GB2266136A

GB2266136A - Heat exchanger with baffle

Info

Publication number: GB2266136A
Application number: GB9307463A
Authority: GB
Inventors: Peter Wright
Original assignee: LABGAS RES LAB Ltd
Current assignee: LABGAS RES LAB Ltd
Priority date: 1992-04-16
Filing date: 1993-04-08
Publication date: 1993-10-20
Anticipated expiration: 2013-04-08
Also published as: GB9208509D0; GB9307463D0; GB2266136B

Abstract

A heat exchanger is formed from two identical parts 10. These comprise a base portion 12 with two end walls 14 and a baffle 16 comprising a fin 18 projecting from the base 12 between the end walls 16. Ribs 20 are arranged along either side of the fin. The arrangement of the ribs and fins is such that when two parts 10 are relatively inverted and placed together (as in figure 3) to define a passage between them, fluid flowing along the passage is forced to take a convoluted path, rather than flowing straight through the gap. <IMAGE>

Description

Heat Exchanger The present invention relates to heat exchangers.

Heat exchangers are used, for instance, in gas fires of the type known as "inset" gas fires. An inset gas fire consists of an inner box in which the gas is burnt, and an outer box in which the inner box is housed.

A gap between the inner and outer boxes provides a path for air to enter from the space being heated, to move through the fire, and to return to the space. This air is heated as it follows the path. A heat exchanger can be used to pass waste gases from the fire through the air path before leaving through a chimney. This increases the heating effect on the air moving between the inner and outer boxes, and reduces the amount of heat lost up the chimney.

An inset gas fire may project forward from a fireplace in which it is installed, on to the hearth. This forward projection is limited by regulations. Similarly, the rearward projection is limited by the need to maintain a debris catchment area behind the fire, to receive debris from the chimney. These two factors limit the size of heat exchanger which can be used in the fire.

It is an object of the invention to provide an improved heat exchanger which can be used, for instance, in an inset gas fire to increase the amount of heat recovered from waste gases, thereby increasing the overall efficiency of the fire.

According to the invention, there is provided a heat exchanger comprising passage means which, in use, define a passage through which heated fluid may flow, and around which fluid to be heated may pass, there being baffle means within the passage to cause the heated fluid to follow a convoluted path along the passage.

The baffle means may prevent the heated fluid following a straight path, i.e. any path other than a convoluted one. The baffle means may comprise at least one fin which projects into the passage. The fins may project generally radially into the passage. The fins may project into the passage from two opposed regions of the passage walls. The fins projecting from the opposed regions may be staggered with respect to each other. The or each fin may extend along the passage wall or walls generally transversely of the direction of flow.

The or at least one fin may incorporate rib means which extend along the passage walls generally parallel to the direction of flow. The rib means may provide at least one surface which is not parallel with the passage axis, whereby fluid which comes into contact with the said surface will be deflected from an axial path. The or each fin may incorporate a plurality of ribs.

Preferably a plurality of ribs are located on each side of the or each said fin. The ribs located on one side of the or each said fin may be staggered with respect to the ribs located on the other side thereof.

Each fin preferably projects substantially half way across the passage.

The passage means may comprise at least two parts which define the passage between them. The two parts may be identical. The baffle means are preferably so formed on the two parts as to be staggered when the two parts are placed together to form the passage.

Each part may further provide external fin means on outwardly facing surfaces thereof, to increase the surface area of each part in contact with the fluid to be heated. The external fin means may be off-centre, whereby adjacent external fin means are staggered when two heat exchangers as aforesaid are placed alongside each other.

The invention also provides a heat exchanger part for use in forming a heat exchanger having any or all of the features set out above, the part partially defining a passage as aforesaid, and comprising baffle means which, alone or in conjunction with baffle means on another similar part, cause heated fluid to follow a convoluted path as aforesaid.

The invention also provides a heat exchanger comprising a plurality of heat exchangers as aforesaid, arranged side by side to define a plurality of generally aligned passages for heated fluid, and wherein fluid to be heated may pass around and between the heat exchangers.

The invention also provides a gas fire comprising an inner box which is heated, in use, by combustion, and an outer box, there being a path between the boxes for air to pass from the space being heated, through the fire, and back to the said space, and wherein at least one heat exchanger as aforesaid is provided to define a passage through which waste gases may pass from the inner box out of the outer box across the said path, and wherein air in the said path passes around the heat exchanger to be heated thereby.

One embodiment of the present invention, and its manner of use, will now be described in more detail, by way of example only, and with reference to the accompanying drawings, in which: Fig. 1 is a perspective view of a heat exchanger part for use in the preferred embodiment; Fig. 2 is a partial elevation of the part of Fig.

1; Fig. 3 is a vertical section through a heat exchanger formed by two parts of the type shown in Figs.

