Heat exchanger for room air conditioners

Abstract

The header pipe itself and the fittings connected to it are given corrosion protection to improve corrosion resistance. [Solution] A heat exchanger for a room air conditioner, comprising a pair of header pipes 2a, 2b, a plurality of heat exchange tubes 3 connected in communication with both header pipes, corrugated fins 4 arranged between the heat exchange tubes, and joint piping 7 connected to the header pipes, brazed together, wherein the header pipe comprises a core material and a brazing material on the outside of the core material, the core material contains, by mass%, Si: 0.1~0.3%, Fe: 0.1~0.3%, Cu: 0.3~0.6%, Mn: 1.0~1.2%, Ti: 0.1~0.2%, with the remainder being Al and unavoidable impurities, and the brazing material has a composition by mass%, containing Si: 7.0~9.0%, Fe: 0.2~0.3%, Cu: 0.1% or less, Mn: 0.1% or less, Zn: 0.8~2.0%, with the remainder being Al and unavoidable impurities.

Description

Technical Field

[0001] This invention relates to a heat exchanger for a room air conditioner, and more particularly, to a heat exchanger for a room air conditioner made of aluminum.

Background Art

[0002] Conventionally, as this type of heat exchanger for a room air conditioner, there is known a parallel flow type heat exchanger for a room air conditioner in which a pair of opposed header pipes formed of aluminum members, a plurality of heat exchange tubes communicatively connected to the both header pipes in parallel with each other, corrugated fins arranged in parallel between the heat exchange tubes, and joint pipes for pipe connection connected to the header pipes and used for inflow and outflow of a heat medium are brazed and joined (see, for example, Patent Document 1).

[0003] In the heat exchanger described in Patent Document 1, the corrosion resistance of the heat exchange tubes is maintained by utilizing the sacrificial anticorrosion function of the corrugated fins. In other words, by making the natural potential of the corrugated fins low and the natural potential of the heat exchange tubes high, the corrugated fins are preferentially corroded, the corrosion of the heat exchange tubes is retarded, and the corrosion resistance of the heat exchange tubes is maintained by utilizing the sacrificial anticorrosion function for preventing the corrosion (pitting corrosion) in the depth direction of the heat exchange tubes.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, since this type of heat exchanger for room air conditioners is used in harsh outdoor environments, the header pipe itself and the fittings connected to the header pipe, which are used for the inflow and outflow of the heat transfer medium, require further corrosion protection, as these parts are less durable and difficult to protect from corrosion. While measures are taken to protect header pipes and fittings from corrosion by covering the entire header pipe, including the fittings, with a resin cover to supplement the corrosion protection function, it is desirable to have corrosion protection function in the header pipe and fittings of the heat exchanger themselves without using a separate cover.

[0006] This invention has been made in view of the above circumstances, and aims to provide a heat exchanger for a room air conditioner that improves corrosion resistance by providing corrosion protection to the header pipe itself and the joint piping connected to the header pipe and used for the inflow and outflow of the heat transfer medium. [Means for solving the problem]

[0007] To achieve the above objectives, this invention provides a heat exchanger for a room air conditioner comprising a pair of opposing header pipes, each made of aluminum, a plurality of heat exchange tubes connected to both header pipes in parallel, corrugated fins arranged in parallel between the heat exchange tubes, and joint piping connected to the header pipes, all of which are brazed together, wherein the header pipes comprise a core material and a brazing material on the outside of the core material, and the header pipes The core material of the pipe contains, by mass%, Si: 0.1-0.3%, Fe: 0.1-0.3%, Cu: 0.3-0.6%, Mn: 1.0-1.2%, Ti: 0.1-0.2%, with the remainder being Al and unavoidable impurities, and the brazing material of the header pipe contains, by mass%, Si: 7.0-9.0%, Fe: 0.2-0.3%, Cu: 0.1% or less, Mn: 0.1% or less, Zn: 0.8-2.0%, with the remainder being Al and unavoidable impurities, characterized in that (Claim 1).

[0008] By configuring it in this way, the natural potential difference between the core material of the header pipe, the brazing material, the heat exchange tube, and the fitting piping can be kept within an appropriate range for corrosion protection, and the brazing of the header pipe, heat exchange tube, and fitting piping can be ensured.

