Preparation method of a flat-plate loop heat pipe capillary wick evaporator

Abstract

The present invention discloses a method for preparing a flat-plate loop heat pipe capillary wick evaporator. The evaporator prepared by this method mainly includes a shell, a gradient capillary wick and an arc-shaped substrate with grooves. The main feature is that the evaporator shell, the gradient capillary wick and the arc-shaped substrate are integrally sintered and formed during the preparation process, which reduces the mechanical processing steps of the traditional flat-plate evaporator capillary wick and improves the production efficiency of the loop heat pipe evaporator; the substrate with steam grooves is set to an arc shape, which effectively increases the steam discharge space and can improve the heat exchange efficiency of the loop heat pipe. The liquid storage chamber and the grooved arc-shaped substrate are separated by a gradient capillary wick, and the liquid storage chamber is connected to the reflux liquid inlet of the upper end cover of the shell; the space between the side wall of the shell and the base forms a steam collecting chamber, which is connected to the steam outlet on the side wall of the shell. The gradient structure of the capillary wick is achieved by changing the particle size of the capillary wick raw material powder and adding a pore-forming agent to the raw material. The evaporator preparation method involved in the present invention is simple and suitable for mass production.

Description

Technical Field

[0001] The invention relates to a preparation method of a flat-plate loop heat pipe capillary wick evaporator, belongs to the technical field of loop heat pipe capillary phase change circuit, and particularly relates to the preparation of a high-efficiency flat-plate loop heat pipe evaporator. Background Art

[0002] A loop heat pipe (LHP) is a passive circulating heat exchange device that utilizes the capillary suction force of the capillary wick in the evaporator and the phase change heat transfer of the working fluid. It can effectively solve the heat dissipation problem of various equipment and instruments under high heat flux density. It has the advantages of strong heat transfer capacity, good isothermal performance, long heat transfer distance, light weight, and small heat exchange temperature difference. As the core component of the LHP, the evaporator has the dual key functions of absorbing heat from the heat source and providing power for the working fluid circulation. The more common structural form of the evaporator includes an evaporator shell, a capillary wick and a liquid inlet pipe. The liquid absorption performance of the capillary wick provides a liquid evaporation interface and realizes liquid supply, while blocking the vapor generated on the outside of the capillary wick from entering the liquid storage chamber. Currently, most of the practical applications are flat-plate evaporators LHP, and the capillary wick is made of metal material with high thermal conductivity.

[0003] The evaporator structure and wick performance determine the operating efficiency of a loop heat pipe. During LHP operation, if the steam in the evaporator cannot be promptly removed, it can easily cause "heat leakage" and "sidewall heat conduction" in the heat exchange system. This can lead to an increase in the temperature of the liquid storage chamber, causing the working fluid to undergo a vapor-liquid phase transition within the liquid storage chamber, resulting in increased pressure in the liquid storage chamber, making it difficult for the wick to draw the working fluid, increasing system operating resistance and ultimately causing the liquid storage chamber to "burn dry." The invention patent (CN105371676B), "A Double-Wick Evaporator," discloses a double-wick evaporator structure. This double-wick design improves the startup speed of the evaporator system. The use of a secondary wick increases the thermal resistance of heat conduction from the sidewall to the liquid storage chamber, thereby reducing the system's operating temperature and increasing system stability. The double-wick evaporator offers fast startup, low operating temperature, excellent system stability, and increased heat flux density. Compared to traditional evaporators, it can transfer more heat with the same effective heat transfer area and can handle a wider range of heat loads. However, the structure of this evaporator is relatively complex, and only when the heating surface and back surface of the double capillary wick evaporator are heated at the same time, the start-up speed of the evaporator system will be more significantly improved. In addition, when reducing "heat leakage", only the thermal resistance from the side wall to the liquid storage chamber is increased, resulting in an insignificant increase in the steam overflow speed.