1 and 2; and Fig. 4 is a vertical section through an inset gas fire in which the heat exchanger of Fig. 3 is in use.

Fig. 1 shows a heat exchanger part 10. This may be cast from metal or other good heat conducting material.

The part 10 comprises a base portion 12 which is generally rectangular in shape, and two end walls 14 which extend generally at right angles away from one face of the base 12.

A baffle 16 projects from the same face of the base 12, between the end walls 14. The baffle 16 consists of a fin 18 and a plurality of ribs 20. The fin 18 is a generally planar wall which projects from the base 12 substantially perpendicular thereto, to substantially the same distance as the end walls 14. It can be seen from Fig. 1 that the fin 18 is off-centre in relation to the base 12.

Several ribs 20 are located along each side of the fin 18. Each rib 20 is of the same general form. A rectangular face 20a slopes down to the base 12 from that edge of the fin 18 which is furthest from the base 12.

To either side of the rectagular face 20a, there are triangular sloping faces 20b which slope from the rectangular face 20a to the base 12 and to the side face 22 of the fin 18. It is to be noted that the rectangular face 20a is not parallel with the base 12, nor with the fin 18, and neither is any of the faces 20b. It is also to be noted that the ribs 20 on one side of the fin 18 are staggered with respect to the ribs on the other side of the fin. That is, ribs are located alternately on one side and the other of the fin. This arrangement is not symmetrical about the mid-point of the fin, for reasons described below.

A heat exchanger can be constructed from two identical parts 10, in the following manner. The two parts are placed together after one has been reversed with respect to the other, to abut the edges 24 of the end walls 14. This is shown more clearly in Fig. 3. The fins 18 do not abut, neither do the ribs 20. This arises because the fins 18 are off-centre, and the ribs 20 are staggered in an asymmetric manner.

When the heat exchanger shown in Fig. 3 is in use, heated fluid, such as waste gases, are allowed to flow between the two parts 10, along the passage formed between the bases 12. Fluid to be heated is in the region 26, outside the passage walls. This is the envisaged arrangement, but it will be understood that the locations of the fluid to be heated and the fluid providing the heat could be reversed. Heat transfers from the passage through the walls of the heat exchanger (principally the base 12 of each part 10) to the fluid outside. It can be seen from Fig. 3 that the baffles provided by the fins 18 and the ribs 20 deflect the heated fluid from a straight path, causing it to follow a convoluted path along the passage, as indicated by the arrows 28.

The convoluted or tortuous passage followed by the fluid is defined firstly by the fins 18, which project substantially half way across the passage. This makes it impossible for fluid to pass straight along the passage, forcing it to take a non-straight path. However, it may be desirable for the fins to project slightly less than this, so that a narrow straight path does exist along the central axis of the passage. However, turbulence created elsewhere in the fluids is likely to deflect fluid passing along this narrow path, so that no fluid will in fact pass straight along the passage.

In addition to the convolutions defined by the fins 18, the slanting faces of the ribs 20 cause fluid to be deflected, thereby causing turbulence within the fluid.

The creation of this turbulence is enhanced by the stagger of the various fins, which further convolutes the paths available through the heat exchanger.

It can be seen particularly from Fig. 3 that the fins 18 project generally radially into the passage from two opposed regions of the passage walls, and extend generally transversely along the passage walls, that is, transverse to the direction of flow. However, the ribs 20 extend generally axially along the passage (parallel to the flow) and each provide several surfaces which are not parallel with the passage axis, so that fluid is deflected from travelling axially along the passage.

It is expected that the convoluted path followed by the fluid, and the turbulence created within the heat exchanger , will cause much greater mixing of gases within the heat exchanger, thereby enhancing the efficiency of the heat exchange process.

Fig. 4 shows one application of heat exchangers of the type described above, in an inset gas fire.

The fire 30 has an inner box 32 and an outer box 34. There is a debris catchment area 35 behind the outer box 34. Gas is burnt within the inner box 32, at 36.

Air can flow between the inner and outer box from an inlet at 38 to an outlet at 40.

A heat exchanger is located at 42, to provide a path for waste gases to leave the inner box and rise up a chimney 44. The heat exchanger at 42 is shown only in outline, and consists of several pairs of parts 10, arranged face to face as indicated in Fig. 3. Each pair is then located between the walls of the inner and outer boxes to provide a passage through the heat exchanger for the waste gases, and to allow air to pass around the heat exchanger to the outlet 40. The pairs of parts 10 are arranged side by side to create a plurality of passages for waste gas, and a plurality of routes for air to pass around them.

Returning to Fig. 3, it can be seen that each part 10 includes a fin 46 on its outer surface. These increase the area of contact between the heat exchanger walls and the fluid to be heated. This further increases the efficiency of the heat exchanger. It is to be noted from Fig. 3 that the fins 46 are off-centre on the base 12, so that pairs of parts 10 can be placed close to one another without the fins 46 interfering with each other.

