EP0086559A2

EP0086559A2 - Improvements relating to heat exchangers

Info

Publication number: EP0086559A2
Application number: EP83300209A
Authority: EP
Inventors: Anthony Phillip Banton; Clive Winston Wilson
Original assignee: Unipart Group Ltd
Current assignee: Unipart Group Ltd
Priority date: 1982-02-16
Filing date: 1983-01-17
Publication date: 1983-08-24
Also published as: EP0086559A3; JPS58193092A

Abstract

A motor vehicle radiator has fins 11 which are self spacing by virtue of spacing members 14 raised out of the material of the fin. The spacing members each have an elongate shape in cross-section in a plane parallel to the fin which is set at an angle of incidence to the air flow through the radiator, whereby to disturb the air flow and improve the heat transfer efficiency.

Description

This invention relates to heat exchangers, and in particular to those having a plurality of fins and at least one tube passing through apertures in the fins.
Such heat exchangers commonly include a multiplicity of tubes, often arranged in rows, which pass through apertures, which may be either holes or slots in the side edges, in fins arranged in a stack in planes at right angles to the tube axes. Fin spacing is achieved by interposing elements between the fins to hold them apart. The spacing members often take the form of tabs raised out of the material of the fins themselves, and are each arranged to contact the surface of an adjacent fin to ensure a gap between it and the fin from which the spacing member is raised. The spacing members are commonly produced by plunging, and it is usual to arrange that the free end of the spacing member is wider than its base where it is connected to the fin to ensure that the fins will not nest, with the spacing members simply passing through the plunged holes in adjacent fins. Hitherto it has always been the case that such spacing members were aligned as much as possible with the fluid flow between the fins, at least in those regions of the matrix where the fluid flow rate is high, in order to minimise the pressure drop across the heat exchanger.
It has been recognised for some time that heat transfer should be optimised by ensuring the correct amount of turbulence in the fluid flow between the fins. This has been achieved hitherto by providing louvres, dimples or other irregularities on the fin surface, but such features add difficulties and cost to the design, manufacture and maintenance of the tools for producing the fins.
According to the invention there is provided a heat exchanger including a plurality of fins and at least one tube passing through apertures in said fins, wherein a pair of fins are spaced apart by means of a spacing member located in a region of substantial air flow rate in use having an elongate shape in a cross-sectional plane substantially parallel to the plane of at least one of said pair of fins, and wherein, in use, the spacing member is set at an angle of incidence to fluid flow between the fins in said plane, whereby to improve the heat transfer to said fluid.
Thus the spacing members are used to disturb the fluid flow to induce turbulence between the fins instead of being arranged for minimum drag. As a result, it may be possible in a given heat exchanger design to reduce the requirement for louvres, dimples etc.
The invention extends to a motor vehicle including such a heat exchanger.
An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Figure 1 shows part of a fin for a heat exchanger in accordance with the invention;
Figure 2 shows a cross-section on the line B-B in side view, part of a stack of fins similar to that shown in Figure 1;
Figure 3 shows the detail of a plunged hole flanked by spacing members raised out of the hole, in the fin of Figure 1;
Figure 4 is a graph showing the relationship between the heat transfer capability and the angle of incidence of the spacing members to the fluid flow through a heat exchanger in accordance with the invention; and
Figure 5 is a graph showing the relationship between the pressure drop across the heat exchanger of Figure 4 in fluid flowing between the fins and the angle of incidence of the spacing members to the flow.