[0009] Furthermore, in this invention, it is preferable that the heat exchange tube contains, by mass%, Si: 0.15% or less, Fe: 0.05~0.35%, Cu: 0.1~0.6%, Mn: 0.2% or less, Zr: 0.02~0.05%, Ti: 0.003~0.015%, Cr: 0.03% or less, with the remainder being Al and unavoidable impurities; the corrugated fin consists of a core material and a brazing sheet in which brazing material is clad on both sides of the core material, the core material of the corrugated fin contains, by mass%, Zn: 1.3~2.2%, with the remainder being Al and unavoidable impurities; and the brazing material of the corrugated fin contains, by mass%, Zn: 0.7~1.3%, with the remainder being Al and unavoidable impurities (Claim 2).

[0010] By configuring it in this way, the natural potential difference between the corrugated fins, brazing material, and heat exchange tube can be kept within a range appropriate for corrosion protection. [Effects of the Invention]

[0011] According to this invention, as configured as described above, the header pipe itself and the fittings connected to the header pipe and used for the inflow and outflow of the heat transfer medium can be given a corrosion-preventive function, thereby improving corrosion resistance even when used in harsh environments. [Brief explanation of the drawing]

[0012] [Figure 1] These are schematic front view (a), enlarged cross-sectional view of part I of (a) (b), and enlarged cross-sectional view of part II of (a) (c), showing an example of a heat exchanger for a room air conditioner according to this invention. [Figure 2] This is a perspective view showing a cross-section of a portion of the heat exchanger described above. [Figure 3] This is a perspective view showing the piping connection side of the heat exchanger shown above. [Figure 4] This is an enlarged cross-sectional view showing the brazed joint state of the header pipe and heat exchange tube in this invention. [Figure 5] This is an enlarged cross-sectional view showing the brazed joint state of the header pipe and fitting pipe in this invention. [Figure 6] This is an enlarged cross-sectional view showing the brazed joint state of the heat exchange tube and corrugated fins in this invention. [Figure 7] This is a schematic diagram showing the process of spraying brazing material onto a joint pipe in this invention, where (a) is a side view, (b1) is a front view showing spraying from two directions, (b2) is a front view showing spraying from three directions, and (b3) is a front view showing spraying from four directions. [Figure 8] This is a schematic front view showing a heat exchanger for evaluation testing. [Figure 9] This is a schematic cross-sectional view showing the evaluation results of the comparative example. [Figure 10] This is a schematic cross-sectional view showing the evaluation results of the embodiment. [Modes for carrying out the invention]

[0013] The embodiments for carrying out this invention will be described in detail below with reference to the attached drawings.

[0014] The room air conditioner heat exchanger 1 according to the present invention (hereinafter referred to as the heat exchanger 1) is, as shown in FIG. 1, a pair of header pipes 2a and 2b made of aluminum (including aluminum alloy) facing each other on the left and right, and a plurality of flat heat exchange tubes 3 (hereinafter referred to as the heat exchange tubes 3) arranged horizontally and connected in parallel between these header pipes 2a and 2b, and corrugated fins 4 (hereinafter referred to as the fins 4) interposed between adjacent heat exchange tubes 3, and a joint pipe 7 for the refrigerant inlet pipe 9a connected to the upper part of the header pipe 2a and used for the inflow of the heat medium and a joint pipe 7 for the refrigerant outlet pipe 9b connected to the lower part of the header pipe 2a and used for the outflow of the heat medium are brazed. The connection between the header pipes 2a and 2b and the heat exchange tubes 3 is made in a state where the heat exchange tubes 3 are inserted into slits (not shown) provided on the side surfaces of the header pipes 2a and 2b. The connection between the header pipes 2a and 2b and the joint pipe 7 is made by connecting (joining) with a ring-shaped brazing material (not shown) and the brazing material 11 of the header pipe 2a in a state where the joint pipe 7 is inserted into a circular hole (not shown) provided on the side surface of the header pipes 2a and 2b. Note that (JIS A 4045) is used for the ring-shaped brazing material. The refrigerant inlet pipe 9a and the refrigerant outlet pipe 9b are formed of stainless steel pipes and are connected in a state of being inserted into the enlarged diameter portion of the joint pipe 7.

[0015] A plurality of heat medium flow paths 3a partitioned into a plurality are formed in the heat exchange tubes 3. In addition, side plates 5 made of aluminum are brazed to the upper outer side and the lower lower side of the fins 4 at the upper and lower ends, respectively. Further, end caps 6 made of aluminum are brazed to the upper and lower open ends of the header pipes 2a and 2b.

[0016] Note that a refrigerant inlet pipe 9a is connected to the upper part of one header pipe 2a (the left side in FIG. 1) via a joint pipe 7, and a refrigerant outlet pipe 9b is connected to the lower part of the header pipe 2a via the joint pipe 7. A first partition plate 8a is disposed at approximately 1 / 3 of the upper side position of the header pipe 2a, and a third partition plate 9c is disposed at approximately 1 / 3 of the lower side position of the header pipe 2a. A second partition plate 8b is disposed at approximately 1 / 2 of the position of the other header pipe 2b (the right side in FIG. 1).

