DE102015112833A1 - Heat exchanger and vehicle air conditioning - Google Patents

Abstract

The invention relates to a heat exchanger with an arrangement of parallel flat tubes (1a, 1b), which are intended that in them the coolant is guided and evaporated. Between the tubes slats (2) are mounted, which form in the direction perpendicular to the course of the tubes air guide slots and thus define the flow direction of the air to be cooled. The tubes form at least two assemblies (11), which are arranged one behind the other in the flow direction (3) of the air. The assemblies (11, 12) differ in the free inner cross-sectional area (W1, W2) of the tubes (1a, 1b) for the coolant.

Description

The invention relates to a heat exchanger for vehicle air conditioning with the particular air is cooled by means of a vaporizing coolant, which is taken into account in increasing the effectiveness in the design of the heat exchanger, that the vaporizing decreasing density of the coolant leads to a reduced further heat absorption capacity. This is achieved by the flat tubes form assemblies with different cross-sectional area of the individual tubes for the coolant flow. In the present application, the term "heat exchanger" is used synonymously with "evaporator", "evaporator" or "evaporator".

Furthermore, the invention relates to a vehicle air conditioning system. Air conditioning systems, especially for vehicles, are usually equipped with heat exchangers in which a cooled by pressure reduction and liquefied refrigerant evaporates in thin pipelines, whereby the air that flows past the pipes with the coolant, heat and thus causes a decrease in temperature of the air.

For this purpose, there are in the prior art, a number of heat exchangers with different designs. In particular, round and flat tubes are used, as well as serpentine-shaped tubes or tubes arranged in parallel between collectors. Typical designations in the art for this are "plate and fin", "parallel flow", "serpentine type" and "tube and fin".

Heat exchangers for air conditioning systems in vehicles must meet a number of requirements. In particular, they must be able to transmit up to 9 kW heat output in the short term, they must be as small as possible so that they can be arranged under the dashboard of the vehicle, the coolant flow can be up to 10 kg / min, and for the airway it should be as low a pressure drop give. In addition, a splash protection is required because splashing, which arises in particular as condensate water on the evaporator can be transferred to the heater, evaporates there and later condenses on the (relatively) cold windshield so that it fogs. The condensate from the air to be cooled must therefore be safely removed and must not, even temporarily, enter the passenger compartment via the air conditioning system.

These requirements in their entirety are considered to be very high and have led to a number of optimizations in recent years and decades. In the process, more and more heat exchangers with parallel flat tubes were used, which are ultimately best adapted to the requirements of vehicles.

The US 2007/0215331 A1 shows a heat exchanger in which the refrigerant is guided descending and ascending in similar parallel flat tubes, the coolant first, in the descending channels at the back, meets the (already cooled) outlet air, and only last, in the ascending channels forward which meets (warmer) inlet air (countercurrent procedure). The fact that the coolant loses heat absorption capacity on its way through the heat exchanger by reducing its density is not considered.

Similarly, it is the heat exchanger according to the EP 0 325 844 A1 , Here, the air flows past six similar assemblies arranged one behind the other. Because of the unused space between the assemblies, this arrangement is less effective and also because of the variety of pipes and pipe connections also costly. In order to take into account the density dependence of the heat absorption capacity of the coolant, this arrangement could be operated so that initially two assemblies are flooded with their pipes in parallel, and in the further course of the coolant path, the remaining four modules in parallel. The EP 0 325 844 A1 However, does not discuss such a leadership of the coolant.

A heat exchanger that cools air in counterflow in a total of six floods, shows the DE 195 15 526 C1 , These floods consist of a number of flat tubes of uniform design. Here, the density dependence of the heat absorption capacity of the coolant is taken into account by increasing the number of groups of flat tubes forming the floods of two to five monotonically in the successively traversed floods and thus the total cross-section of the coolant flow is gradually increased, wherein the flow rate of the coolant correspondingly reduced ("progressive circuiting"). A disadvantage here proves that when operating with higher pressure drop or overheating at the coolant outlet at countercurrent a smaller temperature difference to the air temperature at the inlet can form than when operating in DC.

