EP0401752A2 - Refrigerant condensor for a vehicle air conditioner - Google Patents

Abstract

The invention relates to a condenser for a refrigerant of a vehicle air-conditioning system with ribbed heat exchange tubes (6) through which the refrigerant is guided in cross-flow to the ambient air flowing in, the heat exchange tubes (6) being arranged in several rows of tubes arranged one behind the other in the flow direction of the ambient air, the respective ones Heat exchange tubes are connected in cross-countercurrent, the rows of tubes are divided into several assemblies (14, 16) arranged one behind the other in the flow direction of the ambient air, the ribs (12) of which are decoupled in terms of thermal conductivity, and the assemblies (14, 16) are refrigerated in series in counterflow to the upstream direction of the Ambient air are connected. According to the invention it is provided that adjacent assemblies (14, 16) are mechanically connected via their ribbing (12, 30), and that in a connecting zone (38) between two adjacent assemblies (14, 16), however, the average thermal conductivity λ _m is less than 20% of the thermal conductivity λ of the material of the ribbing of the two adjacent assemblies (14, 16).

Description

The invention relates to a condenser for a refrigerant of a vehicle air conditioning system with finned heat exchange tubes through which the refrigerant is led in cross-flow to the ambient air flowing in, the heat exchange tubes being arranged in a plurality of rows of tubes arranged one behind the other in the flow direction of the ambient air, the respective heat exchange tubes being connected in cross-counterflow . The ribbing preferably, but not exclusively, consists of foils made of Al, Cu or alloys of these materials with a thickness of less than 0.15 mm.

Such condensers for vehicle air conditioning systems are commercially available. So far, all heat exchange tubes have been provided with a common ribbing with fins, which, if necessary, has already been exhibited for the purpose of improving the heat transfer. Such exhibitor-like interruptions were each oriented so that there was an optimal heat flow from the tube into the exhibitor of the interruption in question. Such exhibitor-like interruptions accordingly ran along the connecting line of pipes of the same row of pipes or along the connecting line of directly adjacent pipes of adjacent rows of pipes. However, the heat flow between adjacent tubes of the same row of tubes or directly adjacent rows of tubes is not reduced. In addition, the pattern of such exhibitor-like interruptions that increase the efficiency of the heat transfer is evenly distributed over the entire ribbing.

In these known liquefiers, the ribs between adjacent flows flow in opposite directions Due to their good heat-conducting connection, rows of pipes enter a medium temperature level, which has a performance-reducing effect. This reduction in performance is so pronounced that a cross-countercurrent, which can theoretically produce a significantly higher effective temperature difference, practically brings little improvement in performance compared to a simple cross-current. This effect is increased in the case of condensers for a refrigerant in a vehicle air conditioning system in that the tubes of adjacent tube rows (calculated in each case in the direction of flow of the ambient air) are very small and the heat flow transmitted via the ribbing between the tubes of adjacent tube rows is particularly large. In the present context, only the particularly serious heat losses via heat conduction are considered, while the heat losses via radiation, which are approximately one order of magnitude smaller, should be disregarded.

A known condenser (see DE-GM 16 85 651) for the refrigerant of a refrigeration machine - i.e. not for the purpose according to the invention in a vehicle air conditioning system - consists of one assembly or several identical assemblies, depending on the performance requirement, which then according to the features of the preamble arranged of claim 1 and connected in cross-countercurrent. All assemblies each contain only one row of tubes and are physically and therefore also thermally completely separate from each other.

With complete mechanical and thus also thermally conductive decoupling of adjacent assemblies, there are problems with mechanical strength of the entire condenser and considerably higher production costs, since practically at least two separate condensers have to be produced and connected in terms of flow in a space that is as constant as possible. These problems are greatly exacerbated by condensers for a refrigerant in a vehicle air conditioning system due to the small dimensions which are adapted to only a small amount of space in motor vehicles.

The invention has for its object the advantages of operating in cross-countercurrent for use in make a condenser of a refrigerant usable in a vehicle air conditioning system.

This object is achieved in a condenser with the features of the preamble of claim 1 by the characterizing features.

In the liquefier according to the invention, several assemblies, preferably all of them, are physically united by means of a common ribbing. As a result, the mechanical strength of the entire condenser, which can even be produced in one piece, is increased, particularly in the small dimensions of condensers for vehicle air conditioning systems, but at least with the combination of several assemblies or several rows of pipes. A largely thermal decoupling is carried out by appropriate design of the ribbing between the modules. Only by combining the assemblies is it possible to manufacture and handle the small-sized condensers for vehicle air conditioning systems, or at least of combined parts, in a practical and practical way.

Conceivable options for thermally decoupling adjacent assemblies from continuous ribbing are e.g. the installation of insulation material, a cross-sectional weakening, a change in resistance through doping or the like. However, such options are relatively complex, so that the construction according to claim 3 is preferred.

