Flexible uniform-temperature plate based on 3D printing combined imprinting technology and preparation method of flexible uniform-temperature plate

Abstract

The invention discloses a flexible uniform-temperature plate based on a 3D printing combined imprinting technology and a preparation method of the flexible uniform-temperature plate. The invention discloses a flexible vapor chamber of a 3D printing combined imprinting technology. The flexible vapor chamber comprises an upper cover made of a flexible heat conduction material, a lower cover made of a flexible heat conduction material, an FEP film and a liquid absorption core, the upper cover, the liquid absorbing core and the lower cover are overlapped from top to bottom, an FEP film is clamped between the upper cover and the lower cover, and the FEP film is located on the periphery of the liquid absorbing core; a pore structure is arranged on the liquid absorbing core; a vertical steam flowing space and a horizontal steam flowing space which are alternately arranged are arranged on the liquid absorbing core, are communicated with each other and are butted and communicated with the pore structure; and the upper ends of the vertical steam flowing space and the horizontal steam flowing space are opened. On one hand, the steam flowing path can be more regular, and the steam flowing resistance is reduced; and on the other hand, the mutually connected supporting structures are better in structural strength in the bending process.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible heat dissipation materials, and in particular to a flexible temperature homogenizing plate and a preparation method thereof. Background Art

[0002] As electronic devices develop towards high power and flexibility, heat dissipation has increasingly become a bottleneck in technological progress. Traditional rigid heat sinks cannot adapt to curved surfaces or bendable structures, making them difficult to directly apply to flexible electronic devices, limiting the further development of the devices.

[0003] Flexible heat dissipation technology has therefore become a hot topic of research, using flexible materials to adapt to the shapes and sizes of different devices while providing effective heat dissipation performance. This technology is particularly critical for bendable electronic devices because it can effectively disperse heat and improve heat dissipation efficiency, thereby ensuring the stability and reliability of the device.

[0004] Although some solutions have been proposed, the life and reliability of flexible heat sinks (also known as flexible temperature spreaders) remain major challenges. Existing technologies for preparing capillary wick structures are still mostly sintered at high temperatures in a vacuum environment (or nitrogen environment), and copper mesh sintering is generally used to prepare porous structures. However, this method is limited in the choice of flexible substrate materials, and is more expensive than in an air environment, and has limitations in improving wicking performance.

[0005] In addition, the support structure of the existing flexible temperature equalizer is mostly prepared by CNC processing on the upper cover plate, and is fitted with the lower cover covered with the liquid wick to form a vacuum chamber. However, this connection method leads to the problem of increased contact thermal resistance.

[0006] In addition, the existing flexible temperature equalizer support structure generally adopts a raised cylinder or square column, and the rest of the support structure is a steam flow space. On the one hand, the steam expansion flow space is disordered, resulting in greater resistance; on the other hand, during the bending process, the support structure is more easily damaged. Summary of the invention

[0007] In view of the problems existing in the prior art, the present invention provides a flexible temperature equalizing plate of 3D printing combined with imprinting technology and a preparation method thereof, which has solved at least one of the above-mentioned technical problems.

[0008] The technical solution of the present invention is: a flexible temperature-averaging plate of 3D printing combined with embossing technology, characterized in that it comprises an upper cover of a flexible thermally conductive material, a lower cover of a flexible thermally conductive material, a FEP film and a liquid-absorbing core;

[0009] The upper cover, the liquid absorbent core and the lower cover are overlapped from top to bottom, and the FEP film is sandwiched between the upper cover and the lower cover. The FEP film is located at the periphery of the liquid absorbent core. The FEP film is used to melt and adhere the upper cover and the lower cover to form a steam cavity, and a coolant is arranged in the steam cavity;

[0010] The liquid wick is located in the steam chamber;

[0011] The liquid wick is formed by embossing a thin layer formed by copper ion ink through a cavity mold with ribs formed by 3D printing;

[0012] The liquid wick is provided with a pore structure;

[0013] The liquid absorbent core is provided with alternately arranged vertical steam flow spaces and horizontal steam flow spaces, the vertical steam flow spaces and the horizontal steam flow spaces are interconnected and connected to the pore structure.

