EP4718009A1

EP4718009A1 - Heat exchanger and refrigeration cycle device comprising said heat exchanger

Info

Publication number: EP4718009A1
Application number: EP23938390.4A
Authority: EP
Inventors: Yoji ONAKA; Rihito ADACHI; Nanami KISHIDA; Takashi Nakajima
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 2023-05-22
Filing date: 2023-05-22
Publication date: 2026-04-01
Also published as: JPWO2024241417A1; JP7706650B2; WO2024241417A1; CN121219545A

Abstract

A heat exchanger includes a plurality of flat tubes each extending in a top-bottom direction with a flat external shape and each having a plurality of refrigerant flow paths in a form of through-holes; and a pair of headers connected to end portions of the plurality of flat tubes on both sides in the top-bottom direction and including respective L-bent portions each having an L shape in top view. The plurality of flat tubes are each shaped to have a major axis and a minor axis in a normal section taken to be normal to a tube-axis direction. At least one or two or more flat tubes included in the plurality of flat tubes and connected to the L-bent portions each have a wall thickness that increases toward two end portions in the normal section and decreases toward a central portion in the normal section, the two end portions and the central portion being located in a major-axis direction that is parallel to the major axis.

Description

Technical Field

The present invention relates to a heat exchanger including flat tubes, and to a refrigeration cycle apparatus including the heat exchanger.

Background Art

A hitherto known heat exchanger includes a pair of headers located opposite each other at a distance from each other, and a plurality of flat tubes provided between the pair of headers and arranged at intervals from one another, with end portions of the flat tubes on both sides in a tube-axis direction being connected to the pair of headers (see Patent Literature 1, for example). The heat exchanger disclosed in Patent Literature 1 has an L shape when viewed in a direction in which the flat tubes extend. The pair of headers include respective L-bent portions that are bent in an L shape.
The heat exchanger disclosed in Patent Literature 1 employs a technique of preventing the damage to brazed parts between the headers and the flat tubes that may occur at the bent portions of the pair of headers when the headers are bent into an L shape. In the heat exchanger disclosed in Patent Literature 1, each of the flat tubes has a greater outer perimeter at the two end portions located in the tube-axis direction and connected to the headers than at portions other than the two end portions, whereby a satisfactory margin for brazing is provided. Thus, the L-bent portions of the headers and the flat tubes are strongly connected to each other, preventing the occurrence of damage.

Citation List

Patent Literature

Patent Literature 1: Japanese Patent No. JP 7 037 090 B2

Summary of the Invention

Technical Problem

In the heat exchanger disclosed in Patent Literature 1, the flat tube has a greater outer perimeter at the two end portions located in the tube-axis direction than at the other portions. That is, the outer perimeter is not constant in the tube-axis direction. Therefore, the process of manufacturing the flat tube itself tends to be complicated. Under such circumstances, heat exchangers are required to exhibit increased strength at the connections, with the outer perimeter of each flat tube, or the external shape of the flat tube, being constant in the tube-axis direction.
One possible method of increasing the strength at the connections is increasing the strength of the flat tube by increasing the wall thickness of the flat tube. Nevertheless, to increase the wall thickness of the flat tube of the heat exchanger without changing the external dimensions of the flat tube, the flow-path sectional areas of refrigerant flow paths provided inside the flat tube need to be reduced, which increases the loss of refrigerant pressure.
The present invention is to solve the above problem and is to provide a heat exchanger in which a pair of headers include respective L-bent portions; increased strength is provided to flat tubes; and the increase in the pressure loss is suppressed, and to also provide a refrigeration cycle apparatus including the heat exchanger.

Solution to the Problem

A heat exchanger according to an embodiment of the present invention includes a plurality of flat tubes each extending in a top-bottom direction with a flat external shape and each having a plurality of refrigerant flow paths in a form of through-holes; and a pair of headers connected to end portions of the plurality of flat tubes on both sides in the top-bottom direction and including respective L-bent portions each having an L shape in top view. The plurality of flat tubes are each shaped to have a major axis and a minor axis in a normal section taken to be normal to a tube-axis direction. At least one or two or more flat tubes included in the plurality of flat tubes and connected to the L-bent portions each have a wall thickness that increases toward two end portions in the normal section and decreases toward a central portion in the normal section, the two end portions and the central portion being located in a major-axis direction that is parallel to the major axis.
A refrigeration cycle apparatus according to another embodiment of the present invention includes a compressor, a condenser, a decompressor, and an evaporator. At least one of the condenser and the evaporator is the above heat exchanger.

Advantageous Effects of Invention

In the heat exchanger and the refrigeration cycle apparatus according to the above embodiments of the present invention, the at least one or two or more flat tubes connected to the L-bent portions each have a wall thickness that increases toward the two end portions in the normal section that are located in the major-axis direction parallel to the major axis and decreases toward the central portion in the normal section that is located in the major-axis direction. One of the two end portions in the normal section that are located in the major-axis direction parallel to the major axis is located on a bend outer side at the L-bent portions of the pair of headers.
Therefore, in the heat exchanger and the refrigeration cycle apparatus according to the above embodiments of the present invention, the wall thickness of the flat tubes at the L-bent portions of the pair of headers is greater on the bend outer side. Thus, increased strength is provided to the flat tubes, and the occurrence of damage to the flat tubes is suppressed. Furthermore, in the heat exchanger and the refrigeration cycle apparatus according to the above embodiments of the present invention, the wall thickness of each of the flat tubes is smaller at the central portion located in the major-axis direction than at the two end portions located in the major-axis direction.
Therefore, compared with a configuration in which the wall thickness at the central portion located in the major-axis direction is set as large as the wall thickness at the two end portions, a satisfactory flow-path sectional area is provided, and the increase in the pressure loss is suppressed. That is, in the heat exchanger and the refrigeration cycle apparatus, while increased strength is provided to the flat tubes, the increase in the pressure loss is suppressed.

Brief Description of the Drawings

FIG. 1 is a schematic perspective view of a heat exchanger according to Embodiment 1.
FIG. 2 illustrates a configuration of a flat tube included in the heat exchanger according to Embodiment 1.
FIG. 3 is a schematic perspective view of part of the heat exchanger according to Embodiment 1 where flat tubes are connected to a header.
FIG. 4 is an enlarged plan view of an L-bent portion of the header included in the heat exchanger according to Embodiment 1.
FIG. 5 is a diagram for denoting dimensions of each of the flat tubes included in the heat exchanger according to Embodiment 1.
FIG. 6 is a sectional view illustrating a configuration of the flat tube included in the heat exchanger according to Embodiment 1.
FIG. 7 is a diagram for denoting dimensions of the flat tube included in the heat exchanger according to Embodiment 1.
FIG. 8 illustrates a normal section of a flat tube according to Comparative Example with some inner pillars thereof broken.
FIG. 9 illustrates a process of manufacturing the heat exchanger according to Embodiment 1.
FIG. 10 illustrates a normal section of a flat tube included in a heat exchanger according to Embodiment 2.
FIG. 11 illustrates a normal section of a flat tube included in a heat exchanger according to Embodiment 3.
FIG. 12 illustrates how the flow of liquid refrigerant is deflected in a header.
FIG. 13 illustrates a normal section of a flat tube included in a heat exchanger according to Embodiment 4.
FIG. 14 illustrates a normal section of a flat tube included in a heat exchanger according to Embodiment 5.
FIG. 15 illustrates a normal section of a flat tube included in a heat exchanger according to Embodiment 6.
FIG. 16 is a graph illustrating relationships established in the heat exchanger according to Embodiment 7 among a major-axis length T_w of the flat tube, a pitch D_p of the flat tubes, and a possible bend radius R₀ of the L-bent portion.
FIG. 17 is a refrigerant circuit diagram schematically illustrating a configuration of a refrigeration cycle apparatus according to Embodiment 8.

