US20070023172A1

US20070023172A1 - Heat exchanger for a motor vehicle air conditioning system

Info

Publication number: US20070023172A1
Application number: US11/522,481
Authority: US
Inventors: Frank Obrist; Norbert Tessendorf; Peter Kuhn; Martin Graz
Original assignee: Obrist Engineering GmbH
Current assignee: Obrist Engineering GmbH
Priority date: 2004-03-18
Filing date: 2006-09-15
Publication date: 2007-02-01
Also published as: DE112005000305A5; DE102004011608A1; WO2005088219A1

Abstract

In an air/refrigerant heat exchanger, particularly for a motor vehicle air conditioning system, including a plurality of flat tubes arranged in closely spaced relationship so that a narrow flow passage for air is formed therebetween, the flat tubes include passages through which refrigerant is conducted in the longitudinal direction of the flat tubes and are provided on their outer surfaces with longitudinal parallel recesses and projections such that the flat tubes are wave-shaped the recesses and projections flattening out toward the narrow ends of the flat tubes and provide for narrow flat rectangular end sections.

Description

This is a Continuation-In-Part Application of International Application PCT/EP2005/002537 filed 10 Mar. 2005 and claiming the priority of German application 10 2004 011 608.3 filed 18 Mar. 2004.

BACKGROUND OF THE INVENTION

The invention relates to an air/refrigerant heat exchanger, particularly for a motor vehicle air conditioning system, with several flat tubes which extend parallel to one another and are exposed to an air flow while refrigerant is conducted through the tubes. Opposite wall areas of adjacent flat tubes form therebetween flow channels for the air and several flat tubes are connected at their ends to a refrigerant distributor which is provided with a tube connector for connection to a circuit system.
Heat exchangers of this type are known in many configurations as shown for example in U.S. Pat. No. 5,941,303 and the relevant state of the art listed therein. This publication as well as DE 103 06 786 are concerned essentially with the configuration of the connection distributor and the possible flow guide structures for the medium to be conducted through the numerous tubes. All these tubes connected to the connection distributor are provided with wave-like profiled ribs for increasing their outer, that is, air-side, surface area since the air-side heat transfer is multiple times smaller than that of the internal tube surfaces which are in contact with the operating medium of the air conditioning system.
Although, in the figures of U.S. Pat. No. 5,941,303, the wave-shaped ribs are not depicted in order to simplify the drawings, the second paragraph of the detailed description states that such ribs are considered to be necessary. It is stated that without such ribs, in a similarly compact design as it is needed for use in motor vehicles, the heat transfer surface area obtainable would be insufficient to obtain the heat transfer needed for an air conditioning system.
The provision of ribs on the tubes including their soldering to the tubes is time-consuming and expensive and furthermore, the solder connections are often faulty as a result of incomplete soldering contact areas along the relatively long length of the solder joint. Furthermore, the corner areas formed between the ribs and the tubes form collecting structures for partially organic contamination particles precipitated from the air with the result of hygienic loading and odor generation in the air conducted from the heat exchanger to the passenger compartment. Furthermore, the surfaces of the corrugated ribs and the corner areas form extensive collection spaces for moisture which is formed during cooling operation of the air conditioning system by condensation from the cooled air and which will not flow out of the heat exchanger. A changeover of such a heat exchanger to a selective heating operation of the air conditioning system would result in a sudden vaporization of the moisture and its condensation at the windshield of the motor vehicle. To avoid this, it would be necessary to provide a second parallel heat exchanger for heating the air which is space-consuming and expensive.
It is the object of the present invention to provide a heat-exchanger of the type as referred to above, wherein however the heat exchange between the refrigerant and the air is improved. Furthermore, the heat exchanger should be compact and it should also be relatively insensitive to soiling and wetting so that it is usable for cooling as well as heating, particularly in a CO₂air conditioning system.

