liquid, not only are added heating costs involved, but also the liquid in the immediate vicinity of the finned tubes may be overheated or decomposed, with consequent possibilities of clogging the spaces between the fins with solid decomposition products or even of incurring danger of explosion from gaseous products of decomposition.

In general, in order to achieve a high rate of heat transfer in a given length of heat exchanger, it is desirable that each finned tube of the bundle be of the hairpin type comprising two straight finned tube sections joined .at one end by a return bend. Furthermore, to enable the heat exchanger to be easily assembled and disassembled for inspection, cleaning, or repair, it is desirable that the straight portions of each hairpin tube of the bundle be connected at only one end of the bundle to inlet and outlet means and to the shell, the other end of the bundle being free of connections to the shell, so that the bundle of hairpin tubes can be withdrawn or inserted as a unit from one end of the shell. The finned tubes themselves within the bundle must be readily accessible after disassembly of the heat exchanger, particularly if it is used in certain chemical services. The hairpin tubes also should be capable of moving relatively to the shell, to permit them to bow or bend along their length under the influence of heat or to move somewhat as a result of pulsations of the fluid in the tubes, thereby to prevent the development of stresses sufficient to cause breakage or leakage of the tubes.

Furthermore, the relatively light gauge heat exchange fins which make possible desired heat transfer efficiencies must not be subjected to striking or chafing against each other or any other part of the heat exchanger during such movements of the tubes relative to the shell, should not be subjected to bearing or other pressures sufiicient to damage the fins during use, and should be protected during assembly or disassembly of the heat exchanger.

The solution of these problems is particularly difficult in larger heat exchangers of this type in which the bundle of finned tubes may be twenty feet or more in length. in such cases there are dangers of excessive bending of end-supported tubes, as well as damage to the fins from this cause and from the heavy pressure applied to the fins by supporting means during use or handling; and these dangers must be guarded against.

These and other important factors have not been taken into account in prior attempts to insure that fluid within the shell of a heat exchanger will closely contact tubes in the shell containing another fluid in order to achieve maximum feasible heat exchange. For example it has been heretofore proposed to reduce the bypassing flow of fluids in the wide peripheral spaces between a cylindrical shell and a plurality of finless, bare heat exchange tubes arranged within the shell in a bundle of polygonal cross section, by surrounding the bundle with a housing of similar cross section, the tubes being fixed at both ends to tube sheets carried by the shell and the housing also being fixed at both ends to the shell and supported independently of the tubes. In such prior device, the relatively wide clearances between the housing and the tubes permits considerable bypassing or short circuiting of the fluid between the tubes and the housing, with a considerable loss of heat transfer effectiveness. Since the tubes are fixed at both ends, they are completely restrained against movements due to temperature changes or vibrations and hence subject to stresses which could cause breakage or leakage. Gn the other hand, if the tubes could move, they would contact or chafe against the independently supported housing, with consequent damage. Moreover the connections of the tubes and housing at both ends to the shell tube in the prior device make it impossible to readily disassemble such device and hence it cannot be used effectively in services which require periodic inspection cleaning or repair. These problems are accentuated if long tubes are used; added difficulties result since sagging of such long tubes causes them to come into contact With the independently supported enclosure, and increases the clearances between the upper tubes and the enclosure with a consequent increase in the above-described bypassing or short circuiting of fluid.

A general object of the present invention is to provide heat exchangers which overcome the problems and satisfy the requirements described above, while avoiding the deficiencies of prior devices. Another object of the invention is to provide heat exchangers in which the abovedescribedbypassing or short circuiting of the fluid flowing within the heatexchanger shell is substantially eliminated, and substantially all of the fluid is constrained to flow along and in close proximity to the finned tubes, and preferably within the spaces between the fins. Another object of the invention is to provide a heat exchanger in which a plurality of finned tubes disposed in an elongated shell of circular cross section are arranged in a bundle having a polygonal cross section, which is covered with a helical wrapping, preferably formed of light gauge sheet metal, closely and tightly engaging the fins at the outer periphery of the bundle to constrain the fluid to flow within the wrapping and substantially entirely between the fins of the tubes to provide increased heat exchange. It is another object of the present invention to provide such a heat exchanger in which only one end of the wrapping engages the shell adjacent the inlet into the shell, and the other end of the wrapping is open, so that the fluid passing through the shell is constrained to flow entirely within said wrapping but the spaces between the wrapping and the shell is accessible to fluid Within the shell to permit equalization of pressures on both sides of the wrapping. A further object of the invention is to provide such a heat exchanger in which the finned tubes in the bundle are hairpin tubes connected to the shell at only one end of the bundle so that the bundle of tubes can be inserted or withdrawn as a unit from one end of the shell while carrying the wrapping, and the wrapping itself can be easily removed from the bundle after withdrawal from the shell for inspection, c-leanin or repair of the finned tubes. A further object is to provide a heat exchanger having a. tube assembly, which may be of substantial length, comprising a bundle of finned tubes with separating means inside the bundle preventing intermeshing of the fins of the tubes while permittingthe tubes to be positioned in close proximity to each other, and a wrapping closely contacting fins of outer tubes in the bundle to hold the bundle of tubes together :and cooperate structurally with the fins and such separating means to increase substantially the strength of the tube assembly while permitting movements of the bundle of tubes relative to the shell in response to temperature changes, vibrations, or other causes, sufficient to prevent the development of harmful stresses. Another object of the invention is to provide a heat exchanger having such a wrapping, and also means closing wider interstices between the finned tubes and between the tubes and the wrapping to constrain the flow of substantially all fluid into the spaces between the fins. Another object is the provision of heat exchangers having these advantageous characteristics which can be manufactured readily and at reasonable costs.

