HEAT EXCHANGER

Abstract

 In a parallel-flow-type heat exchanger, the shape of corrugated fins is improved such that heat exchange performance is enhanced and that it is possible to perform smooth draining of defrost water and condensed water. The heat exchanger (1) includes a plurality of horizontal header pipes (2) and (3) arranged parallel at an interval from one another in the vertical direction, a plurality of vertical flat tubes (4) arranged at an interval from one another in the horizontal direction between the header pipes (2) and (3), with refrigerant passage (5) inside the flat tubes (4) communicate with the insides of the header pipes (2) and (3) respectively, and corrugated fins (6) arranges between the flat tubes (4). The corrugated fins (6) include upwind-side corrugated fins (6U) whose fin surface has a downward slope toward the downwind side and downwind-side corrugated fins (6D) whose fin surface has an upward slope toward the downwind side, the former and the latter being arranged with a gap (9) secured therebetween. The gap (9) is so sized as to enable water droplets sticking to the downwind-side ends of the upwind-side corrugated fins (6U) and water droplets sticking to the upwind-side ends the downwind-side corrugated fins (6D) to coalesce.

Description

Technical Field

[0001] The present invention relates to a parallel-flow-type heat exchanger.

Background Art

[0002] A parallel-flow-type heat exchanger having a plurality of flat tubes arranged between a plurality of header pipes, with refrigerant passages inside the flat tubes communicating with the insides of the header pipes, and with corrugated fins arranged between the flat tubes, is widely used in car air conditioners and the like. An example is seen in Patent Document 1.

[0003] The heat exchanger described in Patent Document 1 has a plurality of header pipes arranged horizontally, and has a plurality of flat tubes arranged vertically, and corrugated fins between the flat tubes are shaped like valleys with their bottom at a central part of the heat exchanger in the depth direction. At the valley-bottom part of the corrugated fins, where they join the flat tubes, through holes are formed; when defrosting operation is performed to melt frost sticking to the heat exchanger, the water resulting from the frost melting is drained through the through holes.
[Patent Document 1] JP-A-2005-24187

Disclosure of the Invention

Problems to be Solved by the Invention

[0004] In the parallel-flow-type heat exchanger, the fact that the corrugated fins are not flat but so shaped as to form valley bottoms, that is, V-shaped to have a downward slope and an upward slope, is effective in increasing the heat-dissipation area and enhancing the heat exchange efficiency. However, the problem of how to deal with the condensed water or frost that forms when the heat exchanger is used as an evaporator remains.

[0005] When frost sticks to the flat tubes or the corrugated fins, it hinders circulation of air, lowering the heat exchange efficiency. For this reason, it is necessary to perform, from time to time, defrosting operation in which the evaporator and the condenser exchange their roles, in order to melt frost. Inconveniently, even when through holes like those described in Patent Document 1 are formed to drain defrost water resulting from frost melting, the surface tension of water causes a bridging phenomenon (producing a film of water), and hinders water from flowing down smoothly through the holes. The bridging phenomenon also occurs between the corrugations of the corrugated fins, often causing a situation in which water that has flowed down to the ends of the corrugated fins simply forms a film and does not drip down. This is true not only with defrost water but also with condensed water before forming frost.

[0006] If, to overcome a situation like the above, for example, the diameter of the through holes are increased, the contact area between the flat tubes and the corrugated fins is reduced, lowering the heat exchange performance; if the ridge-valley pitch of the corrugated fin is increased, the heat-dissipation area of the corrugated fin is reduced, likewise lowering the heat exchange performance.

[0007] The present invention is devised in view of the foregoing, and its obj ect is to provide a parallel-flow-type heat exchanger in which the shape of corrugated fins is so improved as to enhance heat exchange performance and that allows smooth draining of defrost water and condensed water.

Means for Solving the Problem

[0008] To achieve the above obj ect, according to the present invention, a heat exchanger comprises: horizontal header pipes arranged parallel at an interval from one another in the vertical direction; a plurality of vertical flat tubes arranged at an interval from one another in the horizontal direction between the header pipes, with refrigerant passages inside the flat tubes communicating with the insides of the header pipes respectively; and corrugated fins arranged between the flat tubes. Here, the corrugated fins comprise upwind-side corrugated fins whose fin surface has a downward slope toward the downwind side and downwind-side corrugated fins whose fin surface has an upward slope toward the downwind side. The downwind-side ends of the upwind-side corrugated fins and the upwind-side ends of the downwind-side corrugated fins are arranged with a gap secured therebetween, and the gap is so sized as to enable water droplets sticking to the downwind-side ends of the upwind-side corrugated fins and water droplets sticking to the upwind-side ends of the downwind-side corrugated fins to coalesce.