[0004] The preparation process of a flat-plate loop heat pipe capillary wick evaporator is relatively complicated. It is usually completed by assembling the evaporator shell and capillary wick after precision machining. During the process, the capillary wick needs to be processed secondary to form a steam channel on the capillary wick base and make the surface of the capillary wick steam channel close contact with the evaporator shell to ensure heat transfer efficiency. In addition, the secondary machining of the capillary wick can easily lead to blockage of the capillary wick pores, which ultimately affects the liquid absorption performance of the capillary wick.

[0005] Based on the above problems, the present invention provides a method for preparing a flat-plate loop heat pipe capillary wick evaporator. By arranging an arc-shaped substrate with a steam channel in the evaporator, the contact area between the substrate and the capillary wick is increased, so that the effective heat transfer area is increased, more heat can be transferred, and the range of heat load that can be carried is also wider. The capillary wick on the arc-shaped substrate has a gradient pore structure, which can reduce the "heat leakage" of the capillary wick to the liquid storage chamber, making the steam overflow speed increase more significantly, reducing the heat flowing to the liquid storage chamber, and thus lowering the system operating temperature and increasing the system operation stability; at the same time, the evaporator shell, gradient capillary wick and steam channel arc-shaped substrate are integrally sintered in the preparation process, and no secondary machining of the capillary wick is required, which avoids the pore blockage of the capillary wick due to machining, shortens the preparation process of the evaporator, and improves production efficiency. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a flat-plate loop heat pipe capillary wick evaporator to solve the technical problems raised in the above embodiments.

[0007] The present application provides a method for preparing a flat-plate loop heat pipe capillary wick evaporator, wherein the capillary wick evaporator is mainly composed of a lower shell, an arc-shaped substrate, a steam channel, a liquid injection port, a gradient capillary wick, a liquid storage chamber, an upper end cover, a steam cavity, and a steam outlet portion; the upper end cover is fixedly connected to the lower shell, forming a cavity inside, and the arc-shaped substrate and the gradient capillary wick are arranged in the cavity; the gradient capillary wick and the upper end cover form a liquid storage chamber, and a liquid injection port is opened on the upper end cover; the space between the side wall of the lower shell and the arc-shaped substrate forms a steam chamber, and the upper end cover forms a steam chamber. The arc-shaped base plate is in close contact with the lower shell, and a plurality of steam channels perpendicular to the chord length are formed on the arc-shaped base plate; the gradient capillary wick is in close contact with the upper surface of the arc-shaped base plate and the side wall of the lower shell; the steam formed by the working fluid in the gradient capillary wick being heated and vaporized flows out from the steam channels and is collected in the steam chamber; a steam outlet communicating with the steam chamber is provided on the side wall of the lower shell, and the steam outlet is connected to an external cooling device; the upper end cover and the lower shell are both square structures, and the upper end cover and the lower shell are tightly connected by welding;

[0008] In addition, a preparation method of a flat-plate loop heat pipe capillary wick evaporator is characterized in that the preparation process is:

[0009] Step 1: Prepare the evaporator lower shell and a curved base plate with steam channels according to the shape and dimensions of the flat-plate loop heat pipe capillary wick evaporator to be manufactured. Apply brazing material evenly to the bottom of the curved base plate and place it into the lower shell, ensuring that it is tightly bonded to the bottom and side walls of the lower shell.

[0010] Step 2: Weigh a certain amount of ammonium bicarbonate powder and fill it into the steam channel and steam cavity on the curved substrate in the lower shell in step 1, and flatten it;

[0011] Step 3: Weigh a certain amount of pure nickel powder and spread it on the surface of the arc-shaped substrate in the lower shell in step 2, and then weigh a certain amount of mixed powder of pore-forming agent and pure nickel powder and spread it on the surface of the pure nickel powder layer;

[0012] Step 4: Place a ceramic compact on the surface of the powder inside the lower shell obtained in step 3, and then place it in a vacuum furnace for sintering. The sintering temperature is 700°C, the holding time is 30 minutes, and the vacuum degree is better than 5×10 -2 Pa; finally, the furnace is cooled, and the ceramic compact is removed to obtain a semi-finished capillary wick evaporator;

[0013] Step 5: Weld and assemble the semi-finished evaporator obtained in step 4 to the upper end cover with the liquid injection port, and open a hole at the steam chamber position on the side wall of the lower shell, which is the steam outlet; finally, the finished evaporator is obtained.

