A method for manufacturing a small channel heat exchanger

Abstract

The application relates to a preparation method of a small-channel heat exchanger. The small-channel heat exchanger comprises an upper aluminum plate and a lower aluminum plate. A composite coating and a graphite coating are arranged between the upper aluminum plate and the lower aluminum plate. The upper aluminum plate and the lower aluminum plate are combined through the composite coating. The upper aluminum plate and the lower aluminum plate form a heat exchange channel at the graphite coating. The melting temperature of the composite coating is 250-350 DEG C. The preparation method comprises cutting forming, printing the composite coating, drying the composite coating, printing the graphite coating, drying the graphite coating, punch forming, assembling and fusion welding. The application can prepare a small-channel heat exchanger with a diameter of less than 4 mm, has wide applicability, high heat exchange efficiency, simple processing procedure and easy temperature control.

Description

Technical Field

[0001] This application relates to a method for preparing a small-channel heat exchanger, which is applicable to the technical field of heat exchange equipment. Background Technology

[0002] Currently, blown-type heat exchangers are widely used in the refrigeration and heat exchange industry. Their main advantages are simple manufacturing, good sealing, and corrosion resistance. Blown-type heat exchangers are generally made of aluminum, and can therefore be flat, L-shaped, or folded into a square shape to form a three-dimensional space. The blown-type heat exchanger mainly utilizes the high-temperature fusion of two aluminum plates. Before fusion, a graphite coating is printed on the fusion surface of the two aluminum plates to form the heat exchanger's pipe arrangement. After fusion, the two aluminum plates do not fuse at the areas with the graphite coating. Compressed air is then introduced into these non-fused areas, deforming the aluminum plates to form the heat exchange channels. This process is currently widely used in the manufacture of blown-type heat exchangers, but it is suitable for heat exchangers with relatively large heat exchange channels, generally with an equivalent circle diameter greater than 6 mm. In this application, the equivalent circle diameter refers to four times the pipe cross-sectional area divided by the pipe's perimeter. This type of large-diameter blown-type heat exchanger suffers from a small total surface area, resulting in a small heat exchange area and consequently, low heat transfer capacity. If the equivalent circle diameter of the heat exchange channel can be reduced to less than 4 mm, or even as small as 1 mm, the heat exchange area can be effectively increased. However, in reality, existing blow-forming processes cannot fabricate small-channel heat exchangers with diameters less than 4 mm.

[0003] CN114346626A discloses a method for producing a blow-type evaporator for new energy equipment, including the following steps: a) annealing an aluminum plate; b) roughening the aluminum plate with a roller brush to form a rough aluminum plate; c) printing ink on the rough aluminum plate; d) drying the printed rough aluminum plate in an oven; e) laminating an aluminum plate onto the rough surface of the rough aluminum plate to form a double-layer aluminum plate; f) heating the double-layer aluminum plate; g) hot rolling the double-layer aluminum plate; h) cold annealing the hot-rolled double-layer aluminum plate; i) leveling and drilling the double-layer aluminum plate; j) blowing air into the holes of the double-layer aluminum plate to form an expansion shape. In step a, the annealing of the aluminum plate and the roughening of the aluminum plate in step b are performed simultaneously by an integrated annealing and roughening machine; in step e, an aluminum plate is laminating the rough surface of the rough aluminum plate, and the rough surfaces of the two rough aluminum plates are laminated face to face to form a double-layer aluminum plate. CN102699648A discloses a method for producing a blown-up evaporator, similar to the method in the aforementioned patent. This method involves steps such as annealing, roller brushing, printing, covering, hot rolling, blowing, powder spraying, and drying / curing of an aluminum plate to form the blown-up evaporator. In this method, the aluminum plate is directly heated, causing the contact surfaces to melt. This inevitably leads to a large area of ​​the molten contact surfaces sticking together during hot rolling, requiring subsequent drilling and gas-filling expansion operations, increasing the number of steps and processing difficulty. More importantly, due to the large equivalent circle diameter of the heat exchange channel, the thickness of the two aluminum plates is also relatively large to withstand the blowing pressure and meet structural strength requirements, resulting in high thermal resistance and reduced heat exchange efficiency.

