All-glass heat pipe vacuum tube with built-in metal solid heat absorbing member and its processing method

Abstract

The application discloses a full-glass heat-pipe type vacuum tube with a built-in metal solid heat-absorbing part and a processing method thereof. The full-glass heat-pipe type vacuum heat-collecting tube with the built-in heat-absorbing part comprises a glass outer tube and a glass heat pipe. The evaporation section of the glass heat pipe is located in the internal vacuum layer of the glass outer tube, the condensation section of the glass heat pipe extends out of the glass outer tube, and the glass heat pipe has working fluid therein. A metal heat-absorbing part is arranged in the evaporation section of the glass heat pipe, the metal heat-absorbing part is coated with a heat-absorbing coating, and the metal heat-absorbing part is fixed by arranging a heat-absorbing part support on the heat-absorbing part. The application can not only improve the heat exchange efficiency, but also solve the problem that a large amount of heat is accumulated on the glass outer tube of the traditional heat-pipe type vacuum heat-collecting tube in an extreme environment on a plateau, thereby causing deformation and even damage of the heat pipe. The design is simple in structure and easy to produce, and can be applied on a large scale.

Description

TECHNICAL FIELD

[0001] The present application relates to a full-glass heat-pipe vacuum tube with a built-in metal solid heat-absorbing member and a processing method thereof, and belongs to the technical field of solar heat collection and heating. BACKGROUND

[0002] A heat-pipe vacuum tube realizes high-efficiency heat transfer through evaporation and condensation, and the heat conductivity coefficient can reach 10 5 W / m℃ order of magnitude, which is hundreds of times of that of general metal materials. Due to the high efficiency, the heat-pipe vacuum tube can be widely used in the field of solar heating. The heat-pipe vacuum tube is mainly divided into a metal heat-pipe vacuum tube and a full-glass heat-pipe vacuum tube. The metal heat-pipe vacuum tube is 5 times as expensive as an ordinary vacuum tube due to the difficulty in glass-metal sealing technology, and is prone to tearing and damage in plateau areas with large temperature difference. The full-glass heat-pipe vacuum tube is prone to explosion due to large local thermal stress caused by thermal shock under high-intensity and fluctuating solar radiation.

[0003] In a traditional heat-pipe vacuum tube structure, the heat-pipe vacuum tube includes a glass outer tube and a glass heat pipe arranged in the glass outer tube. A working fluid is in the glass heat pipe, and a coating is directly arranged outside the inner glass heat pipe. Heat is absorbed at the coating, and then the heat is absorbed by the working fluid in the heat pipe. This structure has simple manufacturing process, good heat exchange performance, and has been widely used. However, due to the high solar radiation value in plateau areas, the temperature difference between the coating area and the non-coating area of the full-glass heat pipe is too large, and the heat accumulation phenomenon may occur. Under the action of thermal stress, the full-glass heat pipe is prone to deformation and even damage in the special environment of the plateau area, which affects the safe and stable use. SUMMARY

[0004] To solve the above problems, the present application discloses a full-glass heat-pipe vacuum tube with a built-in metal solid heat-absorbing member and a processing method thereof. A new design and construction idea is adopted, that is, a metal solid heat-absorbing member with a selective absorption coating is placed in the full-glass heat-pipe vacuum tube. The glass-metal sealing is removed, and the manufacturing cost is reduced. The problems of poor glass heat conductivity and pipe explosion and damage during the starting stage are solved.

[0005] To achieve the above purpose, the technical scheme of the present application is as follows:

[0006] The application provides a full-glass heat pipe type vacuum tube with a built-in metal solid heat absorbing element. The full-glass heat pipe type vacuum heat collecting tube comprises a glass outer tube and a glass heat pipe. The evaporation section of the glass heat pipe is located in the internal vacuum layer of the glass outer tube, the condensation section of the glass heat pipe extends out of the glass outer tube, and the glass heat pipe contains working fluid. The evaporation section of the glass heat pipe is provided with a metal heat absorbing element. The metal heat absorbing element is coated with a heat absorbing coating and is fixed in the glass heat pipe through a heat absorbing element support. The width, length and minimum distance of the heat absorbing element from the end point of the evaporation section of the glass heat pipe need to meet the following formula:

[0007]

[0008]

[0009]

[0010] wherein, the width of the heat absorbing element, the inner diameter of the glass heat pipe, the equivalent thermal expansion coefficient of the heat absorbing element, the temperature change of the heat absorbing element; the length of the heat absorbing element, the length of the evaporation section of the full-glass heat pipe, the minimum solar elevation angle under the most unfavorable condition of the local place, the inclination angle of the heat pipe, which is the average solar elevation angle of the local place; the minimum distance of the heat absorbing element from the end point of the evaporation section of the glass heat pipe.