[0009] With this structure, owing to the fact that the upwind-side corrugated fins and the downwind-side corrugated fins each have a sloped fin surface, the corrugated fins as a whole extend long in the air flow direction, resulting in an increased heat-dissipation area and enhanced heat exchange performance. On the other hand, the upwind-side corrugated fins and the downwind-side corrugated fins are not in close contact with each other, but the downwind-side ends of the upwind-side corrugated fins and the upwind-side ends of the downwind-side corrugated fins are arranged with a gap secured therebetween that is so sized as to enable water droplets sticking to the downwind-side ends of the upwind-side corrugated fins and water droplets sticking to the upwind-side ends to the downwind-side corrugated fins to coalesce. Thus, in a case where defrosting operation produces defrost water, when water droplets on the upwind-side corrugated fins and water droplets on the downwind-side corrugated fins meet at the gap, they break each other's surface tension and coalesce, and flow out through the gap without causing a bridging phenomenon. As a result, on return from defrosting operation to normal operation, it will not occur that water droplets that have remained without being drained freeze and impair heat exchange performance. Condensed water before forming frost flows out likewise, and thus it will not occur that water narrows the sectional area of the air circulation passage and lowers heat exchange performance.

[0010] In the heat exchanger structured as described above, the downwind-side ends of the upwind-side corrugated fins and the upwind-side ends of the downwind-side corrugated fins may be kept in partial contact with each other so that the gap is produced elsewhere than in a contact part.

[0011] With this structure, by simply putting together the downwind-side ends of the upwind-side corrugated fins and the upwind-side ends of the downwind-side corrugated fins to bring them into partial contact with each other, gaps are produced elsewhere than in their contact part; it is thus possible to assemble the heat exchanger easily and with high productivity.

Advantages of the Invention

[0012] According to the present invention, it is possible to realize a parallel-flow-type heat exchanger that offers enhanced heat exchange performance and simultaneously allows sure drainage of defrost water and condensed water.

Brief Description of Drawings

[0013] 

[Fig. 1] A schematic vertical sectional view showing an outline of the structure of a heat exchanger

[Fig. 2] A sectional view cut along line A-A in Fig. 1

[Fig. 3] An enlarged partial horizontal sectional view of the heat exchanger

[Fig. 4] A sectional view cut along line B-B in Fig. 3

[Fig. 5] A perspective view of a suite of a flat tube and corrugated fins

[Fig. 6] A side view of a suite of a flat tube and corrugated fins

[Fig. 7] A perspective view of a suite of a flat tube and corrugated fins according to a second embodiment

[Fig. 8] A side view of a suite of a flat tube and corrugated fins according to the second embodiment

[Fig. 9] A perspective view of a suite of a flat tube and corrugated fins according to a third embodiment

[Fig. 10] A side view of a suite of a flat tube and corrugated fins according to the third embodiment

[Fig. 11] A perspective view of a suite of a flat tube and corrugated fins according to a fourth embodiment

[Fig. 12] A side view of a suite of a flat tube and corrugated fins according to the fourth embodiment

[Fig. 13] A perspective view of a suite of a flat tube and corrugated fins according to a fifth embodiment

[Fig. 14] A side view of a suite of a flat tube and corrugated fins according to the fifth embodiment

[Fig. 15] A sectional view similar to Fig. 2 according to a sixth embodiment

[Fig. 16] A sectional view similar to Fig. 2 according to a seventh embodiment

[Fig. 17] A table of the results of experiments conducted to study the effect of the size of a gap on drainage

[Fig. 18] A graph of the above results of the experiments

List of Reference Symbols

[0014] 

