heat exchanger

Abstract

To suppress a reduction in the life of a heat exchanger.SOLUTION: A heat exchanger 10 including a header 20 and a plurality of heat transfer pipes 30 has anticorrosive sacrifice layers 26, 32 including zinc formed on the surface layers of the header 20 and each heat transfer pipe 30. Into holes 23 penetrating through the header 20, the heat transfer pipe 30 is inserted via a connection part 15. At the connection part 15, the header 20 and the heat transfer pipe 30 are brazed. The zinc concentration of the second anticorrosive sacrifice layer 32b on the heat transfer pipe 30 at the connection part 15 is lower than the zinc concentration of the first anticorrosive sacrifice layer 32a on the heat transfer pipe 30 located outside the header 20.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present disclosure relates to a heat exchanger.

Background Art

[0002] Conventionally, a heat exchanger is known that includes a header and a plurality of heat transfer tubes, and in which the header and the heat transfer tubes are brazed with the heat transfer tubes inserted into holes penetrating the inside and outside of the header (see Patent Document 1). In the heat exchanger, in order to provide a corrosion-resistant sacrificial layer containing zinc on the surface layers of the header and the heat transfer tubes, a material (for example, a clad material) having a layer containing zinc on the surface of a base material (for example, an aluminum alloy) is used. In the header and the heat transfer tubes having the corrosion-resistant sacrificial layer, corrosion of the base material is suppressed by selectively corroding the corrosion-resistant sacrificial layer.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the conventional heat exchanger, when the corrosion-resistant sacrificial layer present in the portion where the header and the heat transfer tubes are brazed (hereinafter referred to as the connection portion) corrodes, a gap may occur between the header and the heat transfer tubes. For this reason, in the heat exchanger, there is a concern that holes may form in the connection portion of the header and the heat transfer tubes and the life may be reduced.

[0005] An object of the present disclosure is to suppress a reduction in the life of a heat exchanger.

Means for Solving the Problems

[0006] (1) The heat exchanger of the present disclosure includes a header and a plurality of heat transfer tubes, wherein a corrosion-resistant sacrificial layer containing zinc is formed on the surface of the header and the heat transfer tubes, and the heat exchanger has a connection portion in which the heat transfer tubes are inserted into holes penetrating the inside and outside of the header, and the header and the heat transfer tubes are brazed at the connection portion, wherein the zinc concentration of the corrosion-resistant sacrificial layer of the heat transfer tubes at the connection portion is lower than the zinc concentration of the corrosion-resistant sacrificial layer of the heat transfer tubes located outside the header.

[0007] The heat exchanger of this disclosure can suppress corrosion at the connection points between the header and the heat transfer tubes. This can suppress the reduction in the lifespan of the heat exchanger.

[0008] (2) In the heat exchanger of the present disclosure, the header and the heat transfer tubes are made of an aluminum alloy mainly composed of aluminum, and it is preferable that in the corrosion-resistant sacrificial layer of the header and the heat transfer tubes, the mass fraction of zinc to aluminum on the radially outward side is higher than that on the radially inward side.

[0009] In this case, a heat exchanger with a corrosion-resistant sacrificial layer can be manufactured without using cladding material, and the reduction in the lifespan of the heat exchanger can be suppressed.

[0010] (3) In the heat exchanger of the present disclosure, it is preferable that the mass fraction of zinc to aluminum in the corrosion-resistant sacrificial layer of the heat transfer tubes at the connection portion is less than 0.2%.

[0011] In this case, corrosion at the connection points between the header and heat transfer tubes can be more reliably suppressed. This, in turn, can more reliably suppress the reduction in the lifespan of the heat exchanger.

[0012] (4) In the heat exchanger of the present disclosure, it is preferable that the mass fraction of zinc to aluminum in the corrosion-resistant sacrificial layer of the heat transfer tubes located outside the header is 0.2% or more and 3.0% or less.

