FR2467371A1 - SPACER GRID FOR TUBULAR BEAMS - Google Patents

Abstract

Spacer grid for the tube bundle of a heat exchanger. It consists of a thick flat sheet hollowed out on each face by a series of parallel grooves, in different directions for each face; the sum of the depths of the grooves, respectively on each face, is greater than the thickness of the sheet. The invention is applicable to the steam generators of a nuclear power station. (CF DRAWING IN BOPI)

Description

The present invention relates to a spacer grid for beams

  tubulars, more particularly intended as an example for

  tubular rings of steam generators of nuclear power plants.

  The steam generators of nuclear power plants with water

  have a tubular beam of great length, straight or in U. traversed by the primary fluid from the reactor core, and

  bathed by the secondary fluid that enters in liquid form to

  fired in the form of steam after taking a large part of the

lories of the primary fluid.

  For the correct and efficient operation of such an exchange

  However, whatever the thermal constraints, it is necessary

  the long and thin tubes of the beam are well maintained at their

  optimal spacing, and at the same time the circulation of the secondary fluid

  around the beam can be carried out without significant loss of

aunt.

  For this purpose, and more particularly in the case of

  tubular U-shaped sheaths, the tubes are usually kept radially

  at several points by holding and spacing grids.

  The most conventional grids are constituted by a simple flat plate pierced with holes, at the pitch of the tube bundle and of diameter

  slightly greater than the outside diameter of these, to

  inevitable misalignments when mounting the generator.

  These grids further comprise a mesh of additional orifices for the circulation of the secondary fluid; we try of course to keep between the holes sections sufficient to resist

  radial forces, so that the cross sections of the fluid remain

  are relatively weak and restrict its circulation. In addition, this solution facilitates the appearance of corrosion in the transition zones between the actual support zone of the tube on the spacer and the

  crescent area o appears the game due to differences in diameters.

  It has been possible to improve the perforated planar grids by producing trifoliated or quadrifolated orifices, for example, in which each

  tube orifice has only three or four

  Incomplete columns with a diameter slightly larger than the outer diameter

  of the tube, and between these are formed

  constitute zones of passage of the secondary fluid. Such realities

  sations improve circulation of the secondary fluid and reduce the risk of corrosion, but require machining by broaching,

  which is expensive and requires the use of special machine tools.

  Complex grids, composed of several

  networks of parallel bars superimposed and crossed to form a mail-

  lage enclosing the tubes. The networks must then be assembled together by mechanical assembly or welding. We thus obtain a system

  allowing good circulation conditions of the secondary fluid.

  But the need for many delicate assemblages increases the difficulty of

  the assembly and its cost; in addition these systems do not all give

  full satisfaction for the resumption of lateral efforts.

  The present invention allows the realization of spacer grids

  its low manufacturing cost thanks to simple machining, without

  tight tolerances, and achievable on conventional machines, while ensuring

  with a good rigidity of the whole, a good maintenance of the tubes and

  a large section of passage of the secondary fluid.

  According to the invention, the spacer grid is constituted by a flat sheet having on each face a series of parallel grooves,

  of different direction for each face, with depth of reason

  respectively, relative to each face, such as their sum

  greater than the thickness of the sheet, the number, the pitch and the

  grooves being determined according to the characteristics

  corresponding tubular bundle.

  The invention will be better understood with reference to embodiments given by way of example and represented by the accompanying drawings. FIG. 1 is a perspective view of a portion of

  spacer grid made according to the invention.

  Figure 2 is a section on II-II of Figure 1.

  Figure 3 is a section on III-III of Figure 1.

  Figure 4 is a section on IV-IV of Figure 1.

  FIG. 5 is a partial partial view of FIG.

  which tubes are shown in place in the spacer.

  Figures 6, 7 and 8 show more schematically

laughing.

