US2749600A - Method of making heat exchangers - Google Patents

Description

June 12, 1956 o. PERSSON METHOD oF MAKING HEAT EXCHANGERS Filed Feb. 14, 1955 IN1/EN TOR.

wz- W @SCA/Q PEQsso/v A 7 rok/vf x United States Patent O F NIETHIOD F MAKING HEAT EXCHANGERS Oscar Persson, Bromma, Stockholm, Sweden, assignor to Aktiebolaget Rosenblads Patenter, Stockholm, Sweden, a Swedish company Application February 14, 1955, Serial No. 488,090

Claims priority, application Sweden February 18, 1954 3 Claims. (Cl. 29-157.3)

This invention relates to tubular heat exchangers comprising a bundle of long and slender heat exchanger tubes arranged in parallel interrelation between two end plates and spaced from each other by spacing elements in the form 'of metallic wires extending helically around each one of at least certain of said tubes to the full length thereof between the end plates, the arrangement being such as to enable the withdrawal of any one of the tubes through either end plate without obstruction from said spacing elements.

More particularly the invention relates to a method of providing tubes with such spacing wire coils in the course of assembling a tube bundle of the kind described.

The most obvious method would be to try to wind an initially straight wire directly onto the tube fitted in the end plates. Attempts made to this end, however, have involved great d-iiliculties, iirstly in respect of threading the wire through the narrow clearance between adjacent tubes, and, secondly, in respect of winding the wire to assume a true helical shape close to the slender tube without at the same time also bending this tube inadvertently so as to buckle the same at its points of attachment to the end plates. Such attempts have led to the idea of rst giving the wire coil its final shape as mounted, and subsequently threading the tube through the end plates and through the wire helix. However, due to the considerable length of such a wire coil, it will be extremely diicult to keep the coil in store and to transport and handle it in large numbers without causing deformation thereof.

The invention has for its object to avoid such inconveniences and is mainly characterized by the following combined features. The wire coil is pre-fabricated by irst winding a wire in a helix in the shape of a coil having the desired number of turns with which the wire shall encircle the tube, but having an inner helix-diameter considerably larger than the outer diameter of the tube and an axial helix-length considerably less than the distance between the end plates. However, at each one of its ends the wire is wound one or a few turns at a low pitch and to an inner helix-diameter at least approximately equal to the outer diameter of the tube. The length of the wire is so dimensioned that when, upon longitudinal extension of the large-diameter turns of the wire, the wire is extended to a length corresponding to the distance between the tube mounting end plates, said turns will con tract to an inner helix-diameter at least approximately equal to the outer diameter of the tube. In its unextended condition the wire coil is threaded over the tube between the end plates as the tube is introduced therein, and subsequently the wire coil is extended in the manner just described so as to cause it to reach both end plates, whereupon the wire coil at each end is welded to the respective end plates without securing it to the tube. Thereafter, if necessary, after having introduced the tube into the end plates, the wire coil may be after-tensioned by compressing the end turns of the wire coil at one end,

Patented June l2, 1956 at least, so as to cause the coil to engage the tube accurately. Such a wire helix is applied to one only of any two adjacent tubes, and the tubes are fitted in their respective positions in the end plates in such a sequential order that a tube to be provided with a wire coil will be introduced as an outer tube relative to tubes previously tted.

The invention will now be described more closely in conjunction with the accompanying drawing in which:

Fig. l is a side view of a tube set and illustrates one stage of the assembling method according to the invention,

Fig. 2 is a similar side view illustrating two tubes mounted in accordance with this method, and

Figs. 3 and 4 illustrate each, to a larger scale, a crosssection through a portion of a tube set with triangular tube pitch and square tube pitch, respectively, said tube sets being also produced in accordance with the method according to the invention.

As illustrated in Fig. l, a tube 1a is iitted in the tube carrying end plates 2 and 3, respectively. An adjacent tube 1b to be equipped with a spacing wire helix or coil is being introduced through the end plate 2, and threaded over the portion of this tube projecting into the zone between the two end plates is a wire coil 4a pre-fabricated in accordance with this invention. The continued buildingaup of the tube set, according to the present invention,

vmay be carried out, for instance, in the following manner:

At one end the wire coil is secured to the end wall 2 by being welded thereto at a point 5a suitably located at a place on the end wall where the distance to adjacent tubes is as large as possible. The tube is then displaced further into the end wall 3 to the position shown in Fig. 2, the wire coil preferably being extended simultaneously with this displacement so as to reach this end wall with its other end. The coil is then welded at its latter end t0 the end wall at a point 5b in the same manner as the coil was welded to the end wall 2 at the point 5a. 'Ihereafter the wire coil will have the shape as illustrated in Fig. 2, possibly after having been subjected to after-tensioning by compressing the more tightly wound turns at one or both ends of the coil, the latter forming, in this condition, an ethcient spacing element relative to adjacent tubes in the set.

