All-glass heat pipe type vacuum pipe with built-in metal solid heat absorption piece and processing method of all-glass heat pipe type vacuum pipe

Abstract

The invention discloses an all-glass heat pipe type vacuum pipe with a built-in metal solid heat absorption piece and a machining method thereof.The all-glass heat pipe type vacuum pipe with the built-in metal solid heat absorption piece comprises a glass outer pipe and a glass heat pipe, and an evaporation section of the glass heat pipe is located in an inner vacuum layer of the glass outer pipe; a condensation section of the glass heat pipe extends out of the glass outer pipe, and working medium fluid is arranged in the glass heat pipe; a metal heat absorption piece is arranged in an evaporation section of the glass heat pipe, a heat absorption coating is coated on the metal heat absorption piece, and the metal heat absorption piece is fixed in the mode that a heat absorption piece support is arranged on the heat absorption piece. The heat exchange efficiency can be improved, and the problems that a large amount of heat is accumulated on the glass outer tube in the plateau extreme environment of a traditional heat tube type vacuum heat collection tube, and consequently deformation occurs, and even the heat tube is damaged can be solved. The design structure is simple, production is easy, and large-scale application can be achieved.

Description

Technical Field

[0001] The invention relates to a full-glass heat pipe type vacuum tube with a built-in metal solid heat absorbing component and a processing method thereof, belonging to the technical field of solar energy heat collection and heating. Background Art

[0002] Heat pipe vacuum tubes achieve efficient heat transfer through evaporation and condensation, and the thermal conductivity can reach 10 5 W / m℃ is hundreds of times higher than that of general metal materials. Due to its high efficiency, it has great potential in the field of solar heating. It is mainly divided into metal heat pipe vacuum tubes and all-glass heat pipe vacuum tubes. Metal heat pipe vacuum tubes are 5 times more expensive than ordinary vacuum tubes due to the difficulty of glass-metal sealing technology. At the same time, they are prone to tearing damage in plateau areas with large temperature differences. All-glass heat pipe vacuum tubes suffer from thermal shock under high-intensity and large fluctuations of solar energy due to poor thermal conductivity of glass, and burst due to large local thermal stress. These existing problems make it difficult to promote and apply high-efficiency heat transfer elements - heat pipe vacuum collectors on a large scale.

[0003] In the traditional heat pipe vacuum tube structure, the heat pipe vacuum tube includes a glass outer tube and a glass heat pipe placed in the glass outer tube. The working fluid is in the glass heat pipe, and the coating is directly arranged on the outside of the internal glass heat pipe, where the heat is absorbed, and then the heat is absorbed by the working fluid in the heat pipe. This structure has a simple manufacturing process and good heat exchange performance, and has been widely used. However, due to the high solar radiation value in the plateau area, the temperature difference between the coated area and the non-coated area on the all-glass heat pipe is too large, and the heat accumulation phenomenon may occur. Under the action of thermal stress, it will cause it to be frequently deformed or even damaged during use in the special environment of the plateau, affecting its safe and stable use. Summary of the invention

[0004] To solve the above problems, the present invention discloses a full-glass heat pipe type vacuum tube with a built-in metal solid heat absorbing component and a processing method thereof, which adopts a new design and construction idea, that is, a metal solid heat absorbing component with a selective absorption coating is placed in the full-glass heat pipe type vacuum tube. The glass-metal seal is removed, the manufacturing cost is reduced, the poor thermal conductivity of glass is solved, and the problem of tube explosion and damage during the startup stage is solved.

[0005] To achieve the above object, the technical solution of the present invention is as follows: The present invention first provides an all-glass heat pipe type vacuum tube with a built-in metal solid heat absorbing component. The all-glass heat pipe type vacuum heat collecting tube with a built-in heat absorbing component comprises a glass outer tube and a glass heat pipe. The evaporation section of the glass heat pipe is located in the inner vacuum layer of the glass outer tube, and the condensation section of the glass heat pipe extends outward from the glass outer tube. The glass heat pipe contains a working fluid. The evaporation section of the glass heat pipe is arranged with a metal heat absorbing component, and the metal heat absorbing component is coated with a heat absorbing coating. The metal heat absorbing component is fixed to the inside of the glass heat pipe through a heat absorbing component bracket, and the width of the heat absorbing component is ,length , the minimum distance reserved between the heat absorber and the end point of the evaporation section of the glass heat pipe The following formula must be satisfied: , , , in, is the width of the heat absorber, is the inner diameter of the glass heat pipe, is the equivalent thermal expansion coefficient of the heat absorber, is the temperature change of the heat absorber; is the length of the heat absorber, is the length of the evaporation section of the all-glass heat pipe, To obtain the minimum solar altitude angle under the most unfavorable local conditions, is the heat pipe inclination angle, taking the local average solar altitude angle; The minimum distance reserved for the end point of the heat absorber and the evaporation section of the glass heat pipe.