[0014] The present invention optimizes the structure of the liquid absorbent core, and uses the alternately arranged vertical steam flow space and horizontal steam flow space as the steam flow space, and the remaining space of the liquid absorbent core as the porous support structure. On the one hand, this advantage can make the steam flow path more regular and reduce the steam flow resistance; on the other hand, the interconnected support structure has better structural strength during the bending process. Compared with the solid support structure, the liquid absorbent core with a porous structure of the present invention has a better condensation effect on steam.

[0015] Further preferably, the absorbent core is provided with at least three steam flow spaces arranged along the width direction;

[0016] Adjacent steam flow spaces are separated by support structures;

[0017] The steam flow space is arranged in sequence along the length direction with the vertical steam flow space and the horizontal steam flow space being alternately arranged;

[0018] The length direction of each steam flow space is parallel to the length direction of the absorbent core and parallel to the horizontal steam flow space;

[0019] The upper ends of the vertical steam flow space and the horizontal steam flow space are both open.

[0020] Further preferably, the volume of the cooling liquid accounts for 30% to 80% of the volume of the steam chamber.

[0021] Further preferably, the coolant is deionized water or thermal oil.

[0022] Further preferably, the material of the upper cover is copper foil, copper polyimide or polyimide;

[0023] The material of the lower cover is copper foil, copper polyimide or polyimide.

[0024] Further preferably, the porosity of the liquid absorbent core is greater than 50%, and the pore size of the pore structure is less than 20 μm;

[0025] Further preferably, the outer surface of the liquid-absorbing core is provided with a nanoscale papillary structure.

[0026] Further preferably, the thickness of the upper cover is 20 μm, and the thickness of the lower cover is 50 μm.

[0027] A method for preparing a flexible temperature-averaging plate using 3D printing combined with embossing technology, characterized in that it comprises the following steps:

[0028] Step 1, preparing the upper cover and the lower cover;

[0029] Step 2: Prepare a cavity mold with ribs by 3D printing;

[0030] Step 3, using copper ion ink to prepare a copper ion ink thin layer;

[0031] Step 4, using a cavity mold to emboss a thin layer of copper ion ink to prepare a liquid wick;

[0032] Step 5, the upper cover, the FEP film, the wick and the lower cover are assembled, the FEP film is melted, and the upper cover and the lower cover are attached together to form a steam chamber;

[0033] Step 6: After the steam chamber is evacuated, coolant is injected and the steam chamber is sealed.

[0034] Further preferably, in the step three, the copper ion ink is prepared by uniformly mixing micron copper particles, copper formate tetrahydrate, isobutanolamine, anhydrous ethanol, ethylene glycol and glucose using a magnetic stirrer at 600 r / min for 3 hours.

[0035] Copper formate, as a precursor, can be reduced to nano copper particles at a temperature below 300°C and sintered with pre-added micron copper particles to form a porous structure. Isobutanolamine, as a ligand, forms a complex with the central copper ion, lowers the reduction temperature, and makes the porous structure have a higher porosity. Ethylene glycol and glucose provide a reducing environment, hinder excessive oxidation during low-temperature sintering, and weaken the structural strength and thermal conductivity caused by oxidation.

[0036] Further preferably, in step three, a tape with a thickness of 500 μm and a width of 5 mm is adhered to the four sides of the lower cover, the prepared copper ion ink is poured into the reserved space on the lower cover within the area surrounded by the tape, the copper ion ink is evenly scraped with a scraper, and then the tape around the lower cover is removed, retaining the ink film in the reserved space.

[0037] Further preferably, in step 4, the cavity mold is vertically placed on the lower cover, and the lower cover is placed on a constant temperature heating plate to preliminarily dry the ink film, and the cavity mold is removed, at which time, the ink film of the lower cover is formed;

[0038] The lower cover formed with the ink film is placed in a muffle furnace, the temperature is raised to 250-300° C., and maintained for 25-35 minutes, and then cooled naturally to prepare a liquid absorbent core with a porous structure.

[0039] Further preferably, in step six, at least one of the upper cover and the lower cover is provided with an opening connected to the steam chamber, or a needle tube is sandwiched between the upper cover and the lower cover, and the inner hole of the needle tube is used as the opening connected to the steam chamber;

[0040] Connect the vacuum pump through the opening and use the vacuum pump to evacuate the steam chamber to a vacuum pressure of 10^-3 to 10^-2 standard atmospheric pressure (atm);

[0041] After the steam chamber is evacuated, coolant is injected into the steam chamber through the opening;

[0042] After filling is complete, close the opening.

