Heat Exchanger
A heat exchanger (1), particularly for motor vehicles, comprises flat tubes (2) whose interior can be flowed through by first fluids and whose exterior can be subjected to the action of a second fluid. The flat tubes (2) are situated essentially transversal to the flowing direction of the second fluid while being parallel to one another and are interspaced in such a manner as to form flow paths for the second fluid that pass through the heat exchanger (1). Cooling ribs (3) extending between adjacent flat tubes (2) are situated in the flow paths. A number of corrugated ribs are provided, which are located one behind the other in the flowing direction of the second fluid and which are offset with regard to one another in the flowing direction of the first fluid.
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The invention relates to a heat exchanger, especially one for motor vehicles, having the features of the preamble to claim 1.
Such a heat exchanger may be designed, for example, as an integrated heat exchanger having a condenser of an air-conditioning system and a coolant radiator for motor vehicles. The heat exchanger usually has a number of flat tubes arranged side by side and running parallel to one another in a plurality of rows. First fluids, in the above example a refrigerant and a coolant, flow in these rows of flat tubes. The flat tubes are connected to manifolds or collecting pipes and exposed to the flow of a second fluid, for example ambient air, in order to produce a transfer of heat between the fluids. Flow paths for the second fluid are formed between the spaced individual flat tubes.
In order to improve the heat transfer between the fluids, cooling fins are arranged between the flat tubes and fixed to the latter. In the heat exchanger disclosed by DE 198 13 989 A1, the surfaces of the cooling areas are fundamentally situated transversely to the direction of flow of the second fluid. This means that there is a flow resistance to the second fluid. Designing the cooling fins to obstruct the flow is purposely intended to reduce the rate of flow of the second fluid. This, on the one hand, increases the time which the second fluid spends flowing through the heat exchanger, that is to say the time in which the second fluid can absorb heat from a first fluid or transmit heat to this. On the other hand, however, the low rate of flow of the second fluid limits the amount of heat transferable between the first and the second fluid, that is to say the efficiency of the heat exchanger.
A further heat exchanger with cooling fins is disclosed, for example, by U.S. Pat. No. 4,676,304. In this heat exchanger the cooling fins lie fundamentally parallel to the direction of flow of the second fluid (in this case, air). Despite the formation of baffle louvers on the individual cooling fins, it is nevertheless impossible to prevent some of the second fluid that flows through the heat exchanger from flowing between adjacent cooling fins without absorbing significant amounts of energy from these or giving off energy to these fins. This problem is particularly important when the heat exchanger has small dimensions in the direction of flow of the second fluid. In this case a high mass flow of the second fluid does not necessarily result in a high heat transfer coefficient. Only a relative small proportion of the available temperature difference between the first and second fluid is utilized.
With integrated heat exchangers, the problem often arises that heat passes from one individual heat exchanger to the other via a common corrugated fin, i.e. via integrally formed corrugated fins of the individual heat exchangers. To reduce this undesirable heat transfer, it has been proposed, for example in EP 0 773 419 A2, to provide the integrated corrugated fin of a heat exchanger of this type with slots in a region between the two individual heat exchangers. However, this has the drawback that the air is swirled up in the region of the slot, thereby increasing the flow resistance and therefore the pressure drop for the air.
The object of the invention is to specify a heat exchanger of the type mentioned in the introduction having cooling fins which are designed to promote flow and which at the same time reduce thermal coupling between a plurality of first fluids.
According to the invention, this object is achieved by a heat exchanger having the features of claim 1. Here the heat exchanger has flat tubes through which first fluids can flow and which can be externally exposed to a second fluid, and which are arranged fundamentally parallel to one another and transversely to the direction of flow of the second fluid, in such a way that flow paths for the second fluid are formed, in which cooling fins are arranged, which in each case extend between adjacent flat tubes. The cooling fins here take the form of corrugated fins, multiple corrugated fins being arranged in series in the direction of flow of the second fluid and laterally offset in relation to one another, that is offset in the direction of flow of the first fluids. Successively offsetting the corrugated fins means that a very high proportion of the second fluid flowing through the heat exchanger is used for heat transfer. In the case of corrugated fins with gills, a greater overall mass flow of the second fluid may possibly flow through gills that are arranged in the area of that side of a fin on the downstream side for the second fluid than is the case without an offset between the corrugated fins. This may give rise to an increased heat transfer coefficient in this area. In addition, this has an influence on a thermal boundary layer, which may form at a tube wall, so that any heat transfer from the tube wall to the second fluid or vice-versa may be increased. The offset arrangement of the corrugated fins simultaneously reduces undesirable heat transfer between different rows of tubes via the corrugated fins, even though the fins are formed from one common strip. This in turn has manufacturing technology advantages, since a plurality of corrugated fins which are arranged in series and are formed from a common strip, i.e. as a single piece, can easily be inserted between the rows of tubes of the heat exchanger. The corrugated fins, including the gills, can be produced in particular by rolling from a metal strip.
