EP3015808B1

EP3015808B1 - Heat exchanger, heat exchanger structure, and fin for heat exchanger

Info

Publication number: EP3015808B1
Application number: EP13888478.8A
Authority: EP
Inventors: Hideaki Tatenoi; Yoshihiro Hara; Katsuhiro Saito; Yoichi Uefuji; Yasutaka Aoki
Original assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Current assignee: Mitsubishi Heavy Industries Thermal Systems Ltd
Priority date: 2013-06-28
Filing date: 2013-06-28
Publication date: 2018-08-29
Anticipated expiration: 2033-06-28
Also published as: WO2014207785A1; EP3015808A1; EP3015808A4; JPWO2014207785A1

Description

Technical Field

The present invention relates to a heat exchanger used for an air A heat exchanger according to the preamble of claim 1 is known from JPS 53 26694 .

Background Art

In an air conditioner that provides both cooling and heating by a common refrigeration cycle, one heat exchanger functions as a condenser during a cooling operation and as an evaporator during a heating operation.
A heat exchanger in an outdoor unit functions as an evaporator during the heating operation. When the evaporator performs the heating operation during cold weather, for example, when the outside air temperature is as low as about -5°C, a frosting phenomenon occurs in the evaporator in which moisture in the air attaches to the evaporator as frost. Usually, frosting occurs from the upwind side of the heat exchanger, and the frost gradually grows toward the downwind side. If frosting occurs on the heat exchanger, a fin heat transfer area for directly exchanging heat with the air is reduced, thereby reducing a heating capability. In addition, the frosting narrows a ventilation path between fins to reduce the volume of air, which also reduces the heating capability. Accordingly, a defrosting operation is performed, for example, regularly, for removing the attached frost during the heating operation in a low outside air temperature. The heating operation is stopped during the defrosting operation, which might decrease the comfort of a user of the air conditioner. Hence, various techniques have been proposed for reducing likelihood of frosting on the upwind side of a heat exchanger (evaporator). Here, representative examples of the defrosting operation include melting the frost by switching the refrigeration cycle into the one in the cooling operation and working the outdoor heat exchanger as a condenser, and then flowing a high temperature refrigerant.
In addition to the problem of frosting on the upwind side of the heat exchanger, water generated when frost is melted by the defrosting operation (melt water, hereinafter) is not drained entirely during the defrosting operation, and sometimes remains on the fins. If the heating operation is resumed after the defrosting operation with the melt water accumulating on the fins, the melt water freezes to cause frosting again, thereby easily clogging the ventilation path.
The present inventors have disclosed in Patent Literature 1 a heat exchanger that inhibits frosting during the heating operation while facilitating drainage of melt water generated by the defrosting operation. In the proposal, the fin has thermal conduction control portions extending along a direction of an outside air flow. According to the heat exchanger of Patent Literature 1, heat conduction from tubes to the fin is controlled on the upwind side in the direction of the outside air flow relative to the downwind side. The proposal of Patent Literature 1, therefore, suppresses temperature drop of the fin at portions on the upwind side in the outside air flow direction when the heat exchanger in an outdoor unit functions as an evaporator, thereby controlling frosting. Also, the heat exchanger in Patent Literature 1 drains melt water downward through slits formed as thermal conduction control portions during the defrosting operation, and thus has excellent drainage.
Patent Literature 2, 3 and 4 each disclose other examples of heat exchangers.

Citation List

Patent Literature

Patent Literature 1: Japanese Patent Laid-Open No. 2012-72955
Patent Literature 2: JP 2002 130973
Patent Literature 3: JP S59 18179
Patent Literature 4: JP H06 347185

Summary of Invention

Technical Problem

The present invention aims to provide a heat exchanger that can, even when frosting occurs on the upwind side of the heat exchanger, exchange heat continuously on the downwind side of a fin by securing a ventilation path, and in addition, further improve drainage of melt water, from a different viewpoint than that in Patent Literature 1.

