Heat exchanger, air conditioning device provided with heat exchanger, and method for manufacturing heat exchanger

Abstract

This heat exchanger comprises: heat transfer tubes in each of which there is formed a flow path through which a refrigerant flows, the vertical direction being employed as the tube extension direction, and a plurality of heat transfer tubes being disposed at intervals in the lateral direction orthogonal to the vertical direction and the longitudinal direction, which is the ventilation direction; fins that are respectively disposed between every two heat transfer tubes adjacent to each other in the lateral direction, the fins being each joined to the two heat transfer tubes on the left and right across the vertical direction; an upper header into which the upper ends of the heat transfer tubes are inserted; and a lower header into which the lower ends of the heat transfer tubes are inserted. The electric potential of the heat transfer tubes is configured to be lower than that of the fins, and the difference in electric potential between the fins and the heat transfer tubes that are joined to each other is greater in the lower parts than in other portions in the vertical direction.

Description

Heat exchanger, air conditioner equipped with heat exchanger, and method for manufacturing heat exchanger

[0001] The present disclosure relates to a heat exchanger having a plurality of heat transfer tubes and fins, an air conditioning apparatus including the heat exchanger, and a method for manufacturing the heat exchanger.

[0002] Conventionally, there are heat exchangers that suppress corrosion of heat transfer tubes (see, for example, Patent Document 1). Patent Document 1 discloses a configuration in which a sacrificial layer is provided on the surface of the heat transfer tube, and the thickness of the sacrificial layer is different between the indoor heat exchanger and the outdoor heat exchanger. It also discloses a configuration in which the thickness of the sacrificial layer varies depending on the location within the heat exchanger, for example, by making the thickness of the sacrificial layer thicker in a portion where air with a high salt content, which is a corrosion factor, flows than in a portion where air with a low salt content flows. This configuration suppresses corrosion of the heat transfer tubes in the corrosion-prone portion.

[0003] JP 2023-51137 A

[0004] The degree of corrosion in a heat exchanger is affected by the presence or absence of water, and corrosion is more likely to progress in areas where water is likely to remain. However, Patent Document 1 does not take into consideration the likelihood of water remaining in the heat exchanger, so corrosion progresses in areas where water is likely to remain, resulting in a problem of a decrease in the heat exchange performance of the heat exchanger.

[0005] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a heat exchanger that can suppress the progression of corrosion in areas where water is likely to remain and suppress the deterioration of heat exchange performance, an air conditioning device equipped with a heat exchanger, and a method for manufacturing a heat exchanger.

[0006] The heat exchanger according to the present disclosure has a flow path formed therein through which a refrigerant flows, and the tubes extend in the vertical direction. The heat exchanger comprises a plurality of heat transfer tubes arranged at intervals in a left-right direction perpendicular to the vertical direction and the front-to-back direction which is the ventilation direction; fins arranged between two adjacent heat transfer tubes in the horizontal direction and joined to the two left and right heat transfer tubes in the vertical direction; an upper header into which the upper ends of the heat transfer tubes are inserted; and a lower header into which the lower ends of the heat transfer tubes are inserted. The potential of the heat transfer tubes relative to the fins is low, and the potential difference between the heat transfer tubes and the fins, which are joined to each other, is larger at the lower parts in the vertical direction than at other parts.

[0007] An air conditioning apparatus according to the present disclosure includes the above-described heat exchanger.

[0008] Furthermore, a method for manufacturing a heat exchanger according to the present disclosure is a method for manufacturing the above-described heat exchanger, comprising the steps of spraying zinc onto the surfaces of the heat transfer tubes, assembling the heat transfer tubes, the upper header, and the lower header, applying a zinc-containing flux to the surfaces of the lower parts of all of the heat transfer tubes, assembling the fins, applying a zinc-free flux to the entire surfaces of all of the heat transfer tubes, and furnace brazing in an electric furnace.

[0009] According to the heat exchanger, air conditioner including a heat exchanger, and method for manufacturing a heat exchanger disclosed herein, the potential of the heat transfer tube relative to the fins is low, and the potential difference between the heat transfer tube and the fins in areas where water is likely to remain is greater than the potential difference between the heat transfer tube and the fins in areas where water is not likely to remain. Because corrosion progresses first from materials with a relatively low potential, the lower the potential of the heat transfer tube relative to the fins, the more likely corrosion of the heat transfer tube takes precedence over corrosion of the fins, making the fins less susceptible to corrosion. Due to the structure of a heat exchanger including heat transfer tubes extending vertically and fins arranged between two adjacent heat transfer tubes in the horizontal direction, water is more likely to remain on the fins and less likely to remain on the heat transfer tubes. Therefore, by lowering the potential of the heat transfer tube relative to the fins as described above in areas of the heat exchanger where water is likely to remain, corrosion of the heat transfer tube takes precedence over corrosion of the fins, making the fins less susceptible to corrosion. This can suppress the progression of fin corrosion in areas where water is likely to remain, thereby preventing a decrease in heat exchange performance due to fin corrosion.

[0010] 1 is a refrigerant circuit diagram of an air conditioner equipped with a heat exchanger according to embodiment 1. FIG. 2 is a perspective view of the heat exchanger according to embodiment 1. FIG. 3 is a perspective view of a top-flow outdoor unit equipped with the heat exchanger according to embodiment 1. FIG. 4 is a front view schematically showing the heat exchanger according to embodiment 1. FIG. 5 is a perspective view schematically showing a heat exchanger according to embodiment 1 and a ceiling-mounted indoor unit equipped with the heat exchanger according to a first modification of embodiment 1. FIG. 6 is a front view schematically showing the heat exchanger according to a first modification of embodiment 1. FIG. 7 is a cross-sectional schematic view of a heat transfer tube of the heat exchanger according to embodiment 1. FIG. 8 is a schematic view showing a joint between the heat transfer tube and fins of the heat exchanger according to embodiment 1. FIG. 9 is a schematic view showing a joint between the heat transfer tube and fins of the heat exchanger according to embodiment 1. FIG. 10 is a schematic view showing a potential difference distribution in the heat exchanger core of the heat exchanger according to embodiment 1. FIG. 11 is a schematic view showing the zinc concentrations of the heat transfer tubes and fins in the center of the heat exchanger core of the heat exchanger according to embodiment 1. Fig. 1 is a schematic diagram showing zinc concentrations of heat transfer tubes and fins near a lower header of a heat exchanger core of a heat exchanger according to embodiment 1. Fig. 2 is a schematic diagram showing potential difference distribution in a heat exchanger core of a heat exchanger according to a third modified example of embodiment 1. Fig. 3 is a schematic diagram showing potential difference distribution in a heat exchanger core of a heat exchanger according to embodiment 2. Fig. 4 is a schematic diagram showing potential difference distribution in a heat exchanger core of a heat exchanger according to embodiment 3. Fig. 5 is a diagram showing differences in surface zinc concentration depending on each part in the heat exchanger core of a heat exchanger according to embodiment 1.