  Referring firstly to all of Figures 1 to 4, Figure 1 shows the angle of a thick plate machined according to the invention to form a spacer grid. It is to facilitate the drawing and

  description which is shown here a part of a rectangular sheet,

  but of course, especially for use in a generator

  of steam, the contour of the sheet before machining will most often be

  lar. On its upper side the sheet 1 is here cut by a series of parallel grooves profile 2 U-shaped. On the underside it is also hollowed by a series of parallel grooves profile

  3 inverted U, the groove directions 2 and 3 being perpendicular

  res. The depths of the grooves 2 and 3 are here greater than half

  thickness of the sheet, so that there is interpenetration of the grooves and

  appearance of lights 5 at their intersections. If, like here, the grooves

  res 2 and 3 are equidistant, of the same width and perpendicular,

  obtains a regular network of orifices 5 whose profile is square when

  we look at the sheet perpendicular to one or other of its

these.

  The sheet thus perforated remains a single piece, so particularly

  rigidly, and presents itself as the offset superposition of two crossed networks of parallel bars 7 and 8, rigidly joined by

  connecting parts 9. It should be noted that the two series of grooves can

  can be made on quite classic machine tools like

  planers or milling machines, and with tools quite

  suels, ie in very economical conditions of realization.

  It has thus been realized, at low cost, a spacer grid that functionally behaves like the complex grids mentioned

  higher, and like these allows a good flow of fluid se-

  ondary. We can now refer to Figure 5, which corresponds to

  to a part of Figure 1, but with tubes It engaged in the lu-

  5 of the plate. In the upper part of the plate the tubes 11 are held between the parallel bars 7; in the lower part they are held between the bars 8. It is seen that in the plane of the upper face of the spacer grid, the free section of the fluid passage

  secondary pressure around a tube corresponds to the area between the

  tangle 13 drawn in phantom, and the circle 14, also in phantom and which represents the outer contour of the tube. It is the same in the plane of the lower face, where the rectangle would then be of the same surface but oriented at 900 with respect to rectangle 13. It can be seen that this surface is relatively large, and considered sufficient for the two bars 7 and 8 do not constitute an obstacle to the circulation of the secondary fluid. In the zone between the two faces of the grid, the passage section is also important because

  that it corresponds to the perforated parts in the side walls of each

  than groove. It should be noted that the passage sections between

  bars on the lower and upper sides of the spacer

  than the characteristics of the tubes, that is to say of their step and

  their diameter; on the other hand the section of passage inside the en-

  treness depends on the relative values of the groove depths and

  the thickness of the blank sheet, so that the choice of these various parameters

  will depend on the residual section that we want to leave to the bar-

  7 and 8, ie the importance of the radial efforts that one

want to make them bear.

  Of course, the invention is not strictly limited to the mode

  described by way of example, but it also covers

  which would differ only in details, for

  alternative embodiments, or by the use of equivalent means.

  Thus it is not strictly necessary that the two series of grooves are of the same depth, and it is enough to make appear

  the lights necessary for the passage of the tubes that the sum of the depths

  of each series is greater than the initial thickness of the plate.

  Inequality in groove depths would lead to unequal

  thickness of bars 7 and 8, which can be sought if the

  transversal efforts may be preponderant in some

  rection. Among the various possible variants of detail, it would also be possible to provide small complementary simple machining operations, for example to better guide the tubes as in FIG.

  slightly increase the cross sections of the fluid as on the

Figure 7.

  We could still imagine many variations playing

  on the direction, the pitch or the relative widths of the grooves. The

  FIG. 8 schematically illustrates an embodiment for a triangular mesh.

  tubular tube, where the two series of grooves instead of being

  pendiculars are inclined at 600; the holes of passage of tubes

  then, seen from above, a diamond shape.

  It might also be possible to create more rigid zones by removing

  locally some grooves, or to further facilitate the circulation

  secondary fluid by profiling the outer edges of the bars 7 and 8.

  Finally, and without this limiting the possible variants, we

  would still imagine using two overlapping grids, each with half the number of bars, and with alternating supports for each tube, which

  would further increase the passage section of the secondary fluid.

Claims (1)

CLAIM   1.- spacer grid for the tubular bundle of a heat exchanger, for transverse holding of the tubes while allowing the longitudinal circulation of the fluid bathing the tubes externally, characterized in that it is constituted by a flat sheet having   on each face a series of parallel grooves, of different   ferent for each face, with groove depths respectively   each face, such that their sum is greater than the thickness sheet metal,   the number, pitch and width of the grooves being determined according to   corresponding characteristics of the tubular bundle.