FIN FOR A HEAT EXCHANGER
A fin for a heat exchanger, comprising a fin plate which is corrugated in a longitudinal direction and which is arranged between two structures and comprising a multiplicity of fin flanks formed by the corrugation, wherein the fin plate can be traversed in a depth direction by a flow of an in particular gaseous fluid for the purpose of transferring heat between the structures and the gaseous fluid, and wherein a multiplicity of gills with a gill depth and with a gill angle with respect to the depth direction is provided in the fin plate, said gills being arranged one behind the other on the fin flanks, running on a neutral line and extending substantially transversely with respect to the depth direction. The fin flanks have, at least in regions, a substantially undulating structure profile, resulting in an arrangement of the gills which runs on an undulating neutral line.
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The invention relates to a fin for a heat exchanger according to the preamble of claim 1.
In present-day heat exchangers, for example coolant coolers or charge air coolers, fins with gills, which are produced as corrugated fins by means of a rolling process, are often used for the transfer of heat to the air or to a gas to be cooled. These corrugated fins are soldered to tubes or disks in order thereby to ensure the transfer of heat. For example, corrugated fins with oblique gills are known. Corrugated fins with oblique gills are used because they make it possible, inter alia, to have a rapid and cost-effective production process. Their shape depends greatly upon the production process, and as regards their function as a heat-transmitting fin they represent a compromise which has weaknesses for the actual task of low-loss heat transfer.
For example, the corrugated fins are produced by a rolling process in which a pair of forming rollers emboss in a metallic strip, for example aluminum, a wavy structure in which each upswing and downswing constitutes a fin. The gills arise in that the rollers are composed of a plurality of disks where each is ground such that, during rolling, gills are also cut into the strip in addition to the wavy structure. In this case, the gills usually have a constant gill depth and a constant gill angle. This makes it possible to use a large number of identical parts in tool making. Alternatively, there are processes in which the gills are cut into the flat strip material and the fins are corrugated only thereafter. The gill angle usually amounts to between 20° and 30°. This is intended to serve the purpose of adapting the ratio of pressure loss and heat transfer to the local flow state.
DE 10 2009 021 179 A1 discloses a fin for a heat exchanger, in which the gills have a gill angle of between 14° and 30° and a gill depth either in the range of 0.3 mm to 0.6 mm or in the range of 1.1 mm to 1.8 mm.
Tests have revealed, however, that, in practice, constant gill angles and constant gill depths disclose, inter alia, the following weaknesses:
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- deflection and impact losses, particularly in the first gill, during deflection in the middle and in the last gill;
- losses due to breakaway: breakaways also occur at the deflections within wide Reynolds' number ranges and mean that the following gill is located in the breakaway zone and is not correctly used;
- in an identical distribution of gill depth and gill angle, what may happen in the case of conventional fin densities is that gills come into alignment in the flow direction after only one gill length and there is therefore no boundary layer restart.
- with gills which vary in the flow direction, uneven flow cross sections arise which lead to pressure losses and an unequal distribution of the mass flow density.
The object on which the invention is based is to provide a fin of the type initially mentioned, by means of which the weaknesses or loss mechanisms described can be significantly improved or reduced.
This object is achieved by means of a fin having the features of claim 1. Advantageous refinements are the subject matter of the sub claims.
The object is achieved, according to the invention, in that the fin flanks have, at least in regions, an essentially wavy structural profile, thus giving rise to an arrangement of the gills which runs along a wavy neutral line. The individual gills are arranged directly in succession to one another on a neutral line or are formed around this. This allows a uniform distribution of the flow cross sections and optimal utilization of the gills. The wave shape must preferably be selected such that the vertical offset of the gills due to the wavy structure compensates the difference in the vertical attitude of the successive gills on account of different gill angles. Thus, successive gills preferably have at least slightly different gill angles. The gills in this case run with their axial longitudinal mid point on the wavy neutral line and are preferably rotated slightly differently about the longitudinal midpoint. Depending on the number of gills or on the length of the fin flank, at least two gills having the same orientation may also subsequently be provided. To improve mechanical stability, the fin flanks are regularly arranged at an angle to one another, but may also run parallel to one another, as required.