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the present disclosure is not limited to the embodiments described below. Also, the size relationships of the components in the drawings may differ from those in reality.

[0012] Embodiment 1. <Configuration of Air Conditioning Apparatus 100> Fig. 1 is a refrigerant circuit diagram of an air conditioning apparatus 100 equipped with a heat exchanger 30 according to Embodiment 1. Note that solid arrows in Fig. 1 indicate the flow of refrigerant during cooling operation, and dashed arrows in Fig. 1 indicate the flow of refrigerant during heating operation.

[0013] As shown in Fig. 1 , a heat exchanger 30 according to the first embodiment is mounted on the outdoor unit 10 of an air conditioning apparatus 100 that includes an outdoor unit 10 and an indoor unit 20. In addition to the heat exchanger 30, the outdoor unit 10 includes a compressor 11, a flow path switching device 12, and a fan 13. The indoor unit 20 includes a throttling device 21, an indoor heat exchanger 22, and an indoor fan 23.

[0014] The air conditioner 100 also includes a refrigerant circuit in which a refrigerant circulates, with the compressor 11, flow path switching device 12, heat exchanger 30, expansion device 21, and indoor heat exchanger 22 connected by refrigerant piping. The air conditioner 100 can operate in both cooling and heating modes by switching the flow path switching device 12.

[0015] The compressor 11 draws in a low-temperature, low-pressure refrigerant, compresses the drawn refrigerant, and discharges a high-temperature, high-pressure refrigerant. The compressor 11 is, for example, an inverter compressor whose capacity, which is the amount of refrigeration per unit time, is controlled by changing the operating frequency.

[0016] The flow path switching device 12 is, for example, a four-way valve, and switches between cooling operation and heating operation by switching the direction of refrigerant flow. During cooling operation, the flow path switching device 12 switches to the state shown by the solid line in Fig. 1, connecting the discharge side of the compressor 11 to the heat exchanger 30. During heating operation, the flow path switching device 12 switches to the state shown by the dashed line in Fig. 1, connecting the discharge side of the compressor 11 to the indoor heat exchanger 22.

[0017] The heat exchanger 30 exchanges heat between the outdoor air and the refrigerant. During cooling operation, the heat exchanger 30 functions as a condenser that radiates heat from the refrigerant to the outdoor air to condense the refrigerant. During heating operation, the heat exchanger 30 evaporates the refrigerant and cools the outdoor air with the heat of vaporization.

[0018] The fan 13 supplies outdoor air to the heat exchanger 30, and the amount of air blown to the heat exchanger 30 is adjusted by controlling the rotation speed.

[0019] The expansion device 21 is, for example, an electronic expansion valve that can adjust the aperture, and by adjusting the aperture, controls the pressure of the refrigerant flowing into the heat exchanger 30 or the indoor heat exchanger 22. In the first embodiment, the expansion device 21 is provided in the indoor unit 20, but it may also be provided in the outdoor unit 10, and the installation location is not limited.

[0020] The indoor heat exchanger 22 exchanges heat between the indoor air and the refrigerant. During cooling operation, the indoor heat exchanger 22 functions as an evaporator that evaporates the refrigerant and cools the outdoor air with the heat of vaporization. During heating operation, the indoor heat exchanger 22 functions as a condenser that radiates heat from the refrigerant to the outdoor air to condense the refrigerant.

[0021] The indoor fan 23 supplies indoor air to the indoor heat exchanger 22, and the amount of air blown to the indoor heat exchanger 22 is adjusted by controlling the rotation speed.

[0022] <Configuration of Heat Exchanger 30> Fig. 2 is a perspective view of the heat exchanger 30 according to embodiment 1. Note that the outline arrows in Fig. 2 indicate the flow of air generated by the fan 13.

[0023] 2 , the heat exchanger 30 has multiple heat exchanger cores 31 arranged along the air flow direction. Specifically, the heat exchanger 30 has a first heat exchanger core 31a on the upwind side and a second heat exchanger core 31b on the downwind side. However, the number of heat exchanger cores 31 is not limited to the above, and the heat exchanger 30 may have one heat exchanger core 31 or three or more heat exchanger cores 31. The heat exchanger core 31 has multiple heat transfer tubes 38 and multiple fins 39.

[0024] The heat transfer tubes 38 are arranged in parallel in the left-right direction (horizontal direction) at intervals so that the air generated by the fan 13 can flow therethrough, and the refrigerant flows vertically through the tubes extending in the up-down direction (vertical direction). The fins 39 improve the heat exchange efficiency between the air and the refrigerant and are connected between adjacent heat transfer tubes 38 to transfer heat to the heat transfer tubes 38. Note that although the heat transfer tubes 38 in the first embodiment are flat tubes, the present invention is not limited thereto and may be, for example, circular tubes. Furthermore, although the fins 39 in the first embodiment are corrugated fins, the present invention is not limited thereto and may be, for example, plate-like fins.

[0025] A first lower header 34a is provided at the lower end of the first heat exchanger core 31a. The lower ends of the heat transfer tubes 38 of the first heat exchanger core 31a are directly inserted into the first lower header 34a. The first lower header 34a is connected to the refrigerant circuit of the air conditioning apparatus 100 via liquid piping 36. The first lower header 34a is also referred to as a liquid header. An opening (not shown) is formed in the portion of the first lower header 34a to which the liquid piping 36 is connected. The first lower header 34a allows low-temperature, low-pressure two-phase refrigerant to flow into the heat exchanger 30 during heating operation, and allows low-temperature, high-pressure liquid refrigerant after heat exchange in the heat exchanger 30 to flow out to the refrigerant circuit during cooling operation.

[0026] A second lower header 34b is provided at the lower end of the second heat exchanger core 31b. The lower ends of the heat transfer tubes 38 of the second heat exchanger core 31b are directly inserted into the second lower header 34b. The second lower header 34b is arranged in parallel with the first lower header 34a. The second lower header 34b is connected to the refrigerant circuit of the air conditioning apparatus 100 via a gas pipe 37. The second lower header 34b is also referred to as a gas header. An opening (not shown) is formed in the portion of the second lower header 34b where the gas pipe 37 is connected. The second lower header 34b allows high-temperature, high-pressure gas refrigerant from the compressor 11 to flow into the heat exchanger 30 during cooling operation, and allows low-temperature, low-pressure gas refrigerant after heat exchange in the heat exchanger 30 to flow out into the refrigerant circuit during heating operation.