[0011] Further, the heat absorbing element comprises a main metal layer and selective absorption coatings on both sides of the main metal layer. The overall thickness of the heat absorbing element is not greater than 3 mm. The equivalent thermal expansion coefficient of the heat absorbing element is calculated according to the following formula:

[0012]

[0013] wherein, the equivalent thermal expansion coefficient of the heat absorbing element, the thermal expansion coefficient of the selective absorption coating, the elastic modulus of the selective absorption coating, the thickness of the selective absorption coating, the thermal expansion coefficient of the main metal layer, the elastic modulus of the main metal layer, ​​​​​​​The thickness of the main metal layer.

[0014] Furthermore, the heat absorber bracket is arranged under the metal heat absorber for support, and the heat absorber bracket adopts a 60-degree arc-shaped base, which is distributed at the front and rear ends of the heat absorber.

[0015] Furthermore, the heat-absorbing component support is arranged on the left and right sides of the heat-absorbing component to fix the heat-absorbing component.

[0016] Another object of the present invention is to provide a method for processing the above-mentioned all-glass heat pipe vacuum tube with built-in metal solid heat absorber, the method comprising the following steps:

[0017] Step 1: One-piece stamping and molding process to create the glass outer tube and glass heat pipe:

[0018] A coefficient of thermal expansion of 3.3 × 10⁻ was selected. 6 3.3 borosilicate glass at / ℃ is melted at 1200-1300℃ using a high-temperature tube drawing process to form an integrated structure consisting of a glass heat pipe with an outer diameter of 47mm and a wall thickness of 1.75mm, and a glass outer tube with an outer diameter of 58mm and a wall thickness of 1.80mm. The glass outer tube is connected to the glass heat pipe at nine-tenths of its length. The condensation section of the glass heat pipe and the bottom of the glass outer tube are both open. An annular hole needs to be reserved in the glass outer tube to facilitate the subsequent vacuuming process.

[0019] Step 2: Prefabrication and installation of metal heat-absorbing components:

[0020] Processing width ,length The metal plate is pre-treated, and then black or blue film is selected and coated according to the process. After coating, the heat absorber bracket is installed by welding or fastener connection. Then the pre-made heat absorber and 20%±5% of the heat transfer medium are placed into the glass heat pipe.

[0021] Step 3: Welding and sealing of the outer glass tube and glass heat pipe:

[0022] The support components, evaporative getter, and other structures are installed inside the glass outer tube. Then, the glass heat pipe and the opening of the glass outer tube are heated to about 1200-1300℃ and fused together to form a one-piece structure. After the fusion is completed, annealing is performed to relieve stress.

[0023] Step 4: Vacuuming:

[0024] The annular hole on the outer glass tube is used as an exhaust channel. The air in the interlayer between the outer glass tube and the glass heat pipe is extracted by a vacuum pump to achieve a high vacuum state. Then, the high-frequency induction heating device is activated to activate the evaporative getter. The active barium metal released by the getter can adsorb the residual gas, ensuring that the vacuum degree of the interlayer between the outer glass tube and the glass heat pipe is maintained at 5×10⁻²Pa for a long time. After the standard is met, the reserved annular hole is immediately sealed with flame. After completion, the entire outer glass tube and glass heat pipe assembly needs to be annealed to eliminate processing stress.

[0025] The advantages of this invention compared to the prior art are:

[0026] 1. Compared with the traditional heat pipe vacuum tube structure, the all-glass heat pipe vacuum tube with built-in metal solid heat absorber of the present invention eliminates the glass-metal sealing, reducing manufacturing costs; it also solves the problem of poor thermal conductivity of glass and the problem of tube bursting during the start-up stage.