Solution to Problem

To achieve the above object, a heat exchanger of the present invention is defined in claim 1, and includes a plurality of tubes each having a flowpath through which a refrigerant flows, and a corrugated fin including a plurality of heat transfer walls that are arranged in a running direction of the tubes and span from one to the other of adjacent tubes among the plurality of tubes, the fin being capable of exchanging heat with the tubes. The heat transfer walls in the present invention include a first heat transfer piece leading to a first edge portion positioned on an upwind side of a passing airflow, and a second edge portion indented relative to the first edge portion toward a downwind side in a direction of the airflow, and the first heat transfer piece is disposed at least on every other layer of the arrangement of the heat transfer walls.
The heat exchanger of the present invention includes the heat transfer walls including a first edge portion and a second edge portion indented toward the downwind side relative to the first edge portion, and the first edge portion and the second edge portion are each disposed at least on every other layer in the direction of the arrangement. Accordingly, a fin pitch between the first edge portions adjacent to each other in the arrangement direction can be widened. As a result, even if frosting occurs locally on the first edge portions positioned on an upwind side end of the fin, the heat exchanger can exchange heat continuously on the downwind side because the ventilation path is secured.
Because, in the heat exchanger of the present invention, the second edge portions are present that are indented toward the downwind side, the heat transfer walls are discontinuous on the upwind side relative to the second edge portion. This shortens the distance for the melt water generated during the defrosting operation to flow down the fin. Accordingly, the heat exchanger of the present invention drains the melt water to the outside of the heat exchanger in a short time compared with a heat exchanger in which the melt water flows down the fin while meandering. Additionally, in the heat exchanger of the present invention, the discontinuation of the heat transfer walls reduces boundary portions with the tubes where the melt water is particularly likely to accumulate, thereby reducing the accumulation amount of the melt water. Therefore, a heat transfer area of the fin can be secured appropriately even if the melt water solidifies after resumption of the heating operation.
Each heat transfer wall in the present invention includes the first heat transfer piece leading to the first edge portion positioned on the upwind side of the passing airflow, and the second edge portion indented relative to the first edge portion toward the downwind side in the direction of the airflow, and the first heat transfer piece may be disposed alternately on the side closer to one tube and on the side closer to the other tube of adjacent tubes.
In the heat exchanger of the present invention, the heat transfer walls include the first edge portion and the second edge portion indented toward the downwind side relative to the first edge portion, and the first edge portion and the second edge portion are disposed alternately in the arrangement direction of the heat transfer walls. Accordingly, there is a portion without a heat transfer wall between the first edge portions adjacent in the arrangement direction for the second edge portions are indented toward the downwind side, thereby widening the fin pitch. As a result, even if frosting occurs locally on the first edge portions positioned on an upwind side end of the fin, the heat exchanger can exchange heat continuously on the downwind side because the ventilation path is secured.
In the present invention, the heat transfer walls are each preferably equipped with heat transfer facilitating means on the upwind side.
Provision of the heat transfer facilitating means on the upwind side improves the heat transfer performance of the heat transfer walls on the upwind side.
Further, in the present invention, the heat transfer walls are each preferably equipped with heat transfer facilitating means on the downwind side.
Provision of the heat transfer facilitating means on the downwind side improves the heat transfer performance of the heat transfer walls on the downwind side.
In the present invention, each of the heat transfer walls preferably includes a second heat transfer piece leading to a third edge portion positioned on the downwind side of the airflow, and a fourth edge portion indented toward the upwind side relative to the third edge portion, and the second heat transfer piece is preferably disposed on every other layer of the arrangement on both of a side closer to one tube and a side closer to the other tube of adjacent tubes such that the second heat transfer piece appears alternately on both sides.
Because there is a region without a heat transfer wall also on the downwind side, the drainage of the melt water can be improved also on the downwind side. Further, even if the remaining melt water solidifies, a heat transfer area of the fin available for exchanging heat directly with the air can be secured appropriately, and in addition, the ventilation path can be prevented from becoming easily clogged.
A heat exchanger structure of the present invention is a collection of a plurality of heat exchangers arranged in the direction of the passing airflow, the heat exchangers including a plurality of tubes arranged in a predetermined direction, the tubes each including a flowpath through which a refrigerant flows, and a corrugated fin provided between adjacent tubes among the plurality of tubes, the fin being capable of exchanging heat with the tubes. Among the heat exchangers, one disposed on the most upwind side in the direction of the airflow is the heat exchanger according to the present invention.
By providing the heat exchanger according to the present invention on the most upwind side in the direction of the airflow, the airflow is dehumidified while it passes through the heat exchanger on the upwind side, which reduces the frosting to the following heat exchangers.
A fin for heat exchanger used in the heat exchanger of the present invention is a corrugated fin that is provided between adjacent tubes and is capable of exchanging heat with the tubes.

