US3256932A

US3256932A - Heat exchanger tube arrangement

Info

Publication number: US3256932A
Application number: US249152A
Authority: US
Inventors: Schlichting John
Original assignee: Babcock and Wilcox Co
Current assignee: Babcock and Wilcox Co
Priority date: 1963-01-03
Filing date: 1963-01-03
Publication date: 1966-06-21
Anticipated expiration: 1983-06-21

Description

3 Sheets-Sheet 1 Filed Jan. 5, 1963 FIG. 2

FIG. 1

INVENTOR.

John Schlichfing ATTORNEY June 21, 1966 J. SCHLICHTING HEAT EXCHANGER TUBE ARRANGEMENT 3 Sheets-Sheet 2 Filed Jan. 5, 1963 FIG. 3

INVENTOR. John Schlichring June 21, 1966 J, SCHLICHTING 3,256,932

HEAT EXcHANGER TUBE ARRANGEMENT Filed Jan. :3, 1963 5 Sheets-Sheet 5 FIGURE 6 United States Patent 3,256,932 HEAT EXCHANGER TUBE ARRANGEMENT John Schlichting, Akron, Ohio, assignor to The Babcock &-Wilcox Company, New York, N.Y., a corporation of New Jersey Filed Jan. 3, 1963, Ser. No. 249,152 Claims. (Cl. 165-163) This application is a continuation-in-part of the copending application, now Patent No. 3,112,735 issued December 3, 1963, entitled Liquid Metal Heated Vapor Generator, to John Schlichting et al.

This invention relates in general to an arrangement of tubes for a heat exchanger and more particularly to the arrangement of a bundle of helically coiled tubes in which the developed lengths of all of the tubes may be substantially equal irrespective of their position in the bundle.

In recent years developments in heat exchanger design have become increasingly directed to the problem of providing the maximum amount of tubular heating surface in heat exchangers, particularly those of the shell and tube indirect heat transfer type, while at the same time keeping the total number of tubes to a minim-um and also in minimizing the number of different tube contours. Another problem has been that of Obtaining a tube arrangement which affords the most efficient transfer of heat from one fluid to another. Further, because of the nature of certain of the heating fluids employed, such as liquid metals, there has been a tendency to avoid the use of tube sheets because of the corrosion ditfieulties they present.

Shell and tube-type heat exchangers are among the most common varieties of indirect heat transfer apparatus employed in transferring heat from one (fluid to another. In such heat exchangers straight tubes extending between a pair of spaced tube sheets are usually utilized with the result that the length of the tubes and the heating surface is fixed by the longitudinal distance between tube sheets.

Further, the thickness of the tube sheets is dependent on the number of tubes to be secured within a given tube sheet area since, as the number of tube holes or openings in a tube sheet increases, the ligament is reduced and the sheet thickness 'must be correspondingly increased to provide adequate structural strength to account for the loss of metal resulting from the tube hole drillings. Another disadvantage in this type of heat exchanger stems from the less than optimal heat transfer characteristics of the fluid flowing over the tubes or as occasioned by laning and recirculation of the ifi-uid within particular zones of the tube bundle, which thereby precludes mixing of the fluid stream.

It is a primary object of this invention to provide a heat exchanger tube bundle arrangement in which the tubes are helically Wound in coils of different diameters to afford tubes of substantially equal developed length and heating surface.

Another object of the invention is to provide a tube bundle'mploying a minimum number of tubes of maximum length within a given size of shell.

An additional object is to furnish a tube bundle assembly which does not require the use of conventional flat tube sheets to secure the tubes at their inlet and outlet ends.

A further object is to disclose a tube bundle arrangement which will provide the optimum of heat transfer characteristics as applying to both the heating and the heated fluid.

. 24 between the container and the shell.

3,256,932 Patented June 21, 1966 A still further object is to provide a helically coiled tube bundle having the tubes arranged in vertically extending, concentric circular rows wherein the tubes may be uniformly spaced both in the longitudinal and transverse directions so the side and back spacings may be uniform throughout the bundle.