Further objects and advantages of the invention will become apparent from the following description of a preferred form thereof reference being made to the accompanying drawings, in which:

FIGURE 1 is a longitudinal sectional view with parts broken away showing a preferred form of heat exchanger embodying my invention.

FIGURE 2 illustrates the assembly comprising the tube bundle'of the heat exchanger of FIGURE I removed from the shell, and with parts broken away.

FIGURE 3 is a transverse sectional view taken along line 3-3- of FIGURE 1.

FIGURE 4 is an enlarged sectional view showing the sealing means and means for closing spaces between the tubes in the bundle; and

FIGURE 5 is a fragmentary sectional view along line 55'- of FIGURE 4 and to the same scale.

As shown in FIGURE 1 of the drawings, one preferred form of heat exchanger embodying the present invention comprises-a cylindrical shell 10 having an open end provided with a flange 11 and a closed end 12 to which a fluid connection 13 is secured. Another fluid connection 14 is made laterally through the wall adjacent the open end thereof. One of the connections constitutes an inlet for fluid to the shell while the other constitutes the outlet. Ordinarily the lateral connection 14 is utilized as the inlet and the end connection 13 is the outlet, but the connections may be reversed if desired. In either event the flow of fluid between the connection 13 and 14 is longitudinally of the shell 10. The shell is mounted upon arcuate supporting members 15.

Heat exchange is effected by causing the fluid within the shell to flow over and along a bundle indicated in general at 16 and made up of a plurality of tubes 17 having straight portions 18 that are provided with parallel longitudinally extending radial fins on the exterior thereof. In the form of the invention shown in the drawing, the tubes are in the form of hairpins, the straight finned portions 18- being connected by return bends 19, and the straight portions 18 of tubes 17 in the bundle being parallel. The ends 21. of the tubes 17 opposite the return bends project beyond the finned portions 18 and are secured as by rolling to a tube sheet 23. The tube sheet 23 is clamped between the flange 11 on the shell 10 and a flange 24 on the header 25, appropriate gaskets or other seals being disposed between the tube sheet and the flanges to provide leakproof joints.

The header 25 may be of known design and includes an inlet pipe 27 which leads to the inlet chamber 28 and is used to supply fluid to the interior of the tubes 17. The inlet chamber 28 constitutes the upper half of the space within the header and is separated from the discharge chamber 29, which constitutes the lower half of the space within the header, by means of a partition 31 preferably formed integrally with the header 25 and engaging a sealing gasket 32 on the surface of tube sheet 23. A return connection 34 formed in the header 25 is in communication with the discharge chamber '29 and provides for connection to a return conduit for the fluid that has p-assedwthrough the finned tubes from the inlet chamber 28 to the discharge chamber 29. Heat exchangers of this sort may be used with a wide variety of fluids; for example the illustrated heater may be used to advantage to heat viscous fluids such as oil passing through a pipe line, in which case steam is supplied to the conduit 27 and condensate returned to the connection 34.

As shown particularly in FIGURE 3, the finned tubes in the bundle are preferably disposed as close together as possiblein substantially tangential relation to cause the fluid flowing within the shell and through the bundle on the exterior of the tubes to pass close enough'to the external surfaces of the tubes or to the fins to be in good heat exchange relation thereto. Advantageously, the finned tubes are kept from intermeshing by separating means tangentially contacting fins of adjacent tubes in the bundle; in the preferred form such separating means are bands 36 wrapped around the fins of individual tubes and contacting fins of adjacent tubes, as described and claimed in my prior Patent No. 2,499,901 issued March 7, 1950. It is to be noted that the bands 36 offer substantially no obstruction to the longitudinal flow of fluid through the bundle and that there are no other supports, bafiles or the like in the spaces between the fins of the finned tubes in the bundle, so that longitudinal flow of the fluid through such spaces is unimpeded, while the tubes are so closely spaced that little if any transverse flow takes place within the bundle. With the tubes arranged in this fashion, the cross sectional shape of the bundle is generally polygonal, as shown in FIGURE 3; that is, lines tangent to the outer fins in the bundle would define a polygon. As also shown in FIGURE 3, when the polygonal bundle is located within the round cylindrical shell, substantially wide spaces as indicated at 37, 38, and 39 exist between the periphery of the bundle and the interior surface of the shell. Fluid flowing through these spaces would be heated only slightly if at all, by the fluid within the finned tubes and yet a large percentage of the fluid flowing through the shell would flow through these spaces in a heat exchanger of conventional construction.