Description of Embodiments

Embodiments will now be described with reference to the drawings. Note that the following embodiments do not limit the present invention. The drawings including FIG. 1 to be referred to below may not be to scale, including the shapes and other factors of individual elements. In the drawings to be referred to below, the same reference signs denote the same or equivalent elements, which applies throughout this specification. Terms such as top, bottom, right, left, front, and rear to be used in the following description refer to directions defined for the heat exchanger viewed from the front. Such terms related to directions are only used for convenience of description and do not limit the position and orientation of the apparatus or components thereof.

Embodiment 1

Overall Configuration of Heat Exchanger 100

FIG. 1 is a schematic perspective view of a heat exchanger 100 according to Embodiment 1. The top-bottom direction in FIG. 1 corresponds to the direction of gravity. The heat exchanger 100 according to Embodiment 1 is used as an element of a refrigeration cycle apparatus and is an air heat exchanger configured to exchange heat between air and refrigerant. In this specification, the positional relationships between individual elements, the directions in which individual elements extend, and the directions in which individual elements are arranged side by side are defined with the heat exchanger 100 installed for use, in principle.
As illustrated in FIG. 1, the heat exchanger 100 includes a plurality of flat tubes 10, which each extend in the top-bottom direction; a pair of headers 20, which are provided at both ends of the plurality of flat tubes 10 in the direction in which the flat tubes 10 extend; and a plurality of corrugated fins 30, which are each provided between adjacent ones of the flat tubes 10. The heat exchanger 100 is not limited to such a configuration including corrugated fins 30 and may be a finless heat exchanger that includes no corrugated fins 30 or may be a plate heat exchanger that includes a plurality of plate fins through which a plurality of flat tubes 10 extend.
The heat exchanger 100 has an L shape when viewed in the top-bottom direction and includes a first heat-exchanger portion 101, which extends in the left-right direction; a second heat exchanger portion 102, which extends in the front-rear direction; and a third heat exchanger portion 103, which connects the first heat exchanger portion 101 and the second heat exchanger portion 102 to each other. The first heat-exchanger portion 101, the second heat-exchanger portion 102, and the third heat-exchanger portion 103 each include a plurality of flat tubes 10, part of the pair of headers 20, and a plurality of corrugated fins 30.
The plurality of flat tubes 10 each extend in the top-bottom direction. The plurality of flat tubes 10 are arranged side by side and at intervals from one another. The plurality of flat tubes 10 are each inserted at end portions thereof on both sides in the top-bottom direction (tube-axis direction) into the pair of headers 20 and are brazed to the headers 20.
The headers 20 are each a cylindrical body with the two ends thereof closed to provide thereinside a space through which refrigerant is allowed to flow. While the headers 20 exemplified in FIG. 1 each have a rectangular cross-sectional shape, the cross-sectional shape of the header 20 is not limited to a rectangular shape and may be a circular shape or an oval shape. That is, the cross-sectional shape of the header 20 may be changed as appropriate. The form of the header 20 is not limited to the above cylindrical body with two closed ends and may be, for example, a stack of plate members having slits. The pair of headers 20 may have different external shapes or cross-sectional shapes from each other.
One of the headers 20 has an inlet 20a, through which the refrigerant flows in. The other header 20 has an outlet 20b, through which the refrigerant flows out. The refrigerant flowing into the one header 20 through the inlet 20a is distributed to the plurality of flat tubes 10. The distributed portions of the refrigerant flow through the individual flat tubes 10 from the lower ends to the upper ends and merge together at the other header 20. Then, the merged refrigerant flows out through the outlet 20b.
The pair of headers 20 each have an L shape when viewed in the top-bottom direction. The headers 20 each include a first linear portion 21, which extends in the left-right direction; a second linear portion 22, which extends in the front-rear direction; and an L-bent portion 23, which connects the first linear portion 21 and the second linear portion 22 to each other.
FIG. 2 illustrates a configuration of each of the flat tubes 10 included in the heat exchanger 100 according to Embodiment 1. FIG. 3 is a schematic perspective view of part of the heat exchanger 100 according to Embodiment 1 where some flat tubes 10 are connected to the header 20. FIG. 4 is an enlarged plan view of the L-bent portion 23 of the header 20 included in the heat exchanger 100 according to Embodiment 1. In FIG. 4, to illustrate the positional relationship between the header 20 and the flat tubes 10, the outlines of the flat tubes 10 are represented by dotted lines. FIG. 5 is a diagram for denoting dimensions of each of the flat tubes 10 included in the heat exchanger 100 according to Embodiment 1. FIGS. 2 and 5 each illustrate a section of the flat tube 10 that is taken to be normal to the tube-axis direction of the flat tube 10 (hereinafter, the section is referred to as a normal section).
As illustrated in FIG. 2, the flat tube 10 has a cross-sectional shape that is flat in one direction, such as an oblong shape. The flat tube 10 has a flat external shape, with the normal section thereof having a major axis and a minor axis. The flat tube 10 has a symmetrical structure with respect to a center line L1, to be described separately below.
The flat tube 10 has a pair of major edges 11 and a pair of minor edges 12. The major edges 11 extend in a major-axis direction, which is parallel to the major axis. The minor edges 12 extend in a minor-axis direction, which is parallel to the minor axis. The flat tube 10 has a pair of curved portions 13, which connects respective ends of the pair of major edges 11 that are located on one side (the left side in FIG. 2) to two respective ends of a minor edge 12a, which is one of the pair of minor edges 12.
The flat tube 10 has a pair of curved portions 14, which connects respective ends of the pair of major edges 11 that are located on the other side (the right side in FIG. 2) to two respective ends of a minor edge 12b, which is the other of the pair of minor edges 12. In the pair of minor edges 12, the minor edge 12a is located on a bend outer side, and the minor edge 12b is located on a bend inner side. Herein, as illustrated in FIGS. 3 and 4, the bend outer side corresponds to a bend outer side with respect to the L-bent portion 23 of the header 20, and the bend inner side corresponds to a bend inner side with respect to the L-bent portion 23 of the header 20.
The flat tube 10 is a flat multi-port tube having a plurality of refrigerant flow paths 10a, which are in the form of through-holes. The plurality of refrigerant flow paths 10a are arranged side by side in the major-axis direction. While the flow-path cross-sectional shape of each of the refrigerant flow paths 10a exemplified in the drawings is a rectangular shape, the flow-path cross-sectional shape is not limited to a rectangular shape and may be any other shape such as a circular shape.

