GB2032091A

GB2032091A - Heat exchangers

Info

Publication number: GB2032091A
Application number: GB7932658A
Authority: GB
Original assignee: CTC AB
Current assignee: CTC AB
Priority date: 1978-09-26
Filing date: 1979-09-20
Publication date: 1980-04-30
Also published as: DK151512C; DK151512B; BE879027A; NO793075L; DE2938249A1; IT7925995A0; AT363500B; FR2437594A1; CH649373A5; IT1123335B; FR2437594B1; SE7810113L; GB2032091B; JPS5546396A; NO147283C; CA1118761A; NO147283B; DK403779A; NL7907022A; ATA625579A

Abstract

A heat exchanger for exchanging heat between a first medium passing through a serpentine tube system 12 and a second medium which flows around the tube system. The tube system comprises a plurality of tubes 13 to 16 which are connected in parallel between an inlet 10 and an outlet 11 for the first medium. The tube system is enclosed in a casing 19 so designed that a serpentine channel 22 is formed for the second medium from an inlet 23 to an outlet 24. <IMAGE>

Description

SPECIFICATION Heat exchangers The present invention relates to heat exchangers.

According to the invention, there is provided a heat exchanger comprising: a plurality of serpentine tubes providing respective serpentine parallel flow paths for a first medium; and a casing enclosing said tubes and.having an inlet and an outlet for a second medium, there being a gap between the or each adjacent pair of said tubes and said casing being internally shaped to define for said second medium a serpentine flow path passing between said tubes.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example to the accompanying drawings in which: Figure 1 shows partly in section a plan view of a heat exchanger; Figure 2 shows the heat exchanger of Figure 1 from below; Figure 3 shows schematically the paths of flow through the heat exchanger; Figures 4 and 5 show on a greater scale and in a section details of the heat exchanger; and Figures 6, 7 and 8 show various types of flow guides which may be provided in the heat exchanger.

Referring to Figure 1, a first medium is supplied to an inlet 10 and leaves the heat exchanger through an outlet 11. As can be seen in Figure 4, which on a larger scale and in a section shows the inlet 10, this inlet is connected to a tube system 12 consisting of four tubes 13, 14, 1 5 and 16 and the outlet 11 is designed in a similar way.

As can be seen in Figure 5, which shows a section along a plane indicated V in Figure 1, the tubes 13, 14, 15 and 16 are flattened and arranged in such a way that narrow slits are formed between adjacent tubes. In the illustrated embodiment it is assumed that the tube system comprises four tubes which are connected in parallel and flattened, but it is not essential to use four tubes. In some applications it may be suitable to have a larger or smaller number of tubes in the tube system.

As can be seen from Figure 1, the tube system 1 2 which is connected between the inlet 10 and the outlet 11 follows a modified zig-zag or serpentine form. A number of straight parts 1 7 are connected with each other by means of semicircular parts 18. The tube system is placed in a casing 19 which is made of two halves 20 and 21 (Figures 2 and 5). Each half consists of a formpressed metal sheet defining a channel 22 therebetween. The channel 22 surrounds the tube system 12 and extends from an inlet 23 to an outlet 24 for the second medium.

The flow pattern for the two media and especially for the second medium which is obtained in this way is shown schematically in Figure 3. The second medium enters through the inlet 23 whereupon it is forced through the narrow slits between the tubes 1 3 to 1 6 of the tube system within the straight part of the channel 22 is designated 25. As indicated schematically in Figure 3 there is no direct connection on the outer side of the semi-circular part 1 8 between two successive straight parts of the channel 22 and this produces the result that the second medium is forced through the narrow slits in the tube system 12 after it has passed the schematically shown partition 26. This means that the second medium wili be forced to and fro in the narrow slits of the tube system with repeated changes of direction.

The same result is achieved in the embodiment shown in Figure 1 in that small plates 27 are placed in the channel 22 in such a way that medium flow along the outer side of the semicircular parts 1 8 of the tubes is prevented. In this way the second medium is forced to flow through the narrow slits of the tube system.