According to the present invention, however, the bypassing or short circuiting of the fluid through the peripheral spaces between the exterior of the tube bundle and the interior surface of the shell is eliminated, and substantially all of the fluid is constrained to flow longitudinally along and through the tube bundle in close proximity to the finned tubes making up the bundle. This is accomplished in the preferred form of the invention shown herein by providing an open ended wrapping around the exterior of the bundle in the zone of the finned portions 18 of the tubes and by causing the fluid entering the inlet id to flow within the wrapping. The wrapping preferably is composed of light gauge sheet metal, although it may be made of any other suitable impermeable material, such as a sheet plastic, that will withstand the temperatures at which the heat exchanger operates and which will not be attacked by the fluid flowing through the shell. The wrapping material is thin, flexible and tough enough so that it can be wrapped tightly around the tube bundle so as to conform to the polygonal shape thereof, and may be held in place by one or more straps indicated at 43 and 44 in FIGURES 1 and 2. The thickness of the wrapping and the straps is necessarily somewhat exaggerated in the drawing. Preferably a strip 45 of wrapping material is wound helically around the bundle as shown in the drawings with an overlapping seam as shown at 46. The seam may be sealed by welding, brazing, soldering, heat sealing or the like, depending on the material used; however with a helical wrapping and an overlapping seam as shown, it is ordinarily unnecessary to seal the seam, because there is no substantial pressure difference between the fluid on the inside and the fluid on the outside of the wrapping and because the direction of the overlap is such that the internal edges of the strip face downstream (i.e., away from the inlet 14 and toward the outlet 13) so that the flow of fluid tends to draw fluid into the wrapping rather than force it out of the wrapping. This type of seam results when the helical strip is wound from the end of the bundle adjacent the inlet to the shell toward the end of the bundle near the outlet from the shell.

in order substantially to prevent fluid from flowing through the spaces 37, 38, and 39 between the exterior of the wrapping 42 and the interior of the shell 16, sealing means is disposed at one end of the wrapping, preferably adjacent the inlet for the fluid into the shell which is the conduit 14- in the embodiment shown.

The sealing means 5i"? comprises a ring-shaped metal member 51 having an interior opening 52 conforming to the polygonal shape of the exterior of the wrapping 42, and an external tapered conical surface 53 facing away from the connected end of the tube bundle 16. Member 51 may be fixed to the exterior of the wrapping, as by welding or bolting it. A cooperating annular metal member 54- is fixed to the inner surface of the shell by welding or other suitable means; it has an internal conical surface 55 facing toward the connected end of tube bundle 16. Surface 55 surrounds but is spaced from the conical sur face 53 of member 51 and the surfaces 53 and 55 are (iii sloped at different angles so that the space 56 between the conical surfaces 53 and is tapered or wedge-shaped, being widest at the end nearest the connected end of the tube bundle. A suitable sealing ring 57 formed of resilient material, such as an O ring, is disposed in this space between these two conical surfaces 53 and 55 of members 51 and 54. It is apparent that the sealing means 50 is such that the parts of it can be easily assembled and disassembled when the tube bundle is inserted or withdrawn from the open end of the shell 10 in assembly or disassembly of the heat exchanger. Moreover, the pressure of the fluid entering the shell tends to drive the sealing ring 57 more tightly into the wedge-shaped space 56 between members 51 and 54, thus enhances the sealing action.

To aid the wrapping 42 in directing the flow of fluid into the spaces etween the fins and prevent bypassing or short circuiting of such spaces, means may be provided substantially to fill or block other spaces of substantial width or cross section lying within the enclosure formed by the wrapping 42-. For example in the illustrated embodiment and as shown in FIGURES 3 and 4 the relatively wide spaces 61 within the bundle of finned tubes and defined by the fin peripheries of the two innermost rows or" finned tubes in the bundle which are not staggered relative to each other, are substantially closed by filler means 62; and the spaces 63 of generally triangular cross section defined by the wrapping and the fin peripheries of the finned tubes at the outer periphery of the bundle are substantially closed by filler means 64. Vfhile these filler means may take various forms and have a variety of cross sections including those of circular configuration, it is most convenient and economical that they be formed of rods or bars of metal or other suitable materials of sizes and cross-sectional shapes as will closely fit, extending longitudinally through in such spaces as shown.