Terms and Dimensional Denotations of Individual Elements

Terms that are used in this specification will first be summarized with reference to FIGS. 2, 3, and 4.
R1, R2, R3, and R4 denote four respective regions in the normal section of the flat tube 10 that are defined by the center line L1 and a pair of midpoint virtual lines L3. The region R1, the region R2, the region R3, and the region R4 are located in that order from the bend outer side toward the bend inner side.

Rc: a central region in the normal section of the flat tube 10, on the inner side relative to the pair of midpoint virtual lines L3
Ro: an outer-end region in the normal section of the flat tube 10, on the outer side relative to the pair of midpoint virtual lines L3

In FIG. 3, a portion hatched with sparse dots corresponds to the central region Rc, and a portion hatched with dense dots corresponds to the outer-end region Ro. The central region Rc is also regarded as an area including the region R2 and the region R3. The outer-end region Ro is also regarded as an area including the region R1 and the region R4.
Here, the following itemsare defined.

L1: the center line in the normal section of the flat tube 10, passing through the center of the flat tube 10 that is located in the major-axis direction
L2: a pair of outer-edge virtual lines in the normal section of the flat tube 10, extending along edges of the flat tube 10 that are located at both ends in the major-axis direction, the pair of outer-edge virtual lines being parallel to the center line L1
L3: a pair of midpoint virtual lines in the normal section of the flat tube 10, passing through the respective midpoints between the center line L1 and the pair of outer-edge virtual lines L2
L4: a pair of virtual lines along flow-path minor-axis-end edges in the normal section of the flat tube 10, extending along edges of the plurality of refrigerant flow paths 10a that are located at both ends in the minor-axis-direction
L5: a pair of virtual lines along flow-path major-axis-end edges in the normal section of the flat tube 10, extending along edges of the plurality of refrigerant flow paths 10a that are located at both ends in the major-axis direction

The flat tube 10 viewed in the normal section includes first outer pillars 15, inner pillars 16, and second outer pillars 17. The density of the dots in FIG. 2 become more sparse in order of the first outer pillars 15, the inner pillars 16, and the second outer pillars 17. The first outer pillars 15, the inner pillars 16, and the second outer pillars 17 are defined as follows.
First outer pillars 15: portions in the normal section that are located on the inner side relative to the pair of virtual lines L4 along flow-path minor-axis-end edges and on the outer side relative to the pair of virtual lines L5 along flow-path major-axis-end edges

Inner pillars 16: portions in the normal section that are located on the inner side relative to the pair of virtual lines L4 along flow-path minor-axis-end edges and between adjacent ones of the refrigerant flow paths 10a
Second outer pillars 17: portions in the normal section that are located on the outer side relative to the pair of virtual lines L4 along flow-path minor-axis-end edges

The first outer pillars 15 are two pillars located at two respective ends in the major-axis direction. Occasionally, the first outer pillars 15 are distinguished from each other by denoting the one on the bend outer side as a first outer pillar 15a and the other on the bend inner side as a first outer pillar 15b.
Dimensional denotations and other definitions of individual elements that are used in this specification will now be summarized with reference to FIG. 5.

T_w: the major-axis length of the normal section, regarded as the length of the flat tube 10 in the major-axis direction
D_p: the pitch of the flat tubes 10 in the normal sections thereof
δ₁: the wall thickness in the major-axis direction for an inner pillar 16a, which is one of the plurality of inner pillars 16 that is closest to the center line L1
δ₂: the wall thickness in the major-axis direction for an inner pillar 16b, which is one of the plurality of inner pillars 16 that is farthest from the center line L1
t_x: the wall thickness in the major-axis direction for each of the first outer pillars 15
t_y: the wall thickness in the minor-axis direction for each of the second outer pillars 17

At the L-bent portion 23, the pitch is different between the bend inner side and the bend outer side. Therefore, the pitch D_p refers to the pitch before bending is performed or the pitch at a portion other than the L-bent portion 23.
In the heat exchanger 100, the flow-path cross section of each of the refrigerant flow paths 10a of the flat tube 10 may be circular, as described above. If the flow-path cross section of the refrigerant flow paths 10a is circular, the dimensions are as illustrated in FIGS. 6 and 7.
FIG. 6 is a sectional view illustrating a configuration of a flat tube 10 included in the heat exchanger 100 according to Embodiment 1. FIG. 7 is a diagram for denoting dimensions of the flat tube 10 included in the heat exchanger 100 according to Embodiment 1. The dimensions of the refrigerant flow paths 10a each having a rectangular flow-path cross section substantially apply to the case of the refrigerant flow paths 10a each having a circular flow-path cross section. Therefore, only particular ones of the dimensions that need to be described herein are listed below.

δ₁: the wall thickness in the major-axis direction for the narrowest portion of the inner pillar 16a, which is one of the plurality of inner pillars 16 that is closest to the center line L1
δ₂: the wall thickness in the major-axis direction for the narrowest portion of the inner pillar 16b, which is one of the plurality of inner pillars 16 that is farthest from the center line L1
t_x: the wall thickness in the major-axis direction for the narrowest portion of each of the first outer pillars 15
t_y: the wall thickness in the minor-axis direction for the narrowest portion of each of the second outer pillars 17

In the heat exchanger 100, the headers 20 each have the L-bent portion 23. That is, during the manufacturing process, some flat tubes 10 receive a stretching force acting on the bend outer side as illustrated by arrows a in FIG. 4, whereas the flat tubes 10 receive a contracting force acting on the bend inner side as illustrated by arrows b in FIG. 4. The directions represented by the arrows a and the arrows b correspond to the minor-axis direction.
FIG. 8 illustrates a normal section of a flat tube 1000 according to Comparative Example with some inner pillars 160 thereof broken. Regarding the flat tube 1000 according to Comparative Example, the left side in the drawing is the bend outer side, and the right side in the drawing is the bend inner side. In the Comparative Example, during a bending process for forming an L-bent portion, the flat tube 1000 receives a stretching force acting on the bend outer side and in the direction of arrows a (the minor-axis direction). Therefore, some inner pillars 160 are broken, damaging the flat tube 1000. Referring to FIG. 8, the farther from the center of the flat tube 1000 in the major-axis direction, in other words, the closer to the two ends of the flat tube 1000 that are located away from the center of the flat tube 1000 in the major-axis direction, the greater the amount of deformation in the minor-axis direction and the greater the force applied to the inner pillars 160. Such an example shows that if the wall thickness of those inner pillars that are closer to the two ends of the flat tube in the major-axis direction where a greater force is applied during the bending process is increased, the strength of the flat tube at the L-bent portion is increased while a satisfactory flow-path sectional area is provided.
In view of the above, the flat tubes 10 of the heat exchanger 100 according to Embodiment 1 employs the following structure, which suppresses the occurrence of damage to the flat tubes 10, particularly the breakage of the first outer pillars 15 and the inner pillars 16.