A flow-enhancing design for the corrugated fins is preferably achieved in that their surfaces lie fundamentally parallel to the direction of flow of the second fluid, that is to say the normals to the surfaces of the corrugated fins fundamentally enclose a right angle with the direction of flow of the second fluid. This flow-enhancing design of the corrugated fins notwithstanding, the lateral offsetting of corrugated fins arranged in series ensures that only a smaller proportion of the second fluid flows between the flat tubes unused, that is to say without significant heat transfer, than is the case without such an offset. This advantage is all the more manifest the greater the spacing b between two fins. Two or three similarly shaped corrugated fins are preferably successively offset in relation to one another. In order to ensure a high heat transfer coefficient, the individual corrugated fins are preferably arranged directly adjoining one another, that is to say without any spacing in the direction of flow of the second fluid. This gives a large heat exchanger surface. Alternatively, a spaced arrangement of in this case narrower corrugated fins may be provided in order to reduce the flow resistance.
According to a preferred development, the corrugated fins have gills to direct the second fluid. A so-called swelling flow developing at the gills, which has a high temperature gradient in one area of the corrugated fin, ensures a better heat transfer between the second fluid and the corrugated fins.
All gills of a corrugated fin section enclosed between two flat tubes are preferably angled in the same direction in relation to the direction of flow of the second fluid. A uniform angling of the gills within a fin section has the advantage that, where necessary, the flow can thereby be purposely directed towards a downstream fin section.
The gills of successively offset fin sections are preferably angled in opposite directions, so as to define a longer flow path for the second fluid flowing through the heat exchanger. The gills of two adjacent gilled panels may also be angled in the same direction, it then possibly being advantageous for the gills of a gilled panel arranged upstream or downstream of the two adjacent gilled panels to be angled in the opposite direction to the gills of the two adjacent gilled panels.
A uniform coverage of the flow cross-section through which the second fluid passes is preferably achieved in that successively offset fin sections run parallel to one another. In this case the offset fin sections are preferably perpendicular to the flat tubes. If the fin surfaces deviate somewhat (up to approximately 6 degrees) from parallel, these surfaces in the context of the invention still being regarded as substantially parallel, this has scarcely any adverse effect on the thermodynamic advantages of the offset fins. The use of so-called V-fins or fins with any degree of rounding is equally feasible. The fin geometry according to the invention can be used, in particular, in motor vehicle heat exchangers such as radiators, heating elements, condensers and evaporators.
According to an advantageous development of the invention a gill depth LP in the range from 0.7 to 3 mm at a gill angle of 20 to 30 degrees improves efficiency, because this increases the flow angle, that is to say the deflection of the second fluid from one channel into the adjacent channel, in turn producing a longer flow path for the second fluid. The fin height for such a system advantageously lies in the range from 4 to 12 mm. The fin density for this system advantageously lies in the range from 40 to 85 fins/dm, corresponding to a fin interval or fin spacing of 1.18 to 2.5 mm.
Examples of embodiments of the invention will be explained in more detail below with reference to a drawing, in which:
Corresponding parts are provided with the same reference numerals in all figures.
Two (
Gills 7, which extend transversely to the direction of flow S2 of the second Fluid FL2 and transversely to the direction of flow S1 of the first fluid FL1 are formed out of the fin sections 4b, as can be seen in particular from
Two corrugated fins 3 arranged in series between two flat tubes 2 are offset in relation to one another by half the width b between two adjacent fin sections 4b. In the case of three corrugated fins 3 arranged in series, as shown in
Two or three adjacent corrugated fins 3, which extend over the depth T of the heat exchanger 1, are produced by rolling from one sheet 8. In rolling, the sheet 8 is cut in the area of the respective offset between the two (
The fin sections 4a of the corrugated fins 3 adjoining the flat tubes 2 do not have any gills. In this area therefore a laminar flow of the fluid FL2 tends to form more readily than in the fin sections 4b that are provided with gills 7 and which connect the adjacent flat tubes 2. Over a longer distance the laminar flow may lead to the formation of a boundary layer with falling temperature gradient at the flat tube 2. This effect is limited to an insignificant amount in that the flow of the second fluid FL2 forming between two adjacent fin sections 4b of a corrugated fin 3 is already disrupted even after the short distance T/2 (
According to the present invention two, three or even more similarly shaped corrugated fins (cooling fins) are preferably successively offset in relation to one another, that is to say the one corrugated fin with baffle louvers (gills) may be offset in multiple planes. At the same time the number of corrugated fins which are arranged in series, viewed in the direction of flow of the second fluid, may be chosen as a function of the depth of the heat exchanger and/or the depth of the corrugated fins. For example, 2, 3 or more rows may be used for an overall depth of 12 to 18 mm, 2, 3, 4 or more rows for an overall depth of up to 24 mm, 2, 3, 4, 5 or more rows for an overall depth of up to 30 mm, 2, 3, 4, 5, 6 or more rows for an overall depth of up to 36 mm, 2, 3, 4, 5, 6, 7 or more rows for an overall depth of up to 42 mm, 2, 3, 4, 5, 6, 7, 8 or more rows for an overall depth of up to 48 mm, 2, 3, 4, 5, 6 7, 8, 9 or more rows for an overall depth of up to 54 mm, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more rows for an overall depth of up to 60 mm, and 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or more rows for an overall depth of up to 66 mm.
