Low-temperature heat pipe filling device and method with carbon dioxide as working medium

Abstract

The invention discloses a low-temperature heat pipe filling device with carbon dioxide as a working medium and a method thereof.The filling device comprises a liquefying tank, the two sides of the top of the liquefying tank are provided with a dry ice input opening and a round pipe connector respectively, and the bottom of the liquefying tank is provided with a liquid filling pipe; the round pipe joint is respectively connected with a safety valve, a pressure gauge and a vacuum system through a ferrule type four-way pipe joint; the filling process comprises the steps of weighing and feeding dry ice, vacuumizing, sublimating and liquefying, filling and sealing. According to the invention, a cold trap device is not needed to reduce the saturated vapor pressure of carbon dioxide for liquefaction, the complexity of a filling device and an operation process is reduced, the operation is more convenient, and the energy consumption is also reduced; the filling amount of carbon dioxide can be accurately controlled; the filling device is suitable for various types of heat pipes, has no special requirement on the pipe diameter of the heat pipes, and can realize filling of micro-channel heat pipes and micro heat pipes.

Description

Technical Field

[0001] The present invention belongs to the technical field of heat pipe filling, and in particular relates to a low-temperature heat pipe filling device and method using carbon dioxide as a working fluid. Background Art

[0002] Carbon dioxide, as an environmentally friendly heat pipe working fluid, possesses excellent flow and heat transfer properties. At 0°C, its viscosity is 0.58 times that of ammonia and 0.055 times that of water, and its thermal conductivity is 1.4 times that of dichlorodifluoromethane. Its triple point is -56.4°C, and its critical temperature is 31.06°C. As a low-temperature heat pipe working fluid, carbon dioxide can achieve a lower lower operating temperature limit than most freons and ammonia. In its saturated state, carbon dioxide exhibits physical properties such as high latent heat, low viscosity, and low surface tension, enabling high heat flux transfer over small temperature gradients. These properties significantly reduce the size of heat pipes, making the system very compact and economical. Furthermore, carbon dioxide is non-toxic and non-flammable, remaining stable even at high temperatures and not decomposing to produce toxic substances. Therefore, carbon dioxide holds great promise as a low-temperature heat pipe working fluid.

[0003] At present, most heat pipes using carbon dioxide as the working fluid are filled by directly connecting to gas cylinders or gas storages. A cold trap device must be installed for pretreatment operations. The process is complex and the energy consumption is high, which leads to large-scale and complex equipment, and faces problems such as high-pressure leakage and low-temperature safety hazards.

[0004] Chinese patent application (201711348046.2) discloses a precise heat pipe refrigerant filling system and method. The system includes a component to be filled, a vacuum unit, a filling temperature and pressure measurement and control unit, a refrigerant storage unit, and a cold trap. The temperature and pressure measurement and control unit collects pressure and temperature information from the gas reservoir via a gas reservoir and a temperature and pressure acquisition mechanism to calculate and control the filling volume. The method controls the filling volume by calculating the pressure within the gas reservoir at the completion of filling based on the gas reservoir temperature and pressure and the mass of the gas refrigerant to be filled. This method requires connection to a gas reservoir for filling, making it difficult to pressurize the liquid refrigerant under normal conditions. Therefore, a cold trap must be used to reduce the saturated vapor pressure of the refrigerant for liquefaction and refilling.

[0005] In addition, Chinese patent (201910307312.X) discloses a low-temperature gravity heat pipe using carbon dioxide as the working fluid and its filling method. The pipe includes a one-way needle valve, a tube body, a Dewar flask, and male and female quick-release one-way valves. The filling method is divided into an emptying method and a vacuuming method. When filling using the emptying method, the male quick-release one-way valve is first opened. After adding dry ice, the heat pipe is inverted and the lower one-way needle valve is used to expel non-condensable gases. When filling using the vacuuming method, the heat pipe is first placed in a -60°C low-temperature Dewar flask to reduce the saturated vapor pressure of the working fluid. The male quick-release one-way valve is opened, dry ice is added, and then tightened to the female quick-release one-way valve. The pipe is connected to a molecular pump through a suction tube to evacuate the pipe to the specified vacuum level. After that, the vacuum system is disconnected to complete the filling. When filling using the emptying method described in this patent, the complete expulsion of non-condensable gases cannot be guaranteed, and the amount of carbon dioxide filled is extremely difficult to control. The vacuum filling method described in this patent requires the use of a -60°C low-temperature bath (cold trap), which increases operational complexity. Furthermore, both methods require dry ice to be placed directly inside the heat pipe shell before further operation, making them unsuitable for heat pipes with smaller diameters.