SUMMARY OF THE INVENTION

In an air/refrigerant heat exchanger particularly for a motor vehicle air conditioning system including a plurality of flat tubes arranged in closely spaced relationship so that a narrow flow passage for air is formed therebetween, the flat tubes include passages through which refrigerant is conducted in the longitudinal direction of the flat tubes and on their outer surfaces longitudinal parallel recesses and projections are provided such that the flat tubes are wave-shaped the recesses and projections flattening out toward the narrow ends of the flat tube and forming narrow flat rectangular end sections.
Preferably, the surface ratio between the inner refrigerant-side surface and the outer air-side surface of the flat tubes is between 0.7 and 1.5 and, particularly, 1.
Advantageous embodiments of the invention will be described below in greater detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a planar view of the heat exchanger seen in the direction of the airflow to the heat exchanger,
FIG. 2 is a side view of the heat exchanger of FIG. 1 shown in an inclined mounting position,
FIG. 3 is a perspective view of a corrugated flat tube of the heat exchanger, which flat tube is formed by stamping,
FIG. 4 is a partial perspective view showing the front side of the heat exchanger via which air is supplied to the front entrance area of the heat exchanger,
FIG. 5 is a partial cross-section through a wave-shaped air channel,
FIG. 6 is a vertical cross-sectional view of a part of a bottom end connection distributor with paired flat tubes,
FIG. 7 is a side view of the connection distributor of FIG. 6,
FIG. 8 is a vertical, longitudinal cross-sectional view of the connection side area of a triple flat tube arrangement,
FIG. 9 shows a vertical longitudinal cross-section through the connection area of not bundled flat tubes,
FIG. 10 shows in a horizontal cross-sectional view the top end connection distributor,
FIG. 11 shows in a horizontal cross-sectional view the bottom end connection distributor,
FIG. 12 is a vertical cross-sectional view of a top end connection distributor,
FIG. 13 is a vertical cross-sectional view of a bottom end connection distributor,
FIG. 14 is a vertical cross-sectional view of another embodiment of a top end connection distributor,
FIG. 15 shows in a perspective view a guide insert for the supply flow channel of the connection distributor according to claim 13,
FIG. 16 is an overall view of the heat exchanger according to the invention as seen in the direction of the air flow to the heat exchanger wherein the profile of the flat tubes is only partially indicated,
FIG. 17 is a side view of the heat exchanger as shown in FIG. 16 with the profile of the flat tubes not being visible,
FIG. 18 shows in a longitudinal cross-sectional view the bottom end connection distributor of the heat exchanger of FIG. 15,
FIG. 19 shows the bottom wall of FIG. 18 in a planar view,
FIG. 20 shows a vertical section through the bottom end connection distributor of the heat exchanger according to FIG. 16,
FIG. 21 shows schematically the flow distribution in a heat exchanger according to the invention,
FIG. 22 shows in a schematic top view a section of a comb-like spacer member,
FIG. 23 is a perspective view of another embodiment of a flat heat exchanger tube according to the invention,
FIG. 24 is a cross-sectional view taken along line Z-Z of a flat tube as shown in FIG. 23,
FIG. 25 shows in a cross-sectional view taken along line Y-Y of FIG. 26 another flat tube according to the invention,
FIG. 27 is a top view of another bottom wall according to the invention similar to that of FIG. 19, and
FIG. 28 shows, in a longitudinal cross-sectional view taken along line X-X, the bottom wall of FIG. 27.

