DE9400687U1 - Evaporator for air conditioning systems in motor vehicles with multi-chamber flat tubes - Google Patents

Description

U 952 Ma

Evaporators for air conditioning systems in motor vehicles with multi-chamber flat tubes

The invention relates to an evaporator for air conditioning systems in motor vehicles with multi-chamber flat tubes according to the preamble of claim 1. Such evaporators are known either from US-A-5 205 347 or EP-Al-O 325 844. In both known evaporators, at least two multi-chamber flat tubes are arranged one behind the other in the flow direction of the outside air, each of which is flowed through in one direction. The individual multi-chamber flat tubes are each grouped together in groups lying next to one another and one behind the other, each of which has its own round tube-like collector on its two ends. It is necessary to connect several collectors to one another in a communicating manner in order to ensure that the evaporator flows through in several streams with flow reversal from the inlet side to the outlet side. This type of construction is complex due to the large number of tube-like collectors and multi-chamber flat tubes.

Evaporators of the above-mentioned type with at least partial parallel connection of the above-mentioned multi-chamber flat tubes are more efficient than evaporators in which a single multi-chamber flat tube is folded in a meandering shape due to the possible cross-countercurrent connection (cf. US-A-5 179 845).

The invention is based on the object of simplifying the construction of an evaporator of the type mentioned at the beginning.

This object is achieved according to the invention in an evaporator having the features of the preamble of claim 1 by its characterizing features.

It is already known for multi-chamber flat tube heat exchangers with several parallel circuits for use in motor vehicles, but not specifically for evaporators, to use a single multi-chamber flat tube for two counter-rotating flows in the direction of flow of the outside air and to achieve the flow connection on the reverse side of the flows by means of a circular milling of the intermediate webs between the chambers of the individual multi-chamber flat tubes. This design, which is specifically intended for engine coolers and heating heat exchangers, requires a relatively large amount of manufacturing effort, not only due to the milling itself, but also due to the necessary removal of the milling chips. In addition, there are no plans to provide a normal multi-chamber flat tube, but rather a special production is planned, which has a solid spacer strip in its middle zone between the chambers of the two counter-rotating flows, which must be provided with a milling for the tight attachment of a central collector partition wall between an inlet side and an outlet side chamber of a single collector. A tight seal, which is also suitable for the operating conditions of an evaporator, is not provided, but rather only a squeezing in the area of the flow connection between the two flows.

A combined cooler/condenser heat exchanger according to US-A-5 129 144 has a similar design. Here too, a special design of multi-chamber flat tubes with a specially designed partition wall is required. Although the flow diversion between successive counter-rotating flows is avoided here by means of milling work, the use of a separate tube-like collector provided for this purpose, however, means a similarly high construction effort.

·♦

The two latter known heat exchangers cannot therefore be a model in the sense of the task of the invention.

The invention takes up the idea of the last two known heat exchangers, namely to use only one single multi-chamber flat tube in the direction of flow. However, the evaporator according to the invention creates a design that allows the use of special forms of multi-chamber flat tubes, but without these special forms being necessary. Rather, it will generally be possible to get by with normal multi-chamber flat tubes with the same or variable cross-section of the individual chambers, without requiring a special design of the flat tube between individual flows.

In addition, it was recognized that in the area of flow reversal between successive streams, both the mechanical cohesion of the evaporator and the creation of the flow connection are possible using a single, appropriately shaped sheet or other flat part with the same effect. This significantly simplifies the design without having to make any compromises in terms of performance. In fact, it is even easier to achieve a known progressive switching of the free channel cross-sections of the individual streams in order to adapt to different liquid/gas compositions of the refrigerant (see claim 13). In addition, the space used is also reduced due to the saving of a larger number of round tube-like collectors. The evaporator according to the invention is at least as durable and reliable as the known evaporators. The smaller number of even simpler components and the relatively simple assembly also reduce the costs in comparison to the known comparable evaporators.

The mentioned advantages of the evaporator according to the invention become most apparent when in the flow direction

Only one multi-chamber flat tube is arranged in the air.

It is fundamentally possible to use multi-chamber flat tubes of various designs within the scope of the invention, e.g. those that are bent into the final profile from solder-coated sheet metal and then soldered. Of particular importance is the use of multi-chamber flat tubes designed as extruded parts, which have long been widely used in condensers and engine coolers and can therefore be readily obtained on the market.