[0027] 2. In this invention, after the built-in heat absorber is incorporated, the coating is arranged on the metal heat absorber. After the heat is absorbed by the coating, it is transferred to the working fluid through short-flow convection heat transfer. This directly avoids the deformation and damage that would occur if the glass heat pipe were involved in heat absorption. Furthermore, since there is no direct connection between the heat absorber and the glass heat pipe, the problems that may arise from using a glass-metal connection, as described in the background section, are prevented. During startup, the metal heat absorber can also quickly transfer heat, preventing localized overheating.

[0028] 3. Compared to traditional vacuum heat pipes, the heat exchange efficiency of this invention, featuring an all-glass heat pipe with an internal heat absorber, is improved. Figure 2 It can be seen that the main difference between the two is that the heat conduction process is eliminated, which realizes efficient heat transfer and improves the heat collection efficiency of the vacuum heat collection tube. Attached Figure Description

[0029] Figure 1 : Schematic diagram of the all-glass heat pipe vacuum collector tube with built-in heat absorber of the present invention;

[0030] Figure 2 A comparison diagram of the heat transfer methods between a traditional all-glass heat pipe vacuum tube collector and the all-glass heat pipe vacuum tube with heat-absorbing element of the present invention.

[0031] Figure 3 : A schematic diagram of the structure of one embodiment of the present invention;

[0032] Figure 4 : Figure 3 Cross-sectional view;

[0033] Figure 5 : A schematic diagram of the screw fixing structure in this embodiment;

[0034] Figure 6 : A schematic diagram of another embodiment of the present invention;

[0035] Figure 7 : Figure 6 Cross-sectional view;

[0036] Figure 8 : A schematic diagram of the screw fixing structure in this embodiment;

[0037] Figure 9 : Cross-sectional view of screw fixing in this embodiment.

[0038] Meaning of the markings in the attached diagram:

[0039] 1. Glass outer tube; 2. Glass heat pipe; 2-1. Evaporation section of glass heat pipe; 2-2. Condensation section of glass heat pipe; 3. Vacuum layer; 4. Fluid working medium; 5. Solid metal heat absorber; 6. Solid metal heat absorber support; 7. Reserved screw holes; 8. Screws. Detailed Implementation

[0040] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0041] Example 1

[0042] like Figure 1 As shown, the all-glass heat pipe vacuum collector tube with built-in heat absorber of the present invention includes a glass outer tube 1 and a glass heat pipe 2. The evaporation section 2-1 of the glass heat pipe is located in the inner vacuum layer 3 of the glass outer tube 1, and the condensation section 2-2 of the glass heat pipe extends outward from the glass outer tube 1. The glass heat pipe contains a working fluid 4. A metal heat absorber 5 is arranged inside the evaporation section 2-2 of the glass heat pipe, and the metal heat absorber is coated with a heat-absorbing coating.

[0043] The solid heat absorber coated with a selective absorption coating is placed inside an all-glass heat pipe vacuum tube, and the heat transfer medium is placed inside the heat pipe. During evaporation and condensation, the medium surrounds the solid heat absorber and participates in absorbing ultraviolet rays, protecting the selective absorption coating from being oxidized and damaged by the strong oxidizing effect of ultraviolet rays. The glass-metal seal is eliminated, reducing manufacturing costs. The glass does not participate in absorbing solar energy, avoiding thermal cracking during the start-up phase.

[0044] The metal heat absorber is rectangular and made of steel or copper. It is coated with a selective absorption coating, which is a black or blue film. The metal is mainly made of steel.

[0045] The metal heat absorber is installed inside the heat pipe via a movable bracket to avoid tearing caused by the difference in thermal expansion.