1

heat exchanger

2, 3

header pipe

2U, 3U

upwind-side header pipe

2D, 3D

downwind-side header pipe

4

flat tube

4U

upwind-side flat tube

4D

downwind-side flat tube

5

refrigerant passage

6

corrugated fin

6U

upwind-side corrugated fin

6D

downwind-side corrugated fin

9

gap

Best Mode for Carrying Out the Invention

[0015] Referring now to Figs. 1 to 6, a first embodiment of the present invention will be described. A heat exchanger 1 has two horizontal header pipes 2 and 3 arranged parallel at an interval from each other in the vertical direction, and has a plurality of vertical flat tubes 4 arranged at an interval from each other and with a predetermined pitch in the horizontal direction between the header pipes 2 and 3, with refrigerant passages 5 inside the flat tubes 4 communicating with insides of the header pipes 2 and 3. The header pipes 2 and 3 and the flat tubes 4 are fixed by welding. Between the flat tubes 4, corrugated fins 6 are arranged. The flat tubes 4 and the corrugated fins 6 also are fixed by welding. The header pipes 2 and 3, the flat tubes 4, and the corrugated fins 6 are all formed of a metal (for example, aluminum) with high thermal conductivity. In Fig. 1, the top side of the page is the top side in the vertical direction, and the bottom side of the page is the bottom side in the vertical direction. Between the top-side header pipe 2 and the bottom-side header pipe 3, a plurality of flat tubes 4 are arranged with a predetermined pitch with their length direction kept vertical.

[0016] Owing to the structure in which a large number of flat tubes 4 are provided between the header pipes 2 and 3 and corrugated fins 6 are provided between the flat tubes 4, the heat-dissipation (heat-absorption) area of the heat exchanger 1 is large, allowing efficient heat exchange. At one end of the bottom-side header pipe 3, a refrigerant inflow port 7 is provided, and, at one end of the top-side header pipe 2, a refrigerant outflow port 8 is provided at a position diagonal to the refrigerant inflow port 7.

[0017] Next, the structure of the corrugated fins 6 will be described with reference to Figs. 2, 3, 5, and 6. In Figs. 2, 3, and 6, the left side of the page is the upwind side, and the right side of the page is the downwind side; in Fig. 5, the near-left side of the page is the upwind side, and the far-right side of the page is the downwind side. Incidentally, in a vertical sectional view like Fig. 2, the left side of the page is the upwind side, and the right side of the page is the downwind side; in a perspective view like Fig. 5, the near-left side of the page is the upwind side, and the far-right side of the page is the downwind-side; in a side view like Fig. 6, the left side of the page is the upwind-side, and the right side of the page is the downwind-side. This upwind/downwind relationship applies equally to the drawings illustrating the second and following embodiments.

[0018] As shown in Figs. 2 and 3, the corrugated fins 6 divide into upwind-side corrugated fins 6U and downwind-side corrugated fins 6D, and are individually welded to the flat tubes 4. The upwind-side corrugated fins 6U have a fin surface with a downward slope toward the downwind side; the downwind-side corrugated fins 6D have a fin surface with an upward slope toward the downwind side. The downward slope of the upwind-side corrugated fins 6U and the upward slope of the downwind-side corrugated fins has the same angle. In the air flow direction, the horizontal direction length of the upwind-side corrugated fins 6U and the horizontal direction length of the downwind-side corrugated fins 6D are equal.

[0019] Seen from the direction perpendicular to the flow of air, the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D appear to be a large number of V shapes arranged in the up/down direction. The V shapes here, however, are not closed but open at their bottom part. Specifically, the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D are not in close contact with each other, but are arranged with a gap 9 secured between them. The gap 9 is so sized as to enable water droplets sticking to the downwind-side ends of the upwind-side corrugated fins 6U and water droplets sticking to the upwind-side ends downwind-side corrugated fins 6D to coalesce.

[0020] When refrigerant is passed through the heat exchanger 1 while air is circulated with an unillustrated fan, in an operation mode in which the heat exchanger 1 is used as an evaporator (for example, when heating operation is performed by use of the heat exchanger 1 in the outdoor unit of a separate-type air conditioner comprising an indoor unit and an outdoor unit, the heat exchanger 1 acts as an evaporator), the heat exchanger 1 absorbs heat from the air, and in return releases cold into the air. Since the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D each have a sloped fin surface, compared with in a case where corrugated fins have no slope and are arranged horizontally, the corrugated fins 6 as a whole extend longer in the air flow direction, achieving high heat exchange performance.