In one embodiment, the neutral line has a continuous wavy profile with at least one wave portion such that the wave portion, commencing in parallel to the main flow direction, rises continuously in an arc to maximum deflection and then falls again correspondingly to the rise such that it runs out parallel to the main flow direction. It in this case essentially resembles a cosine profile of 0° to 360°. The wavy neutral line in this case differs markedly from a production-induced deformation of the neutral line which runs either in a V-shaped manner or in a circle-like arc without any significant inflections.
Preferably, a plurality of successive wave portions may be provided for each fin flank. The ultimate number of wave portions may depend on the length of the fin flank. Where very deep systems are concerned, it may be expedient to select the wavelength such that a plurality of wave portions arise in the flow direction. Consequently, the maximum deflection of the flow can be limited and the heat exchanger matrix at the tube ends can be better utilized.
In a further embodiment, at least one first and one second gill group are provided for each wave portion, to which case the gill angles of the gill groups may have different orientations. Thus, for example, a fluid can be conducted through the fin plate first in one direction and then in the opposite direction.
Advantageously, due to the adjacent gills of two fin flanks, an unaligned arrangement of the individual gills with respect to one another is obtained.
For example, the gill angle may amount to between 20° and 60°, preferably to between 30° and 50°. If appropriate, the gill angle may even be lower, for example if it is not possible to have a weaker rating by means of a reduced fin density. This may be necessary, for example when the internal pressure resistance requirement necessitates a support of cooler tubes by means of a high fin density.
The fin density in the longitudinal direction preferably amounts in general to between 70 fin/dm and 120 fin/dm. The unit fin/dm is in this case to be understood to mean the number of fin flanks per decimeter given by the corrugation.
The deflection per fin ideally amounts to no more than 7°. If the number of gills is very high so that a deflection of less than 7° will be necessary per fin in order to achieve overall deflection as far as the middle of the gill field, a plurality of gills may also be formed identically, thus reducing the tool complexity. Ideally, the gills are arranged such that the free flow cross section matching the gills amounts to ⅓ of the spacing between the fins (reciprocal value of the fin density). The uniform distribution of the flow to the gills is thus achieved. In this case, the neutral line also reaches an offset of approximately ⅓ of the fin spacing in the middle. More specifically, the wavy neutral line may have in the highest wave region an offset of preferably ⅓ to the straight portions of adjacent fin flanks.
Moreover, according to claim 9, the object of the invention is achieved for a heat exchanger by the provision of a fin according to the invention.
In an advantageous organization of details, the heat exchanger is designed as a heat exchanger of a motor vehicle, in particular as an electric heating body, liquid-operated heating body, evaporator or condenser of a vehicle air conditioning system, charge air cooler or coolant cooler. In motor vehicles, optimizing the heat exchanger performance for given construction space is an especially stringent requirement. The fin according to the invention is in this case suitable particularly for use with a heating body, since, for a given airstream and a given temperature difference, said fin makes it possible to have an especially low pressure drop. This reduces noises and makes it possible, for example, for a heating blower to have a particularly low rating. In the case of a heat exchanger in the form of an electrically operated heating body, the structures are designed, for example, as electric heating bars, preferably PTC heating elements (PTC=Positive Temperature Coefficient). In a possible alternative version of the heating body, the structures may also be flat tubes or round tubes, in which, for example, heated coolant of an engine cooling circuit flows.
Further advantages, features and details of the invention may be gathered from the following description in which exemplary embodiments of the invention are described with reference to the drawings. In this case, the features mentioned in the claims and in the description may be essential in the invention in this case individually in themselves or in any desired combination.