[0006] Furthermore, the heat absorbing element includes a main metal layer and a selective absorption coating on both sides of the main metal layer. The overall thickness of the heat absorbing element is not greater than 3 mm. The calculation formula of the equivalent thermal expansion coefficient of the heat absorbing element is: , in: is the equivalent thermal expansion coefficient of the heat absorber, is the thermal expansion coefficient of the selective absorbing coating, is the elastic modulus of the selective absorbing coating, is the thickness of the selective absorbing coating, is the thermal expansion coefficient of the main metal layer, is the elastic modulus of the main metal layer, is the thickness of the main metal layer.

[0007] Furthermore, the heat absorbing component bracket is arranged at the lower part of the metal heat absorbing component for support, and the heat absorbing component bracket adopts a 60-degree arc base and is distributed at the front and rear ends of the heat absorbing component.

[0008] Furthermore, the heat absorbing component bracket is arranged on the left and right sides of the heat absorbing component to fix the heat absorbing component.

[0009] Another object of the present invention is to provide a method for processing the above-mentioned all-glass heat pipe type vacuum tube with built-in metal solid heat absorber, the method comprising the following steps: Step 1: One-step stamping to produce an integrated glass outer tube and glass heat pipe: The expansion coefficient is selected as 3.3×10⁻ 6 / ℃ 3.3 borosilicate glass is melted at a temperature of 1200-1300℃ through a high-temperature tube drawing process to draw a glass heat pipe with an outer diameter of 47mm and a wall thickness of 1.75mm and an integrated structure of 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 glass heat pipe. The condensation section of the glass heat pipe and the lower end of the glass outer tube are both open. An annular hole needs to be reserved in the glass outer tube to facilitate the subsequent vacuum process.

[0010] Step 2: Prefabrication and installation of metal heat absorbers: Processing width ,length The metal plate is pretreated on the surface, and then black film or blue film is selected and coated according to the process. After coating, the heat absorption component bracket is installed and installed by welding or fixing. Then the prefabricated heat absorption component and 20%±5% of the volume of the heat transfer medium are placed in the glass heat pipe.

[0011] Step 3: Welding and sealing of glass outer tube and glass heat pipe: The supporting parts, evaporative getter and other structures are installed in the glass outer tube, and then the opening of the glass heat pipe and the glass outer tube are heated to about 1200-1300°C for welding to form an integrated structure. After the welding is completed, annealing is performed to eliminate stress.

[0012] Step 4: Vacuuming: The annular hole on the glass outer tube is used as an exhaust channel. The air in the interlayer between the glass outer 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 started to activate the evaporative getter. The active barium metal released can adsorb the residual gas to ensure that the long-term vacuum degree of the interlayer between the glass outer tube and the glass heat pipe is maintained at 5×10⁻²Pa. After reaching the standard, the reserved annular hole is immediately sealed with a flame. After completion, the entire set of glass outer tube and glass heat pipe assembly needs to be annealed to eliminate processing stress.

[0013] Compared with the prior art, the present invention has the following beneficial effects: 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 seal, reduces the manufacturing cost, solves the poor thermal conductivity of glass, and solves the problem of tube explosion during the startup stage.

[0014] 2. After the heat absorber is built into the present invention, the coating is arranged on the metal heat absorber. After the heat is absorbed by the coating, the heat is transferred to the working fluid by short-flow convection heat exchange. This directly avoids deformation and damage of the glass heat pipe due to heat absorption. And because there is no direct connection between the heat absorber and the glass heat pipe, the problems described in the technical background due to the use of glass-metal connection are prevented from occurring. At startup, the metal heat absorber can also quickly transfer heat to prevent local overheating.