[0017] In the heat exchanger 1 configured as described above, the heat medium (refrigerant) flows into the upper side in the header pipe 2a partitioned by the first partition plate 8a via the refrigerant inlet pipe 9a, then flows into the upper side in the header pipe 2b partitioned by the second partition plate 8b via the heat exchange tube 3, and then flows into the middle side in the header pipe 2a partitioned by the first partition plate 8a and the third partition plate 8c via the heat exchange tube 3. Next, it flows into the lower side in the header pipe 2b partitioned by the second partition plate 8b via the heat exchange tube 3, flows into the lower side in the header pipe 2a partitioned by the third partition plate 8c via the heat exchange tube 3, and then flows to the outside via the refrigerant outlet pipe 9b.

[0018] The composition, corrosion resistance, and brazing of the header pipes 2a and 2b, the heat exchange tubes 3, the fins 4, and the joint pipes 7 will be described below.

[0019] <Composition of Header Pipe> As shown in FIG. 4, the header pipes 2a and 2b are formed in a bent cylindrical shape from a brazing sheet obtained by cladding a brazing material 11 on the surface of a core material 10. Note that the header pipes 2a and 2b do not necessarily have to be cylindrical, and may be square cylindrical. The addition amounts of the following elements are all in mass%. The core materials of the header pipes 2a and 2b contain Si: 0.1 to 0.3%, Fe: 0.1 to 0.3%, Cu: 0.3 to 0.6%, Mn: 1.0 to 1.2%, Ti: 0.1 to 0.2%, and the balance consists of Al and unavoidable impurities. Here, Cu is an element that contributes to maintaining the pitting potential and suppresses deep pitting corrosion, and it is necessary to include at least 0.3% Cu in order to ensure the pitting potential. However, if the amount of Cu is too high, it may form Al-Cu compounds and promote intergranular corrosion, so the upper limit should be set at 0.6%. Furthermore, Ti is important for refining the crystal grains and stabilizing the structure, and it is preferable to include 0.1% or more. However, if the content is too high, coarse intermetallic compounds will be formed, so the upper limit should be set at 0.2%.

[0020] The brazing material for header pipes 2a and 2b has a composition containing Si: 7.0-9.0%, Fe: 0.2-0.3%, Cu: 0.1% or less, Mn: 0.1% or less, and Zn: 0.8-2.0%, with the remainder being Al and unavoidable impurities.

[0021] As described above, by adjusting the composition of the core material 10 and brazing material 11 of the header pipes 2a and 2b, the natural potential difference between the core material 10 and brazing material 11 of the header pipes 2a and 2b can be set to a range appropriate for corrosion protection. Furthermore, by setting the Zn content of the brazing material 11 to 0.8-2.0%, brazing can be ensured while leaving the fillet 12, which is the brazed joint between the header pipes 2a and 2b and the heat exchange tube 3. However, if the Zn content is too high, exceeding 2.0%, a large amount of Zn will flow into the fillet, which is the joint between the header pipes 2a and 2b and the heat exchange tube 3. The Zn-concentrated fillet will have a lower potential and will corrode preferentially to other parts. If preferential corrosion occurs in the fillet in this way, there is a concern that the fillet will disappear and penetrate, causing refrigerant leakage. Therefore, the upper limit is set at 2.0%, but from the viewpoint of corrosion protection and durability, it is preferable to set it to 0.8-1.8% (more preferably 1.0-1.8%).

[0022] <Composition of pipe fittings> As shown in Figures 1 and 3, the fitting pipe 7 is formed in the shape of a cylindrical pipe with one end enlarged. The fitting pipe 7 is made of an Al-Mn aluminum alloy (JIS A 3003 material) having a composition containing Si: 0.6%, Fe: 0.7%, Cu: 0.05~0.20%, Mn: 1.0~1.5%, and Zn: 0.1%, with the remainder being Al and unavoidable impurities. Zn is thermally sprayed onto the fitting pipe 7.

