Loop heat pipe with porous Tesla valve evaporation end and manufacturing method thereof

Abstract

The invention discloses a loop heat pipe with a porous Tesla valve evaporation end and a manufacturing method of the loop heat pipe. The loop heat pipe comprises the evaporation end, a gas channel, a condensation end and a liquid channel which are sequentially arranged in the working medium circulation direction. The evaporation end and the liquid channel are filled with a first solid medium, the first solid medium is a porous heat-conducting medium, and the condensation end is filled with a second solid medium; a first Tesla micro-channel is arranged in the first solid medium at the evaporation end, and a second Tesla micro-channel is arranged in the second solid medium at the condensation end. One-way flowing of a working medium is maintained through the Tesla micro-channels, and the liquid working medium at the condensation end is sucked to the evaporation end under the capillary action of the porous heat-conducting medium; and the evaporation efficiency of the liquid working medium at the evaporation end is improved.

Description

Technical Field

[0001] This invention relates to heat exchange technology, and in particular to a loop heat pipe with a porous Tesla valve evaporation end and a method for manufacturing the same. Background Technology

[0002] With the advancement of technology and the rapid development of science and technology, electronic devices, as the backbone of the information industry, have been widely used in modern technological products. However, Moore's Law states that the number of components per unit area in semiconductors is growing exponentially, roughly doubling every 18-24 months. This leads to a sharp increase in heat generation, causing electronic devices to deviate from normal operating conditions, reduce their lifespan, and even fail or burn out. Therefore, to meet the high heat flux requirements of electronic devices and ensure system reliability, the development of stable and efficient new heat dissipation technologies is becoming increasingly important. Loop heat pipes, as a typical passive heat dissipation technology, connect the evaporator and condenser ends in a loop, allowing for the separation of vapor and liquid phase flows and enabling more flexible and convenient system layout. They offer advantages such as long transmission distance, high reliability, stable operation, and long service life.

[0003] However, in conventional heat pipes, if the heat flux density is too high, the refrigerant absorbs a large amount of heat at the evaporation end and undergoes a phase change to become a gas. Its volume increases rapidly, which can easily lead to reverse flow. This impacts the liquid refrigerant flowing from the condensation end, resulting in an increase in the overall pressure drop in the heat pipe. It also hinders the replenishment of liquid from the condensation end to the evaporation end, leading to a reduction in the heat transfer efficiency of the entire loop heat pipe. Therefore, it is necessary to directionally adjust the flow direction of the refrigerant in the loop heat pipe.

[0004] Existing heat dissipation devices typically include several sets of parallel unidirectional conduits for both the radiator and condenser. Each set of unidirectional conduits includes at least three Tesla valves connected end-to-end. The pressure change generated by the phase change of the phase change medium allows for unidirectional circulation, thus regulating the flow of the working fluid to some extent. However, both the radiator and the condenser return pipes are machined from solid parts. If the radiator is located above the condenser, the fluid must overcome gravity to rise to the evaporation end, resulting in limited liquid replenishment capacity and consequently affecting the overall heat dissipation performance of the device. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a loop heat pipe with a porous Tesla valve evaporation end that can effectively improve insufficient liquid replenishment at the evaporation end, and its manufacturing method.

[0006] Technical solution: The loop heat pipe of the present invention includes an evaporation end, a gas channel, a condensation end and a liquid channel arranged sequentially along the working fluid circulation direction;

[0007] Both the evaporation end and the liquid channel are filled with a first solid medium, and the condensation end is filled with a second solid medium. A first Tesla microchannel is provided in the first solid medium of the evaporation end, and a second Tesla microchannel is provided in the second solid medium of the condensation end. The first Tesla microchannel and the second Tesla microchannel cooperate to enable the working fluid to flow in one direction.

[0008] The first solid medium is a porous thermally conductive medium, which is used to draw the liquid working fluid from the condensation end to the evaporation end through capillary action and increase the evaporation efficiency of the liquid working fluid at the evaporation end.

[0009] Optionally, the first solid medium is formed by sintering metal powder.

[0010] Optionally, the metal powder is spherical or irregular in shape, with a particle size of 25~150μm.