As is shown to advantage in FIGURES 4 and 5, moreover, t e filler bars 62 and 64 are restrained against movement longitudinally of the tube bundle 16 by being con nected to the member 51 of the sealing means 50. The end of each of the filler bars 62 adjacent the inlet into the shell is fixed to a member 65 which may be suitably connected, as by welding or bolting, to the member 51. Each of the filler bars 64 at the periphery of the tube bundle is fixed to a lug 66 at its end adjacent the shell inlet 14; such lug extends radially outwardly to member 51 to which it is connected, as by welding or bolting. The filler bars are thus secured against movement longitudinally of the finned tubes so that the liquid flowing through the bundle of finned tubes will not force such filler bars out of the spaces between the tubes.

It will be evident that with the arrangement described above, all fluid entering the shell It) through the conduit 14 is constrained to flow within the wrapping 42, and because of the fluid flow-directing functions of such Wrapping and of the filler bars 62, and 64, substantially all such fluid is constrained to flow within the spaces between the fins on the finned tubes.

The spaces 37, 38, and 39 outside of the periphery of the tube bundle are effectively blocked against any flow of fluid by the wrapper 42. and the sealing means 5%; wt er spaces within the periphery of the tube bundle, such as spaces st and 63, re also blocked against any substantial flow of fluid by the filler bars 62 and 64.

' However, since the end of the wrapping 42 remote from sealing means 5% is not connected to the shell, the fluid within the shell fills the spaces between the wrapping and the interior of the shell, so that the pressures on the interior and the exterior of the wrapping are equalized. Consequently the wrapping can be made of light gauge material. Since there is no substantial movement of fluid within the shell on the exterior of the wrapping the presence of the fluid in the peripheral spaces outside of the wrapping has negligible effects on the heat exchange capacities of the heat exchanger; in fact the fluid in these places acts primarily as an insulator to conserve heat which would otherwise be wasted.

1 In order to support the unconnected end of tube bundle 16 within the shell 10 duringoperation, and to prevent damage to the wrapping 42 when the exchanger is being assembled or when the tube bundle is being withdrawn for inspection, cleaning, or repair, I preferably provide asupporting shoe 67 adjacent the end of the wrapping 42 remote from the sealing means 50. Shoe 67 may be held in position by being spot welded or otherwise secured to strap 43 and has an arcuate bottom surface 68 and an upper surface 69 that engages the lower portion of the wrappin and distributes the weight of the tube bundle widely over the downwardly extending fins. on the tubes at the bottom of the bundle. The shoe thus provides a surface which can be easily slid along the bottom of the interior of the shell when the tube bundle is being inserted into or withdrawn from the shell.

The other or connected end of the tube bundle 16 is supported by the ends 21 of the tubes 17 which are secured to the tube sheet 23.

From the foregoing description of a preferred form of the invention it will be evident that I have provided a heat exchanger of the type embodying a shell and a bundle of longitudinally finned tubes in which the heat exchange potentials provided by the extended heat transfer surfaces of the fins are substantially fully utilized and to a far greater extent than otherwise possible.

Ordinarily, fluids, and particularly heavy viscous fluids, have a tendency to bypass the narrow spaces between the heat transfer fins because the extended heat transfer surfaces offer higher surface resistance to the flow of fluid than do wider spaces which have less surface area in relation to volume; hence the fluid would tend to flow through wider spaces suchas peripheral spaces 37, 38, and 39 and thelarger intrabundle spaces such as 61 and 63 if they were unblocked, with most passing through spaces 37, 38, and 39 because they are widest. In the heat exchanger illustrated, however, the wide peripheral spaces are blocked by the sealing means and the wrapper 42, and all fluid entering the shell through inlet 14 of the shell is required by the sealing means 50 to flow'through the wrapping 42. The wrapping 42 of thin impermeable material closely contacts and bears against the outer fins of the finned tubes at the periphery of the bundle and therefore conforms closely to the shape of thebundle; it provides no clearances within the wrapping other than the spaces between the fins and the openings resulting from the circular cross sections of the finned tubes tangentially arranged relative to the wrapping and to each other. And, as described above, the preferably used filler bars 62 and 64 substantially close all passages through which the fluid passing within the wrapping could bypass the spaces between the fins. Since the Wider spaces outside the periphery and within the periphery of the bundle are thus blocked by the wrapping 42, sealing means 50 and the filler bars 62 and 64, substantially all the fluid flowing through the shell is caused to flow in excellent heat transfer relation through the spaces between the fins of the finned tubes. The heat exchange inefficiencies which would result from bypassing or short circuiting of these spaces by the fluid are eliminated, the effectiveness of the extended heat transfer surfaces of the fins is substantially fully utilized, and the heat exchange efficiency of the heat exchanger is substantially increased as compared to prior heat exchangers lacking the present invention.

