GB2116687A

GB2116687A - Flat tube heat exchanger

Info

Publication number: GB2116687A
Application number: GB08305831A
Authority: GB
Inventors: Dieter Steeb
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-03-13
Filing date: 1983-03-03
Publication date: 1983-09-28
Also published as: GB8305831D0; IT8312448A1; DE3209240A1; GB2116687B; FR2523288A1; IT1172640B; IT8312448A0; DE3209240C2

Abstract

A heat exchanger has a pack of flat tubes (10) spaced by fins (12) to form air flow passages (11). Each tube (10) is formed by a pair of plates (13) and forms between its plates (13) oppositely directed (antiparallel) flow chambers for the medium to be cooled. A header box (24) has appropriate inflow and outflow connections. The upper end of each flat tube (10) leads into a semi- circular deflecting portion by which the medium is turned from the top of one flow chamber down into the other. In the deflecting portion the two plates (13) of each flat tube (10) are spaced apart by inwardly projecting curved ribs (19). <IMAGE>

Description

SPECIFICATION Heat exchanger comprising a packet of flat tubes This invention relates to a heat exchanger comprising a packet of flat tubes which are spaced apart by fins to form flow chambers for air. Each flat tube comprises a pair of metal plates spaced apart by spacer strips to form two antiparallel flow chambers for the medium to be cooled. By "antiparallel" is meant that the flow in the two chambers is in opposite directions. One end of each flat tube opens into a connecting box having an inflow and an outflow aperture for the medium to be cooled while the other end opens into a deflecting chamber.

Such heat exchangers are used inter alia as radiators, e.g. oil radiators for engines, for screw compressors or the like by flange connection the connecting box to the radiator or compressor block so that the packet of flat tubes extends as a free standing unit from the connecting flange.

In the known heat exchangers of this type, the antiparallel flow chambers of the flat tubes are connected by a receiving box which is similar in construction to the connecting box at the other end of the flat tubes. Since the receiving box is required to withstand high pressures from the medium to be cooled, it is relatively heavy and constructed from a large quantity of expensive material. The distance of this deflecting receiving box from the connecting flange and the iarge mass of the receiving box combine to impose severe stress on the connection between the flat tubes and the connecting box in the event of vibrations of the engine or compressor block. As a result, the known heat exchangers of this type have a much shorter service life than, for example, the engine or the screw compressor.

Welding of the deflecting box to the free ends of the flat tubes is relatively labour intensive; moreover, additional spacer strips between the flat tubes are necessary to ensure that the internal space of the receiving box is closed off from the outside; this results in a further increase in the vibrating mass.

It is an object of the present invention to provide a heat exchanger which will have a substantially longer service life and require much less material and labour for its construction.

To solve this problem in a heat exchanger of the type defined above, the deflecting chamber is formed by projections from the plates of the flat tubes, projecting over the ends of the flat tubes and joined together by impressing or stamping in at least one projection. Since each flat tube is connected to its own deflecting chamber formed by plates belonging to the flat tube, deflection of the medium to be cooled from one flow chamber of the flat tube into the other requires a minimum of material, especially since the space between the deflecting chambers which are formed by the projections of the plates can be left free so that the material forming the walls surrounding these spaces in conventional receiving boxes can be dispensed with. Since air can now also flow through these spaces, the deflecting chambers also contribute to increased efficiency of the heat exchanger.Since the projections on the plates are joined together by stamping, no additional material is required for connecting the projections. If these stamped portions are suitably arranged and extend in suitable directions, the strength of the deflecting chambers can be adapted to any pressure in the medium to be cooled without any additional mate rial being required.

Stamped portions extending round the projections of the plates may close the deflecting chambers off from the outside. In one advantageous embodiment of the invention, however, the spacer strip provided on each flat tube to keep the external edges of the plates of the tube spaced apart consists of a single U-shaped strip forming a web which closes the deflecting chamber off from the outside. If the two antiparallel flow chambers of each flat tube are separated by a straight strip extending from the connecting box to the deflecting chamber, a heat exchanger of surprisingly simple construction is obtained. To build up the packet of flat tubes, the U-shaped strip is placed on one plate which has the stampings of the plate projection directed upwards, so that this strip extends along the lateral edges and the projection of the plate.The straight strip which is to separate the two antiparallel flow chambers for the medium to be cooled is then placed centrally between the two straight arms of the U-shaped strip.

The second plate of the flat tube is then placed on this arrangement, and an airfin is then placed on the second plate, and a second flat tube is then assembled on the air fin in the same manner as before. If solder plated material is used, a packet assembled as described above need only be introduced into an oven or a soldering bath to solder all the parts together to form the packet of flat tubes, to which the connecting box is then welded at the end remote from the deflecting chambers.

The invention will now be described in detail with reference to an embodiment illustrated by way of example in the drawings, in which Figure 1 is a perspective view of one exemplary embodiment, Figure 2 is a longitudinal section through the flat tube which is seen from the frontin Figure 1, and Figure 3 is a section taken on the line Ill-Ill through a deflecting chamber of a flat tube.

The example illustrated in the drawing consists of a packet of flat tubes generally indicated by the reference numeral 10, with the tubes spaced apart by air fins 12 to form flow chambers 11 for air. The air fins 12 are formed in known manner from a corrugated metal sheet.

Each flat tube 10 consists of a pair of metal plates 13 held apart by two strips, one of which, indicated by the reference 14, is bent to form a U-shaped strip.

The two straight arms 15 of this U-shaped strip 14 constitute the straight, lateral walls of each flat tube 10 whose interior space is sub-divided into two antiparallel flow chambers by the second strip 16.