[0004] Another type of flat tube heat exchanger exists in the prior art. Although it can achieve an equivalent circle diameter of less than 4mm, it requires extrusion processing, and existing extrusion machines cannot produce flat tubes with a width exceeding 100mm. Therefore, flat tube heat exchangers cannot meet the requirements of wider environments. For example, CN1710367A discloses a flat tube heat exchanger formed by extrusion, where the microchannel cross-sectional diameter of the heat exchange flat tube is 0.7-1.2mm. While the microchannel flat tube in this patent increases the flow velocity of the heat exchange medium within the microchannel and also increases the heat exchange area of ​​the internal heat exchange medium, the heat exchange efficiency of the external medium does not increase. The heat exchange area of ​​the external medium is much smaller than that of the internal heat exchange medium. Therefore, heat dissipation aluminum fins are usually brazed onto the microchannel flat tube to promote heat dissipation balance. The placement of heat dissipation fins occupies a large amount of space, which in turn limits the number of heat exchange flat tubes, thus affecting the improvement of heat exchange efficiency. Furthermore, because the aluminum fins are very thin, typically 0.1-0.4 mm thick, temperature control during brazing is crucial; otherwise, the aluminum fins will melt. Therefore, this type of flat tube heat exchanger not only has limited width and lower heat exchange efficiency, but also involves complex manufacturing processes and requires high precision in temperature control.

[0005] Therefore, there is a need in the prior art for a method to prepare small-channel heat exchangers with an equivalent circular diameter of less than 4 mm, which can not only be applied to heat exchangers of any required width, but also meet the requirements of high heat exchange efficiency, simple processing steps, and easy temperature control. Summary of the Invention

[0006] The purpose of this application is to design a method for manufacturing a small-channel heat exchanger, which can be used to manufacture a small-channel heat exchanger with an equivalent circular diameter of 1-4 mm. The channel is formed by coupling two aluminum plates, which solves various problems existing in the prior art.

[0007] This application relates to a method for manufacturing a small-channel heat exchanger, the small-channel heat exchanger comprising an upper aluminum plate and a lower aluminum plate, wherein a composite coating and a graphite coating are spaced apart between the upper aluminum plate and the lower aluminum plate, the upper aluminum plate and the lower aluminum plate are bonded together by the composite coating, and a heat exchange channel is formed between the upper aluminum plate and the lower aluminum plate at the graphite coating, the melting temperature of the composite coating being 250–350°C, and the manufacturing method comprising the following steps:

[0008] (1) Cutting and shaping: Cut aluminum plates according to the dimensions required for the heat exchanger;

[0009] (2) Printing composite coating: Make a coating screen according to the size of the aluminum plate and the arrangement of the heat exchange channels. Apply the composite coating evenly to the aluminum plate through the coating screen. Print the composite coating on the upper and lower aluminum plates according to the corresponding position relationship of the upper and lower aluminum plates.

[0010] (3) Drying the composite coating: Dry the aluminum plate with the composite coating. The drying temperature is controlled at 300-350℃ and the time is 18-22 minutes.

[0011] (4) Printing graphite coating: Graphite mesh is made according to the size of the aluminum plate and the arrangement of the heat exchange channels. Graphite coating is applied to the aluminum plate through the graphite mesh. The upper and lower aluminum plates are printed according to the corresponding position relationship of the graphite coating.

[0012] (5) Drying the graphite coating: Dry the aluminum plate with the graphite coating. The drying temperature is controlled at 160-180℃ and the time is 2-3 minutes.

[0013] (6) Stamping: The aluminum plate is placed in the mold, and the area coated with graphite coating is stamped into the shape of a heat exchange channel, while the area coated with composite coating remains unchanged.

[0014] (7) Assembly: Couple the upper aluminum plate and the lower aluminum plate to form a complete heat exchange channel, so that the upper aluminum plate and the lower aluminum plate are tightly bonded together in the area coated with the composite coating.