DESCRIPTION OF PREFERRED EMBODIMENTS

The heat exchanger according to the invention is provided mainly for installation in the air flow of a CO₂vehicle air conditioning system where, during cooling operation, it is used as an evaporator. To this end, it is installed in an air supply housing which also includes a blower. Consequently, the heat exchanger must be compact with dimensions of for example 235 mm width and 250 mm height. In order to ensure a heat exchange capacity corresponding to the desired performance of the air conditioning system a relatively large air-side heat exchange surface must be provided since, at this side, the heat transfer is only about one fifth of that at the inside surfaces of the heat exchange tubes which are in heat exchange contact with the operating medium of the air conditioning system such as condensing CO₂. In modified embodiments, other refrigerants may be provided such as water, NH₃, R404A, R407C, R410A, R22, SF6, etc.
The heat exchanger tubes generally are extruded flat tubes 2 consisting of an aluminum alloy and include parallel inner passages 3. By dividing the interior of the flat tubes 2 into numerous inner passages 3 with a diameter of for example 0.6 mm while the flat tubes have a thickness of for example 1.2 mm, they can accommodate a high internal pressure of substantially more than 100 bar as it can be expected to occur in a CO₂air conditioning system when it is operated during heating operation. Furthermore, with the numerous narrow inner passages 3, an advantageous uniform flow distribution over the cross-section of the flat tubes 2 with a relatively large internal heat exchange surface area can be obtained. The diameter of the inner passages 3 is preferably selected to be relatively small but larger diameters may be provided depending on the application and the refrigerant used.
In order to provide a sufficiently large heat exchange surface area at the outside of the flat tubes 2 of the heat exchanger 1 without encountering the disadvantages mentioned earlier, the adjacent flat tubes 2 are arranged in closely spaced relationship without intermediate heat exchange ribs at a distance of less than 3 mm, preferably about 2 mm, in such a way that the opposite surfaces 4, 5, 6, 7, that is the walls of adjacent flat tubes 2, without contacting one another form therebetween smooth flow channels 8, 9 for the air flowing therethrough. Preferably, the flat tubes 2 are oriented in their installation position such that their longitudinal axes extend essentially vertically or at an acute angle with respect to a vertical line, while the air flows essentially horizontally through the heat exchanger. Any water condensing on the outer surfaces 4 to 7 of the flat tubes 2 can then flow along the tube surfaces downwardly so that the heat exchange is not detrimentally affected by the moisture on the tubes. By the smooth and plain configuration of the surfaces 4 to 7 deposition of contaminants in the flow channels 8, 9 which may result in an unhygienic contamination of the air is prevented so that also the development of undesirable odors in the air is avoided.
Preferably, the surfaces 4 to 7 are so surface-treated or have such a surface structure that the natural surface tension of water at the surfaces 4 to 7 is reduced. In particular, the surfaces 4 to 7 may be provided with a hydrophilic coating. A hydrophilic surface coating may be obtained for example by a chemical surface treatment of the flat tubes formed from an aluminum alloy with chromic acid as it is known for the prime coating of surfaces for example in the manufacture of airplanes as chromic acid anodizing procedure. Alternatively, other chemical surface treatment methods such as silicic acid anodizing methods may be used. Alternatively, or additionally, mechanical surface treatments may be employed which generate a hydrophilic surface structure on at least one of the surfaces 4-7. Furthermore, various hydrophilic coatings may be provided which may be applied in various thicknesses to the surfaces 4 to 7 (possibly by heat treatment procedures). This may include for example coatings of chromium nitride (CrN), titanium dioxide (TiO₂) zirconium-niobium compounds (Zr2.5Nb) or similar compounds. Generally, also coatings with monomer dispersive nano- and/or microparticles may be used. Furthermore, alternatively or additionally a polyvinyl pyrolidone coating may be provided.
With the surface treatment and coating procedures mentioned above hydrophilic surfaces can be generated on the flat tubes 2 so that water can be condensed on the surfaces without forming droplets, that is, the condensed water spreads and forms a thin film which runs off rapidly or evaporates. A collection of water on the heat transfer surfaces is effectively avoided. Furthermore, with the prevention of water collection on the heat exchanger surfaces, the heat exchanger cannot only be used for cooling but also for heating the passenger space of a motor vehicle as, upon switching over to heating, only a relatively small amount of condensed water is evaporated and little moisture is conducted in into the passenger compartment where in larger amounts it would fog up the windshield in an endangering manner.
A further improved moisture rejection of the smooth surfaces 4 to 7 of the flat tubes 2 and an improved heat transfer at these surfaces 4 to 7 is obtained by stamping several parallel corrugation-like impression 11 into the flat tubes 2 which extend over the whole cross-section of the flat tubes 2 so that the flat tubes are wave-shaped at both sides.
Preferably, the impressions 11 are so deep and the distance between the flat tubes 2 is so small that the convex side of a particular impression 11 of a flat tube 2 forms with the convex side of the respective impression 11 of the adjacent flat tube 2 wave-shaped air flow channels 12. In other words, in opposite walls 4, 5, 6, 7 of adjacent flat tubes 2 elongated depression 11 are formed and so arranged that corresponding elongated projections of the adjacent tube extend into the depressions such that the cross-section of the flow passages between adjacent tubes is wave-shaped but not essentially reduced. This is shown in the enlarged representation of FIG. 5.