In principle, it is possible within the scope of the invention to arrange the two collectors on opposite ends of the multi-chamber flat tubes if the number of reciprocating flows is odd. For reasons of simplifying production and saving space, however, it is preferred if both collectors are arranged on the same end of the multi-chamber flat tubes, so that only the sheet metal profiled with beads according to the invention needs to be arranged on the other end.

The invention makes it possible to simply cut regular multi-chamber flat tubes in the area of the respective flow reversal and not to rework them at all, as was done in one previously known case with great effort by milling. A certain amount of reworking, which can however be done by simply pressing, is preferred in the sense of claim 5. This not only makes it possible to keep the drag coefficient small in the area of the flow reversal, but also makes it possible to reduce the depth of the beads formed in the sheet metal, into which the individual flat tubes tightly engage, without reducing the flow cross-section in the deflection area. This is because the deflection does not only take place in the free flow-connecting space within the beads, but already in the end area of the individual multi-chamber flat tubes, where the bent ends of the webs are separated from the inside of the wall of the multi-chamber flat tubes and therefore cross-communication is possible. You can then also see the wall in the longitudinal area of the depth of the bent webs

of the multi-chamber flat tube at least on the two flat sides. The effect is the same as bending the webs. The bulging makes it possible to make the beads in the sheets wider and thus reduce their depth with the same total flow cross-section in the flow-connecting space.

Within the scope of the invention, two alternative designs are considered in particular to prevent further cross-communication along the sheet metal outside the flow-connecting spaces of the beads in the sheet metal. To this end, the sheet metal can be simply soldered to an intermediate web between two consecutive chambers of the multi-chamber flat tube according to one alternative (claim 7). However, if the manufacturing process is not precisely controlled, it is conceivable that sealing problems could arise. This can be counteracted even more if, according to the alternative of claim 8, the seal is not made against a single web, but against the entirety of both limiting webs of a flow-dead chamber of the multi-chamber flat tube, if necessary with a corresponding dent of the sheet metal into the free end of this chamber and the additional mechanical form fit thereby achieved. The term "chamber kept free of flow" does not have to mean that this chamber is kept completely free of coolant. There is nothing wrong with it, and in special cases it is even preferable, if a chamber that is closed off in terms of flow is filled with coolant, which is then constantly drawn into the evaporation process by heat conduction from the environment, albeit with a delay. Since modern multi-chamber flat tubes have chamber numbers of ten to thirty (or even more), preferably twenty to twenty-five, the closing off of a single chamber or a small number of chambers for the purpose of mechanically tight connections does not make much difference to the overall dimensioning of the evaporator and can be

praxi be neglected.

Claim 9 relates to a particularly simple design and arrangement of the two remaining tube-like collectors, whereby the arrangement option according to claim 10 is particularly stable, but again requires the closure of one chamber per collector.

Particularly important is the development of the invention according to claim 11, which also has an independent meaning independent of the invention of claims 1 to 10. The basic idea here is that when a collector communicates directly with the inlet area of the flat tubes or the first flow, no even distribution of gas and liquid is achieved between the individual connected flat tubes. In contrast, the allocation of the incoming coolant from the inlet tube to the intermediate chamber via the nozzles, similar to a dynamic pressure distributor, results in an even distribution of the coolant to the individual flat tubes in terms of the proportion of liquid and gas. This measure is useful within the scope of the invention to increase efficiency without using additional construction work in the sense of the invention, but can also be used in other types of generic evaporators.

Claim 12 relates to a preferred possibility of combining the latter design in the manner of a dynamic pressure distributor with the designs of the collectors according to claims 9 or 10.

Claim 14 specifies a construction in which, within the scope of the task of the invention, the front end walls of the collectors can also be designed and mounted simply and reliably.

In principle, it is not impossible to manufacture the evaporator according to the invention from any material that conducts heat well, and in general from metal. However, manufacturing from aluminum or an aluminum alloy in the sense of claim 15 is typical for modern automotive engineering, which, with regard to automotive engineering,

has the particular advantage of being lightweight. In terms of manufacturing technology, a brazing coating of the ribbing, the collector and/or the sheet metal is advisable in order to be able to pre-assemble the individual parts of the evaporator and then solder them together in a brazing furnace.