[0015] (8) Fusion welding: The upper aluminum plate and the lower aluminum plate are sent into the fusion welding device for fusion welding. The fusion welding temperature is controlled at 550-630℃ and the fusion welding time is 18-22 minutes, so that the upper aluminum plate and the lower aluminum plate are tightly welded together at the composite coating to form a small channel heat exchanger.

[0016] In step (1), the installation positions of the connecting pipes are reserved at the inlet and outlet of the heat exchanger; in step (8), the workpiece formed by the upper aluminum plate and the lower aluminum plate is first placed on the graphite plate, and then the graphite plate is covered on the workpiece. Then the workpiece and the graphite plate are preheated, welded and cooled along the high temperature tunnel conveyor belt respectively; after the small channel heat exchanger is prepared, it can be leak tested; after the leak test, the heat exchanger can be dried again.

[0017] The equivalent circle diameter of the heat exchange channel can be 1-4 mm; the thickness of the upper aluminum plate and the lower aluminum plate can be 0.1-1 mm, and the thickness of the composite coating can be 2.5-80 μm; preferably, the thickness of the upper aluminum plate and the lower aluminum plate is 0.5-0.8 mm, and the thickness of the composite coating is 20-60 μm; the spacing of the graphite coating can be equal to the width of the composite coating, and the spacing of the composite coating can be 1-4 mm.

[0018] The method for manufacturing a small-channel heat exchanger according to this application has the following technical advantages:

[0019] (1) The preparation method of this application does not require the blowing process, which allows the equivalent circle diameter of the small channel heat exchanger prepared in this application to be reduced to 1-4 mm, thereby increasing the heat exchange area of ​​the heat exchanger and increasing the heat exchange efficiency; at the same time, it is not limited by the width in the flat tube heat exchanger, and small channel heat exchangers of any specification can be prepared according to the width requirements, making it more widely applicable.

[0020] (2) The small channel heat exchanger of this application uses a composite coating to bond the upper and lower aluminum plates together. The thickness of the composite coating is much smaller than that of the aluminum plate, which avoids the phenomenon of direct melting and bonding of aluminum plates and the accumulation of deposits around the bonding part, thus blocking the heat exchange pipe. It also avoids the problems of large heat exchange channel cross-sectional size, limited strength and complex process caused by the use of the blowing process.

[0021] (3) The composite coating of this application uses brazing paste with a melting temperature of 250-350℃ and the drying temperature is controlled at 300-350℃, so that the composite coating of this application is in a molten but non-flowing state during drying, ensuring the uniformity and consistency of the composite coating during the drying process; the welding temperature is controlled at 550-630℃, which is lower than the melting temperature of the aluminum plate, so that the aluminum plate can maximize the activity of molecular movement at the contact surface with the composite coating in the unmelted state, thereby improving the overall connection strength. Attached Figure Description

[0022] Figure 1 This is a cross-sectional schematic diagram of the small channel heat exchanger of this application. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be arbitrarily combined with each other.

[0024] like Figure 1 As shown, the small-channel heat exchanger according to this application has an equivalent circular diameter of 1-4 mm and includes an upper aluminum plate 1, a lower aluminum plate 2, a composite coating 3, and a graphite coating 4. The upper aluminum plate 1 and the lower aluminum plate 2 are thin aluminum plates with specific dimensional requirements, typically with a thickness of 0.1-1 mm, preferably 0.5-0.8 mm, and their thickness is mainly related to the working pressure of the heat exchange medium within the heat exchange channel. The composite coating 3 is applied to the upper aluminum plate 1 and the lower aluminum plate 2, and its thickness can be 2.5-80 μm, preferably 20-60 μm, much smaller than the thickness of the aluminum plates. The composite coatings 3 have a certain spacing, for example, 1-4 mm, and the spacing between the composite coatings 3 is covered by the graphite coating 4. Preferably, the spacing of the graphite coatings 4 is equal to the width of the composite coatings 3. A heat exchange channel 5 is formed between the graphite coatings 4 of the upper aluminum plate 1 and the lower aluminum plate 2.

