DE19758886B4 - Two-flow and single-tube brazed flat tube evaporator in the air direction for an automotive air conditioning system - Google Patents

Abstract

Double-finned and air-line single-brazed flat tube evaporator made of aluminum or an aluminum alloy for an automotive air conditioning system, in which a distributor (24, 28) of the refrigerant on the inlet side of individual flat tubes (2) or in particular groups thereof is arranged and the flat tubes are extruded multi-chambered tubes, between which zigzag fins (12) are sandwiched, the front fronts of the zigzag fins (12) projecting over the adjacent end faces (6) of the flat tubes (2), wherein - the depth (B) of the evaporator is at least 25 mm and at most 50 mm ; and - the space (LH) occupied by a zigzag blade (12) between two adjacent flat tubes (2) is more than 6 mm and less than 8 mm.

Description

The invention relates to a double-flow and einreihigen in the air direction brazed flat tube evaporator made of aluminum or an aluminum alloy for a motor vehicle air conditioning with the features of the preamble of claim 1. Such a double-flow flat tube evaporator is in addition to more than double-flow embodiments of the DE 195 15 526 C1 known.

From the EP 0 030 072 A2 is a double-flow heat exchanger with aluminum flat tubes known. On the inlet side, a distributor of the refrigerant is arranged on inputs of individual flat tubes. The flat tubes are extruded multi-chamber tubes, between which corrugated fins are nested. The corrugated fins each have an end face, which protrude downstream of adjacent end faces of the flat tubes.

On the market flat tube evaporator of such a type have only just become known prototypes a depth of 60 mm, while the overall depth is comparable to comparable plate evaporators 66 to about 100 mm.

As already shown in the generic publication, there has been a desire to increase the efficiency, if desired, in the transition to more than double-flow evaporator.

In addition, efforts have been made in double-flow and double-flow evaporators to charge the individual flat tubes with a ratio of liquid to gaseous refrigerant that is as constant as possible and, as already provided for generically, to supply the refrigerant to the inputs on the inlet side of groups of flat tubes to distribute. Equivalent to this is included in the genus also currently not detectable from the prior art for flat tube evaporator idea to make this distribution also in relation to each individual flat tube. Such a distribution to individual tubes of an evaporator, but not expressly a flat tube evaporator, is in itself from the EP 0 566 899 A1 known.

In all such distributions of the inlet-side refrigerant on flat tubes at the same time a distribution to all chambers of the respective flat tube, which extend in the direction of the depth of the evaporator in a row. The depth of the evaporator is identical in the limiting case with the corresponding width dimension of the flat tube. However, the width dimension of the flat tube may also be slightly lower, in particular if one includes a corresponding front projection of the ribbing by the zigzag fins.

Now is just the installation of components in motor vehicles, a major problem always the available installation space in the vehicle. It is therefore generally the case of components for installation in motor vehicles endeavor to keep the outer dimensions minimal for a given output. It is to be taken for granted that this basic idea was also based on all the known generic flat-tube evaporators which are on the market. It can be deduced from this that experts in such flat-tube evaporators have not considered a depth of less than 60 mm to be suitable in consideration of all requirements.

The invention is based on the recognition that this assumption is based on a prejudice.

Rather, the invention is based on the finding that even with otherwise constant parameters known generic flat tube evaporator, a reduction of the depth is at least partially compensated by the fact that while the efficiency of the distribution device is increased. Because with a reduced structural depth on the inlet side, the refrigerant needs to be distributed only to a smaller number of chambers of the flat tubes per inlet chamber fed by the distribution channel.

In this sense, the invention describes a way instead of obtaining over the path of increasing the number of floods beyond the Zweiflutigkeit an optimization by reducing the depth.

Accordingly, the invention has for its object to increase the efficiency of a generic double-flow flat tube evaporator in a structurally particularly simple manner.