In the construction according to claim 3, the material of the ribbing of the heat exchange tubes of adjacent assemblies can be the same as in the known condensers for motor vehicle air conditioning systems. By suitably arranging interruptions along the connection zone between the two assemblies, however, the heat flow there is significantly reduced by conduction. It has been shown that even if the ribbing is formed as foils with a thickness of less than 0.15 mm by the interaction of these foils as a tight package, there is still sufficient mechanical strength of the entire condenser with mechanical assembly of the assemblies, in the borderline case without any additional consolidation measure can be achieved. In addition, the advantage is retained that the heat exchange tubes of different assemblies can be finned in one operation, as in the case of a conventional condenser, and thus retain the manufacturing advantages of the known condensers. Dimensions according to claim 5 are preferred, but thermal decouplings that are lower than the values according to claim 5 can also result in a significant increase in the temperature difference between the refrigerant and the ambient air.

In the practically preferred further development of claim 3 according to claim 4, the fin area of each row of tubes assumes the temperature of the refrigerant of the respective row of tubes practically immediately and practically without interaction with other rows of tubes. It has been shown that surprisingly unusually high efficiency improvements can be achieved in comparison with conventional best comparable condensers. With the same use of material or the same depth and the same air-side pressure loss, efficiency improvements of around 25% can be achieved, which can be used, for example, in a correspondingly smaller depth with the same cooling capacity.

In all condensers according to the invention for vehicle air conditioning systems, a deliberate design of the ribbing of all heat exchange tubes is deliberately used and instead a thermally conductive decoupling of at least two assemblies is selected, which are flowed through in each case in the opposite direction during the operation of the countercurrent flow. It can remain open in detail how the heat exchange pipes are connected in each individual assembly, for example in each assembly in cross flow or even in cross counterflow. It is also possible to combine known interconnection elements of this type in each assembly. In the limit, one could even assign an assembly to each row of pipes and flow through each row of pipes in an opposite direction. However, it has been shown that for practical applications it is usually possible to make do with only two thermally decoupled assemblies, even if these assemblies are individual or both contain more than one row of pipes. Three or four rows of pipes are preferred, one row of pipes being arranged in one assembly and the other two rows of pipes being arranged in a second assembly in the former case, while in the second case two rows of pipes are arranged in each of the two assemblies.

In a condenser according to the invention for vehicle air conditioning systems, an average temperature can no longer be established in a common ribbing of adjacent heat exchange pipes from different assemblies, but a more or less pronounced temperature jump occurs between the two assemblies, which in the borderline case a mechanically complete separation of the ribbing of adjacent assemblies occurs is clearest.

The effective temperature difference between the refrigerant on the one hand and the ambient air on the other hand can be significantly increased once again by designing the condenser according to claim 18. In this case, dimensions according to claims 19 and 20 are preferably used for the two modules mentioned. The meaning of these measures will be explained in more detail later on using functional diagrams of the essential parameters (FIGS. 9 to 11). From DE-AS 1 072 257 it is known per se to change the number of tubes through which the flow passes in parallel along the flow path of the refrigerant such that the pressure gradient is essentially constant over the entire flow path.

According to claims 6 and 7, the material of the ribbing can be removed, in particular punched out, in the interruptions in the connection zone between adjacent assemblies. In this case, narrow slots are preferably used in order to lose as little ribbing material as possible. But you can also use according to claims 9 and 10, the material of the ribbing in the area of the interruptions to exhibitors, which additionally promote the heat transfer between refrigerant and ambient air.

It has been shown that not all interruptions within the connecting zone between adjacent assemblies, but that the previously mentioned known exhibitor-type interruptions, which were previously only intended to promote heat transfer, can be included in the thermally conductive decoupling of the two adjacent assemblies (claim 11).

In the embodiment according to claim 11, claim 12 preferably provides that the interruptions known per se are formed on blinds, while the other interruptions, which are additionally provided for the thermal separation of the rows of tubes, can be designed as simple thermal interruptions without the formation of blinds. In this regard, reference is made in particular to the alternative possibilities in FIG. 8.

It is possible to choose the connection zone between adjacent assemblies as a straight line or a straight zone that runs parallel to the rows of pipes. Claim 13 shows, however, that a polygonal or wave-shaped course of the connecting zone between adjacent assemblies, that is in particular composed of straight-line sections or curved sections, can even be preferred. This applies in particular to the case where the tubes are offset from one another in the direction of flow of the ambient air and known, exhibitor-like recesses of known type for increasing the heat transfer are included in the sequence of the recesses intended for thermal decoupling between adjacent assemblies (claim 3).

Different possible arrangements of the interruptions for this case are addressed in claims 14 to 16.