[0046] A crucial aspect of this design is the size of the heat absorber. The length of the heat absorber should completely cover the evaporation section, and its width should be sufficiently wide. This is because the heat absorber is the primary heat-absorbing component of the entire vacuum heat pipe. If the working fluid cannot directly contact the heat absorber, heat transfer will be impossible, resulting in extremely low thermal efficiency and significantly impacting the vacuum heat pipe's thermal performance. However, its size cannot be too large. The thermal expansion of the metal heat absorber after heat absorption must be considered, and sufficient space must be provided to prevent damage to the glass heat pipe due to thermal expansion. The following is the calculation method for the heat absorber's dimensions:

[0047] Calculation of the equivalent thermal expansion coefficient of the heat-absorbing component:

[0048] The heat absorber is primarily made of metal, with selective absorption coatings on both sides, resembling a sandwich structure. The coating is either black or blue. The formula for calculating the equivalent thermal expansion coefficient of the heat absorber is:

[0049] ,

[0050] in:

[0051] The equivalent thermal expansion coefficient of the heat-absorbing component;

[0052] The coefficient of thermal expansion of selective absorption coatings;

[0053] : Selectively absorbs the elastic modulus of the coating;

[0054] : The thickness of the selective absorption coating;

[0055] : Coefficient of thermal expansion of metals;

[0056] : The elastic modulus of a metal;

[0057] The thickness of the metal.

[0058] Determining the width of the heat absorber:

[0059] Considering the thermal expansion of the heat-absorbing components, measures are taken to prevent damage to the heat pipe due to thermal expansion. A formula exists:

[0060] ,

[0061] in:

[0062] Width of the heat-absorbing component;

[0063] : Diameter of the inner tube of the glass heat pipe;

[0064] The equivalent thermal expansion coefficient of the heat-absorbing component;

[0065] : Temperature change of the heat-absorbing element.

[0066] Determining the length of the heat-absorbing component:

[0067] The shading method is used in the calculations to ensure that the heat absorber completely covers the evaporator section of the heat pipe, allowing all sunlight entering the heat pipe to reach the heat absorber. The thermal expansion of the heat absorber must also be considered to prevent damage to the bottom of the all-glass heat pipe due to thermal expansion.

[0068] The formula for calculating the length of the heat-absorbing component using the shading method is as follows:

[0069] ,

[0070] in:

[0071] Length of heat-absorbing component;

[0072] Length of the evaporator section of the all-glass heat pipe;

[0073] : Take the minimum solar altitude angle under the most unfavorable local conditions;

[0074] The heat pipe tilt angle is taken from the local average solar altitude angle.

[0075] The length of the heat absorber has been determined through calculations using the shadow method. However, a certain distance also needs to be reserved at the end of the evaporation section of the glass heat pipe; this distance is... This is because the thermal expansion of the heat-absorbing component needs to be taken into account, to prevent the glass heat pipe from being damaged by thermal expansion. The calculation method includes a formula:

[0076] ,

[0077] in:

[0078] The minimum distance reserved between the heat absorber and the end of the evaporation section of the glass heat pipe;

[0079] Length of heat-absorbing component;

[0080] The equivalent thermal expansion coefficient of the heat-absorbing component; : Temperature change of the heat-absorbing element;

[0081] Calculations show that the length of the heat-absorbing element is... Furthermore, the heat-absorbing element should be located a distance from the bottom of the heat pipe. This is to prevent damage to the heat pipe due to thermal expansion.

[0082] The absorber element should be sufficiently thin, with an overall thickness not exceeding 3mm. A thinner absorber element ensures extremely high heat transfer efficiency. Furthermore, a thinner element allows for a lighter weight, preventing the metal absorber from affecting the all-glass heat pipe structure. The specific dimensions of the absorber element can be determined using the above calculation methods.

[0083] The heat absorber is primarily placed directly inside the heat pipe. It is secured and stabilized by a heat absorber support bracket (6). This design eliminates the need for a glass-metal connector, reducing costs and simplifying the manufacturing process. More importantly, it avoids deformation and damage caused by differences in thermal expansion coefficients. During production, installation is simply completed by placing the heat absorber inside the glass heat pipe, resulting in a simple and inexpensive process. The heat absorber is lightweight, so securing it only requires preventing positional shift.

[0084] The method of fixing the heat-absorbing component is as follows: Figure 3 The heat absorber support is arranged at the bottom of the heat absorber for support. Its cross-sectional view is shown below. Figure 4 As shown, a circular base at a 60-degree angle is arranged at the lower part of the heat absorber, distributed at both ends of the heat absorber. The base is not directly connected to the glass heat pipe, but only serves to fix the heat absorber. In actual use, the base will automatically shift under the action of gravity, so that the relative position of the heat absorber remains unchanged.