[0023] To spray molten Zn onto the surface of the fitting pipe 7, the Zn is melted and softened using a heat source such as a combustion flame or electrical energy, and then sprayed onto the surface of the fitting pipe 7 before it is expanded in diameter. Specifically, as shown in Figure 7, kinetic energy is given to the molten Zn, and the Zn is sprayed onto the surface of the cylindrical fitting pipe 7 before it is expanded in diameter by a nozzle 20 using a high-speed gas flow or the like. In this case, as a method of spraying Zn, for example, a method of spraying Zn from two directions using two nozzles 20 positioned perpendicular to each other with respect to the fitting pipe 7 (see Figure 7(b1)), a method of spraying Zn from three directions using three nozzles 20 positioned at 120° intervals with respect to the fitting pipe 7 (see Figure 7(b2)), or a method of spraying Zn from four directions using four nozzles 20 positioned at 90° intervals with respect to the fitting pipe 7 (see Figure 7(b3)) can be appropriately selected according to the size and shape of the fitting pipe 7, so that Zn can be uniformly sprayed onto the surface of the fitting pipe 7.

[0024] <Composition of heat exchange tubes> The heat exchange tube 3 has a composition containing Si: 0.15% or less, Fe: 0.05-0.35%, Cu: 0.1-0.6%, Mn: 0.2% or less, Zr: 0.02-0.05%, Ti: 0.003-0.015%, and Cr: 0.03% or less, with the remainder being Al and unavoidable impurities.

[0025] <Fin composition> The fin 4 consists of a core material 4a and a brazing sheet in which brazing material 4b is clad on both sides of the core material 4a. The core material 4a of the fin 4 has a composition containing Zn: 1.3-2.2%, with the remainder being Al and unavoidable impurities. The brazing material 4b of the fin 4 has a composition containing Zn: 0.7-1.3%, with the remainder being Al and unavoidable impurities.

[0026] The amount of Zn added to the core material 4a and brazing material 4b was determined so that, after brazing, the relationship between the natural potential with the heat exchange tube 3 is maintained within a range appropriate for corrosion protection, for example, 50±20mV, in the order of fin 4, fillet 4c (joint), and heat exchange tube 3, as shown in Figure 6. The reason for setting the appropriate range for corrosion protection at 50±20mV is that in long-term atmospheric exposure tests, a potential difference exceeding 70mV accelerates sacrificial corrosion, and a potential below 30mV makes corrosion unstable, potentially leading to corrosion in various parts.

[0027] Next, we will describe an evaluation test to examine the corrosion resistance of the heat exchanger 1 according to this invention. <Test Heat Exchanger> The test heat exchanger 1 is constructed in the same manner as the embodiment, except that the joint piping 7 is connected to the central part of a pair of header pipes 2a and 2b, which are formed in the same manner as the heat exchanger 1 of the above embodiment. The same parts are denoted by the same reference numerals and their descriptions are omitted. In this test, the header pipes 2a and 2b are formed in a cylindrical shape by bending a brazing sheet, which has a core material 10 with a wall thickness of 1.2 mm and a brazing material 11 clad on its surface.

[0028] <Testing Method> Evaluation of maximum pitting depth (μm) and fillet retention / disappearance after 3000 hours using the Acidic Artificial Seawater Spray Test (SWAAT). Table 1 shows the composition values ​​of Examples 1, 2, 3, and 4 and Comparative Examples 1, 2, 3, and 4 that were the subjects of the test. In Comparative Example 3, the Cu content of the core material was 0.05-0.2%, and the Zn content of the brazing material was 1.0%. On the other hand, in Comparative Example 4, the Cu content of the core material was 0.54%, and the Zn content of the brazing material was 3.6%.

[0029] [Table 1]

[0030] The maximum pitting depth after 3000 hours of acidic artificial seawater spray testing (SWAAT) was examined. As shown in Table 2, Example 1 had a depth of 155 μm, Example 2 had 110 μm, Example 3 had 110 μm, and Example 4 had 130 μm. Comparative Example 1 had a depth of 175 μm, Comparative Example 2 had 125 μm, and Comparative Example 4 had 150 μm. In contrast, Comparative Example 3 had a depth of 300 μm. As a result, the corrosion resistance evaluation for Examples 1, 2, 3, and 4 and Comparative Examples 1, 2, and 4 was good (○), but the corrosion resistance evaluation for Comparative Example 3 was poor (×).

[0031] [Table 2]

[0032] The differences in the maximum pitting depth for corrosion resistance evaluation between Comparative Example 3 and Comparative Example 4 are explained below with reference to Figures 9 and 10.

[0033] Figure 9 shows a schematic cross-sectional view of the sample of Comparative Example 3. (a) shows the condition before the test, and (b) shows the condition after 4 weeks of the Acidic Artificial Seawater Spray Test (SWAAT). Surface erosion of the Zn sacrificial layer progresses, but corrosion progresses inward starting from the exposed Al. (c) shows the condition after 8 weeks of the Acidic Artificial Seawater Spray Test (SWAAT), showing further corrosion before penetration.

