Heat Exchanger, in Particular a Flat Pipe Evaporator for a Motor Vehicle Air Conditioning System

Abstract

The invention relates to a heat exchanger, in particular a flat pipe evaporator (1) for a motor vehicle air conditioning system, comprising at least one collecting tank (2) made of sheet steel which is divided in the longitudinal direction into at least two chambers and the ends of the pipe, in particular, flat pipes, are introduced in the base thereof. Said collecting tank (2) comprises a tunnel-shaped part (5), an essentially flat part (4) which forms the base, and covers (6) which are arranged on the front side thereof. At least one cover (6) is embodied in a flat manner in at least the outer edge area thereof and is positioned in a positive fit in the collecting tank.

Description

In the drawing,

FIG. 1 shows a perspective representation of a collecting tank,

FIG. 2 shows a detailed view of the collecting tank in FIG. 1,

FIG. 3 shows the collecting tank in FIG. 1 before installation of the cover applied from the front side,

FIG. 4 shows a detailed view of FIG. 3,

FIG. 5 shows a detailed view of the collecting tank in FIG. 1, where the right-hand one of the two covers is not represented,

FIG. 6 shows a detailed view corresponding to FIG. 5 from a different perspective,

FIG. 7 shows a side view of the cover,

FIG. 8 shows a section along line A-A in FIG. 7,

FIG. 9 shows a sectioned representation corresponding to FIG. 8 without a cover,

FIG. 10 shows a section through both covers with the suction pipe and the injection pipe assembled,

FIG. 11 shows a section in the longitudinal direction of the collecting tank for the representation of a separating wall,

FIGS. 12 a, 12b show views of two corrugated rib sheets, where a previously disclosed form is represented in FIG. 12a, and a form for a larger pipe density is represented in FIG. 12b,

FIGS. 13 a, 13b in each case show a section through a corrugated rib of an evaporator with various geometries,

FIG. 14 shows the stored quantity of water as a function of the heat exchange surface,

FIG. 15 shows the stored quantity of water depending on the rib height (in operation at a set operating point and for identical heat exchange surfaces), and

FIG. 16 shows the critical air quantity in respect of the spraying of an evaporator depending on the rib height.

A flat pipe evaporator 1 (represented only partially) for a motor vehicle air conditioning system exhibits, as already described above with reference to DE 198 26 881 A1, two collecting tanks 2, flat pipes (not represented here), which run between the two collecting tanks 2, and corrugated ribs 3, which are arranged between the flat pipes. Every collecting tank 2 is formed in accordance with the illustrative embodiment from a base plate, which is stamped from a metal sheet and is then formed in such a way that a flat collecting tank part 4 and two tunnel-shaped collecting tank parts 5 connected to its longitudinal edges are formed (see in particular FIGS. 4 and 6). The longitudinal edges are provided with a number of brackets arranged distributed over their length, which are inserted through slots in the flat collecting tank part 4 and are secured on the outside facing towards the flat pipes. The front ends are closed by means of covers 6 described at a later point.

Formed in the flat collecting tank part 4 are a number of raised rim passages 7, into which the flat pipes are introduced, in conjunction with which the opening for the raised rim passages 7 corresponds to the outer form of the flat pipes in essential respects.

Because of their relatively low overall depth, the two tunnel-shaped collecting tank parts 5 exhibit an essentially semicircular form, as can be appreciated from the representation in FIG. 7, for example. Because of the improved strength characteristics as a consequence of the semicircular form of the collecting tank parts 5 and/or the smaller overall depth, wall thicknesses of 0.8 to 1 mm are possible by comparison with the customary wall thicknesses of 1.2 to 1.5 mm.

Provided on the inside of the collecting tank 2 are one or more separating walls 8, by which the flow path for a fluid, such as the cooling medium through the heat exchanger, and in particular its flat pipes, can be determined. The separating walls 8 are capable of being introduced through slots 9, preferably in a flat collecting tank part 4, which separating walls 8 are arranged in each case between two openings or raised rim passages 7 for the pipes, such as flat pipes, and the distance between the raised rim passages 7 is preferably not changed by the separating walls 8. A separating wall slot for this purpose is stamped or applied in some other way, for example in one area of the collecting tank 2, so that under certain circumstances no raised rim passage is formed, and/or a guide element, such as a guide groove, for example with a depth of 0.2 to 0.3 mm, is provided as a guide for the separating wall 8 in another area (see FIG. 11).