[0027] That is, in the heat exchanger 30, during cooling operation, the refrigerant inlet is the gas pipe 37 connected to the second lower header 34b, and the refrigerant outlet is the liquid pipe 36 connected to the first lower header 34a. Also, during heating operation, the refrigerant inlet is the liquid pipe 36 connected to the first lower header 34a, and the refrigerant outlet is the gas pipe 37 connected to the second lower header 34b.

[0028] An upper header 33 is provided at the upper ends of the first heat exchanger core 31a and the second heat exchanger core 31b, into which the upper ends of the heat transfer tubes 38 inserted in the first lower header 34a and the second lower header 34b are inserted. The upper header 33 is a row header that circulates refrigerant between the heat transfer tubes 38 of the first heat exchanger core 31a and the heat transfer tubes 38 of the second heat exchanger core 31b. Hereinafter, the first lower header 34a and the second lower header 34b will be collectively referred to as the lower header 34.

[0029] The plurality of heat transfer tubes 38, fins 39, lower header 34, upper header 33, liquid pipes 36, and gas pipes 37 are all made of aluminum and are joined by brazing.

[0030] The heat exchanger 30 is manufactured by assembling the heat transfer tubes 38, fins 39, lower header 34, and upper header 33, each having a zinc sprayed surface, and then applying flux to the entire surfaces of the heat transfer tubes 38, lower header 34, and upper header 33, and brazing them in an electric furnace. Note that the fins 39, lower header 34, and upper header 33 can be made of clad material with a brazing material on their surfaces.

[0031] <Cooling Operation> The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 flows into the heat exchanger 30 via the flow switching device 12. The high-temperature, high-pressure gas refrigerant that has flowed into the heat exchanger 30 exchanges heat with the outdoor air taken in by the fan 13, condenses while releasing heat, and becomes low-temperature, high-pressure liquid refrigerant, which then flows out of the heat exchanger 30. At this time, the refrigerant flowing through the heat exchanger 30 flows in the following order: gas piping 37, second lower header 34b, second heat exchanger core 31b, upper header 33, first heat exchanger core 31a, first lower header 34a, and liquid piping 36. The low-temperature, high-pressure liquid refrigerant that has flowed out of the heat exchanger 30 is decompressed by the expansion device 21, becoming low-temperature, low-pressure two-phase gas-liquid refrigerant, which then flows into the indoor heat exchanger 22. The low-temperature, low-pressure two-phase gas-liquid refrigerant that has flowed into the indoor heat exchanger 22 exchanges heat with the indoor air taken in by the indoor fan 23, evaporating while absorbing heat, cooling the indoor air, and turning into low-temperature, low-pressure gas refrigerant, which then flows out of the indoor heat exchanger 22. The low-temperature, low-pressure gas refrigerant that has flowed out of the indoor heat exchanger 22 is drawn into the compressor 11, where it again becomes high-temperature, high-pressure gas refrigerant.

[0032] <Heating operation> The high-temperature, high-pressure gas refrigerant discharged from the compressor 11 flows into the indoor heat exchanger 22 via the flow switching device 12. The high-temperature, high-pressure gas refrigerant that has flowed into the indoor heat exchanger 22 exchanges heat with the indoor air taken in by the indoor fan 23, condensing while releasing heat, heating the indoor air, and turning into a low-temperature, high-pressure liquid refrigerant, which flows out of the indoor heat exchanger 22. The low-temperature, high-pressure liquid refrigerant that has flowed out of the indoor heat exchanger 22 is decompressed by the expansion device 21 and turns into a low-temperature, low-pressure two-phase gas-liquid refrigerant, which flows into the heat exchanger 30. The low-temperature, low-pressure two-phase gas-liquid refrigerant that has flowed into the heat exchanger 30 exchanges heat with the outdoor air taken in by the fan 13, evaporates while absorbing heat, and turns into a low-temperature, low-pressure gas refrigerant, which flows out of the heat exchanger 30. At this time, the refrigerant flowing through the heat exchanger 30 flows in the following order: liquid piping 36, first lower header 34a, first heat exchanger core 31a, upper header 33, second heat exchanger core 31b, second lower header 34b, and gas piping 37. The low-temperature, low-pressure gas refrigerant flowing out of the heat exchanger 30 is drawn into the compressor 11, where it becomes high-temperature, high-pressure gas refrigerant again.

[0033] Fig. 3 is a perspective view of the heat exchanger 30 according to embodiment 1 and the top-flow outdoor unit 10 equipped with the heat exchanger 30. Fig. 4 is a front view schematically showing the heat exchanger 30 according to embodiment 1. As shown in Fig. 3, the heat exchanger 30 according to embodiment 1 is equipped in, for example, a top-flow outdoor unit 10.

[0034] 3, the outdoor unit 10 includes a casing 15 formed in a vertically long box shape, a heat exchanger 30 provided along the outer surface of the casing 15, and a fan 13 provided at the upper interior portion of the casing 15. The casing 15 further includes a bottom plate 15c forming the bottom surface, a pair of support legs 15d supporting the bottom plate 15c, four pillars 15b extending upward from the four corners of the bottom plate 15c, a front panel 15a covering the front opening, and a fan casing 14 provided around the fan 13.

[0035] The casing 15 has intake ports 16 for taking air into the interior formed on the left and right side surfaces and the back of the outer periphery, which has four pillars 15b as its four corners, and heat exchangers 30 are arranged along the intake ports 16. In other words, three heat exchangers 30 are arranged in the casing 15. The heat exchangers 30 exchange heat between the refrigerant supplied to the heat exchanger 30 and the air passing through the heat exchanger 30. As shown in FIG. 4, the heat exchanger 30 has a vertically long rectangular shape when viewed from the front.

[0036] As shown in Figure 3, the casing 15 has four pillars 15b at its four corners, and two decorative front panels 15a, made of metal, attached to the front side of the outer periphery. The front of the casing 15 is closed by the front panels 15a. The left and right side edges of the front panels 15a are fixed to the pillars 15b with fastening members such as screws.

[0037] Furthermore, internal components that constitute the refrigerant circuit, such as the compressor 11, are installed in the lower interior of the casing 15. By removing the front panel 15a from the casing 15 to open the interior of the outdoor unit 10, maintenance of the internal components, such as the compressor 11, can be performed.

