US20110036550A1

US20110036550A1 - Fin and heat exchanger having the same

Info

Publication number: US20110036550A1
Application number: US12/806,323
Authority: US
Inventors: Jianlong Jiang; Linjie Huang
Original assignee: Danfoss Sanhua Hangzhou Micro Channel Heat Exchanger Co Ltd
Current assignee: Sanhua Holding Group Co Ltd; Danfoss AS
Priority date: 2009-08-13
Filing date: 2010-08-10
Publication date: 2011-02-17
Also published as: EP2295919A3; EP2295919A2; CN101619950B; CN101619950A; EP2295919B1

Abstract

A fin includes straight segments and substantially circular arc segments connected with the straight segments in turn along a longitudinal direction such that the arc segments form respective wave crests and wave troughs of the fin. The fin is divided in a lateral direction into first and second end portions and an intermediate portion between the first and second end portions. Each arc segment at least forming the wave troughs in the first end portion is separated from the respective arc segment of the corresponding intermediate portion via a longitudinal slot. A top of each arc segment at least forming the wave troughs in the first end portion is formed with a lateral slot along the lateral direction such that each arc segment at least forming the wave troughs in the first end portion is divided into first and second straight portions separated from each other.

Description

BACKGROUND OF INVENTION

1. Field of Invention
The invention relates, generally, to a fin and, more particularly, to a heat exchanger having a fin.
2. Description of Related Art
When the heat exchanger of the so-called “parallel flow” type is used as an evaporator, condensation water will be generated on the surface of the heat exchanger. In order to improve the water drainage performance thereof, the headers of the heat exchanger of the “parallel flow” type are conventionally disposed horizontally, and the tubes thereof are disposed vertically between the headers.
FIG. 10 is a structural schematic view of the conventional heat exchanger, and FIG. 11 is an enlarged view of portion “G′” in FIG. 10. For example, as shown in FIGS. 10 and 11, in order to improve the water-drainage performance of the heat exchanger, the headers 3 a′ and 3 b are disposed horizontally and parallel to and spaced from each other, and the tubes 2′ are disposed vertically and parallel to each other between the headers 3 a′ and 3 b′, in which fins 1′ are disposed between adjacent tubes 2′, respectively.
However, the conventional disposition manners of the headers and tubes are not suitable for heat exchangers of some types, such as “prolate” type (that is, heat exchanger having a length greater than a height thereof). With the heat exchanger of “prolate” type employing the conventional disposition manners of the headers and tubes, there may be the following disadvantages.
The headers should be very long such that the manufacturing costs thereof are high, and it is difficult to achieve a uniform distribution of the refrigerant. Since the headers do not participate ventilation and heat transfer, the longer the headers, the larger the area blocking the air flow, thus decreasing the effective heat-transfer area. The tubes are short in length and large in number; that is, the number of the flow path of the refrigerant is large so that the flow speed of the refrigerant in the tubes is low, thus causing poor heat-transfer performance.
Concerning the above, with the heat exchanger of “prolate” type, the headers are disposed vertically, and the tubes are disposed horizontally between the headers conventionally, thus decreasing the length of the headers, increasing the length of the tubes, and decreasing the number of the tubes.
However, because the conventional heat exchanger of “prolate” type with vertically disposed headers and horizontally disposed tubes employs conventional fins, there are some problems with the drainage of the condensation water. For example, as shown in FIG. 12, if the air is blown along direction “D′,” due to the surface tension of the condensation water, most condensation water will be accumulated at the leeward side (i.e., region “F′” shown in FIG. 12 of the heat exchanger) and cannot be drained smoothly.
Thus, there is a need in the related art for improved water-drainage performance. More specifically, there is a need in the related art for smoother drainage of condensation water such that the condensation water does not tend to accumulate on the fin. Also, there is a need in the related art for lower manufacturing costs, uniform distribution of refrigerant, an increase in heat-transfer coefficient and effective heat-transfer area, better heat-transfer performance, and regular arrangement of the fin in the heat exchanger.

