GB2254687A

GB2254687A - Heat exchanger

Info

Publication number: GB2254687A
Application number: GB9107574A
Authority: GB
Inventors: Ian Karl Pawson; Julian Garath Crossley
Original assignee: INT RADIATOR SERVICES Ltd
Current assignee: INT RADIATOR SERVICES Ltd
Priority date: 1991-04-10
Filing date: 1991-04-10
Publication date: 1992-10-14
Anticipated expiration: 2011-04-10
Also published as: GB2254687B; AU1408592A; GB9107574D0

Abstract

A heat exchanger element comprises an outer tube 10 having a flattened portion and an inner tube 20 positioned inside and in thermal contact with the outer tube. The axes of the tubes are substantially parallel. The tubes are preferably bonded together by a solder or brazing alloy. <IMAGE>

Description

HEAT EXCHANGER This invention relates to a heat exchanger.

More specifically it relates to a vehicle radiator in which engine coolant is cooled by air.

One known form of such a heat exchanger comprises an array of parallel tubes connected between two tanks.

The ends of the tubes are of circular cross-section where they are connected to the tank, but between the ends and over a major portion of their length the tubes are of flattened form enabling corrugated fins to be readily positioned between and bonded to the flattened areas of adjacent tubes by means of solder or brazing alloy, thereby increasing the cooling surface area.

However, sometimes a core is formed in the fluid flowing through the tubes, this core having a higher temperature compared with the surrounding fluid. This "hot core" effect means that the heat exchange performance is reduced and it is an object of the present invention to reduce or overcome this disadvantage.

In accordance with the present invention a metallic heat exchange element comprises an outer tube and an inner tube, the outer tube having a flattened portion and the inner tube being positioned inside of and in heat conducting contact with the outer tube, the axes of the inner and outer tubes being substantially parallel.

Preferably the inner tube is connected to the outer tube by a metallic bonding agent such as solder or brazing alloy, thus ensuring good heat conducting contact. The inner tube may also be of flattened configuration, the major cross-sectional axes of both tubes being co-extensive, thus providing a larger area for heat transference than would be the case if, for example, the inner tube were of circular cross-section.

The invention also includes a heat exchanger comprising a plurality of heat exchange elements as defined above.

Two embodiments of the invention will now be described by way of example only with reference to the accompanying drawings of which: Figure 1 is a longitudinal section of a heat exchange element in accordance with the invention and end fittings; Figure 2 is a section on line II-II of Figure 1 on an enlarged scale; Figure 3 is a cross-section on line III-III of Figure 1 on an enlarged scale; Figure 4 is a view similar to that of Figure 3 of a modified form of the heat exchange element shown in Figure 1; and Figure 5 is a cross-sectional view of a heat exchange element according to a second embodiment of the invention.

A heat exchanger, particularly a vehicle radiator, comprises a plurality of tubular heat exchange elements each in the form of a tube 10 supported between an upper tube plate 12 and a lower tube plate 11 of heat exchange tanks, one adjacent each end of the tubes.

In Figure 1 only one heat exchange element is shown for clarity. The tubes may be of copper or a suitable copper alloy supported in brass tube plates or alternatively of aluminium or aluminium alloy supported in tube plates of similar material.

Each tube 10 has a flattened central section 13 which extends over a major portion of the length of the tube and two end portions 14, 15 wherein the tube shape changes to a circular cross-section immediately adjacent tube ends. The cross-sectional shape of the flat central section is that of two parallel flat strips spaced apart by two semi-cylindrical portions at the longitudinal edges of the strip. It is to these flattened surfaces of the tubes that corrugated fins (not shown) are bonded by solder or brazing alloys. The circular cross-section part 14 at the lower part of the heat exchanger is swaged to form a circumferentially extending flange 16, which is spaced apart from the tube extremity and used for locating the tube, the flange resting on the upper surface 21 of a rubber ferrule 17.The other end part 15 is not formed with a flange but in use is positioned within a ferrule 18.

As can be seen in Figure 1, each circular crosssection end part 14, 15 fits into a respective rubber ferrule 17, 18 which in turn fits into an aperture in a respective tube plate 11, 12. By not providing a flange on the upper end part 15, slight variations in tube length due to manufacturing tolerances and expansion and contraction in use can be readily accommodated.

As can be seen in Figure 3, the central flattened section of the tube 10 has another flattened tube 20 located therein, the length of the inner tube being equal to that of the length of the central section 13 of the outer tube. The tubes are positioned so that the major and minor axes of the tubes are each co-extensive and the whole of the outer area of the flat surfaces of the inner tube is in contact with the inner surface of the flattened section of the outer tube. Thus, as can be seen in Figure 3, two channels 1, 3 of the same cross-sectional area are formed one on each side of the inner tube, which defines an inner channel 2.

The inner tube 20 is bonded to the outer tube 10 by means of a layer of solder or brazing alloy depending on the material of the tubes and the required operating temperature of the radiator.

