EP1108963A2 - Combustion gas heat exchanger - Google Patents

Abstract

A flue gas heat exchanger composed of two housing shells (10, 11) has a flue gas inlet (16) coupled to a combustion chamber (15) and a flue gas duct (17) connecting the flue gas inlet (16) to a flue gas outlet (25). At least one transverse rib (26 to 30) is provided on at least one of the inner walls (31, 32) of the flue gas channel (17) and extends essentially perpendicular to a flow direction of the flue gas. The efficiency of the heat exchanger can be improved by means of the cross rib. <IMAGE>

Description

The invention relates to a flue gas heat exchanger according to the preamble of claim 1.

Such a heat exchanger is, for. B. used in gas heaters generated by a gas flame and with the flue gas flow from the flame Extract heat to heat room air or water. For this purpose, the hot flue gas flow is through a flue gas duct led while the medium to be heated on the outside of the Flue gas channel flows past.

Such a flue gas heat exchanger is known from DE 197 45 424 A1, where the flue gas is fed into a container via a flue gas inlet is in which several parallel to each other and in the direction of flow extending baffles are arranged, the flue gas in a serpentine Force the flow direction inside the tank until that Flue gas leaves the tank via a flue gas outlet. Because of the longer flow time of the flue gas and thus the longer dwell time In the container, the heat can be transferred to the outside of the tank more efficiently Containers existing medium are released.

Another flue gas heat exchanger is explained with reference to FIG. 3, which a plan view of the inside of a housing half-shell of a known heat exchanger shows. An associated second housing shell is not shown, which is substantially symmetrical with the first housing shell and on which first housing shell can be placed.

By joining the two housing shells on one underside an opening 1 at which a burner, e.g. B. an atmospheric LPG burner can be applied. One generated by the burner, not shown Gas flame extends into a combustion chamber 2. The combustion chamber 2 goes smoothly into a flue gas duct 3, the one above the flame arranged imaginary flue gas inlet 4 begins and at a flue gas outlet 5 ends. At the flue gas outlet 5 is an exhaust pipe, not shown connectable, through which the flue gas is discharged to a chimney can.

The flue gas duct 3 runs between the flue gas inlet 4 and the Flue gas outlet 5 meandering and makes several 90 ° deflections, to achieve the longest possible path for the flue gas flow and one to enable compact construction of the heat exchanger.

Are on the outside of the two heat exchanger housing half-shells ribs, each not shown, are provided to the surface to the outside increase and thus the heat emission to the surrounding medium (here: the warming air). Furthermore, on the inside of the Housing half-shells provided a plurality of longitudinal ribs 6, which for a Enlargement of the inner surface of the heat exchanger and thus also ensure an increase in heat transfer. The flue gas is through the Longitudinal ribs 6 guided in the direction of flow. Only at the deflection points no longitudinal ribs are provided. The large number of longitudinal ribs ensures for a clear channel narrowing and thus a delay in flow velocity, which also improves heat transfer.

In the heat exchanger described, it is disadvantageous that the additional Longitudinal ribs on the inner wall of the half-shells require a considerable amount of material required to achieve the efficiencies common today. The cost of materials increases not only the manufacturing costs, but also that Weight of the heat exchanger, which is particularly important for portable heaters, as they e.g. B. used in caravans is a disadvantage.

A ceramic heat exchanger is known from DE 37 30 137 A1, at in a heat exchanger interior that is insulated from the outside of ceramic base plates parallel to and offset from each other are arranged. On the top of each base plate are across Ribs running flue gas flow arranged. Opposite spaces between the ribs are on the underside of an opposite one Base plate formed in the ceramic material of the base plate in each case pipelines, through which the medium to be heated flows. The surfaces of the Pipelines are in relation to the overall dimension of the heat exchanger low, so that only small amounts of heat can be transferred. Furthermore, the base plates are made of ceramic material, which is good corrosion resistance, but has only low heat conduction properties.

The invention is based on the object of a flue gas heat exchanger specify at least one degree of efficiency with a low cost of materials can be achieved, the efficiency of heat exchangers with longitudinal ribs.

According to the invention, the object is achieved by a flue gas heat exchanger solved the features of claim 1. Advantageous further developments the invention can be found in the dependent claims.

The flue gas heat exchanger according to the invention is characterized in that that at least one of the inner walls of the flue gas duct Cross rib is provided, which is substantially perpendicular to a Extends the direction of flow of the flue gas. Advantageously, there are several Cross ribs provided on different inner walls of the flue gas duct are arranged.

