GB2201505A - Heat exchangers for immersion in primary fluid - Google Patents

Description

1 9 1 220 1505 A HEAT EXCHANGER The subject-matter of this invention

consists of a Weat exchanger which uses as its primary and secondary fluid a liquid, preferdbly'liquia sodiumv and which his a tube bundle formed by a single bank of U-shaped tubes.

These tubes art immersed in the primary fluid while-the secondary fluid flows through them.

More in particular, the invention concerns.a heat exchanger for the removal of the residual power of a, nuclear reactor of the so-called "fast" type.

These exchangees generally consist of a bundle of tubes extended between two headers.

The two headers hydraulic circuit i ing media, flows.

The tube bundle is partly or completely immersed in the primary fluid to be cooled.

Said primary fluid circulates around the tubes of the exchanger.

A known exchanger of this type is illustrated for example in figure 1, described in detail later.

Another known exchanger of the above type isvillustrated in Italian patent application no..12541A/62, And the tube bundle are part of a n which a secondary fluid, the coolgenerally consisting of liquid sodium, i 1 1 which comtitutes an improvement on the exchanger illustrated-in figure 1.

Yet another known variant is described in French patent no.,2,519.462.

These known solutions generally envisage a tube bundle consisting of several banks of tubes.

The tube bundle immersed in the primary fluid is surrounded-by at least one shell, generally equipped with more or less large openings! so that the primary sodium circulates around the tubes-of said tube bundle along paths which run partly parpendicular to the tubes of the bundle and partly parallel to same.

In these known types of exchangers the tubes of the various circles of the tube bundle clearly cannot all have the same temperature.

It thus follows that the secondary sodium leaving the various tubes does not all have the same temperature and therefore there is a radial thermal gradient in the tube plate of the heat exchanger output header.

It should be noted that, as shown in figure 1, the output headef actually consists of an annular chamber formed by two vertical cylindrical plate casings which come to find themselves at different temperatures due to the lack of radial uniformity in the temperacure of the sodium.

-1 The upper tube plate may be made in the known manner, in two concentric annular parts separated by an expansion joinW also annular in shape '. the cold -secondary fluid passes through the internal circular plate while the secondpry fluid heated by the primary fluid passes through the outer annular plate.

As described above, the secondary fluid leaving the various circles of tubes has different temperatures and therefore in this case too- the annular tube plate has a. radial thermal gradient.

The purpose W this invention is to overcome this draw back by using tubes which, being arranged in a single circle, al-1 have a practically identical heat behaviour.

According to the invention, the tube plate has only two annular circles, one leading downwards and the other. upwards.

The upper ends of the two brancher of each pipe end, on the outer annular plate, in two circles of holes while an the inner circular plate they end in four circles of holes.

Each tube lies on a substantially radial plane, which makes them relatively simple to assemble.

To absorb the expansion differential between the downward branch and the upward branch, loops are i 4 provided, which are also developed on A substantially radial plane. The main characteristics of the invention are summarized and schematically described in the,claims aims and advantages are also illustrated in the following description tovering jorms of embodiment chosen by way of example only With particular reference to the attached drawings, in which: - as already mentioned, figure I shows a heat exchanger of the traditional type; figurn 2 shows the heat exchanger according to the invention, 'on a very small scale, to allow a comparison with the the one illustrated in the preceding figure; figure 3/A shows the upper part of figure 2, on a larger f igure on an f igure bundle; f igure of the D; larger scale; figure 3/B shows the lower part of figure 2, on a scale; 4/A shows the upper part of the tube bundle, even larger scale; 4/B shows the- lower oart of the same tube shows all together partial cross-sections tube plate along planes MA, B-B, C-C and D- t, - figure 6 is a partial crnss-section along planes V1VI of figure 3/B.

Figure 1 is an illustration of a known type of he& exHang& used to dispose of the residual power of a fast nuclearreactor.

In this figure 10 indicates the primary fluid contained in the reactor tanR, the floor of which 11 is visible.

This f loor is passed through, sealed by joints a.

known type, by a secondary fluid feeder pipe 12, this secondary fluid also being liquid sodium.

The feeder pipe 12 crosses through. the floor 11, an upper tube plat4 13 and then a lower tube plate -14.

Below the lower tube plate 14 there is a header 15,into which the seconday fluid flowing down the column 12 is deviated towards the lower tube plate 14 to which the lower ends of a bundle of vertical pipes 16 - represented schematically in the figure by a pair of dashed and dotted lines - are connected.

The tubes of the bundle 16 cross through the upper tube plate 13 and the heated secondary fluid is conveyed through an annular shaped header 17 to an input pipe 16.

