GB2057669A - Supporting grid for heat exchanger elements and method of making such grids - Google Patents

Abstract

A supporting grid for mutually spaced parallel cylindrical heat exchange members, such as rods or tubes 1, comprises a plurality of generally annular elements 2 each disposed in a plane which is normal to the axes of the members 1, and each being arranged between a group of three or four of said members 1, each element 2 being in contact with others of said elements and rigidly interconnected thereto (e.g. by welding). <IMAGE>

Description

SPECIFICATION Supporting grid for heat exchanger elements, and method of making such grids This invention relates to a supporting grid for heat exchanger elements. Known supporting grids of this kind consist of drilled flat plates or rods extending crosswise between rows of tubes. The disadvantage of these grids is that longitudinal flow around the cylindrical members is impossible, or else only at the cost of a considerable pressure drop.

German Patent Specification 26 42 521, for example, also discloses supporting grids consisting of inter-connected sheet-metal strips, in which spring tongues bent out of the strips support the tubes. The advantage of this is that the supported members are widely exposed to the cooling action of the flow medium and any vibrations of the members are damped by friction on the spring tongues. A disadvantage, however, is that the supported members can undergo considerable deflection in the event of high shock loading transversely of said members as may occur in earthquakes.

The object of the invention is to provide a supporting grid which allows a longitudinal flow around the cylindrical members with a minimum pressure drop and holds the members as rigidly as possible in the event of earthquakes.

Accordingly the present invention provides a supporting grid for mutually spaced parallel cylindrical members, such as rods or tubes which are intended to participate in a heat exchange, including a plurality of generally annular elements which are each disposed in a plane which is normal to the axes of the members, and are arranged between each group of three or four of said members so as to be in contact with one another and rigidly inter-connected.

A special advantage of this arrangement is that manufacture of the grids is very simple and cheap and assembly does not give rise to any difficulty while making high accuracy possible to achieve.

Preferably the annular elements have concave portions to receive the elements so that a large proportion of the annular elements remain within the flow interface of the cylindrical members, and this resuits in a very low pressure drop. In addition, this construction allows the grid structure to deflect only to a slight extent under high loading such as earthquakes.

Preferably the annular elements have flat outer surfaces to engage one another and this contributes to stiffening the portions of the annular elements extending between adjacent cylindrical members.

Preferably the annular elements have a slit in one of such flat outer surfaces which enables small in-accuracies in the manufacture of the annular elements to be compensated for so that the supporting grid can be produced to a close tolerance.

The invention also extends to a method of making such supporting grids.

In order to promote a fuller understanding of the above and other aspects of the present invention, some embodiments will now be described, by way of example only with reference to the accompanying drawings in which: Figure 1 is a cross-section through a heatexchanger.

Figure 2 is a plan view of an annular element in Figure 1 to an enlarged scale.

Figure 3 is a longitudinal section through a part of an annular element abutting a tube.

Figures 4a to 4d show stages in the manufacture of an annular element, the illustration not being to scale.

Figure 5 is a plan view of an assembly plate showing two grid edges for the assembly of a supporting grid.

Figure 6 shows part of a supporting grid connected to an outer grid edge in plan view.

Figure 7 is a section through the edge portion VIl-VIl in Figure 6.

Figure 8 is an elevation of an annular element with apertures.

Figure 9 is a cross-section through the annular element of Figure 8.

Figure 10 is a cross-section through a heat exchanger in which the cylindrical members are represented by tubes arranged in a square pattern and the annular elements accordingly are situated between each four tubes, and, Figure 11 is a cross-section through a heat exchanger with staggered tubes, supporting corrugations being provided in the region of one edge of the annular elements in each case.

Referring to Figure 1 , five heat exchanger tubes 1 of a heat exchanger, are shown in section in a regularly staggered arrangement. A generally annular element 2 is disposed in the space formed between each group of three tubes 1. As will be seen from Figure 2 each annular element consists of three concave side portions 4, three flat portions 5 and six rounded edges 6 therebetween.