[0038] An air outlet 17 is formed on the top surface of the casing 15, and a fan 13 is disposed within the casing 15 directly below the air outlet 17. The fan 13 is, for example, a propeller fan or the like, and is driven by a motor (not shown). When the fan 13 is driven, air is drawn into the casing 15 through the air inlet 16, passes through the heat exchanger 30 to exchange heat with the refrigerant, and is then discharged through the air outlet 17 via the fan 13. The fan 13 is surrounded by a fan casing 14 attached to the casing 15. The fan casing 14 is disposed above the front panel 15a and the heat exchanger 30 on the outer periphery of the casing 15, with four pillars 15b at its four corners, and surrounds the fan 13.

[0039] FIG. 5 is a perspective view schematically illustrating a heat exchanger 30a according to a first modification of Embodiment 1 and a ceiling-mounted indoor unit 20a equipped with the heat exchanger 30a. FIG. 6 is a front view schematically illustrating the heat exchanger 30a according to the first modification of Embodiment 1. As shown in FIG. 5, the heat exchanger 30a may be mounted in, for example, a ceiling-mounted indoor unit 20a. In this case, the indoor unit 20a includes a casing 25 formed in a horizontally elongated box shape. The heat exchanger 30a has an L-shape in plan view, and two independent heat exchangers 30a are mounted within the casing 25 so as to form a rectangular shape in plan view. The heat exchanger 30a does not necessarily have to have an L-shape in plan view. The heat exchanger 30a may have an I-shape in plan view, and four independent heat exchangers 30a may be mounted within the casing 25 so as to form a rectangular shape in plan view. Furthermore, the two or four independent heat exchangers 30a do not necessarily have to be strictly rectangular in plan view. As shown in Fig. 6, the heat exchanger 30a has a horizontally elongated rectangular shape in front view.

[0040] FIG. 7 is a cross-sectional schematic diagram of a heat transfer tube 38 of a heat exchanger 30 according to the first embodiment. As shown in FIG. 7 , the heat transfer tube 38 according to the first embodiment is a flat tube having a rectangular shape with rounded corners in a plan view. The heat transfer tube 38 includes a core material 61 having a plurality of refrigerant flow paths 62 formed therein along the longitudinal direction, and a zinc sacrificial layer 63 formed on the outer surface of the core material 61. The zinc sacrificial layer 63 is formed by zinc diffusing toward the interior of the heat transfer tube 38 during the furnace brazing process, resulting in a zinc sacrificial layer 63 having a thickness of several tens to several hundred micrometers on the surface of the heat transfer tube 38. Furthermore, the zinc sacrificial layer 63 formed by this diffusion has a higher zinc concentration toward the surface of the sacrificial layer, resulting in a zinc sacrificial layer 63 with a surface zinc concentration of up to several wt % within the sacrificial layer.

[0041] FIG. 8 is a schematic diagram showing a joint between a heat transfer tube 38 and a fin 39 of a heat exchanger 30 according to the first embodiment. The fin 39 according to the first embodiment is a corrugated fin. As shown in FIG. 8 , the corrugated fin 39 has peaks 39A protruding toward the heat transfer tube 38, and the peaks 39A are brazed to the surface of the heat transfer tube 38 at brazing portions 64. The corrugated fin is made of a material containing zinc at a few wt %, for example, 0.75 wt %. However, the zinc concentration of the corrugated fin material is not limited to 0.75 wt %. Although FIG. 8 only shows the joint between the heat transfer tube 38 and the fin 39 on the right side, there is also a joint on the left side, which has a similar configuration.

[0042] FIG. 9 is a schematic diagram showing a joint between a heat transfer tube 38 and a fin 39a of a heat exchanger 30 according to a second modification of the first embodiment. The fin 39a may be a plate-shaped fin. In this case, as shown in FIG. 9 , the plate-shaped fin 39a has a flange 39aA extending downward in the same direction as the heat transfer tube 38. The flange 39aA is brazed to the surface of the heat transfer tube 38 at a brazing portion 64. The plate-shaped fin is made of a material containing a few wt % of zinc, e.g., 0.75 wt %. However, the zinc concentration of the plate-shaped fin material is not limited to 0.75 wt %. While FIG. 9 only shows the joint between the heat transfer tube 38 and the fin 39 on the right side, a similar joint is also present on the left side.

[0043] The lower part of the heat exchanger 30, where adhering moisture is more likely to remain, is set to have a larger potential difference between the heat transfer tubes 38 and the fins 39. Here, the lower part of the heat exchanger 30 is the part where the heat exchanger 30 is in contact with water for a longer period of time when water is discharged outside the system of the heat exchanger 30, and where moisture is more likely to remain within the surface of the heat exchanger 30.

[0044] FIG. 10 is a schematic diagram showing the potential difference distribution in the heat exchanger core 31 of the heat exchanger 30 according to the first embodiment. As shown in FIG. 10 , the potential difference between the heat transfer tubes 38 and the fins 39 increases with increasing distance from the lower header 34 in the heat exchanger core 31. In other words, in the first embodiment, the potential difference between the heat transfer tubes 38 and the fins 39 varies in the up-down (vertical) direction in the heat exchanger core 31. In FIG. 10 , the distribution of the potential difference between the heat transfer tubes 38 and the fins 39 in the heat exchanger core 31 is represented by shading. The darker the shading in the heat exchanger core 31, the larger the potential difference between the heat transfer tubes 38 and the fins 39. That is, the potential difference between the heat transfer tubes 38 and the fins 39 increases from the center to the bottom of the heat exchanger core 31. This potential difference can be achieved by increasing the surface zinc concentration of the heat transfer tubes 38 located in the lower part of the heat exchanger core 31 compared to the heat transfer tubes 38 in the central part. The potential of the heat transfer tubes 38 relative to the fins 39 decreases toward the bottom of the heat exchanger core 31 .

[0045] Fig. 11 is a schematic diagram showing the zinc concentrations of the heat transfer tubes 38 and the fins 39 in the central portion of the heat exchanger core 31 of the heat exchanger 30 according to embodiment 1. Fig. 12 is a schematic diagram showing the zinc concentrations of the heat transfer tubes 38 and the fins 39 in the vicinity of the lower header 34 of the heat exchanger core 31 of the heat exchanger 30 according to embodiment 1.