In the drawings:
Provided on the fin plate 2 are a plurality of gills 5 which are arranged one behind the other on the fin flanks 3 and run on a wavy neutral line 4 and which extend essentially transversely with respect to the depth direction.
The fin flanks 3 have, at least in regions, an essentially wavy structural profile, thus giving rise to the arrangement of the gills 5 in which these run on the wavy neutral line 4.
The gills 5′ are arranged in succession about an axial longitudinal midpoint 7 on the neutral line 4′ and arranged so as to be in each case offset slightly to the adjacent gill 5′. The neutral line 4′ around which the gills 5′ are formed is thus not made straight (see L1), as has been customary hitherto, but instead along the wavy neutral line 4′. This arrangement allows the uniform distribution of the flow cross sections 8 and optimal utilization of the gills 5′. In this case, an unaligned arrangement of the individual gills 5′ with respect to one another (see 9) is obtained by means of the adjacent gills 5′ of two fin flanks 3′, 3″.
The gills 5′ have a gill angle KW which preferably amounts to between 30° and 50°.
A marginal gill 5a and 5b is provided in each case at the start of the first gill group 10 and at the end of the second gill group 11. Between the gill groups 10, 11, a roof gill 5c is in each case provided, which ensures a crossover between the differently oriented gill groups 10, 11.
The gills 5′ are arranged such that the free flow cross section between the gills 5′ preferably amounts to ⅓ of the spacing between the fin flanks. A uniform distribution of the flow to the gills 5′ is consequently achieved. In this case, the neutral line 4′ also reaches an offset of approximately ⅓ of the fin spacing in the middle M.
Claims
1. A fin for a heat exchanger, comprising a fin plate corrugated in a longitudinal direction and arranged between two structures, and a plurality of fin flanks formed by the corrugation, a particularly gaseous fluid for the transmission of heat between the structures and the gaseous fluid being capable of flowing through the fin plate in a depth direction, and there being provided in the fin plate a plurality of gills which are arranged one behind the other on the fin flanks and run on a neutral line and which extend essentially transversely with respect to the depth direction, with a gill depth and a gill angle with respect to the depth direction, wherein the fin flanks have, at least in regions, an essentially wavy structural profile, thus giving rise to an arrangement of the gills which runs on the wavy neutral line.
2. The fin as claimed in claim 1, wherein the neutral line has a continuous wavy profile with at least one wave portion such that the wave portion, commencing in parallel to the main flow direction, rises continuously in an arc to maximum deflection and then falls again correspondingly to the rise such that it runs out parallel to the main flow direction.
3. The fin as claimed in claim 2, wherein a plurality of successive wave portions are provided for each fin flank.
4. The fin as claimed in claim 1, wherein at least one first and one second gill group are provided for each wave portion, gill angles of the gill groups having different orientations.
5. The fin as claimed in claim 4, the orientations being designed in such a way that an unaligned arrangement of the individual gills with respect to one another is obtained by means of the adjacent gills of two fin flanks.
6. The fin as claimed in claim 1, wherein the gill angle amounts to between 20° and 60°, preferably to between 30° and 50°.
7. The fin as claimed in claim 1, wherein the maximum deflection per fin flank preferably amounts to 7°.
8. The fin as claimed in claim 1, wherein the wavy neutral line has in the highest wave region an offset of preferably ⅓ to the straight portions of adjacent fin flanks.
9. A heat exchanger, comprising a fin as claimed in claim 1.
10. The heat exchanger as claimed in claim 9, wherein the heat exchanger is designed as a heat exchanger of a motor vehicle, in particular has an electric heating body, liquid-operated heating body, evaporator of a vehicle air conditioning system, condenser of a vehicle air conditioning system, charge air cooler or coolant cooler.
Type: Application
Filed: Feb 17, 2012
Publication Date: Dec 5, 2013
Applicant: BEHR GMBH & CO. KG (Stuttgart)
Inventor: Eberhard Pantow (Winnenden)
Application Number: 13/985,936
