Patent Number: 
Section: claims

1. A heat exchanger assembly for exchanging heat between a first fluid and a second fluid, the assembly comprising:an outer enclosure presenting a central axis and provided with at least one inlet and outlet for the first fluid and with at least one inlet and outlet for the second fluid;a central manifold extending along the central axis and communicating with one of the inlet and the outlet for the first fluid;an annular manifold disposed around the central manifold and communicating with the other one of the inlet and the outlet for the first fluid;a plurality of heat exchangers distributed around the central axis and radially interposed between the central manifold and the annular manifold;a plurality of axial inlet manifolds communicating with the inlet(8) for the second fluid, and a plurality of axial outlet manifolds communicating with the outlet for the second fluid, the axial inlet and outlet manifolds being circumferentially interposed between the heat exchangers; andeach heat exchanger comprises a plurality of channels for flow of the first fluid between the central and annular manifolds, and a plurality of channels for flow of the second fluid from at least one inlet manifold towards at least one outlet manifold;the assembly including an inlet chamber provided at a first axial end of the heat exchangers and putting the inlet(s) for the second fluid into communication with at least a plurality of axial inlet manifolds. 2. An assembly according to claim 1, wherein the inlet chamber is annular in shape and surrounds the central manifold. 3. An assembly according to claim 1, including an outlet chamber provided at a second axial end of the heat exchangers opposite from the first axial end and putting the outlet(s) for the second fluid into communication with at least a plurality of axial outlet manifolds. 4. An assembly according to claim 3, including an inspection channel extending the central manifold axially from the second end, and isolated therefrom by a removable hatch, the outlet chamber being annular in shape and surrounding the inspection channel. 5. An assembly according to claim 4, wherein at least the heat exchangers, the inlet and outlet chambers, and the axial inlet and outlet manifolds are united in a mechanical subassembly that can be extracted as a single piece from the enclosure. 6. An assembly according to claim 5, wherein the enclosure has a vertical central axis, the enclosure comprising a vessel within which the subassembly is disposed and presenting towards the top an opening for extracting said subassembly, and a removable closure head for closing the opening of the vessel in leaktight manner. 7. An assembly according to claim 6, wherein the vessel comprises a cylindrical shell coaxial with the central axis and having the inlet and outlet for the second fluid formed therein, the inlet and outlet chambers being connected in leaktight manner to the inlet and outlet for the second fluid by removable sleeves that can be retracted into the chambers. 8. An assembly according to claim 7, wherein the sleeves are suitable for being dismounted from inside the chambers. 9. An assembly according to claim 7, wherein the enclosure has a plurality of inlets for the second fluid and a plurality of outlets for the second fluid, these inlets and outlets being brought together in a single circumferential half of the shell. 10. An assembly according to claim 6, wherein the subassembly comprises a cylindrical outer envelope coaxial about the central axis, defining the outlet chamber and the annular manifold radially outwards. 11. An assembly according to claim 10, including bottom inlet and outlet manifolds that are coaxial and in communication respectively with the inlet and outlet for the first fluid, and that are disposed beneath the subassembly, the bottom of the subassembly being defined by a frustoconical envelope converging from the cylindrical envelope, said frustoconical envelope surrounding the central manifold and co-operating therewith to define the annular manifold, the bottom manifolds being terminated upwards by flanges suitable for receiving the bottom free ends of the central manifold and of the frustoconical envelope in leaktight manner merely by mutual engagement. 12. An assembly according to claim 4, wherein the central manifold presents an inspection hole that is closed by a removable hatch, and that communicates with the inlet chamber, and the inspection channel presents an opening communicating with the outlet chamber. 13. An assembly according to claim 1, wherein the enclosure presents a bottom end wall, and wherein the assembly includes a circulation member fastened to the bottom end wall and suitable for sucking in the first fluid coming from the annular channel or from the central channel and of delivering it to the outlet for the first fluid. 14. An assembly according to claim 1, wherein the axial inlet and outlet manifolds, the central manifold, and the annular manifold, all have through sections that are sufficient to enable an operator to act directly on the heat exchangers. 15. An assembly according to claim 1, wherein the inlet and the outlet for the first fluid are coaxial. 16. An assembly according to claim 1, wherein the heat exchangers are disposed regularly spaced apart in a circle around the central axis, each axial manifold being defined both inwards and outwards by respective inner and outer circumferential sheets welded to the two heat exchangers between which said manifolds extend. 17. An assembly according to claim 16, wherein the annular manifold is defined inwardly by the heat exchangers and by the outer sheets. 18. An assembly according to claim 16, wherein the central manifold is defined by the heat exchangers and by the inner sheets. 19. An assembly according to claim 16, wherein each heat exchanger comprises a plurality of heat exchange modules that are stacked axially. 20. An assembly according to claim 16, wherein the modules present, perpendicularly to the central axis, a section that is rectangular, and present corners that are machined over the full axial height of the heat exchanger, the heat exchanger further including forged and/or machined metal bars disposed in the machined corners and onto which the modules are welded. 21. An assembly according to claim 20, wherein each bar presents a flange projecting circumferentially relative to the modules and towards the neighboring axial manifold, having the inner or outer sheet defining said axial manifold welded thereto. 22. The use of an assembly according to claim 1 for a first fluid mainly comprising helium and a second fluid mainly comprising helium and/or nitrogen. 23. The use of the assembly according to claim 1, with a first fluid mainly comprising helium and a second fluid mainly comprising water, the second fluid being vaporized in the heat exchanger assembly. 24. The use of an assembly according to claim 1, with first and second fluids mainly comprising water, the second fluid being vaporized in the heat exchanger assembly. 25. The use according to claim 22, wherein one of the first and second fluids comes from a nuclear reactor.