GB2354315A - Heat exchanger core - Google Patents

Abstract

The heat exchanger core (6) comprises a body of layered sheet elements having flow passages therebetween which can be used to carry counter-flowing air currents. The body is easily manufactured from a single folded sheet (18) which is repeatedly folded in a zigzag manner back on itself to build up the core (6). The body of the core has a generally S shape in plan view. The construction enables long flow paths of a sinuous nature for good heat transfer to be provided in a specified volume.

Description

2354315 Heat Exchan2er Core

The present invention relates to the technical field of heat exchangers and particularly to a core for a heat exchanger.

In public venues such as restaurants and nightclubs, there is a need to ensure that cigarette smoke and other pollutants are removed from inside the venue and replaced with fresh air. It is common to use a cross-flow heat exchanger containing a core comprising a stack of flat plates or sheets spaced apart to provide flow passages therebetween. The flow passages are divided into two groups or sets of alternate flow passages, so that a flow passage of one set has, above and below it in the stack, flow passages of the other set. One set of flow passages can carry, say, incoming fresh air and the other set of flow passages can carry, as a counter flow, the hot and stale air. In this way, the incoming fresh air is warmed before it is expelled into the venue.

A problem with the known heat exchanger is that, whilst the heat exchanger efficiency is reasonable at low flow rates, the efficiency drops off substantially as the flow rate is increased to a level that may typically be needed to ensure satisfactory ventilation of a larger venue, According to a first aspect of the present invention, there is provided a heat exchanger core comprising:

a body of layered sheet elements having flow passages therebetween; wherein the sheet elements and flow passages are curved.

The curved nature of the flow passages induces turbulence into the air that,in use, flows along the passages and thus improves heat exchange between the air in a particular passage and the wall surfaces of the sheet elements of the body of the heat exchanger core. This contrasts with the prior art where the straight nature of the flow passages meant largely that any flow therealong was a laminar flow.

Also, the curved nature of the flow passages means that they will be of longer length than straight flow passages which flow from the same starting point to the same end point. Thus, a longer total length of flow passages may be incorporated in a housing of a given width. This is useful for increasing the dwell time of air within the heat exchanger core, so as to help to maintain a high 2 efficiency at high through flow rates. This also removes the need to provide any sophisticated fan control for trying to use the fan itself to maintain a high heat exchanger efficiency at a high flow rate.

Preferably, the layered sheet elements are provided by one or more folded sheets. This simplifies manufacture of the heat exchanger core because the body may be fabricated from a reduced number of components since a particular sheet serves to provide a plurality of the individual sheet elements through simply being folded into shape. The maximum benefit is achieved if a single sheet is folded to produce all of the sheet elements. Such a sheet could, for example, be run as a strip off a drum of sheeting material and then repeatedly be folded in a jig to produce the assembly of sheet elements that forms the body.

Preferably, the sheet elements are corrugated with the corrugations running axially of the body, or else the sheet elements are provided with other roughened features of surface configuration. In use, when air flows over the corrugations it will be made more turbulent and this will increase the heat exchange efficiency. The corrugations may be provided at discrete positions or else may be provided along the full length of the sheet elements. If a long strip is to be repeatedly folded to produce the sheet elements, the corrugations could be incorporated in the strip during its manufacturing process. Alternatively, a flat strip could be bent to impart corrugations to it as it is folded to manufacture the body of the core.

Preferably, the core further comprises first and second end caps on respective axial ends of the body of sheet elements; and the flow passages comprisea first set of flow passages which start at one side of the body, curve generally across the body and turn into one or both end caps and a second set of flow passages which start at the other side of the body, curve generally across the body and turn into one or both end caps.

Having two entries or exits into the side of the body and two entries or exits into one or both of the axial ends of the body makes it easier to separate apart the entries/exits to separate the respective air flows, rather than having all four of the entries and exits in the side of the body.

3 According to a second aspect of the present invention, there is provided a method of manufacturing a heat exchanger core, comprising:

(i) putting a longitudinal curve in a first length of a strip of sheeting; (ii) folding the next length back on the previous length, putting a longitudinal curve in said next length so that it follows the shape of said previous length and fixing said next length relative to said previous length to provide a curved flow passage therebetween; and (iii) repeating step (ii) one or more times.