In addition to the above advantages of directing fluid flow to achieve maximum heat exchange eificiency, the wrapping of the invention provides other important and unique advantages. Thus the wrapping 42 around the bundle of finned tubes and the bands 36 around individual finned tubes cooperate with the finned tubes to form a strong coherent lightweight tube assembly structure; thebands in effect tangentially hold the individual 8 finned tubes apart only sufficiently so that their fins cannot intermesh or entangle to become damaged or impede the flow of fluid between the fins, while themselves offering little resistance to fluid flow; the tightly wound wrapping 42 in effect holds the entire bundle of finned tubes together in as close relation as possible consistent with the separating action of the bands 36. This holding pressure exerted by the wrapper is substantially equally distributed over the entire length of the tube bundle, through the outer fins of the outer tubes and through contact of the bands 36 with the fins of adjacent tubes. There is no localized pressure which can crush, twist or otherwise damage the fins and impede fluid flow or reduce heat exchanger efficiency. The wrapper 42 and bands 36 also operate to minimize sagging or deflection.

of the tube bundle as a whole, and to prevent movement of the finned tubes relative to each other in the bundle due to individual tube sagging or other reasons, which could cause damage to the fins. This advantage is particularly important in larger heat exchangers, some of which may be twenty-five feet or more in length and having finned tube sections twenty feet long or longer. Therefore, despite the fact that the fins are individually relatively fragile and the wrapper 42 itself is formed of such thin, flexible material that it cannot form an independent, self-supporting structure, the wrapper 42, bands 36 and fins cooperate to utilize the tensile strength of the wrapper and the considerable aggregate strength of the fins to cause them to act as structural elements providing a. unitary bundle or finned tubes having a beam structure of considerably greater transverse strength than the total of the individual strengths of the tubes.

The wrapping 42- also protects the relatively fragile fins during handling of the tube bundle in the manufacturing plant, insertion for assembly of the bundle of tubes into the shell of the heat exchanger, or withdrawal of the bundle from the shell for disassembly. The invention provides particular advantages when employed in heat exchangers having a bundle of hairpin tubes so designed that the tubes can be inserted into or withdrawn from one end of the shell. Since the wrapping is carried by the hairpin tubes and has flat seams with no projecting joints or flanges, it can be easily moved into or out of the shell from one end of the shell; during such movement, it aids in holding the tube bundle together and provides considerable strength and protection for the tube bundle, while adding little to the weight of the assembly. Furthermore the wrapper can easily be unwrapped or removed from the bundle of tubes after removal from the shell to expose the finned tubes, if desired. The easilydisassembled heat exchangers made possible by the nvention have great utility in services in which they must be periodically taken apart for inspection, cleaning or repair, as in services where highly viscous heavy fluids such as oils, or certain chemicals are heated. The strength of tube bundle, fin protection and other advantages described in connection with assembly and disassembly are exceptionally important in larger heat exchangers of the sizes mentioned above.

The widely distributed bearing of the wrapper 42 along the length of the finned tubes also provides other substantial benefits in the type of heat exchanger having a bundle of hairpin tubes which is connected at only one end of the bundle to the shell. In such an exchanger, the unconnected end of the bundle must be supported from the shell since the connections of the tubes at the other end of the shell cannot be made strong enough as a practical matter to support the laterally projecting hairpin tubes which in certain services may be as much as twenty feet or more long. Since the wrapping has such widely distributed bearing over the bundle, supporting pressure from a supporting member bearing on the Wrapper near the unconnected end of the tubes is distributed over a substantial area of the bundle of finned tubes. This avoids the possibility of crushing, bending aces res b or otherwise damaging the fins in a localized area which could occur it the supporting member bore directly on the fins.

The wrapping also provides substantial advantages because it does not harmfully restrict necessary movements of the bundle of finned tubes as a whole relative to the shell. Thus, bending or bowing of the bundle of finned tubes may tend to occur due to heat expansion of the metal of the tubes during operation of the heat exchanger; this tendency is particularly prevalent in heat exchangers in which the tubes are of the hairpin type and connected only at one end of the exchanger. Similarly, vibrations, such as those occurring from fluid or pump pulsations, tend to cause movement of the tubes relative to the shell. If the tubes were completely restrained against such movements, damaging stresses causing fractures and leakage could occur. However, since the wrapping is carried by the bundle of finned tubes, is of light weight, and can move with the bundle as a whole, particularly when the wrapping is formed of a helical strip of metal providing some sliding movement of the overlapping metal edges at the helical seam so that the wrapping as a whole can deflect somewhat, the bundle of tubes as a whole can move sumciently to relieve harmful stresses which otherwise could cause damage. Moreover the fins cannot be damaged by striking or chafing against the wrapping or against the tins of adjacent tubes, since there is little if any individual movement of the tubes relatively to the wrapper or to each other. Similar advantages obtain it the tubes tend to deflect somewhat due to their weight and length, as often occurs in heat exchangers having exceptionally long tubes.