The invention is explained in more detail below using schematic drawings of several exemplary embodiments. They show:

Fig. 1 is a view of a first embodiment of an evaporator according to the invention with four counter-rotating flows;

Fig. 4 a section in the direction of flow A of the incoming outside air (cf. Fig. 1), a variant of the evaporator according to Fig. 1 with six counter-rotating flows;

Fig. 2 is a view of an evaporator according to the invention according to Fig. 1 or Fig. 4, here as a further variant with a different connection of the inlet and outlet of the coolant (flow arrows B) in the direction of the collecting pipes;

Fig. 3 is a plan view of the evaporator according to Fig. 2 in the direction of extension of the flat tubes;

Fig. 5 a cross-section through a multi-chamber flat tube with typically twenty to twenty-five chambers of the same free flow cross-section, here twenty-three such chambers;

Fig. 6 shows an enlarged view of an alternative to detail X in Fig. 4 regarding the tight connection of the sheet metal with the flat tubes;

Fig. 7 and 7a show, on an enlarged scale, partial views of two variants of the insertion of the flat tubes into the corrugations of the sheet with flow connection with two counter-rotating successive flows, in the viewing direction of Fig. 2;

Fig. 8 in an enlarged partial section of Fig. 4 the arrangement of a collector with adjoining sheet metal, illustrating a variant regarding the web shape in the

* ·

Multi-chamber flat tubes connected to the flow connection between two counter-flowing streams; and

Fig. 8a shows a further variant of Fig. 8 with regard to a different design of the inlet-side collector.

All variants given can be exchanged and combined with each other.

An evaporator 2 for air conditioning systems in motor vehicles is shown in an external view in Fig. 1. The front side of the evaporator 2 visible in Fig. 1 is a flat side 4 of a multi-chamber flat tube 6. This multi-chamber flat tube 6 extends over the entire installation depth of the evaporator 2 measured in the flow direction A of the incoming outside air, so that only a single multi-chamber flat tube 6 is arranged along this installation depth.

In the view of Fig. 1, behind the multi-chamber flat tube 6 described, further similar multi-chamber flat tubes 6 are arranged at the same mutual distance, each of which has zigzag lamellae 8 between them, which are soldered to the flat tubes using a hard solder to form a rectangular block. Without limiting the generality, only three multi-chamber flat tubes 6 are shown in Fig. 1; in fact, in practical embodiments, typically five to thirty such multi-chamber flat tubes are arranged in the block mentioned. The installation depth of the evaporator in the flow direction A of the incoming outside air, i.e. the length of the cross section of the respective multi-chamber flat tube 6, is typically 50 to 100 mm and the installation width defined by the nesting of multi-chamber flat tubes 6 and zigzag lamellae 8 is typically 100 to 350 mm. The length of the individual flat tubes is typically 150 to 300 mm. All of these details refer to passenger vehicles, while in the possible application of commercial vehicles, especially buses, the dimensions can be many times larger. A cross-section of a typical flat tube 6 is

shown in Fig. 5 - This multi-chamber flat tube has here in the preferred areas indicated elsewhere twenty-three individual chambers 10, each of which has the same free flow cross-section and is separated from each other by a web 12. Fig. 5 shows the typical profile of a multi-chamber flat tube 6 manufactured as an extruded profile.

Within the scope of the invention, it is also possible to select different free flow cross-sections of the individual chambers for special purposes.

The coolant is guided in the evaporator 2 according to the arrows B. It enters an inlet 14 (in Fig. 1) or 14a (in Fig. 2) into an inlet-side collector 16, runs from there in several counter-current flows through successive groups of chambers 10 of the multi-chamber flat tubes 6 in the longitudinal direction of the cross section according to Fig. 5 and then enters an outlet-side collector 18, which is provided with an outlet 20 (according to Fig. 1) or 20a (according to Fig. 2).

In the embodiment according to Fig. 1, inlet 14 and outlet 20 are each arranged on the outer surface of the collector 16 and 18, respectively, while in the variant according to Fig. 2, inlet 14a and outlet 20a are each arranged on an end face of the inlet-side collector 16 and the outlet-side collector 18. In a manner not shown, a combined arrangement could also be provided once on an end face and once on an outer surface. In addition, Fig. 1 shows that there is variability with regard to the specific location of the arrangement of inlet and outlet on the outer surface of the respective collector, e.g. here once more in the center and once more in the end area of the collector without restricting generality.