[0085] The bracket and the heat absorber can be connected by screws or welding. If screws are used, corresponding screw holes 7 should be pre-drilled on both the solid metal heat absorber and the bracket. During installation, simply screw the screws 8 in to complete the fixation. The specific structure is as follows... Figure 5 As shown.

[0086] The processing method of the above-mentioned all-glass heat pipe vacuum tube with built-in metal solid heat absorber includes the following steps:

[0087] Step 1: One-piece stamping and molding process to create the glass outer tube and glass heat pipe:

[0088] A coefficient of thermal expansion of 3.3 × 10⁻ was selected. 63.3 borosilicate glass at / ℃ is melted at 1200-1300℃ using a high-temperature tube drawing process to form an integrated structure consisting of a glass heat pipe with an outer diameter of 47mm and a wall thickness of 1.75mm, and a glass outer tube with an outer diameter of 58mm and a wall thickness of 1.80mm. The glass outer tube is connected to the glass heat pipe at nine-tenths of its length. The condensation section of the glass heat pipe and the bottom of the glass outer tube are both open. An annular hole needs to be reserved in the glass outer tube to facilitate the subsequent vacuuming process.

[0089] Step 2: Prefabrication and installation of metal heat-absorbing components:

[0090] Processing width ,length The metal plate is pre-treated, and then black or blue film is selected and coated according to the process. After coating, the heat absorber bracket is installed by welding or fastener connection. Then the pre-made heat absorber and 20%±5% of the heat transfer medium are placed into the glass heat pipe.

[0091] Step 3: Welding and sealing of the outer glass tube and glass heat pipe:

[0092] The support components, evaporative getter, and other structures are installed inside the glass outer tube. Then, the glass heat pipe and the opening of the glass outer tube are heated to about 1200-1300℃ and fused together to form a one-piece structure. After the fusion is completed, annealing is performed to relieve stress.

[0093] Step 4: Vacuuming:

[0094] The annular hole on the outer glass tube is used as an exhaust channel. The air in the interlayer between the outer glass tube and the glass heat pipe is extracted by a vacuum pump to achieve a high vacuum state. Then, the high-frequency induction heating device is activated to activate the evaporative getter. The active barium metal released by the getter can adsorb the residual gas, ensuring that the vacuum degree of the interlayer between the outer glass tube and the glass heat pipe is maintained at 5×10⁻²Pa for a long time. After the standard is met, the reserved annular hole is immediately sealed with flame. After completion, the entire outer glass tube and glass heat pipe assembly needs to be annealed to eliminate processing stress.

[0095] Example 2

[0096] The difference between this embodiment and Embodiment 1 is that the fixing method is as follows: Figure 6 The heat absorber support 6 is arranged on the left and right sides of the heat absorber 5 to fix the heat absorber. The method for determining the size of the heat absorber is the same as that in Embodiment 1, and will not be repeated here. Supports are arranged at the front and rear ends of the heat absorber to ensure the relative position of the heat absorber is fixed. Fixing the heat absorber on the left and right sides can prevent displacement of the heat absorber.

[0097] This fixing method also allows for two ways to connect the heat absorber to the bracket. If welding is used, the cross-sectional diagram is as follows: Figure 7 As shown. If screws are used for fixing, such as Figure 8 As shown, two screw holes 7 need to be pre-drilled on the "T"-shaped bracket. Screwing in two screws 8 will complete the installation. The specific structure is as follows: Figure 8 As shown, its cross-sectional view is as follows Figure 9 .