Dimensions Set for Flat Tube 10

The wall thickness of the flat tube 10 increases toward end portions in the normal section that are located on both sides in the major-axis direction and decreases toward a central portion in the normal section that is located in the major-axis direction. Specifically, as illustrated in FIG. 5, the end portions in the normal section on both sides in the major-axis direction correspond to the first outer pillars 15. The wall thickness t_x of each of the first outer pillars 15 is greater than δ₁, which corresponds to the wall thickness at the central portion located in the major-axis direction. That is, in the flat tube 10, a relationship of t_x > δ₁ holds.
The expression "the wall thickness of the flat tube 10 increases toward end portions in the normal section that are located on both sides in the major-axis direction and decreases toward a central portion in the normal section that is located in the major-axis direction" implies that the wall thickness at the two end portions in the normal section that are located in the major-axis direction only needs to be greater than the wall thickness at the central portion in the normal section that is located in the major-axis direction, and encompasses a configuration in which a plurality of portions of the normal section that are located between the central portion and the end portions in the major-axis direction have the same wall thickness.
It is sufficient that the wall thickness of the flat tube 10 increases toward the end portions in the normal section that are located on both sides in the major-axis direction and decreases toward the central portion in the normal section that is located in the major-axis direction. Accordingly, the flat tube 10 has at least one of the following features (1) to (4).

(1) The flat tube 10 is shaped such that the wall thickness is greatest at the two end portions located in the major-axis direction and gradually decreases toward the central portion located in the major-axis direction. That is, the first outer pillars 15 at the end portions located in the major-axis direction have the greatest wall thickness, and the wall thickness of the inner pillars 16 gradually decreases toward the central portion located in the major-axis direction.
(2) In the flat tube 10, a relationship of δ₂ > δ₁ holds.
(3) In the flat tube 10, a relationship of t_x ≥ δ₂ > δ₁ holds.
(4) In the flat tube 10, a relationship of δ₂ > δ₁ > t_y holds.

In the heat exchanger 100 including the flat tubes 10 each having the above features, the wall thickness of the flat tubes 10 at the L-bent portion 23 is greater on the bend outer side on which the amount of stretching is greater. Thus, increased strength is provided to the flat tubes 10, and the occurrence of damage to the flat tubes 10 is suppressed.
If a heat exchanger includes flat tubes each having a wall thickness that is generally and uniformly increased with no changes in the external dimensions of the flat tubes, although the occurrence of damage to the flat tubes is suppressed, the flow-path sectional areas of the refrigerant flow paths need to be reduced. That is, if a heat exchanger includes flat tubes each having a generally and uniformly increased wall thickness, although the occurrence of damage to the flat tubes is suppressed, the fluid loss of refrigerant increases, leading to a performance deterioration.
In contrast, the heat exchanger 100 employs the above features for increasing the wall thickness of the flat tubes 10 on the bend outer side. Thus, the occurrence of damage to the flat tubes 10 is suppressed, with the wall thickness at the central portion located in the major-axis direction remaining thin. Therefore, satisfactory flow-path sectional areas are provided, and the increase in the pressure loss is suppressed. That is, in the heat exchanger 100, while increased strength is provided to the flat tubes 10, the increase in the pressure loss is suppressed.
In the heat exchanger 100, all of the plurality of flat tubes 10 may have the above features, or some of the plurality of flat tubes 10 may have the above features. In the latter case, only one or two or more flat tubes 10 connected to the L-bent portions 23 of the pair of headers 20 of the heat exchanger 100 need to have the above features. That is, in the heat exchanger 100, at least one or two or more flat tubes 10 that are included in the plurality of flat tubes 10 and are connected to the L-bent portions 23 of the pair of headers 20 only need to have the above features.

Method of Manufacturing Heat Exchanger 100

FIG. 9 illustrates a process of manufacturing the heat exchanger 100 according to Embodiment 1. FIG. 9 includes plan views of the heat exchanger 100, with the outlines of the flat tubes 10 represented by dotted lines on the header 20 for the illustration of the positional relationship between the header 20 and the flat tubes 10. In FIG. 9, the refrigerant flow paths 10a are not illustrated.
FIG. 9(a) illustrates an integrated body 100A, which is obtained by inserting the end portions of the plurality of flat tubes 10 that are located on both sides in the tube-axis direction into connection ports (not illustrated) provided in the pair of headers 20, and performing brazing thereon for integration of the whole. The integrated body 100A is then bent into an L shape as illustrated in FIG. 9(b), whereby a heat exchanger 100 including a first heat-exchanger portion 101, a second heat-exchanger portion 102, and a third heat-exchanger portion 103 is obtained.
In the heat exchanger 100 obtained through the above manufacturing process, at least those flat tubes 10 that are connected to the L-bent portions 23 have the above features. Therefore, the occurrence of damage to the flat tubes 10 is suppressed, leading to high reliability.
During the manufacturing process, as described above, such flat tubes 10 receive a stretching force acting in the minor-axis direction and on the bend outer side, and a contracting force acting in the minor-axis direction and on the bend inner side. Therefore, the heat exchanger 100 obtained as a finished product may lack the above features at the connections between such flat tubes 10 and the headers 20 at the two end portions of the flat tubes 10 in the tube-axis direction.
For example, the heat exchanger 100 obtained as a finished product may include a flat tube 10 whose wall thickness in the normal sections taken at each of the connections between the flat tubes 10 and the headers 20 at the two end portions of the flat tubes 10 in the tube-axis direction is the same between the end portions and the central portion in the normal section that are located in the major-axis direction. Nevertheless, such a flat tube 10 of the heat exchanger 100 obtained as a finished product has the above features in portions other than the two end portions located in the tube-axis direction.

Advantageous Effects of Heat Exchanger 100 According to Embodiment 1

The heat exchanger 100 according to Embodiment 1 includes a plurality of flat tubes 10 each extending in a top-bottom direction with a flat external shape and each having a plurality of refrigerant flow paths 10a in a form of through-holes, and a pair of headers 20 connected to end portions of the plurality of flat tubes 10 on both sides in the top-bottom direction and including respective L-bent portions 23 each having an L shape in top view. The plurality of flat tubes 10 are each shaped to have a major axis and a minor axis in a normal section taken to be normal to a tube-axis direction. At least one or two or more flat tubes 10 included in the plurality of flat tubes 10 and connected to the L-bent portions 23 each have a wall thickness that increases toward two end portions in the normal section and decreases toward a central portion in the normal section, the two end portions and the central portion being located in a major-axis direction that is parallel to the major axis.
In the heat exchanger 100 configured as above, one of the end portions in the normal section that are located on both sides in the major-axis direction parallel to the major axis is located on the bend outer side at the L-bent portions 23 of the pair of headers 20. Therefore, in the heat exchanger 100 configured as above, the wall thickness of the flat tubes 10 at the L-bent portions 23 of the pair of headers 20 is greater on the bend outer side on which the amount of stretching is greater. Thus, increased strength is provided to the flat tubes 10, and the occurrence of damage to the flat tubes 10 is suppressed. Furthermore, in the heat exchanger 100 configured as above, the wall thickness of each of the flat tubes is smaller at the central portion located in the major-axis direction than at the two end portions located in the major-axis direction. Therefore, compared with a configuration in which the wall thickness at the central portion located in the major-axis direction is set as large as the wall thickness at the two end portions, a satisfactory flow-path sectional area is provided, and the increase in the pressure loss is suppressed. That is, in the heat exchanger 100, while increased strength is provided to the flat tubes 10, the increase in the pressure loss is suppressed.
The one or two or more flat tubes 10 each have at least one of the features listed as (1) to (4) above.
In the heat exchanger 100 configured as above, the wall thickness of the flat tubes 10 at the L-bent portions 23 of the pair of headers 20 is greater on the bend outer side on which the amount of stretching is greater. Thus, increased strength is provided to the flat tubes 10, and the occurrence of damage to the flat tubes 10 is suppressed.

