GB2354817A - Fin construction - Google Patents

Abstract

A corrugated fin 18 for a heat exchanger is formed by folding a thin piece of planar material, e.g. Aluminium foil, in a concertina fashion so as to produce a set of leaves 24. Each leaf (e.g. 24a) is further divided into several strip sections 26 by making parallel slits at regularly spaced intervals along the length of the leaf and displacing the portions between the slits alternately to one side or the other side of the leaf. Each strip section lies in a plane parallel to the original leaf plane.

Description

2354817 Fin Construction This invention relates to a fin construction f or

use in gas/liquid and gas/gas heat exchangers, and in particular 5 to motor vehicle radiators.

Conventional heat exchangers used as motor vehicle radiators have a matrix or core which consists of an array of parallel tubes (which carry liquid coolant) and a series of fins which bridge the spaces between the tubes, are in intimate heat exchange contact with the tubes and are traversed by air when air is forced through the radiator, either as a result of motion of the vehicle or as a result of cooling fan operation. It is known to construct the fins in such a way that they optimise the air flow over them, to maximise the heat exchange effect between the air and the f ins.

The conventional f in construction is a slotted, louvre fin form. Slits are formed in the fin material at right angles to the air flow, and the sections of fin material between the slits are distorted to incline the faces of these sections to the air flow.

These fins have disadvantages in that the louvre form f irst of all results in a resistance to air flow.

Secondly, flow separation of the air from the fin surface can take place. Both of these factors cause a significant pressure drop across the radiator core. Thirdly, at low flow rates, much of the air bypasses the louvres and thus desirable heat exchange characteristics are not achieved.

According to the invention, there is provided a fin for a heat exchanger, the fin being formed from sheet material and having a generally planar form with sections of the material being displaced from the plane of the f in, alternately to one side or to the other side of the plane, whilst maintaining the plane of each section substantially parallel to the plane of the fin.

Although reference is made above to a single fin, in a radiator or other heat exchanger, there will be very many fins arranged between each heat exchanger tube. In a common arrangement, an array of fins are all formed from a single strip of initially flat material folded into a zigzag or concertina configuration to form a plurality of parallel or generally parallel leaves, with each leaf having a generally planar form with sections of the material being displaced from the plane of the leaf, alternately to one side or to the other side of the plane, whilst maintaining the plane of each section substantially parallel to the plane of the leaf.

Substantially parallel, in relation to the displaced 20 sections includes displaced sections which lie inclined at angles of up to 70 to the plane of the leaf.

manufacturing considerations may make it difficult to ensure closer parallelism.

The displaced sections are preferably generally rectangular in form with the long edges of the displaced sections separated from the adjacent material and the short edges remaining connected to the adjacent material. when considered in a direction at right angles to the long edges of the displaced sections, the sheet material is displaced alternately to one side or to the other side of the plane, and preferably no material remains in the original plane of the material between adjacent sections.

The fin sections therefore lie either on one side or on the other side of the original plane of the material, and there are no fin sections which remain in the original plane of the material. However it is also possible to have f in sections which do remain in the plane of the 5 material, and this may be desired f or some applic ations.

The long edges of the displaced sections preferably lie at right angles to the concertina f olds.

The invention also extends to a method of making a heat exchanger fin from a piece of initially planar material, the method comprising the steps of making a plurality of parallel slits through the material, each slit stopping before reaching an edge of the material, and then displacing the sections of the material between the slits alternately to one side or to the other side of the plane whilst maintaining the plane of each section substantially parallel to the plane of the fin.

When the material is initially in the f orm of a strip, a plurality of sets of parallel slits can be made at regularly spaced positions along the length of the strip, with the sections of the material between the slits being displaced alternately to one side or to the other side of the plane of the strip whilst maintaining the plane of each section substantially parallel to the plane of the fin, and with the strip being folded concertina fashion to define leaves between each fold, wherein one set of slits lies on each of the leaves.

A preferred material for the fin is an aluminium foil, of the type already known for heat exchanger fin construction.

By maintaining the fin sections substantially parallel to the plane of the fin, and thus substantially parallel to the air flow across the fin, the resistance to air flow is decreased with the result that more air flows over the surfaces of the fin sections, and over both surfaces to produce a marked improvement in the quantum of heat transferred from the fins to the air.

Although the invention will be described particularly with reference to motor vehicle applications and to gas/liquid heat exchange, the scope of the invention is not limited to such applications.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a motor vehicle radiator in which a fin in accordance with the invention can be used; Figure 2 is a view of a fin according to the invention at an intermediate stage during manufacture; Figure 3 is a perspective view of part of a concertina fin construction, with parts of the heat exchanger shown and parts omitted, for clarity; and Figure 4 is a cross section through the f in of Figure 3 taken in the direction of the arrow A in Figure 3.

Figure I shows part of a motor vehicle radiator with a header tank 10 connected to a heat exchange matrix 12. The matrix 12 comprises coolant tubes 14 which carry liquid coolant between the header tank 10 and an equivalent tank at the opposite end of the matrix, and fins 16 which are brazed or otherwise intimately connected to the external surfaces of the tubes 14. In use, hot coolant flowing through the tubes 14 gives up its heat to the tube walls, the tube walls give up their heat to the fins and the f ins give up their heat to the air which f lows across the fins.