[0015] 3. Compared with the traditional vacuum heat collecting tube, the heat exchange efficiency of the all-glass heat pipe vacuum heat collecting tube with built-in heat absorbing parts is improved. Figure 2 It can be seen that the main difference between the two is that the heat conduction process is eliminated, efficient heat transfer is achieved, and the heat collection efficiency of the vacuum collector tube is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 : Schematic diagram of the all-glass heat pipe type vacuum heat collecting tube with built-in heat absorbing element of the present invention; Figure 2 : A comparison diagram of heat transfer modes between a conventional all-glass heat pipe type vacuum tube heat collector and an all-glass heat pipe type vacuum tube heat collector with a heat absorbing member provided in the present invention; Figure 3 : A schematic structural diagram of an embodiment of the present invention; Figure 4 : Figure 3 sectional view of; Figure 5 : Schematic diagram of the structure of screw fixing in this embodiment; Figure 6 : A schematic structural diagram of another embodiment of the present invention; Figure 7 : Figure 6 sectional view of; Figure 8 : Schematic diagram of the structure of screw fixing in this embodiment; Fig. 9 : A cross-sectional view of the screw fixation of this embodiment.

[0017] Meaning of the symbols in the attached drawings: 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 bracket; 7. Reserved screw holes; 8. Screws. DETAILED DESCRIPTION

[0018] In order 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.

[0019] Example 1

[0020] like Figure 1 As shown, the all-glass heat pipe type vacuum heat collecting tube with built-in heat absorption component of the present invention comprises 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 internal vacuum layer 3 of the glass outer tube 1, the condensation section 2-2 of the glass heat pipe extends outward from the glass outer tube 1, and the glass heat pipe has a working fluid 4 inside; a metal heat absorption component 5 is arranged in the evaporation section 2-2 of the glass heat pipe, and a heat absorption coating is coated on the metal heat absorption component.

[0021] A technical solid heat absorber coated with a selective absorption coating is placed in an all-glass heat pipe vacuum tube, and a heat transfer medium is placed in the heat pipe. During evaporation and condensation, the heat transfer medium surrounds the solid heat absorber and absorbs ultraviolet rays, thereby protecting the selective absorption coating from being oxidized and destroyed by strong oxidizing ultraviolet rays. The glass-metal seal is removed, reducing manufacturing costs. The glass does not participate in absorbing solar energy, thus avoiding thermal cracking during the startup phase.

[0022] The metal heat absorber is rectangular and made of steel or copper. It is plated with a selective absorption coating, which is a black or blue film. The metal is mainly made of steel.

[0023] The metal heat absorber is installed in the heat pipe through a movable bracket to avoid tearing due to the difference in thermal expansion.

[0024] The more important issue in 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 wide enough, because the heat absorber is the main heat absorbing part of the entire vacuum tube. If the working fluid cannot directly contact the heat absorber, heat transfer will not be possible, and the thermal efficiency will become extremely low, which greatly affects the thermal performance of the vacuum tube. However, its size cannot be too large. It is necessary to consider the thermal expansion of the metal heat absorber after absorbing heat, and reserve a certain amount of space to prevent the heat absorber from damaging the glass heat pipe after thermal expansion. The following is the calculation method for calculating the size of the heat absorber: Calculation of equivalent thermal expansion coefficient of heat absorber: The heat absorber is made of metal, with selective absorption coating on the left and right sides, similar to a sandwich structure. The coating is black or blue. The equivalent thermal expansion coefficient of the heat absorber is calculated as: , in: : Equivalent thermal expansion coefficient of the heat absorber; : Coefficient of thermal expansion of the selective absorbing coating; : elastic modulus of the selective absorption coating; : thickness of the selective absorption coating; : Thermal expansion coefficient of metal; : elastic modulus of metal; : The thickness of the metal.

[0025] Determination of the width of the heat absorber: Consider the thermal expansion of the heat absorber to prevent it from damaging the heat pipe. There is a formula: , in: : Width of heat absorber; : inner diameter of glass heat pipe; : Equivalent thermal expansion coefficient of the heat absorber; : Temperature change of the heat absorber.

[0026] Determination of the length of the heat absorber: The shadow method is used for calculation so that the heat absorber can completely cover the evaporation section of the heat pipe and all sunlight entering the heat pipe can reach the heat absorber. At the same time, the thermal expansion of the heat absorber must also be considered to prevent the heat absorber from damaging the bottom of the all-glass heat pipe due to thermal expansion.

[0027] The shadow method is used to calculate the length of the heat absorber. The formula is: , in: : Length of heat absorber; : Length of the evaporation section of the all-glass heat pipe; : The minimum solar altitude angle when the local conditions are the most unfavorable; : The heat pipe inclination angle is the local average solar altitude angle.

[0028] The length of the heat absorber has been determined by the shadow method. However, a certain distance must be reserved at the end of the evaporation section of the glass heat pipe. This is because the thermal expansion of the heat absorbing component is taken into consideration to prevent the heat absorbing component from thermally expanding and damaging the glass heat pipe. The calculation method is as follows: , in: : The minimum distance reserved between the heat absorber and the end point of the evaporation section of the glass heat pipe; : Length of heat absorber; : Equivalent thermal expansion coefficient of the heat absorber; : Temperature change of heat absorbing element; After calculation, we know that the length of the heat absorber is , and the heat absorber should be at a distance of , to prevent damage to the heat pipe due to thermal expansion.