Preferably, in step (ii) a divider is inserted between the two lengths of the sheeting to define the spacing between the two lengths.

Thus, the person fabricating the heat exchanger core simply needs to follow a process of putting in place a divider and then folding the strip back on itself so that it may be pressed up against the divider and fixed in position. Conveniently, the dividers may be used in pairs, one at each axial end of the core, so that during the folding both of the side edges of the strip fold back into the required position.

Non-limiting embodiments of the present invention will now be described with reference to the accompanying drawings, in which:- Fig. 1 is a cross-sectional view in a vertical plane through a heat exchanger incorporating a core in accordance with the present invention, the heat exchanger being mounted on a wall; Fig. 2 is a diagrammatic perspective view showing an early stage of folding a metal strip to produce the heat exchanger core; Fig. 3 shows a later stage of the manufacturing process; Fig. 4 shows a yet further later stage of the manufacturing process; Fig. 5 is a diagrammatic perspective view of the top of the finished core, showing the counter flow of air through the core; Figs. 6A and 6B are respectively a perspective view of the folded sheet metal of a finished core and a diagram showing the counter-flow air currents through the core; and Fig. 7 is a perspective view showing two half-size cores in accordance with the present invention.

4 Referring to Fig. 1, a heat exchanger I is mounted on two air pipes 2, 3 which extend through the wall 4.

The heat exchanger 1 has a housing 5 which contains at its centre a core 6. Above the core are two top chambers 7, 8 separated by a dividing partition 9. The annular space around the core 6 is divided into two middle-level chambers 10, 11 by the partition 9. At the bottom of the housing, there are two bottom chambers 12, 13 which are separated by the partition 9. Also at the bottom level of the housing is a fan 14 used to force the hot and cold air through the heat exchanger.

Following the series of arrows A, cool, fresh air is sucked in by the fan 14 from outside the building and passes through the wall 4 into the bottom chamber 12 and then upwards into the middle-level chamber 10. It then flows into one side of the core 6, generally across to the other side of the core and is then diverted to flow axially upwards into top chamber 8 and out of an opening 15.

Hot, stale air is sucked into the heat exchanger 1 by the fan 14 through an opening 16 and into the bottom chamber 13. As indicated by the series of arrows B, the hot air passes upwards into the middle-level chamber 11, enters the righthand side of the core 6 and flows generally across the core to the left-hand side where it is diverted upwards and enters the chamber 7 to exit along the pipe 2 to the outside environment through the wall 4.

The two air currents A and B, as they pass through the core 6, pass adjacent to each other in a counter-flow arrangement so that heat is transferred from the flow B to the flow A so that the cool, fresh air is warmed up before it is introduced intothe room.

The heat exchanger 1 incorporates replaceable filters 17.

Referring to Figs. 2-4, the manufacturing process for the core 6 of the heat exchanger 1 will now be described. A single sheet or foil of metal in the form of a strip 18 is repeatedly folded in a zigzag manner back on itself to build up a core. As shown in Fig. 2, the strip 18 is arranged so that its width is extending generally vertically. A starting end 19 of the strip is folded around a thin insert 20 which has a curved profile so as to impart a curve in the longitudinal direction of the strip to a first length of the strip. At position 21, the strip 18 is folded back on itself and onto a divider 22 which has been put into position after the first length has been folded onto the insert 20. The divider 22 is about the same height as the insert 20 and its width is chosen so as to correspond to the desired size of the air gap that is to be created between the first and second lengths of the strip. Before reaching the end 23 of the divider 22, another fold 24 is put into the strip so that a third length may be folded back around and onto the second length of the strip. Before the fold 24 is created, a further divider 25 is put into position, resting against the outer surface of the second length of the strip.

In Fig. 2, the free end 26 of the third length of the strip is shown before it is folded back on itself. A divider 27 is shown placed in position ready to receive the folded-back fourth length of the strip.

