WO1997042458A1

WO1997042458A1 - Flue gas heat exchanger and fin therefor

Info

Publication number: WO1997042458A1
Application number: PCT/DK1997/000207
Authority: WO
Inventors: Jens Otto Ravn Andersen; Jesper Førster
Original assignee: East Consult A/S
Priority date: 1996-05-06
Filing date: 1997-05-06
Publication date: 1997-11-13
Also published as: EP0897521A1; DK53596A; DE69701520D1; EP0897521B1; AU2693497A; DE69701520T2; DE69701520T9; DK172656B1

Abstract

The invention relates to a heat exchanger for cooling a gas by means of a medium, preferably water. The flue gas exchanger comprises a jacket (3), along which fins (10) provided with inlets and outlets for a flue gas, which is intended to be conducted through the jacket. The jacket (3) consists of an inner jacket (3) and an outer jacket (4), between which a chamber (5) for a cooling medium is formed. The fins (10) are produced individually and assembled into blocks (11) on a central guiding element (13) extending through the jacket (3). The inlets and the outlets preferably consist of sections of a circle, which conduct the flue gas out towards the jacket (3), and which reduce the flow resistance considerably.

Description

FLUE GAS HEAT EXCHANGER AND FIN THEREFOR

Background of the invention The present invention relates to a flue gas exchanger comprising fins that extend along and inside a jacket, and said fins being arranged at a mutual distance and forming channels between adjacent fins, and said fins being provided with at least one first opening forming an inlet, alternatively an outlet, and optionally a second opening forming an outlet, alternatively an inlet, for a flue gas, which is intended to extend from a first end of the jacket through the inlets and outlets of the fins to a second end ofthe jacket.

DE 888 255 describes a flue gas exchanger comprising a chamber with a ribbed tube that extends along the chamber. The ribbed tube comprises ribs extending perpendicu- larly in relation to a longitudinal axis ofthe chamber. The ribs are provided with inlets and outlets for the flue gas. The inlets and outlets are constituted by sections of a cir¬ cle having a constantly decreasing or increasing height. A cooling medium extends through a central tubing ofthe ribbed tube.

The flue gas exchanger described in the above publication possesses some disadvan¬ tages. It involves large costs to produce a ribbed tube and at the same time the pro¬ duction has to be made for a specific dimensioning of the flue gas exchanger. Besides, a flue gas exchanger with a ribbed tube of the above-mentioned type with inlets and outlets constituted by sections of a circle has a limited capacity. The flue gas will be conducted to a centre of the jacket and cooling the ribs must take place by means of the central tubing having a limited surface area. Furthermore, the degree of rib effect is poor in a tube with external ribs. Finally, a ribbed tube having ribs that are provided with sections of a circle has a certain flow resistance towards the flue gas.

Thus, it is the object of the present invention to provide a flue gas exchanger that does not possess the disadvantages discussed above and which consequently increases the possibility of cooling the flue gas and reduces the flow resistance in order to increase the capacity.

This object is obtained by a flue gas exchanger that is characterised in that a total open area of inlets and outlets in the fins amounts to a multiple of between 1.0 and 1.5, preferably 1.1, of the size of a cross section area ofthe channels between adjacent fins.

By constructing a flue gas exchanger with this characteristic, one obtains a flue gas exchanger having a very low flow resistance. This means that the capacity is exclu- sively determined by the physical dimensions of the flue gas exchanger and the cool¬ ing taking place in the flue gas exchanger and is not limited by unfavourable flow conditions in the flue gas exchanger.

The fins are preferably produced as individual fins, which are positioned on a central guiding element. The number and dimensions of the fins may vary in order to provide the flue gas exchanger with different capacities and with different other physical and thermal characteristics. This means that the diameter and length of the flue gas ex¬ changer may be altered by using fins of a different diameter or by using a different number of fins.

In a preferred embodiment the flue gas exchanger is characterised in that the fins con¬ sist of individual discs, and that the inlets and outlets in the fins consist of sections of a circle.

Fins in which inlets and outlets consist of sections of a circle have the advantage that the flue gas is conducted towards outer areas of the ribs. Thus, cooling of the ribs may take place at the jacket, which has a considerably larger surface area than any central tubing. The jacket and the ribs correspond to a tube with internal ribs as opposed to a tube with external ribs, in which cooling takes place at the internal tube having a small surface area. This increases the capacity of the flue gas exchanger and, also, the flue gas exchanger according to the invention with a given capacity has considerably smaller dimensions than known flue gas exchangers with the same capacity. Thus, the invention also relates to a fin for a flue gas exchanger.