[0046] Next, the zinc concentration and potential difference at each portion of the heat exchanger core 31 will be described. FIG. 11 shows the zinc concentration of the heat transfer tubes 38 and fins 39 in the central portion (portion A in FIG. 10 ) of the heat exchanger core 31 of the heat exchanger 30. In FIG. 11 , the zinc concentration of the fins 39 is 0.75 wt %, and the surface zinc concentration of the heat transfer tubes 38 is 1 wt %. FIG. 12 shows the zinc concentration of the heat transfer tubes 38 and fins 39 in the vicinity of the lower header 34 of the heat exchanger core 31 of the heat exchanger 30 (portion B in FIG. 10 ). In FIG. 12 , the zinc concentration of the fins 39 is 0.75 wt %, and the surface zinc concentration of the heat transfer tubes 38 is 2 wt %. In this way, the surface zinc concentration of the heat transfer tubes 38 located in the lower portion of the heat exchanger core 31 is higher than that in the central portion, and the potential of the heat transfer tubes 38 relative to the fins 39 is lower the closer to the lower header 34 of the heat exchanger core 31. In this case, the potential difference is, for example, 25 mV at the center of the heat exchanger core 31 and 105 mV near the lower header 34. In this way, the potential difference between the heat transfer tubes 38 and the fins 39 is greater at the lower part of the heat exchanger core 31 than at the center part.

[0047] On the surface of the heat exchanger core 31, corrosion progresses from the material with a relatively low potential. Therefore, when the zinc concentration on the surface of the heat transfer tubes 38 is made higher than the zinc concentration on the fins 39 as in the first embodiment, the potential of the heat transfer tubes 38 relative to the fins 39 is lower, and corrosion of the heat transfer tubes 38 takes precedence over corrosion of the fins 39, making the fins 39 less susceptible to corrosion. Furthermore, due to the structure of the heat exchanger 30, which includes heat transfer tubes 38 extending in the up-down direction (vertical direction) and fins 39 respectively disposed between two adjacent heat transfer tubes 38 in the left-right direction (horizontal direction), water is likely to remain on the fins 39 but is unlikely to remain on the heat transfer tubes 38. Therefore, the heat exchanger core 31 is configured so that the zinc concentration on the surface of the heat transfer tubes 38 increases toward the lower part. This increases the potential difference between the heat transfer tubes 38 and the fins 39 in the lower portions where adhering moisture is more likely to remain, giving priority to corrosion of the heat transfer tubes 38 over corrosion of the fins 39 and making it more difficult for the fins 39 to corrode. As a result, the progression of corrosion of the fins 39 in the portions where water is more likely to remain can be suppressed, and deterioration of heat exchange performance due to corrosion of the fins 39 can be suppressed.

[0048] As described above, in the heat exchanger 30 according to the first embodiment, the corrosion of the heat transfer tubes 38 is prioritized over the corrosion of the fins 39, making the fins 39 less susceptible to corrosion, the lower the heat exchanger 30. This makes it possible to suppress a decrease in heat exchange performance due to corrosion of the fins 39. This is particularly effective in a heat exchanger 30 in which the extension direction of the heat transfer tubes 38 is vertical (up and down), because moisture tends to remain on the fins 39. Note that the configuration of the first embodiment can also be applied to a heat exchanger having corrugated fins with improved drainage, which are provided with drainage holes or louvers (not shown) that allow water on the top surface of the fins to drop to the bottom and drain.

[0049] In addition, when the corrosion of the heat transfer tubes 38 is prioritized over the corrosion of the fins 39, the potential difference between the heat transfer tubes 38 and the fins 39 is preferably 50 mV or more, and in the first embodiment, the zinc concentration of the heat transfer tubes 38 in the region where the corrosion of the heat transfer tubes 38 is prioritized over the corrosion of the fins 39 is preferably 1.3 wt % or more. This allows the potential difference between the heat transfer tubes 38 and the fins 39 to be 50 mV or more.

[0050] FIG. 13 is a schematic diagram showing the potential difference distribution in the heat exchanger core 31 of a heat exchanger 30b according to a third modification of the first embodiment. In FIG. 13, the distribution of the potential difference between the heat transfer tubes 38 and the fins 39 in the heat exchanger core 31 is indicated by shading. In the heat exchanger 30 according to the first embodiment, as shown in FIG. 10, the potential difference in the heat exchanger core 31 is shown with a gradation. However, the present invention is not limited to this. As shown in FIG. 13, the potential difference between the heat transfer tubes 38 and the fins 39 from the lower portion to the center of the heat exchanger 30b may be larger than the potential difference between the heat transfer tubes 38 and the fins 39 from the upper portion to the center without a gradation. In this case, the potential difference between the heat transfer tubes 38 and the fins 39 is the same in the range from the lower portion to the center, and the potential difference between the heat transfer tubes 38 and the fins 39 is the same in the range from the upper portion to the center. Even with this configuration, the same effect as that of the heat exchanger 30 described above can be obtained.

[0051] As described above, the heat exchanger 30 according to the first embodiment has a flow path 62 formed therein through which a refrigerant flows, and the heat exchanger 30 has a tube extension direction in the vertical direction, and is equipped with a plurality of heat transfer tubes 38 arranged at intervals from each other in the left-right direction perpendicular to the up-down direction and the front-to-back direction which is the ventilation direction, fins 39 arranged between two adjacent heat transfer tubes 38 in the left-to-right direction and joined to the two left and right heat transfer tubes 38 in the up-down direction, an upper header 33 into which the upper ends of the heat transfer tubes 38 are inserted, and a lower header 34 into which the lower ends of the heat transfer tubes 38 are inserted, and the potential of the heat transfer tubes 38 relative to the fins 39 is low, and the potential difference between the heat transfer tubes 38 and the fins 39 which are joined to each other is larger in the vertical direction at the lower part than at other parts.

[0052] According to the heat exchanger 30 of the first embodiment, the potential of the heat transfer tubes 38 relative to the fins 39 is low, and the potential difference between the heat transfer tubes 38 and the fins 39 in the portions where water is likely to remain is greater than the potential difference between the heat transfer tubes 38 and the fins 39 in the portions where water is not likely to remain. Because corrosion progresses from materials with a relatively low potential, the lower the potential of the heat transfer tubes 38 relative to the fins 39, the more prioritized corrosion of the heat transfer tubes 38 becomes over corrosion of the fins 39, making the fins 39 less susceptible to corrosion. Due to the structure of the heat exchanger 30, which includes heat transfer tubes 38 extending in the vertical direction and fins 39 arranged between two heat transfer tubes 38 adjacent in the horizontal direction, water is likely to remain in the fins 39 and is less likely to remain in the heat transfer tubes 38. Therefore, in the lower portion of the heat exchanger 30 where water is likely to remain, the potential of the heat transfer tubes 38 relative to the fins 39 is lowered as described above, so that corrosion of the heat transfer tubes 38 takes precedence over corrosion of the fins 39, making the fins 39 less susceptible to corrosion. As a result, the progression of corrosion of the fins 39 in the portion where water is likely to remain can be suppressed, and a decrease in heat exchange performance due to corrosion of the fins 39 can be suppressed.