SUMMARY OF INVENTION

The invention overcomes the disadvantages in the related art in a fin including straight segments and substantially circular arc segments connected with the straight segments in turn along a longitudinal direction such that the arc segments form respective wave crests and wave troughs of the fin. The fin is divided in a lateral direction into first and second end portions and an intermediate portion between the first and second end portions. Each arc segment at least forming the wave troughs in the first end portion is separated from the respective arc segment of the corresponding intermediate portion via a longitudinal slot. A top of each arc segment at least forming the wave troughs in the first end portion is formed with a lateral slot along the lateral direction such that each arc segment at least forming the wave troughs in the first end portion is divided into first and second straight portions separated from each other.
The invention overcomes the disadvantages in the related art also in a heat exchanger having a plurality of the fin. The heat exchanger includes a first header disposed vertically, a second header disposed vertically and spaced apart from the first header, and a plurality of tubes each of which defines two ends of the tube being connected and communicated with the first and second headers, respectively. Each fin is disposed between adjacent tubes and defines a first end portion of the fin being extended out from a first side of the adjacent tubes in a lateral direction.
One advantage of the fin and heat exchanger of the invention is that water-drainage performance is improved.
Another advantage of the fin and heat exchanger of the invention is that drainage of condensation water is smoother such that the condensation water does not tend to accumulate on the fin.
Another advantage of the fin and heat exchanger of the invention is that manufacturing costs are lower.
Another advantage of the fin and heat exchanger of the invention is that distribution of refrigerant is uniform.
Another advantage of the fin and heat exchanger of the invention is that the heat-transfer coefficient and effective heat-transfer area is increased.
Another advantage of the fin and heat exchanger of the invention is that the heat-transfer performance is better.
Another advantage of the fin and heat exchanger of the invention is that arrangement of the fin in the heat exchanger is regular.
Another advantage of the fin and heat exchanger of the invention is that the first straight portion and the straight segment connected therewith may be in the same plane and the second straight portion and the straight segment connected therewith may be in the same plane as well.
Another advantage of the fin and heat exchanger of the invention is that when it is disposed between adjacent tubes of a heat exchanger, one end of the fin may be extended beyond the tubes in the lateral direction so that the condensation water may easily flow downwardly along the first and second straight portions and the straight segments to drop off the fin and may not be accumulated on the fin.
Other objects, features, and advantages of the fin and heat exchanger of the invention will be readily appreciated as the same becomes better understood while reading the subsequent description taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF EACH FIGURE OF DRAWING

FIG. 1 is a perspective view of a length of the fin according to an embodiment of the invention in which one arc segment and two straight segments are shown.

FIG. 2 is a view of the fin shown in FIG. 1 after being flattened.

FIG. 3 is a lateral side view of a length of the fin according to an embodiment of the invention.

FIG. 4 is an enlarged schematic view of a portion of the fin shown in FIG. 3.

FIG. 5 is a schematic view of the fin according to an embodiment of the invention after being assembled and welded to the tubes of a heat exchanger.

FIG. 6 is a structural schematic view of the heat exchanger according to an embodiment of the invention.

FIG. 7 is an enlarged schematic view of Portion “E” in FIG. 6.

FIG. 8 is a lateral side view of a fin mounted between two tubes.

FIG. 9 is a perspective schematic view of a portion of the fin shown in FIG. 8.

FIG. 10 is a structural schematic view of a conventional heat exchanger.

FIG. 11 is an enlarged view of portion “G′” shown in FIG. 10.

FIG. 12 is a lateral side view of the conventional fin mounted between two tubes.