From FIG. 5, it is apparent that, with the distance 13 as measured between adjacent flat tubes, the width of the flow channels 8, 9 between adjacent tubes changes periodically providing for a minimal distance 14 and a maximum distance between the tubes corresponding to the above distance 13. This, together with the wave-shaped flow channel results in turbulence in the air flow through the channels whereby the heat transfer is improved and the downward flow of moisture and the discharge thereof is enhanced.
Preferably, the impressions extend in a straight line at an angle to the longitudinal axis (main axis) of the flat tubes 2 as shown in FIGS. 2, 3 and 4. In this way, the internal passages 3 extending in the longitudinal directions of the flat tubes are wave-like curved whereby the heat transfer is improved also at the inside of the flat tubes 2 and the formation of large droplets is prevented. In other words: On opposite walls 4, 5, 6, 7 of adjacent flat tubes 2 longitudinal impressions 11 are so arranged that the longitudinal axes of the impressions extend at an angle to the flow direction of the air flow (which is about horizontal and parallel to the surfaces 4 to 7) and at an angle to the refrigerant flow direction (which is about in the direction of the main, or respectively, longitudinal axis of the flat tubes). The longitudinal impressions are disposed directly opposite correspondingly dimensioned longitudinal raised areas so that the flow cross-section between adjacent flat tubes 2 at the air side is not substantially reduced by the curvatures.
In order to improve the incident angle of the horizontal incoming air flow to the inclined impressions 11 and to improve also the discharge or outflow of condensate, the heat exchanger 1 is tilted forwardly at an angle of about 5° as shown in FIG. 2.
The free end areas of the flat tubes 2 terminate in chambers 15, 16, 17 of the two connection distributors 10, 18 provided at the bottom and top ends of the heat exchanger 1. They are firmly closed by solder jointures.
The web walls 19, 20, 21 which delimit the secondary chambers 15, 16, 17 and extend parallel to the flat tubes 2 and the longitudinal web walls 22, 23, 24 which extend parallel and interconnect the web walls 19, 20, 21 as shown in FIGS. 10 and 11 strengthen the side wall of the connection distributor 10, 18 at the side thereof facing the flat tubes so that they are capable of accommodating the maximum internal pressure. Furthermore, they provide for a division of the operating medium of the air conditioning system admitted and discharged by way of the primary passages 25 to 29 of the connection distributor 10, 18 for conducting the operating medium in a known manner through the heat exchanger 1 that is through the flat tubes thereof in several partial guided reverse flow paths resulting in a substantially uniform temperature distribution in the heat exchanger and consequently a maximum average temperature drop for an optimal heat transfer. An example of such a flow distribution is shown in FIG. 21 for the connection distributor 53 of FIG. 20.
For an improved division of the operating medium flow to the areas of the flat tubes 2 divided by the web walls 21, 23, 24, in the embodiment with bottom end admission of the operating medium, the supply channel 33 includes a guide insert 34, which includes screw-like ribs providing for a rotating flow of the operating medium through the supply channel 33 and consequently contributes to the mixing of the operating medium of the air conditioning system.
In order to position the flat tubes 2, inspite of a given distance between the web walls 20, 21 delimiting the secondary chambers 16, 17, at a smaller distance 13 from one another than that shown in FIG. 9, preferably two or three flat tubes 2 are bundled in the connecting distributor 10, 18 as shown in FIGS. 6 and 8 by bending the end area of at least one of the flat tubes 2 so as to form an offsetting 36 with respect to the other tubes whereby the adjacent tubes can be tightly joined in the end areas 37 thereof. The tightly joined end areas 35, 37 are soldered together and to the wall 38 of the connection distributor 10, 18 surrounding the bundled tube ends for example by an earlier application of solder material by an immersion procedure and heating to soldering temperature after assembly.
The connection distributors 10, 18 consist in accordance with FIG. 14 preferably of extruded profiled strands 40 provided with a number of internal channels 41 formed by intermediate walls 42, The internal channels increase the pressure resistance of the connection distributors 10, 18 and form flow guide structures. For flow communication with the upper end areas 35, 36 of the flat tubes 2, these internal channels 41 are in communication with one another via circular arc-shaped cut- outs 43, 44, which form accommodating slots for the flat tubes 2 or, respectively, bundles of flat tubes 2. A web part 22′ between the cutouts 43, 44 corresponds to the web section 22 of FIG. 10 and consequently provides for a flow separation in two cross-section areas 45, 46 of the flat tubes 2.
In order to further improve the air-side heat transfer at the smooth surfaces 4, 5, 6, 7 of the flat tubes 2, turbulence is generated in the air flow being admitted already at the front edge 47 of the flat tubes 2 by the tooth-like profile thereof. FIG. 4 shows an embodiment of a suitable edge profiling. In addition or alternatively the front edges 47 of the flat tubes 2 may be provided with one or several comb-like spacers 70 a section of one of which is shown in FIG. 22. A spacer 70 includes teeth 71 which extend into some or all of the spaces between the individual flat tubes 2 (not shown in detail). To this end, the spacer 70 is placed onto the edges 47 oriented about horizontally and transverse to the main axes of the parallel flat tubes 2 and is soldered to the flat tubes 2. To facilitate its manufacture a spacer 70 is manufactured from a solder-plated metal sheet particular one which consists of the same material as the solder plated metal sheets of which the connection distributors 50, 53 consist.