[0014] As an improvement, the evaporator lower shell, gradient capillary core and arc-shaped base plate with steam channels are integrally sintered, reducing the machining process of the traditional flat-plate evaporator capillary core.

[0015] As an improvement, a curved base plate is added to the evaporator, and steam channels are opened on the curved base plate.

[0016] As an improvement, a steam cavity is left between the side wall of the lower shell and the arc-shaped base plate, and the steam channels are all connected to the steam cavity, and the steam enters the steam cavity along the steam channels.

[0017] As an improvement, during the overall sintering process of the evaporator lower shell, curved substrate and gradient capillary core, a ceramic pressing block is placed on top of them to provide sintering compressive stress, and the sintering compressive stress range is 0.1~10kPa; the size of the ceramic pressing block is consistent with the internal size of the lower shell; the sintering atmosphere can be a vacuum, or a hydrogen or argon protective atmosphere, and the sintering temperature range is 500~900℃.

[0018] As an improvement, when the curved substrate is assembled with the lower shell before sintering, the bottom of the curved substrate is evenly coated with brazing paste, which includes silver-copper brazing paste, nickel-based brazing paste and stainless steel brazing paste. The specific type is selected according to the sintering temperature of the capillary wick evaporator.

[0019] As an improvement, the shape of the arc-shaped substrate arranged in the lower shell is not limited to an upward convex arc, but can also be a downward concave arc; the steam channels on the arc-shaped substrate are not in the same horizontal plane, and the cross-sectional shapes of the steam channels are inconsistent.

[0020] As an improvement, the size and shape of the evaporator shell can be adjusted to achieve the preparation of flat-plate evaporators of different specifications and shapes. The shape of the evaporator can be square, rectangular or circular.

[0021] As an improvement, the gradient capillary wick has a gradient pore structure characteristic, and its pore structure is formed by laying capillary wick powder layers of different particle sizes on the upper part of the arc substrate, or by adding pore-forming agents of different particle sizes or different particle sizes to different capillary wick powder layers.

[0022] As an improvement, the filling powder used for the steam channels and steam cavities on the curved substrate can be the same as or different from the pore-forming agent; the pore-forming agent powder can be PMMA (polymethyl methacrylate), NH4HCO3 (ammonium bicarbonate), PVA (polyvinyl alcohol), or NaCl (sodium chloride); the mass fraction of the pore-forming agent ranges from 3% to 20%, and the particle size ranges from 13 to 50 μm.

[0023] As an improvement, when the pore-forming agent powder or the steam channel filling powder is NaCl, the evaporator needs to be desalted after being sintered as a whole.

[0024] As an improvement, the material of the gradient capillary wick is metal, which can be pure nickel, nickel-based alloy, pure copper or stainless steel. The particle size distribution range of the capillary wick metal powder is 0.3 to 6.0 μm; the material of the evaporator shell can be the same as or different from the material of the gradient capillary wick.

[0025] The key points of the preparation method involved in the present invention are: (a) the evaporator lower shell, gradient capillary wick and curved substrate are integrally sintered and formed, which reduces the mechanical processing steps of the traditional flat-plate evaporator capillary wick, avoids the pore blockage phenomenon of the capillary wick due to machining, and improves production efficiency; (b) the curved substrate and the non-parallel steam channel design make it easier for the steam in the steam channel to enter the steam cavity, which can improve the overall heat exchange efficiency of the loop heat pipe system; (c) the contact area between the gradient capillary wick and the curved substrate is larger than the contact area of ​​the flat-plate substrate, the capillary wick has a large heating area, and can shorten the startup time of the loop heat pipe system; the capillary wick with a gradient pore structure can inhibit the formation of bubbles in the liquid storage chamber, reduce the temperature of the liquid storage chamber, and improve the operating stability of the loop heat pipe system.

