AU598965B2 - Improved heat exchanger fins - Google Patents

Description

i i- 598965 COMMONWEALTH OF AUS2.ALIA The Patents Act 1952-1969 Name of Applicant: Address of Applicant: KING SONS PTY. LTD.

114-178 Montpelier Road Bowen Hills Q. 4006 Australia a ft 'f Actual Inventors: Address for Service: G.R. CULLEN COMPANY, Patent Trade Mark Attorneys, Dalgety House, 79 Eagle Street, Brisbane, Qld. 4000, Australia.

COMPLETE SPECIFICATION FOR THE INVENTION ENTITLED: S4 IMPROVED HEAT EXCHANGER FINS 17.

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Url; The following statement is a full description of the invention including the best method of performing it known to me: 's i 2 THIS INVENTION relates to an improved heat exchanger fin. In particular, the invention is directed to an improved fin sheet for use in a vehicle radiator core although the invention is not limited to such use.

Heat exchangers, such as those found in vehicle radiator cores, typically comprise a number of metal tubes passing through apertures in layered spaced-apart thin metallic sheets which are usually called "fins", "plate fins" or "fin sheets". (Throughout this specification, such sheets shall be referred to as "fin sheets".) There is normally a tight fit between the tubes and the fin sheets so as to create a direct metal connection between the tubes and the fin sheets.. Heat is extracted from the engine cooling' fluid passing through the tubes and is dissipated by the fin sheets to the air passing between them. In this manner, the fin sheets act as cooling fins for the tubes.

SThe fin sheets are made thin.in order to maximise the ratio of surface area to volume of material, and to minimise weight. However, an inherent disadvantage of thin sheets is that they lack structural strength and rigidity.

Consequently, the fin sheets may deviate from their flat configuration and uniform spacing in use, and may not provide sufficient lateral support for 'he tubes passing Stherethrough. In particular, the fin sheets may bend during assembly when the tubes are pushed through the apertures in the fin sheets.

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3 In order to strengthen the fin sheets, it is known to form reinforcing ribs on the sheets, for example by stamping or pressing. U.S. Patent No. 1,927,325 discloses a radiator fin construction wherein the fin sheets are provided with embossments in order to increase turbulence in the air stream between the cooling tubes and thereby increase the efficiency of heat exchange. The embossments consist of short parallel ribs which reinforce the fin sheet in one direction but not in the orthogonal direction.

U.S. Patent No. 4,449,581 discloses a fin sheet ret which is provided with corrugations having a "dog-bone" pattern which are intended to alter the fluid flow CC r characteristics to increase the heat transfer efficiency.

Due to the two dimensional natur. of the "dog-bone" pattern, the corrugations reinforce the fin sheet in both orthogonal directions alonq the fin sheet. U.S. Patent No. 4,592,420 t discloses another fin sheet having H-shaped deformations for reinforcing the fin sheet, particularly in the region around S, the apertures for the cooling tubes. The H-shaped deformations provide reinforcement in orthogonal directions along the sheet.

However, the fin sheets of the '581 and '420 U.S.

patents possess several inherent disadvantages, including since the ribs of the prior art fin sheets consist of relatively short individual deformations, the ribs do not Ak 1^ y j p

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i (ii) 9* 9, .9 9 ,0 99 0990 9 9'* 99 9 99 9 999 9 ;I 0: (iii) (iv) 4 provide continuous reinforcement across the width of the sheets, the patterns of individual deformations in the prior art fin sheets are designed for fin sheets of fixed widths, and are not entirely suitable for use with machines which produce fin sheets of different widths; for example, application of the pattern of the '420 patent to a part-width fin sheet may result in a deformation being located along the edge of the fin sheet, the fin sheets described in the prior art patents are awkward to assemble using the table assembly method, the "dog-bone" pattern utilized in the '581 patent leaves no room between the tubes for the provision of louvres, a design feature which is used to increase turbulence in the air flow between the sheets, and the pattern of H-shaped deformations used in the '420 patent is not particularly suitable in heat exchangers having offset or staggered tube configurations.

It is an object of the present invention to ~I overcome, or substantially ameliorate, one or more of the abovedescribed disadvantages of the prior.art by providing an improved fin sheet for use in. neat exchangers.

In one broad form, the present invention provides a fin sheet suitable for use in a heat exchanger of the type comprising a plurality of tubes passing through respective apertures in layered spaced-apart fin sheets; said fin sheet comprising a thin metal sheet having a plurality of apertures therein in a predetermined spacial arrangement, said 0 apertures being shaped and dimensioned to receive respective -tubes therethrough; and a plurality of ribs formed on said sheet, said ribs being generally of wavy configuration and ~xtending substantially across the whole width of said fin sheet.

C E c The term "wavy" as used herein is intended to Ct t include staggered,, undulating or similar wave-like format.ons.