Extensive tests have shown that the use of Cross ribs in the flue gas duct, d. H. on the inside walls of the flue gas duct, the flue gas flow in a longer way between flue gas inlet and smoke outlet can be forced. At the same time, the speed the flow is reduced so that the dwell time of the hot Flue gas and thus the heat transfer can be significantly improved. It was also found that only a few transverse ribs are required, to achieve the desired efficiency improvement. Accordingly performs a heat exchanger with cross ribs compared to one with longitudinal ribs with a significantly lower weight a similar or better efficiency.

In a particularly advantageous embodiment of the invention, the Cross ribs alternately on two opposite inner walls of the Flue gas duct arranged. This forces the flue gas flow meandering back and forth between the two housing shells, causing a noticeable lengthening of the mean flow path is achieved.

The number and spacing of the transverse ribs is advantageously chosen so that that the core flow, which initially breaks off when a transverse rib flows over it and swirled again to rest against the inner walls of the flue gas duct comes before it is disturbed again by the next cross rib. Thereby the heat of the flue gas flow to the metallic one is particularly effective Lead outside wall of the flue gas duct, which causes the heat transfer is improved.

Fig. 1

einen erfindungsgemäßen Rauchgas-Wärmetauscher in zerlegtem Zustand;

Fig. 2

einen Schnitt durch den zusammengebauten Wärmetauscher entlang einer Linie A in Fig. 1;

Fig. 3

eine Draufsicht auf die Innenseite einer Gehäusehalbschale eines bekannten Wärmetauschers; und

Fig. 4

Beispiele für unterschiedliche Querrippenformen bei dem erfindungsgemäßen Rauchgas-Wärmetauscher.

These and other features and advantages of the invention are explained in more detail below using an example with the aid of the accompanying figures. Show it:

Fig. 1

a flue gas heat exchanger according to the invention in a disassembled state;

Fig. 2

a section through the assembled heat exchanger along a line A in Fig. 1;

Fig. 3

a plan view of the inside of a housing half-shell of a known heat exchanger; and

Fig. 4

Examples of different transverse fin shapes in the flue gas heat exchanger according to the invention.

Fig. 1 shows the flue gas heat exchanger according to the invention in disassembled State in which two housing shells 10, 11 are separated from one another. To the The two housing shells 10, 11 can be assembled on a fictitious line B folded up and by means of their flanges 12, 13 in a suitable and on are known to be connected to each other. Expediently a seal is inserted between the flanges 12 and 13 prior to assembly. The housing shells 10, 11 are preferably made of cast aluminum manufactured.

However, for better understanding, the invention is not based on the assembled Heat exchanger, but based on the two open housing shells 10, 11 explained, the inside of which are clearly visible in FIG. 1.

Analogous to the known heat exchanger and explained with reference to FIG. 3 form the housing shells 10, 11 on its underside an opening 14 at the an atmospheric burner, not shown, can be used. The Burner is preferably operated with liquid gas and forms together with the heat exchanger is a heater that is particularly suitable for caravans.

The flame generated by the burner extends into a combustion chamber 15, which are seamlessly defined on one to explain the invention, but otherwise Flue gas inlet 16 into a flue gas duct that is not recognizable in terms of features 17 passes. The flue gas duct 17 extends in a meandering shape in a riser 18, a first transverse channel 19, a first vertical Channel 20, a second transverse channel 21, a second vertical channel 22, a third transverse channel 23 and a third vertical channel 24 into one flue gas outlet 25 serving as an exhaust connection.

Five transverse ribs are provided in the course of the flue gas duct 17, namely a first transverse rib 26, a second transverse rib 27, a third transverse rib 28, a fourth transverse rib 29 and a fifth transverse rib 30.

Each of the transverse ribs 26 to 30 extends substantially perpendicular to one Flow direction of the flue gas and is in one piece with its long side molded onto an associated inner wall 31 or 32 of the housing shells 10, 11. The end faces of the transverse ribs 26 to 30 run into the narrower ones Inner or side walls of the housing shells 10, 11.

The first, third and fifth transverse ribs 26, 28, 30 are on one housing shell 10 formed while the second and fourth transverse ribs 27, 29 the other housing shell 11 are provided. That means the cross ribs 26 to 30 alternately on the two opposite inner walls 31, 32 of the flue gas duct 17 are arranged. Due to the special arrangement the transverse ribs 26 to 30 take the one passing through the flue gas duct 17 Flue gas flow a serpentine course. The as flow obstacles acting cross ribs 26 to 30 force the flue gas flow each in a different direction, opposite the transverse rib in question, whereby the flow at the cross rib breaks off and only in the further course, with a certain distance after the cross rib, to rest against the walls of the housing shells 10, 11 come through before the flue gas flow the next cross rib in the other direction, d. H. now to the opposite Housing shell, is deflected.

