GB2125529A - Heat transfer fin for a heat exchanger - Google Patents

Abstract

Rows of rectangular openings 12 are formed in a fin stack 10, each opening having a tall projection 13 upstanding from its longer edges. Each projection 13 contacts the next fin in the stack and provides support during insertion of tubes. To prevent the fin stack from skewing as a result of the tube insertion process, the projections 13 in alternate rows extend from one surface of the fin, while the projections in the rows in between extend from the opposite surface of the fin. Alternatively, all of the projections extend from the same side of the fin, but the taller projections 13 in alternate rows are disposed on one side of their respective openings 12 while the taller projections 13 in the rows in between are disposed on the opposite side of openings 12. The projections may alternate from opening to opening in each row, rather than from row to row. <IMAGE>

Description

SPECIFICATION Heat transfer fin for a heat exchanger This invention relates to a heat transfer fin for a heat exchanger.

In our published UK patent application no.

2088035A there are described heat transfer fins which are self-spacing, i.e. when a plurality of the fins are stacked one upon another prior to the insertion of tubes through aligned openings in the fins, upstanding projections on the fins serve to space each fin at an appropriate distance from its neighbours. In order to provide support for the fins where it is most needed when the tubes are inserted as aforesaid, the projections are disposed along edges of the tube openings. In one particular example, each opening has projections of unequal height along its opposite edges, with only the taller of the two projections contacting the next adjacent fin in the stack. This construction has the advantage that a sufficient spacing can be provided between adjacent fins even when the projection is formed from the material which is removed to produce the respective tube opening.However, as disclosed in the above-mentioned application, all of the projections in all of the fins extend from the same side of their respective openings and in the same direction. This gives rise to the problem that each opening is supported on one side only during insertion of the tubes, this side being the same from opening to opening, and consequently there is a marked tendency for the fin stack to skew as the tubes are inserted through the openings. This skewing is difficult to correct in the final assembled heat exchanger.

It is an object of the present invention to provide an improved version of the heat transfer fin disclosed in the above-mentioned application, whereby the skewing problem can be eliminated.

According to one aspect of the present invention, there is provided a heat transfer fin having a plurality of openings therein through which tubes are passed in use, each opening having projection means upstanding from its periphery, each projection means being taller on one side of the respective opening than on the opposite side thereof, the projection means being composed of a first type wherein the taller part thereof upstands from one surface of the fin and is disposed on one side of the respective opening with respect to a predetermined direction, and at least one of a second type wherein the taller part upstands from said one surface of the fin and is disposed on the opposite sides of the respective opening with respect to said predetermined direction and a third type wherein the taller part upstands from the opposite surface of the fin and is disposed on said one side of the respective opening with respect to said predetermined direction.

In a particular embodiment the openings are disposed in rows which are generally mutually parallel, and the projection means in each row are all of the same type. Alternatively, the projection means in each row can alternate between the first type and one of the second and third types.

In order to prevent the taller part of each projection means from entering the adjacent opening in a neighbouring fin when a plurality of such fins are stacked one upon another, said taller part preferably has on an edge thereof remote from the fin proper one or more protrusions which extend laterally therefrom. The protrusions can take the form of bent-over ears at the ends of said remote edge, for example.

Conveniently, each opening is rectangular or oblong in shape, and the respective projection means is provided only along the longer edges thereof.

According to a second aspect of the present invention, there is provided a heat exchanger comprising a plurality of heat transfer fins as defined in any one of the last three preceding paragraphs which are stacked one upon another such that said openings therein are mutually aligned, and a plurality of tubes passing through the aligned openings, an edge of said taller part of each projection means on each fin which is remote from the fin proper being engaged with the next adjacent fin in the stack.

The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a plan view of part of a heat transfer fin according to one embodiment of the present invention; Figure 2 is a sectional side view of a heat exchanger including a plurality of fins of the type shown in Fig. 1, the fins being depicted along the section ll-ll in Fig. 1; Figure 3 is a section taken along the line Ill-Ill in Fig. 2; and Figure 4 is a plan view of part of a heat transfer fin according to a second embodiment of the invention.