Furthermore, such movement or deflection of the tubes does not form any wider clearance between the tubes and the wrapper through which the fluid could bypass the spaces between the fins, because the wrapper is carried by, tightly encloses, and moves with the tube bundle.

The helical wrapping, and the filler bars, which provide such important advantages may be incorporated into heat exchangers at low costs Without using special equipment, tools or dies. These parts may be made of readily available materials without high fabrication costs; therefore it is not necessary to employ pressed or cast parts which would be excessively costly at the small production runs obtaining in the heat exchanger field.

Furthermore, the wrapping provides such protection, strength, and wide distribution of supporting and handling loads on the finned tubes as described above that the fins and even the tubes themselves may be made of lighter gauge, and hence less expensive, metals than would be the case in the absence of the wrapping.

The present invention therefore provides heat exchangers in which substantially all of the fluid flowing through a shell tube is caused to pass through the spaces between the fins of the bundle of finned tubes, thus substantially fully utilizing the heat transfer potentialities of the fins and making possible exceptionally high heat transfer eficiencies. Moreover such a heat exchanger may be of the type in which hairpin finned tubes are connected at one end only to the shell, so that the exchanger can be readily disassembled for inspection, cleaning or repair by withdrawing from one end of the shell the bundle of finned tubes carrying the wrapper, and then stri ping the wrapper from the tubes; this is extremely important when the heat exchanger is used in services where it must be periodically checked. Since there is no fluid passing through spaces at a considerable distance from the fins there is no need to heat such fluid by the use of tube temperatures so high as to cause deterioration to or decomposition of the fluid adjacent the fins, or damage to the heat exchanger itself.

Because the wrapper cooperates to form a strong strucural assembly of tubes, which however, can move or deflect as necessary to relieve temperature, vibratory or other stresses, and since adequate support and protection it) are provided to the fins and finned tubes during assembly, disassembly and operation, the durability and life of the fins and the heat exchanger as a Whole are greatly increased. These advantages are made possible at little additional cost.

Those skilled in the art will appreciate that the invention may be adapted to other types of heat exchangers embodying bundles of longitudinally finned tubes, and that various changes and modifications can be made in the invention without departing from the spirit and scope thereof. The essential characteristics of the invention are defined in the appended claims.

I claim:

1. A heat exchanger CG; rprising an elongated shell of circular cross section; an inlet adjacent one end of said shell; an outlet adjacent the other end of said shell; a bundle of elongated heat exchange tubes within said shell, each of said tubes having a plurality of spaced, longitudinally extending, generally radially projecting fins thereon, said tubes being positioned in said bundle so that the peripheries defined by the outer edges of the fins of said tubes are in substantially tangential, close, substantially parallel relationship and the outermost edges of fins of outer tubes in said bundle define a bundle periphery which is generally polygonal in cross section and which causes peripheral spaces to exist between said bundle periphery and the interior of said shell; means for passing fluid longitudinally inside said finned tubes; means for causing fluid flowing outside of said tubes through said shell from said inlet to said outlet to pass in close proximity to said tubes in said bundle and for preventing said fluid from flowing through said peripheral spaces, said means comprising an open ended wrapping on said bundle made up of a strip of flexible, thin, impermeable sheet material tightly wound helically around and conforming to the generally polygonal shape of said bundle with the helical turns of the strip overlapping and the internal edges of said turns facing away from said inlet and toward said outlet, said helically wound strip engaging and being entirely supported by the outermost fins of the outer tubes of said bundle and forming with'the tubes in the bundle a beam structure having greater transverse strength than the total of the strengths of the individual tubes in the bundle, said wrapping alone being incapable of acting as an independent self-supporting structure; and means connecting said wrapping to the interior of said shell to block the flow of fluid through the spaces between the exterior of said wrapping and the interior of said shell.