Claims

1. A vacuum tube with an internal metal solid heat absorber, comprising an outer glass tube and a glass heat pipe, wherein the evaporation section of the glass heat pipe is located in the inner vacuum layer of the outer glass tube, the condensation section of the glass heat pipe extends outward from the outer glass tube, and the glass heat pipe is filled with a working fluid; characterized in that, A solid metal heat absorber is arranged inside the evaporation section of the glass heat pipe. The solid metal heat absorber is coated with a heat-absorbing coating. The solid metal heat absorber is fixed inside the glass heat pipe by a solid metal heat absorber bracket, and the width of the solid metal heat absorber is... ,length The minimum distance reserved at the end of the evaporation section of the solid metal heat absorber and the glass heat pipe. The following formula must be satisfied: in, Width of the solid metal heat absorber The inner diameter of the glass heat pipe. is the equivalent thermal expansion coefficient of a solid metal heat-absorbing component. This refers to the temperature change of a solid metal heat absorber. The length of the solid metal heat absorber. The length of the all-glass heat pipe evaporation section. To obtain the minimum solar altitude angle under the most unfavorable local conditions, The tilt angle of the heat pipe is taken as the local average solar altitude angle; The minimum distance reserved at the end of the evaporation section of the solid metal heat absorber and the glass heat pipe.

2. The all-glass heat pipe vacuum tube with built-in metal solid heat absorber according to claim 1, characterized in that, The solid metal heat absorber includes a main metal layer and selective absorption coatings on both sides of the main metal layer. The overall thickness of the solid metal heat absorber is no more than 3 mm. The formula for calculating the equivalent thermal expansion coefficient of the solid metal heat absorber is: in: is the equivalent thermal expansion coefficient of a solid metal heat-absorbing component. The coefficient of thermal expansion of the selectively absorbent coating is... To selectively absorb the elastic modulus of the coating, To selectively absorb the thickness of the coating, The coefficient of thermal expansion of the main metal layer is... The elastic modulus of the main metal layer. The thickness of the main metal layer.

3. The all-glass heat pipe vacuum tube with a built-in metal solid heat absorber according to claim 1, characterized in that, The heat absorber support is arranged under the solid metal heat absorber for support. The solid metal heat absorber support adopts a 60-degree arc-shaped base and is distributed at the front and rear ends of the solid metal heat absorber.

4. The all-glass heat pipe vacuum tube with a built-in solid metal heat absorber according to claim 1, characterized in that, The solid metal heat absorber support is arranged on the left and right sides of the solid metal heat absorber to fix the solid metal heat absorber.

5. A method for processing an all-glass heat pipe vacuum tube with an internal metal solid heat absorber as described in any one of claims 1-4, characterized in that, The method includes the following steps: Step 1: One-piece stamping and molding process to create the glass outer tube and glass heat pipe: A coefficient of thermal expansion of 3.3 × 10⁻ was selected. 6 3.3 borosilicate glass at / ℃ is melted at 1200-1300℃ using a high-temperature tube drawing process to form an integrated structure of a glass heat pipe with an outer diameter of 47mm and a wall thickness of 1.75mm and a glass outer tube with an outer diameter of 58mm and a wall thickness of 1.80mm. The glass outer tube is connected at nine-tenths of the length of the glass heat pipe. The condensation section of the glass heat pipe and the bottom of the glass outer tube are both open. An annular hole needs to be reserved in the glass outer tube to facilitate the subsequent vacuuming process. Step 2: Prefabrication and installation of solid metal heat absorbers: Processing width ,length The metal plate is pre-treated on the surface. After that, black film or blue film is selected and coated according to its process. After the coating is completed, the solid metal heat absorber bracket is installed. The installation is carried out by welding or fastener connection. Then, the pre-made solid metal heat absorber and heat transfer medium with a volume of 20%±5% are put into the glass heat pipe. Step 3: Welding and sealing of the outer glass tube and glass heat pipe: The support and evaporative getter are installed inside the glass outer tube. Then, the glass heat pipe and the opening of the glass outer tube are heated to about 1200-1300℃ and fused together to make them a one-piece structure. After the fusion is completed, annealing is performed to relieve stress. Step 4: Vacuuming: The annular hole on the outer glass tube is used as an exhaust channel. The air in the interlayer between the outer glass tube and the glass heat pipe is extracted by a vacuum pump to achieve a high vacuum state. Then, the high-frequency induction heating device is activated to activate the evaporative getter. The released active barium metal can adsorb the residual gas, ensuring that the vacuum degree of the interlayer between the outer glass tube and the glass heat pipe is maintained at 5×10⁻²Pa for a long time. After the standard is met, the reserved annular hole is immediately sealed with flame. After completion, the entire set of outer glass tube and glass heat pipe assembly needs to be annealed to eliminate processing stress.

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