This object is achieved in a flat tube evaporator with the features of claim 1; In this case, not only a small depth range is selected, but also determined by a zigzag lamella intermediate space between two adjacent flat tubes in terms of value.

The meaning of this combination of values can best be explained, for example. If, for example, one goes from the smallest conventional construction depth of 60 mm instead to 42 mm in the sense of an average value of the combination according to the invention and thereby also the space between the flat tubes smaller than customary or at least selects in the value range according to the invention, one obtains a configuration in which the essential for a motor vehicle saving in construction depth is largely compensated by a relatively large number of juxtaposed flat tubes. This effect is superimposed on the already discussed better distribution of the refrigerant in a favorable sense. The structurally particularly simple design of the twin-flow flat-tube evaporator according to the invention can already be seen from the fact that the increase in the relative efficiency allows a significant savings in overall depth, especially in the small installation space of motor vehicles, without having to degrade the heat output of the evaporator. There is also a saving of building material in Bautiefenrichtung and caused by Mehrflutigkeit longitudinal transverse walls are unnecessary.

The EP 0 414 433 A2 does not show as the flat tube evaporator according to the invention a single row in the direction of air training, which determines the depth, but a two-row in the air direction training (so-called duplex arrangement) and an evaporator (Sp. 6, Z. 34-37) with two flat tubes using separate heat exchanger blocks , which are arranged at a mutual distance in the direction of air one behind the other. This arrangement is based on the concept of winning the heat output, in contrast to the invention, not with reduction, but with increasing the installation depth. Even with overlapping of dimensions in the individual heat exchanger block of this duplex arrangement with the value combination according to the invention, the combination according to the invention can not be excited in a flat tube evaporator with a single-row design.

The DE 30 20 424 A1 relates generally to a flat-tube type heat exchanger developed under the conditions of a motor radiator of automobiles. This prior publication is based on the prior art of a radiator engine with a depth of 32 to 35 mm and lowered it in another combination of values to 23 mm and less. A transfer of these conditions of a heat exchanger such as a water cooler in motor vehicles on a flat tube evaporator in motor vehicles is not possible. This is already clear from the fact that the conventional flat tube evaporators previously knew no smaller installation depth than 60 mm.

In the further subclaims there is an accompanying optimization of parameters which are recognized as essential in connection with the invention and which, in interaction, even make it possible not only to achieve the heat output of commercially available generic flat tube evaporators, but even to exceed them somewhat.

In addition to the above-mentioned depth and each occupied by a zigzag lamella between two adjacent flat tubes (claims 2 and 3) takes place an accompanying optimization on the measured between their flat sides thickness of the flat tubes (claims 4 to 7), the wall thickness of the flat tubes between them Outer surface and its respective inner chamber (claims 8 to 12) and on the pitch of the zigzag blades (claims 13 to 17). The length of the flat tubes has proven to be uncritical and can be adapted to the corresponding space in the vehicle.

In the context of the invention, partly deviating from the use in some specialist companies, the spacing of adjacent vertexes of the same zigzag lamella is understood as being divided, or the repetition distance between identical phases of the zigzag lapping.

The invention will be explained in more detail below with reference to schematic drawings. Show it:

1 in perspective and partially broken view of an example of a double-tube flat-tube evaporator, to which the dimensions of the invention relate;

2 a plan view of the tube plate of the manifold serving as a collector from the interior, and with respect to an inlet chamber into a group of flat tubes;

3 a cross section through the zig-zag fins sandwiched ribbed block of the flat tubes of the evaporator according to 1 and 2 ;

4 a diagram with the depth B as the abscissa, the heat exchange coefficient k × A _A as the ordinate and the space LH as a parameter curve family,

5 a diagram with the free distance LH as abscissa, the obstruction of the flat tubes in relation to the total inflow area in% as ordinate and the tube thickness d as a parameter curve family,

6 a diagram with the depth B of the evaporator as abscissa, the flow cross-sectional area F for the refrigerant as ordinate and the space LH as a parameter curve family,

7 a diagram with the depth B as the abscissa, the heat exchanger efficiency η as ordinate and the fin pitch T as a family of curves.