• Fig. 1 einen Rundrohrlamellenwärmetauscher mit Prin­zipschaltbild a) und perspektivischer Darsteller der Lamellen­blöcke ohne Verschaltung in der Variante b);
• Fig. 2 einen Flachrohrverflüssiger in perspektivischer Ansicht mit Verschaltungsdarstellung;
• die Fig. 3 bis 5 verschiedene Ausführungsformen eines Rundrohrverflüssigers mit Darstellung bevorzugter Verschaltungen der das Kältemittel führenden Wärmetauschrohre; und
• Fig. 4b eine schematische Darstellung der Verschaltung der Wärmetauschrohre eines vierreihigen Verflüssigers mit vier Baugruppen. Soweit dabei die Baugruppen in den Fig. 1 bis 5 kör­perlich getrennt dargestellt und beschrieben sind, ist eine gemeinsame Lamellenverrippung mit wärmeleitmäßiger Entkopplung im Sinne der Erfindung ergänzt zu denken.
  Es zeigen ferner
• die Fig. 6 und 7 in Draufsicht auf eine gemeinsame Lamelle zwei verschiedene Anordnungen von Unterbrechungen in der Verbindungszone zwischen benachbarten Baugruppen unter Einbezie­hung von an sich bekannten ausstellerartigen Unterbrechungen für die Erhöhung des Wärmeübergangs;
• Fig. 8 mögliche Bauformen solcher Unterbrechungen, welche im Rahmen der Erfindung zusätzlich zur wärmeleitmäßigen Entkopplung vorgesehen sind, in drei Varianten a), b) und c) als ausstellerartige Unterbrechungen, wie sie insbesondere in der Fig. 7 dargestellt sind, oder in der Variante d) als einfacher Schlitz, wie er insbesondere in Fig. 6 dargestellt ist; Ausbil­dungen mit ausstellerartigen Unterbrechungen in der Anordnung nach Fig. 6 oder mit schlitzförmigen Unterbrechungen wie bei der Ausführungsform nach Fig. 7 sind jedoch ebenfalls möglich;
• die Fig. 9 bis 11 drei Funktionsdiagramme;
  dabei
• Fig. 11b ein Kältemittelzustandsdiagramm, in welchem Kältemittelkreisläufe eingetragen sind, welche den anhand der Fig. 10 und 11 diskutierten verschiedenen Auslegungen des Ver­flüssigers in bezug auf den kältemittelseitigen Druckverlust entsprechen;
• Fig. 12 in Anlehnung an Fig. 7 eine Draufsicht auf eine erfindungsgemäße Lamelle eines Verflüssigers;
• Fig. 13 einen Schnitt nach der Linie B-B in Fig. 12;
  und
• die Fig. 14 und 15 schematisierte Verschaltungen der Kältemittel führenden Rohre des Standes der Technik, von dem die Erfindung ausgeht, und zwar nach Fig. 14 im Kreuzstrom und nach Fig. 15 im Kreuzgegenstrom.

The invention is explained in more detail below with the aid of schematic drawings using several exemplary embodiments. Show it:

• 1 shows a round tube fin heat exchanger with basic circuit diagram a) and perspective view of the fin blocks without interconnection in variant b);
• 2 shows a flat tube condenser in a perspective view with a circuit diagram;
• 3 to 5 different embodiments of a round tube condenser with a representation of preferred interconnections of the heat exchange tubes carrying the refrigerant; and
• Fig. 4b is a schematic representation of the connection of the heat exchange tubes of a four-row condenser with four assemblies. To the extent that the assemblies in FIGS. 1 to 5 are shown and described in a physically separate manner, a common lamella ribbing with thermally conductive decoupling is to be thought of in the sense of the invention.
  It also show
• Figures 6 and 7 in plan view of a common lamella two different arrangements of interruptions in the connection zone between adjacent modules, including known exhibitor-like interruptions for increasing the heat transfer.
• Fig. 8 possible designs of such interruptions, which are provided in the context of the invention in addition to the thermal decoupling, in three variants a), b) and c) as exhibitor-like interruptions, as shown in particular in FIG. 7, or in the variant d) as a simple slot, as shown in particular in Fig. 6; Formations with exhibitor-like interruptions in the arrangement according to FIG. 6 or with slot-shaped interruptions as in the embodiment according to FIG. 7 are, however, also possible;
• 9 to 11 show three functional diagrams;
  there
• 11b is a refrigerant state diagram in which refrigerant circuits are entered, which correspond to the various designs of the condenser discussed with reference to FIGS. 10 and 11 with respect to the pressure drop on the refrigerant side;
• FIG. 12, based on FIG. 7, a top view of a fin of a condenser according to the invention;
• FIG. 13 shows a section along line BB in FIG. 12;
  and
• 14 and 15 are schematic connections of the refrigerant pipes of the prior art, from which the invention is based, namely in FIG. 14 in cross flow and in FIG. 15 in cross counter flow.

The flow direction of the ambient air is illustrated by the arrows A in FIGS. 14 and 15 provided to illustrate the known condensers. In both exemplary embodiments, four rows of pipes are arranged transversely to the direction of flow.

14, the refrigerant is introduced through a connection 2 into a collector 4 to which the four rows of ribbed heat exchange tubes 6 are connected on the input side. All heat exchange tubes 6 have a common, uniform ribbing. On the output side, the four rows of heat exchange tubes 6 are connected to a further collector 8, which is provided with an outlet 10 of the refrigerant. It can be seen that the refrigerant flows in parallel in the four rows from the collector 4 to the collector 8 and crosses the incoming ambient air.

In Fig. 15, the same configuration of ribbed heat exchange tubes 6 is connected in cross-counterflow with respect to the incoming ambient air. Here, between the two inlet and outlet collectors 4 and 8, four opposite directions are shown, in which the refrigerant on the one hand crosses the incoming ambient air and, on the other hand, is guided in counterflow to it from the inlet-side collector 4 to the outlet-side collector 8.