EP 0 571 881 describes a heat exchanger formed by fins, which are assembled into a block. The fins comprises openings that constitute sections of a circle. The fins are assembled in such a manner that two helical channels are formed in the block. The heat exchanger described may be used for both fluent and gaseous media.

The fins of this heat exchanger have the disadvantage that they are not to a sufficient extent able to create a forced flow, e.g. of a flue gas. The object of the heat exchanger described is to reduce the flow resistance. However, a helical channel established with this known technique will not to a sufficient extent ensure proper cooling of the flue gas since the latter will be conducted through a short channel with a large flow cross- section. The fins are not provided with an actual inlet and outlet but merely help to form the helical channels. Thus, two openings form two channel systems. Besides, the material consumption is very large compared to the heat transmission area, and the surface in the channels is angular, which increases the flow resistance.

Thus, it is the object to provided fins that will to a sufficient extent ensure a forced flow of a flue gas in a flue gas exchanger, but which will at the same time keep the flow resistance at a minimum.

This object is obtained by a fin that is characterised in that the fin consists of a disc, that in a plane part of the fin said fin is provided with inlet and outlet for a single channel system, and that the inlets and outlets ofthe fins consist of sections of a circle.

The sections of a circle help to obtain the low flow resistance. The sections of a circle vary in size in such a manner that in a block of fins there is a constant reduction of the open area ofthe inlets while at the same time there is a constant widening of the open area of the outlets through the block. The total area of inlet and outlet is identical for each fin. A simple way of producing the sections of a circle in each fin is using a punching tool having the shape of a section of a circle and with an angle corresponding to the small¬ est section to be made in a fin. Other sections of a circle are produced as a multiple of the smallest section by using the same punching tool and simply perform a number of adjacent punchings corresponding to the required multiple ofthe smallest section. The fins of a preferred embodiment are produced from aluminium.

The flue gas exchanger according to the invention may be used in many contexts, e.g. as a heat exchanger from a fuel device in a central heating installation. It is also pos- sible to use the flue gas exchanger according to the invention for different kinds of vessels.

Description of the drawing

The invention will now be described in further detail with reference to the accompany- ing drawing, wherein

Fig. 1 is a section view through an embodiment of a heat gas exchanger according to the invention, Fig. 2 is plan views of fins according to the invention, Fig. 3 is a side view of a fin according to the invention, and

Fig. 4 is a plan view of a block with several fins according to the invention.

Fig. 1 shows a section view through an embodiment of a flue gas exchanger according to the invention. The flue gas exchanger comprises a front cover 1 and a rear cover 2. An inner jacket 3 and an outer jacket 4 extend between the covers 1, 2. A chamber 5 between the inner jacket 3 and the outer jacket 4 is sealed by packings 6, 7 contacting the covers 1, 2. An inlet 8 for flue gas extends through the inner jacket 3 and the outer jacket 4. The inlet 8 may alternatively be provided in the front cover 1. A correspond¬ ing outlet 9 for the flue gas extends through the rear cover 2.

Fins 10 are assembled into blocks 11 , which extend through the inner jacket 3. In the embodiment shown the flue gas exchanger comprises eight blocks 11 with eight adja- cent fins 10 in each. Openings 20-34 (see Fig. 2A-2H) form an inlet chamber 35 and an outlet chamber 36 for each block 11. The inlet chamber and the outlet chamber are indicated by hatching. The fins 10 are mounted on a guiding element 13 extending through openings in a central part of the fins 10 (see Fig. 2). The guiding element 13 preferably has a rectangular cross section, and the openings in the fins 10 a corre¬ sponding rectangular cross-section (see Fig. 2). Hereby the fins 10 are prevented from rotating around the guiding element 13. The guiding element 13 is fastened to the rear cover 2 by means appropriate for the purpose (not shown).

A flow gas, illustrated by means of flow lines 14, extends through the flue gas ex¬ changer from the inlet 8 to the outlet 9. The flue gas passes the fins 10, all of which, except from a frontmost fin and a rearmost fin, are provided with both an inlet and an outlet (see Fig. 2A-2H). Inlet and outlet are formed in the fins in such a manner that the flue gas is conducted towards the inner jacket 3. The frontmost fin is only provided with an inlet and the rearmost fin is only provided with an outlet.