Advantageous Effects of Invention

According to the present invention, by widening the fin pitch of the corrugated fin in the area close to the end positioned on the upwind side, the portion with the wide fin pitch is secured as the ventilation path even if frosting occurs locally on the first edge portion, which is an end of the fin, and thus the heat exchanger can exchange heat continuously on the downwind side of the fin. In an air conditioner using the heat exchanger of the present invention, therefore, the time between defrosting operations is increased, thereby decreasing the frequency of the defrosting operation.
According to the present invention, the first edge portion and the second edge portion are disposed alternately in the direction of the heat transfer wall arrangement, allowing the melt water to be drained to the outside of the heat exchanger in a short time. Thus, the drainage of the melt water can be improved. Further, according to the present invention, because the amount of the melt water to accumulate is reduced, a heat transfer area of the fin can be secured appropriately even if the melt water solidifies after resumption of the heating operation.

Brief Description of Drawings

[FIG. 1] FIG. 1 is a perspective view showing a heat exchanger according to an embodiment of the present invention.
[FIG. 2] FIG. 2 is a partially exploded perspective view showing a heat exchanger according to a first embodiment of the present invention.
[FIGS. 3A to 3C] FIGS. 3A to 3C show the heat exchanger of the first embodiment in which FIG. 3A is a plan view showing an area between adjacent tubes, FIG. 3B is a view schematically showing a side cross section of a fin, and FIG. 3C is a developed view of the fin.
[FIG. 4] FIG. 4 is a schematic view explaining the effects of the first embodiment.
[FIGS. 5A to 5D] FIGS. 5A to 5D are schematic views explaining the effects of the first embodiment in which FIG. 5A shows a side cross section of the fin of the embodiment, FIG. 5B shows a side cross section of a conventional fin, FIG. 5C shows a side cross section of the heat exchanger of the embodiment, and FIG. 5D shows a side cross section of a conventional heat exchanger.
[FIGS. 6A to 6D] FIGS. 6A to 6D are perspective views showing a modification of the fin in the first embodiment.
[FIGS. 7A to 7D] FIGS. 7A to 7D is a side cross-sectional view showing another modification of the fin in the first embodiment.
[FIG. 8B] FIG. 8B is a side cross-sectional view showing still another modification of the fin in the first embodiment.
[FIGS. 8A, 8C and 8D] FIGS. 8A, 8C and 8D are side cross-sectional views showing still another modification of the fin in the first embodiment that are not part of the presently claimed invention.
[FIGS. 9A to 9C] FIGS. 9A to 9C are partially exploded perspective views showing a heat exchanger according to a second embodiment of the present invention in which FIG. 9A shows an example of providing a louver on the downwind side; FIG. 9B shows an example of providing undulations on the upwind side and a louver on the downwind side, and FIG. 9C shows an example of providing louvers on both the upwind side and the downwind side.
[FIGS. 10A to 10C] FIGS. 10A to 10C show a heat exchanger according to a third embodiment of the present invention in which FIG. 10A is a partially exploded perspective view, FIG. 10B is a plan view showing an area between adjacent tubes, and FIG. 10C is a developed view of a fin.
[FIG. 11] FIG. 11 is a perspective view showing a heat exchanger structure according to a fourth embodiment of the present invention.
[FIGS. 12A and 12B] FIGS. 12A and 12B are views showing a modification of the present invention.

Description of Embodiments

Hereinafter, embodiments of the heat exchanger of the present invention will be described with reference to the drawings.

[First Embodiment]