Referring first to Figs. 1 to 3, the heat exchanger shown therein comprises generally a stack of heat transfer fins 10 for, in this embodiment, radiating heat from a fluid which is passed through a plurality of flatsided tubes 11. The tubes 11, which can be lock seam, seam welded or solid drawn, pass through respective oblong or substantially rectangular openings 1 2 which are punched out of the fins 1 0. The punching operation is also arranged to produce a pair of projections 1 3 and 1 4 bounding the longer sides of each opening 1 2 respectively, the projections being upstanding from the remainder of the respective fin 10 and being metallurgically bonded to the tube 11 that passes through the respec tive opening 1 2. The projection 1 3 of each pair is taller than the projection 14, and an edge thereof remote from the fin proper abuts against the neighbouring fin in the stack. In order to prevent the projection 1 3 from entering the adjacent opening 1 2 in the neighbouring fin, a pair of bent-over ears 1 5 are provided at opposite ends respectively of its said remote edge.The projections 1 3 thus serve to space the fins apart from one another and provide support where it is needed (i.e. directly adjacent the openings 12) when the tubes 11 are inserted during manufacture of the heat exchanger.

As can be seen to advantage in Fig. 1, the openings 1 2 are provided in mutually parallel rows in each fin10. In every other row, the projections 1 3 and 14 all upstand from one surface of the fin 10, while in the rows in between the projections are upstanding from the opposite surface of the fin. Although only one example of each row is shown in Fig. 1, it is to be appreciated that these rows alternate across the full width of the fin.

When the fins 10 are stacked upon one another and tubes 11 are inserted through the openings 12 in a given one of the rows, all of the projections 1 3 in that row will bend in the same direction under the applied load, resulting in a tendency for the fin stack to skew so that the tubes do not become oriented in the desired manner at right-angles to the fins. On the other hand, when tubes 11 are inserted through the openings 1 2 in an adjacent row, the projections 1 3 (since they extend in the opposite direction to their counterparts in the first-mentioned row) bend in the opposite direction, giving a tendency for the fin stack to skew in the opposite sense.Overall, these two effects balance one another so that, when all of the tubes 11 have been inserted, there is no net skewing of the fin stack relative to the tubes. (It is to be noted that, for this effect to work, the projections 1 3 in all of the rows must be disposed on the same side of their associated openings 12, this being the righthand side as viewed in Fig. 1).

As can be seen to advantage in Figs. 2 and 3, in the resulting heat exchanger the projections 1 3 in every other row in each fin 10 contact the fin above, while the projections 1 3 in the intervening rows contact the fin below.

An alternative form of heat transfer fin is shown in Fig. 4, in which the openings 1 2 are once again arranged in mutually parallel rows. In this fin, the projections 1 3 and 14 in all of the rows upstand from the same surface of the fin. However, the taller projections 1 3 are now disposed on one side of their associated openings 1 2 in every other row, while in the rows in between the projections 1 3 are disposed on the opposite side of the openings 12. As with Fig. 1, only one example-of each row is shown in Fig. 4, but it is to be understood that these rows alternate across the full width of the fin.

In a similar manner to the fin shown in Fig.

1, when tubes 11 are inserted through the openings 12, the taller projections 1 3 in alternate rows bend in opposite direction, thereby cancelling out any skewing effects.

In both of the embodiments described above, the projections 1 3 in each row all upstand from the same surface of the fin and are all disposed on the same side of their respective openings 12, with the projections 1 3 in alternate rows either upstanding from opposite surfaces of the fin or being disposed on opposite sides of their openings 12. In other words, the openings and projections in one row are all of one type, while the openings and projections in the adjacent rows are all of a different type. In an alternative arrangement (not illustrated), the openings and projections alternate in type along the rows themselves, in addition to or as an alternative to alternating in type between adjacent rows.

Thus, the fin shown in Fig. 1 could be modified such that every other opening 1 2 in each row has its associated projection 1 3 upstanding from one surface of the fin 10, with the openings in between having their projections 1 3 upstanding from the opposite surface of the fin. Similarly, the fin of Fig. 4 could be modified such that every other opening 1 2 in each row has its projection 1 3 disposed on the left-hand side thereof, while the openings in between have their projections 1 3 disposed on the right-hand side thereof.