Embodiment 2

A heat exchanger 100 according to Embodiment 2 differs from the heat exchanger 100 according to Embodiment 1 in the configuration of the flat tubes 10. In Embodiment 1 described above, the wall thickness of the flat tubes 10 is specified. In Embodiment 2, the sectional wall area of the flat tubes 10 is specified. The following description focuses on features of Embodiment 2 that are different from those of Embodiment 1. Features not described in Embodiment 2 are the same as those of Embodiment 1.
FIG. 10 illustrates a normal section of a flat tube 10 included in the heat exchanger 100 according to Embodiment 2. The flat tube 10 of the heat exchanger 100 according to Embodiment 2 has at least one of the following features (a) and (b).

(a) In the flat tube 10, a relationship of Ao > Ac holds.
(b) In the flat tube 10, relationships of Ao1 = Ao2 and Ao > Ac hold.

Here, the following items are defined.

Ao: the sectional wall area of portions located in the outer-end regions Ro and on the inner side relative to the pair of virtual lines L4 along flow-path minor-axis-end edges
Ac: the sectional wall area of portions located in the central region Rc and on the inner side relative to the pair of virtual lines L4 along flow-path minor-axis-end edges.
Ao1: the sectional wall area in the region R1
Ao2: the sectional wall area in the region R4

Ac corresponds to the total sectional wall area of portions located in the region R2 and the region R3 and on the inner side relative to the pair of virtual lines L4 along flow-path minor-axis-end edges. Ao corresponds to the total sectional wall area of portions located in the region R1 and the region R4 and on the inner side relative to the pair of virtual lines L4 along flow-path minor-axis-end edges. In FIG. 10, the total area of portions hatched with dense dots is the sectional wall area Ao, and the total area of portions hatched with sparse dots is the sectional wall area Ac.
The condition given in (b) above relates to the region R1 and the region R4 located at the two respective ends in the major-axis direction among the four regions R1, R2, R3, and R4, and defines that the sectional wall area Ao1 in the region R1 and the sectional wall area Ao2 in the region R4 are equal to each other. This condition specifies that the normal section of the flat tube 10 does not have, for example, a wedge shape but has a shape defined by the outer pillars 17 each extending symmetrically or nearly symmetrically with respect to the center line L1.

[Advantageous Effects of Heat Exchanger 100 According to Embodiment 2]

The heat exchanger 100 according to Embodiment 2 produces the same advantageous effects as Embodiment 1.

Embodiment 3

A heat exchanger 100 according to Embodiment 3 differs from the heat exchanger 100 according to Embodiment 1 in the configuration of the flat tubes 10. Embodiment 3 relates to the flow-path sectional area of the refrigerant flow paths 10a of each flat tube 10. The following description focuses on features of Embodiment 3 that are different from those of Embodiment 1. Features not described in Embodiment 3 are the same as those of Embodiment 1.
FIG. 11 illustrates a normal section of a flat tube 10 included in the heat exchanger 100 according to Embodiment 3. In the flat tube 10 of the heat exchanger 100 according to Embodiment 3, as illustrated in FIG. 11, the sum total of the flow-path sectional areas of a plurality of refrigerant flow paths 10a2 located in the outer-end regions Ro is smaller than the sum total of the flow-path sectional areas of a plurality of refrigerant flow paths 10al located in the central region Rc. In FIG. 11, the flow-path sectional area of each of the refrigerant flow paths 10a2 located in the outer-end regions Ro is hatched with dense dots, and the flow-path sectional area of each of the refrigerant flow paths 10a1 located in the central region Rc is hatched with sparse dots.
With the above configuration, the heat exchanger 100 according to Embodiment 3 produces the same advantageous effects as Embodiment 1.
FIG. 12 illustrates how the flow of liquid refrigerant is deflected in a header 120. In this heat exchanger, liquid refrigerant having flowed into the header 120 is deflected at an L-bent portion 123 under a centrifugal force. Consequently, an excessive amount of liquid refrigerant may flow on the bend outer side at the L-bent portion 123, as enclosed by a dotted line in FIG. 12. The dots in FIG. 12 represent the liquid refrigerant stagnated at the L-bent portion 123.
In the flat tube 10 of the heat exchanger 100 according to Embodiment 3, the sum total of the flow- path cross-sections of the refrigerant flow paths 10a2 located in the outer-end regions Ro is smaller than the sum total of the flow-path sectional areas of the refrigerant flow paths 10a1 located in the central region Rc. Therefore, in the heat exchanger 100, it is more difficult for liquid refrigerant to flow into the refrigerant flow paths 10a2 located on the bend outer side among the plurality of refrigerant flow paths 10a arranged side by side in the major-axis direction in the normal section of the flat tube 10 than to flow into the refrigerant flow paths 10a1 located in the central portion located in the major-axis direction. Thus, in the heat exchanger 100 according to Embodiment 3, liquid refrigerant is less likely to excessively flow into the refrigerant flow paths 10a2 located on the bend outer side.

Advantageous Effects of Heat Exchanger 100 According to Embodiment 3

The heat exchanger 100 according to Embodiment 3 produces the same advantageous effects as Embodiment 1. Furthermore, in the flat tube 10, liquid refrigerant is less likely to excessively flow into the refrigerant flow paths 10a2 located on the bend outer side.

Embodiment 4

A heat exchanger 100 according to Embodiment 4 is specific to the flow-path sectional area of the refrigerant flow paths 10a of the flat tube 10, as with the heat exchanger 100 according to Embodiment 3. The following description focuses on features of Embodiment 4 that are different from those of Embodiment 3. Features not described in Embodiment 4 are the same as those of Embodiment 3.
FIG. 13 illustrates a normal section of a flat tube 10 included in the heat exchanger 100 according to Embodiment 4. The flat tube 10 according to Embodiment 4 is configured such that the width between the centers, in the major-axis-direction, of adjacent ones of the inner pillars 16 decreases from the central portion of the flat tube 10 toward the outer side in the major-axis-direction. Specifically, the flat tube 10 illustrated in FIG. 13 has a width W1 and a width W2, which are defined as the width between the centers of adjacent ones of the inner pillars 16 in the major-axis-direction. The width W2 is shorter than the width W1.
The configuration in which the width between the centers of adjacent ones of the inner pillars 16 in the major-axis-direction decreases from the central portion of the flat tube 10 toward the outer side in the major-axis-direction is also regarded as a configuration in which the length of the refrigerant flow paths 10a themselves in the major-axis direction decreases from the central portion of the flat tube 10 toward the outer side in the major-axis direction. The flat tube 10 illustrated in FIG. 13 has a width W1a and a width W2a, which are defined as the widths of the refrigerant flow paths 10a themselves in the major-axis-direction. The width W2a is shorter than the width W1a.

Advantageous Effects of Heat Exchanger 100 According to Embodiment 4

The heat exchanger 100 according to Embodiment 4 produces the same advantageous effects as Embodiment 3.