The in 1 to 3 illustrated flat-tube evaporator consists in all its illustrated parts of aluminum or an aluminum alloy and is brazed on its parts.

The flat tubes 2 each have parallel similar flat sides 4 as well as frontal ends 6 on, without limiting the generality here have a streamline profile, but also rounded or even square or dull can be formed at right angles to the flat sides. Within each flat tube are chambers as each continuous channels 8th through partitions 10 separated. The number of essentially equal-sized chambers considered in the context of the invention is preferably between 5 and 15, depending on the actual overall depth.

The flat tubes 2 are with each constant mutual distance LH as a block over sandwiched intermediate zigzag fins stripped together, which preferably on the air inlet side with the relevant end faces 6 are flush and preferably for better water drainage at the air outlet side slightly opposite the flat side there 4 according to the drawings in 3 survive. In 3 is also the depth B as the distance between the two front fronts of the zigzag fins 12 indicated in the direction of flow LR of the outside air, wherein on the inflow side, as mentioned, the front end with the relevant end face 6 the flat tubes is flush or aligned in the transverse direction of the direction of flow LR, while downstream the front end on the adjacent end faces 6 the flat tubes 2 survives.

The mutual distance between adjacent flat sides 4 a pair of adjacent flat tubes 2 is therefore designated LH, because it is identical to the so-called lamella height of the respective zigzag lamella.

Every flat tube 2 has one between its two opposite flat sides 4 measured pipe thickness d and a wall thickness w between each chamber 8th and the outer flat side 4 of the relevant flat tube 2 ,

Every zigzag lamella 12 also has a pitch T which describes the spacing of adjacent like phases of the zigzag sipe, such as the spacing of adjacent peaks on one side of the respective zigzag sipe.

The external admission of serving as heat exchange tubes of the evaporator flat tubes 2 takes place by outside air in the motor vehicle according to the arrow LR (air direction) in 1 and 3 ,

The internal admission of each flat tube 2 is double-ended according to the inverse arrow UP in 1 , For the flow reversal at the one end of the respective flat tubes in the block serve according to 1 individual end caps 14 , whose function can also be taken over by a common deflection box or other fluid deflection.

The supply of the refrigerant into the evaporator takes place in accordance with the inlet arrow Z in 1 through a connecting piece 16 at the front of a collecting tank 18 from tube bottom 20 and lid 22 , The end caps 14 opposite ends of the flat tubes 2 are in slots or outer and / or inner collars of the tube sheet 20 so taken as to match the interior of the collector 18 to be able to communicate.

The inlet-side connecting piece 16 of the collector 18 goes into this in a manifold 24 a distributor over, which is closed at its free end and at its periphery depending on an outlet opening 26 each having an inlet chamber 28 a group of more than one in the tubesheet 20 stuck flat tube 2 communicated. The number of flat tubes associated with an inlet chamber may be the distance of the respective outlet opening 26 depending on the connecting piece 16 change what's in 2 However, not realized, where without limiting the generality of two flat tubes, each with an inlet chamber 28 communicate. In practice, in connection with the invention, in particular the number of only one flat tube 2 per inlet chamber up to five flat tubes per inlet chamber in question, as mentioned both with constancy of this number and with adapted variability between the mentioned limits 1 and 5.

The second flow in the flow direction of the refrigerant of all flat tubes communicates with a common outlet chamber 30 in the collector 18 which extends over its entire length and from one also along the collector 18 in this extending longitudinal partition 32 from the individual entry chambers 28 is separated by flow. The entrance chambers 28 in turn are separated from each other by transverse walls 34 at least for the most part or completely separated. The transverse walls 34 extend at right angles from the output chamber 30 opposite side of the longitudinal partition 32 out.

The exit chamber 30 communicates with an external flow outlet 36 of the refrigerant from the evaporator.