In the embodiment shown, each counter-turn connects only two adjacent pipes in a row. It is also known to increase the pressure loss in each flow-through branch between the collectors 4 and 8 to increase the number of pipes per row up to the limit case that only a single coil or counter-turn is arranged between the inlet-side connection 2 and the outlet 10 is.

The common ribbing of all heat exchange tubes by foils, in particular made of aluminum or an aluminum alloy with a thickness of less than 0.15 mm, usually up to about 0.1 mm, is shown at 12.

The known embodiments of FIGS. 14 and 15 relate specifically to round tube heat exchangers.

In Fig. 1, the invention is now also illustrated using a round tube heat exchanger.

Here, the condenser is divided into two assemblies 14 and 16, each of which contains two rows of pipes without restricting generality. The special case of only two assemblies 14 and 16 is addressed, of which assembly 14 is arranged on the inlet side of the refrigerant and assembly 16 is arranged on the outlet side of the refrigerant, both assemblies being connected in the opposite direction (illustration variant a)).

In the embodiment shown, each assembly has its own ribbing with foils made of Al, Cu or alloys of these materials with a thickness of less than 0.15 mm to a minimum of 0.08 mm according to current rolling technology. The same connection method can, however, also be provided for assemblies which, according to exemplary embodiments to be discussed later, have common ribbing from such foils.

In FIG. 2, the circuitry according to FIG. 1 is transferred to two assemblies 14 and 16, which are designed here as flat tube heat exchangers and also each have their own fin fins with foils, which here have thicknesses between 0.15 and 0.25 mm .

Both in the embodiment according to FIG. 1 and in that according to FIG. 2, the direction of flow of the refrigerant is indicated by arrows B.

The pipe connection between the two assemblies 14 and 16 that describes the opposite direction is also designated 18 in both exemplary embodiments.

While the interconnection of the tubes of the respective assembly 14 or 16 is left open in FIG. 1, the interconnection is device in the embodiment according to FIG. 2 in a pure cross flow in the individual assembly 14 and 16 respectively.

1 shows that the first assembly 14, through which the refrigerant flows, is designed with a relatively low pressure drop on the cold side, and the second assembly 16, through which the refrigerant flows, is designed with a relatively high pressure drop on the cold side.

A corresponding design is further clarified in the flat tube condenser according to FIG. 2 by the connection of the individual heat exchange tubes in the respective assembly 14 and 16. The relatively low pressure loss is obtained here by groups of relatively large numbers of heat exchange tubes, here with the numbers 5, 4, 4 and 3, being moved back and forth between individual sections 20 of the inlet-side header 22, the departments of the header being separated by partition walls 24 are divided. In the second assembly 16 on the output side, a corresponding back and forth of tube groups is provided, but each tube group has only two tubes. This is achieved in that two parallel coils are nested and are connected to each other by simple pipe bends. By reducing the number of tubes per group, a considerable increase in the pressure loss in the assembly 16 relative to the assembly 14 is obtained even with a constant cross section of the individual heat exchange tubes 6. It can thus be seen that the requirements for the pressure loss in the respective tube group can also be achieved solely by means of interconnection means, even without changing the cross section of the heat exchange tubes.

3, 3a, 4 and 5, preferred circuit diagrams of the individual assemblies are shown, in the embodiments of FIGS. 3, 3a and 4 each on a four-row condenser and in the embodiment of FIG. 5 on one three-row condenser.

In the first embodiment according to FIG. 3, 14 refrigeration circuits are connected in parallel in the first assembly, as is the case with this is shown in Fig. 13 for the known condenser as a whole and not only as in Fig. 3 for an assembly.

In Fig. 3, the second assembly is formed by only two circuits connected in parallel, so that again the pressure loss is increased substantially in relation to the assembly 14 with a constant internal cross section of the heat exchange tubes 6 in the assembly 16.

Fig. 3a varies this basic series connection of four circuits with two circuits in that a stage with a further increased pressure loss is installed in the assembly 16, by connecting two flow circuits in parallel on the input side, as in the case of Fig. 3, but on the output side a single flow circuit are connected.

In a manner not shown, parallel connections of the type of the assembly 14 could also be continued in the input area of the assembly 16 or circuit measures of the type shown in the assembly 16 could already begin in the assembly 14.

In the two embodiments of FIGS. 3 and 3a, an intermediate collector 22 is interposed between the two assemblies 14 and 16.

In Fig. 4a is initially illustrated that the circuit measure of FIG. 3 with four circuits in the assembly 14 and two circuits in the assembly 16 can also be obtained by a different type of pipe connection. In addition, an intermediate collector is dispensed with, in that the individual circuits of the assembly 14 are transferred in pairs by means of tripods 26 into the two further circuits.

It goes without saying that the circuit measures described can also be implemented analogously with different numbers of circuits in the individual assemblies. However, the numbers and configurations shown here are preferred.

In Fig. 4b is the same condenser as in Fig. 4a, but in consistent application of claims 1 and 3, Darge poses.

The four rows of pipes shown are all decoupled in terms of thermal conductivity by individual assemblies 54, 56, 58 and 60.

In addition, the assemblies 54, 56 to 58, 60 increase the pressure drop on the refrigerant side by interconnecting parallel circuits 62 to a circuit using a tripod 26.