[0026] The present invention is further described in detail below through the accompanying drawings and examples. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the three-view cross-section of the gradient capillary wick evaporator;

[0028] Figure 2 Schematic diagram of the upward convex arc substrate structure;

[0029] Figure 3 Schematic diagram of the concave arc substrate structure;

[0030] Figure 4 This is a photo of the steam channels and steam cavities on the concave curved substrate after being filled with pore-forming agent powder;

[0031] Figure 5 This is a photo of the evaporator lower shell, curved substrate, and gradient capillary wick after integral sintering.

[0032] Figure 6 This is a photo of the evaporator lower shell and upper end cover after assembly;

[0033] Figure 7 This is the SEM photo of the gradient pore structure of the gradient capillary wick.

[0034] In the accompanying drawings, the same reference numerals are used to represent the same components or structures, wherein: 1—lower shell, 2—arc-shaped substrate, 3—steam channel, 4—liquid injection port, 5—gradient capillary wick, 6—liquid storage chamber, 7—upper end cover, 8—steam chamber, 9—steam outlet. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0036] The structure of the gradient capillary wick evaporator provided by the embodiment of the present invention is as follows Figure 1 As shown, it includes a lower shell 1, an upper convex arc-shaped substrate 2, a steam channel 3, a liquid injection port 4, a gradient capillary wick 5, a liquid storage chamber 6, an upper end cover 7, a steam cavity 8, and a steam outlet 9, wherein the arc-shaped substrate 2 and the lower shell 1 are tightly combined by vacuum brazing, the gradient capillary wick 5 and the arc-shaped substrate 2 are connected together by high-temperature sintering, and the lower shell 1 and the upper end cover 7 are packaged by welding. A liquid storage chamber 6 is formed between the lower shell 1 and the gradient capillary wick 5 and the upper end cover 7 for collecting reflux liquid; a steam channel 3 perpendicular to the chord length is opened on the upper convex arc-shaped substrate 2, and the steam channel 3 is in close contact with the gradient capillary wick 5; the gap between the side wall of the inner cavity of the lower shell 1 and the substrate in the slotting direction is 2 mm, and the steam enters the steam cavity 8 through the slotting direction of the steam channel; the steam outlet 9 is arranged on the side wall of the lower shell 1; the shape of the steam cavity is determined according to the specific shapes of the substrate and the gradient capillary wick; the steam channel 3 is obtained by wire cutting, as shown Figure 2and Figure 3 The specific preparation process of the evaporator is as follows:

[0037] The first step is to prepare the evaporator lower shell 1 and the curved substrate 2 with the steam channel 3. Apply evenly the brazing material on the bottom of the curved substrate 2, and then place it into the lower shell 1 so that it is tightly bonded to the bottom and side walls of the lower shell 1. The internal dimensions of the lower shell are 40*40*15mm, and the wall thickness is 1.0mm. The dimensions of the curved substrate 2 are 40*38*5.4mm. The width of the steam channel 3 is 2.0mm, and the depth is 2.0mm. The second step is to fill the steam channel 3 and the steam chamber 8 with NaCl powder and flatten it. The powder state after flattening is as follows: Figure 4 As shown. The third step is to prepare the gradient capillary core by layering powder: first, pure nickel powder is laid on the curved substrate 2, and the thickness of the powder layer to the top of the curved substrate is 3.0 mm; secondly, pure nickel powder with pore-forming agent NaCl is laid on the above powder layer; the total thickness of the gradient capillary core powder layer to the top of the curved substrate is 7.0 mm. The particle size of pure nickel powder is 1.0 to 3.0 μm; the amount of pore-forming agent NaCl added is 10% by mass. The fourth step is to place a ceramic compact on the surface of the gradient capillary core powder layer in the lower shell 1, and then put it into a vacuum furnace for sintering. The sintering temperature is 700 ° C, the holding time is 30 minutes, and the vacuum degree is better than 5×10 -2 Pa, the pressure of the ceramic block is 1.5kPa; finally, the furnace is cooled, and the ceramic block is removed to obtain a semi-finished capillary wick evaporator, such as Figure 5 As shown. The fifth step is to desalinate the semi-finished evaporator. The sixth step is to weld and assemble the desalted semi-finished evaporator with the upper end cover 7 with the liquid injection port 4, and open a hole at the steam chamber 8 on the side wall of the lower shell 1, which is the steam outlet 9; finally, the evaporator product is obtained, as shown. Figure 6 shown.