Preferably, the ribs are formed by linear S, indentations, ridges, channels or like deformations in the fin sheet, and adjacent pairs of ribs are mirror opposites of each other.

In the preferred embodiment, the tubes are of flattened cross-section and the apertures in the fin sheet are therefore of corresponding shape. The apertures are aligned in rows extending longitudinally along the fin sheet, apertures in successive rows being staggered or offset with rr *if 11 6 respect to the preceding row. The ribs are suitably arranged to pass adjacent the longitudinal sides of the staggered or offset apertures in successive rows to strengthen the fin sheet. in the vicinity of the tubes.

The wavy configuration of the mirror-image ribs results in spaces being formed between pairs of ribs between adjacent apertures in each row. Advantageously, louvres are provided in the fin sheets in the spaces between the apertures. The louvres create turbulent air flow between 10 the fin sheets, thereby increasing the heat exchange j t efficiency of the fin sheets. The louvres are preferably j cr 'provided in sets of divided pairs, the louvres in each pair being of opposite orientation to create equal bidirectional turbulent air flow.

Increasing the number of .ouvres results in greater turbulence. However, if more louvres are used the louvres must be made narrower to fit within the same space, and the structural strength and rigidity of the fin sheet is thereby 1 reduced. According to another aspect of this invention, half-width louvres are used at the beginning and end of each set of louvres in order to increase the number of louvre discontinuitie3 within a given dimension.

Instead of louvres, sine wave undulations may be formed in the fin sheet between apertures.

The fin sheet is suitably made from copper or other metal having good heat conductivity.

r 7 1 i 7 In order that the invention may be mni e- fully understood and put into practice, preferred embodiments thereof will now be described with reference to the accompanying drawings, in which: Fig. 1 is a pictorial plan view of a portion of a fin sheet of a first embodiment; Fig. 2 is a schematic plan view of a fin sheet of another embodiment, the louvres only being partially shown, Fig. 3 is a cross-sectional view of a fin sheet I) without louvres, Fig. 4 is a cross-sectional view along A-A of the !j fin sheet of Fig. 2; Fig. 5 is a cross-sectional view along B-B of the fin sheet of Fig. 2; .Fig. 6 is a plan view of a portion of a fin sheet according to yet another embodiment of the invention; 'Fig. 7 is an enlarged plan view of a portion of the fin sheet of Fig. 6; ;Fig. 8 is an elevational view of the fin sheet of 2- :Fig. 7; and Fig. 9 is a cross-sectional view along C-C of the fin sheet, of Fig. 7 (inverted).

As shown in Fig. 1, the fin sheet of a first embodiment is in the form of a generally flat elongated sheet 10 having a plurality of apertures 11 punched or stamped \i i therein. The apertures 11 are shaped and dimensioned to iL i 8 receive respective tubes therethrough in a tight or interference fit. The tubes carry a first fluid of a heat exchanger. Typically, the fin sheet 10 is used in vehicle radiators and the first fluid is the engine cooling water.

The tubes (not shown) and apertures 11 have an elongated or flattened cross-section and are aligned in rows extending longitudinally along the sheet. Apertures 11 in successive rows are offset or in staggered formation relative to the preceding row in order to increase exposure of the tubes to a second fluid of the heat exchanger passing between the or sheets 10. In a vehicle radiator, such second fluid is the ci 'cooling air.

The number and spacial arrangement of the tubes and apertures can be chosen to suit the particular application of 1e5 the heat exchanger.

The construction of a slightly modified fin sheet is shown in more detail in Figs. 2 to 5, this fin cheet differing in the orientations of the louvres as described in S" more detail below.

A heat exchanger, such as a vehicle radiator core, is formed by stacking the sheets 10 in spaced-apart layers and pushing tubes through the registered apertures 11 in the sheets 10. The interference or tight fit between the sheets and the tubes ensures good heat transfer between the two.

When the apertures 11 are punched in the sheets flanges 12 are f^rmed around the periphery of the apertures

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9 as can be seen in Figs. 4 and 5. The flanges 12 abut directly against the sides of the tubes passing through the apertures 11 to thereby increase the thermal conductivity between the tubes and the fin sheets The tubes can be brazed, welded or soldered to the fin sheets to provide rigid metallic connection between the tubes and tie sheets, and the flanges 12 assist in connecting the tubes to the sheet. In one method of manufacture, the tubes are coated with a heat fusible compound before insertion through the apertures 11. The assembly is then heat cured to form the direct metallic connection between the tubes and the fin sheets. In use, the sheets 10 act as heat transfer fins for the tubes, transferring heat between the fluid (water) within the tubes and the fluid (air) passing between the sheets. The tubes and sheets can be made of any t t E suitable thermally conductive material, srch as copper or steel.