The arrangement of the transverse ribs can be seen particularly well from FIG a section along the line A in Fig. 1, but in the assembled state of the heat exchanger shows.

2 shows in particular the first, the second and the third transverse rib 26, 27, 28 recognizable, each alternately on the opposite inner walls are arranged. The hot flowing up from the riser 18 Flue gas flow is in the first after the flue gas duct 17 has been bent Cross channel 19 first from the first transverse rib 26 in the direction of the housing shell 11 deflected before passing through the second transverse rib 27 in the direction the other housing shell 10 is forced. The third transverse rib 28 in turn redirects the flue gas flow towards the housing shell 11.

It is also the case with other embodiments of the invention, not shown possible to arrange all cross ribs only on one of the inner walls. In in this case the serpentine flow movement of the flue gas falls not as serious as in the example shown in the figures.

Another embodiment, also not shown, has transverse ribs, which extend from the side, narrower inner walls of the housing shells, however, only occupy part of the width of the flue gas duct. In in this case both casing shells consequently have inner ribs at the same point, which, however, only cover part of the canal.

In yet another embodiment of the invention, the transverse ribs can be arranged such that they are screw-shaped or vortex-shaped Force the course of the flue gas flow.

In a further embodiment of the invention, the transverse ribs are in Form of crosspieces provided that the flue gas flow from the center of the Displace the flue gas duct to the side walls.

The number and arrangement of the transverse ribs 26 to 30 is for the function of the Heat exchanger, d. H. especially for reliable cold start behavior and crucial for optimizing heat transfer. The number of five transverse ribs has been shown in numerous laboratory tests proven to be particularly useful, since it is precisely this division that ensures is that the core flow always goes over a cross rib comes fully back to the side walls, d. H. the spatial distance between the transverse ribs is large enough. A larger number of cross ribs would only increase the heat exchanger weight lead, but no noticeable improvement in efficiency or Heat distribution on the outside of the housing shells 10, 11 cause. With A smaller number of cross ribs can provide the desired heat distribution not be adjusted as well anymore.

The transverse ribs 26 to 30 should be arranged in the flue gas duct 17 in this way be that on the outside of the heat exchanger as uniform as possible Temperature curve is reached. The position is particularly important the first transverse rib 26, which is flown by the flue gas with the highest temperature becomes. The first transverse rib 26 is located in the first transverse channel 19, ie immediately after the riser 18 of the heat exchanger, in the the flue gas is the hottest. The flow velocity is determined by the first transverse rib 26 significantly reduced, so the hot flue gases last longer Linger time in riser 18, which resulted in a significantly improved Heat transfer leads. However, the first transverse rib 26 must not be directly on the Deflection from the riser 18 to the first transverse channel 19, to prevent the hot flue gases from burning. As optimal a position for the first transverse rib 26 after approximately one fifth to one Quarter of the total length of the transverse channel 19 result.

The second transverse rib 27 is shortly before the transition of the first transverse channel 19 provided in the first vertical channel 20, because there is still a vertical impact of the flue gas flow is possible, which makes it special high heat transfer coefficients can be achieved.

The third transverse rib 28 is in the transition between the first vertical Channel 20 and the second transverse channel 21 arranged and facing the second Cross rib 27 at about the same distance, i.e. H. mean flow path length, like the second transverse rib 27 to the first transverse rib 26.

The fourth transverse rib 29 is exactly in the middle of the third transverse channel 23 with approximately the same Distance to the third transverse rib 28 is arranged.

Finally, the fifth transverse rib 30 in turn points to the fourth transverse rib 29 the same distance as the previous transverse ribs 26 to 29 and is positioned immediately in front of the flue gas outlet 25. To achieve a the flow onto the transverse ribs 26 to 30 should have good heat transfer as vertical as possible.

In addition to the number of cross ribs and their positioning, that also plays The height of the transverse ribs plays an important role in terms of starting behavior, efficiency, maximum heat exchanger temperatures and low pollutant emissions in the different operating modes. Height means the value around which a cross rib touches the one with its long side Raises inner wall of the housing shells 10, 11. By the height of the cross ribs 26 to 30 is the cross section of the flue gas duct 17 on the relevant one Places significantly reduced, which increases the flow resistance. The height of each of the transverse ribs 26 to 30 is such that none Cross rib more than half of the flue gas duct cross section on the relevant one Spot covers. The transverse ribs 26 to 30 should therefore not be higher than the flue gas duct depth in the associated housing shell 10, 11.