DETAILED DESCRIPTION OF EMBODIMENTS OF INVENTION

An embodiment of a fin according to the invention is described in detail with reference to FIGS. 1-5, wherein like numerals represent like structure, and generally indicated at 1. As shown in FIG. 3, the fin 1 is substantially corrugated and comprises straight segments 11 and substantially circular arc segments 12 connected with the straight segments 11 in turn along longitudinal direction “B,” in which the arc segments 12 form respective wave crests and wave troughs of the fin 1.
As shown in FIGS. 1-2, the fin 1 is divided in lateral direction “C” into a first end portion 112, a second end portion 114, and an intermediate portion 113 between the first and second end portions 112, 114. As shown in FIG. 2, the width of the first end portion 112 in lateral direction “C” is S1, and the width of the second end portion 114 in lateral direction “C” is S2. S1, S2, and the width of the intermediate portion 113 in lateral direction “C” may be determined according to the specific applications and not be particularly limited in the invention.
Each of the arc segments 12 at least forming the wave troughs in the first end portion 112 and a respective arc segment 12 of the corresponding intermediate portion 113 are split from each other in the up-and-down direction in FIG. 1. In other words, each of the arc segments 12 at least forming the wave troughs in the first end portion 112 is separated from a respective arc segment 12 of the corresponding intermediate portion 113 via a longitudinal slot 111 extended downwardly to the straight segments 11, as shown in FIG. 1. Meanwhile, a lateral slot 110 is formed along lateral direction “C” in a top of each of the arc segments 12 at least forming the wave troughs in the first end portion 112, and the lateral slot 110 is extended through the whole first end portion 112 such that each of the arc segments 12 at least forming the wave troughs in the first end portion 112 is divided into a first straight portion 12 a and second straight portion 12 b separated from each other. The first straight portion 12 a and straight segment 11 connected to the first straight portion 12 a are in the same plane, and the second straight portion 12 b and straight segment 11 connected to the second straight portion 12 b are in the same plane as well, as shown in FIG. 1. At this time, the arc segment 12 of the corresponding intermediate portion 113 is still arcuate.
When the fin 1 is disposed between adjacent tubes 2 (FIG. 8), the first end portion 112 of the fin 1 may be extended out from a first side of the adjacent tubes 2 (i.e., the right side in FIG. 8) along lateral direction “C”; that is, the first end portion 112 of the fin 1 may be extended beyond the tubes 2 in lateral direction “C.” Because each of the arc segments 12 at least forming the wave troughs in the first end portion 112 is divided into the first straight portion 12 a and second straight portion 12 b, the surface tension of the condensation water is destroyed. As such, when the air is blown along direction “D,” the condensation water may not be accumulated at area “F” of the fin 1 and may easily flow downwardly along the straight segments 11 and first and second straight portions 12 a, 12 b to drop off the fin 1, thus improving the water-drainage performance of the fin 1.
In an embodiment, each of the arc segments 12 at least forming the wave crests in the first end portion 112 is also divided into a first straight portion 12 a and second straight portion 12 b via the longitudinal slot 111 and lateral slot 110. In this way, when the fin 1 is disposed between adjacent tubes 2, the surface tension of the condensation water is destroyed by the first straight portion 12 a and second straight portion 12 b. And, the condensation water may easily flow downwardly along the first and second straight portions 12 a, 12 b of the arc segments 12 forming the wave crests, straight segments 11, and first and second straight portions 12 a, 12 b of the arc segments 12 forming the wave troughs so as to drop off the fin 1, thus further reducing the possibility of the accumulating of the condensation water in area “F” of the fin 1 and improving the water-drainage performance of the fin 1.
In another embodiment, each of the arc segments 12 at least forming the wave troughs in the second end portion 114 of the fin 1 is also divided into a first straight portion 12 a and second straight portion 12 b via the longitudinal slot 111 and lateral slot 110. Further, each of the arc segments 12 at least forming the wave crests in the second end portion 114 also can be divided into a first straight portion 12 a and second straight portion 12 b via the longitudinal slot 111 and lateral slot 110.
Therefore, when the fin 1 is disposed between adjacent tubes 2, the second end portion 114 may be extended out from a second side of the tubes 2 (i.e., the left side in FIG. 8) along lateral direction “C”; that is, the second end portion 114 of the fin 1 may be extended beyond the tubes 2 in lateral direction “C.” Because each of the arc segments 12 forming the wave troughs (or both the wave troughs and wave crests) in the second end portion 114 is divided into the first straight portion 12 a and second straight portion 12 b, the surface tension of the condensation water is destroyed. For example, when air is blown along a direction opposite to direction “D” (i.e., the “leftward” direction in FIG. 8), the condensation water may not be accumulated in an area symmetrical to area “F” of the fin 1 and may easily flow downwardly along the first and second straight portions 12 a, 12 b of the second end portion 114 and the straight segments 11 to drop off the fin 1, thus further improving the water-drainage performance of the fin 1.