Embodiment 5

A heat exchanger 100 according to Embodiment 5 differs from the heat exchanger 100 according to Embodiment 1 in the configuration of the flat tubes 10. The following description focuses on features of Embodiment 5 that are different from those of Embodiment 1. Features not described in Embodiment 5 are the same as those of Embodiment 1.
FIG. 14 illustrates a normal section of a flat tube 10 included in the heat exchanger 100 according to Embodiment 5. Among a plurality of refrigerant flow paths 10a of the flat tube 10 that are arranged side by side in the major-axis direction, refrigerant flow paths 10al located in the central portion each have a rectangular shape, and at least end-portion refrigerant flow paths 10a21 located on both sides in the major-axis direction each have a rectangular shape with the four corners thereof rounded. Since the end-portion refrigerant flow paths 10a21 have rounded corners, the flow-path sectional area of each of the end-portion refrigerant flow paths 10a21 is smaller than the flow-path sectional area of each of the other refrigerant flow paths 10a. Instead, the wall around the end-portion refrigerant flow path 10a21 has a greater thickness. That is, the flat tube 10 has a greater wall thickness around the end-portion refrigerant flow paths 10a21 than around the other refrigerant flow paths 10a.
In the heat exchanger 100 according to Embodiment 5 configured as above, the flat tube 10 has an increased wall thickness at end portions in the normal section on both sides in the major-axis direction. Thus, the breaking strength of the flat tube 10 is increased. While FIG. 14 illustrates a case where, among the plurality of refrigerant flow paths 10a, only the end-portion refrigerant flow paths 10a21 at the two ends in the major-axis direction each have a rounded rectangular shape with four curved corners, such an embodiment is not limiting. For example, among the plurality of refrigerant flow paths 10a of the heat exchanger 100, not only the end-portion refrigerant flow paths 10a21 at the two ends in the major-axis direction but also refrigerant flow paths 10a3 on the inner side relative to the end-portion refrigerant flow paths 10a21 may each have a rounded rectangular shape with four curved corners.

Advantageous Effects of Heat Exchanger 100 According to Embodiment 5

The heat exchanger 100 according to Embodiment 5 produces the same advantageous effects as Embodiment 1.

Embodiment 6

A heat exchanger 100 according to Embodiment 6 differs from the heat exchanger 100 according to Embodiment 1 in the configuration of the flat tubes 10. The following description focuses on features of Embodiment 6 that are different from those of Embodiment 1. Features not described in Embodiment 6 are the same as those of Embodiment 1.
FIG. 15 illustrates a normal section of a flat tube 10 included in the heat exchanger 100 according to Embodiment 6. In the flat tube 10, among the plurality of refrigerant flow paths 10a arranged side by side in the major-axis direction, the refrigerant flow paths 10a1 located in the central portion each have a rectangular shape, whereas at least the end-portion refrigerant flow paths 10a21 located at the two ends in the major-axis direction each have a D shape. The D shape refers to a shape defined in the normal section of the flat tube 10 by a curve that is convex outward in the major-axis direction and a straight line that connects the two ends of the curve to each other. Since the end-portion refrigerant flow paths 10a21 each have a D shape, the flow-path sectional area of each of the end-portion refrigerant flow paths 10a21 is smaller than the flow-path sectional area of each of the other refrigerant flow paths 10a. Instead, the wall around each of the end-portion refrigerant flow paths 10a21 has a greater thickness. That is, the flat tube 10 has a greater wall thickness around the end-portion refrigerant flow paths 10a21 than around the other refrigerant flow paths 10a.
In the heat exchanger 100 according to Embodiment 6 configured as above, the flat tube 10 has an increased wall thickness at ends of the normal section on both sides in the major-axis direction. Thus, the breaking strength of the flat tube 10 is increased. While FIG. 15 illustrates a case where, among the plurality of refrigerant flow paths 10a, only the end-portion refrigerant flow paths 10a21 at the two ends in the major-axis direction each have a D shape, such an embodiment is not limiting. For example, among the plurality of refrigerant flow paths 10a of the heat exchanger 100, not only the end-portion refrigerant flow paths 10a21 at the two ends in the major-axis direction but also refrigerant flow paths 10a3 on the inner side relative to the end-portion refrigerant flow paths 10a21 may each have a D shape.

Advantageous Effects of Heat Exchanger 100 According to Embodiment 6

The heat exchanger 100 according to Embodiment 6 produces the same advantageous effects as Embodiment 1.

Embodiment 7

In a heat exchanger 100 according to Embodiment 7, the relationship among a major-axis length T_w [mm] of the flat tube 10, a pitch D_p [mm] of the flat tubes 10, and a possible bend radius R₀ [mm] of the L-bent portion is specified that suppresses the breakage of the flat tube 10. The following description focuses on features of Embodiment 7 that are different from those of Embodiment 1. Features not described in Embodiment 7 are the same as those of Embodiment 1.
FIG. 16 is a graph illustrating relationships established in the heat exchanger 100 according to Embodiment 7 among the major-axis length T_w of the flat tube 10 and the possible bend radius R₀ of the L-bent portion. In FIG. 16, the horizontal axis represents the major-axis length T_w [mm] of the flat tube 10, and the vertical axis represents the possible bend radius R₀ [mm] of the L-bent portion 23. In FIG. 16, the possible bend radius R₀ with respect to the major-axis length T_w of the flat tube 10 is plotted for different values of δ₂/δ₁ varied among 1, 2, 3, and 4. The possible bend radius R₀ refers to the minimum bend radius of the L-bent portion 23 that suppresses the breakage of the flat tube 10.
The graph of "δ₂/δ₁ = 1" shows that if a relationship of "δ₂/δ₁ = 1" holds in the flat tube 10, the possible bend radius R₀ is 400 [mm] with respect to a major-axis length T_w of the flat tube 10 of 30 [mm]. Accordingly, in the heat exchanger 100, if a relationship of "δ₂/δ₁ = 1" holds in the flat tube 10, setting the bend radius R of the L-bent portion 23 to a value greater than the possible bend radius R₀ specified by the graph of "δ₂/δ₁ = 1" suppresses the breakage of the flat tube 10. The above reading also applies to the other graphs in FIG. 16.
The graphs in FIG. 16 are each obtained by substituting the value of δ₂/δ₁ into the right side of Expression (1) below.
[Math. 1] $R > \frac{D_{p} \times T_{w}}{(\frac{δ_{2}}{δ_{1}})} \times (0.00002 \times T_{w}^{3} - 0.00222 \times T_{w}^{2} + 0.09886 \times T_{w} + 0.09867)$
If a relationship of 1 < δ₂/δ₁ holds in the flat tube 10, the heat exchanger 100 satisfies the relationship of Expression (1) above. That is, in the heat exchanger 100, letting the value on the right side of Expression (1) above that is obtained by substituting δ₂/δ₁ = 1 into the right side be R1, the bend radius R of the L-bent portion 23 satisfies R > R1. In such a heat exchanger 100, the breakage of the flat tube 10 is suppressed.
If a relationship of 2 ≤ δ₂/δ₁ holds in the flat tube 10, the heat exchanger 100 satisfies the relationship of Expression (1) above. That is, in the heat exchanger 100, letting the value on the right side of Expression (1) above that is obtained by substituting δ₂/δ₁ = 2 into the right side be R2, the bend radius R of the L-bent portion 23 satisfies R > R2. In such a heat exchanger 100, the breakage of the flat tube 10 is suppressed.

