GB2154311A

GB2154311A - Finned heat exchanger modules

Info

Publication number: GB2154311A
Application number: GB08502860A
Authority: GB
Inventors: James Martin Robertson
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1984-02-17
Filing date: 1985-02-05
Publication date: 1985-09-04
Also published as: GB2154311B; GB8404249D0; GB8502860D0

Abstract

A heat exchange module 10 comprises a thick member having thin close-spaced internal fins on one side, and thick widely-spaced external fins 18, 19 on the other side to define wide, open channels 26. When the module 10 is assembled in a housing 32, the channels 26 of one module 10 are superimposed on the channels 26 of an adjacent module 10, and combine to form relatively large ducts 33 for the passage of hot flue gas. When the modules 10 are subsequently removed from the housing 32, the open channels 26 allow access for deposits from the flue gas to be removed. The internal fins may be sandwiched between two plate members. The module may be tubular (Figs. 5 to 7). <IMAGE>

Description

SPECIFICATION A plate-fin heat exchanger This invention relates to plate-fin heat exchangers and more particularly, but not exclusively to plate-fin heat exchangers used for waste heat recovery.

A plate-fin heat exchanger usually comprises relatively thin heat transfer fins sandwiched between two conductive, relatively thin plates to define a multiplicity of relatively small passages, and an assembly would comprise a stack of spaced apart plates with intervening relatively thin finning therebetween. However, when used in waste heat recovery, the small passages can become blocked by deposits from flue gases contaminated with particles of material or containing corrosive acids, and are extremely difficult to clean.

The invention therefore provides a heat exchange module for a plate-fin heat exchange assembly, the module comprising, relatively close-spaced, relatively thin internal heat transfer fins at one side of a relatively thick heat exchange member, to define a multiplicity of relatively narrow passages, and relatively thick external heat exchange fins at the other side of the member at a spacing substantially greater than that of the internal fins to define with the member relatively wide open channels therebetween.

The member may comprise a heat transfer plate, and the internal fins might be sandwiched between two said plates. Alternatively, the member may be of tubular form.

For some applications, the external fins of a said module may be between 2 mm and 5 mm thick, be spaced apart at a spacing between the centres of the external fins of between 10 mm and 26 mm, and might be between 10 mm and 26 mm high. Each heat exchange plate might be between 5 mm and 10 mm thick, and might be spaced about 10 mm from the other said plate. The internal fins might be at a mean spacing of about 1.0 mm, and might be about 0.25 mm thick.

The invention also includes a plate-fin heat exchange assembly comprising a housing, and a plurality of modules of the invention, the modules being disposed in the housing adjacent to one another and such that the channels of one said module are adjacent to said channels of another said module.

The invention further includes a heat exchange assembly comprising at least one module of the invention having a member of tubular form and rotatably mounted in a housing, and means for rotating the module.

Cleaning elements may extend between radially extending external fins of the module to remove any deposits therein as the module is rotated.

The invention will now be further described by way of example only with reference to the accompanying drawings, in which: Figure 1 shows an end view of a representation of a heat exchange module; Figure 2 shows a sectional view on the line ll-ll of Figure 1; Figure 3 shows a sectional view of an assembly of the modules of Figure 1; Figure 4 shows a fragmentary sectional view of part of the module of Figure 2; Figure 5 shows an end sectional view of a representation of another heat exchange module; Figure 6 shows a sectional view on the line IV-IV of Figure 5, and Figure 7 shows a sectional fragmentary representation to a reduced scale of a heat exchange assembly incorporating the module of Figures 5 and 6.

Referring now to Figures 1 and 2, a platefin heat exchange module 10 is shown, and comprises relatively thick heat exchange members in the form of upper and lower aluminium plates 1 2 and 14 respectively separated by two relatively thick aluminium bars 1 5.

Relatively thin aluminium internal fins 1 6 are close-packed and sandwiched between the inside surfaces of the plates 12, 14 in a folded or corrugated configuration to define relatively narrow passages 1 7 therebetween. Aluminium, relatively thick external fins 1 8 and 1 9 respectively, as shown in Figure 2, extend from outside faces 22, 24 respectively transversely with respect to the internal fins 16, the external fins 18, 1 9 being spaced apart such as to define between them relatively wide channels 26.It is because of this reduced number of external fins 18, 19, that the relatively thick upper plate 1 2 and lower plate 14 are necessary to spread heat from the few external fins 18, 1 9 to the many internal fins 16.