The heat exchanger 1′ of the embodiment shown in FIGS. 16-20 includes connection tubes 51, 52 provided on a top end connection distributor 50 for the supply and, respectively, the removal of, the operating medium of the air conditioning system. The connecting tubes 51, 52 are connected to the grid-like distribution system of the connection distributor 5 in a way similar to that shown in FIG. 11 in order to supply the operating medium uniformly to the various flat tubes 2, or, respectively, a certain cross-sectional part thereof and to remove it again from the flat tubes 2.
In this embodiment, the operating medium flows through the adjacent flat tube 2 in opposite directions. Furthermore, there is an intermediate separation 49 of the connection distributor 50, 53, which causes a flow transfer to the transversely adjacent part of the heat exchanger 1′ in accordance with a cross-counter flow arrangement. In this way, disadvantages resulting from a non-uniform distribution of the liquid phase over the whole cross-section of the heat exchanger 1′ of the air conditioning system can be counteracted. Particularly advantageous is an internal circuit arrangement of the heat exchanger with cross-counter flow and a division of the flat tubes of the heat exchanger into two blocks with four rows each as shown in FIG. 21. In order to reinforce this effect, refrigerant can be conducted through individual flat tubes in different amounts.
With the division of the flow of the operating medium of the air conditioning system into a relatively large number of partial flows with several reversals and correspondingly long flow paths at a predetermined size of the air side outer heat transfer surface area, the operating medium side heat transfer surface area is substantially, that is about four times, larger than that of conventional heat exchanger because of the larger number of flat tubes 2. As a result, a correspondingly larger flow cross-section is available so that an increase of the operating medium-side flow resistance is avoided. Because of this larger inner or respectively, operating medium-side surface of the heat exchanger according to the invention a size ratio of the air side and operating medium-side heat transfer area of about 0.7 to 1.5, particularly 0.5 to 1.1 is obtained. In motor vehicle air conditioning systems an air side surface area of 1.5-2.5 m²is common.
According to the invention, a correspondingly large refrigerant-side heat exchange surface area is provided.
Since the operating medium entering the heat exchanger comprises during cooling operation different proportions in the liquid and vapor phase, there is, because of gravity forces, a non-uniform distribution of the liquid phase in the inlet and outlet areas over the width of the heat exchanger 1′ and a non-uniform distribution of the temperature, resulting in an inefficient utilization of the theoretical performance capability. In order to counteract such a non-uniform distribution over the width of the heat exchanger 1′, in accordance with another embodiment of the invention the bottom-end connection distributor 53 has a bottom wall 54 with, for example, four longitudinal channels 55 to 58 which are at opposite sides delimited by a web wall 22″ and become deeper up to a center area of their longitudinal extension and then become again shallower toward the end thereof. The change in depth is continuously that is they have a cross-section like that of a flat bowl structure. The change in depth may also be stepwise so that, at each upward step 59 to 62, in flow direction a flow backup that is a turbulence occurs which has a component directed upwardly toward the flat tubes 2 whereby a part of the liquid phase is directed into the tubes instead of into a side area of the heat exchanger.
A stepped bottom surface in the longitudinal channels 55, 58 can be made for example by cutting the steps with a rotary cutter into a light metal plate, for example, by a rotary cutter rotating about a vertical axis so that the vertical step surfaces 59 to 62 (FIG. 18) are semicircular. They generate a flow pattern which is directed centrally upwardly toward the longitudinal flow axis.
FIG. 23 is a perspective view of another embodiment of the flat tube 2 according to the invention. In this embodiment, alternately V-shaped recesses 80 and V-shaped projections 8 are provided which are arranged in the longitudinal direction of the flat tubes one after the other. Since the recesses 80 as well as the projections 81 become continuously flatter toward the edge of the tube 2 the side edge 82 of the flat tube 2 is essentially straight that is without any waves. At the narrow front edge of the flat tube, the openings of the numerous internal passages 3 extending through the flat tube are visible.
FIG. 24 shows a cross-section through the flat tube according to FIG. 23 taken along the line Z-Z. Herein, the points A and B belong to a single projection 81 and the points C and D belong to an adjacent depression 80. A center line of the flat tube wall extends at “M”. It is apparent from the cross-sectional view that the outer area L forming the air side of the flat tube as well as the inner passages 3 forming the refrigerant side are wave-shaped. The flat tube 2 is in accordance with the invention so installed that the tip of the V-shaped depressions 80 and the projections 81 point vertically upwardly that is they have a reversed V-shaped profile in a corresponding heat exchanger. In this way, it is made sure that the condensate can flow easily downwardly without being collected anywhere.