Advantageous Effects of Heat Exchanger 100 According to Embodiment 7

The heat exchanger 100 according to Embodiment 7 produces the same advantageous effects as Embodiment 1.

Embodiment 8

Embodiment 8 relates to a refrigeration cycle apparatus, such as an air-conditioning apparatus, including the heat exchanger 100 according to any of Embodiments 1 to 7.
FIG. 17 is a refrigerant circuit diagram schematically illustrating a configuration of a refrigeration cycle apparatus 300 according to Embodiment 8. The refrigeration cycle apparatus 300 has a refrigerant circuit in which a compressor 200, a suction muffler 201, a four-way switching valve 202, an outdoor-side heat exchanger 203, a decompressor 204 such as an electric expansion valve, and an indoor-side heat exchanger 205 are connected to one another by pipes. The outdoor-side heat exchanger 203 and the indoor-side heat exchanger 205 each serve as a condenser or an evaporator depending on the switching of the four-way switching valve 202.
In the refrigeration cycle apparatus 300, the four-way switching valve 202 may be omitted. That is, the refrigeration cycle apparatus 300 may be constituted by the compressor 200, a condenser, a decompressor, and an evaporator. In the case of an air-conditioning apparatus, the indoor-side heat exchanger 205 is installed in an indoor device, the other elements including the compressor 200, the four-way switching valve 202, the outdoor-side heat exchanger 203, and the decompressor 204 are installed in an outdoor device.
The compressor 200 is configured to suction refrigerant and compress the refrigerant into a high-temperature high-pressure state. The compressor 200 is a displacement compressor whose operating frequency is variable. The compressor 200 is not limited to the one operated at variable frequencies and may be a compressor operated at a constant speed. The four-way switching valve 202 is connected to the discharge side of the compressor 202 and is configured to switch flows of the refrigerant received from the compressor 200.
The outdoor-side heat exchanger 203 is a fin-and-tube heat exchanger including tubes in which the refrigerant is to flow, and fins into which the tubes are inserted. The decompressor 204 is configured to expand the refrigerant. The decompressor 204 is, for example, an electronic expansion valve or thermostatic expansion valve whose opening degree is adjustable, or may be constituted by capillary tubes or other like elements whose opening degree is not adjustable. The indoor-side heat exchanger 205 is a fin-and-tube heat exchanger including tubes in which the refrigerant is to flow, and fins into which the tubes are inserted. The refrigeration cycle apparatus 300 employs the heat exchanger 100 according to any of Embodiments 1 to 7 as at least one of the outdoor-side heat exchanger 203 and the indoor-side heat exchanger 205.
In a heating operation in a case where the refrigeration cycle apparatus 300 is applied to an air-conditioning apparatus, the four-way switching valve 202 is connected as illustrated by solid lines in FIG. 17. The high-temperature high-pressure refrigerant obtained through the compression by the compressor 200 flows into the indoor-side heat exchanger 205, where the refrigerant is condensed and liquefied. The liquefied refrigerant is decompressed by the decompressor 204 into a low-temperature low-pressure two-phase state and flows into the outdoor-side heat exchanger 203, where the refrigerant is evaporated and gasified. Then, the refrigerant flows through the four-way switching valve 202 and returns to the compressor 200.
That is, the refrigerant circulates as represented by solid-line arrows illustrated in FIG. 17. During the circulation, in the outdoor-side heat exchanger 203 serving as an evaporator, the refrigerant exchanges heat with outdoor air and receives heat therefrom. The refrigerant thus received heat is delivered to the indoor-side heat exchanger 205 serving as a condenser, in which the refrigerant exchanges heat with indoor air and thus heats the indoor air.
In a cooling operation, the four-way switching valve 202 is connected as illustrated by broken lines in FIG. 17. When the operation changes from the heating operation to the cooling operation, the indoor-side heat exchanger 205 having served as a condenser comes to serve as an evaporator, while the outdoor-side heat exchanger 203 having served as an evaporator comes to serve as a condenser. The high-temperature high-pressure refrigerant obtained through the compression by the compressor 200 flows into the outdoor-side heat exchanger 203, where the refrigerant is condensed and liquefied. The liquefied refrigerant is decompressed by the decompressor 204 into a low-temperature low-pressure two-phase state. The low-temperature low-pressure two-phase refrigerant flows into the indoor-side heat exchanger 205, where the refrigerant is evaporated and gasified.
Then, the refrigerant flows through the four-way switching valve 202 and returns to the compressor 200. That is, the refrigerant circulates as represented by broken-line arrows illustrated in FIG. 17. During the circulation, in the indoor-side heat exchanger 205 serving as an evaporator, the refrigerant exchanges heat with indoor air and receives heat therefrom, thereby cooling the indoor air. The refrigerant thus received heat is delivered to the outdoor-side heat exchanger 203 serving as a condenser, where the refrigerant exchanges heat with outdoor air and thus transfers heat to the outdoor air.
The refrigerant to be used is an R407C refrigerant, an R410A refrigerant, or an R32 refrigerant, for example.
The refrigeration cycle apparatus 300 configured as above employs the heat exchanger 100 according to any of Embodiments 1 to 7. Therefore, while increased strength is provided to the flat tubes 10, the increase in the loss of refrigerant pressure is suppressed.
The refrigeration cycle apparatus 300 is applicable to apparatuses other than an air-conditioning apparatus. The refrigeration cycle apparatus 300 may be applicable to a refrigeration cycle apparatus intended for uses such as a refrigerator, a freezer, a vending machine, a refrigeration apparatus, and a water heater.

List of Reference Signs

10: flat tube,
10a: refrigerant flow path,
10a1: refrigerant flow path,
10a2: refrigerant flow path,
10a21: end-portion refrigerant flow path,
10a3: refrigerant flow path,
11: major edge,
12: minor edge,
12a: minor edge,
12b: minor edge,
13: curved portion,
14: curved portion,
15: first outer pillar,
15a: first outer pillar,
15b: first outer pillar,
16: inner pillar,
16a: inner pillar,
16b: inner pillar,
17: second outer pillar,
20: header,
20a: inlet,
20b: outlet,
21: first linear portion,
22: second linear portion,
23: L-bent portion,
30: corrugated fin,
100: heat exchanger,
100A: integrated body,
101: first heat-exchanger portion,
102: second heat-exchanger portion,
103: third heat-exchanger portion,
120: header,
123: L-bent portion,
160: inner pillar,
200: compressor,
201: suction muffler,
202: four-way switching valve,
203: outdoor-side heat exchanger,
204: decompressor,
205: indoor-side heat exchanger,
300: refrigeration cycle apparatus,
1000: flat tube,
Ac: sectional wall area,
Ao: sectional wall area,
Ao1: sectional wall area,
Ao2: sectional wall area,
L1: center line,
L2: outer-edge virtual line,
L3: midpoint virtual line,
L4: virtual line along flow-path minor-axis-end edge,
L5: virtual line along flow-path major-axis-end edge,
R: bend radius,
R₀: possible bend radius,
R1: region,
R2: region,
R3: region,
R4: region,
Rc: central region,
Ro: outer-end region,
a: arrow,
b: arrow,
t_X: wall thickness