[0053] Second Embodiment A second embodiment will be described below, but explanations of parts that overlap with those of the first embodiment will be omitted, and parts that are the same as or equivalent to those of the first embodiment will be given the same reference numerals.

[0054] The heat exchanger 30c according to the second embodiment has substantially the same configuration as the heat exchanger 30 according to the first embodiment, but differs in the region where the potential difference between the heat transfer tube 38 and the fin 39 is large.

[0055] Fig. 14 is a schematic diagram showing the potential difference distribution in the heat exchanger core 31 of the heat exchanger 30c according to the second embodiment. In Fig. 14, the distribution of the potential difference between the heat transfer tubes 38 and the fins 39 in the heat exchanger core 31 is indicated by shading. In the second embodiment, as shown in Fig. 14, the potential difference between the heat transfer tubes 38 and the fins 39 varies in the left-right direction (horizontal direction) in the heat exchanger core 31. The left and right sides of the heat exchanger 30c are shaded by the pillars 15b provided at the four corners of the casing 15 of the outdoor unit 10, where moisture is likely to remain. Therefore, the potential difference between the heat transfer tubes 38 and the fins 39 located near the pillars 15b, where moisture is likely to remain, is made larger than that in other parts.

[0056] Also, similar to the first embodiment, the potential of the heat transfer tubes 38 relative to the fins 39 is configured to be low. In this way, the potential of the heat transfer tubes 38 relative to the fins 39 is lowered, and the potential difference between the heat transfer tubes 38 and the fins 39 in the left and right sides of the heat exchanger 30d located near the column sections 15b, where adhering moisture is likely to remain, is made larger relative to other parts. This prioritizes corrosion of the heat transfer tubes 38 in the areas where adhering moisture is likely to remain over corrosion of the fins 39, making the fins 39 less likely to corrode. As a result, the progression of corrosion of the fins 39 in the areas where water is likely to remain can be suppressed, and a decrease in heat exchange performance due to corrosion of the fins 39 can be suppressed.

[0057] As described above, the heat exchanger 30 according to the second embodiment has a flow path 62 formed therein through which a refrigerant flows, and includes a plurality of heat transfer tubes 38 arranged at intervals in the left-right direction, perpendicular to the up-down direction and the front-to-back direction, which is the direction of ventilation, and fins 39 arranged between two adjacent heat transfer tubes 38 in the left-to-right direction and joined to the two left and right heat transfer tubes 38 in the up-down direction, an upper header 33 into which the upper ends of the heat transfer tubes 38 are inserted, and a lower header 34 into which the lower ends of the heat transfer tubes 38 are inserted, the potential of the heat transfer tubes 38 relative to the fins 39 being low, and the potential difference between the heat transfer tubes 38 and the fins 39, which are joined to each other, is larger in the left and right parts in the left-to-right direction than in other parts.

[0058] According to the heat exchanger 30 of the second embodiment, the potential of the heat transfer tubes 38 relative to the fins 39 is low, and the potential difference between the heat transfer tubes 38 and the fins 39 in the portions where water is likely to remain is greater than the potential difference between the heat transfer tubes 38 and the fins 39 in the portions where water is not likely to remain. Because corrosion progresses from materials with a relatively low potential, the lower the potential of the heat transfer tubes 38 relative to the fins 39, the more prioritized corrosion of the heat transfer tubes 38 becomes over corrosion of the fins 39, making the fins 39 less susceptible to corrosion. Due to the structure of the heat exchanger 30, which includes heat transfer tubes 38 extending in the vertical direction and fins 39 arranged between two heat transfer tubes 38 adjacent in the horizontal direction, water is likely to remain in the fins 39 and less likely to remain in the heat transfer tubes 38. Therefore, in the left and right sides of the heat exchanger 30, where water is likely to remain, the potential of the heat transfer tubes 38 relative to the fins 39 is lowered as described above, so that corrosion of the heat transfer tubes 38 takes precedence over corrosion of the fins 39, making the fins 39 less susceptible to corrosion. This makes it possible to suppress the progression of corrosion of the fins 39 in the parts where water is likely to remain, and to suppress a decrease in heat exchange performance due to corrosion of the fins 39.

[0059] Third Embodiment Hereinafter, a third embodiment will be described, but explanations of parts that overlap with those of the first and second embodiments will be omitted, and parts that are the same as or equivalent to those of the first and second embodiments will be denoted by the same reference numerals.

[0060] The heat exchanger 30d according to the third embodiment combines the region in which the potential difference between the heat transfer tubes 38 and the fins 39 according to the first embodiment is large with the region in which the potential difference between the heat transfer tubes 38 and the fins 39 according to the second embodiment is large.

[0061] 15 is a schematic diagram showing the potential difference distribution in the heat exchanger core 31 of the heat exchanger 30d according to the third embodiment. In FIG. 15 , the distribution of the potential difference between the heat transfer tubes 38 and the fins 39 in the heat exchanger core 31 is indicated by shading, with the darker areas of the heat exchanger core 31 indicating larger potential differences between the heat transfer tubes 38 and the fins 39. In the third embodiment, as shown in FIG. 15 , the potential differences between the heat transfer tubes 38 and the fins 39 are differentiated in the up-down direction (vertical direction) and the left-right direction (horizontal direction) in the heat exchanger core 31. In this manner, the potential difference between the heat transfer tubes 38 and the fins 39 in the lower part of the heat exchanger 30d, where adhering moisture is likely to remain, is made larger in the up-down direction (vertical direction) than in other parts. Furthermore, the potential difference between the heat transfer tubes 38 and the fins 39 in the left-right direction (horizontal direction) is made larger in the left-right direction than in other parts. In Figure 15, the potential difference in the heat exchanger core 31 has a gradation distribution in the up and down direction (vertical direction) as in Figure 10, but this is not limited to this, and the potential difference in the heat exchanger core 31 does not have to have a gradation distribution as in Figure 13.

[0062] As in the first embodiment, the potential of the heat transfer tubes 38 relative to the fins 39 is configured to be low. In this way, corrosion of the heat transfer tubes 38 in the lower portion of the heat exchanger 30d where adhering moisture is likely to remain, as well as in the left and right portions where adhering moisture is likely to remain, is prioritized over corrosion of the fins 39, making the fins 39 less susceptible to corrosion. This makes it possible to further suppress the progression of corrosion of the fins 39 in the portions where water is likely to remain, compared to the first and second embodiments, and further suppress the deterioration of heat exchange performance due to corrosion of the fins 39.