The evaporator according to Fig. 1 has four counter-rotating streams in the respective multi-chamber flat tube 6, while the variant according to Fig. 4 has six counter-rotating streams. The even number of counter-rotating streams makes it possible to

&iacgr;&ogr; .:

inlet-side collector 16 and outlet-side collector 18 are to be arranged on the same end sides of the individual flat tubes, i.e. in the illustration in Fig. 1 both on the top of the evaporator 2. This does not exclude the possibility of one collector being arranged on one end side of the flat tubes and the other collector on the other end side, which is typical for odd-numbered flood numbers with flow reversal.

The evaporators according to the invention have at least two counter-rotating streams. The total number of streams is basically unlimited. In practice, however, a maximum of ten counter-rotating streams will probably suffice.

Particularly preferred are evaporators with six flow channels and also evaporators with four or eight flow channels, all of which show the arrangement of the collectors on one end of the multi-chamber flat tubes.

It is known that when the coolant passes through successive counter-current flows, the ratio of liquid to gas in the coolant shifts towards a larger gas proportion. In order to compensate for this effect, it is known to gradually increase the total free flow area in the flows that follow one another in the direction of flow of the coolant. In the multi-chamber flat tube shown on the front in Fig. 1, the chamber groups of the individual flows are separated from one another by dashed lines. It can be seen that in the sense of the step-by-step progression mentioned, the first flow takes up a smaller length portion of the cross section of the multi-chamber flat tube 6 and thus a smaller number of chambers than the subsequent flows, whose length portion of the cross section of the multi-chamber flat tube increases gradually. This is particularly clear in the cross-sectional representation of the variant according to Fig. 4. Here, in the same multi-chamber flat tube, the successive flows have the following number of chambers: 2-3-3-4-4-5 (21 in total according to Fig. 5).

This progressive increase in the number of chambers requires the same free flow cross-section of the individual chambers.

mem. Alternatively, in the limiting case, the number of chambers could be left the same and the free cross-sections of the individual chambers could be chosen differently during the manufacture of the multi-chamber flat tubes in the specified progression.

The invention is now particularly concerned with the creation of the flow connection in the connection area of flows communicating with one another under flow reversal as well as an adapted, simple design of the two collectors 16 and 18. The invention also creates a particularly simple adaptation to differently selectable progressions of a gradual change in the free flow cross-section of the coolant in successive flows.

The flow connection, generally designated 22, between successive flows is effected according to the invention in the respective end side area of the multi-chamber flat tubes 6 by a sheet 24, whereby this sheet 24 can be a single component on the two end sides of the multi-chamber flat tubes, which only has additional slots 54 for the multi-chamber flat tube or exclusively beads 30 for the flow connection 22, depending on whether or not collectors are still present on this end side.

This sheet is, in the preferred design shown, largely flat with the following exceptions:

Firstly, Fig. 1 shows that the sheet 24, which is arranged on the end side of the multi-chamber flat tubes 6 facing away from the collectors, can also take on the function of a mounting bracket and for this purpose has a bevel 26 on each of the two laterally projecting edges, whereby the edge of the sheet 24 protruding over the block of multi-chamber flat tubes 6 and the zigzag slats 8 as well as the bevels 26 can be used for assembly purposes in a manner not described in more detail. This sheet serving as a mounting bracket has, without limiting the general

In the embodiment shown, the second sheet 24 has the same dimensions in both depth and width as the second sheet 24 on the side of the collectors 16 and 18 and can also be used for assembly tasks there with the overhang. The special feature here is that the latter sheet 24 is only used with its central area for the flow connection 22 and is otherwise included in the structure of the collectors 16 and 18.

In the two sheets 24 arranged on the two end sides of the multi-chamber flat tubes 6, the flow connection 22 is designed in the same way so that it is sufficient to describe a single flow connection 22.

As can be seen particularly clearly from Fig. 7 and 7a, the free ends 28 of the multi-chamber flat tubes 6 are each inserted over a certain depth into a bead 30 in the sheet metal 24 assigned to each flat tube 6, so that hard soldering can take place there over the entire circumference of the wall 32 of the respective flat tube with the sheet metal 24, which is pre-coated with hard solder in the connection area.