In order to increase the coefficient of thermal transfer it is advantageous to make the tubes 13 to 1 6 of the tube system with cross grooves in a manner known per se. Cross grooves of this kind (previously known for instance from Swedish Patent No. 363 164) also contribute to give the narrow slit between two adjacent tubes and between the outer tubes and the casing 1 9 optimum width so that the desired high coefficient of thermal conductance can be achieved. In an aiternative embodiment, the flattened tubes may be smooth and in such case metal strips which have a relief pattern in the transverse direction may be positioned between the tubes and between the tubes and the casing so that the height of this relief pattern determines the width of the slits.

One embodiment in which such metal strips are used is shown in Figure 6 in a plan view and in Figure 7 in section. In Figure 6 one part of the channel 22 of the casing 1 9 in which the tube system (not shown in Fig. 6) is to be placed, is shown. Between the tubes of the tube system, as well as between these tubes and the casing, metal strips 28 are arranged and the length of these metal strips is substantially the same as the length of the straight parts 1 7 of the channel 22. Each metal strip 28 (shown in a section in Figure 7) is provided with a number of flanges or bulges 29.

The height of these bulges determines the width of the slit between the tubes through which the second medium flows. It is suitable to make the bulges 29 with an S-shape as shown in Figure 6 so that the medium flow is thereby guided in accordance with the arrows shown in the drawing.

An alternative form of metal strips is shown in Figure 8. In this case a metal strip 30 has been given a rectangular zig-zag form so that successive surfaces of the metal strip alternatingly abut the tubes 1 4 and 15, respectively. In a similar way, metal strips are placed in the outer slits of the tube system. Such a design of metal strips gives inter alia an increase of the active outer surface of the tubes and, as a result, increased heat transfer.

Claims

1. A heat exchanger comprising: a plurality of serpentine tubes providing respective serpentine parallel flow paths for a first medium; and a casing enclosing said tubes and having an inlet and an outlet for a second medium, there being a gap between the or each adjacent pair of said tubes and said casing being internally shaped to define for said second medium a serpentine flow path passing between said tubes.

2. A heat exchanger according to claim 1 wherein said casing is formed of two halves defining therebetween said flow path for the second medium.

3. A heat exchanger according to claim 2 wherein the two halves are substantially identical.

4. A heat exchanger according to claim 1,2 or 3 wherein said casing is generally planar.

5. A heat exchanger according to claim 4 wherein the centre line of each said tube lies in a plane parallel to the mean plane of the casing.

6. A heat exchanger according to claim 5 wherein said tubes are flattened in planes parallel to said mean plane and form narrow and elongate slits for the second medium between adjacent tubes.

7. A heat exchanger according to any one of claims 1 to 6 wherein said serpentine tubes are contained in a serpentine channel defined by said casing.

8. A heat exchanger according to claim 7 wherein said channel is formed from a plurality of straight substantially parallel portions linked together by substantially semi-circular portions.

9. A heat exchanger according to claim 8, wherein a plate is provided in at least one semi circular portion of the channel and extends from the channel wall to the tubes.

10. A heat exchanger according to any one of the preceding claims wherein the tubes are provided with cross grooves.

11. A heat exchanger according to any one of the preceding claims wherein metal strips are positioned between adjacent tubes and between the tubes and the casing which strips are provided with transverse flanges or bulges.

12. A heat exchanger for exchanging heat between a first medium passing through a tube system and a second medium flowing around the tube system, in which the tube system comprises a plurality of tubes which are connected in parallel between an inlet and an outlet for the first medium, wherein the tube system is enclosed in a casing which is composed of two halves, which casing is so designed that a channel is formed for the second medium from an inlet to an outlet for this second medium, said channel being formed by mutually substantially parallel parts connected with each other by means of semi-circular parts and enclosing the tubes, which form the tube system, and have corresponding straight parts and semi-circular parts so that the second medium is forced to flow through the slits formed between the tubes of the tube system with repeated changes of direction.

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