As will be seen from Figure 3, a pair of shallow corrugations 8 is provided in each of the concave parts 4 and, for example, have flat surfaces 10 facing the adjacent exchanger tube.

Each annular element 2 has a slit 12 in the middle of one of the flat parts 5. The dimensions of the annular elements are such that the adjacent elements are each in contact at the flat parts 5, while the flat surfaces 10 of the corrugations 8 abut the tubes or are spaced therefrom by a specific tolerance. Adjacent annular elements are interconnected, preferably welded, in the region of the flat parts 5 in each case. Welding may be carried out just at the top and bottom edges or by spot welding or roil welding at one or more points.

Instead of two rows of corrugations, just one may be provided, e.g. at mid-height of the annular element. Such corrugations may alternatively be completely dispensed with, so that the annular elements bear against the tubes with varying-size zones of their concave surfaces.

The corrugations 8 stiffen the annular elements. They also have the advantage that the points of support for the exchange tubes 1 can be accurately located during manufacture.

Figure 4 is an example with two rows of corrugations showing the four steps a to d for the production of an annular element 2 according to Figure 2. Three concave surfaces 14 with a pair of corrugations 8 in each case are pressed from a flat sheet-metal strip 13 (Figure 4a) and two narrow surfaces are bent up at the ends (Figure 4b). In the next step, the pre-pressed workpiece is bent along two edges 1 5 (Figure 4c) and finally in the last step the workpiece is bent into the form of the annular element by bending it along the parallels 16 (Figure 4d).

Figure 5 shows part of an assembly jig 20 from which 35 pins 22 project upwardly, being disposed in staggered relationship over a sector of an angle of 600 at the centre. Another pair of pins 22' is provided, on each side of this sector. Three stops 23 are also provided on the plate 20 in such a manner that a circular outer edge 25 of a grid can be fitted between these stops 23 and adjacent pins 22. In the same way, two stops 24 are provided on the other side of the pin arrangement and together with adjacent pins 22 they retain a likewise insertable circular inner edge 26 of a grid.

Annular elements 2 are fitted on the assembly plate between each three pins 22 in each case in such a manner that two flat slotted portions 5 of adjacent elements are never in contact with one another. If all the spaces between the pins 22 have been filled, the adjacent annular element portions are welded together at the edge or at least in their top half. When a 600 sector has been welded together at least at one end in this way, it is removed from the assembly plate, moved through 600, and re-fitted to the assembly plate, the two corresponding pins 22t acting as locating pins. The spaces between the pins 22 of the 600 sector are then again filled with annular elements, which are welded together and to the elements of the first sector. After this has been done five times, the result is a complete grid in the form of a circular ring.If just the top sides of the elements were originally welded, the grid is then turned over and fitted six times in succession to the plate and the second side is welded sector by sector.

As shown in Figures 6 and 7, the supporting grid can be connected to the outer grid edge 25 by fillers 30 either during the sector-by-sector construction or else after the circular ring has been closed. The same applies to the inner edge 26. To this end, the grid edges 25 and 26 are provided on the inside, preferably on both sides, with recesses 32 so that the fillers 30 can be fitted on the one hand against the shoulders 33 of these recesses and on the other hand against the sides of the corrugations 8. The fillers 30, for example, are connected by two weld seams 34 to the outer edge 25 and similarly to the inner edge 26.

To increase the heat transfer at the cylindrical members, the annular elements 2 may be provided with apertures 40 in these sides as shown in Figures 8 and 9, preferably in the concave portions between the corrugations. In these conditions a coolant flow occurs in the region of these apertures and, if required, in the intermediate zone 41.

To intensify the flow between the concave portions of the annular elements 2 and the cylindrical members 1, it may be advantageous for the corrugations to extend over only part of the width of the concave portions 5 as shown at 8' in Figure 8. A disadvantage of this step is that the annular element loses its stiffness in these conditions.

Figure 10 shows a supporting grid for a square arrangement of the cylindrical members 1. The portions having the slits 12 in the annular elements 2 extend alternately in different directions. Consequently, the grid has the same strain characteristics in both main directions; and in addition, any inaccuracies in manufacturing the elements can be compensated for on assembly.