Because each of the arc segments 12 forming the wave troughs (or both the wave troughs and wave crests) in both the first end portion 112 and second end portion 114 of the fin 1 is divided into the first straight portion 12 a and second straight portion 12 b, when the fin 1 is disposed between adjacent tubes 2, both the first end portion 112 and second end portion 114 are extended out from the respective two sides of the tubes 2 along lateral direction “C.” It is not necessary to consider the air blowing in direction “D” during mounting, thus improving the mounting efficiency and water-drainage performance of the fin 1.
In some embodiments, as shown in FIGS. 3-5, adjacent straight segment 11 and arc segment 12 are connected via a substantially circular arc-transition segment 13, in which R>r, “R” is a radius of the arc segment (its center of circle is “O1”), and “r” is a radius of the arc-transition segment (its center of circle is “O2”).
As shown in FIG. 3, each end of one arc segment 12 is connected with an end of one arc-transition segment 13, and the other end of the arc-transition segment 13 is connected with an end of another straight segment 11. The other end of the straight segment 11 is connected with another arc-transition segment 13, thus forming a substantially corrugated fin 1 extending along longitudinal direction “B.” In some embodiments, two straight segments 11, two arc segments 12, and four arc-transition segments 13 form one cycle of the fin 1, and one cycle length of the fin 1 is “P.” The fin 1 may be made, for example, by rolling metal foil. It may be understood by those having ordinary skill in the related art that the “cycle” number of the fin 1 may be determined based on specific requirements and is not particularly limited.
During manufacturing of the heat exchanger when the fin 1 is assembled between and pressed against the tubes 2, because radius “R” of the arc segment 12 is larger than radius “r” of the arc-transition segment 13, the arc segment 12 is easier to deform so as to become straight and clings to the surface of the tubes 2, as shown in FIGS. 5 and 9. Whereas, the straight segments 11 and arc-transition segments 13 with a smaller radius keep their shape unchanged.
Furthermore, the deformation Of the arc segments 12 are regular, and the deformation of each of the arc segments 12 is uniform so that the deformation of the fin 1 is regular and easy to control, the fin 1 is arranged uniformly in the heat exchanger, and the shape of the fin 1 may meet the design requirements and be much more stable. After welding, areas “A” are surrounded by two adjacent straight segments 11, the arc segments 12 become straight, the tubes 2 become substantially trapezoid, and the shape of each of areas “A” is uniform, as shown in FIG. 5. The heat exchanger of the embodiments has an increased heat-transfer coefficient on the air-blowing side, an improved heat-transfer performance, and a much more regular and aesthetic appearance. In some embodiments, by changing the size of the arc segments 12, areas “A” may be substantially rectangular or square after welding.
In some embodiments, the “radius” ratio “R/r” of radius “R” of the arc segment 12 to radius “r” of the arc-transition segment 13 is larger than 2 so that the arc segment 12 is easier to deform. Compared with “r,” the larger radius “R” is, the easier the deformation of the arc segment 12 is. For example, “R” may be 5 times larger than “r,” and “r” is 0.2 mm if “R” is 1 mm.
As shown in FIG. 4, when the arc segment 12 becomes straight, the compressed distance of the arc segment 12 is “N” (i.e., the “chordal” height of the arc segment 12). In some embodiments, in order to make the manufacture of the fin 1 easier and more feasible, the compressed distance “N” is controlled within 0.01-0.1 mm, i.e., 0.01 mm ≦R[1−cos(α/2)]≦0.1 mm, “R” is the radius of the arc segment 12, and “α” is the central angle of the arc segment 12. Additionally, in order to make the manufacture more convenient, in an embodiment, central angle “α” of the arc segment 12 is set in a range of about 30° to about 170°.
In other embodiments, in order to make the shape of area “A” regular (such as rectangular or trapezoid-shaped) after the fin 1 is assembled and welded to the tubes 2, [2×R×α×(π/180)]≧0.85, “R” is the radius of the arc segment 12, “α” is the central angle of the arc segment 12, “π” is circumference ratio, and “P” is one cycle length of the fin 1. In other words,
“P” is the length of the straight line between two points having same phase (for example, the distance between the lower ends of the two straight segments 11 inclined upwardly and rightward in FIG. 3 or the distance between the vertices of the two arc segments 12 forming the adjacent wave crests or wave troughs).
As shown in FIGS. 1-3 and 5, in some embodiments, the deformation of the fin 1 is mainly presented by the deformation of the arc segments 12 (becoming straight), and the straight segments 11 are substantially not deformed so that the straight segments 11 may be formed with a window 14, thus further improving the heat-transfer coefficient and performance of the heat exchanger. The window 14 may be formed by extending, such as punching, a middle portion 15 of the straight segment 11 away from the plane in which the straight segment 11 is located. The window 14 may be also formed by cutting a slot in the straight segment 11 and then punching to turn the portion 15 of the straight segment 11 from the plane in which the straight segment 11 is located so that the portion 15 may not be separated from the straight segment 11, thus further improving the heat-transfer coefficient and performance.