Wherever a flow connection 22 is to be made between the chambers 10 of successive flows of the respective multi-chamber flat tube 6, the respective bead is provided with a construction depth D that exceeds the insertion depth d. The excess space 34 in the respective bead 30 obtained by the difference D minus d then serves to provide a flow connection between the successive flows in the respective individual multi-chamber flat tube in the reversal area of the flow direction.

In the variant according to Fig. 7, it is then shown that the multi-chamber flat tube 6 in question can engage in the bead 30 over the insertion depth d mentioned by slightly pressing in its free end 28, or in the borderline case without any deformation. This assembly option is used in particular when the multi-chamber flat tube 6 is simply cut to length during production.

However, the cut flat tube can also be modified by means of a pressing process so that the ends 36 of the webs 12 between the chambers 10 in the area of the respective flow connection 22 are bent out in the flow direction B of the coolant. This is a first measure to move a portion of the flow connection 22 into the free end 28 of the respective multi-chamber flat tube 6 and thereby reduce the construction depth D of the respective bead 30 while maintaining the same free flow cross-section of the flow connection 22.

If the free ends 36 of the webs 12 are then severed from the inner surface of the wall 32 of the respective multi-chamber flat tube during the pressing process, the option according to Fig. 7a can be used as a second variant. It is shown there that the wall 32 of the respective multi-chamber flat tube 6 is tufted up like a cup along the depth of the bent ends 36 of the webs on both of its flat sides 4. This results in a larger width of the respective bead 30, which in turn means that the construction depth D of the respective bead 30 can be reduced again with the flow cross-section within the flow connection 22 remaining the same.

It is now essential that the respective flow connection 22 in the area of the greater construction depth D of the relevant bead 30 only becomes effective for the flow connection between successive chambers 10 of the respective multi-chamber flat tube where the relevant flow short circuit is desired as a flow connection between the successive flows with flow reversal, but not with respect to adjoining chambers 10 of previous or subsequent flows. This also means that if several flow connections 22 are to be provided on one end of each multi-chamber flat tube, a seal must be provided between the successive flow connections 22.

For this sealing, the invention provides alternative

in particular the two possibilities shown in detail X in Fig. 4 or in the special drawing in Fig. 6 .

The first variant according to detail X in Fig. 4 represents a particularly simple possibility which makes maximum use of the installation space of the evaporator 2. In this case, it is provided that the sheet 24 in the connection area of two successive flow connections 22 and thus in the main plane of the sheet 24 is hard-soldered directly to a web 12 on its free end face, which results in the desired seal between the successive flow connections 22.

However, if one does not want to rely on the reliability of a single sealing seam, as is only available in the previously described variant, one can use the mechanically and sealingly more solid design according to Fig. 6, with a slight restriction on the full use of the evaporator's construction depth. Here, it is provided that a chamber 10a, which lies between the two successive flow connections 22, is kept free from the flow of the coolant, which is also made clear in Fig. 6 by the fact that no flow case B is drawn in this chamber 10a with regard to the coolant. This does not rule out the possibility that the chamber 10a in question fills up with coolant as a dead space of the actual flow and thus remains included in the evaporator process.

According to the variant of Fig. 6, the sheet metal 24 can now be firmly and tightly connected to both limiting webs 12b of the chamber 10a, which is cut out of the flow, using hard solder. In doing so, the sheet metal can even be pressed a little from its main plane into the free end of the chamber 10a and the free ends of the webs 12b can be pressed outwards in the manner of a slight bulge. This not only creates a pure weld seam, but also a certain form-fitting engagement, which, beyond pure soldering, improves the mechanical fatigue strength and durability.

tightness guaranteed.

For example, it can be seen from Fig. 5 that a single dead chamber with a number of chambers between twenty and twenty-five accounts for 4 to 5% of the construction depth of the evaporator or the longitudinal extent of the cross section of the respective multi-chamber flat tube 6. Due to the high effectiveness of the evaporator according to the invention, it is therefore also justifiable to not only deaden the flow of a single chamber, but even several chambers, especially since, as mentioned, these remain partially included in the evaporation process by being filled with coolant, albeit with an exclusion from the actual flow.

In addition, it is preferable to design chambers that one wishes to shut off from the flow with a smaller free cross-section from the outset.