The folding process and addition of dividers is repeated a number of times to arrive at the intermediate stage of construction shown in Fig. 3, where the free end 26 of the strip is waiting to be folded back after a divider has been put into position.

After a couple of more folds and additions of dividers, the construction progresses from the stage shown in Fig. 3 to the stage shown in Fig. 4. The finished core 6 is shown in Fig. 5.

A typical height is 400mm and a typical diameter is 600mm. This core could be housed in a housing having an overall height of 1300mm and a diameter of 800mm.

The two inserts 20 and the series of dividers 22, 25, 27 etc., at the top of the core, function as a top end cap. There is a corresponding arrangement of. inserts and dividers at the bottom of the core, but these are not shown in the figures, and they function as a bottom end cap. The dividers serve to space apart the individual folded lengths of the elongate sheet or strip 18 so that the folded lengths function as sheet elements which are spaced apart relative to one another but which are, for the sake of manufacturing convenience, all folded up out of the same strip.

Flow passages exist between the folded lengths of the strip such that each flow passage has a width almost equal to the full height of the core 6. In the longitudinal direction of each flow passage, it curves first in one direction and then 6 in the opposite direction, so as to impart turbulence to airflow therealong. Each passage is entered from the side of the core and exits axially upwards through the top end cap by passing out of ports in the dividers.

The apertures in the side of the core to the right of a notional dividing line C-C provide entry into a first set of flow passages between the sheet elements. The air that flows along these flow passages is bent first one way and then the other way in the longitudinal direction of the sheet, and finally is turned to flow upwards axially of the core to exit through ports 28 in the distal ends of the dividers which cap the top of these particular flow passages.

A second set of flow passages start at respective positions in the side of the core to the left of the notional dividing line C-C. These passages bend first one way and then the other way in the longitudinal'direction of the strip 18, and then turn upwards to exit through ports 29 at the distal ends of the dividers which cap the top of these particular passages.

Relating Fig. 5 to Fig. 1, the start of the first set of passages could be in communication with the chamber 11, and the ports 28 in communication with the chamber 7. The second set of passageways could start off in communication with the chamber 10 and finish in communication with the chamber 8 through the ports 29.

It can be seen from Fig. 5 that the heat exchanger core 6 is essentially drumlike and provides two sets of serpentine air passages (generally Sshaped in this embodiment) which can be used to carry counter-flow air currents and to transfer. heat therebetween. The average length of the serpentine air passages is greater than the simple diameter of the core 6 and thus the dwell time of air in the core is increased compared with a core having passages which are not curved and which are only of the length of the diameter of the core. By increasing the length of the passages, the dwell time of air in the core is increased so as to increase the heat transfer between the two counter-flow air currents. Overall, the effect is to be able to provide comparatively long flow paths for the air in a relatively small volume.

7 The repeated changes of direction provided by the serpentine air passages encourages turbulence of the air so as to increase heat transfer between the two counter-flow air currents.

The core 6 is substantially radially symmetric about the central point D, in the sense that rotation through 180" will reveal that the old position superimposes on the new position. The consequence of this is that, if the total number of dividers in an end cap is n, only n/2 types of divider need to be produced, since each type of divider may be used twice in each of the end caps at the top and the bottom of the core.

The strip 18 as it is folded about the inserts 20 and the dividers may be glued to those components so as to achieve the necessary rigidity of the core.

It can be seen, by looking at Fig. 5, that adjacent folds are successively moved around the periphery of the core so as to ensure that the finished core has a drum-like or cylindrical overall appearance.

Fig. 6A shows a finished core with the inserts and dividers removed for the sake of clarity, so that all that is shown is the folded strip 18. Fig. 6B is a diagrammatic horizontal section through the core of Fig. 6A showing a typical one of the individual air flows through one of the first set of passages, and a typical one of the air flows through one of the second set of passages, so as to illustrate the counter-flow nature of the two composite air currents.