Accordingly, the present invention provides a tube arrangement for a heat exchanger in which a vertically extending bundle of helically coiled tubes is disposed within a shell or container. The bundle is made up of a number of groups of tube coils with each group forming a concentrically arranged vertically extending circular row.

The pitch of the tubes within the bundle is substantially equal for all of the rows. The lead, however, while-being the same for the tubes in a single circular row, varies from row to row in direct proportion to the diameter of the row.

Additionally, the present invention supplies an arrangement in which each tube in the bundle has the same angle of lead irrespective of its position within the bundle.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there has been illustrated and described preferred embodiments of the invention.

Of the drawings:

FIG. 1 is a vertical cross-sectional view of a vapor generator which embodies this invention, taken along line 1 -1 of FIG. 2;

FIG. 2 is a'horizontal cross-sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a simplified schematic view showing a typical arrangement of helically wound tubes arranged according to this invention; p

FIG. 4 is an enlarged sectional view of the encircled portion of the tube bundle designated by the numeral 4 in FIG. 1;

'FIG. 5 is a greatly enlarged sectional view of the encircled portion designated by the numeral 5 in FIG 1; and

FIG. 6 is a perspective view, partially broken away, showing a modification of the present invention.

Referring now to the drawings, FIG. 1 shows a vertically elongated cylindrical shell 12 having top and bottom generally elliptically-

shaped heads

14, 16, respectively, integrally attached thereto to form a pressure vessel 10. A cylindrically-shapedcontainer 18 with an open upper end 20 and a closed, generally elliptical lower end 22 is located within the pressure vessel 10, concentric with its vertical axis. The wall thickness of the container 18 is considerably less than that of the shell of the pressure vessel 10.

The container 18 is closely spaced laterally from the pressure vessel shell 12 to form a narrow annular space In addition, the container is arranged along the vertical axis of the pressure vessel so that

open spaces

26 and 28, of considerable volume, are provided between the upper and

lower ends

20, 22 of the container and the

heads

14, 16 of the pressure vessel, respectively. These

open spaces

26, 28 in combination with annular space 24 form a continuous gas space 30 which completely envelops the container.

A conduit 32 is arranged within the container 18 concentric with the vertical axis of the pressure vessel 10.

each of the circular rows in the bundle.

The conduit 32 is circular in cross section and has a diameter in this instance shown as approximately one-third that of the container 18 so that an annular-shaped chamber 34 is formed between the conduit and the wall of container 18. The vertical dimension of the conduit 32 is less than that of the container 18 and the conduit is arranged to provide an upper and a lower

open space

36, 38, respectively, within the container at opposite ends of the conduit. 7

A bundle of closely spaced, helically wound tubes 40 is arranged within the annular-shaped chamber 34 formed by the conduit 32 and the container 18. The vertical height of the bundle of tubes 40 is approximately equal to and extends for the length of the conduit 32. The tubes 40 are disposed in a number of concentric, vertically arranged circular layers or rows. The configuration is such that each of the tubes 40 in the bundle is helically wound so that it appears in but one of the circular rows. As for example, of the tubes comprising bundle 40, those in row 40A, or row 40B, or row 40C of FIG. 3 will remain in the same circular row throughout their helical path in forming the bundle.

For purposes of. describing the helically coiled tube arrangement the words pitch, lead and angle of lead shall have the following definitions:

Pitchthe distance as measured between a point on one of the helically coiled tubes in a circular row and a corresponding point on an adjacent tube in the same circular row.

Lead-the distance measured along the axis corresponding to one complete revolution or turn of the helix generated by a tube in a circular row.

Angle of lead-is the angle whose tangent is defined by the numerical ratio of one-half of the lead of an individual helically coiled tube in a circular row to the diameter of that circular row.

As is illustrated in FIGS. 1, 2 and 6, each circular row contains a number of tubes 40. Because of the difference in the diameter of each circular row a tube in an outer row will have a larger diameter and thus a greater developed length for a single helical turn than will a tube in an inner row. It should be obvious, therefore, that the developed length of a single turn of each tube is proportional to the diameter of the circular row in which the tube is located.

