US3400759A

US3400759A - Heat exchanger with imbricated bundles of exchange tubes

Info

Publication number: US3400759A
Application number: US497039A
Authority: US
Inventors: Legrand Pierre
Original assignee: Individual
Current assignee: Individual
Priority date: 1965-10-18
Filing date: 1965-10-18
Publication date: 1968-09-10
Anticipated expiration: 1985-09-10

Description

P. LEGRAND Sept. 10, 1968 HEAT EXCHANGER WITH IMBRICATED BUNDLES OF EXCHANGE TUBES Filed Oct. 18, 1965 2 Sheets-Sheet 1 Sept. 10, 1968 P. LEGRAND 3,400,759

HEAT EXCHANGER WITH IMBRIGATED BUNDLES OF EXCHANGE TUBES Filed Oct. 18, 1965 2 Sheets-Sheet 2 United States Patent 3,400,759 HEAT EXCHANGER WITH IMBRICATED BUNDLES 0F EXCHANGE TUBES Pierre Legrand, 98 Rue de Rennes, Paris, France Filed Oct. 18, 1965, Ser. No. 497,039 9 Claims. (Cl. 165-173) ABSTRACT OF THE DISCLOSURE This invention relates to a heat exchanger comprising a compact nest of straight and parallel exchange tubes disposed along the nodes of a centered hexagonal lattice, said tubes being distributed among imbricated elementary bundles having particular connections with their headers and each consisting of at least three tubes spaced from each other by pairs by a distance V3times the side of one mesh of the lattice.

The present invention primarily relates to a heat exchanger pertaining in particular to the type comprising a compact nest of straight and parallel tubes in which circulates a first fluid and about which circulates a second fluid preferably in a counter-flow direction.

When, for some reasons, one must dispense with tube plates which conventionally collect the many ends of such tube bundles, one is compelled for manufacturing and mounting reasons, in particular to provide access to the welds, to avoid the separate connection of each tube to its header; therefore, one is led to locally arrange in groups the adjacent tubes of elementary clusters, so that the number of connections to the header is reduced to a sub-multiple of the. total member of tubes in proportion of the number of tubes composing each elementary nest, bundle or cluster.

The tubes being in general distributed over the crosssection of the exchanger in a regular manner and at equal distance from each other, for example along the nodes of a centered hexagonal lattice, 'it could have seemed advantageous that every ,elementary nest or bundle order to minimize the length of the internal connections of said elementary nest or bundle; moreover, itis advantageous that the tubes so arranged be distributed in a pattern such that all the tubes of the exchanger may be arranged Now, in use, one may be led to cut off the circulation of fluid within one or several elementary nests, bundles or clusters and this for two reasons:

At first, one is'led to definitively shut off the circulation of fluid within a tube which has begun to leak. In a not veryclosely packed tube network system, this maybe simply obtained by cutting or severing and obturation of the tube involved; in a close-packed tube network system however, these operations are practically rendered impossible due to the difiicult access to thetube involved; yet, since the tubes are arranged in elementary nests or bundles, which alone are connected to the header, it

'remains the possibility to cut definitively off the circulation of fluid in the elementary nest comprising the failing tube upon breaking its connection to the header.

Secondly, one may be led to temporarily out off the circulation of fluid within a significant fraction of the total number of tubes in the exchanger when these latter consists of a number of immediately adjacent tubes, in

ice

are arranged in independent sets each one connected to its proper header or headers, as is the case, for safety reasons, with heat exchangers of a very large bulk integrated in nuclear reactors.

The interruption of the circulation of internal fluid in an elementary nest or bundle involves two detrimental local consequences, the one of thermal character and the other of mechanical character.

The first drawback is due to that the external fluid which circulates about the separate elementary nest or bundle, does not give off its heat and therefore forms a longitudinal column or sheet of fluid at a substantially constant temperature, constituting a thermal shunt. This results in a decrease of the overall etficiency of the exchanger.

The second drawback is involved in the local temperature distortions attending the aforesaid thermal shunt and producing mechanical distortions between adjacent tubes, which is detrimental if the connections between tubes are short and lack flexibility.