Fig. 7 shows two individual cores, each of which only shows the individual sheet elements, with the inserts and dividers at the top and bottom being omitted for the sake of clarity. It can be seen that the sheet elements are not folded up from a single strip of material but are, instead, separately provided. However, the curved nature of the flow passages between the sheet elements is apparent, with these flow passages having serpentine paths bending first in one direction and then in the opposite direction to impart turbulence to air flowing therealong. Also, the air passages are comparatively long relative to the overall width of the core.

The cores of Fig. 7 could be folded up from a single strip in a manner analogous to the technique shown in Figs. 2-4.

8 A heat exchanger could use just one of the cores shown in Fig. 7, or else could use the two of them in parallel or in series.

The two cores of Fig. 7 could be axially slotted together to produce a core similar to that shown in Fig. 6A.

Claims (23)

9 CLAIMS

1. A heat exchanger core comprising: a body of layered sheet elements having flow passages therebetween; wherein the sheet elements and flow passages are curved.

2. A heat exchanger core according to claim 1, wherein the layered sheet elements are provided by one or more folded sheets.

3. A heat exchanger core according to claim 2, wherein the layered sheet elements are provided by a single folded sheet.

4. A heat exchanger core according to any preceding claim, wherein the body of layered sheet elements curves firstly in one direction and then in the opposite direction.

5. A heat exchanger core according to claim 4, wherein the body of layered sheet elements is generally S-shaped.

6. A heat exchanger core according to any preceding claim, wherein the sheet elements have ends lying on a notional cylindrical side surface of the body.

7. A heat exchanger core according to any preceding claim, wherein the body has axial ends which are generally flat.

8. A heat exchanger core according to any preceding claim, wherein the body is substantially radially symmetric about a central axis.

9. A heat exchanger core according to any preceding claim, wherein the sheet elements are corrugated with the corrugations running axially of the body.

10. A heat exchanger core according to any preceding claim, wherein:

the core further comprises first and second end caps on respective axial ends of the body of sheet elements; and the flow passages comprise a first set of flow passages which start at one side of the body, curve generally across the body and turn into one or both end caps and a second set of flow passages which start at the other side of the body, curve generally across the body and turn into one or both end caps.

11. A heat exchanger core according to claim 10, wherein at least one of the end caps comprises a plurality of curved elongate dividers which are arranged side-byside and fix the sheet elements in mutually spaced apart positions with the flow passages therebetween.

12. A heat exchanger core according to claim 11, wherein both end caps comprise the curved elongate dividers.

13. A heat exchanger core according to claim 11 or 12, wherein the curved elongate dividers of said at least one of the end caps have end ports into which the flow passages turn and pass through.

14. A heat exchanger core according to any one of claims 11 to 13, wherein said at least one of the end caps ftirther comprises inserts which fill in the indentations. into the array of side-by-side dividers to give a roundish appearance to the respective axial end of the body of sheet elements.

15. A heat exchanger comprising a housing containing a heat exchanger core according to any preceding claim.

16. A heat exchanger according to claim 15, wherein the heat exchanger core is in accordance with any one of claims 10 to 14 and the housing provides first to fourth chambers at respective ends of the first and second sets of flow passages.

11

17. A heat exchanger according to claim 15 or 16, further comprising a fan arranged to produce first and second air flows in a counter-flow arrangement through the heat exchanger core.

18. A method of manufacturing a heat exchanger core, comprising:

(i) putting a longitudinal curve in a first length of a strip of sheeting; (ii) folding the next length back on the previous length, putting a longitudinal curve in said next length so that it follows the shape of said previous length and fixing said next length relative to said previous length to provide a curved flow passage therebetween; and (iii) repeating step (ii) one or more times.

19. A method according to claim 18, wherein in step (ii) a divider is inserted between the two lengths of the sheeting to define the spacing between the two lengths.

20. A method according to claim 18 or 19, wherein adjacent folds successively progress around the periphery of the heat exchanger core.

21. A heat exchanger core substantially as herein described with reference to, or with reference to and as illustrated in, the accompanying drawings.

22. A heat exchanger substantially as herein described with reference to, or with reference to and as illustrated in, the accompanying drawings.

23. A method of manufacturing a heat exchanger core, substantially as herein described with reference to the accompanying drawings.