[0021] As operation that absorbs heat from the air continues, on the surface of the upwind-side corrugated fins 6U, on the surface of the downwind-side corrugated fins 6D, and also on the surface of the flat tubes 4, moisture in the air condenses. As initially fine water droplets combine into larger water droplets, they flow down along the sloped surfaces of the upwind-side corrugated fins 6U or the downwind-side corrugated fins 6D, and reach a gap 9. If the gap 9 is wide, water droplets end up causing a bridging phenomenon at the downwind-side ends of the upwind-side corrugated fins 6U or at the upwind-side ends of the downwind-side corrugated fins 6D. However, since the gap 9 is so sized as to enable water droplets sticking to the downwind-side ends of the upwind-side corrugated fins 6U and water droplets sticking to the upwind-side ends of the downwind-side corrugated fins 6D to coalesce, when water droplets on the upwind-side corrugated fins 6U and water droplets on the downwind-side corrugated fins 6D meet at the gap 9, they break each other's surface tension and coalesce, and flow out through the gap 9 without causing a bridging phenomenon.

[0022] In an operation mode in which the heat exchanger 1 is used as an evaporator (an operation mode in which the heat exchanger 1 absorbs heat from the air), depending on the ambient air temperature condition and the operation condition, moisture in the air may, in the form of frost, stick to the surface of the flat tubes 4 and the corrugated fins 6. As time passes, frost gets thicker and lowers heat exchange performance; thus it is necessary to perform, from time to time, defrosting operation to melt frost. Trickles of defrost water resulting from frost melting also, when they meet at the gap 9, break each other's surface tension and coalesce, and flow out through the gap 9 without causing a bridging phenomenon. Thus, on return from defrosting operation to normal operation, it will not occur that water droplets that have remained without being drained freeze and impair heat exchange performance.

[0023] The downward slope of the upwind-side corrugated fins 6U and the upward slope of the downwind-side corrugated fins 6D can be selected within the range of 5° to 40°. The sharper the slope, the larger the heat exchange area and thus the easier it is to drain, but the higher the resistance to the circulation of air. It is therefore advisable to set the angle at an appropriate value through experiments. Other relevant dimensions are as follows: the interval between the flat tubes 4 is 5.5 mm; the thickness of the flat tubes 4 is 1.3 mm; in the air flow direction, the horizontal direction length of both the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D is 18 mm; the ridge-valley pitch of both the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D is 2 mm to 3 mm; the size of the gap 9 is 0.5 mm at the maximum. Needless to say, these values are merely examples, and are not meant to limit the contents of the invention.

[0024] Next, other embodiments of the present invention will be described.

[0025] A second embodiment of the present invention is shown in Figs. 7 and 8. The second embodiment differs from the first embodiment in the angles of the slopes of the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D. Specifically, the downward slope of the upwind-side corrugated fins 6U is gentler than in the first embodiment, and by contrast the upward slope of the downwind-side corrugated fins 6D is sharper than in the first embodiment.

[0026] A third embodiment of the present invention is shown in Figs. 9 and 10. The third embodiment differs from the first embodiment in that the gap 9 between the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D is arranged displaced to the upwind side from the center of the width of the flat tubes 4 in the air flow direction. Specifically, in a case where the horizontal-direction lengths of the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D in the air flow direction are equal and in addition are greater than in the first embodiment, the arrangement is such that the upwind-side ends of the upwind-side corrugated fins 6U extend off the upwind-side ends of the flat tubes 4 and that the downwind-side ends of the downwind-side corrugated fins are flush with the downwind-side ends of the flat tubes 4.

[0027] In other words, the arrangement is such that the sum of the horizontal-direction lengths of the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D in the air flow direction and the horizontal-direction width of the gap 9 (hereinafter this sum will also be referred to as the corrugated fin horizontal-direction length) is greater than the width of the flat tubes 4 in the air flow direction, and that the downwind-side ends of the downwind-side corrugated fins 6D are flush with the downwind-side ends of the flat tubes 4. For example, suppose that the horizontal-direction length of the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D in the air flow direction are both 18 mm, and that the horizontal-direction width of the gap 9 is 0.5 mm. Then the corrugated fin horizontal-direction length is 36.5 mm. When the width of the flat tubes 4 in the air flow direction is 30 mm, the gap 9 is arranged about 3 mm to 3.5 mm displaced to the upwind side from the center of the flat tubes 4, and the upwind-side ends of the upwind-side corrugated fins 6U extend 6.5 mm off the upwind-side ends of the flat tubes 4.

