Heat Exchanger
The invention relates to a heat exchanger and a rib (1), in particular a corrugated rib (1), especially for a flat tube heat exchanger, in particular a coolant or charge-air cooler for motor vehicles. The corrugated rib (1) is arranged between flat tubes (3) of the heat exchanger, is connected thereto in a material fit, comprises gills (6, 8), can be exposed to a flow of air and comprises moulded reinforement means.
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The invention relates to a heat exchanger, such as, in particular, a flat tube heat exchanger, and to a fin, such as, in particular, a corrugated fin, for example for a flat tube heat exchanger, in particular for a coolant or charge-air cooler or condensers or evaporators for motor vehicles according to the precharacterizing clause of patent claim 1.
Heat exchangers of this type have been disclosed by EP 0 547 309 B1 by the applicant.
Corrugated fins and flat tubes form a soldered cooling system in which a medium to be cooled, for example a coolant or charge air, flows through the flat tubes and a cooling medium, for example ambient air, flows over the corrugated fins. Soldered cooling systems of this type are used for coolant coolers for cooling an internal combustion engine or as charge-air coolers, for cooling the compressed intake air of internal combustion engines in motor vehicles. Heating elements or condensers or evaporators, for example, are also of similar construction. Fins can also be used in mechanically joined heat exchangers in which the fins and the tubes of the heat exchangers are connected mechanically to one another.
Development tends to go in the direction of higher pressures for the medium to be cooled, in particular in the coolant circuit, with the flat tubes being of extremely slender design on account of the lower pressure drop on the air side, and therefore being extremely unstable to increased internal pressure. The flat tubes therefore tend to “swell”, i.e. to form a bulge, under internal pressurization. This bulge can be counteracted from the inside and outside: in the interior of the flat tube, use is made of soldered-turbulence inserts which act as tie rods, and corrugated fins exert a supporting effect on the flat tubes from the outside. The-flat tubes are provided with gills to improve the heat transfer, which has disadvantages in terms of strength. The corrugated fins therefore tend to buckle at higher internal pressure loading of the flat tubes.
It has therefore been proposed in U.S. Pat. No. 4,693,307-A to mold a stiffening bead into the center of a gilled panel, i.e. an individual double gill which is designed in the shape of a roof and at the same brings about a deflection of the flow.
EP 0 547 309 B1by the applicant has disclosed a corrugated fin for flat tubes, in which a stiffening bead is arranged between two gilled panels and in the center of the flat tube, i.e. the point at which the greatest buckling stress occurs for the corrugated fin. However, only a spot-type stiffening of the corrugated fin is achieved with this, which is no longer adequate if the stress increases as a consequence of increased internal pressure.
It is the object of the present invention to improve a corrugated fin of the type mentioned at the beginning with regard to its supporting effect without its thermodynamic properties, such as heat transfer and pressure drop, being adversely affected.
This object is achieved by the features of patent claim 1 and of claim 11. According to the invention, the stiffening means are integrated in the gills, i.e. in principle all of the gills of the corrugated fin contribute to the supporting effect. The flat tubes are therefore supported over their entire length by a stiffened corrugated fin. Each individual gill advantageously has a buckle-proof profile with which the entire corrugated fin obtains increased security against buckling.
According to an advantageous refinement of the invention, the profile of each gill has an S-shaped cross section. This achieves the advantage of a greater moment of resistance to buckling without the pressure drop on the air side-over the corrugated fin increasing significantly—in contrast, even a lower pressure drop is to be expected. The gills of S-shaped design in cross section therefore have, in contrast to the prior art, a variable gill angle which initially rises from a very low value to a maximum value in the center of the gill length and then goes back again to a minimum value. A “gentle” deflection of the air flow is therefore achieved without—as in the prior art—loss-affected eddies occurring at the incident-flow edge and flow-off edge of the gills. An unexpected combination effect turns out to be advantageous by the buckling resistance of the gills being increased and their pressure drop being reduced at the same time.
According to a further advantageous refinement of the invention, the cross section of the gills is bent twice and has an approximately Z-shaped profile, i.e. the gill bent in accordance with the invention has three gill angles, with the gill angle jumping at the first buckling point from a low to a high value and jumping again at the second buckling point to the low value. In comparison to the S-shape, the Z-shape therefore has a discontinuous profile of the gill angle over the gill length, which affords simplification in terms of manufacturing. Moreover, the advantage is also achieved here of increased buckling resistance, associated with a reduced pressure drop.
According to further advantageous refinements of the invention, advantageous angle dimensions are indicated both for the S-shaped and for the Z-shaped cross section of the gill. In this case, in particular the low incident-flow angle and flow-off angle are advantageous because, as a result—as already mentioned—a formation of eddies behind the incident-flow edge and flow-off edge is avoided. At the same time, the heat transfer capacity of the corrugated fin is not made worse, since, as before, a new starting of the thermal boundary layer takes place at each incident-flow edge of a gill. This mechanism is responsible for a large part of the heat transmission. Finally, the advantage is also achieved thereby that the entire heat exchanger is improved in respect of its efficiency.
Exemplary embodiments of the invention are illustrated in the drawing and are described in more detail below. In the drawing
The production of the above-described gills, i.e. both with an S-profile and with a Z-profile, takes place in a similar manner as in the prior art, i.e. by means of “ribbed cutting rollers”, which cut the gills out of a planar sheet-metal strip and shape them.
Claims
1. A fin, in particular corrugated fin, in particular for a flat tube heat exchanger, in particular a coolant or charge-air cooler for motor vehicles, the fin being arranged between flat tubes of the heat exchanger or being arranged perpendicularly to them and being connected to them with a cohesive material joint or mechanically, being provided with gills and being able to be flowed over by air and having molded stiffening means, characterized in that the stiffening means are integrated in the gills.
2. The fin as claimed in claim 1, wherein the gills have a buckle-proof profile which deviates from a straight line or a rectangular profile.
3. The fin as claimed in claim 2, wherein the profile has an S-shaped cross section with two rounded portions.
4. The fin as claimed in claim 2, wherein the profile has a cross section which is bent twice, three times or multiple times, for example an approximately Z-shaped cross section.
5. The fin as claimed in claim 2, wherein the profile has an approximately V-shaped cross section which is bent once.
6. The fin as claimed in claim, wherein cross section has an incident-flow region and a flow-off region and a deflecting region arranged between them, the incident-flow region and flow-off region respectively having an incident-flow angle and flow-off angle (αs, αz) of approximately the same size, and the deflecting region having a deflecting angle (βs, βz), in that the deflection angle is greater than the incident-flow angle and flow-off angle, i.e. βs>αs and βz αz.
7. The fin as claimed in claim 1 wherein the following ranges apply for the angles αs and βs:
- 0 αs≦10 degrees, and
- 15 βs≦35 degrees.
8. The fin as claimed in claim 1 wherein the following ranges apply for the angles αs and βs:
- 0 αs≦5 degrees, and
- 20 βs≦30 degrees.
9. The fin as claimed in claim 1 wherein the following ranges apply for the angles αz and βz:
Type: Application
Filed: Dec 6, 2004
Publication Date: Aug 14, 2008
Applicant:
Inventor: Wolfgang Kramer (Weinstadt)
Application Number: 10/585,665
International Classification: F28D 1/02 (20060101); F28F 1/02 (20060101);