[0025] The composite coating 3 of this application can use brazing paste with a melting temperature of 250-350℃, while the melting temperature of the aluminum plate is around 660℃. The composite coating melts at a welding temperature of 550-620℃, causing the upper aluminum plate 1 and lower aluminum plate 2 to fuse together in the composite coating area. After cooling, a sealed heat exchange channel 5 with a certain connection strength is formed between the upper aluminum plate 1 and lower aluminum plate 2, enabling the final heat exchanger to withstand the pressure of the heat exchange medium within the channel. The graphite coating 4 acts as a barrier during the welding process of the upper aluminum plate 1 and lower aluminum plate 2, preventing adhesion between them and thus avoiding blockage of the heat exchange channel 5. Therefore, in this application, the bonding of the upper and lower aluminum plates can be achieved solely through the melting of the composite coating. Neither the upper nor lower aluminum plate enters a molten state, preventing the formation of deposits around the melting aluminum plates that could block the heat exchange channel and eliminating the need for subsequent blowing steps. This is because the composite coating is relatively thin and will not form obvious molten deposits around the bonding area, thus preventing blockage of the heat exchange channels.

[0026] A method for preparing a small-channel heat exchanger according to this application includes the following steps:

[0027] (1) Cutting and shaping: Cut aluminum plates according to the required size of the heat exchanger, and reserve the installation position of the connecting pipe at the inlet and outlet of the heat exchanger;

[0028] (2) Printing composite coating: Make a coating screen according to the size of the aluminum plate and the arrangement of the channels inside the heat exchanger. Apply the composite coating evenly to the aluminum plate through the coating screen. Print the composite coating on the upper and lower aluminum plates according to the corresponding position relationship of the upper and lower aluminum plates.

[0029] (3) Drying: Place the aluminum plate with the composite coating into the drying oven for drying. The drying temperature is controlled at 300-350℃ and the time is 18-22 minutes. The oven needs to provide protective gas such as nitrogen to prevent the aluminum plate from oxidizing. The drying temperature and time can be adjusted appropriately according to the grade of the composite coating. The drying temperature is controlled at 300-350℃ and the time is controlled at 18-22 minutes so that the composite coating is in a molten but not flowing state. Under the premise of ensuring the uniformity of the composite coating, the composite coating can be fully bonded to the aluminum plate.

[0030] (4) Printing graphite coating: Graphite mesh is made according to the size of the aluminum plate and the arrangement of the channels inside the heat exchanger. Graphite coating is applied to the aluminum plate through the graphite mesh. The upper and lower aluminum plates are printed according to the corresponding position relationship of the graphite coating.

[0031] (5) Drying: Place the aluminum plate with graphite coating into the oven for drying. The drying temperature is controlled at 160-180℃ and the time is 2-3 minutes. The drying temperature is lower than the melting temperature of the composite coating and the time is also shorter, which can ensure that the composite coating already coated on the aluminum plate is not affected.

[0032] (6) Stamping: The upper aluminum plate and / or the lower aluminum plate are placed into the mold, so that the area coated with graphite coating is stamped into the shape of a heat exchange channel; while the area coated with composite coating remains unchanged.

[0033] (7) Assembly: The upper aluminum plate and the lower aluminum plate are joined together according to the coupling relationship, that is, half of the heat exchange channel on the upper aluminum plate is coupled with half of the heat exchange channel on the lower aluminum plate to form a complete heat exchange channel, and the connecting pipe is placed to form the workpiece.

[0034] (8) Preparation before welding: Place the workpiece on a graphite plate of matching size, and then cover it with another graphite plate so that the upper aluminum plate and the lower aluminum plate are tightly bonded together in the area coated with the composite coating.

[0035] (9) Fusion welding: The workpiece and the graphite plate are preheated, fused, and cooled together along the high-temperature tunnel conveyor belt, so that the upper aluminum plate and the lower aluminum plate are tightly welded together at the composite coating to make the small channel heat exchanger of this application; the fusion welding temperature is controlled at 550-630℃ and the fusion welding time is 18-22 minutes.

[0036] The temperature and time control in the preparation method of this application are mainly related to the materials of the upper and lower aluminum plates, and it is necessary to ensure that the upper and lower aluminum plates themselves do not melt during the welding process. After the small-channel heat exchanger is prepared, it can be inspected by water leak testing or helium leak testing. If water leak testing is used, drying is required after leak testing.