Except for the beads 30 mentioned, the certain positive engagements mentioned in the last variant in the free ends of a flow-dead chamber 10a and other special shapes provided in the edge area, the sheet can otherwise run completely in the main plane already mentioned without this being absolutely necessary. Both sheets 24 also serve as end-side mounts for the actual evaporator block formed by the multi-chamber flat tubes 6 and the zigzag fins 8. These mounts are also particularly important for pre-assembly before brazing the block.

Two preferred embodiments of the collectors 16 and 18 or, in the case of Fig. 8a, the input-side collector 16, are shown particularly clearly in Figs. 8 and 8a, in which the entire outer surface of the collector is formed on the one hand by an outer part 38 and on the other hand by the sheet metal 24.

In both cases, the sheet metal 24 is provided with two outer beads 40 running along the respective collector, into each of which a free edge 42 of the outer part 38 engages.

In the embodiment according to Fig. 8, the outer part has the shape of an approximately semicircular shell, the free edges of which form the free edges 42 of the outer part 38 that interact with the sheet metal.

In the variant according to Fig. 8a, the inlet-side collector 16 has an outer part 38, which forms an inlet pipe 44 connected to the inlet 14, which communicates via nozzles 46, which are evenly distributed over the length of the inlet pipe 44, with an intermediate chamber 48, which in turn is connected in terms of flow to the inlet-side ends of the first flow. For this purpose, two outer flanges 43 protruding from the inlet pipe 44 of the outer part 38 of the collector are formed in one piece on the outside, which in turn form the free edges 42 of the outer part 38, which engage in the outer beads 40.

Inlet 14 or 14a and outlet 20 or 20a are each arranged on the outer part 38.

The front end of both collectors 16 and 18 is each provided with a front end wall in the form of an insert part 50. This is pre-assembled in a slot 52 (or in a manner not shown in another outer bead) of the sheet metal 24 and is then clamped between the sheet metal 24 and the inner surface of the outer part when the collector is assembled if the design of the collector according to Fig. 8 is provided.

In the case of the embodiment according to Fig. 8a, the inlet pipe 44 and the intermediate chamber 48 must also be closed separately at the front, for which a variety of options are possible, either with a one-piece closure or with two front closures.

In the area of the respective collector 16 or 18, i.e. the respective outer flow of the respective multi-chamber flat tube 6, the sheet 24 has an insertion slot 54 for each multi-chamber flat tube 6, so that its free ends, which pass through the respective insertion slot 54, can freely connect with the respective collector or the intermediate chamber 48.

in the case of Fig. 8a.

In order to make this possible and to be able to connect the outer parts 38 of the respective collector tightly to the area of the respective sheet metal forming the flow connections 22, a chamber 10b not included in the flow of the coolant is expediently provided in the area of the inner free edge 42 of the outer part 38, which chamber 10b is open on the collector side in accordance with a smooth cut and has ends 36b of the respective flat side 4 pressed towards one another on the opposite end, which, however, can leave a certain passage gap 56 free in the middle for coolant to be filled, but do not have to.

The sheet 24 runs from the flow connection 22 adjacent to the outer part 38 into the chamber 10b, forms there an outer bead 40 for the free edge 42 of the outer part 38 and then runs back into the main plane, where the insertion slots 54 are then formed in the area of the collector.

In addition, the free edge 42 of the outer part engages in the chamber 10b or in the outer bead 40 formed there. The dimensions are such that the width of the chamber 10b largely corresponds to the material thickness of the incoming sheet 14 on the one hand and the free edge 42 of the outer part 38 on the other hand, including the layer thickness of pre-coatings, so that the free end area of the chamber 10b can be completely sealed during brazing.

Claims (16)

