Heat exchanger and method for manufacturing the same

Abstract

To provide a heat exchanger that facilitates discharge of water between adjacent fins, and a method for manufacturing the same.SOLUTION: A heat exchanger comprises fins, and heat transfer pipes inserted into the fins. Flux containing aluminum and fluorine, or its residue is attached to surfaces of the fins. The flux or its residue comprises a surface layer containing at least aluminum and oxygen.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

[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. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-30032 A Summary of the Invention [Problem to be solved by the invention]

[0004] The embodiments provide a heat exchanger and a method for manufacturing the same that facilitates the drainage of water between adjacent fins. [Means for solving the problem]

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

[0006] [Figure 1] FIG. 2 is a schematic diagram showing a heat exchanger according to an embodiment. [Diagram 2] 5A and 5B are schematic diagrams and graphs showing characteristics of a heat exchanger according to an embodiment. [Diagram 3] 11 is a graph showing other characteristics of the heat exchanger according to the embodiment. [Figure 4] 1A and 1B are graphs and schematic diagrams showing a structure of a heat exchanger according to an embodiment. [Diagram 5] 13 is a graph showing still another characteristic of the heat exchanger according to the embodiment. [Figure 6] 4 is an FT-IR spectrum showing the structure of a heat exchanger according to an embodiment. [Figure 7] 1 is a schematic diagram showing a structure of a heat exchanger according to an embodiment and another graph. [Figure 8] 4 is a flowchart showing a method for manufacturing a heat exchanger according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] Hereinafter, the embodiments will be described with reference to the drawings. The same parts in the drawings are given 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 the actual ones. Even when the same parts are shown, the dimensions and ratios of each part may be different depending on the drawing.

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

[0009] As shown in Fig. 1(a), 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 a through hole formed in the fin 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 a surface of the base material 23. The flux 25 is applied, for example, 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 an ion. 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 also contains at least one of potassium, cesium, and lithium.

[0013] 2(a) and (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 of the heat exchanger 1. Fig. 2(b) is a graph showing the surface characteristics of the fin 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 water can be easily drained from between two adjacent fins 20.

[0015] 2(b) 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, contact angle). The smaller the contact angle, the higher the hydrophilicity of the surface of the fin 20, and the easier it is to drain water. The contact angle is preferably, for example, 20° or less.

[0016] 2(b), 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 (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 contact angle over time when the heat exchanger 1 is immersed in water. FIG. 3(b) shows the change in contact angle over time when the heat exchanger 1 is not immersed in water. Both FIG. 3(a) and (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 tube 10, the heat exchanger 1 is immersed in water for a predetermined time, for example, 3 hours. This makes the contact angle 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°. The contact angle exceeds 50° over time.

[0020] In this way, by immersing the heat exchanger 1 in water, 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. This makes it easier for water to be discharged between two adjacent fins 20.

[0021] 4(a) and (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) in the vicinity of the surface of the flux 25. The horizontal axis shows the number of days of immersion. Fig. 4(b) shows the structure in the vicinity of 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 days pass, 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, OH groups) when the flux 25 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] 5(a) and (b) 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] FIG. 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°, which is the measurement limit. Meanwhile, the closed circles represent the contact angle after aging. The characteristics after aging were measured after leaving the heat exchanger 1 in a constant temperature and high humidity environment (20°C, 80%) for 40 hours for accelerated aging.

[0026] As shown in Fig. 5(a), as the water temperature during immersion increases, the rate of change in the contact angle decreases. At a water temperature of 80°C, the contact angle is kept below 20°. In other words, the surface of the fin 20 can be kept hydrophilic.

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

[0028] 6(a) to (c) are FT-IR spectra showing the structure of the heat exchanger 1 according to the embodiment.

[0029] FIG. 6(a) shows the absorption spectrum of the flux 25 when the water temperature during immersion was 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 seen at 1145 cm -1 Can be seen nearby.

[0030] Figure 6(b) shows the 3500 cm -1 The absorption spectrum shows an enlarged view of the absorption peaks around 100°C. Four peaks are shown in the figure for the case where the sample is not immersed in water (unimmersed) and for the water temperatures of 25°C, 50°C, and 80°C.

[0031] As shown in Fig. 6(b), the OH peak is larger when immersed in water than when not immersed, and the peak becomes larger as the water temperature increases, which indicates that the bonds between fluorine and aluminum on the surface of the flux 25 are replaced by bonds between OH groups and aluminum.

[0032] Figure 6(c) shows the 1145 cm -1 The absorption spectrum shows an enlarged view of the absorption peak around 100°C. The figure shows the characteristics when not immersed and when the water temperatures are 25°C, 50°C, and 80°C.

[0033] As shown in Fig. 6(c), an Al-O absorption peak appears when the water temperature is 80°C. In other words, 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] 7(a) and (b) are a schematic diagram and another graph showing the structure of the heat exchanger 1 according to the embodiment. Fig. 7(a) and (b) 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 the dangling bonds of the aluminum atoms are terminated by OH groups.

[0036] Figure 7(b) shows the FT-IR signal spectrum. Two spectra are shown in the figure, with the FT-IR inspection light having an incidence angle of 25° and 90°. When the incidence 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 incidence angle is 90°, the FT-IR signal light also reflects the structure at a deeper position of the flux 25.

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

[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 time. This makes it easier to drain water between two adjacent fins 20, and improves the heat conversion efficiency.

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

[0040] FIG. 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 step S01 of applying flux 25 containing aluminum and fluorine to the surfaces of fins 20, step S02 of brazing the fins 20 to the heat transfer tubes 10, and step S03 of immersing the fins 20 and the heat transfer tubes 10 brazed to the fins 20 in water. In other words, step S03 is a step of immersing the heat exchanger 1 in water. By manufacturing the heat exchanger through these three steps, the surfaces of the fins 20 can be made hydrophilic, which makes it easier for water to be discharged between two adjacent fins 20, and improves the heat conversion efficiency.

[0041] Although some 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 implemented 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 in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0042] 1...Heat exchanger 10...Heat transfer tube 20…Fin 23...Base material 25…Flux

Claims

1. Finn and A heat transfer tube inserted through the fin; Equipped with A flux containing aluminum and fluorine or a residue thereof is attached to the surface of the fin, A heat exchanger, wherein the flux or a residue thereof has a surface layer containing at least aluminum and oxygen.

2. 2. The heat exchanger according to claim 1, wherein the atomic ratio of oxygen to aluminum in the surface layer of the flux is 1.6 or more.

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

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

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

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