The straight strip 16 has the same length as the straight arms 15 of the U-shaped strip 14 and is arranged exactly centrally between these straight arms.

At the upper end of Figure 2, the two plates 13 of each flat tube form a semi-circular projection 17. The web 18 of the U-shaped portion of the strip 14 forms a circular arc covering the circular edge of the projection 17. Ribs 19 of curved cross section are stamped into each plate projection 17 at locations equidistant from the circular arc of the projecting edge and hence equidistant to the web 18. These ribs project from the plate by an amount equal to half the distance formed between the plates 13 of a flat tube by the spacer strips 14 and 16 so that when two plates 13 are placed together with interposition of the strips 14 and 16 to form a flat tube, the edges of the ribs from the two plates are in contact.

To increase the strength of the flat tubes and at the same time improve their efficiency, turbulators 21 manufactured from sheet material in known manner are arranged in the anti-parallel flow chambers.

As shown in particular in Figure 1, the packet of flat tubes has two rectangular external wall plates 22 between which is situated the stack of flat tubes 10.

Air fins 12 are arranged between the internal surface of each external wall plate 22 and the nearest plate 13 to form a flow chamber 11 for air. Each flow chamber 11 is bounded by a spacer strip 23 at the end shown at the bottom in Figure 1, remote from the end carrying the projections on the plate 13. By using solder plated flat plates 13, this packet of flat tubes can easily be assembled by first placing an air fin 12 and strip 23 on an external wall plate 22 and then building a flat tube 10 on this base by first placing on this base a plate 13 having its ribs 19 extending upwards, and then placing the strips 14 and 16 and turbulators 21 on this plate. The second plate 13 is then placed in position with its ribs 19 extending downwards so that the ribs 19 of the two plates are in contact.Another airfin 12 and another strip 23 are then placed on this flat tube and this method of assembly is continued until the required number of flat tubes have been built up. The second side wall plate 22 is then placed on the air fin 12 and strip 23 which have been placed on the last flat tube 10. The resulting packet is then introduced into a soldering bath or soldering oven to fuse the parts together.

A connecting box 24 is then welded to the resulting flat tube packet in known manner. This connecting box has two receiving chambers 26 and 27 separated by a wall 25 and attached to a connection 31 by inflow and outflow apertures 28 and 29. Due to the presence of the wall 25, the two anti-parallel flow chambers open separately into the receiving chambers 26 and 27. The strips 23 close the receiving chambers 26 and 27 off from the outside so that they are only connected to the anti-parallel flow chambers and the inflow and outflow apertures 28 and 29.

In operation, the medium to be cooled, e.g. oil, flows through the inflow 28 into the receiving chamber 26 and from there into the various flow chambers of the flat tubes 10 through which it then flow in the direction of the arrow 32 into the deflecting chambers bounded by the projections 17 and webs 18 of the strips 14. These deflecting chambers deflect the flow into the flow chamber through which the medium is discharged into the receiving chamber 27 in the direction of the arrow 33 to leave through the outflow aperture 29.

Due to the fact that each deflecting chamber at the free end of the packet of flat tubes is formed only by the projections 17 on the plates and the web 18 of the spacer strip 14 while free spaces open to the top are left between these deflecting chambers, the vibrating mass at the free end of the packet of tubes is limited to a minimum so that in the event of vibration of a body connected to the heat exchanger illustrated, e.g. an engine or compressor block, the strain on the welding connection between the flat tubes and the connection box 24 is reduced to a minimum, whereby the service life of the heat exchanger is substantially increased.

In the example illustrated, the air fins end at the free end of the flow chambers 17 and 18, but they could also extend up to the projections 17 on the plates.

The web 18 of the U-shaped spacer strip 14 and the ribs 19 which are soldered together form a deflecting chamber for medium to be cooled, which is capable of withstanding extremely high pressures without requiring great expenditure in material for its construction.

In the example illustrated, the flat plates 13 are all identical, so that a highly rational production method can be used. The stamped portions need not be in the form of ribs 19 as in the example illustrated but may have any form and if desired may also be formed asturbulators. Moreover, they could be provided on only one of the two plates 13 of a pair, although in that case they would have to extend over the whole thickness of the flat flow chamber in order to make contact with the unstamped projection of the other plate of the same pair.

Claims

1. Heat exchanger comprising a packet of flat tubes spaced apart to form airflow passages and each tube having a pair of flat plates held apart by space means to form two antiparallel flow chambers for a medium to be cooled, one end of each flat tube opening into a connecting box having an inflow and an outflow for the medium and the other end opening into a deflecting chamber, wherein the deflecting chamber is formed by projections on the plates which form part of the flat tubes, which projections extend overthe ends of the flat tube and are joined together by stamped portions formed in at least one projection.

2. Heat exchanger according to claim 1, wherein the spacer strips which space the outer edges of the plates of a flat tube apart comprise, for each flat tube, a single, U-shaped bent strip in which a web closes the deflecting chamber off from the outside.

3. Heat exchanger according to claim 1 or claim 2, wherein the stamped portions are formed in the projections of both plates of each pair of plates and are so arranged that they make contact in the mid-plane of the deflecting chamber.

4. Heat exchanger according to claim 2 or claim 3 when dependent on claim 2, wherein the web of the U-shaped strip is bent to conform to the contour of the projection, the stamped portions being in the form of curved ribs arranged equidistantly from the web.

5. Heat exchanger according to any preceding claim, wherein the two flow chambers of each flat tube are separated by a straight strip extending from the connecting box to the deflecting chamber.

6. Heat exchanger constructed and arranged substantially as herein described and shown in the drawings.