[0038] Although specific embodiments of the present invention have been described above, those skilled in the art will appreciate that these are merely illustrative and that the scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and such changes and modifications are intended to fall within the scope of the present invention.

Claims

1. A method for preparing a flat-plate loop heat pipe capillary wick evaporator, characterized in that The evaporator comprises a lower shell (1), a curved substrate (2), a steam channel (3), a liquid injection port (4), a gradient capillary wick (5), a liquid storage chamber (6), an upper end cover (7), a steam cavity (8), and a steam outlet (9); the upper end cover (7) is fixedly connected to the lower shell (1), and a cavity is formed inside, and the curved substrate (2) and the gradient capillary wick (5) are arranged in the cavity; the gradient capillary wick (5) and the upper end cover (7) form a liquid storage chamber (6), and a liquid injection port (4) is opened on the upper end cover (7); the space between the side wall of the lower shell (1) and the curved substrate (2) forms a steam cavity (8) for collecting steam; the curved substrate (2) is in close contact with the lower shell (1), and a plurality of steam channels (3) perpendicular to the chord length are opened on the arc-shaped substrate (2); the gradient capillary core (5) is in close contact with the upper surface of the arc-shaped substrate (2) and the side wall of the lower shell (1); the steam formed after the working medium in the gradient capillary core (5) is heated and vaporized flows out from the steam channel (3) and is collected in the steam chamber (8); a steam outlet (9) communicating with the steam chamber (8) is provided on the side wall of the lower shell (1), and the steam outlet (9) is connected to an external cooling device; the upper end cover (7) and the lower shell (1) are both square structures, and the upper end cover (7) and the lower shell (1) are tightly connected by welding; The preparation process of a flat-plate loop heat pipe capillary wick evaporator is as follows: Step 1: Prepare the evaporator lower shell (1) and the arc-shaped substrate (2) with the steam channel (3) according to the shape and specifications of the flat-plate loop heat pipe capillary wick evaporator to be prepared, apply evenly soldering material on the bottom of the arc-shaped substrate (2) and place it into the lower shell (1) so that it is tightly combined with the bottom and side walls of the lower shell (1); Step 2: Weigh a certain amount of ammonium bicarbonate powder and fill it into the steam channel (3) and the steam cavity (8) on the inner curved base plate (2) of the lower shell (1) in step 1, and flatten it; Step 3: Weigh a certain amount of pure nickel powder and spread it on the surface of the inner curved substrate (2) of the lower shell (1) in step 2, and then weigh a certain amount of mixed powder of pore-forming agent and pure nickel powder and spread it on the surface of the above pure nickel powder layer; Step 4: Place a ceramic compact on the surface of the powder in the lower shell (1) obtained in step 3, and then place it in a vacuum furnace for sintering. The sintering temperature is 700°C, the holding time is 30 min, and the vacuum degree is better than 5×10 -2 Pa; finally, the furnace is cooled, and the ceramic compact is removed to obtain a semi-finished capillary wick evaporator; In step five, the semi-finished evaporator obtained in step four is welded and assembled with the upper end cover (7) having the liquid injection port (4), and a hole is opened at the position of the steam chamber (8) on the side wall of the lower shell (1), which is the steam outlet (9); finally, the finished evaporator is obtained.