[0013] In this case, the surface layer of the heat transfer tubes located outside the header can be selectively corroded. This suppresses corrosion of the aluminum alloy base material of the heat transfer tubes, thereby reducing the lifespan of the heat exchanger. [Brief explanation of the drawing]

[0014] [Figure 1] A schematic diagram of the heat exchanger of this disclosure. [Figure 2] A schematic partial cross-sectional view showing the connection between the header and the heat transfer tube. [Figure 3] A partially enlarged cross-sectional view showing the formation state of the corrosion-resistant sacrificial layer at the connection point. [Figure 4] A partially enlarged schematic diagram showing the zinc concentration in the corrosion-resistant sacrificial layer. [Figure 5] A schematic diagram illustrating the manufacturing procedure (first embodiment) of the heat exchanger of this disclosure. [Figure 6] A schematic diagram illustrating the manufacturing procedure (second embodiment) of the heat exchanger of this disclosure. [Modes for carrying out the invention]

[0015] (Overview of heat exchangers) Figure 1 is a schematic diagram of the heat exchanger of this disclosure. Figure 2 is a schematic partial cross-sectional view showing the connection between the header and the heat transfer tubes. The heat exchanger 10 shown in Figure 1 is one embodiment of the heat exchanger of this disclosure and is used, for example, in the indoor unit of an air conditioner that implements a vapor compression type refrigeration cycle. The heat exchanger 10 is a fin-and-tube type heat exchanger and comprises a header 20, a plurality of heat transfer tubes 30 and a plurality of fins 40. The header 20 includes a pair of first headers 21 and second headers 22. In this disclosure, the heat exchanger 10 used in the indoor unit of an air conditioner is used as an example for explanation, but the applications of the heat exchanger of this disclosure are not limited to this.

[0016] The heat exchanger 10 mainly includes headers 21 and 22 arranged parallel to each other, a plurality of heat transfer tubes 30 arranged between the headers 21 and 22 while maintaining a spacing in a mutually parallel posture and joined perpendicularly to the headers 21 and 22, and fins 40 brazed to each heat transfer tube 30. The header 20, the heat transfer tube 30, and the fin 40 are made of an aluminum alloy described later.

[0017] A plurality of holes 23 (see FIG. 2) are formed in each of the headers 21 and 22 at equal intervals in the longitudinal direction. As shown in FIGS. 1 and 2, in the heat exchanger 10, the holes 23 are formed at opposite positions on the outer peripheral surfaces of the headers 21 and 22. The ends of the heat transfer tube 30 are inserted into the opposing holes 23 and are brazed to the headers 21 and 22 in this state. In the following description, the portion where the header 20 (the first header 21 and the second header 22) and the heat transfer tube 30 are brazed is referred to as the connection portion 15. In the present embodiment, the header 20 (the first header 21 and the second header 22) is made of a pipe material, but the configuration of the header in the heat exchanger of the present disclosure is not limited to this, and for example, a header (laminated header) formed by laminating a plurality of plate materials may be used.

[0018] (Details of the connection portion) As shown in FIG. 2, the header 20 has a base material layer 25 and a corrosion-resistant sacrificial layer 26 provided on the outer peripheral side of the base material layer 25. The corrosion-resistant sacrificial layer 26 constitutes the outermost layer in the radial direction of the header 20. By providing the corrosion-resistant sacrificial layer 26 on the outer peripheral side of the base material layer 25, a sacrificial corrosion prevention effect can be obtained for the header 20, and the corrosion resistance of the header 20 can be improved.

[0019] As shown in FIG. 2, the heat transfer tube 30 has a base material layer 31 and a corrosion sacrificial layer 32 provided on the outer peripheral side of the base material layer 31. The corrosion sacrificial layer 32 constitutes the outermost layer in the radial direction of the heat transfer tube 30. By providing the corrosion sacrificial layer 32 on the outer peripheral side of the base material layer 31, a sacrificial corrosion effect can be obtained for the heat transfer tube 30, and the corrosion resistance of the heat transfer tube 30 can be improved. In the following description, the portion of the corrosion sacrificial layer 32 located outside the header 20 is referred to as the first corrosion sacrificial layer 32a, and the portion of the corrosion sacrificial layer 32 located at the connection portion 15 is referred to as the second corrosion sacrificial layer 32b.

[0020] In the heat exchanger 10, the header 20 and the heat transfer tube 30 are manufactured using an aluminum alloy containing Si, Fe, Mn, Ti, Cu, etc. as a material. The corrosion sacrificial layers 26, 32 in the heat exchanger 10 are made of an aluminum alloy containing zinc (Zn). Note that although the header 20 and the heat transfer tube 30 of the present embodiment are manufactured using an aluminum alloy as a material, the header and the heat transfer tube in the heat exchanger of the present disclosure may be made of pure aluminum.