[0043] The purpose of vacuuming is to remove air and moisture from the steam chamber to prevent bubbles from being generated during the heat exchange process and ensure the heat exchange efficiency. It also allows the coolant in the steam chamber to reach the boiling point at a lower temperature and utilize the latent heat of phase change in advance.

[0044] The volume of the injected coolant should be controlled between 30% and 80% of the volume of the steam chamber to ensure that there is enough space for the condensation and reflux of the steam.

[0045] By closing the opening, the sealing of the steam chamber is ensured to prevent leakage of the coolant.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] 1) The present invention simplifies the preparation process of the flexible temperature homogenizing plate and reduces the cost; and utilizes the pores of the supporting structure to enhance the condensation process of the steam, thereby significantly improving the heat transfer performance of the temperature homogenizing plate.

[0048] The 20 interconnected regularized steam spaces provide a standardized flow path for the steam expansion process, reducing resistance, and the interconnected support structures are stronger than separate raised rib column structures.

[0049] 3) The liquid-absorbing core is provided with a micron pore structure and a nano-papillary structure, and has ultrafast fluid transport capability.

[0050] 4) Compared with traditional flexible heat sinks, the flexible heat spreader of the present invention can still maintain good heat dissipation performance and mechanical stability after repeated bending, significantly improving the heat dissipation efficiency and reliability of flexible electronic devices. It is expected to provide design ideas for flexible heat spreaders and provide new ideas for flexible heat dissipation materials with high efficiency and low manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 This is an exploded view of a flexible temperature homogenizing plate according to a specific embodiment 1 of the present invention;

[0052] Figure 2 A cross-sectional view of a flexible temperature homogenizing plate according to a specific embodiment 1 of the present invention;

[0053] Figure 3 A top view of the liquid absorbent core of specific embodiment 1 of the present invention;

[0054] Figure 4 A schematic structural diagram of a cavity mold according to a specific embodiment 1 of the present invention;

[0055] Figure 5 It is a bottom view of the cavity mold of the specific embodiment 1 of the present invention;

[0056] Figure 6 This is a SEM photograph of the pore structure of the liquid absorbent core of the present invention at a magnification of 5000;

[0057] Figure 7 This is a SEM photograph of the pore structure of the liquid absorbent core of the present invention at 400 times magnification;

[0058] Figure 8 The SEM photograph of the outer surface of the liquid-absorbing core of the present invention at a magnification of 50,000 shows a nanoscale papillary structure.

[0059] In the figure, 1 is an upper cover, 2 is a liquid wick, 3 is a FEP film, 4 is a lower cover, 5 is a cavity mold, 21 is a supporting structure, 22 is a vertical steam flow space, 23 is a horizontal steam flow space, 52 is a vertical molding column, and 53 is a horizontal molding column. DETAILED DESCRIPTION

[0060] See also Figures 1 to 8, Specific embodiment 1, a flexible temperature equalizing plate of 3D printing combined with embossing technology, comprising an upper cover 1 of a flexible thermal conductive material, a lower cover 4 of a flexible thermal conductive material, a FEP film 3 and a liquid absorbent core 2; the upper cover 1, the liquid absorbent core 2 and the lower cover 4 are overlapped from top to bottom, and a FEP film 3 is sandwiched between the upper cover 1 and the lower cover 4, and the FEP film 3 is located on the periphery of the liquid absorbent core 2. The FEP film melts at about 270°C. The FEP film 3 is used to melt and bond the upper cover 1 and the lower cover 4, thereby enclosing a steam cavity, in which a coolant is arranged; the liquid absorbent core 2 is located in the steam cavity; the liquid absorbent core 2 is formed by embossing a thin layer formed by copper ion ink with a cavity mold 5 with ribs formed by 3D printing; a pore structure is arranged on the liquid absorbent core 2; the liquid absorbent core 2 is provided with alternately arranged vertical steam flow spaces 22 and horizontal steam flow spaces 23, and the vertical steam flow spaces 22 and the horizontal steam flow spaces 23 are mutually conductive, and are connected to the pore structure. The present invention optimizes the structure of the liquid absorbent core 2, and uses the alternately arranged vertical steam flow space 22 and horizontal steam flow space 23 as the steam flow space, and the remaining space of the liquid absorbent core 2 as the porous support structure 21. On the one hand, this advantage can make the steam flow path more regular and reduce the steam flow resistance; on the other hand, the interconnected support structure 21 has better structural strength during the bending process. Compared with the solid support structure 21, the liquid absorbent core 2 with a porous structure of the present invention has a better condensation effect on steam.