[0011] Optionally, the metal powder includes copper powder, nickel powder, and aluminum powder.

[0012] Optionally, the first solid medium in the liquid channel, the first solid medium at the evaporation end, and the first Tesla microchannel are manufactured using an integral molding process.

[0013] Optionally, the second solid medium is made of a dense metal material.

[0014] Optionally, multiple first Tesla microchannels are arranged parallel to each other along the working fluid flow direction, and multiple second Tesla microchannels are arranged parallel to each other along the working fluid flow direction.

[0015] Optionally, the loop heat pipe also includes a base plate and a cover plate arranged opposite to each other, as well as an inner frame and an outer frame fixedly arranged between the base plate and the cover plate. The closed space enclosed by the base plate, the cover plate, the inner frame and the outer frame is a working fluid circulation channel.

[0016] Optionally, the outer frame is provided with an injection port for injecting working fluid into the working fluid circulation channel.

[0017] The manufacturing method of the loop heat pipe of the present invention includes the following steps:

[0018] Second Tesla microchannel fabrication: A second solid medium is set at the condensation end, and a second Tesla microchannel is fabricated on the second solid medium;

[0019] First Tesla microchannel processing: A Tesla microchannel mold is set at the evaporation end, the Tesla microchannel mold being a positive mold with the shape of a Tesla microchannel; metal powder is filled into the liquid channel and the evaporation end, and a sintering process is used to form a first solid medium in the liquid channel and the evaporation end, and a first Tesla microchannel is formed in the first solid medium at the evaporation end, and then the Tesla microchannel mold is removed;

[0020] Working fluid injection and sealing: After completing the processing of the first Tesla microchannel and the second Tesla microchannel, the working fluid is injected into the working fluid circulation channel composed of the evaporation end, the gas channel, the condensation end and the liquid channel and then sealed.

[0021] Beneficial effects: Compared with the prior art, the significant technical effects of the present invention are as follows: (1) The first solid medium in the liquid channel has a porous structure, which can draw the liquid working fluid from the condensing end to the evaporating end through capillary action. At the same time, the pressure difference achieved by the unidirectional flow-guiding action of the first Tesla valve channel further enhances the capillary action, thereby improving the problem of insufficient liquid replenishment at the evaporating end. Even if the evaporating end is located above the condensing end, it can promote the liquid working fluid to overcome its own gravity and flow rapidly from the condensing end to the evaporating end; (2) The first solid medium at the evaporating end has a porous structure and good thermal conductivity, which can efficiently transfer heat to the liquid working fluid. Combined with the capillary action of the first Tesla valve channel wall, the pressure difference further enhances the capillary action, thereby improving the problem of insufficient liquid replenishment at the evaporating end. Even if the evaporating end is located above the condensing end, it can promote the liquid working fluid to overcome its own gravity and flow rapidly from the condensing end to the evaporating end; (3) The first solid medium at the evaporating end has a porous structure and good thermal conductivity, which can efficiently transfer heat to the liquid working fluid. Combined with the capillary action of the first Tesla valve channel wall, the pressure difference achieved by the capillary action further enhances the capillary action, thereby improving the problem of insufficient liquid replenishment at the evaporating end. The local rewetting effect and film evaporation effect achieved by the fine action can increase the evaporation efficiency of the liquid working fluid at the evaporation end; (3) Tesla valves with directional flow characteristics are designed at both the evaporation end and the condensation end. The flow island structure in the valve causes the working fluid to be diverted and changes the flow direction in the Tesla bend, resulting in momentum loss; therefore, the directional circulation flow of the working fluid in the loop heat pipe can be realized; (4) The liquid channel and the first Tesla valve flow channel at the evaporation end are made of powder sintering, which has excellent comprehensive capillary performance. The liquid at the condensation end can be drawn to the evaporation end through capillary suction to complete the rapid circulation and realize the rapid dissipation of local heat source heat. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the internal structure of the loop heat pipe in an embodiment of the present invention;

[0023] Figure 2 This is an exploded view of the overall structure of the loop heat pipe in an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of the flow path of the cooling working fluid in Tesla microchannels;