The tube plate 16-in which the secondary fluid flows is surrounded by a cylindircal plate casing 19, fitted with ouitable openings to allow the passage af the k primary fluid circulatin.g between the pipes of the tube bundle 16 to heat the secondary fluid contained in it.

One drawback of this known type of exchanger is the fact that the various tubes of the tube bundle do not absorb from the primary fluid the same quantity of heat, so that undesired thermal gradients occur between the various pipes of-the bundle.and above all in the upper tube plate.

According to a known variant, the lower header 15 is suppressed together with the only downflow pipe 12' of the secondary f luid.

In their place, the upper tube plate is split up into two concentric _plates, of which the outer one has an annular shape, to which the two ends of a series of Ushaped tubes are connected.

Even in this case, the thermal gradients due to the different heat absorption by the various tubes of the bundle are not eliminated, as the tubes are arranged In different circles.

Furthermore, this solution entails considerable construction difficulties and thus high costs, since these U-shaped tubes each follow a threedimensional path in order to give threm sufficient elasticity to take in the expansion differential between the downflowing and the through which the secondary fluid flows t 1 S v upflowing branches.

According to this invention (see figure 2 and subsequent figures), in order to ensure that each tube in the bundle absorbs the same quantity of heat from the primary fluid, the tubes of the tube bundle are arranged in a double annular circle 116, in the first of which the downflowing parts are located and in the second the upflowing parts.

The upper tube plate 113 consists of two concentric tube plates that is to say a circular inner plate 113' and an annular outer plate 113% The tubes of the bundle are arranged one next to an othe r and are fitted with end loops 31, 32, 33 and 34.

These loops are located on substantially radial planes, and, two by two, they are developed concentrically one inside the other, slightly staggered in a circumferential direction so that they find room in the inner area of the bundle.

Further intermediate loops, 41-42 and 43-44, 51-52 and 53-54, are arranged along the height of the tubs bundle _116.

Theirpurpost is to create expansion joints for the tubes and to allow each single tube to pass through th(. area inside the circle of tubes too, where che primarv fluid flows downwards. Said leops are staggered from.one The me condary fluid feeder pipe the central tube plate 113% whil output pipe_ 118 has an annular pipe to the next. leads to a point above e the primary fluid shape and is connected to the outer annular tube plate- 11M to collect the secondary fluid leaving the tubes of the bundle.

A suitably holed cylindrical plate casing 119 surrounds the tube bundle 116, the purpose of Which is to create preferential paths asligned to the primary fluid circulating between the tube-s of the tube bundle and to provide a seismic support for the bundle.

The simplest form of embodiment of the invention is illustrated in figures 3A and 3% which should be eC amined together.

It can be seen hers that the tubes of the annular tube bundle, arranged in a double annular circle, are connected -to the outer tube plate 21M which is equipped with a-single set of holes arranged in a circle.

It was obvious thak, since the inner tube plate 21M was smaller than the outer one, it would not have been possible to connect the other ends of the tubes forming the bundle to a single circle of holes.

In order to overcome this difficulty, the first lenqtf-t of each tube-of the bundle is connected alternately to R, 1 According res nonds a r ranged 1 n this -.k double circle of holes 61-62 through a slanting end 63-64: in this way it is possible to make passage holes i.n the inner circular tube plate 2.13 at suitable distances from one another. Again it should be remembered that the loops in the tubes of the bundles and the end parts 63 and 64 lie for each tube on a substantially radiaT plane. A constructional solution allowing a greater number at tubes to be installed is that illustrated in detail in figures 4, 5 and 6. to this second form of embodiment (which corto that already illustrated in figure 2), the outer annular tube plate 31X' has two concentric annular circles of holes for the ends of the upflowing parts of the pipes; these upflowing pipes are however in a-single circular circle. case on the inner circular tube plate 3131 there are four circles of holes; the vertical downflowing parts of the tubes of the bundle are connected to these rsoles by means-of small slanting branches 363. in 'this case too the positions and number of the loops, =1 5 C well as the position of the upper slanting parts of the I-uries of the plate are arranged in such a way that the heat e.,,change with the primary fluid is on the jiverEAqe the same for each tube.

n fi,:jure 5 is possible a. fat P.21th placed a u r e 11 o see each single tube s u b, s Et.nt i a I 1.y r a U1 Et Y 6 s h o ix.j s rt o o t..: s 7 1 circular spacers 712 and undu lated supporls 73 for trie tubes Of trie bundle.

These eleffien-,,s are made out of sheet steel and are arranged at preestablished ra.d-Lal intervals.

