Heat exchanger and method for manufacturing same

Abstract

Provided are: a heat exchanger that facilitates discharge of water between adjacent fins; and a method for manufacturing the same. This heat exchanger is provided with fins and heat transfer tubes that are inserted through the fins. A flux containing aluminum and fluorine or a residue thereof adheres to the surfaces of the fins, and the flux or the residue thereof has a surface layer containing at least aluminum and oxygen.

Description

Heat exchanger and manufacturing method thereof

[0001] The embodiments relate to a heat exchanger and a method for manufacturing the same.

[0002] In order to improve the efficiency of a fin-type heat exchanger, it is important to make it easy to drain the water that condenses between adjacent fins.

[0003] JP 2017-30032 A

[0004] The embodiments provide a heat exchanger and a manufacturing method thereof that facilitates the drainage of water between adjacent fins.

[0005] A heat exchanger according to an embodiment includes fins and heat transfer tubes inserted through the fins. A flux containing aluminum and fluorine or a residue thereof adheres to the surface of the fins, and the flux or the residue thereof has a surface layer containing at least aluminum and oxygen.

[0006] FIG. 1 is a schematic diagram showing a heat exchanger according to an embodiment; FIG. 2 is a schematic diagram and graph showing characteristics of a heat exchanger according to an embodiment; FIG. 3 is a graph showing another characteristic of a heat exchanger according to an embodiment; FIG. 4 is a graph and schematic diagram showing the structure of a heat exchanger according to an embodiment; FIG. 5 is a graph showing yet another characteristic of a heat exchanger according to an embodiment; FIG. 6 is an FT-IR spectrum showing the structure of a heat exchanger according to an embodiment; FIG. 7 is a schematic diagram and another graph showing the structure of a heat exchanger according to an embodiment; and FIG. 8 is a flowchart showing a method for manufacturing a heat exchanger according to the present embodiment.

[0007] Hereinafter, embodiments will be described with reference to the drawings. Identical parts in the drawings are assigned the same numbers, and detailed descriptions thereof will be omitted as appropriate, and different parts will be described. Note that the drawings are schematic or conceptual, and the relationship between the thickness and width of each part, the size ratio between parts, etc., are not necessarily the same as those in reality. Furthermore, even when the same part is shown, the dimensions and ratios may be different depending on the drawing.

[0008] 1(a) to 1(c) are schematic diagrams showing a heat exchanger 1 according to an embodiment. Fig. 1(a) is a perspective view showing the appearance of the heat exchanger 1. Figs. 1(b) and 1(c) are partial cross-sectional views showing the structure of fins in the heat exchanger 1. The heat exchanger 1 is installed, for example, in the outdoor unit of an air conditioner.

[0009] 1A, the heat exchanger 1 includes a heat transfer tube 10 and a plurality of fins 20. For example, a refrigerant flows through the heat transfer tube 10. The heat transfer tube 10 is inserted through the plurality of fins 20. In other words, the heat transfer tube 10 is thermally connected to the plurality of fins 20. The heat transfer tube 10 is integrated with the fins 20 by, for example, inserting through holes formed in the fins 20 and continuously inserting through the through holes of adjacent fins 20.

[0010] 1( b), the fin 20 includes a base material 23 and a flux 25. The flux 25 is applied to the surface of the base material 23. For example, the flux 25 is applied to the entire surface of the base material 23. The base material 23 includes, for example, aluminum or an aluminum alloy. The flux 25 is applied to braze the fin 20 and the heat transfer tube 10 together.

[0011] 1(c), the flux 25 contains, for example, potassium (K), aluminum (Al), and fluorine (F). The fluorine is bonded to the aluminum, and the potassium is contained as ions. On the surface of the flux 25, the dangling bonds of the aluminum are terminated by the fluorine.

[0012] However, the embodiment is not limited to this example. The flux 25 may contain cesium (Cs) or lithium (Li) instead of potassium. The flux 25 may also contain at least one of potassium, cesium, and lithium.

[0013] 2(a) and 2(b) are a schematic diagram and a graph showing the characteristics of the heat exchanger 1 according to the embodiment. Fig. 2(a) is a schematic diagram partially showing the side surface of the heat exchanger 1. Fig. 2(b) is a graph showing the surface characteristics of the fins 20.

[0014] 2(a), when the heat exchanger 1 is in operation, water condensed on the surfaces of the fins 20 may accumulate between two adjacent fins 20, reducing the efficiency of heat exchange. To avoid this, it is preferable that the water be easily drained from between two adjacent fins 20.

