US20100193172A1

US20100193172A1 - Fin for a heat exchanger

Info

Publication number: US20100193172A1
Application number: US12/697,586
Authority: US
Inventors: Hermann Knaus; Florian Schmidt; Stefan ROESLER
Original assignee: Behr GmbH and Co KG
Current assignee: Mahle Behr GmbH and Co KG
Priority date: 2007-07-31
Filing date: 2010-02-01
Publication date: 2010-08-05
Also published as: DE102007036308A1; CN101790671B; DE502008002244D1; EP2185884A1; WO2009015805A8; ATE494521T1; CN101790671A; WO2009015805A1; EP2185884B1

Abstract

A fin for a heat exchanger is provided that includes a fin element which extends in a flow direction of a first fluid and has a wall face around which the first fluid flows on both sides, wherein at least one flap is provided in the wall face, which flap forms a cutout, through which the first fluid can flow, in the wall face, wherein a first straight edge of the flap extends substantially perpendicularly to the flow direction and is arranged at a distance from the wall face in order to form the cutout, wherein the flap has an inclined, smooth tab face which terminates at the first straight edge, and wherein the tab face is connected to the wall face via two side walls of the tab, which side walls have a curved profile mirror-symmetrically with respect to each other and, starting from the first edge, have a height which decreases in a manner corresponding to the inclination of the tab face.

Description

This nonprovisional application is a continuation of International Application No. PCT/EP2008/005983, which was filed on Jul. 22, 2008, and which claims priority to German Patent Application No. DE 10 2007 036 308.9, which was filed in Germany on Jul. 31, 2007, and which are both herein incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a fin for a heat exchanger.
2. Description of the Background Art
Heat exchangers are known in which fins are provided in channels through which fluid flows in order to improve the capacity of the exchanger. Such fins can be designed, for example, in the form of smooth fins, gill-shaped fins or also in the form of web fins. In the first case, as a result of the extensively laminar flow, only a relatively small improvement in the performance of the exchanger is achieved, although the drop in pressure of the fluid caused by the fins is also relatively small. Web fins show a particularly clear improvement in the performance of the exchanger for a given size, but also often mean an undesirably large drop in pressure across the flow channel. Amongst other applications, web fins are used in charge air coolers of motor vehicles, predominantly on the charge air side.
DD 0 152 187 describes a strip-shaped tubular installation element for tube bundle heat exchangers in the petrochemical industry field with which trapezoidal flaps are provided for producing turbulence. The flaps have a variable width in the flow direction, wherein the flaps are bent out from the strip by an angle of more than 30° about a longer of two parallel edges of the trapezium.
Research Memorandum Number RM A9L29 of the National Advisory Committee for Aeronautics (NACA), Washington, USA, of 23 Feb. 1950 describes a submerged air inlet for aircraft wings which were being investigated with regard to their flow behaviour in a speed range from Mach 0.6 to Mach 1.08.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a fin for a heat exchanger whose heat transmission is improved for a given drop in pressure.
According to an embodiment, as a result of two mirror-symmetrical side walls of the flaps which have a curved profile with respect to one another and which are oriented perpendicular to the wall face and which, starting from the first edge, have a height which decreases in a manner corresponding to the inclination of the tab face, an improved air flow is achieved in the area of the flaps, as a result of which a greater quantity of heat is transmitted between air and fin for a given drop in pressure.
In an embodiment, the first edge, end-side edges of the side walls, and a second straight edge of the wall can form a rectangle which is oriented perpendicularly to the flow direction and through which the first fluid can flow. A long side of the rectangle can correspond to the first edge and can have a length which is approximately five times the length of short side of the rectangle. The length of the tab face in the flow direction is approximately eight times the length of the short sides of the rectangle. At the same time, the flap can be designed mirror-symmetrically with respect to a central plane of symmetry, and furthermore a width of the tab face preferably reduces with increasing distance from the first edge. In doing so, an end of the tab face opposite the first edge has a smallest width, wherein the smallest width advantageously is no more than one tenth, in particular about one twelfth of the length of the first edge. The curve of one of the side walls also has at least one point of inflection in its course with regard to the direction of curvature. In a preferred embodiment, the inclination of the tab face with respect to the wall face is approximately seven degrees. Overall, this provides a hood-like tab with a particularly low drop in pressure with good heat transfer of the air flowing through it, as has been shown by trials.
In an embodiment, the shape of the tab face starting from the first edge can have approximately the parameterisation [0; 2.500], [0.805; 2.470], [1.610; 2.290], [2.420; 1.910], [3.220; 1.540], [4.030; 1.210], [4.840; 0.980], [5.640; 0.780], [6.440; 0.590], [7.240; 0.400], [8.050; 0.210]. This parameterisation is understood to mean that the first value in each case specifies the distance from the first edge and the second value in each case specifies the distance from a central axis of symmetry to one of the two mirror-symmetrical side walls. Apart from a considerable scaling factor, this parameterisation corresponds to the shape of the air inlet described in the NACA report RM A9L29.
In a further embodiment, the fin can have a plurality of flaps arranged one after the other in the direction of flow, which, particularly in the case of long fins, results in an expedient arrangement for the purpose of deflecting the air several times over the length of the fin. Otherwise, the air flow would only be advantageously affected by the flap over part of the fin.
Furthermore, at least two flaps with different opening directions can be provided in the wall face. As a result of such an alternating arrangement of the flap opening directions, heat can be exchanged with the flowing air particularly uniformly on both sides of the fin.
The invention also relates to a heat exchanger having at least one fin.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