2. A heat exchanger comprising an elongated shell of circular cross section; a shell inlet adjacent one end of said shell; a shell outlet adjacent the other end of said shell; a bundle of elongated hairpin-shaped heat exchange tubes within said shell, each of said tubes comprising two finned sections having a plurality of spaced longitudinally extending, generally radially projecting fins thereon, said tubes being positioned in said bundle so that the peripheries defined by the outer edges of said fins are in substantially tangential, close, substantially parallel relationship and the outermost edges of fins of outer tubes in said bundle define a bundle periphery which is generally polygonal in cross section and which causes peripheral spaces to exist between said bundle periphery and the interior of said shell; inlet and outlet means located at one end only of said shell for passing fluid longitudinally through said finned tubes; means for causing fluid flowing outside of said tubes through said shell from said shell inlet to said shell outlet to pass in close proximity to said tubes in said bundle and for preventing said fluid from flowing through said peripheral spaces, said means comprising an open ended wrapping on said bundle made up of a strip of flexible thin impermeable sheet material tightly Wound helically around and conforming to the generally polygonal shape of said bundle with the helical turns of the strip ovelapping and the internal edges of said turns facing away from said shell inlet and toward said shell outlet, said helically wound strip engaging and being entirely supported by the outermost fins of the outer tubes of said bundle and cooperating with said tubes in said bundle to form a beam structure having greater transverse strength than the total of the strengths of the individual tubes in the bundle, said wrapping along being incapable of acting as an independent self-supporting structure; and means connecting said wrapping to the interior of said shell to block the flow of fluid through the spaces between the exterior of said wrapping and the interior of said shell.

3. A heat exchanger comprising an elongated shell of circular cross section; an inlet adjacent one end of said shell; an outlet adjacent the other end of said shell; a bundle of elongated heat exchange tubes within said shell, each of said tubes having a plurality of spaced longitudinally extending, generally radially projecting fins thereon, said tubes being positioned in said bundle so that theperipheries defined by the outer edges of said fins are in substantially tangential, close, substantially parallel relationship and the outermost edges of fins of outer tubes in said bundle define a bundle periphery which is generally polygonal in cross section and which causes peripheral spaces to exist between the exterior periphery of said bundle and the interior of said shell; separating means engaging the outer edges of fins of adjacent tubes within said bundle to prevent intermeshing of the fins of adjacent tubes while leaving unobstructed the spaces between the fins; means for passing fluid longitudinally inside said finned tubes; means for causing fluid flowing outside of said tubes through said shell from said inlet to said outlet to pass in close proximity to said tubes in said bundle and for preventing said fluid from flowing through said peripheral spaces, said means comprising an open ended wrapping on said bundle made up of a strip of flexible, thin, impermeable, sheet material tightly wound helically around. and conforming to the generally polygonal shape of said bundle with the helical turns of the strip overlapping and the internal edges of said turns facing away from said shell inlet and toward said shell outlet, said helically wound strip engaging and being entirely supported by the outermost fins of the outer tubes of said bundle, said wrapping alone being incapable of acting as an independent self-supporting structure; band m ans. encircling said helically wound wrapping and holding it tightly in place on said bundle, said band means, said'wrapping, and said separating means cooperating with the tubes in the bundle to form a beam structure havinggreater transverse strength than the total of the strengths of the individual tubes in the bundle; and means connectingsaid wrapping to. the interior of said shell to 7 block the flow of fluid through the spaces between the exterior of said wrapping and the interior of said shell.

4-. A heat exchanger comprising an elongated shell of circular cross section; a shell inlet adjacent one end of said shell; a shell outlet adjacent the other end of said shell; a bundle of elongated hairpin-shaped heat exchange tubes within said shell, each of said tubes comprising two finned sections having a plurality of spaced, longitudinally extending, generally radially projecting fins thereon, said tubes being positioned in said bundle so that the peripheries defined by the outer edges of the fins are in substantially tangential, close, parallel relationship and the outermost edges of fins of outer tubes in said bundle define a bundle periphery which is generally polygonal in cross section and which causes peripheral spaces to exist between said bundle periphery and the interior of said shell; separating means engaging the outer edges of fins of adjacent tubes within said bundle to prevent intermeshing of the fins of adjacent tubes while leaving unobstructed the spaces between the fins; inlet and outlet means located at one end only of said shell for passing fluid longitudinally through said finned tubes; means for causing fluid flowing outside of saidtubes through said shell from said shell inlet to said shell outlet to pass, in close proximity to said tubes in said bundle and for preventing said fluid from flowing through said peripheral spaces, said means comprising an open ended wrapping on said bundle made up of a strip of flexible, thin, impermeable, sheet material partly wound helically around and conforming to the generally polygonal shape of said bundle with the helical turns of the strip overlapping and the internal edges of saidturns facing away from said shell inlet and toward said shell outlet, said helically wound strip engaging and being entirely supported by the outermost fins of the outer tubes of said bundle, said wrapping alone being incapable of acting as an independent self-supporting structure; band means encircling said helically wound wrapping and holding it tightly in place on said bundle, said band means, said wrapping, and said separating means cooperating with the tubes in the bundle to form a beam structure having greater strength than the total of the strengths of the individual tubes in the bundle; andmeans connecting said wrapping to the interior of said shell to block the flow of fluid through the spaces between the exterior of said wrapping and the interior of said shell.