[0028] The horizontal-direction lengths of the upwind-side corrugated fins 6U and the downwind-side corrugated fins in the air flow direction do not necessarily have to be equal, but may be different.

[0029] A fourth embodiment of the present invention is shown in Figs. 11 and 12. The fourth embodiment differs from the first embodiment in the length of the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D. Specifically, the horizontal-direction lengths of the upwind-side corrugated fins and the downwind-side corrugated fins 6D in the air flow direction are greater than in the first embodiment, with the upwind-side ends of the upwind-side corrugated fins 6U extending off upwind-side ends of the flat tubes 4, and with the downwind-side ends of the downwind-side corrugated fins 6D extending off the downwind-side ends of the flat tubes 4.

[0030] A fifth embodiment of the present invention is shown in Figs. 13 and 14. The fifth embodiment differs from the first embodiment in the ratio between the lengths of the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D. Specifically, whereas in the first embodiment the horizontal-direction lengths of the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D in the air flow direction are equal, in the fifth embodiment the downwind-side corrugated fins 6Dare longer than the upwind-side corrugated fins 6U.

[0031] As in the examples according to the first to fifth embodiments, by varying the ratio between the corrugated fin horizontal-direction length and the width of the flat tubes 4 and the relative positions of the corrugated fins 6 and the flat tubes 4, it is possible to realize the heat exchanger 1 in different manners.

[0032] A sixth embodiment of the present invention is shown in Fig. 15. The sixth embodiment differs from the first embodiment in the structure of the flat tubes 4. Specifically, whereas in the first embodiment the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D are welded to single flat tubes 4, in the sixth embodiment the flat tubes separate into upwind-side flat tubes 4U and downwind-side flat tubes 4D, with the upwind-side corrugated fins 6U welded to the upwind-side flat tubes 4U, and with the downwind-side corrugated fins 6D welded to the downwind-side flat tubes 4D.

[0033] A seventh embodiment of the present invention is shown in Fig. 16. The seventh embodiment is an advancement one step forward from the sixth embodiment. Specifically, in the seventh embodiment, not only the flat tubes but also the header pipes separate into upwind-side header pipes 2U and 3U and downwind-side header pipes 2D and 3D.

[0034] Unless structurally inconsistent, a plurality of the embodiments described above may be implemented in combination.

[0035] The gap 9 is the distance between the downwind-side ends of the upwind-side corrugated fins 6U and the upwind-side ends of the downwind-side corrugated fins 6D, and therefore not only the distance in the horizontal direction but also the distance in the vertical direction is an element of the gap 9. For example, in the structure of Fig. 2, since the downwind-side ends of the upwind-side corrugated fins 6U and the upwind-side ends of the downwind-side corrugated fins 6D have an equal height, only the horizontal-direction distance between the opposite ends determines the size of the gap 9. Consider here a structure in which the downwind-side ends of the upwind-side corrugated fins 6U and the upwind-side ends of the downwind-side corrugated fins 6D have different heights; then the horizontal-direction distance between the opposite ends with the vertical-direction distance between them considered together determines the size of the gap 9.

[0036] The gap 9 is formed by setting, with an unillustrated fixture, the relative positions of the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D and then welding them to the flat tubes. Instead any other method may be adopted. One such method is to bring the downwind-side ends of the upwind-side corrugated fins 6U and the upwind-side ends of the downwind-side corrugated fins 6D into partial contact with each other so that, elsewhere than in their contact part, the gap 9 is formed.

[0037] For example, the method proceeds as follows. Like the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D shown in Fig. 5, on an elongate aluminum material (for example, a thin rectangular plate-shaped elongate aluminum material), corrugations, that is, ridge-like, shapes are formed obliquely to the length direction of the material. The corrugated fins thus produced have ends that are not straight, and therefore when two of them are put together, they make contact with each other in some part (contact part) but do not make contact with each other in the other part (non-contact part). The non-contact part serves as the gap 9. With consideration given so that the contact part does not unduly hinder the outflow of water, the ratio between the contact part and the non-contact part is determined.