The covers 6 consisting of a metal sheet are attached to the collecting tank 2 from the front side, in conjunction with which they are introduced as far as stops 10 formed by stop abutments, which are formed on the base plate by means of embossing and are locked in position by means of brackets 11 stamped during manufacture of the base plate and bent over after positioning of the cover 6. To permit the easier introduction of the covers 6, insertion tapers are provided on the base plate (see the phase passing over about half of the thickness of the base plate in FIG. 9). Both the brackets 11 and the stops 10 in the tunnel-shaped collecting tank part 5 are present in the longitudinal direction of the collecting tank 2 viewed at the same height in each case. According to the present illustrative embodiment, only one stop 10 and two brackets 11 offset in relation to it are provided for each cover 6 in the flat collecting tank part 4, although according to a variant not represented in the drawing, an arrangement corresponding to the tunnel-shaped collecting tank part 5 is also possible. The brackets 11 are separated from one another by the stops 10 viewed in the longitudinal direction of the collecting tank 2 by the thickness of the sheet metal forming the cover 6, so that exact positioning is possible as a result of a positive-fit connection before soldering.

According to the present illustrative embodiment, the brackets 11 are bent about an axis which runs parallel to the longitudinal axis of the collecting tank. According to a variant that is not represented in the drawing, bending of the brackets towards the cover is also possible, so that only two slots per bracket running in the longitudinal direction of the collecting tank require to be provided in the base plate. Moreover, according to a further variant that is not represented in the drawing, the extent to which the covers are pushed in can be restricted in each case by the first raised rim passage for the flat pipes, so that stops now only need to be provided in the tunnel-shaped collecting tank part, and the overall length of the collecting tank can be utilized to an optimal degree.

The supply and return of the cooling medium takes place, as can be appreciated from FIG. 10, respectively via an injection pipe 13 and a suction pipe 14 attached to a cover 6 provided with an opening 12. The openings 9 in the covers 6 are executed as raised rim passages in the corresponding stamped metal sheet, in conjunction with which the covers 6 are installed in the collecting tank 2 in such a way that the edges of the raised rim passage project outwards in each case. The starting thickness of the sheet metal for the cover 6, i.e. the thickness of the unworked sheet metal, is in the order of 1.5 mm, in order to ensure a secure soldered connection to the narrow sides and an adequate material thickness for the raised rim passages, so that an adequately large connecting surface and thus a secure connection between the pipes can also be assured for the supply and return of the cooling medium and the raised rim passages. In this case, too, the covers 6 can also be executed without raised rim passages, at least in their outer peripheral areas next to the base plate of the collecting tank 2.

The raised rim passage for the injection pipe 13 is embodied in such a way that the injection pipe 13 is pushed into the opening 12 as far as the stops 10. For this purpose, the raised rim passage for the cover 6 exhibits a slightly conical, outwardly decreasing internal diameter over the length of the raised rim passage. The raised rim passage for the suction pipe 14 exhibits an outwardly decreasing external diameter, in conjunction with which the suction pipe 14, which is flared slightly at its end, is pushed on from the outside. The taper in the case of both openings 12 preferably amounts to 2-3°, although it does not exceed 5°.

Five-chamber flat pipes, in particular with a width in the order of 2.5 mm, are preferably used, in conjunction with which the step distance remains unchanged, so that the pressure drop on the air side is increased not at all or only insignificantly compared with previously disclosed evaporators with a normal overall depth. The flow through the evaporator can take place as a six-fold flow, for example, or particularly in the case of small block widths, as a four-fold flow.

In FIG. 13, the rib geometry (opening angle α between neighboring rib sections 101, which are attached to one another via a rib arc 102) is represented comparatively respectively for an 8 mm (FIG. 13a) and a 4.5 mm rib height (FIG. 13b), in each case with 60 ribs per 100 mm. In FIG. 13b, a rib arc 102 is shown with a smaller radius of curvature (compared with FIG. 13a). Reference should be made in this respect to the fact that a radius of curvature can differ at each point on the rib arc 102, and that accordingly, apart from a cross section in the form of the arc of a circle, other symmetrical or asymmetrical forms of the rib arc 102 are also possible.

For an overall depth of T=40 mm, for example, ribs with a rib height h=4.5 mm can be used on the one hand, whereby a large number of ribs and flat pipes and a higher rib efficiency and a greater heat exchange surface can be achieved for an identical size of evaporator. A higher performance density is achieved in this way.

FIG. 14 depicts the stored quantities of water as a function of the heat exchange surface of tested heat exchangers, in conjunction with which rib height 1 is greater than rib height 2, and rib height 2 is greater than rib height 3. A positive influence of the smaller rib height on the storage capacity is noticeable in this case, too. These values were arrived at by means of a simple screening test, in which the evaporator is first immersed in a water bath and, after being removed and after a specific dripping period has elapsed, any residual quantity of water. that is still present in the evaporator is determined by weighing.

In FIG. 15, the stored quantities of water in relation to the heat exchange surface are represented with reference to the rib height, where the rib height decreases towards the right. The values were determined under operating conditions at a given operating point.