Their purpose is to keep the various tubes of the bundle in a correct position.

These supporting and positioning elements are arranged around the tubes of the bundle in such a way that they do not. obstruct the flow of primary fluid circulating within the bundle of tubes.

Although for descriptive reasons this invention has been-based on tha above description and illustrated by way of example only with particular reference to the attached drawings, many changes and variations may be made in the embodiment of the invention.

These changes and variations shall however be deemed as being based on the following claims.

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Claims (17)

CLAIMS:

1. A heat exchanger for transferring heat between a primary fluid anda secondary fluid comprising a plurality of tubes for carrying the secondary fluid, the tubes being coupled together and disposed to form a single inner shell and a single outer shell, the inner shell comprising a first portion of each tube and the outer shell comprising a second portion of each tube.

2. A heat exchanger as claimed in claim 1 wherein the secondary fluid flows in through the first portions and out through the second portions of the tubes.

3. A heat exchanger as claimed in claim 1 or claim 2 wherein the first and second portions of each respective tube are connected by a planar loop of said tube.

4. A heat exchanger according to any one of the preceding claims wherein a said portion of each tube includes at least one inwardly disposed expansion loop.

5. A heat exchanger as claimed in claim 4 wherein each tube includes a plurality of said loops spaced at constant intervals.

6. A heat exchanger as claimed in any one of the preceding claims wherein, the outer shell is of generally cylindrical form.

12

7. A heat exchanger as claimed in any one of the preceding claims further comprising-first and second concentric- plates for coupling, respectively, the first and second portions of said tubes.

8._ A heat exchanger as claimed in claim 7 wherein the second portions are arranged so as to be engaged with one or more concentric circles of openings of the second plate and the first portions are arranged so as to be engaged with openings in the first plate which are disposed on a greater number of concentric circles than the openings in the second plate.

9. A heat exchanger as claimed in claim 8 wherein the first and second portions are connected to the concentric circles of holes in the plates by means of slanting connection lengths.

10. A heat exchanger as claimed in claim 9 as dependent on claim 4 wherein the connection length of a said portion is coplanar with a respective expansion loop.

11. A heat exchariger according to any one of the preceding claims further comprising support means, for holding the tubes in place relative to-one another.

12. Liquid-metal heat exchanger in which the liquid metal consists of molten liquid, in particular sodium, of the-type having a vertically developed tube bundle, in which the two ends of each tube are connected to an inner circular tube plate and to an outer annular tube i 0 13 P 1 ,k Ili plate, coaxial to one another. characterized by the fact that the vertical parts of the tubes of the bundle through which the downflowing sodium runs are arranged in a.single inner annular circle and the vertical parts of said tubes through which the upflowing sodium runs are arranged in a single outer-annular circle.

13. A heat exchanger. according to claim 12, characterized in that the vertical uptlowing and downflowing parts respectively of the various tubes of the bundle are connected by flat loops which lie on substantially radial planes.

14. A heat exchanger. according to claim 12 or claim 13. in which the ends of the vertical upflowing parts of the tubes of the bundle are connected to corresponding holes in the outer annular tube plate and the ends of the vertical downflowing parts of the tube plate are connected to corresponding holes in the inner circular tube plate. wherein the fact that the holes in the outer annular tube plate are arranged on one or more circumferences, while the holes in the inner circular tube plate are arranged on a greater number of concentric circumferences and preferably on double the number of concentric circumferences; in which the holes of the circle belonging to the same plate are staggered circumferentially.

15. A heat exchanger according to any one of claims 1 14 12 to 14. wherein the vertical parts of the pipes have expansion loops in them, facing towards the inner area of the bundle, located on substantially radial planes; these expansion loops being suitably staggered circumferentially and in height at preestablished constant- interval,s-.

16. A heat exchanger according to any one of claims 12 to 15. wherein the vertical downflowing and upflowing lengths of the single tubes are connected to the various concentric circles of holes in the tube plates by means of slanting connecting lengths; these slanting connecting lengths being on the same plane as the expansion loops of their respective tubes.

17. A heat exchanger according to any one of claims 12 to-15. wherein the tubes of the plate are fastened in place by means of supports and spacers arranged in a ring-like fashion-around the tube bundle, so that-the central section of the tube bundle through which the primary sodium shall flow is left free.

U. A heat exchanger substantially as hereinbefore. described with reference to Figure 2 or Figures 3 to 6 of the accompanying drawings.

Published 1988 at The Patent Office, State House, 66171 High Holborn, London WC1R 4TP. Further copies maybe obtained from The Patent Office, i A P