[0061] At least three steam flow spaces arranged along the width direction are provided on the liquid absorbent core 2; adjacent steam flow spaces are separated by a support structure 21; the steam flow spaces are arranged in sequence along the length direction with alternating vertical steam flow spaces 22 and horizontal steam flow spaces 23; the length direction of each steam flow space is parallel to the length direction of the liquid absorbent core 2 and parallel to the horizontal steam flow space 23. The upper ends of the vertical steam flow space 22 and the horizontal steam flow space 23 are both open. The vertical steam flow space 22 is a circular groove with an opening at the upper end. The horizontal steam flow space is a strip groove with an opening at the upper end. The inner diameter of the circular groove is greater than the width direction of the strip groove. The width direction refers to the direction of the short side. The length direction refers to the direction of the long side. The steam flow space is formed by rib embossing of a cavity mold with ribs.

[0062] The inner diameter of the vertical steam flow space 22 is 100-200 μm, and the width of the strip groove is 20-50 μm.

[0063] The depth of the steam flow space is 300um. The spacing between adjacent vertical steam flow spaces in the length direction of the steam flow space is greater than the inner diameter value of the vertical steam flow space.

[0064] The lower cover is provided with an annular groove. The annular groove is located at the periphery of the placement area of ​​the liquid absorbent core. The annular groove is used to embed the melted FEP film to improve the sealing effect.

[0065] The volume of the coolant occupies 30% to 80% of the volume of the steam chamber.

[0066] The coolant is deionized water or thermal oil.

[0067] The material of the upper cover 1 is copper foil, copper polyimide or polyimide; the material of the lower cover 4 is copper foil, copper polyimide or polyimide.

[0068] The thickness of the upper cover 1 is 20 μm, the thickness of the lower cover 4 is 50 μm, and the thickness of the liquid wick is 500 μm.

[0069] See also Figure 6 as well as Figure 7 , the porosity of the liquid absorbent core 2 is greater than 50%, and the pore size of the pore structure is less than 20 μm;

[0070] See also Figure 8 The outer surface of the liquid-absorbing core 2 is provided with a nano-scale papillary structure.

[0071] During the stamping process, the ink film formed by the copper ion ink adheres to the upper side of the lower cover;

[0072] The cavity mold 5 is placed vertically on the lower cover 4, and the lower cover 4 is placed on a constant temperature heating plate to preliminarily dry the ink film, and the cavity mold 5 is removed. At this time, the ink film of the lower cover 4 is formed; the lower cover 4 with the formed ink film is placed in a muffle furnace and allowed to cool naturally to prepare a liquid absorbent core 2 with a porous structure.

[0073] A method for preparing a flexible temperature-averaging plate using 3D printing combined with embossing technology, characterized in that it comprises the following steps:

[0074] Step 1, preparing an upper cover 1 and a lower cover 4;

[0075] Step 2: Prepare a cavity mold 5 with ribs by 3D printing;

[0076] Step 3, using copper ion ink to prepare a copper ion ink thin layer;

[0077] Step 4, using the cavity mold 5 to emboss the copper ion ink thin layer to prepare the liquid absorbent core 2;

[0078] Step 5: Assemble the upper cover 1, the FEP film 3, the wick 2 and the lower cover 4, melt the FEP film 3, and fit the upper cover 1 and the lower cover 4 together to form a steam chamber;

[0079] Step 6: After the steam chamber is evacuated, coolant is injected and the steam chamber is sealed.