The invention is based on this prior art and has the task of providing an additional parameter which can be influenced for optimizing the heat exchanger, which parameter can be used to slow down the coolant flow in the outlet region, in order to obtain the achievable temperature difference and thus the To increase the effectiveness of the heat exchanger at constant external dimensions.

This object is achieved in a first aspect of the invention with a heat exchanger having the following features:
The heat exchanger has a Kühlmittelein- and a coolant outlet and parallel guided flat tubes, which are intended that in them the coolant is guided and evaporated. Slats are mounted between the tubes, which form air guide slots in the direction perpendicular to the course of the tubes and thus define the flow direction of the air flowing through. In this case, the tubes form at least two subassemblies through which coolant flows successively, which are arranged one behind the other in the flow direction of the air, and these subassemblies differ in the size of the internal cross-sectional area of the respective tubes of the subassemblies. The tubes adjacent the coolant inlet have a larger cross-sectional area than the tubes adjacent the coolant outlet.

Thus, an additional parameter is provided for optimizing heat exchangers of entirely different design, namely the variation of the inner free cross-sectional area of the tubes. In addition, the further realization is included that a grading in two or a few different tube types is sufficient for practical purposes. Due to the different tubes, the enlargement of the tube cross-section can also be adapted much more closely to the lower density of the coolant with increasing flow path than with the stepwise increase in the number of identical tubes in the prior art.

Embodiments of the invention utilize this optimization parameter to better account for the prior art that as the coolant passes through the heat exchanger, the density of the coolant decreasing upon evaporation results in reduced further heat absorption capability.

In a first embodiment of the invention, the heat exchanger has a lower and an upper collector, each consisting of a bottom part and a lid. The coolant inlet of the heat exchanger is attached to one of the collectors, and the coolant outlet is attached to the same collector or to the other collector. The ends of the flat tubes are soldered into openings in these collectors. Each of the two collectors either forms only one area or several areas separated from one another by partitions, such that the pipes form at least two floods flowed through in succession by the coolant, wherein at least some of the floods differ in the cross section of the pipes and possibly also in the number of Pipes through which the coolant flows. In this case, the sum of the individual cross sections of the pipes is greater in the case of the flood at the coolant outlet of the heat exchanger than in the case of the flood, which starts from the coolant inlet.

By using flat pipes with a larger cross section for the coolant flowing through, at least in the last flood upstream of the outlet, it is possible to reduce the pressure drop of the coolant in this region, which, for a given outlet pressure, has a lower inlet pressure and a lower inlet temperature and thus allows a greater temperature difference to the incoming air. During the passage through the heat exchanger, the refrigerant continuously reduces its density by evaporation and therefore requires a larger volume to accommodate the same amount of heat ("progressive circuiting"). In this embodiment, however, this larger volume, unlike the prior art, pipes of larger cross-section available without, as in the prior art, by increasing the number of parallel tubes simultaneously more slat surface is provided and for a larger heat exchanger volume required becomes.

Overall, this optimization not only leads to better cooling of the air flowing through, but also due to the reduced pressure drop, to a lower dew point and thus to a better drying of the air.

Optimization calculations have shown that in this embodiment of the invention, the cross-sectional area of the tubes of the second assembly is 1.1 times to 2.5 times, and more preferably 1.2 times to 1.6 times, the cross-sectional area of the tubes of the first assembly should be.

Advantageously complementary and supportive in a further embodiment of the invention, the number of successively arranged in the flow direction of the tubes of the modules and thus the surface of the flow associated slats be different. As a result, the effective fin surface can be optimized independently of the flow cross-section of the coolant.

The entire soldering of the components of the heat exchanger is preferably carried out inexpensively in a single operation.

In a further, particularly simple embodiment of the invention, the heat exchanger consists of exactly two floods, the first flood having tubes of smaller cross section and the second trough having tubes of larger cross section, and wherein the tubes of each tide are each formed by an assembly with tubes which have a uniform cross-section with each other. Already in this simple design can be characterized by heat decreasing density of the coolant advantageously be taken into account in a good approximation.

In a further embodiment, the coolant flow can be further optimized by the tubes form more than two successively flowed through by the coolant floods. In this case, the flow cross sections of the floods, calculated as the product of the number of tubes which contribute to the flood, and the cross-sectional area of one of the identical tubes of this flood, form a monotonically increasing sequence in the flow direction of the coolant.