In FIGURE 1 only a small portion of the entire helically coiled tube bundle is shown, the remainder of the bundle being schematically indicated by dot-dash lines each of which trace the center line of a tube typical of an inner, a middle and an outer circular row, respectively, and designated as in FIG. 3 by 40A, 40B and 40C. From these center lines in FIG. 1 and from the showing in FIG. 6 it willbe apparent that the angle of lead (see FIG. 1) is substantially equal for all of the tubes regardless of the circular row in which they are located. With all of the tubes having the same angle of lead, the lead for the tubes in a circular row will be determined by the diameter of the row.

A primary advantage of this tube arrangement is that all of the tubes can be arranged within the bundle so that their developed lengths are substantially equal. Thus fluid flowing through the bundle, regardless of the location of the tube through which it passes, will have the same length of flow path in heat exchange relationship with the fluid passing over the tubes.

To achieve equal developed lengths for each tube in the bundle it is necessary that there be a correlation between the lead, the pitch and the number of the tubes in The pitch and lead selected for each circular row must be exact multiples one of the other so that the pitch or vertical spacing between adjacent tubes may be maintained uniform throughout the bundle.

The following table is presented as an example of the manner in which the present invention provides a helically coiled tu'be arrangement with tubes of equal length. In this example the inner circular row has a diameter of one foot, the outer circular row has a diameter of two feet and the circular rows are spaced two inches apart, transversely. Further, as a starting reference point, the lead of the inner circular row is one foot.

N0. of Developed Circular Row Diameter of Lead Pitch Individual Length of Row d It Tubes For a Single Row Turn 1 1 1'0 10 2" 6 3.30 1'2 1'2" 2 7 3. S5 114/! 114/! r 8 4. 39! 1/67! 176/! 51/ g 4- 95/ 18 1'8" 2 10 4. 50 1'10 110 2 11 6. 01 2'0 2'0 2 12 6 0 Based on the formula I: where d is the diameter of Row and It is lead.

It will be noted in the example shown in the table that for each successively larger diameter of row one additional tube is added to the row. Further, it will also be noted that there is a definite relationship of length of a single turn of the coil to the diameter of the row, hence it is possible to proportion the coil dimensions as desired to suit design considerations. There-fore, from the table it may be deduced that for a tube bundle four feet high the tubes in Row 1 would have made four complete turns, while those in Row 7 would have made only two complete turns. However, the length of each tube would be the same since in Row 1 each tube makes four turns (4X3.30=13.20 ft.) while the tubes in Row 7 make two turns (Z 6.60:13.2O ft). .For the intermediate Rows 2 to 6 the number of turns may be determined by dividing the height of tube bundle by the lead, resulting in 3.41, 3.00, 2.67, 2.4 and 2.13 turns per row, respectively. If the number of turns per row is multiplied by the developed length I, it will be found that the tubes in each circular row are of substantially equal length (i.e. Row 33 4.39=l3.17 ft., Row 62.18 6.04=l3.l6 ft.). Thus, at any point at which the bundle of helically coiled tubes is terminated, the tubes will all be essentially of equal length.

The feature of equal length is, of course, dependent upon the tubes entering and leaving the bundle in a regular, spaced pattern. If the tubes originate and terminate in a number of headers immediately adjacent the opposite ends of the bundle, then to avoid intricate tube bends, they would be distributed nonuniformly within the helically coiled arrangement. Because of this their lengths would be somewhat unequal, even though the lead angle and pitch were kept the same.

The bundle of helically coiled tubes 40 is suspended from the top head 14 of the pressure vessel by means of vertically arranged support members 48 which are attached to support lugs 49 welded to the head, as shown in FIG. 1. With this construction the bundle of tubes is supported independently of and floats within the container 18. An upper carrying member 44 is attached to the lower end of the support member 48. The upper carrying member 44 is located at the upper end of the conduit 32 in a plane transverse to the vertical axis of the pressure vessel and is made up of a number of radially disposed arms 44A which extend between and are at tached to an inner and an outer ring 44B, 44C. The inner ring 44B fits about the conduit 32 and the outer ring 440 fits within the container 18. These rings are closely spaced from the members they adjoin so that they may move relative thereto. A lower carrying member 46 having substantially the same structural arrangement as the upper carrying member 44 is positioned at the lower end of the conduit 32 and is also arranged for relative movement with respect to the conduit and the container.