[0015] 2B is a graph showing the change over time in affinity for water on the surface of the fin 20. The horizontal axis represents the number of days elapsed, and the vertical axis represents the static contact angle of water (hereinafter referred to as contact angle). The smaller the contact angle, the higher the hydrophilicity of the surface of the fin 20, making it easier for water to be discharged. The contact angle is preferably, for example, 20° or less.

[0016] 2B, even if the initial contact angle of the flux 25 is 20° or less, the contact angle increases over time and exceeds 20°. That is, the surface of the fin 20 becomes water-repellent over time, and the surface tension makes it difficult for water to drain between two adjacent fins 20.

[0017] 3(a) and 3(b) are graphs showing other characteristics of the heat exchanger 1 according to the embodiment. The horizontal axis represents the number of days elapsed, and the vertical axis represents the static contact angle of water. FIG. 3(a) shows the change in the contact angle over time when the heat exchanger 1 is immersed in water. FIG. 3(b) shows the change in the contact angle over time when the heat exchanger 1 is not immersed in water. Both FIGS. 3(a) and 3(b) show the results of measurements taken after the heat exchanger 1 was left in a constant temperature and high humidity environment for 40 hours for accelerated aging.

[0018] In the example shown in Fig. 3(a), after the fins 20 are brazed to the heat transfer tubes 10, the heat exchanger 1 is immersed in water for a predetermined time, for example, 3 hours. As a result, the contact angle becomes 20° or less. Thereafter, the contact angle decreases with the passage of time, for example, to 5° or less.

[0019] On the other hand, as shown in Fig. 3(b), when the heat exchanger 1 is not immersed in water, the initial contact angle is, for example, 40°, and the contact angle exceeds 50° over time.

[0020] By immersing the heat exchanger 1 in water in this way, the contact angle of water on the surfaces of the fins 20 can be set to 20° or less, and the surfaces of the fins 20 can then be maintained hydrophilic, which makes it easier for water to be discharged between two adjacent fins 20.

[0021] 4(a) and 4(b) are a graph and a schematic diagram showing the structure of the heat exchanger 1 according to the embodiment. Fig. 4(a) shows the atomic ratio of oxygen to aluminum (hereinafter, O / Al ratio) near the surface of the flux 25. The horizontal axis represents the number of days of immersion. Fig. 4(b) shows the structure near the surface of the flux 25.

[0022] As shown in FIG. 4( a), after the heat exchanger 1 is immersed for a predetermined time, for example, 3 hours, the O / Al ratio becomes 1.6, and thereafter, as the number of days passes, the O / Al ratio increases and saturates at a value of, for example, around 2.1.

[0023] As shown in Fig. 4(b), the bonds between aluminum and fluorine (see Fig. 1(c)) on the surface of the flux 25 are replaced by bonds between aluminum and hydroxyl groups (hereinafter referred to as OH groups) when the fin 20 is immersed in water. This reduces the contact angle of water on the surface of the flux 25, and the surface of the fin 20 becomes hydrophilic.

[0024] 5A and 5B are a graph and a schematic diagram showing still another characteristic of the heat exchanger 1 according to the embodiment. In this example, the temperature of the water in which the heat exchanger 1 is immersed is changed.

[0025] Figure 5(a) shows the change in contact angle over time for water temperatures of 25°C, 50°C, and 80°C during immersion. The open circles in the figure represent the contact angle after 3 hours of immersion. At all temperatures, the contact angle after treatment is below 5°, the measurement limit. On the other hand, the closed circles represent the contact angle after aging. The characteristics after aging were measured after the heat exchanger 1 was left in a constant temperature and high humidity environment (20°C, 80%) for 40 hours for accelerated aging.

[0026] As shown in Figure 5A, the rate of change in the contact angle decreases as the water temperature increases during immersion. At a water temperature of 80°C, the contact angle is maintained at 20° or less. In other words, the surface of the fin 20 can be maintained hydrophilic.

[0027] FIG. 5(b) shows the O / Al ratio of the flux 25 after aging for water temperatures of 25°C, 50°C, and 80°C during immersion. The O / Al ratio increases as the water temperature increases. The O / Al ratio at a water temperature of 25°C is approximately 1.6, which is a small difference from the value immediately after immersion shown in FIG. 4(a). However, at a water temperature of 80°C, the O / Al ratio increases to 2.1, which is the same as the saturated value 11 days after immersion (see FIG. 4(a)).

[0028] 6(a) to 6(c) are FT-IR spectra showing the structure of the heat exchanger 1 according to the embodiment, and show the FT-IR absorption spectrum of the surface layer of the flux 25.

[0029] 6A shows the absorption spectrum of the flux 25 when the water temperature during immersion is 80° C. As shown in the figure, the absorption peak corresponding to the OH group is at 3500 cm －１ In addition, an absorption peak corresponding to the Al-O bond is observed at 1145 cm －１ can be seen nearby.