Claims

A heat exchanger comprising a plurality of flat tubes each extending in a top-bottom direction with a flat external shape and each having a plurality of refrigerant flow paths in a form of through-holes; and a pair of headers connected to end portions of the plurality of flat tubes on both sides in the top-bottom direction and including respective L-bent portions each having an L shape in top view,
wherein the plurality of flat tubes are each shaped to have a major axis and a minor axis in a normal section taken to be normal to a tube-axis direction,

wherein at least one or two or more flat tubes included in the plurality of flat tubes and connected to the L-bent portions each have

a wall thickness that increases toward two end portions in the normal section and decreases toward a central portion in the normal section, the two end portions and the central portion being located in a major-axis direction that is parallel to the major axis.
The heat exchanger of claim 1,
wherein the one or two or more flat tubes each have,

in the normal section,

a wall thickness that increases toward the two end portions located in the major-axis direction and gradually decreases toward the central portion located in the major-axis direction.
The heat exchanger of claim 1 or 2,
wherein, in the normal section,

when a line passing through a center located in the major-axis direction is defined as a center line;

a pair of lines extending along edges of the plurality of refrigerant flow paths at both ends in a minor-axis direction parallel to the minor axis are defined as a pair of virtual lines along flow-path minor-axis-end edges; and

a portion located on an inner side relative to the pair of virtual lines along flow-path minor-axis-end edges and between adjacent ones of the plurality of refrigerant flow paths is defined as an inner pillar,

the inner pillar of each of the one or two or more flat tubes includes a plurality of inner pillars, and

a wall thickness δ₁, in the major-axis direction, of one of the plurality of inner pillars that is closest to the center line and a wall thickness δ₂, in the major-axis direction, of one of the plurality of inner pillars that is farthest from the center line are in a relationship of δ₂ > δ₁.
The heat exchanger of claim 3,
wherein, in the normal section,

when a pair of lines extending along edges of the plurality of refrigerant flow paths at both ends in the major-axis direction are defined as a pair of virtual lines along flow-path major-axis-end edges; and

portions located on the inner side relative to the pair of virtual lines along flow-path minor-axis-end edges and on an outer side relative to the pair of virtual lines along flow-path major-axis-end edges are defined as first outer pillars,

in each of the one or two or more flat tubes,

the wall thickness δ1, the wall thickness δ2, and a wall thickness t_x of each of the first outer pillars in the major-axis direction are in a relationship of t_x ≥ δ₂ > δ₁.
The heat exchanger of claim 3 or 4,
wherein, in the normal section,

when portions located on an outer side relative to the pair of virtual lines along flow-path minor-axis-end edges are defined as second outer pillars,

in each of the one or two or more flat tubes,

the wall thickness δ1, the wall thickness δ2, and a wall thickness t_y of each of the second outer pillars in the minor-axis direction are in a relationship of δ₂ > δ₁> t_y.
The heat exchanger of any one of claims 3 to 5,
wherein, in each of the one or two or more flat tubes,

a width between centers, in the major-axis direction, of adjacent ones of the plurality of inner pillars decreases from the central portion toward the outer side in the major-axis direction.
The heat exchanger of any one of claims 1 to 6,
wherein, in the normal section,

when a line passing through a center located in the major-axis direction is defined as a center line; a pair of lines extending along edges at both ends in the major-axis direction and being parallel to the center line are defined as a pair of outer-edge virtual lines; a pair of lines passing through respective midpoints between the center line and the pair of outer-edge virtual lines are defined as a pair of midpoint virtual lines; and a pair of lines extending along edges of the plurality of refrigerant flow paths at both ends in a minor-axis direction parallel to the minor axis are defined as a pair of flow-path-edge virtual lines,

the normal section is divided into two kinds of regions of

a central region located on an inner side relative to the pair of midpoint virtual lines; and

outer-end regions located on an outer side relative to the pair of midpoint virtual lines,

in each of the one or two or more flat tubes,

a sectional wall area Ao of portions located in the outer-end regions and on an inner side relative to the pair of flow-path-edge virtual lines is

greater than a sectional wall area Ac of a portion located in the central region and on the inner side relative to the pair of flow-path-edge virtual lines.
The heat exchanger of claim 7,
wherein when the normal section is divided into

four regions by the center line and the pair of midpoint virtual lines,

in each of the one or two or more flat tubes,

two of the four regions that are located at both ends in the major-axis direction have an equal sectional wall area.
The heat exchanger of claim 7 or 8,
wherein, in each of the one or two or more flat tubes,

a sum total of flow-path sectional areas of refrigerant flow paths included in the plurality of refrigerant flow paths and located in the outer-end regions is smaller than a sum total of flow-path sectional areas of refrigerant flow paths included in the plurality of refrigerant flow paths and located in the central region.
The heat exchanger of any one of claims 1 to 9,
wherein, in each of the one or two or more flat tubes,

end-portion refrigerant flow paths included in the plurality of refrigerant flow paths and located at both ends in the major-axis direction each have a rectangular shape with four rounded corners, and a wall thickness around each of the end-portion refrigerant flow paths is greater than a wall thickness around each of the refrigerant flow paths other than the end-portion refrigerant flow paths.
The heat exchanger of any one of claims 1 to 9,
wherein, in each of the one or two or more flat tubes,

end-portion refrigerant flow paths included in the plurality of refrigerant flow paths and located at both ends in the major-axis direction each have a D shape, and a wall thickness around each of the end-portion refrigerant flow paths is greater than a wall thickness around each of the refrigerant flow paths other than the end-portion refrigerant flow paths.
The heat exchanger of claim 3 and any one of claims 4 to 11 as dependent on claim 3,
wherein, in each of the one or two or more flat tubes,

a relationship of 1 < δ₂/δ₁ holds, and a bend radius R of each of the L-bent portions satisfies Expression (1) below:
[Math. 1] $R > \frac{D_{p} \times T_{w}}{(\frac{δ_{2}}{δ_{1}})} \times (0.00002 \times T_{w}^{3} - 0.00222 \times T_{w}^{2} + 0.09886 \times T_{w} + 0.09867)$

where

T_w denotes a major-axis length of the normal section, regarded as a length of the flat tube in the major-axis direction; and

D_p denotes a pitch of the flat tubes in the respective normal sections.
The heat exchanger of claim 3 and any one of claims 4 to 11 as dependent on claim 3,
wherein, in each of the one or two or more flat tubes,

a relationship of 2 ≤ δ₂/δ₁ holds, and a bend radius R of each of the L-bent portions satisfies Expression (2) below:
[Math. 2] $R > \frac{D_{p} \times T_{w}}{(\frac{δ_{2}}{δ_{1}})} \times (0.00002 \times T_{w}^{3} - 0.00222 \times T_{w}^{2} + 0.09886 \times T_{w} + 0.09867)$

where

T_w denotes a major-axis length of the normal section, regarded as a length of the flat tube in the major-axis direction; and

D_p denotes a pitch of the flat tubes in the respective normal sections.
A refrigeration cycle apparatus comprising:
a compressor; a condenser; a decompressor; and an evaporator,

wherein at least one of the condenser and the evaporator is the heat exchanger of any one of claims 1 to 13.