The flat tube as illustrated in FIGS. 23 and 24 can be used in a heat exchanger as described above so that all features and advantages pointed out above apply correspondingly. In particular, all possible combinations with features mentioned earlier may be used. An additional advantage results from the use of the flat tube 2 described on the basis of FIGS. 23 and 24 as it has an increased rigidity in longitudinal as well as transverse direction of the flat tube so that the whole corresponding heat exchanger becomes more rigid. With such an increased rigidity the flat tubes 2 also become very form-stable and the distance between the flat tubes 2 may be reduced to possibly less than 1 mm. With the installation of several flat tubes of the type described in connection with FIGS. 23 and 24 preferably in each case two flat tubes with oppositely oriented end offsets 84 may be combined to a pair (see FIG. 6). Herein the offset areas 84 each have an about rectangular end cross-section; the projections 81 and depressions 80 flatten out in this area to zero.
Finally, FIG. 25 shows schematically a cross-section taken along line Y-Y and FIG. 26 is a perspective view of another flat tube 2 according to the invention. Herein an extruded strand profile is used which includes at its outer surface recesses 90 which are displaced with respect to the inner passages 3 of the tubes. This arrangement results in a reduction of the material requirements in comparison with the flat tube shown in FIGS. 23 and 24 and consequently in a reduced weight. Furthermore, the surface area at the air side is increased so that also the heat transfer is increased. In accordance with FIGS. 25 and 26, the flat tube 2 has a wave shape which is oriented transverse to the longitudinal axes of the flat tube 2 with several (preferably 3 to 10) recesses 91 and projections 92 which provide for a rib-like surface structure of the flat tubes and in this case, extend exactly transverse to the air flow.
The wave-like shape of the flat tube is converted at the ends of the tube (that is, at the small front ends 5) by rolling to a flat shape in order to obtain an oblong cross-section. This procedure is preferably performed using a continuous rolling tool in the direction of the refrigerant flow that is in the direction of the main axis of the flat tube 2. The rolling tool utilizes the recesses (ribbing) preferably as guide structure and brings the flat tube 2 at the ends thereof to the desired width and height. In such a rolling tool, the cutters for cutting the flat tube to the proper length are integrated. In accordance with the rectangular cross-sectional shape generated at the tube ends, the flat tube can be fitted into a rectangular slot in a connection distributor and be soldered there into position.
In a modified embodiment, the recesses 91 and projections 92 have a V-shape (corresponding to the variant of FIGS. 23 and 24) while the recesses 90 still extend parallel to the inner passages 3. Herein the depressions and projections are formed for example by a punching process which is applied to a flat profile provided with the recesses. Additional modifications and combinations corresponding to the earlier described embodiments are possible.
In accordance with another embodiment of the invention, the bottom end connection distributor of a heat exchanger according to the invention is provided analog to FIGS. 18, 19 with a bottom wall 54′ as shown in FIGS. 27 and 28. The bottom wall 54′ provides for an advantageous conduction of refrigerant through different areas of the heat exchanger in accordance with the basic distribution mode according to FIG. 21. The distribution mode according to the invention comprises particularly a division of the heat exchanger in altogether eight groups of 20 to 80 flat tubes each, wherein two groups arranged in series each form a row R1 to R4 and the rows R1 to R4 are delimited at the sides by web walls 22″. Additionally, the heat exchanger is divided centrally into two blocks B1 and B2.
Refrigerant is introduced into a heat exchanger provided with the bottom wall 54′ for example in the section E from the top in the area of the row R1. After introduction, the refrigerant flows through the flat tubes of row R1 in the area E vertically from top to bottom. At the bottom, the refrigerant flow is distributed to four separate parallel longitudinal channels 101 to 104 which are part of the row R1 and which are separated from one another by three small wall structures 100. The refrigerant flows along the bottom wall 54′ from the first block B1 to the second block B2. In the second block B2, the longitudinal channels 101 to 104 of the Row R1 end in different areas as shown in FIG. 27. Particularly, the last third of the second block B2 in the area of the row R1 is only supplied via the longitudinal passage 104. (Some of the respective flat tubes 2 are schematically indicated.) To the second half of the block B2, in which the end areas of the longitudinal passages 103 and 104 are disposed, refrigerant is supplied in the area of the row R1 only via the longitudinal passages 103 and 104. In a modified exemplary embodiment an intermediate part of the block B2 in the area of the row R1 refrigerant is supplied exclusively via the longitudinal passage 103. After a U-shaped flow through the first row R1 (see also FIG. 21), the refrigerant reaches in the second block B2 an upper reversing area U1 and is conducted from the top into the second row R2 through which it flows again in a U-shaped pattern. At the bottom end, the bottom wall 54′ provides again for a separation of the coolant flow. Subsequently, the refrigerant flows in the same way through the rows R3, R4 so that the refrigerant exits the heat exchanger in the section A of the block B1.
In a manner which is advantageous for the refrigerant flow the longitudinal passages end with a radius 59 which backs up the refrigerant flow and forces the refrigerant to flow into the flat tubes (FIG. 28). With a division of the refrigerant flow into several individual flows 101 to 104 (corresponding to the number of longitudinal passages) in each case a controlled distribution in the, in flow direction, subsequent blocks can be obtained. Herein the individual flows are supplied in a controllable manner to different numbers of flat tubes. As a result with each reversal of the flow into another block the refrigerant is newly distributed.
The longitudinal passages 101 to 104 in the form of slot-like cutouts can be formed by cutting with disc cutters or with a grinding disc so that the upwardly directed radii 59 correspond to the radius of the cutting tool.