In FIG. 4 there is shown a fragment of the support arrangement for the tubes 40 within the annular-shaped chamber 34. A number of vertically depending hanger bars 42 are attached at their upper and lower ends, respectively, to the upper and lower carrying

members

44, 46. These hanger bars 42 are arranged at spaced intervals corresponding to the positioning of the radially disposed arms 44A in the annular spaces formed by the concentric tube rows. The inner edge of each hanger bar is recessed or notched to provide alternately a section of notched or scalloped indentations 43A and a-recessed section 43B, the extent of each section being substantially the same. Alternate coils of the helically coiled tubes are supported 'by'the scalloped indentations 43A. The recessed sections 43B, while they do not attord support to the tubes 40, are provided to permit relative movement between the tubes 40, the hanger rods 42 and the shell 12 of the pressure vessel due to diflerential thermal expansion. The opposite edge of the hanger bars is not indented and is very closely spaced from the adjacent row of tubes 40. Each circular row of tubes 40 has a suitable number of the hanger bars 42 disposed around its outer periphery, with the hanger bars supporting adjacent coils of tubes spaced about 30 apart, in staggered array. Tie rings 50 are located at vertically spaced positions along the length of thehanger bars to maintain them in position and alignment.

As seen in FIG. 1 a U-shaped first-fluid inlet header 52 is arranged exteriorly about the lower portion of the pressure vessel. Fluid inlet tubes 54 are connected at their lower ends to the opposing legs of the first-fluid inlet header 5-2 and then extend first upwardly and then inwardly passing through the shell 12 of the pressure vessel '10 at a point below the container 18. A thermal sleeve of conventional construction is provided about each inlet tube 54 as it passes through the shell to keep it out of contact with the shell and to thereby minimize the effect of temperature shock on the shell. After passing through the shell 12 the inlet tubes 54 are again bent upwardly and inwardly passing through the lower end 22 of the container 18 where they are connected to a transition fitting and thermal sleeve combination 55 (see FIG. 5). A thermal sleeve 56 is provided about each of the inlet tubes where they pass through the container.

This thermal sleeve prevents excessive temperature gradients in the container wall through which the tubes pass and thereby keeps the differential thermal stresses within allowable limits. The thermal sleeve 56 is integrallyjoined to the transition fitting and thermal sleeve combination 55.

The inlet tubes 54 have a smaller diameter than the helically coiled tubes 40 and thereby provide sufficient flow resistance to effect equable flow distribution and maintain flow stability in the tubes of the bundle. The transition fitting and thermal sleeve combination 55 is located between each of the inlet tubes 54 and the lower end of each of the helically coiled tubes 40 to providev the necessary transition from one size tube to the other.

At the upper end of the bundle within the annularshaped chamber 34, outlet tubes 58 are connected to the helically coiled tubes 40 to their connection to the firsthelically coiled tubes 40 and extend upwardly, generally parallel with the vertical axis of the pressure vessel. At a point above the top of the container 18 they are bent into a horizontal plane and pass through the shell 12 of the pressure vessel. At the point where the tubes pass through the pressure vessel shell a thermal sleeve is provided to minimize temperature shock on the shell 12. Once outside the pressure vessel, the tubes are bent back into a vertical position and extend upwardly to a point Where they are connected to a first-fluid outlet header 60. The U-shaped first-fluid outlet header 60 (see FIG. 2) is arranged in a plane parallel with the first-fluid inlet header 52 and is located about the top head *14-of the pressure vessel. The outlet tubes 58 enter the outlet header 60 along its opposing legs. The tube arrangement the gas space. within the second-fluid outlet pipe from a point outfluid outlet header 60. This arrangement is also typical for the inlet tubes 54 which are disposed between the first-fluid inlet header 52 and the helically coiled tubes 40.