[0025] Figure 4 This is a schematic diagram of the lower substrate and the second Tesla microchannel in an embodiment of the present invention;

[0026] Figure 5 This is an assembly diagram of the base plate, outer frame, and inner frame in an embodiment of the present invention;

[0027] Figure 6 This is an assembly diagram of the base plate, outer frame, inner frame, and Tesla microchannel mold in an embodiment of the present invention;

[0028] Reference numerals in the attached diagram: 1. Evaporation end; 1-1. First Tesla microchannel; 1-2. First solid medium; 2. Liquid channel; 3. Condensation end; 3-1. Second Tesla microchannel; 3-2. Second solid medium; 4. Vapor channel; 5. Inner frame; 6. Outer frame; 7. Liquid injection port; 8. Cover plate; 9. Base plate; 10. Tesla microchannel mold. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0030] Reference Figure 1 and Figure 2 The loop heat pipe of this invention includes a base plate 9 and a cover plate 8 arranged opposite to each other. An inner frame 5 and an outer frame 6 are fixedly arranged between the base plate 9 and the cover plate 8. The base plate 9, cover plate 8, inner frame 5, and outer frame 6 are all made of materials with good thermal conductivity, including but not limited to copper, stainless steel, and titanium alloy. The base plate 9, cover plate 8, inner frame 5, and outer frame 6 are connected and fixed by means of bonding, welding, etc., and the enclosed space formed by them is the working fluid circulation channel. Along the working fluid circulation direction, there are, in sequence, an evaporation end 1, a gas channel 4, a condensation end 3, and a liquid channel 2. A liquid injection port 7 is provided on the outer frame 6 for injecting the working fluid into the working fluid circulation channel. The working fluid is usually a liquid with high latent heat of vaporization, high thermal conductivity, and low liquid viscosity, such as water or alcohol.

[0031] Reference Figure 1 and Figure 2 Both the evaporation end 1 and the liquid channel 2 are filled with a first solid medium, which is a porous thermally conductive medium. The first Tesla microchannel and porous sidewalls within the first solid medium in the evaporation end 1 together form a liquid microchannel, and the porous structure within the first solid medium in the liquid channel 2 also forms a liquid microchannel. In this embodiment, the first solid medium is sintered from copper powder, which is spherical or irregular in shape with a particle size of 25~150μm. The condensation end 3 is filled with a second solid medium, which in this embodiment is also made of copper and has good thermal conductivity.

[0032] In other feasible implementations, the first solid medium can be sintered from metal powders such as nickel powder and aluminum powder, and the second solid medium can be made of copper alloys, titanium alloys, etc.

[0033] Reference Figure 1 and Figure 2The first solid medium at the evaporation end 1 is provided with a first Tesla microchannel 1-1, which drives the working fluid to flow unidirectionally from the liquid microchannel in the liquid channel 2 to the gas channel 4. The first solid medium in the liquid channel 2, the first solid medium at the evaporation end 1, and the first Tesla microchannel 1-1 are integrally molded. The second solid medium at the condensation end 3 is provided with a second Tesla microchannel 3-1, which drives the working fluid to flow unidirectionally from the gas channel 4 to the liquid microchannel in the liquid channel 2. The first Tesla microchannel 1-1 and the second Tesla microchannel 3-1 cooperate to achieve directional circulation of the working fluid. Multiple first Tesla microchannels 1-1 and second Tesla microchannels 3-1 are arranged parallel to and at equal intervals along the flow direction of the working fluid.

[0034] Tesla's microchannel structure is based on existing technology, for reference Figure 3 Tesla microchannels typically include a main channel and several curved branch channels that are alternately distributed on both sides of the main channel. Several flow islands are arranged at intervals along the direction of fluid flow. The flow islands can be teardrop-shaped or wedge-shaped.