To increase the stiffness of the supporting grid for identical material thickness of the annular elements, the supporting zones of the corrugations 8 can be shifted to the zone near the flat portions 5 as shown in the embodiment of Figure 11. In the annular elements 2' of Figure 11, a narrow corrugation 8" is provided in each case on either side of the flat portions 5 with the slit and the lines of contact 50 thereof are situated near the contact plane E between the two adjacent heat exchange elements. The third corrugation 8"' of the same row in this exemplified embodiment is at one of the two edges 1 6 of the concave portion 4 opposite the slit.

If the annular elements have two rows of corrugations as shown in Figure 3, it may be advantageous to dispose the corrugations 8"' in two rows on the same edge 1 6. However, this means that when two flat portions 5 are connected, each with a corrugation 8"' adjacent to it, the corrugations being directed in opposition, said corrugations must be brought into contact with the associated pins 22 when the annular members are placed in the assembly jig, by means of a slight pressure which can be applied by welding tongs, the two jaws of which engaging the said portions 5 may be provided with spring elements acting in opposition and pressing internally against the corrugation 8"'.

This complication can be avoided if the top corrugation 8"' is symmetrically offset from the bottom corrugation 8"'of each annular element, i.e. a corrugation at each edge 1 6. As a result, if suitably dimensioned, the corrugations 8"' bring the annular elements automatically into contact with the associated pins 22 of the jig by slight elastic torsion, so that ordinary welding tongs can be used. In contrast to the above example, this construction means that not just one form but two reversely identical forms of the annular elements have to be manufactured.

If the provision of corrugations 8, 8', 8" and 8"' is dispensed with, it is advisable for material to be removed from the arcuate edges of the concave portions 4 facing the cylindrical members, or for them to be plastically broken, on the one hand in order to protect the cylindrical exchange elements from engagement by sharp edges and on the other hand to prevent these edges from hooking into the material of the exchange elements, so that relative displacement of the exchange elements in the supporting grids under thermal expansion is possible without high frictional forces, which would result in the grids sagging. Such sagging would in turn increase the frictional forces at adjacent points and might ultimately result in destruction.

Claims (11)

1. A supporting grid for mutually spaced parallel cylindrical members, such as rods or tubes which are intended to participate in a heat exchange, including a plurality of generally annular elements which are each disposed in a plane which is normal to the axes of the members, and are arranged between each group of three or four of said members so as to be in contact with one another and rigidly interconnected.

2. A supporting grid as claimed in Claim 1, in which the generally annular elements have concave portions to receive the heat exchange members.

3. A supporting grid as claimed in Claim 1 or 2, in which the generally annular elements have a flat outer surface at the point where they contact one another.

4. A supporting grid as claimed in Claim 3, in which the generally annular elements have a slit in the middle region of one of said flat outer surfaces.

5. A supporting grid as claimed in Claim 4, in which the generally annular elements are each rigidly connected to the adjacent annular element on either side of said slit, the adjacent elements not being slit at the connecting points.

6. A supporting grid as claimed in any one of Claims 2 to 5, in which the generally annular elements have at least one outwardly directed corrugation in the region of the concave portions.

7. A supporting grid as claimed in any one of Claims 1 to 6, in which the annular elements have apertures in the portions which lie adjacent the cylindrical heat exchange members.

8. A method of making a supporting grid as claimed in Claim 1, in which said generally annular elements are inserted between pins disposed in a suitable pattern on a jig and are preferably welded to connect them together.

9. A method as claimed in Claim 8, in which the annular elements are formed from sheet-metal and are pushed between the pins of the jig, and then adjacent annular elements are welded together on one side, the resulting grid after welding is removed from the plate, turned over, and re-fitted on pins, whereupon the other side of the grid is welded.

10. A supporting grid for heat exchange elements substantially as herein described with reference to the accompanying drawings.

11. A method of making a supporting grid for heat exchange elements substantially as herein described with reference to the accompanying drawings.