Heat exchanger

A large size heat exchanger operating at a high temperature and pressure, particularly of the type used as a steam generator wherein the primary hot fluid consists of the cooling fluid of a nuclear reactor wherein a bundle of heat exchange tubes is arranged in a container, said exchanger comprising:

• a. a outer heavy structure including an outer cylindrical shell, an upper head having an outer wall and an inner coaxial wall defining an annular chamber therein and a large central passage, an annular base plate closing the lower end of said chamber and having a plurality of circular rows of perforations, a lower annular head having a shape similar to the upper head and arranged symmetrically relative thereto, whereby its inner coaxial wall defines a large central passage allowing access to the interior of the structure for mounting and repairing said bundle of tubes in situ, removable closing means for closing said passage, the outer wall of each of said heads being provided with an aperture for the intake and the outlet of the fluid circulating through said tubes, said structures having inlet and outlet apertures for a second fluid circulating along the tubes, said outer heavy structure being assembled, welded and stabilized by annealing before the mounting of said tubes,
• b. a light inner structure comprising an annular bundle of alike axially undulated planar tubes having a quasi-sinusoidal shape, having successive arcuate deflections in opposite directions with an angle of deflection in the order of 60.degree., said tubes being arranged in a plurality of circular tube layers and having their upper and lower ends inserted in the perforations of the corresponding annular base plates of said heads and welded thereto, said bundle of tubes comprising a plurality of series of concentric annular supporting hoops arranged on different axially spaced supporting planes respectively, a pair of concentric hoops being arranged eitherside of each circular layer of tubes, each hoop consisting of a plurality of flexible linear elements engaged with one another end-on-end, curved and welded to each other as they are fitted within the outer structure, radially extending tubular braces having concave lateral faces and each inserted between a pair of adjacent tubes in each supporting plane and welded to the outer and to the inner hoops of each pair of annular hoops arranged eitherside of each circular sheet of tubes respectively to firmly maintain said tubes in said planes without frictional contact between the tubes and the hoops, said tubular braces having substantially the same expansion coefficient as the tubes, the peripheral outer hoop of each supporting plane being attached to the inner surface of the outer shell and the mounting of said circular tube sheets commencing with the peripheral sheet next to the outer shell, a large central shaft made of relatively thin metal sheet arranged in the middle of the annular bundle of tubes extending over the major part of the height of said bundle, having a lower open end welded to the annular base plate of the lower head and a closed upper end to define an annular heat exchange chamber with the outer shell, the peripheral inner hoop of each supporting plane being attached to the outer surface of said central shaft, the diameter of the central free space surrounded by the annular bundle of tubes being in the order of between 1m and 1.5m to provide an access to said bundles after destruction of said central shaft for the purpose of repairing and changing said tubes.