[0030] FIG. 6(b) shows the －１ The figure shows an absorption spectrum in which the absorption peaks around 100°C are enlarged. Four peaks are shown in the figure when the sample is not immersed in water (unimmersed) and when the water temperatures are 25°C, 50°C, and 80°C.

[0031] 6(b), the OH peak is larger when the flux is immersed in water than when it is not immersed, and the peak becomes larger as the water temperature increases, which indicates that the fluorine-aluminum bond is replaced by the OH group-aluminum bond on the surface of the flux 25.

[0032] Figure 6(c) shows the －１The figure shows the absorption spectrum with an enlarged view of the absorption peak around 100°C. The figure shows the characteristics of the sample when not immersed and when the water temperatures are 25°C, 50°C, and 80°C.

[0033] As shown in Figure 6(c), an Al-O absorption peak appears when the water temperature is 80°C. That is, no Al-O absorption peak is observed when the sample is not immersed or when the water temperature is 25°C or 50°C. Thus, it can be seen that when the water temperature during immersion is 80°C, a different structure is obtained from when the water temperature is 50°C or lower.

[0034] 7A and 7B are a schematic diagram and another graph showing the structure of the heat exchanger 1 according to the embodiment, respectively, and show the structure of the flux 25 when the water temperature during immersion is 80°C.

[0035] Fig. 7(a) shows the structure near the surface of the flux 25. The surface layer of the flux 25 is considered to have a so-called boehmite structure based on the absorption spectrum shown in Fig. 6(c). That is, aluminum atoms are bonded to each other via oxygen atoms, and dangling bonds of the aluminum atoms are terminated by OH groups.

[0036] 7(b) shows the FT-IR signal spectrum. This figure shows two spectra obtained when the incident angles of the FT-IR inspection light are 25° and 90°. When the incident angle is 25°, the FT-IR signal light reflects the structure of the surface layer of the flux 25. On the other hand, when the incident angle is 90°, the FT-IR signal light also reflects the structure at deeper positions in the flux 25.

[0037] As shown in Figure 7(b), when the incident angle of the inspection light is set to 25°, a peak corresponding to the Al-O bond is observed. In contrast, when the incident angle is set to 90°, a peak corresponding to the Al-F bond is also observed in addition to the peak corresponding to the Al-O bond. This indicates that aluminum atoms are bonded to oxygen and OH groups in the surface layer of the flux 25, and are bonded to fluorine at deeper positions.

[0038] As described above, in the heat exchanger 1 according to the embodiment, it is preferable to make the surfaces of the fins 20 hydrophilic by immersing them in water for a predetermined period of time, which makes it easier for water to be discharged between two adjacent fins 20 and improves the heat conversion efficiency.

[0039] The flux 25 covering the surface of the fin 20 preferably has an O / Al ratio in the surface layer thereof of, for example, 1.5 or more, and more preferably 2.0 to 2.1.

[0040] 8 is a flowchart showing a method for manufacturing a heat exchanger according to this embodiment. The method for manufacturing a heat exchanger according to this embodiment includes the steps of: applying a flux 25 containing aluminum and fluorine to the surfaces of the fins 20 (step S01); brazing the fins 20 to the heat transfer tubes 10 (step S02); and immersing the fins 20 and the heat transfer tubes 10 brazed to the fins 20 (step S03) in water. Step S03 can also be described as immersing the heat exchanger 1 in water. By manufacturing a heat exchanger through these three steps, the surfaces of the fins 20 can be made hydrophilic. This facilitates the drainage of water between two adjacent fins 20, improving heat conversion efficiency.

[0041] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0042] REFERENCE SIGNS LIST 1... heat exchanger 10... heat transfer tube 20... fin 23... substrate 25... flux

Claims

1. A heat exchanger comprising: fins; and heat transfer tubes inserted into the fins, wherein a flux or a residue thereof containing aluminum and fluorine is adhered to a surface of the fins, and the flux or the residue thereof has a surface layer containing at least aluminum and oxygen.

2. A heat exchanger as claimed in claim 1, wherein the atomic ratio of oxygen to aluminum in said surface layer of said flux is 1.6 or more.

3. The heat exchanger of claim 1, wherein said flux further comprises at least one of potassium, cesium and lithium.

4. A heat exchanger according to claim 1, wherein said surface layer of said flux contains at least one of bonds between aluminum and oxygen and bonds between aluminum and hydroxyl groups.

5. A method for manufacturing a heat exchanger, comprising the steps of: applying a flux containing aluminum and fluorine to a surface of a fin; brazing the fin to a heat transfer tube; and immersing the fin and the heat transfer tube brazed to the fin in water.

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