[0021] (Regarding the corrosion sacrificial layer) FIG. 3 is a partially enlarged cross-sectional view showing the formation state of the corrosion sacrificial layer at the connection portion. FIG. 4 is a partially enlarged schematic view showing the zinc concentration in the corrosion sacrificial layer. In the heat transfer tube 30, the zinc concentrations in the first corrosion sacrificial layer 32a and the second corrosion sacrificial layer 32b are different from each other. More specifically, in the heat transfer tube 30, the zinc concentration in the first corrosion sacrificial layer 32a is higher than the zinc concentration in the second corrosion sacrificial layer 32b. For this reason, in the heat transfer tube 30, the first corrosion sacrificial layer 32a is more likely to corrode than the second corrosion sacrificial layer 32b. As a result, in the heat transfer tube 30, the first corrosion sacrificial layer 32a is selectively corroded, and the corrosion occurring in the first corrosion sacrificial layer 32a is less likely to progress to the second corrosion sacrificial layer 32b.

[0022] As shown in FIG. 3, in the corrosion sacrificial layer 32, the thickness D1 of the first corrosion sacrificial layer 32a is larger than the thickness D2 of the second corrosion sacrificial layer 32b.

[0023] Figure 4 shows the zinc concentration in the corrosion-resistant sacrificial layer 32 of the heat transfer tube 30, indicated by the intensity of the color. As shown in Figure 4, the zinc concentration in the corrosion-resistant sacrificial layer 32 (first corrosion-resistant sacrificial layer 32a and second corrosion-resistant sacrificial layer 32b) is higher on the radially outward side than on the radially inward side. Also, as shown in Figure 4, the zinc concentration in the corrosion-resistant sacrificial layer 26 of the header 20 is higher on the radially outward side than on the radially inward side, similar to the corrosion-resistant sacrificial layer 32.

[0024] (Regarding the manufacturing method of the heat exchanger according to the first embodiment) Figure 5 is a schematic diagram showing the manufacturing procedure according to the first embodiment of the heat exchanger of the present disclosure. The heat exchanger 10 of the present disclosure can be obtained, for example, by manufacturing according to the manufacturing procedure shown in Figure 5. When manufacturing the heat exchanger 10 according to the manufacturing procedure of the first embodiment, as shown in the upper part of Figure 5, first, the header 20 and the heat transfer tubes 30 are temporarily assembled with the ends of the heat transfer tubes 30 inserted into the holes 23, and brazing material 16 is placed at the positions corresponding to the connection parts 15.

[0025] Next, as shown in the middle diagram of Figure 5, flux 50 is applied to the outer surfaces of the pre-assembled header 20 and heat transfer tubes 30. Flux 50 is a chemical agent used to remove foreign matter (oxides, etc.) present on the surfaces of the header 20 and heat transfer tubes 30 in order to promote the formation of a sound joint during brazing, and can be applied by known methods such as brushing or spraying. The flux 50 used in the heat exchanger 10 of this disclosure contains zinc as one of its components.

[0026] Next, the pre-assembled header 20 and heat transfer tubes 30, with flux 50 applied to their outer surfaces, are introduced into a furnace (for example, a conveyor furnace). The inside of the furnace is maintained in an oxygen-free atmosphere. The header 20 and heat transfer tubes 30 are heated in the oxygen-free atmosphere inside the furnace, causing the brazing material 16 placed at the connection portion 15 to melt and connect them. During brazing, the flux 50 removes foreign matter (oxides, etc.) from the surfaces of the header 20 and heat transfer tubes 30, and can also form a zinc-containing layer on the outer layer of the header 20 and heat transfer tubes 30. In other words, the flux 50 used in the manufacturing method of the heat exchanger 10 according to the first embodiment is a zinc-substituted flux.

[0027] As shown in the lower part of Figure 5, in the heat exchanger 10 manufactured using flux 50, a corrosion-resistant sacrificial layer 26 is formed on the outer layer of the header 20, and a corrosion-resistant sacrificial layer 32 is formed on the outer layer of the heat transfer tubes 30.

[0028] In the heat exchanger 10 manufactured according to the procedure shown in Figure 5, the corrosion-resistant sacrificial layer 32 formed on the heat transfer tube 30 includes a first corrosion-resistant sacrificial layer 32a located outside the header 20 and a second corrosion-resistant sacrificial layer 32b located at the connection portion 15.