A novel feature of the fin sheet 10 is the provision of wavy ribs 13 which extend across substantially the whole width of the sheet. The ribs 13 can be formed by linear channel-like indentations or depressions, or ridges, in the fin sheet 10 as shown more clearly in Fig. 4, and at 23 in the embodiment of Fig. 3. The wavy or staggered ribs f w are arranged to pass adjacent to the longitudinal sides of the offset apertures 11 in successive rows as can be seen in Figs. 1 and 2. The ribs serve to strengthen the sheet, and r particularly in the vicinity of 'he tubes, the ribs strengthen the sheet in both orthogonal directions along the sheet.

The wavy or staggered ribs 13 are arranged in pairs which are mirror opposites of each other such that wide and thin portions are formed alternatively betweenr. each pair of ribs. The apertures 11 are located in the thin portions, while louvres 14 may suitably be formed in the wide portions.

The louvres 14 create turbulence in the air stream between Io the layers of fin sheets 10, thereby increasing the rate of c~r heat dissipation from the fin sheets.

Preferably, the louvres 14 are formed in sets of divided pairs which are of opposite orientation as shown in Fig. 2. (The orientation of the sets of louvres is indicated by arrows in Fig. 2).

Increasing the number of louvres in each set results in increased air turbulence and hence an increase in heat exchange efficiency. However, as the area occupied by f C the louvres 14 is limited by the spacing between apertures and rows, it was previously necessary to reduce the width of all the louvres to accommodate a higher number of louvres within the same space. This, in turn, adversely affected the .strength and rigidity of the fin sheet. Another advantageous feature of the fin sheet 10 of the preferred embodiment is 2 the use of "half louvres" at the beginning and end of each row of louvres to increase the number of louvres or at least 11 the number of louvre edge discontinuities without requiring a reduction of width of the remaining louvres in the row. As shown in Fig. 5, each set of louvres begins and ends with a half louvre 15 which is narrower than the others yet still provides a louvre edge discontinuity. For a given area, the use of half louvres therefore enables an extra louvre edge to be included in the set, with a consequent increase in heat exchange efficiency.

In another embodiment of the invention, illustrated 1i in Figs. 6 to 9, a fin sheet 30 has larger but fewer apertures 31 therein. Ribs 33 are provided in the fin sheet 30, the ribs 33 being of wavy or corrugated configuration.

c The ribs 33 are formed by V-shaped linear indentations or depressions extending across the width of the fin sheet Series of undulations 34 are also provided between the ir' apertures 31 instead of louvres to increase turbulence and S" reinforce the fin sheet. The ribs may be formed by any suitable method, e.g. roll forming or transfer press.

E The foregoing describes only some embodiments of the invention, and modifications which are obvious to those skilled in the art may be made thereto without departing from the scope of the invention as claimed in the following claims.

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Claims (9)

1. A fin sheet suitable for use in a heat exchanger of the type comprising a plurality of tubes passing through respective apertures in layered spaced-apart fin sheets; said fin sheet comprising a thin metal sheet having a plurality of apertures therein in a predetermined spacial arrangement, said apertures being dimensioned to receive respective tuoes therethrough; and a plurality of ribs formed on said sheet, said ribs being generally of wavy configuration and extending substantially across the whole width of said finr sheet.

2. A fin sheet as claimed in claim 1, wherein said ribs are formed by linear indentations, ridges or channel deformations in the fin sheet.

3. A fin sheet as claimed in claim 1 or 2, wherein said ribs pass adjacent to the sides of said apertures.

4. A fin sheet as claimed in any preceding claim, further comprising rows of louvres formed in said fin sheet r 'between said apertures.

A fin sheet as claimed in a4s 4, wherein each row of louvres begins and ends with a louvre of substantially smaller width than the other louvres in said row.

6. A fin sheet as claimed in claim 4 or 5 wherein said dlouvres are formed as divided pairs of opposite orientation.

7. A fin sheet as claimed in any one of claims 4 to 6, wherein adjacent ribs are mirror opposites of each other and A c? i' 13 define alternate wide and narrow portions therebetween, said louvres being located in the wide portions between adjacent ribs.

8. A fin sheet as claimed in any preceding claim, wherein said apertures are aligned in rows extending longitudinally along said sheet, apertures in each row being offset with respect to the apertures in the preceding :ow, said apertures being elongated in a direction transverse to said rows, each said rib passing adjacent a longer side of offset apertures in successive rows. -c

9. A heat exchanger comprising at least one fin sheet as claimed in any one of claims 1 to 8. A vehicle radiator core comprising a plurality of tubes passing through respective apertures in layered spaced- apart fin sheets, each said fin sheet comprising a thin metal sheet having a plurality of apertures therein in a predetermined spacial arrangement and dimensioned to receive respective tubes therethrough in a tight fit, and a plurality 'e of rib formations on said sheet, said rib formations being generally of wavy configuration and extending transversely across substantiily the whole width of each said fin sheet. DATED this fifth day of January 1989. KING SONS PTY. L'D. ^by their Patent Attorneys G. R. CULLEN CO i f