The fins shown in Figs. 1 and 4 are preferably produced by apparatus similar to that depicted in Fig. 8 of the above-mentioned UK patent application no. 2088035A. In this apparatus, a continuous strip of material is passed between punch and die rollers which punch out the openings 12 and at the same time form the projections 1 3 and 14, the strip subsequently being cut into desired lengths to form the fins 10. In order to produce the fin shown in Fig. 1, two pairs of punch and die rollers can be provided to operate in series on the strip, with one pair of rollers punching out the openings and projections of every other row while the other pair of rollers punch out the openings and projections of the rows in between. Alternatively, a single pair of rollers can be employed wherein each roller has circumferentially extending rows of punch formations and die formations which alternate across the width thereof, the punch formations of each row on one roller co-operating with the die formations of a respective row on the other roller. The fin of Fig. 4 can be produced using a single pair of rollers, on which the punch formations and die formations are separately provided: on the punch roller, the punch formations will alternate between two different types across the width of the roller to take account of the alternate dispositions of the projections 1 3 from row to row.

In Figs. 1 to 4, reference numeral 1 6 denotes strengthening swages which are provided between the rows of openings 1 2 to stiffen the fin. As can be seen to advantage in Fig. 3, alternate ones of these swages may project on opposite sides of the fin across the width of the latter. Reference numeral 1 7 designates ventillation slits which are formed in the fins 10 to disturb the air flow in the finished heat exchanger and thereby improve the heat transfer characteristics of the latter: these slits can however be replaced by other formations for disturbing and/or disrupting the air flow, or such means can be omitted altogether.

Although the tube openings 1 2 have been described as arranged in rows, other dispositions of the openings can be employed. Moreover, adjacent openings in adjacent rows can be staggered relative to one another, rather than being mutually aligned in the manner depicted in Figs. 1 and 4. Furthermore, the openings can be oriented with their longer edges at an acute angle to the direction of extent of the rows, rather than being perpendicular thereto as shown in the drawings.

Claims (8)

1. A heat transfer fin having a plurality of openings therein through which tubes are passed in use, each opening having projection means upstanding from its periphery, each projection means being taller on one side of the respective opening than on the opposite side thereof, the projection means being composed of a first type wherein the taller part thereof upstands from one surface of the fin and is disposed on one side of the respective opening with respect to a predetermined direction, and at least one of a second type wherein the taller part upstands from said one surface of the fin and is disposed on the opposite side of the respective opening with respect to said predetermined direction and a third type wherein the taller part upstands from the opposite surface of the fin and is disposed on said one side of the respective opening with respect to said predetermined direction.

2. A heat transfer fin as claimed in Claim 1, wherein the openings are disposed in rows which are generally mutually parallel, and the projection means in each row are all of the same type.

3. A heat transfer fin as claimed in Claim 1: wherein the openings are disposed in rows which are generally mutually parallel, and the projection means in each row alternate between the first type and one of the second and third types.

4. A heat transfer fin as claimed in Claim 1, 2 or 3, wherein said taller part of each projection means has on an edge thereof remote from the fin proper one or more protrusions which extend laterally therefrom.

5. A heat transfer fin as claimed in Claim 4, wherein said protrusions take the form of bent-over ears at the ends of said remote edge.

6. A heat transfer fin as claimed in any preceding claim, wherein each opening is rectangular or oblong in shape, and the respective projection means is provided only along the longer edges thereof.

7. A heat transfer fin substantially as here it before described with reference to Figs. 1 to 3 or Fig. 4 of the accompanying drawings.

8. A heat exchanger comprising a plurality of heat transfer fins each being as claimed in any preceding claim which are stacked one upon another such that said openings therein are mutually aligned, and a plurality of tubes passing through the aligned openings, an edge of said taller part of each projection means on each fin which is remote from the fin proper being engaged with the next adjacent fin in the stack.