Fax: (089) 399239 {GR.II/III) Patent Attorneys Telex: 5 29 686 european patent attorneys Telegram/Cable: INVENT MUNICH U 952 Ma (Dr.S/k) 17 January 1994 THERMAL-WERKE Heating, Cooling, Air Conditioning Technology GmbH D-68766 Hockenheim Evaporators for air conditioning systems in motor vehicles with multi-chamber flat tubes Protection claims 1. Evaporator (2) for air conditioning systems in motor vehicles with multi-chamber flat tubes (6) which are arranged parallel with opposite flat sides (4) and are provided with ribs, in particular zigzag fins (8) between their flat sides, whereby the chambers (10) of the multi-chamber flat tubes (6) are arranged in multiple flows with flow reversal of the coolant guided in the multi-chamber flat tubes (6) in the flow direction (A) of the outside air flowing in the longitudinal direction of the cross section of the multi-chamber flat tube (6), a collector (16, 18) is formed on the inlet side and on the outlet side of the coolant (arrows B) into or out of the multi-chamber flat tubes (6), and in the connection area of chambers (10) which communicate with one another with flow reversal, a flow connection (22) is provided, characterized in that at least two flows adjoining one another with flow reversal are each in Chambers (10) of a common multi-chamber flat tube (6), and that the flow connection (22) is formed on a sheet (24) which is formed with beads (30) into which a multi-chamber flat tube (6) is inserted with its wall (32) sealed against the sheet (24) and which each have a construction depth (D) which exceeds the insertion depth (d) and which is provided as a flow-connecting space (22). 2. Evaporator (2) according to claim 1, characterized in that only one multi-chamber flat tube (6) is arranged in the flow direction (A) of the air. 3. Evaporator (2) according to claim 1 or 2, characterized by multi-chamber flat tubes designed as extruded parts (6). 4. Evaporator (2) according to one of claims 1 to 3, characterized in that both collectors (16, 18) are arranged on the same end side of the multi-chamber flat tubes (6). 5. Evaporator (2) according to one of claims 1 to 4, characterized in that the ends (36) of the webs (12) between the chambers (10) of the multi-chamber flat tubes (6) in the region of the respective flow connection (22) are bent out in the flow direction (B) of the coolant. 6. Evaporator (2) according to claim 5, characterized in that along the depth of the bent ends (36) of the webs (12), the wall (32) of the multi-chamber flat tube (6) is tufted at least on the two flat sides (4). 7. Evaporator (2) according to one of claims 1 to 6, characterized in that following a flow connection (22) the sheet (24) is sealed against a web (12a) in the multi-chamber flat tube (6). 8. Evaporator (2) according to one of claims 1 to 6, characterized in that following a flow connection (22) in the multi-chamber flat tube (6), a chamber (10a) is kept free from the flow and the sheet (24) is sealed against the open end of this chamber (10a), whereby preferably the chamber (10a) kept free from the flow has a smaller free cross-section than the chambers (10) included in the flow, at least the neighboring chambers. 9- Evaporator (2) according to one of claims 1 to 8, characterized in that at least one collector (16, 18) has an outer part (38) which engages in a sealed manner on both sides in an outer bead (40) of the sheet metal (24), which has insertion slots (54) for the area of this multi-chamber flat tube (6) assigned to an outer flow of the multi-chamber flat tube (6). 10. Evaporator (2) according to claim 9, characterized by a chamber (10b) of the respective multi-chamber flat tubes (6) which is kept free from the flow and into the free ends of which an outer bead (40) of the sheet metal (24) runs and into which an edge (42) of the outer part (38) engages. 11. Evaporator (2) in particular according to one of claims 1 to 10, characterized in that the inlet-side collector (16) forms an inlet pipe (44) connected to the inlet, which communicates via nozzles (46) distributed over the length of the inlet pipe (44) with an intermediate chamber (48), which in turn is fluidically connected to the inlet-side ends of the first flow stream. 12. Evaporator (2) according to claim 11 and claim 9 or 10, characterized in that the outer part (38) of the collector (16) forms the inlet pipe (44) and two has standing outer flanges (43) which engage in the outer beads (40) of the sheet (24). 13. Evaporator (2) according to one of claims 1 to 12, characterized in that in the flow direction (B) of the coolant the total free flow cross-section per flow increases step by step, with the same flow cross-sections of the chambers (10) the number of chambers per flow increases. 14. Evaporator (2) according to one of claims 1 to 13, characterized in that in at least one collector (16, 18) at least one end wall is formed by an insert part (50) between an outer part (38) of the collector and the sheet metal (24), wherein the insert part (50) is at least partially inserted into an inner groove on the outer part (38) and/or an outer bead or a slot (52) of the sheet metal (24). 15. Evaporator (2) according to one of claims 1 to 14, characterized in that the multi-chamber flat tubes (6), the ribbing, the collectors (16, 18) and/or the sheet (24) consist of aluminum or an aluminum alloy, preferably AlMnI or AlMnCu. 16. Evaporator (2) according to claim 15, characterized in that the ribbing, the collectors (16, 18) and/or the sheet metal (24) are brazing-coated.