The flow outlet can be like the inlet nozzle 16 also as outer connecting piece according to the drawings in 1 be designed. Also come naturally flow entry and flow outlet on any other possible design in question, including one in which the two exits on opposite end faces of the collector 18 are provided. Likewise, one could think of it, the flow outlet or in a special construction, such as using die-cast, the flow inlet on the longitudinal side of the collector 18 provided. Finally, in the context of the invention, it is also not excluded that the input-side and the output-side collecting devices are formed by separate collectors, so that then the longitudinal transverse wall 32 each of these separate collectors is omitted.

In the diagram of 4 is the heat exchange coefficient (k × A _A ) above the depth (B) of the flat tube evaporator applied. The heat exchange coefficient is formed from the product of the heat transfer coefficient (k) and the total external air-contacted surface (A _A ) and has the unit Watt / Kelvin. The depth is plotted in millimeters. The dashed curve applies to a space occupied by the lamella LH = 5 mm, the dash-dotted curve applies to LH = 7 mm, the solid curve for LH = 9 mm.

The total set of curves (LH) applies to a pipe thickness d = 1.8 mm and a fin pitch T = 2.8 mm.

4 illustrates the surprising effect of the invention, that with a suitable choice of the tube thickness (d) and the space occupied by the lamella (LH), the heat exchange coefficient (k × A _A ) at halving the depth (B) can still be kept constant.

So z. B. an evaporator with a depth of 60 mm to be reduced to one of about 30 mm when the space occupied by the lamella (LH) is reduced from 9 mm to 5 mm and a tube thickness of d = 1.8 mm Use comes. Despite significantly lower outer surface, but also with lower internal heat transfer surface this power equality at half the depth (B) is achieved because the missing inner and outer heat transfer surface by an improved refrigerant distribution in the flat tubes reduced depth (B) and by significantly higher heat transfer coefficients both on Inside and on the outside is compensated.

Due to the Bautiefenhalbierung arise when using the evaporator in automotive air conditioning significant advantages in terms of installation space and weight.

When reducing the space occupied by the lamella (LH) must be in accordance with 5 Care should be taken that the air side obstruction (V) of the flat tubes, which are in 5 is plotted as ordinate in percent, not too large, otherwise at a given amount of air, the air velocities in the space occupied by the lamella (LH) are too large and the condensation can no longer run in the fins block in the zigzag fins, without it the air is carried away.

Therefore, an air-side obstruction of 22% should not be exceeded for the installation spaces and air volume flows specified in motor vehicles. This means that when reducing the space occupied by the lamella (LH), the tube thickness (d) must also be reduced. With a clearance (LH) of 5 mm, therefore, a tube thickness (d) of 1-1.5 mm and at a gap (LH) of z. B. 7 mm such a 1.5-2 mm are used.

In addition to the air-side obstruction of the flat tubes, which is crucial for the condensate drain, but also for the air-side pressure loss, the flow area (F) is also crucial.

6 shows the relationship of the flow area (F) (mm ² ) and the depth (B) (mm) with the free space (LH) for a tube thickness of d = 1.8 mm. The dashed line applies to a gap (LH) of 5 mm, while the solid line applies to LH = 9 mm.

For maximum performance, on the one hand, the internal heat transfer coefficient must be very high, which is achieved by a high flow velocity and a small flow cross-section (F), and on the other hand, the refrigerant side pressure loss may not be too large by too high a flow velocity, otherwise the effective temperature difference between the refrigerant and the incoming ambient air is reduced too much. For the maximum of the product between the effective temperature difference and the internal heat transfer coefficient, a flow area (F) of 400-600 mm ^{2 is} required for the medium performance range of automotive air conditioners. This minimum flow area (F) can be reduced as the depth (B) is reduced 6 be achieved effectively by increasing the number of tubes and thus by reducing the space occupied by the lamella (LH).