As shown in FIGS. 1 to 3C, a heat exchanger 10 in the embodiment includes a core 20 formed by alternately stacking a plurality of tubes 21 though which a refrigerant flows and a plurality of fins 22, and a pair of header tubes 30 to which ends of the tubes 21 are connected, and exchanges heat between an outside air and the refrigerant.
The heat exchanger 10 is applied to an outdoor heat exchanger of a heat pump air conditioner. In that case, the heat exchanger 10 is assembled to an outdoor unit of the air conditioner with the tubes 21 standing along a vertical direction Y. The heat exchanger 10 receives an airflow A generated by a fan that is omitted in the drawings, and exchanges heat between the refrigerant and the outside air while the airflow passes through ventilation paths 27, openings formed between the tubes 21 and the fins 22 of the core 20.
The tubes 21 each have a flat cross section and include a flowpath for a refrigerant penetrating therethrough in the axial direction. The tubes 21 are manufactured by extruding copper or a copper alloy, or aluminum or an aluminum alloy that have excellent thermal conductivity, or by roll forming a plate-like material.
The tubes 21 have their both axial ends joined to each header tube 30 by soldering, for example, and the refrigerant flowpaths 21a formed inside the tubes 21 along the axial direction are in communication with a refrigerant flowpath of each header tube 30 that will be described later. This ensures a flow of the refrigerant between the tubes 21 and the header tubes 30.
In the embodiment, the fins 22 use corrugated fins each formed by repeated alternate mountain folds and valley folds. Each fin 22 includes a heat transfer wall 23 and a turn 24 connecting heat transfer walls 23, 23 adjacent to each other with a space therebetween, and meanders between both ends in the width direction X. The spaces between the heat transfer walls 23, 23 ... where a plurality of layers are arranged in the vertical direction Y are set approximately equal. Here, one piece of heat transfer wall 23 is treated as one layer.
The turn 24 has a rectangular shape in the example, although the turn 24 may be in other configurations, such as a V shape. The fin 22 is integrally formed by a fold forming a plate-shaped workpiece made from a material similar to that of the tubes 21. The fin 22 is characterized in the configuration on its upwind side, which will be described later.
The core 20 is constituted by the above described tubes 21 and the fin 22, which are stacked alternately in the width direction X of the heat exchanger 10. The fin 22 arranged between tubes 21, 21 adjacent to each other in the width direction X is joined to the tubes 21, 21 at the turns 24 by, for example, soldering, allowing the fin 22 and the tubes 21 to exchange heat with each other. The core 20 is provided with side plates 26 on both ends in the width direction X. The side plates 26 each function as a reinforcing member of the core 20, and are supported by the header tubes 30 at both end portions in the up-down direction.
The header tubes 30 each have a refrigerant flowpath (not shown) inside.
For example, the header tube 30 placed on the lower side in the figure (a lower header tube 32) is provided with an inlet of the refrigerant at one end side in the width direction X. The refrigerant supplied through refrigerant tubing forming the refrigeration cycle to the inlet passes through the flowpath in the lower header tube 32 and flows into the plurality of tubes 21. The header tube 30 placed on the upper side in the figure (an upper header tube 31) is provided with an outlet of the refrigerant at one end side in the width direction X. The refrigerant having flown through the tubes 21 flows into the upper header tube 31 and flows through the outlet toward the refrigerant tubing forming the refrigeration cycle.
The header tubes 30 may be manufactured from a material similar to that of the tubes 21. The tubes 21 may be manufactured integrally or may be manufactured by combining several members.
If an air conditioner including the heat exchanger 10 as an outdoor heat exchanger is performing the heating operation in a low outside air temperature, frosting occurs on the fin 22 on the upwind side of the airflow A. It is to be noted that, hereinafter, the upwind side of the airflow A may simply be referred to as the upwind side for short. The same applies to the downwind side. The air conditioner performs a defrosting operation, for example, regularly for removing the attached frost. If the melt water remains not being fully drained from the heat exchanger 10 after the defrosting operation, it might freeze after resumption of the heating operation, possibly causing frosting again.
In the heat exchanger 10, a fin pitch at the upwind side of the fins 22 is made wider than that at the downwind side. This allows the heat exchanger 10 to exchange heat continuously on the downwind side even when the frosting occurs, increasing an interval between the defrosting operations. Also, the heat exchanger 10 provides improved drainage of the melt water. Hereinafter, the characteristics of the fin 22 will be described with reference to FIGS. 2 to 4. In FIG. 3B, a side cross section of the fin 22 at an area U on the upwind side is shown by solid lines and a side cross section of the fin 22 at an area D on the downwind side is shown by dashed lines. The same applies to FIGS. 5A to 5D, and 7A to 9C.

[Relation between fin pitch P1 of area U and fin pitch P2 of area D]

In the fin 22, a fin pitch P1 at a predetermined area U (FIG. 3A) on the upwind side is set wider than a fin pitch P2 at an area D on the downwind side relative to the area U, as shown in FIGS. 2 to 3C.
Each heat transfer wall 23 of the fin 22 satisfies the following two conditions for widening the fin pitch P1 compared with the fin pitch P2.
A first condition is that either of the opposite sides of the heat transfer wall 23 divided by the midpoint M in the width direction X is cut out. Because of the cutout, a leading edge portion 23b with the cutout is indented toward the downwind side relative to a leading edge portion 23a without the cutout. The leading edge portion 23a without the cutout is provided with a heat transfer piece 23L and 23R protruding toward the upwind side beyond the leading edge portion 23b.
A second condition is that the heat transfer pieces 23L and 23R are each disposed on every other layer of the heat transfer wall 23, such that the heat transfer pieces 23L and 23R appear alternately on the opposite sides of the midpoint M in the width direction X. In terms of the cutout, the condition is equivalent to that the cutouts are disposed on every other layer of the heat transfer wall 23, alternately on the opposite sides of the midpoint M in the width direction X.
By satisfying the above two conditions, in the area U of the fin 22, the heat transfer piece 23L is provided on every other layer on one side (left side of FIG. 3B) L of the midpoint M. Similarly, also on the other side (right side of FIG. 3B) R, the heat transfer piece 23R is provided on every other layer. In addition, the phase of the fin pitch P1 is shifted by 1/2 cycle (half cycle) between the one side L and the other side R.
It is to be noted that although portions of the heat transfer pieces 23L and 23R corresponding to turns facing the tubes 21 are cut out, and thus the fin 22 has no turns 24 in the area U, the portions however may not be cut out to leave the turns. The heat transfer pieces 23L and 23R may be joined to the tubes 21 at their edges facing the tubes 21 by soldering such that the heat transfer pieces 23L and 23R are able to exchange heat with the tubes 21, or may be separated from the tubes 21.