The chamber 5 between the inner jacket 3 and the outer jacket 4 is designed to contain a cooling agent for cooling the flue gas that extends through the flue gas exchanger. An inlet (not shown) and an outlet (not shown) conduct the cooling medium into the chamber. The cooling medium is preferably a liquid such as water. The flue gas is cooled, and the cooling medium is heated and may subsequently be used as a heating medium, e.g. in a heat exchanger in a central heating installation.

Figs. 2 A-2H show the fins 10 according to the invention seen in a plan view. Shown in the figure are eight different fins 10 corresponding to the eight fins of which each block 1 1 (see Fig. 1) consists. The fins 10 comprise a plane part 15 and are all, except from a first fin, provided with openings, which constitute inlets and outlets. The inlets and outlets are substantially constituted by a section of a circle extending from a cen¬ tral part 16 of each fin 10 to the vicinity of an outer periphery of the fin. The central part 16 of each fin is provided with an opening 18 having a rectangular cross-section.

The guiding element 13 (see Fig. 1) is designed to extend through the openings 18 in each fin 10. Along the outer periphery 17 each fin is provided with a flange 19 (see Fig. 3).

A firsts fin shown in Fig. 2A is provided with a first opening 20 constituting an inlet, alternatively an outlet. Whether the opening 20 constitutes an inlet or an outlet (see Fig. 1), depends on the block 11 in which the fin 10 is positioned. If the fin 10 is posi¬ tioned in a first block, a third block, a fifth block, etc., seen from the left in Fig. 1 , the opening constitutes an inlet. If the fin 10 is positioned in a second block, a fourth block, a sixth block, etc., seen from the left in Fig. 1, the opening constitutes an outlet.

The openings in the fins 10 are produced by punching with a punching tool having the shape of the smallest opening. The larger openings all form a multiple of the smallest opening. Thus, one and the same tool may be used for all openings by performing sev¬ eral adjacent punchings corresponding to the multiple ofthe smallest punching consti- tuted by the opening in question. It is only necessary to produce five different fins in order to provide eight fins such as shown in the figure since the fins in Fig. 2B, 2C, respectively 2D, are identical with the fins in Fig. 2F, 2G, respectively 2H, only ro¬ tated 180° in relation to one another.

As mentioned, the first fin is provided with a first opening 20. The opening is consti¬ tuted by a section of a circle having an angle of 100°. A second fin is provided with a first opening 21 constituted by a section of a circle having an angle of 87.5° and a sec¬ ond opening 22 constituted by a section of a circle of 12.5°. A third fin is provided with a first opening 23 constituted by a section of a circle having an angle of 75° and a second opening 24 constituted by a section of a circle of 25°. A fourth fin is provided with a first opening 25 constituted by a section of a circle having an angle of 62.5° and a second opening 26 constituted by a section of a circle of 37.5°. A fifth fin is pro¬ vided with a first opening 27 constituted by a section of a circle having an angle of 50° and a second opening 28 constituted by a section of a circle of 50°. A sixth fin is pro- vided with a first opening 29 constituted by a section of a circle having an angle of

37.5° and a second opening 30 constituted by a section of a circle of 62.5°. A sixth fin is provided with a first opening 31 constituted by a section of a circle having an angle of 25° and a second opening 32 constituted by a section of a circle of 75°. A sixth fin is provided with a first opening 33 constituted by a section of a circle having an angle of 12.5° and a second opening 34 constituted by a section of a circle of 87.5°. The total open area ofthe openings forming inlet and outlet is identical for each fin.

Fig. 3 shows a fin 10 according to the invention seen in a side view. As mentioned, the fin has a plane part 15 with the central part 16 in which the opening 18 is provided. Along the outer periphery 17 the fin is provided with the flange 19. The opening 18 in the central part 16 is also provided by a flange. The flange 19 along the outer periph- ery 17 gives the fin rigidity while at the same time creating a distance a between adja¬ cent fins in a block 11 (see Fig. 1). The flange 19 is intended to contact the inner jacket 3 in a situation of use.

Fig. 4 shows a block 11 consisting of eight fins 10 as illustrated in fig. 2. The fins 10 are put together in the block 11 in such a manner that the plane part 15 of the first fin contacts the flange 19 of an adjacent second fin. The inlets, alternatively the outlets, are illustrated. It appears that the open area of the inlets, alternatively the outlets, de¬ creases as the flue gas passes through the block 1 1. Simultaneously, the open area of the outlets, alternatively the inlets, increases. These are not illustrated. The channels 12 have a cross section area A seen parallel with the plane of the figure seen in an up¬ ward or downward direction. The cross section area A is determined as the distance a between the fins (see Fig. 3) multiplied by an extension b of the fins. The extension b of the embodiment shown is equal to the diametrical distance of the planes subtracted by an extension c of the guiding element. The total open area of each fin is equal to the cross section area A of each chamber 12 (see Fig. 1) multiplied by a factor of be¬ tween 1.0 and 1.5, preferably 1.1.