More than two offset rows can preferably be distributed on a total of two planes offset in relation to one another, as in the embodiments in
Alternatively, just the area 41 or 44 between two gilled panels 39, 40 and 42, 43 lying in one plane can be offset in relation to the gilled panels 39, 30 and 42, 43 (
The gilled panels 45, 46, 47 of the corrugated fin 10k may also be of different sizes (
A combination of differently sized gilled panels 65, 66, 67, 68, 69 in different planes is also possible, as for the corrugated fin 101 (
The number of gills per row is between 2 and 30 gills, for example, depending on the number of rows and the depth of the heat exchanger. For production engineering reasons the number of gills per gill panel is preferably not identical in the case of an odd number of rows, that is 3, 5, 7, 9, or 11 rows. With an even number of rows, the number of gills per gilled panel may be identical, although this is not essential.
A simulation of an air flow through a heat exchanger having three different corrugated fin configurations is explained below (
The simulation is performed under the following conditions: tube temperature=60°; air inlet temperature=45° C.; air density=1.097 kg/m3; air inlet velocity vL=1 and 3 m/s, fin height=8 mm, fin depth=16 mm. The simulation is partly based on a consideration of one corrugated fin in a row, that is without offset, consisting of a row with two gilled panels separated from one another by a roof-shaped web (prior art). In addition, one corrugated fin with 2 rows and one corrugated fin with 3 rows are considered. In addition to the air-side pressure drop, the simulation also determines the mass flow through the individual louvered openings and the radiated output from the tube to the cooling air.
As can be seen from
As can be seen from
Two (
Gills 7, which extend transversely to the direction of flow S2 of the second fluid FL2 and transversely to the direction of flow S1 of the first fluid FL1a,b are formed out of the fin sections 4b. The gills 7 within a fin section 4b on the one hand produce an especially good heat transfer between the second fluid FL2 and this fin section 4b, and on the other purposely direct the second fluid FL2 to the fin section 4b arranged obliquely behind in the direction of flow S2. In this way virtually full use is made of the mass flow of the second fluid FL2 passing through the heat exchanger 1, efficiently exploiting the temperature difference between the first fluids FL1a,b and the second fluid FL2 for the transfer of heat.
Two corrugated fins 3 arranged in series between two flat tubes 2 are offset in relation to one another. These offset, integrally formed corrugated fins are produced, for example, as explained in connection with
In the intermediate region 9 between the flat-tube rows 1a,b illustrated on a larger scale in
Claims
1. A heat exchanger, especially for motor vehicles, having flat tubes through which first fluids can flow and which can be externally exposed to a second fluid and which are arranged fundamentally parallel to one another and transversely to the direction of flow of the second fluid in at least two rows, each first fluid being assigned at least one row of tubes, with the flat tubes in a row of tubes being spaced apart forming flow paths for the second fluid passing through the heat exchanger, cooling fins being arranged in the flow paths, which in each case extend between adjacent flat tubes, wherein multiple corrugated fins, which are arranged in series in the direction of flow of the second fluid and laterally offset in relation to one another, are provided as cooling fins and in that multiple corrugated fins arranged in series are formed from a common strip.
2. The heat exchanger as claimed in claim 1, wherein the surfaces of the corrugated fins are arranged fundamentally parallel to the direction of flow of the second fluid.
3. The heat exchanger as claimed in claim 1, wherein multiple offset corrugated fins (3) are similarly shaped.
4. The heat exchanger as claimed in claim 1, wherein at least one of the corrugated fins (3) has gills (7) for directing the second fluid (FL2).
5. The heat exchanger as claimed in claim 4, wherein all gills of a fin section bounded by two flat tubes are angled in the same direction relative to the direction of flow of the second fluid.
6. The heat exchanger as claimed in claim 5, wherein the gills of two successively offset fin sections are angled in the same direction.
7. The heat exchanger as claimed in claim 5, wherein the gills of two successively offset fin sections are angled in opposite directions.
8. The heat exchanger as claimed in claim 1, wherein two successively offset fin sections are fundamentally parallel to one another.
9. The heat exchanger as claimed in claim 8, wherein the fin sections e are arranged fundamentally perpendicular to the flat tubes.
10. The heat exchanger as claimed in claim 1, wherein the corrugated fins (3) extend for an equal or similar distance in the main direction of flow of the second fluid.
11. The heat exchanger as claimed in claim 1, wherein different rows of tubes have different fluids flowing through them.
12. The heat exchanger as claimed in claim 1, wherein one fluid flows through different rows of tubes.
Type: Application
Filed: Aug 4, 2004
Publication Date: Nov 22, 2007
Applicant:
Inventor: Gerrit Wolk (Stuttgart)
Application Number: 10/571,295
International Classification: F28F 1/12 (20060101);