A first approach to the solution of these problems has been suggested in the US. application Ser. No. 149,928, filed Nov. 3, 1961, now 'Patent No. 3,249,154, issued May 3, 1966, wherein there are provided exchanger tubes fitted with an axial core and with inner and outer helical projections which determine at any point for a minimal power expenditure, the circulations of fluids, respectively enabling the centrifugation of the internal fluid and the constant transverse diffusion of the external fluid, thereby tending to render the temperature distribution homogeneous within the exchanger tubes throughout the exchanger, thereby preventing the formation of the aforesaid longitudinal thermal shunt.

The presence of a core and of the inner helical projections reduces the cross-sectional area of flow left to the internal fluid; owing to the cross-sectional continuity, the connecting tubes are therefore necessarily of a diameter substantially less than that of the exchanger tubes and therefore have some flexibility to compensate for the dilferential expansions between adjacent tubes.

The object of the present invention is to completely remove the aforementioned drawbacks and may be advantageously combined with the solution stated hereinabove and described in the previously mentioned patent.

A heat exchanger according to the invention, pertaining in particular to the kind wherein the exchanger tubes are arranged at the nodes of a lattice having centered hexagonal meshes and wherein the adjacent tubes are locally arranged to constitute elementary nests, bundles or clusters provided with their particular connections with their headers, collectors or manifolds, is more particularly characterized in that each one of said elementary nests, bundles or clusters consists of at least three tubes which are not immediately adjacent to each other, and

which are spaced from each other by a distance 3 times the side of one mesh of the lattice and located the one at the center of such a mesh and the others on the bisecting lines of at least two distinct sides of said mesh.

According to another feature of the invention, said elementary nests, bundles or clusters are imbricated in such a manner that anyone tube of a bundle is immediately surrounded by six tubes belonging to other bundles.

According to still a further feature of the invention, said bundles or clusters are arranged in parallel rows.

According to still another feature of the invention, the successive bundles or clusters of a same row are connected to different headers or manifolds according to a circular permutation.

'It at once results from the preceding arrangements that in an exchanger constructed according to the method of the invention, the interruption of the circulation of internal fiuid, whether it is definitive in a single bundle or cluster or temporary in a set of bundles or clusters, cannot give rise to any longitudinal thermal shunt of significant importance.

According to an embodiment enabling to put the invention into practice in a particularly convenient manner, said elementary bundles or clusters consist of tubes arranged in a sheet or layer, that is located in a same plane.

Further features, objects and advantages of the invention will become apparent as the following detailed description proceeds, illustrating by Way of example an embodiment with reference to the accompanying drawings, wherein:

FIGURE 1 is diagrammatic view showing an embodiment of arranging exchange tubes of a heat exchanger into nests, carried out according to the invention, this view substantially being a cross-section with respect to the various tubes;

FIGURES 2 and 3 are general schematic diagrams showing how the tubes of the nests or bundles shown in FIGURE 1 are arranged and connected to the headers or manifolds of their respective sets;

FIGURE 4 is an elevational view drawn to a larger scale, showing an elementary nest r bundle of the type used in the preceding figures;

FIGURE 5 is a cross-sectional view drawn to a larger scale and with parts broken away, taken at the level of line VV of FIGURE 4 showing the tubes of some nests or bundles arranged side by side and imbricated, pertaining to the type illustrated by FIGURE 4.

According to the embodiment shown in FIGURES 1 to 3 of the drawings, it has been assumed that the tubes of the exchanger are arranged at the nodes of a lattice having centered hexagonal meshes. In FIGURE 1, four hexagonal meshes formed by such tubes have been shown and denoted 1 to 4. The tubes of these four meshes (which tubes are seven in number for every mesh) have been shown by dots or points. To avoid encumbering the drawing, the other tubes of the nest or bundle have not been shown in general.

According to the invention, the various tubes of the exchanger have been arranged in elementary nests or bundles of seven aligned tubes. Such a nest or bundle of seven tubes, designated at 5, has been shown with its seven tubes designated 6 to 12, respectively. Tube 12 is the most centrally located one of the elementary nest or bundle. To simplify the drawing, the other similar elementary nests or bundles of the exchanger have been designated only by their central tube such as 13, 14 or 15 for example, surrounded on each side by lines representing the approximative size of the three tubes adjacent to each central tube of each elementary nest, bundle or cluster.