With simultaneous reduction of the pipe thickness (d) in connection with a reduced wall thickness (w), an increase of the air-side obstruction (V) can be avoided even with a reduced clearance (LH).

Due to the coordinated design of the intermediate space (LH), the tube thickness (d) and the wall thickness of the tube (w), the in 4 shown constant maintenance of the heat exchange coefficient (k × A _A ) can be achieved at half the depth. However, this is only possible if the fin pitch (T) z. B. as in 1 with T = 2.8 mm is not too large.

7 shows the influence of the fin pitch (T) on the heat exchanger efficiency (η), which is plotted as ordinate above the depth (B) as the abscissa. The parameter curves for the fin pitch (T) apply to a constant fin height (LH) of 7 mm and to a constant tube thickness of d = 1.8 mm.

Surprisingly, with flat tube evaporators of the type described in the preamble, the influence of the fin pitch at small depths is considerably greater than usual large depths of more than 60 mm. This effect can in addition to the influences of the space (LH), the tube thickness (d) and the wall thickness (w) in evaporators with small depths can be harnessed, so that just in the depths of 20-40 mm a significant increase in heat exchange efficiency is achieved by a tighter slat pitch of T = 2 mm to T = 3 mm, which was not foreseeable at usual building depths of more than 60 mm.

Claims (17)

Double-finned and air-line single-brazed flat tube evaporator made of aluminum or an aluminum alloy for an automotive air conditioning system, in which a distributor ( 24 . 28 ) of the refrigerant to the inputs of individual flat tubes ( 2 ) or in particular groups of the same is arranged and the flat tubes are extruded multi-chambered tubes between which zigzag fins ( 12 ) are sandwiched nested, wherein the front fronts of the zigzag blades ( 12 ) downstream of the adjacent end faces ( 6 ) of the flat tubes ( 2 ), wherein - the depth (B) of the evaporator is at least 25 mm and not more than 50 mm; and - that of a zigzag blade ( 12 ) occupied space (LH) between two adjacent flat tubes (2) is more than 6 mm and less than 8 mm. Flat-tube evaporator according to claim 1, characterized in that the overall depth (B) is at most 40 mm. Flat tube evaporator according to claim 1 or 2, characterized in that the overall depth (B) is at least 35 mm. Flat-tube evaporator according to one of claims 1 to 3, characterized in that between its flat sides ( 4 ) measured thickness (d) of the flat tubes ( 2 ) is at most 2 mm. Flat-tube evaporator according to claim 4, characterized in that the thickness (d) is at most 1.8 mm. Flat-tube evaporator according to one of claims 1 to 4, characterized in that the thickness (d) is at least 1 mm. Flat-tube evaporator according to claim 6, characterized in that the thickness (d) is at least 1.5 mm. Flat tube evaporator according to one of claims 1 to 7, characterized in that the wall thickness (w) of the flat tubes ( 2 ) between its outer surface and its respective inner chamber is not more than 0,5 mm. Flat-tube evaporator according to claim 8, characterized in that the wall thickness (w) is at most 0.4 mm. Flat-tube evaporator according to claim 9, characterized in that the wall thickness (w) is at most 0.25 mm. Flat-tube evaporator according to claim 9 or 10, characterized in that the wall thickness (w) is at least 0.2 mm. Flat-tube evaporator according to claim 9 and claim 11, characterized in that the wall thickness (w) is 0.3 mm. Flat tube evaporator according to one of claims 1 to 12, characterized in that the pitch (T) of the zigzag fins ( 12 ) is at most 4 mm. Flat-tube evaporator according to claim 13, characterized in that the pitch (T) is at most 3 mm. Flat-tube evaporator according to claim 12 or 13, characterized in that the pitch (T) is at least 2 mm. Flat tube evaporator according to claim 15, characterized in that the pitch (T) is at least 2.4 mm. Flat-tube evaporator according to claims 14 and 16, characterized in that the pitch (T) is in the range of 2.6 to 2.8 mm.

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