When progressively building up a tube set in this manner it will only be possible to surround one of any two adjacent tubes with a wire coil, since otherwise the wire coil previously fitted would prevent the other coil from being extended in the course of assembling the same, and the tightly wound end turns of adjacent wire coils could not be accommodated in side-by-side relation. Therefore, according to the invention, only the tubes 1b are provided with wire coils, these tubes being distributed in such a manner within the tube set that all tubes 1a adjacent to the same are devoid of Wire coils whereas each tube 1a lacking a wire coil will be secured or substantially secured against bending forces in all directions by the wire coils of adjacent tubes 1b equipped with such coils. This eiect has been attained, in the case of the tube set of Fig. 3, in which the tube-pitch is triangular, by providing every third tube in each row of tubes with a wire coil, such tubes of adjacent tube rows being displaced in relation to each other in the direction of the rows by one and a half tube center spacing. If, on the other hand, the tube-pitch is a square one, then the same elfect will be attained in accordance with Fig. 4 by pro viding every second tube in each row with a wire coil, such tubes being so chosen in adjacent rows as to be displaced in relation to each other in the direction of the rows by one tube center spacing. In order to accommol date the wire coils in their unextended condition 4a on the tubes, according to the invention, the assembly of the tubes is undertaken in such a sequential order that each tube to be provided with a wire coil will be inserted as an outer tube relative to the tubes previously inserted.

It would be obvious that, in a tube set assembled in the manner described, also those tubes having wire coils associated therewith can be withdrawn without being obstructed by such coils, for instance for replacement. The wire coils will t'nus remain in their operative positions without changing their shape during the replacement operation since they are welded to the tube carrying end walls.

It is to be understood that the method described is susceptible of various modifications by those skilled in the art. Thus, for instance, the wire coil in its condition 4a may be wound with its large-diameter turns at a pitch which is larger or smaller than that illustrated. Conveniently, these turns could be wound close to each other. The sequential order of the assembling steps could be varied to a certain extent, so that, for instance, from a starting position according to Fig. 1, pushing home of the tube 1b and the extension of the wire coil could be carried out independently. The wire coil could be extended from its condition 4a to its condition 4b and only thereafter be welded to the end walls, etc.

What I claim and desire to secure by Letters Patent 1. For constructing a bundle of heat exchanger tubes extending side by side between two tube plates, a method of providing such tubes with a metallic wire coil extending close around the tube along its entire length between the tube plates, comprising in combination the steps of winding the metallic wire into the shape of a cylindrical coil of considerably less length than the distance between the tube plates and of considerably larger inner diameter than the outer diameter of the tube to be tted with the coil except at both ends of the coil where a few turns thereof are wound at a small pitch to an inner diameter approximately equal to the outer diameter of the tube, the length of said metal Wire being such that on tensioning the large-diameter turns of said coil axially so that the length of the coil will correspond to the distance between the tube plates these turns will contract to an inner diameter approximately corresponding to the outer diameter of the tube, sliding said coil on to the tube between the tube plates as the tube is inserted in the tube plates, tensioning the coil on the tube so as to reach both tube plates, welding the ends of the coil wire to the respective tube plates but not to the tube, axially compressing the small-pitch end turns at least at one end of the coil, so as to atertension the coil, if so required, so that it will surround the tube closely at all parts of the coil wire, equipping one only of two adjacent tubes with such a coil and Htl-ing the tubes in the tube plates n such a sequential order that a tube to be equipped with a coil Will be introduced as an outer tube in the bundle in relation t0 tubes previously iitted.

2. A method according to claim l for the construction of a bundle of tubes with triangular pitch, comprising the steps of providing a coil on every third tube only in each row of tubes and selecting tubes thus to be itted which are situated one and a half pitch from such tubes in adjacent tube rows counted in the row-directions.

3. A method according to claim 1 for the construction of a bundle of tubes with rectangular pitch, comprising the steps of providing a coil on every second tube only in each row of adjacent tubes and selecting tubes thus to be tted which are situated one pitch from such tubes in adjacent tube rows counted in the row-directions.

References Cited in the le of this patent UNITED STATES PATENTS 2,691,813 Polad Oct. 19, 1954 FOREIGN PATENTS 219,263 Switzerland June 1, 1942

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