[0037] Although the embodiments disclosed in this application are as described above, the content is merely for the purpose of facilitating understanding of this application and is not intended to limit this application. Any person skilled in the art to which this application pertains may make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in this application; however, the scope of patent protection of this application shall still be determined by the scope defined in the appended claims.

Claims

1. A method for preparing a small-channel heat exchanger, characterized in that, The small-channel heat exchanger includes an upper aluminum plate and a lower aluminum plate, with a composite coating and a graphite coating spaced apart between the upper and lower aluminum plates. The upper and lower aluminum plates are bonded together by the composite coating, and a heat exchange channel is formed between the upper and lower aluminum plates at the graphite coating. The melting temperature of the composite coating is 250–350°C. The preparation method includes the following steps: (1) Cutting and shaping: Cut aluminum plates according to the dimensions required for the heat exchanger; (2) Printing composite coating: Make a coating screen according to the size of the aluminum plate and the arrangement of the heat exchange channels. Apply the composite coating evenly to the aluminum plate through the coating screen. Print the composite coating on the upper and lower aluminum plates according to the corresponding position relationship of the upper and lower aluminum plates. (3) Drying the composite coating: Dry the aluminum plate with the composite coating. The drying temperature is controlled at 300-350℃ and the time is 18-22 minutes. (4) Printing graphite coating: Graphite mesh is made according to the size of the aluminum plate and the arrangement of the heat exchange channels. Graphite coating is applied to the aluminum plate through the graphite mesh. The upper and lower aluminum plates are printed according to the corresponding position relationship of the graphite coating. (5) Drying the graphite coating: Dry the aluminum plate with the graphite coating. The drying temperature is controlled at 160-180℃ and the time is 2-3 minutes. (6) Stamping: The aluminum plate is placed in the mold, and the area coated with graphite coating is stamped into the shape of a heat exchange channel, while the area coated with composite coating remains unchanged. (7) Assembly: Couple the upper aluminum plate and the lower aluminum plate to form a complete heat exchange channel, so that the upper aluminum plate and the lower aluminum plate are tightly bonded together in the area coated with the composite coating. (8) Fusion welding: The upper aluminum plate and the lower aluminum plate are sent into the fusion welding device for fusion welding. The fusion welding temperature is controlled at 550-630℃ and the fusion welding time is 18-22 minutes, so that the upper aluminum plate and the lower aluminum plate are tightly welded together at the composite coating to form a small channel heat exchanger.

2. The preparation method according to claim 1, characterized in that, In step (1), the installation positions for connecting pipes are reserved at the inlet and outlet of the heat exchanger.

3. The preparation method according to claim 1, characterized in that, In step (8), the workpiece formed by the upper aluminum plate and the lower aluminum plate is first placed on the graphite plate, and then the graphite plate is covered on the workpiece. Then the workpiece and the graphite plate are preheated, welded and cooled along the high-temperature tunnel conveyor belt.

4. The preparation method according to any one of claims 1-3, characterized in that, The equivalent circle diameter of the heat exchange channel is 1-4 mm.

5. The preparation method according to claim 4, characterized in that, The thickness of the upper aluminum plate and the lower aluminum plate is 0.1 to 1 mm, and the thickness of the composite coating is 2.5 to 80 μm.

6. The preparation method according to claim 5, characterized in that, The thickness of the upper aluminum plate and the lower aluminum plate is 0.5-0.8 mm, and the thickness of the composite coating is 20-60 μm.

7. The preparation method according to any one of claims 1-3 and 5-6, characterized in that, The spacing of the graphite coating is equal to the width of the composite coating, and the spacing of the composite coating is equal to the width of the graphite coating.

8. The preparation method according to claim 7, characterized in that, The spacing of the composite coating is 1-4 mm.

9. The preparation method according to any one of claims 1-3, 5-6, and 8, characterized in that, After the small-channel heat exchanger is manufactured, a leak test is performed on it.

10. The preparation method according to claim 9, characterized in that, After the leak test, the heat exchanger was dried again.

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