[0063] As described above, the heat exchanger 30d according to the third embodiment has a flow path 62 formed therein through which a refrigerant flows, and includes a plurality of heat transfer tubes 38 arranged at intervals in the left-right direction perpendicular to the up-down direction and the front-to-back direction, which is the direction of ventilation, fins 39 arranged between two adjacent heat transfer tubes 38 in the left-to-right direction and joined to the two left and right heat transfer tubes 38 in the up-down direction, an upper header 33 into which the upper ends of the heat transfer tubes 38 are inserted, and a lower header 34 into which the lower ends of the heat transfer tubes 38 are inserted, the potential of the heat transfer tubes 38 relative to the fins 39 being low, and the potential difference between the heat transfer tubes 38 and the fins 39 joined to each other is larger in the lower part in the up-down direction than in other parts, and the potential difference between the heat transfer tubes 38 and the fins 39 joined to each other is larger in the left and right parts in the left-to-right direction than in other parts.

[0064] According to the heat exchanger 30d of the third embodiment, corrosion of the fins 39 on the left and right sides where attached moisture is likely to remain can be suppressed in addition to the lower part where attached moisture is likely to remain. Therefore, compared to the first and second embodiments, the progression of corrosion of the fins 39 in the parts where attached moisture is likely to remain can be further suppressed, and the deterioration of heat exchange performance due to corrosion of the fins 39 can be further suppressed.

[0065] Fourth Embodiment A fourth embodiment will be described below, but explanations of parts that overlap with those of the first to third embodiments will be omitted, and parts that are the same as or equivalent to those of the first to third embodiments will be given the same reference numerals.

[0066] In the fourth embodiment, a method for manufacturing the heat exchanger 30 described in the first embodiment will be described. The manufacturing method for the heat exchanger 30 according to the fourth embodiment includes the following steps: a first step of spraying zinc onto the surfaces of the heat transfer tubes 38; a second step of assembling the heat transfer tubes 38, the fins 39, the lower header 34, and the upper header 33; a third step of applying flux to the entire surfaces of the heat transfer tubes 38, the lower header 34, and the upper header 33; and a fourth step of transporting the assembly to an electric furnace and performing furnace brazing. The heat exchanger 30 is manufactured by sequentially performing the first to fourth steps. In the third step, prior to furnace brazing, a zinc-free flux is applied to the entire surfaces of the heat transfer tubes 38 to remove an oxide film from the aluminum surface and improve brazing jointability. The conditions for the furnace brazing in the fourth step are not limited. For example, the assembly may be transported to an electric furnace in a nitrogen atmosphere, heated to the brazing temperature, maintained at that temperature for the required time, and then cooled from the brazing temperature to room temperature.

[0067] In addition to steps 1 to 4, the manufacturing method of the heat exchanger 30 according to the fourth embodiment includes step 0, in which the heat capacity of the lower header 34 disposed below the heat exchanger core 31 of the heat exchanger 30 is configured to be greater than the heat capacity of the heat transfer tubes 38 and fins 39, i.e., the heat exchanger core 31. Step 0 is performed before step 4. By making the thickness of the lower header 34 greater than the thickness of the heat transfer tubes 38 and fins 39 that constitute the heat exchanger core 31, the heat capacity of the lower header 34 can be made greater than that of the heat exchanger core 31.

[0068] 16 is a diagram showing the difference in surface zinc concentration at various locations on the heat exchanger core 31 of the heat exchanger 30 according to the first embodiment. As shown in FIG. 16 , during furnace brazing, the brazing filler metal melting time (hereinafter referred to as the holding time) near the lower header 34 of the heat exchanger core 31 is shorter than that of the central portion of the heat exchanger core 31, which is farther from the lower header 34. The zinc diffusion time on the surface of the heat transfer tubes 38 near the lower header 34, where the holding time is shorter, is shorter than that of the central portion. Therefore, the surface zinc concentration of the heat transfer tubes 38 near the lower header 34 after furnace brazing can be higher than that of the central portion. Conversely, the holding time is longer in the central portion of the heat exchanger core 31 than in the vicinity of the lower header 34, resulting in a lower surface zinc concentration of the heat transfer tubes 38.

[0069] As described above, according to the manufacturing method of the heat exchanger 30 of the fourth embodiment, the heat transfer tubes 38 located closer to the lower header 34 in the heat exchanger core 31 have a higher surface zinc concentration. In other words, a gradation is created in the potential difference in the heat exchanger core 31. This allows different potential differences to be created between the heat transfer tubes 38 and the fins 39 in different parts of the heat exchanger core 31, making it possible to manufacture the heat exchanger 30 described in the first embodiment.

[0070] In the zeroth step, the heat capacity of the lower header 34 itself, which is a component of the heat exchanger 30, is increased, but this is not limiting. For example, a member other than the component of the heat exchanger 30 may be used as a jig, and the jig may be attached to the lower header 34 to increase the heat capacity of the lower header 34, which also makes it possible to manufacture a similar heat exchanger 30. The jig may be made of a metal that does not melt during furnace brazing, such as an aluminum block.

[0071] Furthermore, the manufacturing method of the heat exchangers 30c to 30d described in the second and third embodiments includes, in addition to the above-described steps 0 to 4 or steps 1 to 4, a fifth step of attaching jigs to the left and right sides of the heat exchanger core 31 near the column sections 15b provided at the four corners of the casing 15 where the heat capacity is to be increased. This fifth step is performed before step 4. Then, by performing steps 0 to 5 or steps 1 to 5, the heat exchangers 30b to 30c can be manufactured.

[0072] In addition to the above manufacturing method, the heat exchanger 30b described in the second modified example of the first embodiment can also be manufactured using a flux containing zinc. This manufacturing method includes steps 2-1, 2-2, and 2-3 instead of the above-described step 2. Step 2-1 is a step of assembling the heat transfer tubes 38, the lower header 34, and the upper header 33. Step 2-2 is a step of applying flux containing zinc to the lower surfaces of all of the heat transfer tubes 38. Step 2-3 is a step of assembling the fins 39. These steps are performed in the order of step 2-1, step 2-2, and step 2-3, and are also performed between step 1 and step 3. In step 2-2, a zinc-containing flux is applied to the region of the heat transfer tube 38 where the surface zinc concentration is desired to be high. Then, by performing furnace brazing in step 4, the surface zinc concentration of the heat transfer tube 38 in the region where the zinc-containing flux is applied becomes higher than in the region where the zinc-containing flux is not applied. Therefore, the potential difference between the heat transfer tube 38 and the fin 39 in the region where the zinc-containing flux is applied can be made larger than in the region where the zinc-containing flux is not applied. This manufacturing method can manufacture the heat exchanger 30b described in the second modified example of embodiment 1. Note that in step 2-2, the zinc-containing flux can be applied to the entire surface of the heat transfer tubes 38 on the left and right sides of the heat exchanger core 31 instead of the lower surfaces of all of the heat transfer tubes 38 in the heat exchanger core 31, thereby manufacturing the heat exchanger 30c described in embodiment 2. Furthermore, in step 2-2, the area to which the zinc-containing flux is applied is extended to the lower surfaces of all of the heat transfer tubes 38 of the heat exchanger core 31, as well as to the entire surfaces of the heat transfer tubes 38 on the left and right sides of the heat exchanger core 31, thereby enabling the manufacture of the heat exchanger 30d described in embodiment 3.

