Undulated heat exchanger fin

DESCRIPTION

Heat exchangers of the type of tubes and fins are well known in the prior art. Such heat exchangers are particularly well suited for use as oil coolers in cars because of their reduced weight and compact size. The configuration of the fins is of extreme importance to promote an efficient transfer of heat from the hot fluid to the cooling fluid. Several sets of the prior art have different configurations of fins, which are all oriented towards the same result: interrupt the boundary layer of hot fluid through the fins to promote turbulence that increases heat transfer.

The United States patent, No. 4,300,629 in the name of Hatada et al., Presents a tube type heat exchanger. The fins are provided with a plurality of blind-shaped elements. These blind-shaped elements have different heights such that their edges are displaced in the direction perpendicular to the plane of the fin. This configuration serves to promote turbulence and ensure more efficient heat transfer.

In the United States patent, n^°4,550,776 in the name of Lu published on November 5, 1985, another fin design is intended to be used in a heat exchanger of the type of tubes and fins. The fin was provided with a plurality of groups of blind-shaped elements. The groups of blind-shaped elements extend radially from each of the tube holes to the next adjacent tube hole in each of six directions. The lower groups are arranged in such a way that they promote mixing only in one direction. This means that the circulation is directed only to one side of the fin. In this arrangement the circulation is not mixed in a lateral direction. In addition the crests of the elements in the form of a blind, include holes and are not interconnected. This decreases the amount of surface air available for heat transfer from the fluid that passes over the fin.

In United States Patent No.^°2,360,123 in the name of Gerstung et al., Published on October 10, 1984, an oil cooler is described. The oil cooler includes a plurality of tubes through which the hot fluid passes. In the inside of the tubes arranged one Estaon corrugated sheets. The ridges of the corrugations are attached to the tubes through which the hot fluid passes. Because the crests are attached to the tubes, they become an integral part of them. This eliminates the ridges as an available surface for heat transfer. Therefore, only the parts between the available bead ridges as heat transfer surfaces.

In JP-A-60202695, a flap intended for use in a heat exchanger is described, the fin having the characteristics presented in the preamble of the claim

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1.

The invention tends to provide a set of heat exchanger of the type of tubes and fins that was provided with an improved fin arrangement that promotes heat transfer.

In accordance with the present invention, a fin is provided for use in a heat exchanger of the type of tubes and fins according to the first part of claim 1, which has the characteristic properties of claim 1.

Accordingly, the present invention provides a fin that is provided with a plurality of undulations to impart a turbulence to the circulation of the fluid on the fin by mixing the circulation of the fluid in two directions: from one side to the other of the fin, and laterally around from adjacent ridges. This configuration of undulations effectively inhibits the formation of a thick boundary layer and results in a more efficient heat transfer than was possible in the prior art.

Other advantages of the present invention were easily understood by reading the description given in the following and in which reference is made to the attached drawings, in which:

Figure 1 is a side view, partially open and in cross-section of an assembly made in accordance with the present invention;

Figure 2 is a plan view of a fin made in accordance with the present invention;

Figure 3 is an enlarged partial view of the zone 3 of Figure 2;

Figure 4 is a cross-sectional view taken substantially along the lines

4- 4 of figure 3; and Figure 5 is a cross-sectional view taken substantially along the lines

5- 5 of figure 3.

In the figures, a heat exchanger of the type of tubes and fins is generally represented by numerical reference 10. The assembly 10 includes a wrapper 12. Said wrapper 12 is generally cylindrical. The envelope 12 includes a hot fluid inlet 14, a hot fluid outlet 16, a cooling fluid inlet 18 and a cooling fluid outlet 20. In the exemplary embodiment shown in Figure 1, the hot fluid and the cooling fluid are represented circulating countercurrently (i.e., that the hot fluid passes through the envelope in the opposite direction to the one followed by the cooling fluid). It was noted that the fluid inlet 14 and the hot fluid outlet 16 can be reversed such that the hot fluid flows in the same direction as the cooling fluid. The envelope 12 also defines a cooling fluid inlet reservoir 19 and a cooling fluid outlet reservoir 21.

The assembly 10 may also have a plurality of baffles 22 stacked in oil. The baffles 22 direct the circulation of the hot fluid through the envelope 12 (as shown by arrows in Figure 1). If the assembly 10 does not include any baffle 22, the heat exchanger assembly 10 will be of the pass type

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Unique (that is, the hot fluid will pass directly from the hot fluid inlet 14 to the hot fluid outlet 16 without being directed).

The assembly 10 also includes a plurality of tubes 24. The tubes 24 are adapted to be located inside the envelope. The tubes have a substantially circular section and extend in a direction parallel to the longitudinal direction of the envelope. The tubes are arranged parallel to each other inside the envelope 12. One end of each of the tubes 24 ensures the communication of the fluid with the cooling fluid inlet reservoir 19, and the opposite end of each of the tubes 24 ensures the communication of the fluid with the cooling fluid outlet reservoir. 21. A cooling fluid, for example water, penetrates the assembly 10 through the cooling fluid inlet 18. The cooling fluid flows directly to the cooling fluid inlet reservoir 19. From the cooling fluid reservoir 19, the cooling fluid flows into each of the tubes 24. Then the cooling fluid leaves each tube 24 and penetrates the cooling fluid outlet reservoir 21. Finally, the cooling fluid flows from the outlet tank 21 to the outlet of cooling fluid 20, from which it leaves the assembly 10.