Moreover, in the example shown hereinabove, it has been assumed that each elementary nest or bundle of seven tubes belongs to one of the four sets of tubes and to distinguish these sets, a proper conventional sign or mark has been used for differentiating them, viz: a triangle, a square, the sign 1 or the sign x, respectively. Each one of these sets has its proper headers or manifolds which are arranged with each set.

Having thus specified the symbols used in FIGURE 1, it is seen that the exchanger may in addition be considered of being made from the juxtaposition of blocks such as designated by 16, 17 and 18, of a substantially rectangular general shape, consisting themselves of the juxtaposition of elementary nests or bundles of seven tubes. A mechanical construction made from elementary blocks thus assembled is of course very practical.

If one considers now anyone of the hexagonal meshes 1 to 4, one can see that any one tube of the exchanger, that is for example the central tube 19 of mesh 3, belonging to the set symbolized by a triangle, is immediately surrounded by six adjacent tubes 20 to respectively, belonging to the other sets (

tubes

20 and 23 belonging to the set symbolized by the sign x,

tubes

21 and 25 belonging to the set symbolized by the sign 2 and

tubes

22 and 24 belonging to the set symbolized by a square). It may be understood that under these circumstances, no significant thermal shunt is to be feared whether one is led to interrupt the circulation in an elementary nest or bundle or even in a whole set of tubes of the exchanger.

This is made possible according to the invention by selecting a spacing between two tubes of a same elementary nest or bundle equal to /3 times the side of the mesh of the lattice used and by constituting each elementary nest or bundle with at least three tubes one of which is located at the center of one mesh of the lattice and the others on the bisecting lines of at least two distinct sides of said mesh. The arrangement of elementary nests or bundles in seven aligned tubes is a particularly convenient embodiment of the invention. However, the arrangement of the tubes in star-shaped elementary nests or in elementary'nests arranged in a herring-bone pattern, complying with the arrangement the formation of which has been set forth in the preceding paragraph, is quite usable for the objects of the invention.

The positioning of each block or pack of tubes such as 16, 17 or 18, consisting of adjacent elementary nests or clusters of seven tubes (such as 5) is carried out by simply successively imbricating these nests or clusters.

In FIGURE 2 have been shown the connections between each nest of tubes and more specifically between each central tube of said nests and their respective headers or manifolds. Thus, one may see the connection with four headers, collectors or manifolds 26 to 29, belonging to the sets symbolized by the signs 1, square, triangle, x, respectively, of the various central tubes of the elementary nests shown in the preceding figure. Thus, notably, the tube 21 is connected to header 26, the tube 22 is connected to header 27, the

tubes

19, 12 and 13 are connected to header 28 and the tube 23 is connected to header 29.

In FIGURE 3, the

blocks

16, 17 and 18 of the preceding FIGURES 1 and 2, have been diagrammatically shown in an elevational view illustrating the positioning of the tubes, of the water and steam headers and of the various connections. Thus, the tubes 6 to 12, of nest or bundle 5 are connected to the water header 28 and to the steam header 28 by their central tube 12. At 30 has been shown the supporting core or Web of the block or pack 16. It must be pointed out that the steam headers are resiliently supported by their tube connecting them with the various central tubes of the elementary nests or bundles. It is seen that the successive nests or bundles of a same block or pack or of a same row such as 16, 17, 18 are connected to the various headers 26 to 29, 26' to 29, through a circular permutation, in other words, starting from any bundle connected to a determined header, the successive bundles in the same row are respectively connected to the other headers along a predetermined order until all the headers are used, and the same arrangement is repeated starting from the next bundle in the row. The various headers connected to the elementary nests or bundles are in turn hierarchically arranged in successive collectors of increasing diameter (not shown) yet keeping within each arrangement the individual character of each set. In the interesting case Where the main water inlet and steam outlet headers must extend through the lower bottom of the exchanger, the aforesaid arrangements within each set of headers are carried out, for the steam, either at the top or at the bottom of the exchanger and in this latter case, the four elementary headers of each block or pack (such as 16) extend separately down for example on the periphery of the block involved wherein some tubes have been omitted to enable such a downward extension while retaining the standard rectangular contour of the block, allowing accurate juxtaposition of such blocks.