Claims

1. An air/refrigerant heat exchanger, particularly for a motor vehicle air conditioning system, comprising a plurality of flat tubes (2) having opposite walls (4, 5, 6, 7) arranged in closely spaced relationship so as to form between the walls of adjacent flat tubes narrow flow passages (8, 9) for the conduction of air therethrough, said flat tubes (2) including each a plurality of passages (3) and being provided at opposite ends with distribution connectors (10, 18) for conducting refrigerant through the passages (3) extending through the tubes (2), said distribution connectors (10, 18) having each at least one line connecter (33, 51, 52) for the connection of the flat tubes (2) in a refrigerant circuit of the air conditioning system, the refrigerant flow direction through the flat tubes (2) being essentially parallel to the main axis of the respective flat tubes (2), opposite walls (4, 5, 6, 7) of adjacent flat tubes (2) including longitudinal recesses (11, 80) and projections (81) such that the flat tubes (2) are wave-shaped, the recesses and projections flattening out toward both narrow opposite ends of the flat tubes (2) and, at the opposite ends, forming narrow flat rectangular end sections.

2. An air/refrigerant heat exchanger according to claim 1, wherein longitudinal axes of the recesses (11, 80) and the projections (81) extend in the longitudinal direction of the flat tube (2) and transverse to the flow direction to an air flow over the outer surfaces of the flat tubes (2) such that the air flow over the tube surfaces is wave-shaped.

3. An air/refrigerant heat exchanger according to claim 1, wherein the flat tubes (2) are provided with V-shaped recesses (11, 80) and projections (81) which extend at an oblique angle to the flow direction of the air flow and to the flow direction of the refrigerant through the flat tubes (2) that is, the longitudinal direction of the tubes (2).

4. An air/refrigerant heat exchanger according to claim 1, wherein the recesses (11) extend through the flat tube (2) so that, at the opposite side of the tube (2) a corresponding projection is formed and the flat tube (2) is profiled at both sides thereof.

5. An air/refrigerant heat exchanger according to claim 1, wherein the flat tube (2) has an end area (35, 37) with a cross-section which, in the direction of the axis of the flat tube (2), is rectangular and constant and a center section with a cross-section which continuously changes over the length of the flat tube (2).

6. An air/refrigerant heat exchanger according to claim 1, wherein the facing surfaces (4, 5, 6, 7) of two adjacent flat tubes (2) are so arranged that at least one depression of a flat tube (2) received a projection of the adjacent flat tube so that a wave-shaped air flow channel is formed between the adjacent flat tubes (2).