With a condenser connected in this way, the short-circuit heat flow between the heat exchange tubes in the fin is minimal.

This also applies to the particularly compact, only three-row embodiment according to FIG. 5.

Here, the assembly 14 is selected analogously to that of FIG. 3. However, there is a flow-related transition of the refrigerant from the four parallel circuits of the first assembly 14 in terms of the refrigerant into only a single circuit of the assembly 16.

In all of the embodiments of FIGS. 1 to 5, a common lamella ribbing with a largely decoupling in terms of thermal conductivity is to be considered, as is described in detail with reference to the following FIGS. 6, 7 or 12 and 13.

6 and 7 each show a top view of a single heat exchange lamella for a four-row arrangement of heat exchange tubes not shown here. In each case one heat exchange tube of a tube bundle heat exchanger is arranged in the usual way in a receiving opening 28 of the lamella 30, which is part of the ribbing 12. The openings can be formed in the usual way, for example with connecting sleeves for connection to the respective heat exchange tube. One can imagine the individual receiving openings 28 as representative of the arrangement of the collective exchange tubes.

The individual lamellae 30 are held in the usual way at a mutual distance by spacers 32 worked out of the lamella, for example lobes of the lamella material that are exposed.

From the arrangement of the receiving openings 28 can be seen First of all, the assignment to those condensers in which the heat exchange tubes 6 are each half-spaced in the flow direction of the ambient air.

Known exhibitor-like openings 34 are initially arranged in the lamella 38 in order to increase the heat transfer, each extending along a row of pipes between adjacent receiving openings 28 and thus also lying transversely to those connection openings which are adjacent in the row after the next row. It can be seen both in the embodiment according to FIG. 6 and in that according to FIG. 7 that such interruptions 34 are not able to decouple neighboring pipes from neighboring rows of pipes from one another in terms of heat conduction.

For the purpose of this thermally conductive decoupling, additional interruptions 36 are provided which, in the embodiment according to FIG. 6, run parallel to the interruptions 34 between the two rows of pipes lying on the inside, but in the embodiment according to FIG. 7, together with the interruptions 34, describe or outline a polygon are arranged at 45 ° to extend the rows of receiving openings 28.

In the embodiment according to FIG. 6, the thermally conductive decoupling is additionally increased in that the interruptions 34 and 36 are arranged to overlap one another. However, a good effect can also be achieved without this overlap, although the overlap is preferred because of the increase in the thermal conductivity.

The sequence of interruptions 34 and 36 describes the direction of extension of a connecting zone 38 between the two modules 14 and 16 and the areas 40 and 42 of the lamella 30 respectively assigned to them.

6, the interruptions 36 are designed as simple slots 44 in the manner of variant d) of FIG. 8 without restricting the generality.

Variants a), b) and c) represent preferred configurations of the exhibitor-like additional interruptions 36 shown in FIG. 7, which, however, also apply to the Interruptions 34 are known per se.

In variant a), the material exhibitors are webs 46 which are bent out of the lamella 30 on one side and are preferably arranged together in the shape of a blind.

In the case of variants b) and c), on the other hand, the material exhibitors are cut out of the ribbing on both sides via interfaces 48, so that highlighted roof-like parts 50 are formed, which are each only integrally connected to the lamella 30 on the end side. The variant b) describes a flat roof and the variant c) a gable roof, various forms being possible and also common in connection with the interruptions 34. Accordingly, the interruptions 34 can also have all the shapes selected in FIG. 8, variants a) to c). In the borderline case, one could also provide simple slots according to variant d) deviating from the usual at these points, so that both the interruptions 34 and the interruptions 36 then serve only for thermally conductive decoupling.

This applies equally to the embodiments of FIG. 6 and that of FIG. 7. Analogously, the arrangement can also be transferred to three-row slats or those with a different number of rows.

The interruptions 36 and with the inclusion of the known interruptions 34 are also separated from one another along the connecting zone 38 by relatively narrow connecting webs 52, so that the heat flow takes place solely through these narrow connecting webs and thereby the average thermal conductivity along the connecting zone 38 in accordance with the ratio between interruption and connecting bridge is reduced.

9 shows the temperature profile of the ambient air flowing through the condenser and of the refrigerant led to the ambient air in a cross-countercurrent with three counter-turns. The refrigerant is guided in the tubes within a module in cross flow to the air and from module to module in opposite directions, ie in counter flow to the air. Within a module, the refrigerant can also cross counterflow with one or two counter-turns if the assembly consists of more than one row of pipes. However, due to the small distance between the neighboring pipes of different rows of pipes, the different temperature is averaged by the lamella, so that the temperature difference which is increased in contrast to the pure cross flow of the pipes is not effective in the case of cross counterflow.

FIG. 9 therefore shows the solution optimized for the effective temperature difference, in which each row of tubes one to four according to FIG. 4b is each assigned to an assembly 54, 56, 58, 60.

With such a division of e.g. four-row condenser in likewise four assemblies 54, 56, 58 and 60, the refrigerant temperature decreasing in the direction of flow of the refrigerant according to FIG. 9 cannot be compensated for by short-circuit heat flows in the ribbing, but the curve drawn in FIG. 9 is established as the ribbing temperature, which is below the refrigerant temperature curve also shown.