In FIGURES 4 and 5 of the drawings, one has shown in a precise manner how may be constituted an elementary nest or bundle of seven tubes of the type used in the preceding FIGURES 1 to 3 and how such nests could be mounted in an imbricated fashion.

The nest or bundle shown in FIGURE 4 may be for example the nest or bundle 5 of the preceding figures. It is clearly seen that the central tube 12 is flanked on either side by three adjacent tubes 6 to 8, and 9 to 11, respectively. These tubes advantageously consist of the exchange tubes previously mentioned and described in the aforesaid patent.

Thus each elementary nest or bundle 5 is somewhat in the form of a flat seven-branched candlestick which for example is supported by means of a flange or collar 31 at the bottom part of the central tube 12, this flange being adapted to be supported in turn by the web (FIGURE 3). The Web 30 rests upon a grid or grate 35 which lies on bearers 36 with rolling heads, which in turn rest on the ground 37.

In FIGURE 5, one can see in a precise manner how the central tubes (such as 12, 32 to 34) of the separate nests or bundles have to be pinched and deformed at their junction with the other tubes of the nest or bundle, so as to enable the positioning of the various elementary nests or bundles of tubes without any loss of space within the exchanger.

The side tubes 6 to 8 and 9 to 11 are kept on two extensions 38, 39 of the central tube 12. These extensions are made from tubes of large thickness and formed to this end with extruded portions 40 to and 46 to 51 which are opposite by pairs and arranged on three levels respectively. To increase the compactness of the exchanger, the extensions 38, 39 in the area of the extruded portions have a flattened rectangular cross-section.

The verticality of the self-supporting elementary nests or bundles is provided by the lateral holding of the upper headers connected themselves by horizontal rods which in turn are either integral with stationary structures or \abutted upon the latter.

The invention is of course not at all limited to the embodiment described and shown which has been given by way of example only.

What I claim is:

1. A heat exchanger, of the type comprising a closepacked nest of substantially straight and parallel tubes disposed at the nodes of a lattice having centered hexagonal meshes, wherein the adjacent tubes are locally arranged to form separate elementary bundles having their particular connections with their headers, characterized in that each one of said elementary bundles consists of at least three tubes spaced from each other by pair's by a distance 3 times the side of one mesh of the lattice and located the one at the center of such a mesh and the others on the bisecting lines of at least two distinct sides of said mesh.

2. An exchanger according to claim 1, wherein said elementary bundles are so imbricated that anyone tube of a bundle is immediately surrounded by six tubes belonging the other bundles.

3. An exchanger according to claim 2, wherein said bundles are arranged in substantially parallel rows or packs.

4. An exchanger according to claim 3, wherein the successive bundles of a same row are connected to differing headers according to a circular permutation.

5. An exchanger according to claim 2, wherein said elementary bundles consist of tubes located in a same plane.

6. An exchanger according to claim 5, wherein saidbundles comprise seven tubes, viz. a central tube and six lateral tubes connected to the first one by their ends.

7. An exchanger according to claim 6, wherein the connections between the corresponding ends of said lateral tubes and of said central tube are made by means of bent connecting tubular members having a diameter less than that of said tubes and comprising flared end portions, the ends of said central tube comprising radial extrusions and the corresponding ends of said lateral tubes terminating in a swaged portion, the diameter of said extrusions and swaged portions corresponding to that of said flared end portions of said connecting tubular members.

8. An exchanger according to claim 7, wherein said central tube comprises at each end an extension of greater thickness with a substantially rectangular cross-section in which are provided said extrusions.

9. An exchanger according to claim 8, wherein the lower extension of said central tube comprises a reduced portion forming an outer shoulder whereby the bundle is supported by support means integral with the structures of the exchanger.

References Cited UNITED STATES PATENTS 3,104,652 9/1963 Tilleguin et al 12232 3,249,154 5/1966 Legrand l64 FOREIGN PATENTS 640,772 4/ 1962 Canada. 1,272,920 8/ 1961 France.

ROBERT A. OLEARY, Primary Examiner.

A. W. DAVIS, Assistant Examiner.