[0029] The first corrosion-resistant sacrificial layer 32a is a layer formed by the diffusion of zinc contained in the flux 50 from the surface to the interior of the heat transfer tube 30, and contains aluminum contained in the base material of the heat transfer tube 30 and zinc added by the flux 50. In the first corrosion-resistant sacrificial layer 32a, the mass fraction of zinc to aluminum is greater on the radially outward side of the heat transfer tube 30 than on the radially inward side. In other words, in the first corrosion-resistant sacrificial layer 32a, the zinc concentration is higher on the radially outward side of the heat transfer tube 30 than on the radially inward side. Here, "mass fraction" refers to the concentration of zinc expressed as the ratio of the mass of zinc to the mass of aluminum.

[0030] The second corrosion-resistant sacrificial layer 32b is formed when a portion of the flux 50 applied to the heat transfer tubes 30 located outside the header 20 travels along the surface of the heat transfer tubes 30 and reaches the heat transfer tubes 30 located at the connection section 15. Therefore, the second corrosion-resistant sacrificial layer 32b, like the first corrosion-resistant sacrificial layer 32a, contains aluminum contained in the base material of the heat transfer tubes 30 and zinc provided by the flux 50. The amount of flux 50 reaching the connection section 15 is less than the amount of flux 50 applied to the heat transfer tubes 30 located outside the header 20. Therefore, the zinc concentration in the second corrosion-resistant sacrificial layer 32b is lower than the zinc concentration in the first corrosion-resistant sacrificial layer 32a. In other words, the mass fraction of zinc to aluminum in the second corrosion-resistant sacrificial layer 32b is lower than the mass fraction of zinc to aluminum in the first corrosion-resistant sacrificial layer 32a.

[0031] In the second corrosion-resistant sacrificial layer 32b, the mass fraction of zinc relative to aluminum is greater on the radially outward side of the heat transfer tube 30 compared to the radially inward side. In other words, in the second corrosion-resistant sacrificial layer 32b, the zinc concentration is higher on the radially outward side of the heat transfer tube 30 compared to the radially inward side.

[0032] Specifically, in the heat exchanger 10, by manufacturing according to the procedure shown in Figure 5, the mass fraction of zinc to aluminum in the second corrosion-resistant sacrificial layer 32b is less than 0.2%, and the mass fraction of zinc to aluminum in the first corrosion-resistant sacrificial layer 32a is between 0.2% and 3.0%.

[0033] For example, when a heat transfer tube 30 is manufactured using clad material, a zinc-containing layer is uniformly formed on the outer layer of the heat transfer tube 30. Therefore, in a heat transfer tube 30 manufactured using clad material, it is difficult to create a difference in zinc concentration between the corrosion-resistant sacrificial layer located at the connection portion 15 and the corrosion-resistant sacrificial layer located outside the header 20. In the heat exchanger 10 of this disclosure, by manufacturing it according to the procedure shown in Figure 5, it is possible to make the zinc concentration of the second corrosion-resistant sacrificial layer 32b located at the connection portion 15 lower than that of the first corrosion-resistant sacrificial layer 32a located outside the header 20. Therefore, in a heat exchanger 10 manufactured according to the procedure shown in Figure 5, selective corrosion of the second corrosion-resistant sacrificial layer 32b of the heat transfer tube 30 can be suppressed, and corrosion that occurs in the first corrosion-resistant sacrificial layer 32a can be suppressed from progressing to the second corrosion-resistant sacrificial layer 32b, thereby suppressing pitting corrosion at the connection portion 15.

[0034] (Regarding the manufacturing method of the heat exchanger according to the second embodiment) Figure 6 is a schematic diagram showing the manufacturing procedure according to the second embodiment of the heat exchanger of the present disclosure. The heat exchanger 10 of the present disclosure can be obtained, for example, by manufacturing according to the manufacturing procedure shown in Figure 6. When manufacturing the heat exchanger 10 according to the manufacturing procedure of the second embodiment, as shown in the upper part of Figure 6, first, the header 20 and the heat transfer tubes 30 are temporarily assembled with the ends of the heat transfer tubes 30 inserted into the holes 23, and the brazing material 16 is placed at the position corresponding to the connection part 15.