In FIG. 16, the critical quantities of air are plotted in relation to the rib height from which spraying of the evaporator commences in each case (values similarly determined under operating conditions). The rib height here increases towards the right.

In the case of evaporators according to the state of the art, the opening angle α is in the order of 14° (for 60 ribs per 100 mm) or lower. With the new rib geometry (H=4.5 mm, T=40 mm), angles in the order of 28° can be achieved (again for 60 ribs per 100 mm) (see also FIG. 13). The opening angle can be further increased in the case of an even smaller execution of the radiuses of curvature of the rib arcs 102.

Given the improved function against spraying, higher rib densities are also possible, and these in turn have a positive effect on the performance, even though the opening angle is slightly reduced once more. In one preferred illustrative embodiment, a 4.5 mm high rib with a rib density of >=70 ribs per 100 mm is used, in which case the opening angle is then in the order of 22°.

The resulting angle for a 6 mm high rib lies between 15° and 22° (evaporators with a 6 mm high rib also already exhibit a significantly better drainage and storage behavior than evaporators with an 8 mm high rib, although the number of drainage surfaces and flat pipes is already greater here). The water separation is favored even further by the presence of a larger available drainage area along the flat pipes and by the larger number of drainage surfaces/flat pipes for a comparable quantity of condensate.

Claims

1. A heat exchanger, in particular a flat pipe evaporator for a motor vehicle air conditioning system, comprising at least one collecting tank made of sheet metal, which is divided in the longitudinal direction into at least two chambers, and the ends of pipes, in particular flat pipes, are introduced in the base thereof, which collecting tank exhibits a tunnel-shaped collecting tank part, an essentially flat collecting tank part, which forms the base, and covers which are arranged in each case on the front side, wherein at least one cover is embodied in a flat manner, at least in the area of its outer edge, and is positioned in the collecting tank with a positive fit.

2. The heat exchanger as claimed in claim 1, wherein the cover is introduced from the front side and on the collecting tank side lies against a number of stops that are formed on the tunnel-shaped part of the collecting tank and/or on the flat part of the collecting tank.

3. The heat exchanger as claimed in claim 1, wherein the cover is preferably secured by means of a number of bent brackets.

4. The heat exchanger as claimed in claim 3, wherein the brackets are part of the tunnel-shaped part of the collecting tank and/or the flat part of the collecting tank.

5. The heat exchanger as claimed in claim 1, wherein the cover exhibits an opening for the supply or return of the cooling medium, the edge of which is bent outwards in particular.

6. The heat exchanger as claimed in claim 5, wherein the opening is executed as a raised rim passage.

7. The heat exchanger as claimed in claim 5, wherein the opening is of conical execution with an angle having a maximum value of 5°, and in particular from 2° to 3°.

8. The heat exchanger as claimed in claim 5, wherein a suction pipe, which is attached to the cover with an opening, exhibits an internal diameter that corresponds more or less to the external diameter of the edge circumscribing the opening.

9. The heat exchanger as claimed in claim 5, wherein an injection pipe, which is attached to a cover with an opening, exhibits an external diameter that corresponds more or less to the smallest internal diameter of the edge circumscribing the opening.

10. The heat exchanger as claimed in claim 1, wherein the edge of the collecting tank metal sheet for the cover exhibits an insertion taper.

11. The heat exchanger as claimed in claim 1, wherein the two tunnel-shaped parts of the collecting tank exhibit an essentially semicircular form.

12. The heat exchanger as claimed in claim 1, wherein separating walls in the heat exchanger are arranged in such a way that the flow through the heat exchanger is four-fold or greater.

13. The heat exchanger in particular as claimed in claim 1, with flat pipes and corrugated ribs, with at least one collecting tank, into the base of which the ends of the flat pipes are introduced, in conjunction with which the corrugated ribs exhibit a rib height which corresponds in each case to the distance between two flat pipes, and in conjunction with which two rib sections connected in each case via a rib arc are inclined towards each other at an opening angle α, wherein the corrugated rib exhibits a height of 3 to 6 mm, and preferably 4 to 5 mm, and a rib density of 50 to 90 ribs, and preferably 60 to 80 ribs, and in particular preferably 70 ribs per 100 mm.

14. The heat exchanger as claimed in claim 1, wherein the opening angle of at least two rib sections, and preferably a large number or all of the rib sections, amounts to 22°+/−7° or 30°+/−10°.

15. The heat exchanger as claimed in claim 1, wherein one or more rib arcs exhibit, at least in some areas, a radius of curvature smaller than 0.4 mm, preferably smaller than or equal to 0.35 mm, and in particular preferably smaller than or equal to 0.3 mm.

16. The heat exchanger as claimed in claim 1 wherein the flat pipes exhibit a width in the order of 1.5 to 3 mm.

17. A motor vehicle air conditioning system, characterized by an evaporator as claimed in claim 1.