A second-fluid inlet connection 62 is arranged in the top of the pressure vessel concentric with the vertical axis thereof. A Venturi-like difluser section 64, connected at its upper end to the second-fluid inlet connec-' tion 62, extends vertically downward to a point closely superjacent'the conduit 32. The diifuser section 64 is circular in cross section and diverges downwardly so that as much pressure energy as possible is regained before the fluid discharges from the diffuser section. A reflector 66 is located across the upper end of the conduit 32 and at the same time provides a seal therefor. Y The deflector is located immediately below the difluser and distributes the flow therefrom into the open space 36 which formsan inlet plenum chamber for the second-fluid.

A plate seal 68 is provided at the lower end of the conduit 32 to prevent leakage of the second-fluid into that space. The open space 38 between the lower end of the conduit 32 and the lower head of the container 18 provides a plenum chamber to receive the second-fluid after it flows over the exterior of the helically coiled tubes. A second-fluid outlet pipe 70 is in communication wit-h the lower open space 38. The outlet pipe 70 supports the container 18 and extends downwardly to and through the bottom head 16 of the pressure vessel 10. This outlet pipe 70 is located directly below the conduit 32 and is concentrically arranged with respect to the vertical axis of the pressure vessel. The connection between the outlet pipe and the pressure vessel provides a thermalsleeve like construction somewhat similar to that shown in FIG. 5 to prevent excessive thermal stressing of the wall forming the pressure vessel bottom head.

A support skirt 72 is integrally attached to the outside of the shell 12 of the pressure vessel 10 at a point just above the bottom elliptical head 16. The skirt is formed by a vertically arranged cylinder which extends downwardly from its connection to the pressure vessel to a point below the bottom of the pressure vessel and is there connected to a support skirt flange 74 which rests in a suitable foundation. 7

A gas inlet connection 76 from an external supply source (not shown) is located in the pressure vessel shell 12 at a point above the top of the container 18. to supply inert gases to the gas space 30 which completely envelops the container 18, and flows into the upper open space 36 and the lower open space 38. At the base of the pressure vessel a connection 77 is arranged through the bottom head 16 to permit drainage of vaporous condensate from A gas inlet line 78 extends upwardly side the pressure vessel to supply inert gas from an external source-(not shown) to the conduit 32. The inlet line 78 passes through the plate 68 at the bottom of the conduit and terminates at that point. A vent 80 having its inlet end arranged at the top of the conduit 32 extends vertically down-ward Within the conduit through the plate 68 and then out through the wall of the heating fluid outlet pipe 70 to a receiver (not shown) outside of the pressure vessel.

The requisite number of flanged access ports 82 are arranged in the pressure vessel shell 12 and the container 18 to permit inspection and maintenance of the helically coiled tubes within the container.

Blowout nozzles with diaphragms 84 are situated in the top head 14 of the pressure vessel 10 to provide the necessary relief in the event excessive pressures are developed due to the interaction of the first and secondfluids within the pressure vessel.

In FIG. 6 the only substantial difference from the arrangement in FIG. 1 is the manner in which the first 7 fluid inlet tubes 54A pass upwardly through the outlet pipe 70 to supply the tube coils. The arrangement of the inlet tubes 54A obviates the need for inlet tube openings in the pressure vessel shell 12 and the container 18.

For an explanation of the manner in which the heat exchanger described herein operates, reference is made to the previously mentioned co-pending application, Serial No. 802,880, now Patent No. 3,112,735.

The advantages of this particular helically coiled tube bundle arrangement have not been present in heat exchangers previously available. These advantages include: First, the ability with this arrangement to provide helically coiled tubes of substantially equal length even though disposed in concentric circular rows of different diameters. This feature permits the installation of maximum length tubes within a given vertical height. Second, the configuration of the bundle minimizes the tendency for flow stratification and laning, which in previous heat exchangers, particularly of the liquid metal heated type, resulted in tube temperature unbalances. Moreover, the sinuous cross-flow pattern of the fluid passing over the exterior helical coil surface is conductive to high heat transfer rates with respect to both the first fluid and the second fluid. Third, this arrangementpermits the maximum tube heating surface for a given shell height. Still another advantage inherent in coiledtubes is their capability for accommodating differential thermal expansion, however, with the arrangement here disclosed, the coiled tubes in each of the concentric rows can independently accommodate this expansion.