A plurality of the heat exchange modules 10 may be assembled together as shown in Figure 3, to form a plate-fin heat exchange assembly 30. The assembly 30 comprises a housing 32 in which four heat exchange modules 10 are located one above the other such that the external fins 18, 1 9 of one module 10 are adjacent to the external fins 1 9, 1 8 of an adjacent module 10 and thus define substantially closed ducts 33 from the combination of the adjacent channels 26. Ports 34 in the housing 32 communicate with each end of the passages 17, the other ends of the housing 32 being clear to allow access into the ducts 33.

In use of the heat exchange assembly 30, clean cool air flows through the passages 17, whilst hot flue gas flows through the ducts 33 and heats the external fins 18, 1 9 which transfer heat through the plates 12, 1 4 and the internal fins 1 6 to the cool air in the passages 1 7. Although there may be a mismatch of heat transfer characteristics at each side of the upper plate 1 2 and the lower plate 14, this is outweighed by the fact that the ducts 33 are now so large that they are less susceptible to clogging from any deposits from the flue gas.When eventually deposits from the flue gas form in the ducts 33, individual modules 10 may be removed from the assembly 30, and the deposits removed from the channels 26, the open relatively wide channels 26 allowing ready access to the deposits.

The external fins 18, 1 9 as shown in Figure 4, may be formed from continuous sheet, and subsequently soldered, brazed, or welded to a base plate 40 to provide efficient heat exchange with the base plate 40. Alternatively, the upper and lower plates 12, 14 and the external fins 18, 19 might be formed by extrusion.

In one example of a heat exchange module 10, the upper plate 1 2 and the lower plate 14 might be between 5-10 mm thick, and spaced about 10 mm apart. The internal fins 1 6 might be about 0.25 mm thick and at a mean spacing of about 1.0 mm, and the external fins 18, 1 9 about 2-5 mm thick, between 10 mm and 26 mm high, and at a spacing between the centres of the external fins 18, 19 of between 10 mm and 26 mm.

The overall area of the module 10 might be about 2 m long and about 0.3 m wide, and the number of modules 10 to be used in a particular heat exchange assembly would be selected on the basis of the heat and pressuredrop available from the hot flue gas. In practice, the limiting factor on the size of the module 10 is likely to be its overall weight to allow convenient handling.

Although adjacent external fins 18, 1 9 in Figure 3 have been shown with a narrow gap therebetween, the adjacent external fins 1 8, 1 9 may be contiguous so that to a certain extent the underlying modules 10 provide support for the upper modules 10, and to ensure this the external fins 18, 1 9 may be aligned slightly skewed in opposite-hand relationship. An even more rigid construction might be provided by the external fins 18, 1 9 being shaped at their ends so as to engage and interlock with adjacent external fins 19, 1 8 respectively having complementary shaping.

Seals (not shown) may be introduced between the housing 32 and the modules 10 to prevent leakage from the passages 1 7 to the ducts 33 or vice versa.

It will be understood that although the module 10 has been described in relation to cross-flow heat exchange between the cool air and the flue gas, the external fins may be aligned so as to permit co-current or countercurrent heat exchange.

The module 10 may be constructed from alternative materials, for example copper, or the external fins 18, 1 9 made from an alternative material provided that they are connected through to the internal fins 1 6 with minimum thermal resistance.

To faciliate connection and withdrawal of the module 10 from the housing, appropriate flanges etc (not shown) may be provided to suit a particular installation.

Although the invention has been described in relation to the use of flat heat exchange members, arcuate or circular heat exchange members may be used as shown in Figures 5 and 6 to which reference is made. In Figures 5 and 6, a heat exchange rotary module 50 is shown and comprises relatively thin aluminium, internal heat exchange fins 52 of closepacked pleated form disposed in an annular space 54 between aluminium tubes 56 and 57 respectively to define a multiplicity of passages 58 therebetween. The tube 56 is of thick wall construction, and supports the internal fins 52 which are brazed to the inside surface of the tube 56.The tube 57 which is of thin wall construction is closed at each end (not shown), and although the internal fins 52 may be joined to the tube 57 this is not necessary, the tube 57 simply acting to confine gas flow in the space 54 to the vicinity of the internal fins 52. Aluminium, flat relatively thick, annular external fins 60 are brazed to the tube 56 at a spacing such as to define between them relatively wide annular channels 62.