One method of manufacturing the element described is to coat the outer surface of the inner tube 20 with a suitable solder or brazing alloy at least on the flattened section, insert the inner tube into the outer tube 10 as shown using a suitable positioning jig, (not shown) and heating the assembly to cause the solder or brazing alloy to melt so that on cooling and solidifying the solder or brazing alloy provides a good thermal connection between the inner and outer tubes. Dimples 19, 29 as shown in Figure 4 may be formed in the tubes to help maintain the required position during the heating step.

Alternatively the circular end portions and flange may be formed after the inner tube has been inserted and bonded to the outer tube.

In a modified form of the invention as shown in Figure 6, a third tube 30 may be provided inside the inner tube and bonded thereto by a suitable solder or brazing alloy. Thus in the second embodiment as shown in Figure 5, five separate channels 4, 5, 6, 7, 8 are provided within the outer tube 10.

It should be noted that the cross-sectional shapes of the tubes as used may be different. For example at least one tube may be of elliptical crosssection.

Among the advantages gained from heat exchange elements in accordance with the invention, is the provision of a plurality of separate coolant flow chambers e.g. three or five, ensuring that heat is conducted with greater efficiency to the outer surface of the outer tube, thus alleviating the "hot core" effect apparent with known heat exchange elements.

Additionally, the provision of one or more inner tubes provides added strength and rigidity, thereby reducing flexing caused by vibration in the whole heat exchanger e.g. a vehicle radiator. This reduces the occurrence of cracks etc. Heat exchange elements in accordance with the invention are relatively cheap to manufacture and thus provide a cost effective means of improving the heat exchange efficiency.

Claims

1. A metallic heat exchange element comprising an outer tube and an inner tube, the outer tube having a flattened portion and the inner tube being positioned inside of and in heat conducting contact with the outer tube, the axes of the inner and outer tubes being substantially parallel.

2. A heat exchange element according to Claim 1 wherein the inner tube is connected to the outer tube by a metallic bonding agent such as solder or brazing alloy.

3. A metallic heat exchange element according to Claim 1 or Claim 2 wherein the inner tube is of flattened configuration.

4. A metallic heat exchange element according to Claim 3 wherein the major cross-sectional axes of both tubes are co-extensive.

5. A metallic heat exchange element according to any one of the preceding claims wherein the inner and outer tubes are each formed with at least one dimple, the dimple in one tube nesting in the dimple in the other tube.

6. A metallic heat exchange element according to any one of the preceding claims comprising a further inner tube.

7. A metallic heat exchange element according to Claim 6 wherein said further inner tube is located within the inner tube, the axes of the further inner and inner tubes being substantially parallel.

8. A metallic heat exchange element according to Claim 6 or Claim 7 wherein the further inner tube and the inner tube are each formed with at least one dimple, the dimple in one tube nesting within the dimple in the other tube.

9. A metallic heat exchange element substantially as described herein with reference to and as illustrated in Figures 1,2 and 3 of the accompanying drawings.

10. A metallic heat exchange element substantially as described herein with reference to and as illustrated in Figures 1,2 and 4 of the accompanying drawings.

11. A metallic heat exchange element substantially as described herein with reference to and as illustrated in Figures 1,2 and 5 of the accompanying drawings.

12. A heat exchanger comprising a plurality of heat exchange elements according to any one of the preceding claims.

Amendments to the claims have been filed as follows 1. A metallic heat exchange element comprising an outer tube and an inner tube, the outer tube having a flattened portion and the inner tube being positioned inside of and in heat conducting contact with the outer tube, the axes of the inner and outer tubes being substantially parallel.

5. A metallic heat exchange element according to any one of the preceding claims wherein the inner tube is positioned relative to the outer tube to define three channels.

6. A metallic heat exchange element according to any one of the preceding claims wherein the inner tube has a length substantially equal to the length of the flattened portion of the outer tube.

7. A metallic heat exchange element according to any one of the preceding claims wherein the inner and outer tubes are each formed with at least one dimple, the dimple in one tube nesting in the dimple in the other tube.

8. A metallic heat exchange element according to any one of the preceding claims comprising a further inner tube.

9. A metallic heat exchange element according to Claim 8 wherein said further inner tube is located within the inner tube, the axes of the further inner and inner tubes being substantially parallel.

10. A metallic heat exchange element according to Claim 8 or Claim 9 wherein the further inner tube is positioned relative to the inner tube and the outer tube to define five channels.

11. A metallic heat exchange element according to any one of Claims 8, 9 or 10 wherein the further inner tube and the inner tube are each formed with at least one dimple, the dimple in one tube nesting within the dimple in another tube.

12. A metallic heat exchange element ' substantially as described herein with reference to and as illustrated in Figures 1,2 and 3 of the accompanying drawings.

13. A metallic heat exchange element substantially as described herein with reference to and as illustrated in Figures 1,2 and 4 of the accompanying drawings.

14. A metallic heat exchange element substantially as described herein with reference to and as illustrated in Figures 1,2 and 5 of the accompanying drawings.

15. A heat exchanger comprising a plurality of heat exchange elements according to any one of the preceding claims.