As can be seen in Figure 1, the f ins 16, between each pair of coolant tubes 14, take up a concertina or zigzag conf iguration. The f ins are made f rom a strip or ribbon of aluminium foil which is shown in the flat condition at 18 in Figure 2. Figure 2 shows, with dotted lines 20a and 20b, the positions where the strip will be folded to take up the concertina form in which the strip will take the form of a plurality of leaves 24 separated by folds at the dotted lines 20a,20b. Between these positions, the strip is slit at a plurality of slit lines 22 each of which extends along the strip 18 towards, but not up to, the positions 20a,20b where the strip will be folded. These strips do not remove any material from the strip but do extend right through the thickness of the strip. They divide the slitted part of each f in leaf 24 into a number of separate sections 26.

Once the slits 22 have been made, the sections 26 def ined by the slits are alternately raised and lowered relative to the plane of the strip 18, and this is done by suitable tooling which presses the sections out of their original plane. This is accompanied by some minor stretching of the ends 34 (Figure 3) of each of the sections to enable the main part of each of the sections to be displaced f rom, but nevertheless remain substantially parallel (that is up to 70 to either side from a strictly parallel - 6 configuration), to the strip 18.

Finally, the strip is folded along the lines 20a, 20b so that it takes up the configuration shown in Figure 3. In 5 practice, the there is likely to be a significant radius aLong the edges 20a and 20b, and the individual leaves 24 may not be exactly parallel. Figure 3 shows only a small section of a f in in position on top of a lower coolant tube 14. The part of the strip between lines 20a and 20b will be brazed or otherwise attached to the tube 14, and the part of the strip between the upper fold lines 20a and 2 Ob will be similarly brazed to an upper tube 14 which is omitted from the drawings, for clarity.

It will be seen from Figure 3, and in particular from the leaf 24a which has been cut in half across its middle that the sections 26 are alternately displaced to one side or the other of the central plane 28 (Figure 4) of the leaf. Figure 4 is a view in the direction of the arrow A, looking down onto the cut edge of the leaf 24a and shows the fin sections 26 which are displaced, as well as two fin sections 30 which are at the edges of the leaf and are not disturbed from their initial position lying in the plane 28 of the fin.

Figure 4 also shows the positions of the slit lines 22, illustrating that at each slit line one section moves to one side of the plane 28 whilst the other section moves to the other side of the plane.

Figure 4 shows the direction in which air 32 will flow over the fin. It is to be expected that under all normal conditions, air will flow across both sides of each fin 26 and there will be no flow separation.

Making the fins in this way substantially enhances the heat exchange characteristics of the fin assembly without increasing the cost or complexity of manufacturing or assembly of the heat exchanger in which the fins are used.

Cla:ims 1 A fin for a heat exchanger, the fin being formed from sheet material and having a generally planar form with sections of the material being displaced from the plane of the fin, alternately to one side or the other side of the plane, whilst maintaining the plane of each section substantially parallel to the plane of the fin.

2. A fin for a heat exchanger, the fin being formed from a strip of sheet material folded concertina fashion along its length into a plurality of leaves, each leaf having a generally planar form with sections of the material being displaced from the plane of the leaf, alternately to one is side or the other side of the plane, whilst maintaining the plane of each section substantially parallel to the plane of the leaf.

Claims (1)

1. 3. A fin as claimed in Claim 1 or Claim 2, wherein the displaced sections

   are generally rectangular in form, with the long edges of the displaced sections separated from the adjacent material and the short edges remaining connected to the adjacent material.

   4. A f in as claimed in any preceding claim, wherein, considered in a direction at right angles to the long edges of the displaced sections, the sheet material is displaced alternately to one side or to the other side of the plane, and no material remains in the original plane of the material, between adjacent sections.

   5. A fin as claimed in Claim 3, when dependent on Claim 2, wherein the long edges of the displaced sections are at right angles to the concertina folds.

   6. A fin as claimed in any preceding claim, wherein the material is an aluminium foil.

   7. A fin as claimed in any one of Claims 2 to 6, wherein the strip is folded so that the leaves are substantially parallel to one another.

   8. A method of making a heat exchanger fin from a piece of initially planar material, the method comprising the steps of making a plurality of parallel slits through the material, each slit stopping before reaching an edge of the material, and then displacing the sections of the material between the slits, alternately to one side or the other side of the plane, whilst maintaining the plane of each section substantially parallel to the plane of the fin.

   9. A method as claimed in Claim 8, wherein the material is initially in the form of a strip, a plurality of sets of parallel slits are made at regularly spaced positions along the length of the strip, the sections of the material between the slits are displaced alternately to one side or the other side of the plane of the strip, whilst maintaining the plane of each section substantially parallel to the plane of the fin, and the strip is folded concertina fashion to define leaves between each fold, so that each set of slits lies on one of the leaves.

   10. A method as claimed in Claim 8 or Claim 9, wherein the material is an aluminium foil.

   11. A fin for a heat exchanger, substantially as herein described with reference to the accompanying drawings.

   12. A method of making a heat exchanger fin, substantially as herein described with reference to the accompanying drawings.