[Fin workpiece 25]

A fin workpiece 25 used for forming the fin 22 is formed from a plate of the above described metal material in the shape of a rectangular in a plan view, as shown in FIG. 3C. The fin workpiece 25 has a plurality of evenly spaced rectangular cutouts 25a at an edge corresponding to the upwind side when assembled as the fin 22 to the heat exchanger 10. Each workpiece portion 25b remaining between adjacent cutouts 25a, 25a forms the heat transfer piece 23L or 23R. The fin workpiece 25 has on the edge the cutouts 25a and the workpiece portions 25b that are repeatedly formed in an alternate manner.

[Operation/Effect]

Next, the operation and effects of the heat exchanger 10 including the forgoing fin 22 will be described.
First, a description will be given on how the heat exchanger 10 exchanges heat continuously on the downwind side with reference to FIG. 4.
In the fin 22, the fin pitch P1 at the area U positioned on the upwind side is made wider than the fin pitch P2 at the area D positioned on the downwind side. As shown in FIG. 4, frosts Fa formed locally on the leading edge portions 23a of the heat transfer walls 23 positioned on the upwind side narrows the ventilation paths 27, but the wide fin pitch P1 can extend the time to clogging on the upwind side by the frosts Fa.
Also, even if frosts Fb attach to the leading edge portions 23b, openings that function as the ventilation paths 27 are secured between the frosts Fa and the frosts Fb for a long time because the leading edge portions 23b are indented toward the downwind side. In particular, the airflow A having reached the leading edge portions 23b contains a reduced amount of moisture as it is dehumidified by the leading edge portions 23a, and therefore, an amount of the frosts Fb on the leading edge portions 23b is less than that on the leading edge portions 23a. This is advantageous in securing openings functioning as the ventilation paths 27.
As described above, the heat exchanger 10 can exchange heat continuously within the area D on the downwind side of the fin 22 for a long time. As a result, an air conditioner using the heat exchanger 10 can decrease the frequency of the defrosting operation.
On the other hand, because the area D has a higher density of the heat transfer wall 23 than that in the area U, the fin 22 can minimize a reduction in heat exchange efficiency.
Next, the improvement in the drainage of melt water will be described with reference to FIGS. 5A to 5D. The improvement of the drainage in the present invention includes reducing the amount of melt water to accumulate in addition to facilitating the drainage itself.
First, the facilitation of the drainage will be described.
Because the heat exchanger 10 is provided with the leading edge portions 23b that are indented toward the downwind side, the heat transfer walls 23 are discontinuous on the upwind side (area U) of the fin 22. As a result, melt waters W generated as frosts F melt during the defrosting operation flow off both sides of the heat transfer pieces 23R and 23L in the width direction X, as shown by arrows Wf in FIG. 5A. The melt waters W flow down the tubes 21 (not shown in FIG. 5A) on the sides opposed to the tubes 21, and drop directly downward on the sides facing the cutout to be discharged to the outside of the heat exchanger 10. In contrast, if there is no leading edge portion 23b indented toward the downwind side, as shown in FIG. 5B, the melt water W would flow down the fin 22 while meandering, as shown by an arrow Wf. In this way, the heat exchanger 10 can remove the melt water W to the outside of the heat exchanger 10 in a short time compared with draining while meandering, because the heat exchanger 10 can drain the melt water W taking a shortcut route.
Next, the reduction of the accumulation will be described.
The melt water W that has not been drained is likely to accumulate at the inside IN of the turns 24 as shown in FIG. 5D. In the heat exchanger 10, however, the leading edge portions 23b are indented toward the downwind side and there are no insides IN of the turns 24 within the area U on the upwind side, where frosting easily occurs, and thus, if the melt water W accumulates, it only accumulates above the boundaries between the heat transfer pieces 23L and 23R and the tubes 21 as shown in FIG. 5C. According to the heat exchanger 10, therefore, because the amount of the melt water W to accumulate on the fin 22 can be reduced, even if the melt water W solidifies after resumption of the heating operation, a wider heat transfer area of the fin 22 can be secured and also the ventilation path can be prevented from becoming easily clogged.
Also, the heat exchanger 10 can ensure a desired heat transfer performance within the area U if the heat transfer pieces 23L and 23R are connected to the tubes 21 such that the heat transfer pieces 23L and 23R are able to exchange heat with the tubes 21.
Some modifications of the embodiment will be described.