[0006] In summary, how to complete the quantitative filling of carbon dioxide heat pipes conveniently and efficiently while adapting to different heat pipe diameters is the current technical difficulty. Summary of the Invention

[0007] The purpose of the present invention is to overcome the shortcomings of existing heat pipe filling technology and provide a safe, simple and high-precision carbon dioxide heat pipe filling device and method to solve the problems of high cost, inconvenient operation, high energy consumption and poor safety of high-pressure filling in the prior art.

[0008] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0009] A low-temperature heat pipe filling device using carbon dioxide as the working fluid includes a liquefaction tank. A dry ice input port and a round pipe joint are respectively provided on both sides of the top of the liquefaction tank. A filling pipe is provided at the bottom of the liquefaction tank. The round pipe joint is connected to a safety valve, a pressure gauge and a vacuum system through a ferrule-type four-way pipe joint.

[0010] Furthermore, the liquefaction tank is the main body of the device, which is made of two stainless steel elliptical heads welded to a cylinder.

[0011] Furthermore, the dry ice input port is a short connecting pipe, and its upper port is sealed by a ferrule plug.

[0012] Furthermore, a first two-way ball valve is installed at the connection between the vacuum system and the ferrule-type four-way pipe joint.

[0013] Furthermore, the outlet of the liquid filling pipe is equipped with a second two-way ball valve.

[0014] A filling method for a low-temperature heat pipe filling device using carbon dioxide as a working fluid includes weighing and adding dry ice, vacuuming, sublimation and liquefaction, filling, and sealing. The specific process is as follows:

[0015] (a) Connect the heat pipe shell to the second two-way ball valve below the liquid filling pipe and adjust the two-way ball valve to the connected state. Then, remove the ferrule plug from the dry ice inlet and quickly add a certain amount of dry ice to the liquefied tank. After completion, reinstall the ferrule plug.

[0016] (b) Start the vacuum system in sequence, open the corresponding first and second-way ball valves, and quickly exhaust the air in the liquefied tank and the heat pipe cavity. When the absolute pressure displayed on the pressure gauge reaches a certain value, close the first and second-way ball valves and vacuum pump in the vacuum pipeline in sequence;

[0017] (c) Wait until the dry ice has been converted into gaseous or liquid carbon dioxide;

[0018] (d) Shake the device to ensure that the liquefied carbon dioxide flows into the heat pipe shell through the filling pipe by gravity, then close the second two-way ball valve connected to the filling pipe, and finally complete the sealing of the filling pipe.

[0019] Further, when the absolute pressure displayed on the pressure gauge reaches 10 -2 ~10 -1 After Pa, close the first two-way ball valve and the vacuum pump in sequence.

[0020] Furthermore, during the waiting phase, observe the changes in the pressure reading. When the reading stabilizes at the saturated vapor pressure of carbon dioxide corresponding to room temperature, 4.51 MPa (10°C) to 8.06 MPa (35°C), for a period of time, and the outer wall temperature of the liquefied tank remains consistent with room temperature, it indicates that all the dry ice has been converted into gaseous or liquid carbon dioxide.

[0021] Compared with the prior art, the present invention has the following advantages: no cold trap device is required to reduce the saturated vapor pressure of carbon dioxide for liquefaction, which reduces the complexity of the filling device and the operation process, makes the operation more convenient, and reduces energy consumption; the filling amount of carbon dioxide can be precisely controlled; it is suitable for various types of heat pipes, has no special requirements on the diameter of the heat pipe, and can realize the filling of microchannel heat pipes and micro heat pipes. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 3 is a structural diagram of a low-temperature heat pipe filling device using carbon dioxide as a working fluid in the present invention.

[0023] In the figure: 1-liquefied gas tank; 2-pressure gauge; 3-ferrule plug; 4-ferrule four-way pipe joint; 5-safety valve; 6-vacuum system; 7-ferrule joint; 8-second two-way ball valve; 9-first two-way ball valve; 10-dry ice inlet; 11-liquid filling pipe; 12-round pipe joint; 13-heat pipe; 14-dry ice. DETAILED DESCRIPTION

[0024] Example 1.

[0025] like Figure 1 As shown, a low-temperature heat pipe filling device using carbon dioxide as the working fluid consists of a liquefaction tank 1, a pressure gauge 2, a ferrule plug 3, a ferrule-type four-way pipe joint 4, a safety valve 5, a vacuum system 6, a ferrule joint 7, a second two-way ball valve 8, a first two-way ball valve 9, a dry ice inlet 10, a filling pipe 11, and a round pipe joint 12. The liquefaction tank 1 is the main body of the device, made by welding two stainless steel elliptical heads to a cylinder. The dry ice inlet 10 is a short pipe located on one side of the liquefaction tank's upper head and sealed by the ferrule plug 3. On the other side of the liquefaction tank's upper head, the safety valve 5, pressure gauge 2, and vacuum system 6 are connected via a ferrule-type four-way pipe joint 4 and a round pipe joint 12. The first two-way ball valve 9 is installed at the connection between the vacuum system 6 and the ferrule-type four-way pipe joint 4. The filling pipe 11 is located at the center of the liquefaction tank's lower head, and the outlet of the filling pipe 11 is equipped with a second two-way ball valve 8.