Another aspect of the invention relates to producing a plurality of heat exchangers of different rated power. This can be optimized by installing one assembly of tubes in a higher heat exchanger as a lower cross-sectional area assembly, and the same assembly in a lower heat exchanger as a larger cross-sectional area assembly.

Other aspects relate to the use of a heat exchanger according to the invention. The heat exchanger can be optimized so that the heat exchange between the air and coolant flow takes place in cocurrent, and therefore the side facing the coolant inlet side of the heat exchanger is facing the air inlet during installation. On the other hand, if the optimization is for countercurrent, the side of the heat exchanger facing the coolant inlet faces the air outlet during installation.

The increased effectiveness of the heat exchanger according to the invention in comparison with the prior art contributes in particular to the fulfillment of the particularly high requirements of use in air conditioning systems in vehicles.

In the drawing shows:

1 a perspective view of an embodiment of a heat exchanger according to the invention;

2 a cross-section through a first embodiment of the invention with two floods;

3 an enlargement of a section 2 in which the different cross-sections of the tubes are recognizable;

4 a vierflutige embodiment of the invention in cross section;

5 another vierflutige embodiment of the invention in cross section; and

6 a cross section through an upper header of the heat exchanger after 5 ,

In 1 to 3 a first embodiment of a heat exchanger according to the invention for an evaporator of an air conditioning system of a vehicle is shown. The heat exchanger has a plurality of - in 1 vertically arranged - parallel flat tubes 1 which are designed to be cooled and evaporated in them.

Between adjacent pipes are slats 2 soldered in the direction perpendicular to the course of the tubes 1 Form air-guiding slots which in 1 run from the back left to the front right. The air flows in just this direction and is through the arrow 3 symbolizes, but only the installation of the heat exchanger decides whether the orientation of the air flow is in accordance with the design of the heat exchanger, ie as in 1 in cocurrent or in countercurrent with the coolant flow.

Top and bottom of the heat exchanger are collectors 4 and 5 arranged, the openings have (in 1 not shown) into which the ends of the tubes 1 are soldered, each of the two collectors if necessary, a plurality of separated by partitions (not shown in the figure) separated areas, such that the tubes form at least two sequentially flowed through by the coolant flows. The collectors 4 . 5 each comprise a trough-like bottom part and a cover closing the respective chamber.

In the simplest case, the top collector 4 in 1 divided by a single partition into a rear area for that via an inlet 8th inflowing coolant and a front area for via an outlet 9 effluent coolant, while the lower collector 5 as a connecting chamber of the floods no partitions needed. This results in two sequentially flowed through by the coolant floods, namely in 1 a rear tide in a first assembly 11 with flow direction from top to bottom and a front flood in a second assembly 12 with flow direction from bottom to top. In the general case, the chambers include 7 the collector 4 and 5 always on the one hand mouths of pipes from which coolant flows into the chamber, and on the other hand, further inlets of pipes, flows into the coolant, which is not only a part of the flat tubes to these tubes 1 belong, but possibly also the inlet 8th or the outlet 9 of the coolant.

2 shows a cross section of the heat exchanger after 1 , Here you can see that the pipes 1 that are perpendicular to the drawing plane, two assemblies 11 and 12 form in flow direction 3 the air are arranged one behind the other, namely a smaller assembly 11 above and a larger one below. The size of the assemblies is determined by the number of flow direction 3 lying pipes 1 determines the units 15 form. In 2 it is in the first (as first flowed through) smaller assembly 11 eight tubes per resulting unit 15 and in the second (second flowed through) larger assembly 12 eleven units 15 (see also 3 ).

3 shows an enlarged detail of 2 , which clarifies this in addition. But here it becomes clear that the assemblies 11 and 12 from pipes 1a . 1b each with different internal cross-sectional area exist. The assembly to which the coolant outlet 9 of the heat exchanger, uses pipes 1a , each having a larger cross-sectional area W ₁ for the coolant than the assembly 12 connected to the coolant inlet 8th borders (pipes 1b ; Cross-sectional area W ₂ ).