FIG. 1 shows a spatial representation of a first exemplary embodiment of a fin according to the invention;

FIG. 2 shows a scale plan view on a flap of a fin according to the invention from above; and

FIG. 3 shows a spatial representation of a second exemplary embodiment of a fin according to the invention.

DETAILED DESCRIPTION

The exemplary embodiment of the invention shown in FIG. 1 comprises a fin 1 made from an aluminium sheet which has been folded several times. A flow channel 2, through which a first fluid of the heat exchanger, in this case air, flows in the direction of the arrow A or also in the opposite direction as shown by the arrow A′, is formed between two parallel wall faces 1 a. The heat exchanger is designed so that a plurality of the fins 1 are arranged adjacent to one another to form parallel adjacent flow channels 2. Exchanger tubes or separating walls (not shown), which form the boundary of a second fluid, are connected to the surface of the fins 1 above and below the fins 1.
A flap 3 which has a smooth tab face 4 and is inclined with respect to the sidewall 1 a is arranged in at least one of the side walls 1 a of the fin 1. The angle of inclination is approximately 7°.
The tab face 4 has a first straight edge 5 which extends perpendicular to the flow direction A, A′ and parallel to the wall face 1 a.
A cutout which is coincident with the tab face and which has a second straight edge 6 is provided in the wall face 1 a. At the same time, the tab face 4 is connected to the wall face 1 a of the fin by means of two side walls 7, 8 which have a curved profile and are arranged mirror-symmetrically with respect to an axis of symmetry S of the flap and to each other. The side walls 7, 8 of the flap are perpendicular to the wall face 1 a of the fin 1. Corresponding to the inclination of the tab face 4, the height of the side walls 7, 8 increases in the flow direction A and decreases in the opposite, likewise possible, flow direction A′. At the same time, edges 7 a, 8 a with the maximum height of the side walls 7, 8 are formed at the end and lie in one plane with the first straight edge 5 of the tab face and the second straight edge 6 of the wall face 1 a, wherein the four edges 5, 6, 7 a, 8 a form a rectangular aperture or opening 9 perpendicular to the wall face 1 a. The rectangle 9 has a side ratio of 1:5, the long sides of the rectangle being formed by the first and second straight edge 5, 6.
In the flow direction A, the curved, mirror- symmetrical side walls 7, 8 are initially at a smallest distance from one another at their beginning, the distance growing steadily over the length L of the tab face. At both the beginning of their path and at the end, the side walls run approximately parallel to the axis of symmetry S so that at the end of their path they meet the first and second straight edge 5, 6 approximately at right angles (see FIG. 2).
Corresponding to the inclination of about 7°, the length L of the tab face 4 is approximately eight times the maximum height of the side walls 7, 8.
The side walls 7, 8 change their direction of curvature approximately halfway through their path so that the curve has exactly one point of inflection. A parameterisation of the path of the side walls of the preferred exemplary embodiment is:
[0; 2.500], [0.805; 2.470], [1.610; 2.290], [2.420; 1.910], [3.220; 1.540], [4.030; 1.210], [4.840; 0.980], [5.640; 0.780], [6.440; 0.590], [7.240; 0.400], [8.050; 0.210].
Here, the first number of a coordinate pair [x; y] in each case means the distance starting from the first edge 6 in the direction of the axis of symmetry S, that is to say in the opposite direction to the flow direction A. The second number y describes the perpendicular distance of a side wall from the axis of symmetry S at this point. In these non-dimensional relative units, the side walls 7, 8 have a maximum height of approximately 1.0 and the maximum width B of the tab face 4 which runs along the first straight edge is correspondingly 5.0.
As a result of the hood-like form of the flap described above with an inclined tab face and ascending side walls in the flow direction, the air flowing through the flow channel 2 along the wall face 1 a can pass through the opening 9, wherein it both swirls and is exchanged with an adjacent flow channel. The ascending path of the tab face and the curved diverging side walls result in a form which is particularly favourable for dynamic flow and which achieves a good exchange of heat with a low drop in pressure.
An improvement of the fin according to the invention is shown in FIG. 3 in which a plurality of flaps 3 are arranged one behind the other in the direction of flow. Here, two consecutive flaps are shown reversed with regard to their opening direction in the wall face 1 a, that is to say alternating. This achieves a uniform and optimum swirling of the air particularly with long flow channels 2.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.