[0029] The thickness of the heat absorber should be thin enough, and the overall thickness should not exceed 3mm. A thinner thickness of the heat absorber can ensure extremely high heat conduction efficiency. And a thinner thickness can ensure that the weight of the metal heat absorber is light, preventing the metal heat absorber from affecting the all-glass heat pipe structure. The specific size of the heat absorber can be determined by the above calculation method.

[0030] The arrangement of the heat absorber in the heat pipe is mainly to place it directly in the heat pipe. The heat absorber is fixed by setting a heat absorber bracket 6 on the heat absorber to keep it stable. The advantage of this design is that there is no connector between the metal heat absorber and the glass heat pipe, so there is no need to design a glass-metal connector, which reduces the cost and simplifies the manufacturing process. More importantly, it avoids problems such as deformation and damage caused by different thermal expansion coefficients. During production, the heat absorber can be installed by placing it in the glass heat pipe. The process is relatively simple and the cost is relatively low. The heat absorber is light in weight, so the fixation of it only needs to ensure that the position of the heat absorber does not shift.

[0031] The fixing method of the heat absorber is as follows: Figure 3 , the heat absorbing component bracket is arranged at the bottom of the heat absorbing component for support. Its cross-sectional view is as follows Figure 4 As shown. A 60-degree circular base is arranged at the bottom of the heat absorber, distributed at the front and back ends of the heat absorber. The base is not directly connected to the glass heat pipe and 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.

[0032] The bracket and the heat absorber can be connected by screw fixing and welding. If screw connection is adopted, corresponding screw holes 7 should be reserved on the solid metal heat absorber and the bracket, and the screws 8 can be directly screwed in to complete the fixation during installation. The specific structure is as follows Figure 5 shown.

[0033] The processing method of the above-mentioned all-glass heat pipe type vacuum tube with built-in metal solid heat absorbing element comprises the following steps: Step 1: One-step stamping to produce an integrated glass outer tube and glass heat pipe: The expansion coefficient is selected as 3.3×10⁻ 6 / ℃ 3.3 borosilicate glass is melted at a temperature of 1200-1300℃ through a high-temperature tube drawing process to draw a glass heat pipe with an outer diameter of 47mm and a wall thickness of 1.75mm and an integrated structure of 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 glass heat pipe. The condensation section of the glass heat pipe and the lower end of the glass outer tube are both open. An annular hole needs to be reserved in the glass outer tube to facilitate the subsequent vacuum process.

[0034] Step 2: Prefabrication and installation of metal heat absorbers: Processing width ,length The metal plate is pretreated on the surface, and then black film or blue film is selected and coated according to the process. After coating, the heat absorption component bracket is installed and installed by welding or fixing. Then the prefabricated heat absorption component and 20%±5% of the volume of the heat transfer medium are placed in the glass heat pipe.

[0035] Step 3: Welding and sealing of glass outer tube and glass heat pipe: The supporting parts, evaporative getter and other structures are installed in the glass outer tube, and then the opening of the glass heat pipe and the glass outer tube are heated to about 1200-1300°C for welding to form an integrated structure. After the welding is completed, annealing is performed to eliminate stress.

[0036] Step 4: Vacuuming: The annular hole on the glass outer tube is used as an exhaust channel. The air in the interlayer between the glass outer 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 started to activate the evaporative getter. The active barium metal released can adsorb the residual gas to ensure that the long-term vacuum degree of the interlayer between the glass outer tube and the glass heat pipe is maintained at 5×10⁻²Pa. After reaching the standard, the reserved annular hole is immediately sealed with a flame. After completion, the entire set of glass outer tube and glass heat pipe assembly needs to be annealed to eliminate processing stress.

[0037] Example 2

[0038] The difference between this embodiment and embodiment 1 is that the fixing method is as follows: Figure 6 , the heat absorbing member bracket 6 is arranged on the left and right sides of the heat absorbing member 5 to fix the heat absorbing member. The method for determining the size of the heat absorbing member is the same as that of Example 1 and will not be repeated. The brackets are arranged at the front and rear ends of the heat absorbing member respectively, and the brackets can ensure the fixation of the relative position of the heat absorbing member. Fixing the heat absorbing member on the left and right sides can prevent the heat absorbing member from being displaced.