In an embodiment, as shown in FIG. 3, taking into consideration the manufacture performance and resistance on the air-blowing side, the length “L” of the window 14 and height “H” of the fin 1 satisfy the equation “0.75≦L/H≦1.05,” thus achieving better performance. It should be noted that length “L” is the length of the window 14 in the longitudinal direction (the direction indicated by arrow “Q” in FIG. 3) of the straight segment 11 and height “H” is the height in the vertical direction (the up-and-down direction in FIG. 5) after formation of the fin 1, i.e., the distance between two parallel arc segment 12 in the up-and-down direction when the arc segment 12 becomes straight, as shown in FIG. 5.
Hereinafter, an embodiment of a heat exchanger according to the invention is described in detail with reference to FIGS. 6-9, wherein like numerals represent like structure. As shown in FIGS. 6-7, the heat exchanger includes a first header 3 a, second header 3 b, plurality of tubes 2, and plurality of fins 1. The first header 3 a is used as inlet header, the second header 3 b is used as outlet header, and the tube 2 may be a flat tube.
The first header 3 a and second header 3 b are substantially disposed vertically, i.e., along the up-and-down direction in FIG. 6. The first header 3 a and second header 3 b are substantially parallel with and spaced apart from each other by a predetermined distance.
The tubes 2 are disposed between the first header 3 a and second header 3 b, and two ends of each flat tube 2 are connected and communicated with the first header 3 a and second header 3 b, respectively. A plurality of micro-channels are formed in each flat tube 2 so that the heat exchanger is referred to as a “micro-channel heat exchanger.” It should appreciated by those having ordinary skill in the related art that the terms “horizontally” and “vertically” are used herein to facilitate description of the relative positions between the tubes 2 and first and second headers 3 a, 3 b and not to limit the invention.
As shown in FIG. 8, each fin 1 is disposed between adjacent tubes 2, and the first end portion 112 of each fin 1 may be extended out from a first side of the adjacent tubes 2 (i.e., the right side in FIG. 8) along lateral direction “C.” The arc segments 12 forming the wave troughs and wave crests in the intermediate portion 113 of each fin 1 are pressed and flattened by the tubes 2, as shown in FIG. 9. Because each of the arc segments 12 forming the wave troughs and wave crests in the first end portion 112 are divided into the first straight portion 12 a and second straight portion 12 b via the longitudinal slot 111 and lateral slot 110, the surface tension of the condensation water is destroyed. Therefore, when blowing air along direction “D,” the condensation water may not be accumulated in area “F” of the fin 1 and may easily flow downwardly along the straight segments 11 and first and second straight portions 12 a, 12 b to drop off each fin 1, thus improving the water-drainage performance of the heat exchanger.
In an alternative embodiment, each of the arc segments 12 forming the wave troughs and wave crests in the second end portion 114 is also divided into the first straight portion 12 a and second straight portion 12 b via the longitudinal slot 111 and lateral slot 110. In this way, when blowing air along a direction opposite to direction “D,” the condensation water may not be accumulated in an area (i.e., the left side in FIG. 8) symmetrical to area “F” of the fin 1 and may easily flow downwardly along the first and second straight portions 12 a, 12 b of the second end portion 114 and straight segments 11 to drop off the fin 1, thus further improving the water-drainage performance of the heat exchanger. And, it is not necessary to consider direction “D” during mounting.
As described above, because the adjacent arc segment 12 and straight segment 11 of the fin 1 are connected via the arc-transition segment 13 in which radius “R” of the arc segment 12 is larger than radius “r” of the arc-transition segment 13, when the fin 1 is disposed between adjacent tubes 2, the arc segments 12 forming the wave troughs and wave crests in the intermediate portion 113 of each fin 1 are pressed and flattened by the tubes 2 more easily, as shown in FIGS. 5 and 8-9. In this way, the shape of areas “A” is regular and uniform. The heat exchanger so manufactured has an increased heat-transfer coefficient, an improved heat-transfer performance, and a much more regular and aesthetic appearance.
With use of the fin and heat exchanger of the invention, water-drainage performance is improved. More specifically, drainage of condensation water is smoother such that the condensation water does not tend to accumulate on the fin. Also, manufacturing costs are lower. Furthermore, distribution of refrigerant is uniform. In addition, the heat-transfer coefficient and effective heat-transfer area is increased. Moreover, the heat-transfer performance is better. Arrangement of the fin in the heat exchanger is regular as well.
The invention has been described in an illustrative manner. It is to be understood that the terminology that has been used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations of the invention are possible in light of the above teachings. Therefore, within the scope of the appended claims, the invention may be practiced other than as specifically described.