[Planar shape of cutout]

Although the cutouts of the fin 22 of the embodiment each have a rectangular shape as seen in a plan view, the cutouts may have any shape as long as the embodiment achieves the objects of the present invention. For example, as shown in FIGS. 6A to 6D, the cutouts may adopt several shapes including a circular cutout (FIG. 6A), a triangular cutout (FIG. 6B), a polygonal cutout (FIG. 6C), and a steplike cutout (FIG. 6D).

[Cross sectional shape of turn of fin]

Also, the turns of the fin 22 may be in any pattern as long as the embodiment achieves the objects of the present invention. FIGS. 7A to 7D and 8B show some patterns adoptable in the present invention, and the present invention may adopt these patterns.
FIG. 7A shows a pattern in which lower portions of each heat transfer wall 23 connected to the turn 24 are cut out. In contrast, FIG. 7B shows a pattern in which upper portions of each heat transfer wall 23 connected to the turn 24 are cut out. In any one of the patterns in FIG. 7A and 7B, the melt water flows downward taking the shortcut route to facilitate drainage of the melt water compared with a conventional corrugated fin in which heat transfer walls 23 are provided almost entirely along the space between the tubes 21, 21.
Although the heat transfer walls 23 are formed along the horizontal direction in the pattern in FIG. 7A, they may be inclined upward toward the middle in the width direction of the fin 22 as shown in FIG. 7C. Similarly, the heat transfer walls 23 in the pattern in FIG. 7B may be inclined downward toward the middle in the width direction of the fin 22 as shown in FIG. 7D. The drainage of the melt water can be further facilitated by thus inclining the heat transfer walls 23.
Next, in the fin 22 of the first embodiment, the heat transfer pieces 23L on one side in the width direction X and the heat transfer pieces 23R on the other side are provided not to overlap with each other as seen in a vertical direction (as seen in a plan view), although the present invention is not limited to this.
As shown in FIG. 8A which is not part of the presently claimed invention, the heat transfer pieces 23L on the one side and the heat transfer pieces 23R on the other side may form overlaps K at the middle portion in the width direction X of the fin 22. This configuration also receives the above beneficial effect obtained by widening the fin pitch P1 of the above described area U because the fin pitch P1 of the heat transfer pieces 23L, 23L ... and the fin pitch P1 of the heat transfer pieces 23R, 23R ... within the area U close to the tubes 21 are twice as wide as the fin pitch P2 of the area D.
Alternatively, in the present invention, gaps G may be provided at the middle portion in the width direction X of the fin 22 between the heat transfer pieces 23L on the one side and the heat transfer pieces 23R on the other side as shown in FIG. 8B which is part of the presently claimed invention. Similarly to FIG. 8A, this configuration also receives the beneficial effect obtained by widening the fin pitch P1 of the area U.
Next, although in the fin 22 of the first embodiment, the fin pitch P1 of the area U is widened by partially cutting out the fin workpiece 25, the present invention is not limited to this.
As shown in FIG. 8C which is not part of the presently claimed invention, the heat transfer pieces 23L, R may be folded downward to form regions corresponding to the cutouts. Then, the fin pitch P1 of the area U can be made wide compared with the fin pitch P2 of the area D similarly to the fin 22 of the first embodiment. Hanging pieces 23e formed by folding the heat transfer pieces each may be in contact with a surface of the heat transfer wall 23 on the lower layer at its tip as shown in FIG. 8C, or the tip may be away from the surface of the heat transfer wall 23 on the lower layer as shown in FIG. 8D which is not part of the presently claimed invention. In any case, the hanging pieces 23e contribute to facilitate drainage by forming paths for guiding the melt water downward. Here, the heat transfer pieces may be folded at any angle.

[Second Embodiment]

Next, the fin 22 may be provided with means for improving the heat transfer performance of one or both of the upwind side and the downwind side, as will be described below.