[0039] This fixing method also has two ways to connect the heat absorber and the bracket. If welding is used, the cross-section diagram is as follows: Figure 7 If screw fixing is used, Figure 8 As shown, two screw holes 7 need to be reserved on the "T"-shaped bracket, and two screws 8 can be screwed in to complete the installation. The specific structure is as follows Figure 8 Its cross-sectional view is shown in Fig. 9 .

Claims

1. A full-glass heat pipe type vacuum tube with a built-in metal solid heat absorber, the full-glass heat pipe type vacuum heat collecting tube with a built-in heat absorber comprises a glass outer tube and a glass heat pipe, the evaporation section of the glass heat pipe is located in the inner vacuum layer of the glass outer tube, the condensation section of the glass heat pipe extends outward from the glass outer tube, and the glass heat pipe is filled with a working fluid; characterized in that: A metal heat absorbing member is arranged in the evaporation section of the glass heat pipe, and a heat absorbing coating is coated on the metal heat absorbing member. The metal heat absorbing member is fixed inside the glass heat pipe through a heat absorbing member bracket, and the width of the heat absorbing member is ,length , the minimum distance reserved between the heat absorber and the end point of the evaporation section of the glass heat pipe The following formula must be satisfied: ， ， ， in, is the width of the heat absorber, is the inner diameter of the glass heat pipe, is the equivalent thermal expansion coefficient of the heat absorber, is the temperature change of the heat absorber; is the length of the heat absorber, is the length of the evaporation section of the all-glass heat pipe, To obtain the minimum solar altitude angle under the most unfavorable local conditions, is the heat pipe inclination angle, taking the local average solar altitude angle; The minimum distance reserved for the end point of the heat absorber and the evaporation section of the glass heat pipe.

2. The all-glass heat pipe type vacuum tube with built-in metal solid heat absorber according to claim 1, characterized in that: The heat absorbing member includes a main metal layer and a selective absorption coating on both sides of the main metal layer. The overall thickness of the heat absorbing member is not greater than 3 mm. The calculation formula of the equivalent thermal expansion coefficient of the heat absorbing member is: ， in: is the equivalent thermal expansion coefficient of the heat absorber, is the thermal expansion coefficient of the selective absorbing coating, is the elastic modulus of the selective absorbing coating, is the thickness of the selective absorbing coating, is the thermal expansion coefficient of the main metal layer, is the elastic modulus of the main metal layer, is the thickness of the main metal layer.

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

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

5. A method for processing an all-glass heat pipe type vacuum tube with a built-in metal solid heat absorber according to any one of claims 1 to 4, characterized in that: The method comprises the following steps: Step 1: One-step stamping to produce an integrated glass outer tube and glass heat pipe: The expansion coefficient is selected as 3.3×10⁻ 6 / ℃ 3.3 borosilicate glass is melted at 1200-1300℃ through high temperature tube drawing process to draw into an integrated structure of glass heat pipe with outer diameter of 47mm and wall thickness of 1.75mm and glass outer tube with outer diameter of 58mm and wall thickness of 1.80mm. The glass outer tube is connected at nine-tenths of the glass heat pipe. The condensation section of the glass heat pipe and the lower end of the glass outer tube are both open. An annular hole needs to be reserved in the glass outer tube to facilitate the subsequent vacuum process. Step 2: Prefabrication and installation of metal heat absorbers: Processing width ,length The metal plate is pre-treated on the surface, and after completion, a black film or a blue film is selected, and the coating is performed according to the process. After the coating is completed, the heat absorbing component bracket is installed, and the installation is performed by welding or connecting with fixing parts, and then the prefabricated heat absorbing component and the heat transfer medium with a volume of 20%±5% are placed in the glass heat pipe; Step 3: Welding and sealing of glass outer tube and glass heat pipe: The supporting parts, evaporative getter and other structures are installed in the glass outer tube, and then the opening of the glass heat pipe and the glass outer tube are heated to about 1200-1300℃ for welding to form an integrated structure. After the welding is completed, annealing is performed to eliminate stress; Step 4: Vacuuming: The annular hole on the glass outer tube is used as an exhaust channel. The air in the interlayer between the glass outer 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 started to activate the evaporative getter. The active barium metal released can adsorb the residual gas to ensure that the long-term vacuum degree of the interlayer between the glass outer tube and the glass heat pipe is maintained at 5×10⁻²Pa. After reaching the standard, the reserved annular hole is immediately sealed with a flame. After completion, the entire set of glass outer tube and glass heat pipe assembly needs to be annealed to eliminate processing stress.

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