[0026] The liquefaction tank 1 is made of 304 stainless steel head and cylinder welded together. Since the working pressure of the liquefaction tank is 2~8 MPa, in order to ensure its mechanical strength, the wall thickness is calculated according to the following formula given in the "Regulations on Safety Technical Supervision of Stationary Pressure Vessels":

[0027]

[0028] Where, δ is the wall thickness of the liquefied tank 1, P c is the design pressure of the liquefied tank. To meet safety requirements, the design pressure is set to 10 MPa. i is the inner diameter of the liquefied tank 1, [σ] t is the allowable stress of the pipe of liquefied tank 1, and Φ is the welding joint coefficient.

[0029] The safety valve 5 can automatically open and release pressure according to the set value (8-10 MPa) when the pressure in the liquefied tank 1 is about to rise to the design pressure, thereby ensuring operational safety.

[0030] The low-temperature heat pipe filling device of this embodiment uses carbon dioxide as the working fluid, and is used for filling small and medium-sized heat pipes with a carbon dioxide filling amount of less than 300g.

[0031] As the preferred embodiment of this invention:

[0032] The cylinder diameter of the liquefaction tank 1 is 63 mm and the length is 100 mm. The head adopts a standard elliptical head and the cylinder wall thickness is 4 mm. A hole is opened on each side of the upper head for welding the dry ice input port 10 and the round pipe joint, and a hole is opened in the center of the lower head for welding the liquid filling pipe 11.

[0033] The safety valve 5 is adjusted to set the safety relief pressure value to 10 MPa.

[0034] The vacuum system 6 uses a rotary vane vacuum oil pump with a maximum vacuum degree of 10 -2 Pa.

[0035] The first two-way ball valve 9 and the second two-way ball valve 8 are two-way ball valves with an interface pipe diameter of 6 mm.

[0036] The dry ice inlet 10 has a length of 50 mm, an outer diameter of 14 mm, and a wall thickness of 2 mm, and can conveniently input columnar dry ice blocks with a diameter of about 3 mm.

[0037] The liquid filling tube 11 has a length of 50 mm, a diameter of 6 mm, and a wall thickness of 1 mm, ensuring that liquid carbon dioxide can flow smoothly into the interior of the heat pipe.

[0038] Example 2

[0039] As described in Example 1, a low-temperature heat pipe filling device using carbon dioxide as a working fluid is used to fill a single-loop carbon dioxide heat pipe (total length 1400 mm, diameter 10×1.5 mm, intended filling volume 8.2 g, corresponding to a filling rate of 25% of the internal volume of the shell) in the following specific method:

[0040] 1) Connect the heat pipe housing 13 to the second two-way ball valve 8 below the liquid filling pipe 11 and adjust the second two-way ball valve 8 to a connected state. Then, remove the ferrule plug 3 from the dry ice inlet 10 and quickly add a fixed amount of dry ice 14 to the liquefaction tank 1. Once completed, reinstall the ferrule plug 3. The amount of dry ice 14 added is 50g.

[0041] 2) Start the vacuum system 6 in sequence, open the corresponding first two-way ball valve 9, and quickly discharge the air in the liquefied tank 1 and the heat pipe cavity. When the absolute pressure displayed on the pressure gauge 2 reaches 10 -1 After Pa, the first two-way ball valve 9 and the vacuum pump in the vacuum line are closed in sequence. Since the vacuuming process lasts for a short time (2 minutes), only a very small amount of dry ice 14 sublimates into carbon dioxide gas during this process and is discharged from the liquefaction tank 1.

[0042] 3) Due to the relatively low temperature of the dry ice 14 inside liquefaction tank 1, heated by the surrounding air, the dry ice 14 will slowly sublime, causing the pressure inside tank 1 to continue to rise. When the pressure inside the tank reaches the saturated vapor pressure of carbon dioxide corresponding to room temperature, the gaseous carbon dioxide begins to liquefy. Therefore, during this waiting period, observe the changes in the reading on pressure gauge 2. When the reading stabilizes at the saturated vapor pressure of carbon dioxide corresponding to room temperature (30°C) (7.21 MPa) for a period of time, and the outer wall temperature of liquefaction tank 1 remains consistent with room temperature, it indicates that all dry ice 14 has been converted to gaseous or liquid carbon dioxide.