As an example, a louver 28 may be formed on the downwind side of the fin 22 (heat transfer wall 23) as shown in FIG. 9A (mode 2-1).
If the fin 22 has a higher heat transfer performance on the downwind side than on the upwind side, the dehumidification can be performed also on the downwind side as a result of suppressing the dehumidification on the upwind side. Here, because frosting is partly caused by the dehumidification by the fin 22, a high heat transfer performance on the downwind side as in the mode 2-1 suppresses local frosting on the upwind side, thereby easily securing the ventilation paths 27. Thus, according to the mode 2-1, in addition to alleviating the decrease in the heating capability due to reduction in the volume of air, a duration of the heating operation can be extended because the heat exchanger 10 can exchange heat continuously on the downwind side. At the same time, the upwind side of the fin 22 is not required to be processed, thereby suppressing increase in the processing cost.
The louver 28 is formed by cutting and raising the heat transfer wall 23 and disturbing the flow of air passing over the louver 28 facilitates heat transfer between the air and the heat transfer wall 23. It is to be noted that the louver 28 facilitates heat transfer more effectively than undulations 29 that will be described later.
The louver 28 may be provided at any region. The region is not limited to the downwind side but the louver 28 may be provided on the upwind side.

The present invention can also improve heat transfer performance on the upwind side.
As an example, the undulations 29 may be formed on the upwind side of the fin 22 (heat transfer wall 23) as shown in FIG. 9B (mode 2-2). The undulations 29 is wavy in a vertical cross section of the heat transfer wall 23 and has a shape of repeated mountain, valley, mountain ... from the upwind side to the downwind side.
Because a heat transfer area is increased on the upwind side by forming the undulations 29 on the upwind side, the heat transfer performance is increased compared with a fin formed by a flat plate. In addition, vortexes are generated when the airflow passes through the undulations 29, which also improves the heat transfer performance.
The louver 28 may be provided instead of the undulations 29 as shown in FIG. 9C for improving the heat transfer performance on the upwind side.

[Third Embodiment]

In the present invention, an end of the fin 22 on the downwind side may be configured similarly to the end of the fin 22 on the upwind side according to the first embodiment. That is, as shown in FIGS. 10A to 10C, either of the opposite sides of the heat transfer wall 23 divided by the midpoint M in the width direction X is cut out. Because of the cutout, a leading edge portion 23d with the cutout is indented toward the upwind side relative to a leading edge portion 23c without the cutout. The leading edge portion 23c without the cutout is provided with heat transfer pieces 23L and 23R protruding toward the downwind side beyond the leading edge portion 23d. In addition, the heat transfer pieces 23L and 23R are each disposed on every other layer of the heat transfer wall 23, such that the heat transfer pieces 23L and 23R appear alternately on the opposite sides of the midpoint M in the width direction X.
Because the frosting also occurs on the downwind side of the fin 22 although in a smaller amount than on the upwind side, the defrosting operation can lead to the accumulation of the melt water also on the downwind side of the fin 22. Then, the third embodiment adopts a configuration of the widened fin pitch also on the downwind side to thereby reduce the amount of the melt water to accumulate on the downwind side. In this way, even if the remaining melt water solidifies after resumption of the heating operation, a heat transfer area of the fin 22 available for exchanging heat can be secured appropriately, and in addition, the ventilation path can be prevented from becoming easily clogged.
The configuration of the widened fin pitch may adopt various forms as described in the first embodiment.

[Fourth Embodiment]

As shown in FIG. 11, the air conditioner may have a plurality of air conditioners 10 (10a and 10b) that are arranged (two air conditioners in the figure) in the direction of the wind flow for achieving a high heat transfer performance. The present invention can be applied to an air conditioner having a plurality of heat exchangers 10.
It is to be noted that the heat exchanger 10a disposed on the upwind side should adopt the present invention, while there is less need to apply the present invention to the heat exchanger 10b disposed on the downwind side. This is because the airflow having passed through the heat exchanger 10a on the upwind side flows into the heat exchanger 10b on the downwind side during the defrosting operation, and the airflow causes little or almost no frosting for the airflow has been dehumidified as it passed through the heat exchanger 10a on the upwind side. Of course, it does not intend to eliminate application of the present invention to the heat exchanger 10b on the downwind side. However, it agrees with the aim of providing the plurality of heat exchangers that the heat exchanger 10b on the downwind side appropriately secures a heat transfer area and minimizes a loss of the heat transfer performance.
Not only in the case of an air conditioner having two heat exchangers, but also in a case of an air conditioner having three or more heat exchangers, it is enough to apply the present invention to the heat exchanger disposed on the most upwind side. The term "application of the present invention", as used herein, includes all individual elements disclosed in the foregoing first to third embodiments.
The embodiments of the present invention have been described hereinbefore. However, some configurations may be selected from those cited in the above embodiments or may be appropriately changed to other configurations, without departing from the scope of the appended claims.
For example, the effects of the widened fin pitch and improved melt water drainage can be achieved even when both widthwise sides of the heat transfer walls 23 are cut out as shown in FIG. 12A. Alternatively, the heat transfer pieces 23L and the heat transfer pieces 23R each can be disposed on every three layers, for example, as shown in FIG. 12B.