Figure 1 shows part of a copper fin 11 from a motor vehicle radiator which has two rows of tubes (not shown) the tubes of one row being staggered with respect to tubes in the other row. Holes 12 are provided to receive the tubes which pass through the fins at right angles thereto.
A plurality of circular holes 13 are plunged in the fin, splitting the circular piece of metal displaced into two semicircles 14 which are raised out of the fin with their free diameters uppermost and remaining attached to the fin by a short bridge extending round a small portion of the circumference of the original circle. As illustrated by Figure 2, the upstanding semicircles 14, act as spacing members to ensure a gap is maintained between fins which is approximately equal to the radius of the holes 13. Thus, in Figure 3, dimension H is approximately half of dimension D. The dimensions are so chosen as to obtain a fin pitch of 14 fins per inch (25.4 millimetres).
It will be appreciated that the shape of the spacing members 14, is such that it will prevent the fins nesting. Other shapes such as diamonds could be used, if they provided a spacing member with a wide free end.
It will be noticed that the spacing members, as seen in Figure 1, are elongate and are set at an angle, A degrees from a line extending at right angles to the edge of the fin. In practice this means that in use of the radiator, if optimally installed, the spacing members will be set at an angle of incidence of A degrees to the air flow between the fins, which impinges on the leading edge 15 of the fin and hence on the leading face of the stack of fins, at right angles thereto.
Setting the spacing members at angle A degrees to the air flow deflects the air flow in such a way as to produce two effects. Firstly, as expected, it increases the pressure drop in the air as it flows through the radiator, thus increasing the flow resistance and drag. This effect is shown in Figure 5 which relates the pressure drop in arbitrary units to varying values of angle A.
Secondly however, it will be seen that the heat transfer efficiency of the radiator is modified by varying the angle A. Figure 4 shows the variation of the specific dissipation, in arbitrary units, which is a measure of heat transfer efficiency, with angle A.
As will be seen, up to 10 degrees the efficiency is little improved while the pressure drop rises rapidly. Between 10 and 20 degrees however, the efficiency improves sharply while the pressure drop increases more slowly than for lower values of A. After 20 degrees the pressure drop rises steadily without benefits in terms of efficiency, and it seems that angles beyond approximately 35 degrees should be avoided.
It is expected that although the optimum value of A can be readily derived as 20 degrees in the present example, the value is likely to vary somewhat with spacing member shape, and with differences in fin pitch which will affect not only the fin spacing, but also'the size of the spacing members relative to the fin-whidth W. For example, in some designs, maximum angles of up to 45 degrees or 50 degress could be used.
The spacing members are distributed along the length of each of the fins of the radiator, not only in the regions of slow moving air around the edges of the radiator matrix, but also in the region where the air flow rate is greatest.
In that region, prior art arrangements have been particularly concerned to avoid features which will disturb the air flow and increase the drag, while the edges of the matrix have received less attention in terms of designing for low drag since the lower air flow rates in those regions make them less significant.
It will be noted that the spacing members are distributed between adjacent tubes in a row, and moreover that half are located directly upstream of tubes in the other row, thus turbulating the air flowing onto the tubes in the other row.
. It will be apparent that if the radiator is necessarily installed in the vehicle such that air flow impinges on the leading face at an angle to the perpendicular thereto, then the spacing members may need to be set at a different angle to the leading face of the radiator to achieve the. desired angle of incidence to the air flow. In general designers will seek to ensure that, for optimum efficiency, the radiator leading face is perpendicular to the mean incident air stream. Arrangements wherein prior art-type spacing members are arranged perpendicularly to the leading face of the radiator, but have a substantial angle of incidence to the mean direction of the air flow incident upon them by virtue of the misalignment of the radiator as a result of its installation, are hereby specifically disclaimed.
In the illustrated embodiment, the adoption of an angle A of 20 degrees for the spacing members removed the need for louvres to be incorporated in the fin, with resulting cost savings.
It will be clear that many variations of the illustrated embodiment can be incorporated while retaining some advantage. Thus differently shaped spacing members could be incorporated, and the spacing members could even be a separate item inserted between the fins. Again the radiator may have different numbers of tube rows, different fin pitch or distribution or ratio of fins to spacing members.

Claims

1 A heat exchanger including a plurality of fins and at least one tube passing through apertures in said fins, wherein a pair of fins are spaced apart by means of a spacing member located in a region of substantial air flow rate in use having an elongate shape in a cross-sectional plane substantially parrallel to the plane of at least one of said pair of fins, and wherein, in use, the spacing member is set at an angle of incidence to fluid flow between the fins in said plane, whereby to improve the heat transfer to said fluid.

2 A heat exchanger as claimed in claim 1, wherein said fins are arranged in a stack whereby said heat exchanger has a leading face defined by the upstream edges of the fins, and wherein said spacing member is arranged at a substantial angle in said plane to the normal to the leading face upstream of said spacing member.

3 A heat exchanger as claimed in claim 1 or claim 2, wherein said angle is greater than 10 degrees.

4 A heat exchanger as claimed in any one of claims 1 to 3, wherein the said angle is less than 50 degrees.

5 A heat exchanger as claimed in claim 4, wherein the said angle is less than 35 degrees.

6 A heat exchanger as claimed in any preceding claim, wherein said angle is approximately 20 degrees.

7 A heat exchanger as claimed in any preceding claim, wherein said spacing member is raised out of the material of a fin.

8 A heat exchanger as claimed in claim 7, wherein the spacing member is formed by plunging.

9 A heat exchanger as claimed in claim 8, wherein a plurality of spacing members is raised from a single plunged hole in the fin.

10 A heat exchanger as claimed in any preceding claim, wherein a multiplicity of tubes pass through the fins in a row, and wherein said spacing members are disposed between adjacent tubes in said row.

11 A heat exchanger as claimed in any preceding claim, wherein said spacing member is arranged substantially directly upstream of a said tube.

12 A heat exchanger substantially as hereinbefore described with reference to the accompanying drawings.

13 A motor vehicle including a heat exchanger according to any preceding claim.