Claims

1. A fin for a heat exchanger comprising:

a fin element configured to extend in a flow direction of a first fluid and has a wall face around which the first fluid flows on both sides; and

at least one flap provided in the wall face, the flap forming an aperture through which the first fluid can flow into the wall face, a first straight edge of the flap being configured to extend substantially perpendicular to the flow direction and being arranged at a distance from the wall face to form the aperture,

wherein the flap has an inclined, smooth tab face that terminates at the first straight edge, and

wherein the tab face is connected to the wall face via two side walls of the tab, which side walls have a curved profile mirror-symmetrically with respect to one another and, starting from the first edge, have a height which decreases in a manner corresponding to the inclination of the tab face.

2. The fin according to claim 1, wherein the first edge, end-side edges of the side walls, and a second straight edge of the wall face form a rectangle that is oriented substantially perpendicularly to the flow direction and through which the first fluid is flowable.

3. The fin according to claim 2, wherein a long side of the rectangle corresponds to the first edge and has a length that is approximately five times the length of a short side of the rectangle.

4. The fin according to claim 2, wherein the length of the tab face in the flow direction is approximately eight times the length of short sides of the rectangle.

5. The fin according to claim 1, wherein flap is mirror-symmetrical with respect to a central axis of symmetry.

6. The fin according to claim 1, wherein a width of the tab face reduces with increasing distance from the first edge.

7. The fin according to claim 6, wherein an end of the tab face opposite the first edge has a smallest width, and wherein the smallest width is no more than one tenth, in particular about one twelfth of the length of the first edge.

8. The fin according to claim 1, wherein a curve of one of the side walls has at least one point of inflection in its course with regard to a direction of curvature.

9. The fin according to claim 1, wherein an inclination of the tab face with respect to the wall face is approximately seven degrees.

10. The fin according to claim 1, wherein a shape of the tab face starting from the first edge has approximately the parameterisation [0; 2.500], [0.805; 2.470], [1.610; 2.290], [2.420; 1. 910], [3.220; 1.540], [4.030; 1.210], [4.840; 0.980], [5.640; 0.780], [6.440; 0.590], [7.240; 0. 400], [8.050; 0.210], wherein the first value in each case specifies the distance from the first edge and the second value in each case specifies the distance from a central axis of symmetry to a side wall.

11. The fin according to claim 1, wherein the fin has a plurality of flaps arranged one after the other in the direction of flow.

12. The fin according to claim 1, wherein at least two flaps with different opening directions are provided in the wall face.