[0035] Next, as shown in the middle diagram of Figure 6, the pre-assembled header 20 and heat transfer tubes 30 are introduced into a furnace (for example, a conveyor furnace). The inside of the furnace is maintained in a nitrogen atmosphere containing zinc vapor. In the manufacturing procedure of the heat exchanger 10 shown in Figure 6, the header 20 and heat transfer tubes 30 are heated in the nitrogen atmosphere containing zinc vapor inside the furnace, and the brazing material 16 placed in the connection part 15 is melted.

[0036] As shown in the lower part of Figure 6, when the header 20 is heated in a nitrogen atmosphere containing zinc vapor, a corrosion-resistant sacrificial layer 26 is formed on the outer layer. When the heat transfer tube 30 is heated in a nitrogen atmosphere containing zinc vapor, a corrosion-resistant sacrificial layer 32 is formed on the outer layer. The corrosion-resistant sacrificial layer 32 of the heat transfer tube 30 manufactured by the procedure shown in Figure 6 includes a first corrosion-resistant sacrificial layer 32a located outside the header 20 and a second corrosion-resistant sacrificial layer 32b located at the connection part 15.

[0037] The first corrosion-resistant sacrificial layer 32a is formed by the diffusion of zinc contained in the flux 50 from the surface to the interior of the heat transfer tube 30, and contains aluminum contained in the base material of the heat transfer tube 30 and zinc added by zinc vapor. The zinc contained in the corrosion-resistant sacrificial layer 32 is added from the outer layer side of the heat transfer tube 30. For this reason, in the first corrosion-resistant sacrificial layer 32a, the mass fraction of zinc to aluminum is greater on the radially outer side of the heat transfer tube 30 than on the radially inner side. In other words, in the first corrosion-resistant sacrificial layer 32a, the zinc concentration is higher on the radially outer side of the heat transfer tube 30 than on the radially inner side.

[0038] The second corrosion-resistant sacrificial layer 32b is formed when zinc vapor present outside the header 20 passes through the gaps between the holes 23 and the heat transfer tubes 30 to reach the heat transfer tubes 30 located at the connection point 15. The second corrosion-resistant sacrificial layer 32b contains aluminum contained in the base material of the heat transfer tubes 30 and zinc added by the zinc vapor. The amount of zinc vapor reaching the connection point 15 is less than the amount of zinc vapor present around the heat transfer tubes 30 located outside the header 20. Therefore, in the heat transfer tubes 30, the zinc concentration in the second corrosion-resistant sacrificial layer 32b is lower than the zinc concentration in the first corrosion-resistant sacrificial layer 32a.

[0039] In the second corrosion-resistant sacrificial layer 32b, the mass fraction of zinc relative to aluminum is greater on the radially outward side of the heat transfer tube 30 compared to the radially inward side. In other words, in the second corrosion-resistant sacrificial layer 32b, the zinc concentration is higher on the radially outward side of the heat transfer tube 30 compared to the radially inward side.

[0040] Specifically, in the heat exchanger 10, by manufacturing according to the procedure shown in Figure 6, the mass fraction of zinc to aluminum in the second corrosion-resistant sacrificial layer 32b is less than 0.2%, and the mass fraction of zinc to aluminum in the first corrosion-resistant sacrificial layer 32a is between 0.2% and 3.0%.

[0041] In the heat exchanger 10 of this disclosure, by manufacturing it according to the procedure shown in Figure 6, it is possible to make the zinc concentration of the second corrosion-resistant sacrificial layer 32b located at the connection portion 15 lower than that of the first corrosion-resistant sacrificial layer 32a located outside the header 20. As a result, in the heat exchanger 10 manufactured according to the procedure shown in Figure 6, selective corrosion of the heat transfer tubes 30 by the second corrosion-resistant sacrificial layer 32b is suppressed, and corrosion that occurs in the first corrosion-resistant sacrificial layer 32a is suppressed from progressing to the second corrosion-resistant sacrificial layer 32b, thereby suppressing pitting corrosion at the connection portion 15.

[0042] [Effects of the Embodiment] (1) The heat exchanger 10 shown in the above embodiment includes a header 20 and a plurality of heat transfer tubes 30, and corrosion-resistant sacrificial layers 26 and 32 containing zinc are formed on the surface of the header 20 and the heat transfer tubes 30. The heat exchanger 10 has a connection part 15 in which the heat transfer tubes 30 are inserted into holes 23 that penetrate the inside and outside of the header 20. In the heat exchanger 10, the header 20 and the heat transfer tubes 30 are brazed at the connection part 15. In the heat exchanger 10, the zinc concentration of the second corrosion-resistant sacrificial layer 32b of the heat transfer tubes 30 at the connection part 15 is lower than the zinc concentration of the first corrosion-resistant sacrificial layer 32a of the heat transfer tubes 30 located outside the header 20.