[0043] 4) Gently shake the filling device to ensure that the liquefied carbon dioxide can flow into the heat pipe shell 13 through the filling pipe 11 by gravity, then close the second two-way ball valve 8 connected to the filling pipe 11. Finally, clamp the filling pipe 11 with hydraulic clamps and spot weld it to complete the sealing.

[0044] In this embodiment, a low-temperature heat pipe filling device and method using carbon dioxide as a working medium is provided. The total amount of dry ice input is m 总 The actual filling volume m1 that you want to fill into the heat pipe (related to the working fluid filling rate of the heat pipe), the vapor mass m2 of the carbon dioxide in the saturated state inside the liquefied tank 1, and the dissipation of dry ice sublimation during the vacuuming process should be considered, so m 总 =1.1-1.3×(m1+m2). Ultimately, this example filled the single-loop heat pipe with 7.7g of carbon dioxide, within 6% of the intended charge. Experimental testing showed that the single-loop carbon dioxide heat pipe immediately began operating when the condensing section temperature fell below the evaporating section temperature, exhibiting excellent thermal response and stable performance. The total heat transfer resistance in the steady-state phase was less than 0.1 K / W.

[0045] The above shows and describes the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the scope of protection of the present invention in any form. All technical solutions obtained by equivalent substitution, etc., fall within the scope of protection of the present invention. Parts not covered by the present invention are the same as the existing technology or can be implemented using existing technology.

Claims

1. A low-temperature heat pipe filling device using carbon dioxide as a working fluid, comprising a liquefaction tank (1), characterized in that: Dry ice inlets (10) and round pipe joints (12) are respectively provided on both sides of the top of the liquefaction tank (1), and a liquid filling pipe (11) is provided at the bottom of the liquefaction tank (1). The round pipe joint (12) is respectively connected to a safety valve (5), a pressure gauge (2) and a vacuum system (6) via a ferrule-type four-way pipe joint (4).

2. A low-temperature heat pipe filling device using carbon dioxide as a working fluid according to claim 1, characterized in that: The liquefaction tank (1) is the main body of the device and is formed by welding two stainless steel elliptical heads to a cylinder.

3. The low-temperature heat pipe filling device using carbon dioxide as a working fluid according to claim 1, characterized in that: The dry ice input port (10) is a short pipe, the upper port of which is sealed by a ferrule plug (3).

4. The low-temperature heat pipe filling device using carbon dioxide as a working fluid according to claim 1, characterized in that: A first two-way ball valve (9) is installed at the connection between the vacuum system (6) and the ferrule-type four-way pipe joint (4).

5. The low-temperature heat pipe filling device using carbon dioxide as a working fluid according to claim 1, characterized in that: The outlet of the liquid filling pipe (11) is equipped with a second two-way ball valve (8).

6. A filling method for a low-temperature heat pipe filling device using carbon dioxide as a working fluid as claimed in claim 1, characterized in that: The filling process includes weighing and adding dry ice, vacuuming, sublimation and liquefaction, filling and sealing. The specific process is as follows: (a) Connect the heat pipe shell (13) to the second two-way ball valve (8) below the liquid filling pipe (11), and adjust the two-way ball valve (8) to a connected state; then, remove the ferrule plug (3) from the dry ice inlet (10), and quickly add a certain amount of dry ice into the liquefied tank (1). After completion, reinstall the ferrule plug (3); (b) starting the vacuum system (6) in sequence, opening the corresponding first two-way ball valve (9), and quickly exhausting the air in the liquefied tank (1) and the heat pipe cavity. When the absolute pressure displayed on the pressure gauge (2) reaches a certain value, closing the first two-way ball valve (9) and the vacuum pump in the vacuum pipeline in sequence; (c) Wait until the dry ice has been converted into gaseous or liquid carbon dioxide; (d) Shake the device to ensure that the liquefied carbon dioxide flows into the heat pipe shell (13) through the liquid filling pipe (11) by gravity, then close the second two-way ball valve (8) connected to the liquid filling pipe (11), and finally complete the sealing of the liquid filling pipe (11).

7. The filling method of a low-temperature heat pipe filling device using carbon dioxide as a working fluid according to claim 6, characterized in that: When the absolute pressure displayed on the pressure gauge (2) reaches 10 -2 ~10 -1 After Pa, close the first two-way ball valve (9) and the vacuum pump in sequence.

8. The filling method of a low-temperature heat pipe filling device using carbon dioxide as a working fluid according to claim 6, characterized in that: During the waiting phase, observe the changes in the pressure reading. When the reading stabilizes at the saturated vapor pressure of carbon dioxide corresponding to room temperature, 4.51MPa (10°C) to 8.06MPa (35°C), for a period of time, and the outer wall temperature of the liquefied tank remains consistent with room temperature, it means that all the dry ice has been converted into gaseous or liquid carbon dioxide.

Images