Reference Signs List

10, 10a, 10b Heat exchanger
20 Core
21 Tube
21a Refrigerant flowpath
22 Fin
23 Heat transfer wall
23L, 23R Heat transfer piece
23a to 23d Leading edge portion
23e Hanging piece
25 Fin workpiece
25b Workpiece portion
26 Side plate
27 Ventilation path
28 Louver
29 Undulations
30 Header tube
31 Upper header tube
32 Lower header tube
A Airflow
F, Fa, Fb Frost
G Gap
IN Inside
M Midpoint
P1 Fin pitch
P2 Fin pitch
D, U Area
W Melt water
X Width direction
Y Vertical direction

Claims

A heat exchanger (10; 10a, 10b) comprising:
a plurality of tubes (21) each having a flowpath (21a) through which a refrigerant flows; and

a corrugated fin (22) including a plurality of heat transfer walls (23) that are arranged in a running direction of the tubes (21) and span from one to the other of adjacent tubes (21) among the plurality of tubes (21), the fin (22) being capable of exchanging heat with the tubes (21), the heat transfer walls (23) that are arranged in a running direction of the tubes (21) and span from one to the other of adjacent tubes (21) among the plurality of tubes (21) defining an arrangement of heat transfer walls (23), wherein

the heat transfer walls (23) each include:
a first heat transfer piece (23L) leading to a first edge portion (23a) positioned on an upwind side of a passing airflow (A); and

a second heat transfer piece (23R) leading to a second edge portion (23b) indented relative to the first edge portion (23a) toward a downwind side in a direction of the airflow (A),

wherein the first edge portion (23a) and the second edge portion (23b) are both arranged on the upwind side of the airflow (A), and

wherein the first heat transfer piece (23L) is disposed at least on every other layer of the arrangement of heat transfer walls (23) on both of a side closer to one tube (21) and the second heat transfer piece (23R) is disposed at least on every other layer of the arrangement of heat transfer walls (23) on both of a side closer to the other tube (21) of adjacent tubes (21) among the plurality of tubes (21) such that first heat transfer piece (23L) and the second heat transfer piece (23R) appears alternately on both sides, and

wherein a first fin pitch (P1) at a predetermined area (U) on the upwind wide is set wider than a second fin pitch (P2) at an area (D) on the downwind side relative to the predetermined area (U), and

characterized in that the first heat transfer piece (23L) and the second heat transfer piece (23R) are provided not to overlap with each other as seen in a vertical direction.
The heat exchanger (10; 10a, 10b) according to claim 1, wherein
the heat transfer walls (23) include
heat transfer facilitating means (28; 29) on the upwind side.
The heat exchanger (10; 10a, 10b) according to any one of claims 1 or 2, wherein
the heat transfer walls (23) include
heat transfer facilitating means (28) on the downwind side.
The heat exchanger (10; 10a, 10b) according to any one of claims 1 to 3, wherein
the first heat transfer piece (23L) of each of the heat transfer walls (23) leads to a third edge portion (23c) positioned on the downwind side of the airflow (A); and
each of the second heat transfer piece (23R) further leads to a fourth edge portion (23d) indented toward the upwind side relative to the third edge portion (23c).
A heat exchanger structure that is a collection of a plurality of heat exchangers (10; 10a, 10b) arranged in a direction of a passing airflow, the heat exchangers (10; 10a, 10b) including:
a plurality of tubes (21) arranged in a predetermined direction, the tubes (21) each including a flowpath (21a) through which a refrigerant flows; and

a corrugated fin (22) provided between adjacent tubes (21) among the plurality of tubes (21), the fin (22) being capable of exchanging heat with the tubes (21), wherein

among the heat exchangers (10; 10a, 10b), one disposed on a most upwind side in the direction of the airflow (A) is the heat exchanger (10; 10a, 10b) according to any one of claims 1 to 4.