Additional advantages implicit in this heat exchanger arrangement are the ease with which true counter-flow of the first and second fluids may be attained, viz. the first fluid, or fluid to be heated entering at the lowermost portion of the tube coils and flowing upwardly therethrough while the second or heating fluid enters the vessel in the vicinity of the topmost coil portions, flowing downwardly through the vessel. This flow pattern is conductive to stability of fluid-flow and thus promotes uniformity in the heat transfer pattern. Moreover, the helical flow path eliminates completely shock losses due to sudden and abrupt changes in the direction of fluid-flow such as are encountederd in heat exchanger tube bundles having right angle or return bend fittings interspersed amongst the straight runs of tubmg.

While in accordance with the provisions of the statutes I have illustrated and described herein the best forms and modes of operation of the invention now known to me, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by the claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

What is claimed is: 1. A tube arrangement for a heat exchange device comprising:

A. a container,

B. a bundle of helically coiled tubes disposed within said container,

C. said bundle comprising a number of concentrically arranged circular rows of tubes,

D. each of said helically coiled tubes being positioned within a single circular row throughout its length within the bundle,

E. the pitch of each of said tubes within said bundle being substantially equal,

F. the lead of each tube in a single circular row being equal and the lead of tubes in different circular rows varying in direct proportion to the diameter of the circular rows,

G. the angle of lead for each of said tubes in said bundle being substantially equal, and

H. the number oftubes per circular row increasing in general relation to the distance from the axial center of the bundle.

2. A tube arrangement for a heat exchange device accordingly to claim 1 wherein said bundle extends longitudinally and the radial spacing between said circular rows is substantially equal throughout the bundle.

3. A tube arrangement for a heat exchange device according to claim 2 wherein a core member is disposed in the center of said bundle of tubes and said bundle has an annular-shaped transverse cross section.

4. A tube arrangement for a heat exchange device according to claim 3 wherein said bundle is disposed within a closed longitudinally extending container having a heat exchange medium inlet at one end thereof and a heat exchange medium outlet at the opposite end.

S. A tube arrangement for a heat exchange device according to claim 4 wherein dependently arranged support means are provided for said tubes whereby the tubes are supported and are permitted to expand and contract.

References Cited by the Examiner UNITED STATES PATENTS 1,678,832 10/1928 Clarkson 122-250 1,777,708 10/1930 Wade 122-250 2,160,644 5/1939 Copper 122250 0 2,508,247 5/1950 Giauque -163 0 KENNETH W. SPRAGUE, Primary Examiner.

Claims

1. A TUBE ARRANGEMENT FOR A HEAT EXCHANGE DEVICE COMPRISING: A. A CONTAINER, B. A BUNDLE FOR HELICALLY COILED TUBES DISPOSED WITHIN SAID CONTAINER, C. SAID BUNDLE COMPRISING A NUMBER OF CONCENTRICALLY ARRANGED CIRCULAR ROWS OF TUBES, D. EACH OF SAID HELICALLY COILED TUBES BEING POSITIONED WITHIN A SINGLE CIRCULAR ROW THROUGHOUT ITS LENGTH WITHIN THE BUNDLE, E. THE PITCH OF EACH OF SAID TUBES WITHIN SAID BUNDLE BEING SUBSTANTIALLY EQUAL, F. THE LEAD OF EACH TUBE IN A SINGLE CIRCULAR ROW BEING EQUAL AND THE LEAD OF TUBES IN DFFERENT CIRCULAR ROWS VARYING IN DIRECT PROPORTION TO THE DIAMETER OF THE CIRCULAR ROWS, G. THE ANGLE OF LEAD FOR EACH OF SAID TUBES IN SAID BUNDLE BEING SUBSTANTIALLY EQUAL, AND H. THE NUMBER OF TUBES PER CIRCULAR ROW INCREASING IN GENERAL RELATION TO THE DISTANCE FROM THE AXIAL CENTER OF THE BUNDLE.