Claims

1. A fin comprising:

straight segments; and

substantially circular arc segments connected with said straight segments in turn along a longitudinal direction such that said arc segments form respective wave crests and wave troughs of said fin,

wherein said fin is divided in a lateral direction into a first end portion, a second end portion, and an intermediate portion between said first and second end portions, each of said arc segments at least forming said wave troughs in said first end portion is separated from respective said arc segment of corresponding said intermediate portion via a longitudinal slot, and a top of each of said arc segments at least forming said wave troughs in said first end portion is formed with a lateral slot along the lateral direction such that each of said arc segments at least forming said wave troughs in said first end portion is divided into a first straight portion and second straight portion separated from each other.

2. The fin as set forth in claim 1, wherein each of said arc segments at least forming said wave troughs in said second end portion is separated from respective said arc segment of corresponding said intermediate portion via said longitudinal slot and a top of each of said arc segments at least forming said wave troughs in said second end portion is formed with said lateral slot along the lateral direction such that each of said arc segments at least forming said wave troughs in said second end portion is divided into a first straight portion and second straight portion separated from each other.

3. The fin as set forth in claim 2, wherein each of said arc segments forming said wave crests and wave troughs in said first and second end portions is separated from respective said arc segment of corresponding said intermediate portion via said longitudinal slot and a top of each of said arc segments forming said wave crests and wave troughs of said first and second end portions is formed with a lateral slot along the lateral direction such that each of said arc segments of said first and second end portions is divided into said first straight portion and second straight portion separated from each other.