The invention has been described above with reference to a specific embodiment of a flue gas exchanger according to the invention and for specific embodiments of fins according to the invention. It will be possible to use alternative embodiments of both flue gas exchanger and fins. Thus, the flue gas exchanger may contain a number of blocks of fins other than eight, and the number of fins in each block may be different from eight. The fins may further have a shape other than circular, and the mutual dis¬ tance between fins may be provided in a manner other than by a flange.

Claims

1. A flue gas exchanger comprising fins (10) that extend along and inside a jacket (3), and said fins (10) being arranged at a mutual distance and forming channels (12) be- tween adjacent fins (10), and said fins (10) being provided with at least one first opening (1 1) forming an inlet, alternatively an outlet, and optionally a second opening (1 1) forming an outlet, alternatively an inlet, for a flue gas, which is intended to ex¬ tend from a first end ofthe jacket (3) through the inlets and outlets of the fins (10) to a second end of the jacket (3), and said inlets, respectively outlets, forming inlet cham- bers, respectively outlet chambers, which are interconnected by the channels (12), c h a r a c t e r i s e d in that a total open area of inlets and outlets in the fins amounts to a multiple of between 1.0 and 1.5, preferably 1.1, of the size of a cross section area (A) ofthe channels (12) between adjacent fins (10).

2. A flue gas exchanger according to claim 1 , c h a r a c t e r i s e d in that the fins are assembled into blocks (11), and that at least one block (1 1 ), preferably five blocks (1 1), extends along the jacket (3).

3. A flue gas exchanger according to claim 2, c h a r a c t e r i s e d in that each block (1 1) comprises eight fins (10), that the inlets and the outlets are constituted by sectors of a circle, that a smallest sector of a circle is between 1° and 22.5°, preferably 12.5°, that a first fin comprises a first sector of a circle of eight times the smallest sector of a circle, that a second fin comprises a first sector of a circle of seven times the smallest sector of a circle and a second sector of a circle of one time the smallest sector of a circle, that a third fin comprises a first sector of a circle of six times the smallest sector of a circle and a second sector of a circle of two times the smallest sector of a circle, that a fourth fin comprises a first sector of a circle of five times the smallest sector of a circle and a second sector of a circle of three times the smallest sector of a circle, that a fifth fin comprises a first sector of a circle of four times the smallest sector of a cir- cle and a second sector of a circle of four times the smallest sector of a circle.

4. A flue gas exchanger according to claim 2 or 3, characterised in that the fins are mounted on a guiding element (13), that the guiding element extends through openings (17) in a central part (16) of the fins (10), that the openings (17) and the guiding elements (13) have a mutual cross section, and that the cross section is non-

5 circular.

5. A flue gas exchanger according to claim 1 or 2, characterised in that the jacket comprises an inner jacket (3) and an outer jacket (4), between which a chamber (5) is formed, that the fins (10) extend along and inside the inner jacket (3), and that

10 the outer jacket (4) is provided with an inlet and an outlet for a cooling medium, said cooling medium being intended to extend though the chamber (5).

6. A fin for a flue gas exchanger, characterised in that the fin ( 10) comprises a plane part (15), that the plane part (15) is provided with an inlet and an outlet for a

15 flue gas in a flue gas exchanger, and that the inlet and outlet in the fin ( 10) consist of sections of a circle extending from a central part (16) to an outer periphery (17).

7. A fin for a flue gas exchanger, characterised in that the fin (10) comprises a plane part (15), that along an outer periphery (17) the fin (10) is provided with a flange

20 (19), that the flange (19) extends substantially perpendicular to the plane part (15), and that the flange (19) is intended to contact an inner side of a jacket (3) in a flue gas ex¬ changer.

8. A fin for a flue gas exchanger, characterised in that the fin (10) comprises a 25 plane part (15), that in a central part (16) the fin (10) is provided with a opening (18) having a non-circular cross-section, and that the guiding element (13) in a flue gas exchanger is designed to extend through the opening (18).

9. A fin according any one of claims 6-8, characterised in that the fin (10) is ^'30 produced from aluminium.

10. A fin according to any one of claims 6-9, characterised in that the fin (10) has an outer periphery (17) that is circular.