7. An air/refrigerant heat exchanger according to claim 1, wherein at least two flat tubes (2) are bundled and the end areas (35) of at least one of the bundled flat tubes (2) is offset relative to the flat tube surface thereof and disposed in close contact with the end area (31) of the adjacent flat tubes (2).

8. An air/refrigerant heat exchanger according to claim 1, wherein the front ends of several flat tubes (2) are joined by a common comb-like spacer (70) which has projections (71) extending into the spaces between adjacent flat tubes (2).

9. An air/refrigerant heat exchanger according to claim 1, wherein opposite surfaces (4, 5, 6, 7) of adjacent flat tubes (2) are provided with hydrophilic coatings which reduce the surface tension of water.

10. An air/refrigerant heat exchanger according to claim 1, wherein the ratio of the inner refrigerant side surface area and the outer air side surface area of the flat tubes (2) is 0.7 to 1.5, preferably about 1.

11. An air/refrigerant heat exchanger according to claim 10, wherein the ratio of the inner refrigerant side surface area and the outer air side surface area of the flat tubes (2) is about 1.

12. An air/refrigerant heat exchanger according to claim 1, wherein the connection distributor (10, 18) is provided with pipe connections (51, 52) and includes a bottom plate (54′) which has at least two longitudinal channels (101 to 104) which divide the refrigerant flow into at least two refrigerant flows such that the refrigerant flow can be supplied, at least partially, to different flat tubes (2) or different numbers of flat tubes.

13. An air/refrigerant heat exchanger comprising a plurality of flat tubes (2) arranged in parallel spaced relationship and including passages through which a refrigerant is conducted, parallel spaced walls (4, 5, 6, 7) of adjacent flat tubes (2) forming air flow channels (3), a plurality of spaced flat tubes (2) being joined at their ends to a connection distributor (10, 18) including at least one pipe connector (33, 51, 52) for connection to a tube system, said spaced walls (4, 5, 6, 7) of adjacent flat tubes (2) having longitudinal recesses (11, 80) and, respectively, projections (81) provided in such a way that they extend obliquely to the flow direction of the refrigerant flow through the flat tubes, the refrigerant flow extending essentially parallel to a main axis of the respective flat tube (2).

14. An air/refrigerant heat exchanger according to claim 13, wherein the narrow front ends of several flat tubes (2) are joined by a common comb-like spacer (70) which has projections extending into the spaces between adjacent flat tubes (2).

15. An air/refrigerant heat exchanger according to claim 13, wherein opposite surfaces (4, 5, 6, 7) of adjacent flat tubes (2) are provided with hydrophilic coatings which reduce the surface tension of water.

17. An air/refrigerant heat exchanger according to claim 13, wherein the ratio of the inner refrigerant side surface area and the outer air side surface area of the flat tubes (2) is 0.7 to 1.5.

18. An air/refrigerant heat exchanger according to claim 17, wherein the ratio of the inner refrigerant side surface area and the outer air side surface area of the flat tubes (2) is about 1.

19. An air/refrigerant heat exchanger according to claim 13, wherein the connection distributor (10, 18) is provided with pipe connections (51, 52) and includes a bottom plate (54′) which includes at least two longitudinal channels (101 to 104) which divide the refrigerant flow into at least two refrigerant flows such that the refrigerant flow can be supplied, at least partially, to different flat tubes (2) or different numbers of flat tubes.

20. An air/refrigerant heat exchanger, particularly for a motor vehicle air conditioning system, comprising a plurality of flat tubes (2) having opposite walls (4, 5, 6, 7) arranged in closely spaced relationship so as to form between the walls of adjacent flat tubes narrow flow passages (8, 9) for the conduction of air therethrough, said flat tubes (2) including each a plurality of passages (3) and being provided at opposite ends with distribution connectors (10, 18) for conducting refrigerant through the passages (3) extending through the flat tubes (2), said distribution connectors (10, 18) having each at least one line connecter (33, 51, 52) for the connection of the flat tubes (2) in a refrigerant circuit of the air conditioning system, the refrigerant flow direction through the flat tubes (2) being essentially parallel to the main axis of the respective flat tubes (2), the flat tubes (2) having end areas (35, 37) with a cross-section which, in the direction of the axes of the flat tubes (2) are rectangular and constant and center sections with a cross-section which continuously changes over the length of the flat tube (2).