In a condenser connected in cross-counterflow according to the prior art according to FIG. 13, provided that the same outlet temperature is to be reached, the ribbing temperature is considerably lower on average, since the heat in the fins from the heat exchange tubes at a higher temperature at the condenser inlet to the Heat exchange pipes of lower temperature flows at the condenser outlet.

The effective temperature difference can be clearly illustrated by the area between the ribbing and the air temperature curve.

9 shows the increase in the effective temperature difference of a condenser connected according to claims 1 and 3 compared to a condenser according to the prior art, also connected in cross-counterflow, as a hatched area (A1).

In contrast to the effective temperature difference of a condenser connected according to the prior art, the is represented by the hatched area (A2), more than a doubling of the effective temperature difference is achieved by the condenser according to the invention. Since the temperature profile shown corresponds to an average operating state of a vehicle air conditioning system, an even greater increase in the effective temperature difference is possible with the condenser according to the invention at lower air speeds, ie greater air heating.

10 and 11 optimization criteria for the refrigerant-side pressure loss are shown. The temperature curve in the refrigerant circuit which arises with different refrigerant-side pressure losses is shown in the refrigerant state diagram in FIG. 11b.

The pressure drop on the refrigerant side must be selected in each individual assembly so that the outlet temperature of the liquefied refrigerant t _{KA is} in the range from its minimum t _KA1 to the minimum of the saturation temperature t _KE1 of the refrigerant entering the condenser.

10, 11a and 11b are explained below using examples.

If you choose a design with a very small pressure drop on the refrigerant side, e.g. 0.05 bar, the internal heat transfer coefficient α, which is plotted qualitatively in FIG. 10 over the pressure drop on the refrigerant side, is minimal.

The minimum effective pressure drop Δp _K on the refrigerant side results in a maximum effective temperature difference designated Δt _log in FIG. 10 between the refrigerant on the one hand and the ambient air on the other hand, since the saturation temperature does not decrease in the course of the refrigerant flow path. On the other hand, the heat transfer coefficient (denoted by K in FIG. 10) is small due to the minimum internal heat transfer coefficient.

The product of heat transfer coefficient with the effective temperature difference (designated in Fig. 10 with K · Δt _log ), which is decisive for the condenser performance, therefore does not reach the maximum value at a pressure loss of 0.05 bar on the refrigerant side.

For this reason, the minimum condensing temperature at the inlet (denoted by t _KE in Fig. 11a) is not reached in a given refrigerant circuit of a vehicle air conditioning system, because due to the smaller heat transfer coefficient K under otherwise constant conditions (such as outer surface, ambient temperature etc. ) The saturation temperature of the refrigerant t _KE and the saturation pressure p _KE must be higher than with a design with a higher heat transfer coefficient. The low pressure drop on the refrigerant side also prevents a lowering of the refrigerant outlet temperature (which is denoted by t _KA in FIG. 11 a), which is desirable for cooling the interior of the motor vehicle.

The refrigerant cycle process, which is used in a condenser with small refrigerant-side pressure drops, e.g. of 0.05 bar, is shown in the refrigerant state diagram in FIG. 11b.

11b shows the limit curve for the liquid state and the limit curve for the gaseous state, which meet at the critical point and can also be referred to as "saturation lines".

• Punkt A: Eintritt in den Verdampfer;
• Punkt B: Austritt aus dem Verdampfer bzw. Eintritt in den Verdichter;
• Punkt C: Austritt aus dem Verdichter bzw. Eintritt in den Verflüssiger;
• Punkt D: Austritt aus dem Verflüssiger bzw. Eintritt in das Drosselorgan des Kältemittelkreislaufes.

The state of the refrigerant is primarily described by the refrigerant pressure P and the enthalpy h, which are plotted as the ordinate or abscissa in FIG. 11b. They represent:

• Point A: entry into the evaporator;
• Point B: exit from the evaporator or entry into the compressor;
• Point C: Leaving the compressor or entering the condenser;
• Point D: Leaving the condenser or entering the throttling element of the refrigerant circuit.

The cycle that occurs in condensers with a pressure loss of 0.05 bar on the refrigerant side is designated A, B, C and D in FIG. 11b, the direction of the refrigerant circuit being indicated by an arrow. Of the three refrigeration circuits shown, there is a medium inlet pressure p _{KE reached} at point C, while the outlet pressure p _KA and thus also the saturation temperature assigned by the vapor pressure curve is by far the highest at point D. Since the subcooling of the liquid refrigerant to values below the saturation temperature corresponding to the pressure assumes comparable values for all condenser designs whose liquid refrigerant can flow freely from the condenser, the refrigerant outlet temperature measured thermometrically at the outlet of the condenser is also comparatively high. Since the enthalpy h increases with the temperature of the liquid refrigerant, the enthalpy of entry of the refrigerant into the evaporator is also highest at point A.