The module 50 is installed, as shown in Figure 7, in a housing 66, being rotatably supported by spindles 68 at each end of the module 50 and driven by means (not shown) connected to one of the spindles 68. A seal 72 between each end of the module 50 and the housing 66 allows cool clean air to flow through ports 73 in the housing 66 through the passages 58 (not shown) in the module 50. A cleaning device 74 extending parallel to the longitudinal axis of the module 50, has the same number of flat, hardened steel cleaning fingers 76 as there are channels 62 in the module 50, each cleaning finger 76 extending into a respective channel 62 so as to remove deposits from the sides and the bottom of the channel 62 as the module 50 rotates.

In operation, cool clean air flows through the ports 73 and through the module 50 in the direction of arrow "A", whilst hot flue gas flows transversely to the module 50 through the channels 62 where heat extracted from the flue gas by the thick external fins 60 is conducted by the tube 56 and the thin internal fins 52 to the cool clean gas in the passages 58. As deposits from the flue gas build up in the channels 62, they are removed by the fingers 76 as the module 50 is rotated either continuously or intermittently.

Although only one module 50 has been shown in Figure 7, a plurality of modules 50 may be installed one behind the other and one below the other with the channels 62 in alignment.

Claims

1. A heat exchange module for a plate-fin heat exchange assembly, the module comprising, relatively close-spaced, relatively thin internal heat transfer fins at one side of a relatively thick heat exchange member, to define a multiplicity of relatively narrow passages, and relatively thick external heat exchange fins at the other side of the member at a spacing substantially greater than that of the internal fins to define with the respective member relatively wide open channels therebetween.

2. A module as claimed in Claim 1, wherein the internal fins and the external fins are in transverse relationship for cross-flow heat transfer.

3. A module as claimed in Claim 1 or Claim 2, wherein the external fins are aligned in a skewed relationship with respect to the sides of the module.

4. A module as claimed in any one Claims 1 to 3, wherein the member comprises a heat transfer plate.

5. A module as claimed in Claim 4, wherein the internal fins are sandwiched between two said plates.

6. A module as claimed in any one of Claims 1 to 5, wherein the external fins are shaped to engage and interlock with the external fins having complementary shaping of another said module.

7. A module as claimed in any one of Claims 1 to 3, wherein the member is of tubular form.

8. A module as claimed in Claim 5, wherein the module comprises aluminium, the external fins of a said module are between 2 mm and 5 mm thick, and each plate is between 5 mm and 10 mm thick.

9. A module as claimed in Claim 8, wherein the external fins are at a spacing between the centres thereof of between 10 mm and 26 mm.

10. A module as claimed in Claim 8 or Claim 9, wherein the external fins are about 10 mm and 26 mm high.

11. A module as claimed in any one of Claims 8 to 10, wherein the plates are about 10 mm apart.

1 2. A module as claimed in any one of Claims 8 to 11, wherein the internal fins are at a mean spacing of about 1.0 mm and are about 0.25 mm thick.

1 3. A heat exchange assembly comprising a housing, and a plurality of modules as claimed in any one of Claims 1 to 6, and 8 to 12, the modules being disposed in the housing adjacent to one another and such that the channels of one said module are adjacent to said channels of another said module.

1 4. A heat exchange assembly comprising a housing, at least one heat exchange module as claimed in Claim 7 rotatably mounted in the housing, and means for rotating the module.

15. An assembly as claimed in Claim 14, wherein the external fins extend radially from the tubular heat exchange member, and cleaning elements extend into the channels to remove any deposits therein as the module is rotated.

1 6. A heat exchange module substantially as hereinbefore described with reference to Figures 1 and 2 of the accompanying drawings.

17. A module as claimed in Claim 16 modified substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.

18. A heat exchange module substantially as herein before described with reference to Figures 5 and 6 of the accompanying drawings.

1 9. A heat exchange assembly comprising a plurality of modules as claimed in Claim 1 6 or Claim 17, and substantially as hereinbefore described with reference to Figure 3 of the accompanying drawings.

20. A heat exchange assembly comprising at least one heat exchange module as claimed in Claim 18, and substantially as hereinbefore described with reference to Figure 7 of the accompanying drawings.