5. The apparatus of claim 1 comprising filler means within said wrapping, contacting the outer edges of the fins of and leaving unobstructed the spaces between fins, to block spaces between the peripheries defined by the outer edges of fins of adjacent finned tubes.

6. The apparatus of claim 5 in which said filler means block spaces between the interior surface of the wrapping and the peripheries defined by the outermost edges of adjacent outer finned tubes.

7. The apparatus of claim 5 in which said filler means block the spaces between the peripheries defined by the outer edges of adjacent finned tubes within said bundle.

8; The apparatus of claim 5 in which said filler means block spaces between the inner surface of said wrapping and the peripheries defined by the outer edges of adjacent outer finned tubes, and also block spaces between the peripheries defined by the outer edges of adjacent finned tubes within said bundle.

References Cited in the file of this patent UNITED STATES PATENTS 1,669,291 Dean May 8, 1928 1,790,151 How Jan. 27, 1931 1,995,407 Walker Mar. 26, 1935 2,183,160 Coulter et a1 Dec. 12, 1939 2,346,104 Gunter Apr. 4, 1944 2,499,901 Brown Mar. 7, 1950 2,520,755 Brown Aug. 29, 1950' 2,910,275 Munro Oct. 27, 1959

Claims (1)

1. A HEAT EXCHANGER COMPRISING AN ELONGATED SHELL OF CIRCULAR CROSS SECTION; AN INLET ADJACENT ONE END OF SAID SHELL; AN OUTLET ADJACENT THE OTHER END OF SAID SHELL; A BUNDLE OF ELONGATED HEAT EXCHANGE TUBES WITHIN SAID SHELL, EACH OF SAID TUBES HAVING A PLURALITY OF SPACED, LONGITUDINALLY EXTENDING, GENERALLY RADIALLY PROJECTING FINS THEREON, SAID TUBES BEING POSITIONED IN SAID BUNDLE SO THAT THE PERIPHERIES DEFINED BY THE OUTER EDGES OF THE FINS OF SAID TUBES ARE IN SUBSTANTIALLY TANGENTIAL, CLOSE, SUBSTANTIALLY PARALLEL RELATIONSHIP AND THE OUTERMOST EDGES OF FINS OF OUTER TUBES IN SAID BUNDLE DEFINE A BUNDLE PERIPHERY WHICH IS GENERALLY POLYGONAL IN CROSS SECTION AND WHICH CAUSES PERIPHERAL SPACES TO EXIST BETWEEN SAID BUNDLE PERIPHERY AND THE INTERIOR OF SAID SHELL; MEANS FOR PASSING FLUID LONGITUDINALLY INSIDE SAID FINNED TUBES; MEANS FOR CAUSING FLUID FLOWING OUTSIDE OF SAID TUBES THROUGH SAID SHELL FROM SAID INLET TO SAID OUTLET TO PASS IN CLOSE PROXIMITY TO SAID TUBES IN SAID BUNDLE AND FOR PREVENTING SAID FLUID FROM FLOWING THROUGH SAID PERIPHERAL SPACES, SAID MEANS COMPRISING AN OPEN ENDED WRAPPING ON SAID BUNDLE MADE UP OF A STRIP OF FLEXIBLE, THIN, IMPERMEABLE SHEET MATERIAL TIGHTLY WOUND HELICALLY AROUND AND CONFORMING TO THE GENERALLY POLYGONAL SHAPE OF SAID BUNDLE WITH THE HELICAL TURNS OF THE STRIP OVERLAPPING AND THE INTERNAL EDGES OF SAID TURNS FACING AWAY FROM SAID INLET AND TOWARD SAID OUTLET, SAID HELICALLY WOUND STRIP ENGAGING AND BEING ENTIRELY SUPPORTED BY THE OUTERMOST FINS OF THE OUTER TUBES OF SAID BUNDLE AND FORMING WITH THE TUBES IN THE BUNDLE A BEAM STRUCTURE HAVING GREATER TRANSVERSE STRENGTH THAN THE TOTAL OF THE STRENGTHS OF THE INDIVIDUAL TUBES IN THE BUNDLE, SAID WRAPPING ALONE BEING INCAPABLE OF ACTING AS AN INDEPENDENT SELF-SUPPORTING STRUCTURE; AND MEANS CONNECTING SAID WRAPPING TO THE INTERIOR OF SAID SHELL TO BLOCK THE FLOW OF FLUID THROUGH THE SPACES BETWEEN THE EXTERIOR OF SAID WRAPPING AND THE INTERIOR OF SAID SHELL.

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