For this reason, a comparatively small enthalpy difference Δh _{o is available} for heat absorption in the evaporator with constant overheating of the refrigerant emerging from the evaporator (point B), so that less heat can be absorbed per kg of refrigerant circulated by the compressor than with the other two with ' or "designated refrigerant cycle processes. This, in turn, leads to a comparatively high evaporation pressure (points A and B) with otherwise constant conditions, with the resultant higher air outlet temperature from the evaporator and finally a comparatively high interior temperature.

If the pressure drop on the _{refrigerant side} is increased to the value of approx. 0.7 bar that is optimal for the condenser and designated in FIG. 10 and 11a by t _KE1 , then the effective temperature difference in FIG. 10 drops, on the other hand the internal heat transfer coefficient _{α 1} decreases and with it the heat transfer coefficient K too. Since, according to FIG. 10, from 0.05 bar refrigerant-side pressure loss to a pressure loss of 0.7 bar, the increase in the heat transfer coefficient is greater than the decrease in the effective temperature difference, the product of effective temperature difference with the heat transfer coefficient K · Δt _log at, which is decisive for the condenser performance, reaches refrigerant-side pressure drop _KE1 t in FIG. 10 be maximum, which is as already explained equivalent to the minimum of the Saetti supply temperature at the inlet of the condenser t _KE according to FIG. 11a. The pressure loss on the _{refrigerant side, which} is 0.65 bar higher at t _{KE1, further lowers} the saturation temperature at the condenser outlet t _KA .

If one looks at the refrigerant condenser described last in the entire refrigeration cycle according to FIG. 11b, one can see the minimum refrigerant _{inlet pressure} P _KE , which is synonymous with the minimally saturated refrigerant _{inlet temperature} t _KE1 in point C ', and the pressure loss ΔP _K des represented by the gradient to the left Condenser with the result that the outlet pressure p _KA and the refrigerant outlet temperature are lower, whereby the enthalpy difference h _o 'available to the evaporator is greater than that of a condenser with a pressure loss of 0.05 bar on the refrigerant side.

As already explained, this results in a comparatively lower evaporation, air outlet and vehicle interior temperature.

A further reduction in the condenser outlet temperature t _KA can be achieved by a further increase in the pressure _drop on the refrigerant side from t _KE1 to t _KE2 .

With this dimensioning, however, the condenser output determined by K · Δt _{log is} no longer maximum, since the effective temperature difference decreases more than the heat transfer coefficient increases, so that the saturation temperature at the condenser inlet also increases (see point C˝ in Fig. 11b).

However, if compressors with a "steep characteristic curve", ie a delivery volume flow that is almost independent of the delivery pressure, are used, the refrigerant inlet pressure p _KE increasing according to the vapor pressure curve with the saturation temperature tKE does not reduce the refrigerant mass flow, so that the refrigerant outlet temperature from the condenser (point D˝ in Fig. 15) resulting maximum enthalpy difference Δh _o ˝ of the refrigerant in the evaporator for a further reduction in the evaporation pressure in points A˝ and B˝ and thus to the minimum possible air outlet temperature from the evaporator and the maximum possible Interior cooling leads.

In the case of the condenser mentioned in FIGS. 12 and 13, three assemblies 14, 15 and 16 are provided without any restriction of generality, each of which is assigned to a single row of tubes. Only one fin of the fin package forming the ribs of the corresponding heat exchange tubes is shown. Each lamella has 30 receiving openings 28, into each of which a heat exchange tube is fitted mechanically firmly and in a heat-conducting manner. It can be seen in FIG. 13 that the corresponding receiving openings 28 protrude from the lamellar plane in the form of a sleeve.

From the distribution of the receiving openings 28 it also follows that the heat exchange tubes are regularly offset from one another in the flow direction A of the ambient air.

In the sequence of interruptions 36 provided between the individual assemblies, known interruptions 34 are included, which are each arranged transversely between pairs of heat exchange tubes (or receiving openings 28), which belong to different rows of tubes of separate assemblies 14, 15 and 16.

The interruptions 34 and 36 thus form a series of interruptions in the lamella 30 along the respective connection zone 38 between the assemblies 14 and 15 or 15 and 16, between which connecting webs 52 remain and which are each arranged between pairs of heat exchange tubes or receiving openings 28 that belong to directly adjacent rows of pipes of the respective neighboring assemblies, here rows of pipes.

The interruptions 36 are here, in particular in accordance with the uppermost variant of FIG. 8, in the form of elongated slots with a one-sided exhibitor. The interruptions 34 known per se, on the other hand, are designed as blinds, the special shape of which is clear from FIG. 13. These are two middle full webs and two outer half webs, which are exhibited parallel to each other and have an angle of attack of preferably 15 to 30 ° to the air.

The interruptions 34 designed as blinds run in the offset pipe arrangement in the same row of pipes with longitudinal extension between adjacent pipes of the same row of pipes or, in other words, with transverse extension, that is to say separating, between adjacent pipes of pipe pairs lying one behind the other in the direction of flow A, each with an intermediate pipe row staggered pipes are separated from each other.

Spacers 64 can also be seen, which are shown at a greater height from the lamella plane on the same side as the sleeves of the receiving openings 28 in order to distance the individual lamellae in the compressed lamella package. Possible shapes and dimensions of such exhibitors are known per se. Figures 12 and 13 show two different preferred possible shapes, which differ in the one or two-sided web display. 13 is expediently tapered so as not to fit into the opposite opening of the next spacer of the adjacent lamella.