[0073] In conventional heat exchangers, the thickness of the sacrificial layer varies depending on the location within the heat exchanger. This requires the use of multiple types of heat transfer tubes with different sacrificial layer thicknesses, resulting in increased manufacturing costs, both for the product itself and for assembly. In contrast, the manufacturing method for the heat exchangers 30, 30b, 30c, and 30d described in the fourth embodiment allows for manufacturing using a single type of heat transfer tube 38 without changing the heat transfer tube 38 used depending on the location in the heat exchanger core 31, thereby reducing manufacturing costs. Furthermore, the potential difference between the heat transfer tube 38 and the fins 39 in each portion of the heat exchanger core 31 can be varied without changing the content of the fourth step.

[0074] REFERENCE SIGNS LIST 10 outdoor unit, 11 compressor, 12 flow path switching device, 13 fan, 14 fan casing, 15 casing, 15a front panel, 15b column portion, 15c bottom plate, 15d support leg, 16 intake port, 17 outlet port, 20 indoor unit, 20a indoor unit, 21 throttle device, 22 indoor heat exchanger, 23 indoor fan, 25 casing, 30 heat exchanger, 30a heat exchanger, 30b heat exchanger, 30c heat exchanger, 30d heat exchanger, 31 heat exchanger core, 31a first heat exchanger core, 31b second heat exchanger core, 33 upper header, 34 lower header, 34a first lower header, 34b second lower header, 36 liquid piping, 37 gas piping, 38 heat transfer tube, 39 fin, 39A Ridge portion, 39a fin, 39aA flange portion, 61 core material, 62 flow path, 63 zinc sacrificial layer, 64 brazed portion, 100 air conditioning device.

Claims

1. A heat exchanger comprising: heat transfer tubes in which a flow path for a refrigerant to flow is formed inside, the heat transfer tubes being arranged in a plurality at intervals in a left-right direction orthogonal to a vertical direction which is a tube extending direction and a front-back direction which is the vertical direction and a ventilation direction; fins respectively arranged between two adjacent heat transfer tubes in the left-right direction and joined to the two left and right heat transfer tubes in the vertical direction; an upper header into which an upper end portion of the heat transfer tube is inserted; and a lower header into which a lower end portion of the heat transfer tube is inserted, wherein the potential of the heat transfer tube with respect to the fin is configured to be low, and in the vertical direction, a potential difference between the heat transfer tube and the fin joined to each other is large in a lower portion compared to other portions.

2. A heat exchanger comprising: heat transfer tubes in which a flow path for a refrigerant to flow is formed inside, the heat transfer tubes being arranged in a plurality at intervals in a left-right direction orthogonal to a vertical direction which is a tube extending direction and a front-back direction which is the vertical direction and a ventilation direction; fins respectively arranged between two adjacent heat transfer tubes in the left-right direction and joined to the two left and right heat transfer tubes in the vertical direction; an upper header into which an upper end portion of the heat transfer tube is inserted; and a lower header into which a lower end portion of the heat transfer tube is inserted, wherein the potential of the heat transfer tube with respect to the fin is configured to be low, and in the left-right direction, a potential difference between the heat transfer tube and the fin joined to each other is large in a left side portion and a right side portion compared to other portions.

3. The heat exchanger according to claim 1, wherein in the vertical direction, the potential difference between the heat transfer tube and the fin joined to each other increases as approaching from a central portion to a lower portion.

4. The heat exchanger according to claim 1 or 3, wherein in the left-right direction, a potential difference between the heat transfer tube and the fin joined to each other is large in a left side portion and a right side portion compared to other portions.

5. An air conditioner comprising the heat exchanger according to any one of claims 1 to 4.

6. A method for manufacturing a heat exchanger according to claim 1, comprising the steps of spraying zinc on the surface of the heat transfer tubes, assembling the heat transfer tubes, the upper header, and the lower header, applying a flux containing zinc to the surfaces of the lower portions of all the heat transfer tubes, assembling the fins, applying a flux not containing zinc to the entire surfaces of all the heat transfer tubes, and performing in-furnace brazing in an electric furnace.

7. A method for manufacturing a heat exchanger according to claim 2, comprising the steps of spraying zinc on the surface of the heat transfer tubes, assembling the heat transfer tubes, the upper header, and the lower header, applying a flux containing zinc to the entire surfaces of the heat transfer tubes on the left and right sides, assembling the fins, applying a flux not containing zinc to the entire surfaces of all the heat transfer tubes, and performing in-furnace brazing in an electric furnace.

8. A method for manufacturing a heat exchanger according to claim 3, comprising the steps of configuring the heat capacity of the lower header to be larger than the heat capacities of the heat transfer tubes and the fins, spraying zinc on the surface of the heat transfer tubes, assembling the heat transfer tubes, the fins, the upper header, and the lower header, applying a flux not containing zinc to the entire surfaces of all the heat transfer tubes, and performing in-furnace brazing in an electric furnace.

9. A method for manufacturing a heat exchanger according to claim 4, which depends on claim 1, comprising the steps of spraying zinc on the surface of the heat transfer tubes, assembling the heat transfer tubes, the upper header, and the lower header, applying a flux containing zinc to the surfaces of the lower portions of all the heat transfer tubes, applying a flux containing zinc to the entire surfaces of the heat transfer tubes on the left and right sides, assembling the fins, applying a flux not containing zinc to the entire surfaces of all the heat transfer tubes, and performing in-furnace brazing in an electric furnace.

10. A method for manufacturing a heat exchanger according to claim 4, which depends on claim 3, the method comprising the steps of: configuring the heat capacity of the lower header to be larger than the heat capacities of the heat transfer tubes and the fins; spraying zinc onto the surface of the heat transfer tubes; assembling the heat transfer tubes, the upper header, and the lower header; applying a flux containing zinc to the entire surface of the heat transfer tubes on the left and right sides; assembling the fins; applying a flux not containing zinc to the entire surface of all the heat transfer tubes; and performing in-furnace brazing in an electric furnace. A method for manufacturing a heat exchanger.

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