2. The method for preparing a flat-plate loop heat pipe capillary wick evaporator according to claim 1, characterized in that The evaporator lower shell (1), the gradient capillary wick (5) and the arc-shaped base plate (2) with the steam channel (3) are integrally sintered.

3. The method for preparing a flat-plate loop heat pipe capillary wick evaporator according to claim 1, characterized in that An arc-shaped substrate (2) is added to the evaporator, and a steam channel (3) is opened on the arc-shaped substrate (2).

4. The method for preparing a flat-plate loop heat pipe capillary wick evaporator according to claim 1, characterized in that A steam chamber (8) is left between the side wall of the lower shell (1) and the curved base plate (2), and the steam in the steam channel (3) enters the steam chamber (8) along the channel (3).

5. The method for preparing a flat-plate loop heat pipe capillary wick evaporator according to claim 1, characterized in that During the integral sintering process of the evaporator lower shell (1), the curved substrate (2) and the gradient capillary wick (5), a ceramic pressing block is placed on the upper portion thereof to provide sintering compressive stress, and the sintering compressive stress range is 0.1-10 kPa; the size of the ceramic pressing block is consistent with the internal size of the lower shell (1); The sintering atmosphere is one of vacuum, hydrogen or argon, and the sintering temperature range is 500~900℃.

6. The method for preparing a flat-plate loop heat pipe capillary wick evaporator according to claim 1, characterized in that When the arc-shaped substrate (2) is assembled with the lower shell (1) before sintering, the bottom of the arc-shaped substrate (2) is evenly coated with brazing paste, which includes silver-copper brazing paste, nickel-based brazing paste and stainless steel brazing paste. The specific type is selected according to the sintering temperature of the capillary wick evaporator.

7. The method for preparing a flat-plate loop heat pipe capillary wick evaporator according to claim 1, wherein the shape of the arc-shaped substrate (2) arranged in the lower shell (1) is an upward convex arc or a downward concave arc.

8. The method for preparing a flat-plate loop heat pipe capillary wick evaporator according to claim 1, characterized in that By adjusting the size and shape of the evaporator shell, the preparation of flat-plate evaporators of different specifications and shapes can be achieved. The shape of the evaporator can be any one of square, rectangular or circular.

9. The method for preparing a flat-plate loop heat pipe capillary wick evaporator according to claim 1, characterized in that The gradient capillary wick (5) has a gradient pore structure characteristic, and its pore structure is formed by laying capillary wick powder layers of different particle sizes on the upper part of the curved substrate (2), or by adding pore-forming agents of different particle sizes and different particle sizes to different capillary wick powder layers; the filling powder used in the steam channel (3) on the curved substrate (2) is the same as or different from the pore-forming agent; the pore-forming agent powder is one of PMMA (polymethyl methacrylate), NH4HCO3 (ammonium bicarbonate), PVA (polyvinyl alcohol), and NaCl (sodium chloride); the mass fraction of the pore-forming agent ranges from 3 to 20%, and the particle size ranges from 13 to 50 μm.

10. The method for preparing a flat-plate loop heat pipe capillary wick evaporator according to claim 7, characterized in that When the pore-forming agent powder or the steam channel filling powder is NaCl, the evaporator needs to be desalted after being sintered as a whole.

11. The method for preparing a flat-plate loop heat pipe capillary wick evaporator according to claim 7, characterized in that The material of the gradient capillary core (5) is metal, and the material type is one of pure nickel, nickel-based alloy, pure copper or stainless steel, and the particle size range of the capillary core metal powder is 0.3~6.0 μm; the material of the evaporator shell is the same as or different from the material of the gradient capillary core (5).

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