[0080] In step three, the copper ion ink is made by uniformly mixing micron copper particles, copper formate tetrahydrate, isobutanolamine, anhydrous ethanol, ethylene glycol and glucose by a magnetic stirrer at 600r / min for 3h. Specifically, the copper ion ink is made of micron copper particles, copper complex (the copper complex includes copper formate tetrahydrate and isobutanolamine, and the chemical dosage ratio of copper formate tetrahydrate to isobutanolamine is 1:1~1:3), and antioxidant organic solution (the antioxidant organic solution includes anhydrous ethanol, ethylene glycol and glucose, and the mass percentage of anhydrous ethanol in the antioxidant organic solution is 25%~60%, the mass percentage of ethylene glycol in the antioxidant organic solution is 60%~25%, and the mass percentage of glucose in the antioxidant organic solution is 15%). The mass percentage of micron copper particles in the copper ion ink is 45%, the mass percentage of copper complex in the copper ion ink is 25%, and the mass percentage of antioxidant organic solution in the copper ion ink is 30%.

[0081] Copper formate, as a precursor, can be reduced to nano copper particles at a temperature below 300°C and sintered with pre-added micron copper particles to form a porous structure. Isobutanolamine, as a ligand, forms a complex with the central copper ion, lowers the reduction temperature, and makes the porous structure have a higher porosity. Ethylene glycol and glucose provide a reducing environment, hinder excessive oxidation during low-temperature sintering, and weaken the structural strength and thermal conductivity caused by oxidation.

[0082] In step 3, a tape with a thickness of 500 μm and a width of 5 mm is attached to the periphery of the lower cover 4, and the prepared copper ion ink is poured into the reserved space on the lower cover 4 in the area surrounded by the tape, and the copper ion ink is evenly scraped by a scraper, and then the tape around the lower cover 4 is removed, leaving the ink film in the reserved space. The tape is adhered to the annular groove area of ​​the lower cover.

[0083] In step 4, a molding cavity is provided in the center of the cavity mold 5, and a rib column for molding a steam flow space is fixed in the molding cavity. The rib column includes a vertical molding column 52 for molding a vertical steam flow space 22 and a horizontal molding column 53 for molding a horizontal steam flow space 23. The vertical molding column 52 and the horizontal molding column 53 are alternately arranged and connected. The bottom of the rib column is higher than the bottom of the molding cavity. The inner wall of the molding cavity and the outer contour of the ink film are nested in an aligned manner.

[0084] In step 4, the cavity mold 5 is placed vertically on the lower cover 4, and the lower cover 4 is placed on a constant temperature heating plate at 90°C for 10 minutes to allow the ink film to be initially dried, and the cavity mold 5 is removed. At this time, the ink film of the lower cover 4 is formed; the lower cover 4 with the ink film is placed in a muffle furnace, and the temperature is increased to 300°C at a heating rate of 5°C / min, and maintained for 30 minutes. After it is naturally cooled, a liquid absorbent core 2 with a porous structure is prepared.

[0085] In step 6, at least one of the upper cover 1 and the lower cover 4 is provided with an opening for connecting to the steam chamber, or a needle tube is sandwiched between the upper cover 1 and the lower cover 4, with the inner hole of the needle tube as the opening for connecting to the steam chamber; a vacuum pump is connected through the opening, and the steam chamber is evacuated using the vacuum pump, and the evacuation pressure reaches 10^-3 to 10^-2 standard atmospheric pressure (atm); after the steam chamber is evacuated, coolant is injected into the steam chamber through the opening. After the injection is completed, the opening is closed.

[0086] The purpose of vacuuming is to remove air and moisture from the steam chamber to prevent bubbles from being generated during the heat exchange process and ensure the heat exchange efficiency. It also allows the coolant in the steam chamber to reach the boiling point at a lower temperature and utilize the latent heat of phase change in advance.

[0087] The volume of the injected coolant should be controlled between 30% and 80% of the volume of the steam chamber to ensure that there is enough space for the condensation and reflux of the steam.

[0088] By closing the opening, the sealing of the steam chamber is ensured to prevent leakage of the coolant.