It can be seen from Fig. 3 that although the heat exchanger causes turbulence in the heated fluid, and provides a large surface area for heat transfer, thereby improving the efficiency of heat exchange, the passage is not constricted to any great extent, so that the overall resistance to the flow of heated fluid is not expected to be excessive. This is important in relation to the inset gas fire application, because if the heat exchanger passage is too restricted, waste gases would tend to be forced out of the fire through other openings, possibly into the room being heated.

Variations and modifications can be made to the apparatus described above, without departing from the spirit and scope of the present invention. In particular, the arrangement and form of the various fins and ribs can be altered, and other materials can be used for manufacture. The heat exchanger could be manufactured as a single piece, in two pieces as described, or in more than two pieces. A heat exchanger could be used for other applications, and for applications involving fluids other than air and waste gas.

Whilst endeavouring in the foregoing specification to draw attention to those features of the invention believed to be of particular importance it should be understood that the Applicant claims protection in respect of any patentable feature or combination of features hereinbefore referred to and/or shown in the drawings whether or not particular emphasis has been placed thereon.

Claims

1. A heat exchanger comprising passage means which, in use, define a passage through which heated fluid may flow, and around which fluid to be heated may pass, there being baffle means within the passage to cause the heated fluid to follow a convoluted path along the passage.

2. A heat exchanger according to claim 1, wherein the baffle means prevent the heated fluid following a straight path along the passage.

3. A heat exchanger according to claim 1 or 2, wherein the baffle means comprise at least one fin which projects into the passage.

4. A heat exchanger according to claim 3, wherein the fins project generally radially into the passage.

5. A heat exchanger according to claim 3 or 4, wherein the fins project into the passage from two opposed regions of the passage walls.

6. A heat exchanger according to claim 3, 4 or 5, wherein the fins projecting from the opposed regions are staggered with respect to each other.

7. A heat exchanger according to any of claims 3 to 6, wherein the or each fin extends along the passage wall or walls generally transversely of the direction of flow.

8. A heat exchanger according to any of claims 3 to 7, wherein the or at least one fin incorporates rib means which extend along the passage walls generally parallel to the direction of flow.

9. A heat exchanger according to claim 8, wherein the rib means provide at least one surface which is not parallel with the passage axis, whereby fluid which comes into contact with the said surface will be deflected from an axial path.

10. A heat exchanger according to claim 8 or 9, wherein the or at least one fin incorporates a plurality of ribs.

11. A heat exchanger according to claim 10, wherein a plurality of ribs are located on each side of the or each said fin.

12. A heat exchanger according to any of claims 8 to 11, wherein the ribs located on one side of the or each said fin are staggered with respect to the ribs located on the other side thereof.

13. A heat exchanger according to any of claims 3 to 12, wherein the or each fin projects substantially half way across the passage.

14. A heat exchanger according to any preceding claim, wherein the passage means comprises at least two parts which define the passage between them.

15. A heat exchanger according to claim 14, wherein the two parts are identical.

16. A heat exchanger according to claim 14 or 15, wherein the baffle means are so formed on the two parts as to be staggered when the two parts are placed together to form the passage.

17. A heat exchanger according to claim 14, 15 or 16, wherein each part further provides external fin means on outwardly facing surfaces thereof, to increase the surface area of each part in contact with the fluid to be heated.

18. A heat exchanger according to claim 17, wherein the external fin means are off-centre, whereby adjacent external fin means are staggered when two heat exchangers as aforesaid are placed alongside each other.

19. A heat exchanger part for use in forming a heat exchanger according to any preceding claim, the part partially defining a passage as aforesaid, and comprising baffle means which, alone or in conjunction with baffle means on another similar part, cause heated fluid to follow a convoluted path as aforesaid.

20. A heat exchanger comprising a plurality of heat exchangers according to any of claims 1 to 18, and arranged side by side to define a plurality of generally aligned passages for heated fluid, and wherein fluid to be heated may pass around and between the heat exchangers.

21. A gas fire comprising an inner box which is heated, in use, by combustion, and an outer box, there being a path between the boxes for air to pass from the space being heated, through the fire, and back to the said space, and wherein at least one heat exchanger according to any of claims 1 to 18 is provided to define a passage through which waste gases may pass from the inner box out of the outer box across the said path, and wherein air in the said path passes around the heat exchanger to be heated thereby.

22. A heat exchanger substantially as described above with reference to the accompanying drawings.

23. A heat exchanger part substantially as described above with reference to Fig. 1 of the accompanying drawings.

24. A gas fire substantially as described above with reference to the accompanying drawings.

25. Any novel subject matter or combination including novel subject matter disclosed, whether or not within the scope of or relating to the same invention as any of the preceding Claims.