The difference in cross-section is small. The preferred ratio of the cross-sectional areas W ₂ / W _{1 of} the tubes of the assemblies 12 and 11 is 1.1 to 2.5 and especially 1.2 to 1.6. In the case of more than two subassemblies, it is possible to choose a cross-sectional value for each subassembly between those of its neighboring subassemblies.

It can also be seen that the width of the tubes 1a . 1b is equal to. Grounds are the first and last pipes 1a . 1b every unit 15 slightly rounded on the outside. Except for these last tubes, the remaining tubes 1a . 1b every unit 15 identical internal cross-sectional areas W ₁ or W _2.

In case of 2 and 3 is the DC method, indicated by the arrow 3 , optimal, because then on average over the entire heat exchanger higher temperature differences between the coolant and air face than the countercurrent. Whether countercurrent or direct current is to be preferred for other constellations has to be re-examined for each individual case.

4 shows an embodiment of the invention with four floods P1, P2, P3 and P4. In this case, P1 and P2 have tubes with a smaller cross-sectional area, and P3 and P4 tubes with a larger cross-sectional area. This embodiment is particularly suitable for overheated operation. Here, the coolant passes through four tubes, twice 1a and twice 1b , In this arrangement, the optimization that the countercurrent process is preferable, here by the arrow 3 indicated from below. Otherwise apply here in connection with the 2 and 3 explained features, be it for example to the cross-sectional ratios or tube widths.

5 shows a further embodiment of the invention with four consecutively flowed through flows P1 to P4, wherein P1, P2 and P3 transversely to the flow direction 3 are juxtaposed and completely covered by P4 in the flow direction. It pass through three floods P1 to P3, from the inlet 8th coming, the area 11 with tubes of smaller cross-section W ₁ , which is in the flow direction of the air 3 per unit 15 comprises twelve tubes (in 5 shown above each other). The first flood P1 includes eight adjacent units 15 of pipes, to the second flood P2 eleven units 15 of pipes and to the third flood P3 fifteen units 15 of pipes. The fourth flood P4 uses the entire area 12 with nine pipes per unit 15 and there everyone 34 adjacent units 15 of tubes with the respective larger cross section W _{2 of} the tubes used. The total cross-sectional areas of the floods are thus as follows:
First tide: 8 · 12 · W ₁ = 96 · W ₁
Second tide: 11 · 12 · W ₁ = 132 · W ₁
Third flood: 15 · 12 · W ₁ = 180 · W ₁ and
Fourth flood: 34 x 9 x W ₂ = 306 x W ₂ = 459 x W ₁
where for the last conversion it was assumed that the ratio of the cross-sectional areas of the tubes 1 in the two floods P4 and P1 to P3 W ₂ / W ₁ = 1.5. Thus, the flow cross sections of the floods in the flow direction of the coolant form a monotonously increasing order to account for the decreasing heat absorption capacity of the coolant: In each tide, the coolant flows more slowly than in the previous, thus compensating for the lower heat absorption capacity. The use of the entire area 12 however, for the fourth tide, with a total of 306 tubes, it allows the strongest cooling to be concentrated there, near the coolant outlet, resulting in optimal DC cooling in this embodiment.

The invention thus makes it possible to realize that, when passing through an evaporator, the proportion of gas in the coolant increases and its density decreases at constant pressure. However, the capacity of the coolant for heat is proportional to the density, so that it requires a uniform and effective heat transfer of an increasing volume and therefore an increasing cross-section of the coolant flow. In the prior art this is made possible by additional channels, however, increase the dimensions of the heat exchanger to the space requirements of just these additional channels. According to the invention, this additional space can be saved at least in part by providing only additional tube volume through the increased tube cross-section, but not additional tube lengths and lamellae are installed. Heat exchangers of the same power can thereby build smaller, or they work more effectively at the same size. It also causes increased heat transfer at the Coolant outlet, especially at low superheat, cooling in the DC can be more effective than in countercurrent.