[0089] The above are only preferred embodiments of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A flexible temperature plate with 3D printing and embossing technology, characterized in that: It includes an upper cover made of a flexible thermal conductive material, a lower cover made of a flexible thermal conductive material, a FEP film, and a liquid wick; The upper cover, the liquid absorbent core and the lower cover are overlapped from top to bottom, and the FEP film is sandwiched between the upper cover and the lower cover. The FEP film is located at the periphery of the liquid absorbent core. The FEP film is used to melt and adhere the upper cover and the lower cover to form a steam cavity, and a coolant is arranged in the steam cavity; The liquid wick is located in the steam chamber; The liquid wick is formed by embossing a thin layer formed by copper ion ink through a cavity mold with ribs formed by 3D printing; The liquid wick is provided with a pore structure; The liquid absorbent core is provided with alternately arranged vertical steam flow spaces and horizontal steam flow spaces, the vertical steam flow spaces and the horizontal steam flow spaces are interconnected and connected to the pore structure.

2. The flexible temperature balancing plate of 3D printing combined with embossing technology according to claim 1, characterized in that: The liquid absorbent core is provided with at least three steam flow spaces arranged along the width direction; Adjacent steam flow spaces are separated by support structures; The steam flow space is arranged in sequence along the length direction with the vertical steam flow space and the horizontal steam flow space being alternately arranged; The length direction of each steam flow space is parallel to the length direction of the absorbent core and parallel to the horizontal steam flow space; The upper ends of the vertical steam flow space and the horizontal steam flow space are both open.

3. The flexible temperature balancing plate of 3D printing combined with embossing technology according to claim 1, characterized in that: The volume of the cooling liquid accounts for 30% to 80% of the volume of the steam chamber.

4. The flexible temperature balancing plate of 3D printing combined with embossing technology according to claim 1, characterized in that: The porosity of the liquid absorbent core is greater than 50%, and the pore size of the pore structure is less than 20 μm.

5. The flexible temperature-averaging plate of 3D printing combined with embossing technology according to claim 1, characterized in that: The outer surface of the liquid-absorbing core is provided with a nanometer-scale papillary structure.

6. The flexible temperature balancing plate of 3D printing combined with embossing technology according to claim 1, characterized in that: The thickness of the upper cover is 20 μm, and the thickness of the lower cover is 50 μm.

7. The method for preparing a flexible temperature-averaging plate using 3D printing combined with embossing technology according to claim 1, characterized in that: The following steps are involved: Step 1, preparing an upper cover and a lower cover; Step 2: Prepare a cavity mold with ribs by 3D printing; Step 3, using copper ion ink to prepare a copper ion ink thin layer; Step 4, using a cavity mold to emboss a thin layer of copper ion ink to prepare a liquid wick; Step 5, the upper cover, the FEP film, the wick and the lower cover are assembled, the FEP film is melted, and the upper cover and the lower cover are attached together to form a steam chamber; Step 6: After the steam chamber is evacuated, coolant is injected and the steam chamber is sealed.

8. The method for preparing a flexible temperature-averaging plate using 3D printing combined with embossing technology according to claim 7, characterized in that: In step three, the tape is adhered to the four sides of the lower cover, and the prepared copper ion ink is poured into the reserved space on the lower cover within the area surrounded by the tape. The copper ion ink is evenly applied with a scraper, and then the tape around the lower cover is removed to retain the ink film in the reserved space.

9. The method for preparing a flexible temperature-averaging plate using 3D printing combined with embossing technology according to claim 8, characterized in that: In step 4, the cavity mold is placed vertically on the lower cover, and the lower cover is placed on a constant temperature heating plate to preliminarily dry the ink film, and the cavity mold is removed. At this time, the ink film of the lower cover is formed; The lower cover formed with the ink film is placed in a muffle furnace, the temperature is raised to 250-300°C, and maintained for 25-35 minutes, and then cooled naturally to prepare a liquid absorbent core with a porous structure.

10. The method for preparing a flexible temperature-averaging plate using 3D printing combined with embossing technology according to claim 7, characterized in that: In step 6, at least one of the upper cover and the lower cover is provided with an opening connected to the steam chamber, or a needle tube is sandwiched between the upper cover and the lower cover, and the inner hole of the needle tube is used as the opening connected to the steam chamber; Connect the vacuum pump through the opening, and use the vacuum pump to evacuate the steam chamber, and the evacuation pressure reaches 10^-3 to 10^-2 standard atmospheric pressure; After the steam chamber is evacuated, coolant is injected into the steam chamber through the opening; After filling is complete, close the opening.

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