[0034] Figure 10 shows a schematic cross-sectional view of the sample of Comparative Example 4. (a) shows the condition before the test, and (b) shows the condition after 4 weeks of the Acidic Artificial Seawater Spray Test (SWAAT). Surface erosion of the Zn sacrificial layer has progressed, and Al is partially exposed, but corrosion of the brazing material layer is progressing preferentially. (c) shows the condition after 8 weeks of the Acidic Artificial Seawater Spray Test (SWAAT). Internal corrosion does not develop until the brazing material layer is almost completely gone.

[0035] In the fillet disappearance evaluation of Examples 1, 2, 3, and 4 and Comparative Examples 1, 2, 3, and 4, the Zn content of the brazing material was 1.0-2.0% in Examples 1, 2, 3, and 4, and the Zn content of the brazing material in Comparative Example 3 was 1.0%. Therefore, fillet retention was confirmed, and the fillet disappearance evaluation was good (○). In contrast, the Zn content of the brazing material in Comparative Examples 1, 2, and 4 was high at 3.6%, so the fillets disappeared, and the fillet disappearance evaluation was poor (×).

[0036] The results of the evaluation of the maximum pitting depth and the persistence or disappearance of fillets after 3000 hours using the above-mentioned acidic artificial seawater spray test (SWAAT) showed that in Examples 1, 2, 3, and 4, both the header pipe corrosion resistance evaluation and the fillet disappearance evaluation were good (○), and the overall evaluation was also good (○). The reason for the disappearance of the fillets is, as mentioned above, that when the Zn content is too high, exceeding 2.0%, a large amount of Zn flows into the fillets at the joints between the header pipe and the heat exchange tube, and between the header pipe and the fittings. As a result, the Zn-concentrated fillets have a lower potential and are corroded preferentially over the heat exchange tubes and fittings.

[0037] Based on the above corrosion resistance evaluation and fillet disappearance evaluation results, by adjusting the core material of the header pipe to have a Cu content of 0.3-0.6% and a Ti content of 0.1-0.2%, and the brazing material to have a Zn content of 0.8-2.0%, it is possible to improve corrosion resistance by providing corrosion protection to the header pipe itself and the fittings connected to the header pipe that are used for the inflow and outflow of heat transfer fluids, even when used in harsh environments. [Explanation of Symbols]

[0038] 1. Heat exchanger (heat exchanger for room air conditioner) 2a,2b Header pipes 3 Heat exchange tubes 4 fins (corrugated fins) 4a Heartwood 4b Brazing material 4c fillet 7. Piping Fittings 9a Refrigerant inflow pipe (piping) 9b Refrigerant outlet pipe (piping) 10 Heartwood 11 Brazing material 12 fillets

Claims

1. A heat exchanger for a room air conditioner, comprising a pair of opposing header pipes, each made of aluminum, multiple heat exchange tubes connected to the two header pipes in parallel, corrugated fins arranged in parallel between the heat exchange tubes, and fittings connected to the header pipes, all brazed together, The header pipe described above comprises a core material and a brazing material on the outside of the core material. The core material of the above header pipe contains, by mass%, Si: 0.1-0.3%, Fe: 0.1-0.3%, Cu: 0.3-0.6%, Mn: 1.0-1.2%, Ti: 0.1-0.2%, with the remainder being Al and unavoidable impurities. The brazing material for the header pipe described above contains, by mass%, Si: 7.0-9.0%, Fe: 0.2-0.3%, Cu: 0.1% or less, Mn: 0.1% or less, Zn: 0.8-2.0%, with the remainder being Al and unavoidable impurities. A heat exchanger for room air conditioners characterized by the following features.

2. A heat exchanger for a room air conditioner according to claim 1, The above heat exchange tube contains, by mass%, Si: 0.15% or less, Fe: 0.05 to 0.35%, Cu: 0.1 to 0.6%, Mn: 0.2% or less, Zr: 0.02 to 0.05%, Ti: 0.003 to 0.015%, and Cr: 0.03% or less, with the remainder being Al and unavoidable impurities. The above corrugated fin consists of a core material and a brazing sheet in which wax material is clad on both sides of the core material. The core material of the above corrugated fin contains Zn: 1.3-2.2% by mass, with the remainder being Al and unavoidable impurities. The brazing material for the above corrugated fins contains 0.7-1.3% Zn by mass, with the remainder being Al and unavoidable impurities. A heat exchanger for room air conditioners characterized by the following features.

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