The slats 30 are also expediently foils made of Al, Cu or alloys of these materials with a thickness of less than 0.15 mm.

With the construction in the sense of FIG. 12 or 13, condensers with three or four rows of pipes are preferably formed, but in the sense of the previous description, condensers with only two rows of pipes are also possible.

The lamella 30 is common to the individual rows of pipes; the cohesion takes place via the connecting webs 52 which remain between the interruptions.

Claims (21)

1. Condenser for a refrigerant of a vehicle air conditioning system with ribbed heat exchange tubes (6) through which the refrigerant is guided in cross-flow to the surrounding air flowing in, wherein
the heat exchange tubes are arranged in a plurality of rows of tubes arranged one behind the other in the flow direction of the ambient air, the respective heat exchange tubes being connected in cross-countercurrent,
the rows of pipes are subdivided into a number of subassemblies (14, 16) arranged one behind the other in the inflow direction (A) of the ambient air, the ribs (12) of which are decoupled in terms of heat conduction,
and the assemblies (14, 16) are connected in series as a refrigerant in counterflow to the direction of flow (A) of the ambient air,
characterized by
that adjacent assemblies (14, 16) are mechanically connected via their ribbing (12),
and that in a connecting zone (38) between two adjacent assemblies (14, 16), however, the average thermal conductivity λ _{m is} below 20% of the thermal conductivity λ of the material of the ribbing (12) of the two adjacent assemblies (14, 16). 2. A condenser according to claim 1, characterized in that in the connecting zone (38) the average thermal conductivity λ _{m is} below 10% of the thermal conductivity λ of the material of the ribbing (12) of the two adjacent assemblies (14, 16). 3. A condenser according to claim 1 or 2, characterized in that (in each case) two adjacent assemblies (14, 16) have a common ribbing (12) which has a consequence along the connecting zone (38) between the two assemblies (14, 16) runs from interruptions (36), between which connecting webs (52) remain and which are each arranged between pairs of heat exchange tubes (6) which belong to directly adjacent rows of tubes of the two adjacent assemblies (14, 16). 4. A condenser according to claim 3, characterized in that each row of tubes of heat exchange tubes forms an assembly (14, 15, 16). 5. A condenser according to claim 3 or 4, characterized in that, measured in the direction of extension of the connecting zone (38), the average length of the connecting webs (52) less than 50%, preferably less than 20%, most preferably less than 10%, of the average The length of the breaks (36) is. 6. Condenser according to one of claims 3 to 5, characterized in that interruptions (36) as material gaps (44), preferably punched out, are formed. 7. A condenser according to claim 6, characterized in that the material gaps are slots (44) extending along the connection zone. 8. A condenser according to one of claims 3 to 7, characterized in that interruptions are formed as material exhibitors (46; 50). 9. A condenser according to claim 8, characterized in that material exhibitors are bent out on one side from the ribs (12), preferably arranged together in the shape of a blind, webs (46). 10. A condenser according to claim 8 or 9, characterized in that material exhibitors (50) on both sides of the ribbing (12) are cut out. 11. A condenser according to one of claims 3 to 10 with heat exchange tubes (6) offset in the flow direction (A) of the ambient air, characterized in that known interruptions (34) are included in the sequence of interruptions (36), each transversely are arranged between pairs of heat exchange tubes (6), which belong to different adjacent tube rows of separate assemblies (14, 16). 12. A condenser according to claim 11, characterized in that the interruptions known per se (34) are designed as blinds. 13. A condenser according to one of claims 1 to 12, characterized in that the connecting zone (38) runs along a polygon or wave train between the (respectively) adjacent two assemblies (14, 16). 14. Condenser according to one of claims 11 to 13, characterized in that all interruptions (34,36) of the sequence describe a polygon. 15. A condenser according to one of claims 11 to 13, characterized in that all interruptions (34, 36) of the sequence run parallel to one another. 16. A condenser according to claim 15, characterized in that adjacent interruptions (34,36) of the sequence overlap each other. 17. A condenser according to one of claims 1 to 16, characterized in that only two assemblies (14, 16) are provided. 18. A condenser according to any one of claims 1 to 17, characterized in that a (first) assembly (14) with a relatively low pressure loss on the cold side and a flow through the refrigerant (second) assembly (16) with a relatively high pressure loss on the cold side flows through the first is designed. 19. A condenser according to claim 18, characterized in that the pressure loss of the first assembly (14) is dimensioned such that the product on the one hand from the effective temperature difference (Δt _log ) between ambient air and refrigerant and on the other hand from the heat transfer coefficient k is maximum. 20. A condenser according to claim 18, characterized in that the pressure loss of the second assembly (16) is dimensioned so large that the outlet temperature (t _KA ) of the liquefied refrigerant in the range from its minimum to the minimum of the saturation temperature (t _KE ) in refrigerant entering the condenser. 21. A condenser according to one of claims 1 to 20, characterized in that the ribbing consists of foils (30) made of Al, Cu or alloys of these materials with a thickness of less than 0.15 mm.

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