[0038] According to the above method, when the heat exchanger 1 is manufactured, it is simply necessary to put together the upwind-side corrugated fins 6U and the downwind-side corrugated fins 6D and weld them to the flat tubes 4. This eliminates the need for accurate measurement of the interval, and thus helps enhance productivity.

[0039] The results of experiments conducted to study the effect of the size of the gap 9 on drainage is shown in a table in Fig. 17 and in a graph in Fig. 18. In the experiments, the heat exchanger 1 that had been dipped in water was lifted out of water, and its mass was measured; the difference between the measured value and the dry weight of the heat exchanger 1 was taken as the retained water amount. Measurements were made every two seconds starting at the moment of lifting-out (with the lapse of time zero). The unit of the retained water amount in the table is the mass of the water retained in the heat exchanger assuming that its surface area is 1 m² (the actual surface area of the heat exchanger was converted in this way).

[0040] The dimensional specifications of the heat exchanger used in the above experiments are as follows: the thickness of the flat tubes is 1.3 mm; the size of the gap between the flat tubes is 3.5 mm; the horizontal width of the flat tubes in the air flow direction is 23 mm; the horizontal width of the upwind-side corrugated fins in the air flow direction and the horizontal width of the downwind-side corrugated fins in the air flow direction are both 18 mm; the vertical-direction length of the upwind-side corrugated fins and the downwind-side corrugated fins are both 160 mm; the ridge-valley pitches of the upwind-side corrugated fins and the downwind-side corrugated fins are both 1.7 mm; the wall thicknesses of the upwind-side corrugated fins and the downwind-side corrugated fins are both 0.1 mm; and the slopes of the upwind-side corrugated fins and the downwind-side corrugated fins are both 32°.

[0041] In the table of Fig. 17 and in the graph of Fig. 18, the state in which the upwind-side corrugated fins and the downwind-side corrugated fins are put together is assumed to be one in which "the size of the gap is 0 mm", and measurements are made while the upwind-side corrugated fins and the downwind-side corrugated fins are increasingly taken apart from each other in steps of 1 mm from that state. Here the statement "the size of the gap is 0 mm" holds true only in the contact part, and elsewhere there is a gap. That is, the statement "the size of the gap is 0 mm" does not mean that there is no drain passage between the upwind-side corrugated fins and the downwind-side corrugated fins.

[0042] The above experiments show that, in experiment samples in which the gap is less than 3 mm, compared with experiment samples in which the gap is 3 mm or more, the retained water amount at the lapse of 20 seconds and more is definitely lower. From this viewpoint, it can be said that it is preferable that the gap be 3 mm or less. With consideration given to the amount of drainage, it is preferable that the gap be 2 mm or less; with consideration given also to the speed of drainage, it is preferable that the gap be about 1 mm.

[0043] The embodiments by way of which the present invention has been described above are not meant to limit the scope of the present invention; the present invention may be implemented with many modifications and variations made within the spirit of the invention.

Industrial Applicability

[0044] The present invention finds wide application in parallel-flow-type heat exchangers.

Claims

1. A heat exchanger comprising:

horizontal header pipes arranged parallel at an interval from one another in a vertical direction;

a plurality of vertical flat tubes arranged at an interval from one another in a horizontal direction between the header pipes, with refrigerant passages inside the flat tubes communicating with insides of the header pipes respectively; and

corrugated fins arranged between the flat tubes,
wherein
the corrugated fins comprise

upwind-side corrugated fins whose fin surface has a downward slope toward a downwind side and

downwind-side corrugated fins whose fin surface has an upward slope toward the downwind side, and
downwind-side ends of the upwind-side corrugated fins and upwind-side ends of the downwind-side corrugated fins are arranged with a gap secured therebetween, the gap being so sized as to enable water droplets sticking to the downwind-side ends of the upwind-side corrugated fins and water droplets sticking to the upwind-side ends of the downwind-side corrugated fins to coalesce.

2. The heat exchanger according to claim 1,
wherein the downwind-side ends of the upwind-side corrugated fins and the upwind-side ends of the downwind-side corrugated fins are kept in partial contact with each other so that the gap is produced elsewhere than in a contact part.

Drawing