Through the transverse ribs 26 to 30, both the boundary layer and the Core flow of the flue gas flow interrupted. Before each cross rib 26 up to 30, the current effect leads to a recirculation area and therefore very small heat transfer coefficients. In the field of Cross ribs themselves occur on the opposite side of heat transfer peaks on that on the local acceleration of the flow and with it related production of turbulent kinetic energy are. The pronounced recirculation area leads downstream from the transverse rib the proximity of the re-application point of the flow to a maximum heat transfer, d. H. at these positions, a lot of heat is released to the outside headed.

It has already been explained in detail above that the arrangement of the transverse ribs can be varied in many ways. The same applies to the shape of the Cross ribs. 4 shows three-dimensionally a section of one Flue gas duct 33, in the example several differently shaped Cross ribs 34 to 39 have been used. 4 is used however only for explanation and does not provide a drawing of a real one according to the invention Flue gas heat exchanger.

The transverse rib 34 is perpendicular to the direction of flow of the flue gas and has an upper edge rising towards one side of the flue gas duct 33 as well as two openings. Flue gas is selectively swirled through the openings, to get a changed heat transfer.

The transverse rib 35 is slightly curved in relation to the direction of flow. she is still essentially perpendicular to the direction of flow. Similar thing applies to the transverse rib 36, which consists of two mutually angular Sections exists. Even if they are no longer exactly perpendicular to the direction of flow of the flue gas, a similar effect can be achieved with it.

As an alternative to the transverse ribs 35 and 36, the transverse ribs 37 and 38 are shown where the transverse ribs are each by a serpentine or zigzag course.

The cross rib 39 finally stands obliquely in the flue gas duct 33. Although it does not have a section that is exactly perpendicular to the flow direction of the Is flue gas, this transverse rib 39 should also be substantially vertical be viewed standing. In any case, also with the sloping one Cross rib 39 to achieve an effect according to the invention.

Claims (11)

Flue gas heat exchanger, with a flue gas inlet (16) coupled to a combustion chamber (15); a flue gas outlet (25); and with a flue gas duct (17) connecting the flue gas inlet (16) to the flue gas outlet (25) and having at least one kink point; characterized in that the flue gas duct (17) is delimited by inner walls (31, 32); heat transfer takes place predominantly via the inner walls (31, 32); and that at least one transverse rib (26 to 30) is provided on at least one of the inner walls (31, 32) of the flue gas duct (17) and extends essentially perpendicular to a flow direction of the flue gas. Flue gas heat exchanger according to claim 1, characterized in that a plurality of transverse ribs (26 to 30) are provided, which are arranged alternately on different inner walls (31, 32) of the flue gas duct (17). Flue gas heat exchanger according to claim 2, characterized in that the transverse ribs (26 to 30) are alternately arranged on two opposite inner walls (31, 32) of the flue gas duct (17). Flue gas heat exchanger according to one of claims 1 to 3, characterized in that one of the transverse ribs (26) is arranged after the kink. Flue gas heat exchanger according to one of claims 1 to 4, characterized in that the distance between two of the transverse ribs (26 to 30) is dimensioned such that between the two transverse ribs (26 to 30) a core flow of the flue gas flow rests against the inner walls ( 31, 32) is guaranteed. Flue gas heat exchanger according to one of Claims 1 to 5, characterized in that the flue gas duct (17) has a substantially vertically extending riser (18) which adjoins the combustion chamber (15) and one which extends from the riser at an angle of 90 degrees has first transverse channel (19); and that a first transverse rib (26) is arranged in the first transverse channel (19). Flue gas heat exchanger according to claim 6, characterized in that a second transverse rib (27) is provided downstream of the first transverse rib (26) in the first transverse channel (19). Flue gas heat exchanger according to one of claims 6 or 7, characterized in that a third transverse rib (28) is provided downstream of the second transverse rib (27), which is spaced from the second transverse rib (27) by the same mean flow path length as that second transverse rib (27) from the first transverse rib (26). Flue gas heat exchanger according to one of claims 6 to 8, characterized in that a last transverse rib (30), viewed in the direction of flow, is arranged on the flue gas outlet (25). Flue gas heat exchanger according to one of claims 1 to 9, characterized in that the height of a transverse rib (26 to 30) is dimensioned such that the transverse rib does not cover more than half of the flue gas duct cross section. Flue gas heat exchanger according to one of claims 1 to 10, characterized in that the flue gas duct (17) is essentially formed by a housing which consists of two housing shells (10, 11).

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