The 6 shows an upper collector 4 of the 5 whose interior is through partitions 6 in chambers 7 is split to divide the coolant flow to a number increasing in the flow direction.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 2007/0215331 A1 [0006]
• EP 0325844 A1 [0007, 0007]
• DE 19515526 C1 [0008]

Claims (13)

Heat exchanger with a coolant inlet ( 8th ) and a coolant outlet ( 9 ), parallel flat tubes ( 1 ; 1a . 1b ), which are intended to carry a refrigerant in them and evaporate, and with between the tubes ( 1 ; 1a . 1b ) attached lamellae ( 2 ) in the direction perpendicular to the course of the tubes ( 1 ) Form air guide slots and so the flow direction ( 3 ) of air flowing through, the pipes ( 1 ) at least two consecutively flowed through by coolant assemblies ( 11 . 12 ), which in the flow direction ( 3 ) of the air are arranged one behind the other, and the assemblies ( 11 . 12 ) in the size of the inner cross-sectional area (W ₁ , W ₂ ) of the respective tubes ( 1a . 1b ) of the assemblies and the tubes ( 1a ) connected to the coolant outlet ( 9 ), a larger cross-sectional area (W ₂ ) than the adjacent to the coolant inlet tubes ( 1b ) to have. Heat exchanger according to claim 1 with an upper and a lower collector ( 4 . 5 ) between which the pipes ( 1 ), wherein parallel flowed through pipes ( 1 ) form a flood (P1-P4) and the floods (P1-P4) successively flowed through by coolant, wherein the coolant inlet ( 8th ) and the coolant outlet ( 9 ) preferably at one of the collectors ( 4 . 5 ) are mounted. Heat exchanger according to claim 2, characterized in that the collectors ( 4 . 5 ) Have openings into which the ends of the tubes ( 1 ) are soldered sealing. Heat exchanger according to claim 2 or 3, characterized in that each of the two collectors has a chamber ( 7 ) or more by partition walls ( 6 ) separated chambers ( 7 ), such that the tubes ( 1 ; 1a . 1b ) form at least two sequentially flowed through by the coolant floods (P1-P4). Heat exchanger according to one of claims 2 to 4, characterized in that the floods (P1-P4) in the number of tubes ( 1 ) and / or in the cross-section of the tubes ( 1a . 1b ), which are flowed through by the coolant, wherein at the coolant outlet ( 9 ) adjacent tide the sum of the cross-sectional areas (W ₂ ) of the tubes ( 1a ), which contribute to this flood, has a greater value than at the high tide, which at the coolant inlet ( 8th ), in particular by 1.1 to 2.5 times, more particularly by 1.2 to 1.6 times. Heat exchanger according to claim 3 or 4, characterized in that the number of flow direction ( 3 ) of the air arranged behind each other ( 1a . 1b ) in the first ( 11 ) and the second assembly ( 12 ) is different. Heat exchanger according to one of the preceding claims, characterized in that the tubes ( 1a . 1b ) exactly two successively flows through the coolant floods, with a first tide, comprising pipes ( 1b ), each having a smaller cross-sectional area (W ₁ ), and a second tide, comprising tubes ( 1a ) each having a larger cross-sectional area (W ₂ ). Heat exchanger according to one of claims 1 to 6, characterized in that the tubes ( 1 ) form more than two flows (P1-P4) through which the coolant flows in succession and that in the flow direction of the coolant the sums of the cross-sectional areas of the respective flows form a monotonously increasing sequence. Heat exchanger according to one of the preceding claims, characterized in that the tubes ( 1 ) of an assembly ( 11 . 12 ) have the same cross-sectional areas. Heat exchanger according to one of the preceding claims, characterized in that an assembly ( 11 . 12 ) has several successively flowed floods (P1-P4) and subsequent floods more pipes ( 1 ) as previous, so that the sum of the cross-sectional areas of the tubes increases. Heat exchanger according to one of the preceding claims, characterized in that a plurality of tubes ( 1 ) to a structural unit ( 15 ), wherein the units have an elongated shape in cross-section and between adjacent units ( 15 ) the slats ( 2 ) are arranged. Vehicle air conditioning system having a heat exchanger according to one of claims 1 to 11, characterized in that air and coolant are operated in the DC while the coolant inlet facing side of the heat exchanger is arranged facing the air inlet. Vehicle air conditioning system having a heat exchanger according to one of claims 1 to 11, characterized in that air and coolant are operated in countercurrent and thereby the coolant outlet facing side of the heat exchanger is arranged facing the air inlet.

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