[0043] With a heat exchanger 10 configured in this way, corrosion at the connection point 15 between the header 20 and the heat transfer tubes 30 can be suppressed. This helps to reduce the lifespan of the heat exchanger 10.

[0044] (2) In the heat exchanger 10 shown in the above embodiment, the header 20 and heat transfer tubes 30 are made of an aluminum alloy mainly composed of aluminum. In the heat exchanger 10, in the corrosion-resistant sacrificial layers 26 and 32 of the header 20 and heat transfer tubes 30, the mass fraction of zinc to aluminum on the radially outward side is higher than that on the radially inward side.

[0045] In this case, the heat exchanger 10 having corrosion-resistant sacrificial layers 26 and 32 can be manufactured without using cladding material, and the reduction in the lifespan of the heat exchanger 10 can be suppressed.

[0046] (3) In the heat exchanger 10 shown in the above embodiment, the mass fraction of zinc to aluminum in the second corrosion-resistant sacrificial layer 32b of the heat transfer tube 30 at the connection part 15 is less than 0.2%.

[0047] In this case, corrosion at the connection point 15 between the header 20 and the heat transfer tube 30 can be more reliably suppressed. This makes it possible to more reliably suppress the reduction in the lifespan of the heat exchanger 10.

[0048] (4) In the heat exchanger 10 shown in the above embodiment, the mass fraction of zinc to aluminum in the first corrosion-resistant sacrificial layer 32a of the heat transfer tube 30 located outside the header 20 is 0.2% or more and 3.0% or less.

[0049] In this case, the surface layer of the heat transfer tube 30 located outside the header 20 can be selectively corroded. This suppresses corrosion of the aluminum alloy base material of the heat transfer tube 30, thereby reducing the lifespan of the heat exchanger 10.

[0050] This disclosure is not limited to the above examples, but is intended to include all modifications within the meaning and scope of the claims as shown, and equivalents of the claims. [Explanation of Symbols]

[0051] 10: Heat exchanger 15: Connection part 20: Header 23: Hole (hole) 26: Corrosion-resistant sacrificial layer 30: Heat transfer tube 32: Corrosion-resistant sacrificial layer 32a: First corrosion-resistant sacrificial layer 32b: Second corrosion-resistant sacrificial layer

Claims

1. It includes a header (20) and a plurality of heat transfer tubes (30), A corrosion-resistant sacrificial layer (26, 32) containing zinc is formed on the surface of the header (20) and the heat transfer tube (30). A heat exchanger (10) having a connection portion (15) in which the heat transfer tube (30) is inserted into a hole (23) that penetrates the inside and outside of the header (20), wherein the header (20) and the heat transfer tube (30) are brazed at the connection portion (15), The corrosion-resistant sacrificial layer (32b) of the heat transfer tube (30) located in the region connected to the connection portion (15), and the corrosion-resistant sacrificial layer (32a) of the heat transfer tube (30) located outside the header (20), are formed radially inward from the surface of the heat transfer tube (30). A heat exchanger (10) in which the zinc concentration of the corrosion-resistant sacrificial layer (32b) located in the region connected to the connection portion (15) is lower than the zinc concentration of the corrosion-resistant sacrificial layer (32a) located outside the header (20).

2. The header (20) and the heat transfer tube (30) are made of an aluminum alloy, mainly composed of aluminum. The heat exchanger (10) according to claim 1, wherein in the corrosion-resistant sacrificial layers (26, 32) of the header (20) and the heat transfer tubes (30), the mass fraction of zinc to aluminum on the radially outward side is higher than that on the radially inward side.

3. The heat exchanger (10) according to claim 2, wherein in the corrosion-resistant sacrificial layer (32b) of the heat transfer tube (30) at the connection portion (15), the mass fraction of zinc to aluminum is less than 0.2%.

4. The heat exchanger (10) according to claim 3, wherein in the corrosion-resistant sacrificial layer (32a) of the heat transfer tube (30) located outside the header (20), the mass fraction of zinc to aluminum is 0.2% or more and 3.0% or less.

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