4. The fin as set forth in claim 1, wherein a substantially circular arc-transition segment is connected between adjacent ones of said straight segments and arc segments, “R” is a radius of said arc segment, “r” is a radius of said arc-transition segment, and R>r.

5. The fin as set forth in claim 4, wherein R/r>2.

6. The fin as set forth in claim 4, wherein “α” is a central angle of said arc segment and 0.01 mm ≦R[1−cos(α/2)]≦0.1 mm.

7. The fin as set forth in claim 4, wherein “P” is one cycle-length of said fin, “α” is a central angle of said arc segment, “π” is a circumference ratio, and [2×R×α×(π/180)]/P ≧0.85.

8. The fin as set forth in claim 4, wherein “α” is a central angle of said arc segment and 30°≦α≦170°.

9. The fin as set forth in claim 4, wherein each of said straight segments is formed with a window.

10. The fin as set forth in claim 9, wherein said window is formed by extending a portion of said straight segment away from a plane in which said straight segment is located.

11. The fin as set forth in claim 9, wherein “L” is a length of said window, “H” is a height of said fin in a vertical direction after said fin is deformed, and 0.85≦L/H≦1.05.

12. A heat exchanger, comprising:

a first header disposed vertically;

a second header disposed vertically and spaced apart from said first header;

a plurality of tubes each of which defines two ends of the tube being connected and communicated respectively with said first and second headers; and

a plurality of fins each of which is disposed between adjacent ones of said tubes and defines a first end portion of the fin being extended out from a first side of said adjacent tubes in a lateral direction;

wherein each fin comprises:

straight segments; and

wherein said fin is divided in the lateral direction into a first end portion, a second end portion, and an intermediate portion between said first and second end portions, each of said arc segments at least forming said wave troughs in said first end portion is separated from respective said arc segment of a corresponding said intermediate portion via a longitudinal slot, and a top of each of said arc segments at least forming said wave troughs in said first end portion is formed with a lateral slot along the lateral direction such that each of said arc segments at least forming said wave troughs in said first end portion is divided into a first straight portion and a second straight portion separated from each other.

13. The heat exchanger as set forth in claim 12, wherein a second end portion of each of said fins is extended out from a second side opposite to said first side of said adjacent tubes in the lateral direction.

14. The heat exchanger as set forth in claim 12, wherein each of said arc segments at least forming said wave troughs in said second end portion is separated from respective said arc segment of corresponding said intermediate portion via said longitudinal slot and a top of each of said arc segments at least forming said wave troughs in said second end portion is formed with said lateral slot along the lateral direction such that each of said arc segments at least forming said wave troughs in said second end portion is divided into a first straight portion and second straight portion separated from each other.

15. The heat exchanger as set forth in claim 14, wherein each of said arc segments forming said wave crests and wave troughs in said first and second end portions is separated from respective said arc segment of corresponding said intermediate portion via said longitudinal slot and a top of each of said arc segments forming said wave crests and wave troughs of said first and second end portions is formed with a lateral slot along the lateral direction such that each of said arc segments of said first and second end portions is divided into said first straight portion and second straight portion separated from each other.

16. The heat exchanger as set forth in claim 12, wherein a substantially circular arc-transition segment is connected between adjacent ones of said straight segments and arc segments, “R” is a radius of said arc segment, “r” is a radius of said arc-transition segment, and R>r.

17. The fin as set forth in claim 16, wherein R/r>2.

18. The fin as set forth in claim 16, wherein “α” is a central angle of said arc segment and 0.01 mm ≦R[1−cos(α/2)]≦0.1 mm.

19. The fin as set forth in claim 16, wherein “P” is one cycle-length of said fin, “α” is a central angle of said arc segment, “π” is a circumference ratio, and [2×R×α×(π/180)]/P ≧0.85.

20. The fin as set forth in claim 16, wherein “α” is a central angle of said arc segment and 30°≦α≦170°.