The assembly 10 also includes a plurality of fins 26. The fins 26 are adapted to be located inside the envelope 12. The deflectors 22 are intercalated between some of the fins 26. Several fins 26 are arranged very close to each other. others. The fins 26 include a generally flat plate 27 and have an upper portion and a generally linear or flat bottom portion and generally curved edges. The curved edges mate with the inner walls of the envelope 12. This prevents hot fluid from circulating around the edges of the fin 26. The upper and lower edges do not mate with the envelope 12 (as can be seen more clearly in Figure 1.). This configuration allows the hot fluid to pass over the top and below the bottom of each fin. The fins 26 are provided with a plurality of holes 28 that pass through them. The tubes 24 extend through the holes 28. The fins 26 are arranged in the shell 12 between the cooling fluid inlet reservoir 19 and the cooling fluid outlet reservoir 21.

The fins 26 are generally constituted by a flat plate 27 and include a plurality of undulations generally indicated at 30. The undulations 30 are preferably of the same size and protrude only in one direction from the fin. However, it will be noted that the undulations 30 can be of unequal size. On the other hand, the undulations 30 can protrude in any direction from the fin 26.

The undulations 30 are arranged in rows 32, 34, 36 between adjacent holes 28. The undulations 30 are separated from each other along the rows 32, 34, 36, and the separation between adjacent undulations 30 varies from one of the rows 32, 34, 36 to the next of said rows 32, 34, 36. The undulations are offset from one of the rows 32, 34, 36 to another one of the rows 32, 34, 36. In other words, the ridges 40 of the undulations 30 of the adjacent rows 32, 34, 36 are not aligned in a direction parallel to the width of the fin (as will be seen more clearly in Figure 5). Rows 32, 34, 36 will be coupled to each other. This means that the undulations 30 are all interconnected to provide a greater heat transfer surface. It is important that the ridges of the undulations 30 be offset from each other and that the rows 32, 34, 36 be coupled with each other. Likewise, the ridges 40 are available as an effective heat transfer surface, by continuous interruption of the boundary layer, as will be described later.

Alternate rows 32, 34, 36 include a flat portion 38 between the undulations 30. The first row 32 of these rows comprises three undulations 30 arranged in positions immediately adjacent to each other. The second row 34 includes two undulations 30 and has a first flat portion 38 between them. A third row 36 includes two of the undulations 30 immediately adjacent to each other.

The ends of the rows 32, 34, 36 are arranged in an arc around the tubes 28. Due to this arc configuration, the hot fluid, passing over the fin 26, and around the tubes 24, is constantly directed by above and through the undulations 30. The circulation of the hot fluid on the flap 26 is generally indicated by the arrows in Figure 2.

The undulations 30 continuously interrupt the formation of a boundary layer in the hot fluid flowing along the fin. The boundary layer is the region of the circulation near plate 27 where the velocity of the fluid is reduced by viscosity forces. If it is not disturbed, the circulation of the fluid in the boundary layer is of the laminar type and will increase to form a thick layer, thus leading to a mediocre heat transfer. This interruption of the boundary layer produced by the undulations 30 results in a thinning of the boundary layer due to the retardation of its growth and the creation of a turbulence due to the mixing of the fluid coming from one side of the fin with the fluid coming from the other. side and due to the mixing of the fluid in a lateral direction between adjacent areas of the undulations 30, thus promoting a more efficient heat transfer. The configuration of the undulations improves the circulation of the fluid from one side of the fin to the other side and around the adjacent undulations 30, thus preventing the formation of a thick lamellar lamellar layer.

During operation, the hot fluid, for example oil, flows into the hot fluid inlet 14 of the assembly 10. A cooling fluid, for example water, penetrates the assembly 10 through the cooling fluid inlet

18. The cooling fluid flows into the cooling fluid inlet reservoir 19 already with 3

018 340 staining flows in each of the tubes 24. The hot fluid flows over the fins 26 and over the tubes 24. While the hot fluid circulates over the fins 26. These undulations induce a turbulance in the hot fluid, thus promoting greater transfer . On the other hand, the ridges 40 of the undulations 30 are available as a surface to promote greater heat transfer. The hot fluid is directed by the baffles 22 so that a certain number of times circulate on the tubes. This creates a multi-pass heat exchanger. Figure 1 represents three baffles. The circulation of the hot fluid is the one indicated by the arrows of Figure 1. In this way, the circulation of hot fluid is directed on the tubes 24 several times before exiting the hot fluid outlet orifice 16. Finally, the cooling fluid exits the tubes 24 and enters the cooling fluid outlet reservoir 21. From the cooling fluid outlet reservoir, the cooling fluid flows through the cooling fluid outlet 20 .

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