[0035] The working principle of Tesla microchannels to achieve unidirectional flow is as follows: Figure 3 As shown, when the fluid flows in the forward direction, the flow resistance is small, and most of the fluid flows smoothly along the main channel. A small amount of fluid enters the curved branch channel. At the junction, the fluid in the curved branch channel flows into the main channel in the forward direction, resulting in minimal energy loss. When the fluid flows in the reverse direction, due to significant frictional resistance and momentum loss, the fluid experiences substantial flow resistance in that direction. Therefore, the fluid can exhibit directional flow in the loop heat pipe. Specifically, the flow divider islands split the fluid into two streams: one flows along the main channel, and the other enters the curved branch channel. The fluid after passing through the curved branch channel collides head-on with the fluid in the main channel, forming eddies and causing energy loss. This process is repeated at each flow divider island, leading to a gradual accumulation of resistance, ultimately hindering the overall forward flow of the fluid, forming a "valve effect." Thus, the reverse flow of the fluid is obstructed, achieving unidirectional fluid conduction. This invention utilizes the unidirectional conduction effect of Tesla microchannels to achieve directional circulation of the working fluid.

[0036] In this embodiment, the first Tesla microchannel 1-1 is obtained by sintering copper powder using a Tesla microchannel mold (a positive mold with the shape of a Tesla microchannel); the second Tesla microchannel 3-1 is obtained by cutting or etching on a copper substrate.

[0037] The working principle of the loop heat pipe described in this invention is as follows: After absorbing heat at the evaporation end 1, the liquid working fluid undergoes a phase change from liquid to gas, expanding in volume. The gaseous working fluid flows to the condensation end 3 through the gas channel 4, releases heat at the condensation end 3, and then re-condenses from gas to liquid. The liquid working fluid then flows back to the evaporation end 1 through the liquid channel 2. Combined with the unidirectional flow guidance of the first Tesla microchannel 1-1 and the second Tesla microchannel 3-1, the working fluid directional circulation achieves efficient heat dissipation. The porous liquid microchannel formed by sintered copper powder in the liquid channel 2 can draw the liquid working fluid from the condensation end 3 to the evaporation end 1 through capillary action. Simultaneously, the pressure difference created by the unidirectional flow guidance of the first Tesla microchannel 1-1 further enhances the capillary action, improving the problem of insufficient liquid replenishment at the evaporation end 1. The sintered copper powder in evaporation end 1 has a porous structure and good thermal conductivity, which can efficiently transfer heat to the liquid working fluid. Combined with the local rewetting effect and thin film evaporation effect achieved by the capillary action of the wall of the first Tesla microchannel 1-1, it can increase the evaporation efficiency of the liquid working fluid in evaporation end 1.

[0038] Another embodiment of the present invention also provides a method for manufacturing the loop heat pipe, specifically including the following steps:

[0039] Step 1, Second Tesla Microchannel Machining:

[0040] A cleaned, decontaminated, and dried copper sheet measuring 54mm in length, 40mm in width, and 0.5mm in thickness was selected as the base plate 9. The base plate 9 has a copper boss measuring 20mm in length, 10mm in width, and 1mm in thickness at the corresponding position of the condensation end 3, which serves as the machining substrate for the second Tesla microchannel 3-1. The second Tesla microchannel 3-1 was machined using a micro-milling cutter, as follows: Figure 4 As shown.

[0041] Select a copper square frame with an outer length of 54mm × width of 40mm × thickness of 1mm and an inner length of 50mm × width of 36mm × thickness of 1mm as the outer frame 6, and a copper square frame with an outer length of 30mm × width of 28mm × thickness of 1mm and an inner length of 26mm × width of 24mm × thickness of 1mm as the inner frame 5. Align the inner frame 5 and outer frame 6 at their corresponding positions on the base plate 9 and then weld them to the base plate 9. Figure 5 As shown.

[0042] Step 2, Machining the flow channel of the first Tesla valve:

[0043] Tesla microchannel mold 10 is machined from a stainless steel sheet measuring 28mm in length, 10mm in width, and 1mm in thickness using wire cutting. Tesla microchannel mold 10 is a male mold with a Tesla microchannel shape. For ease of positioning, Tesla microchannel mold 10 also includes a square portion that abuts against the inner corner of the outer frame 6, thereby positioning Tesla microchannel mold 10 at the corresponding position on the evaporation end 1 of the base plate 9. Figure 6 As shown.

[0044] Fill the gap between liquid channel 2 and evaporation end 1 with copper powder of the required shape and particle size under no pressure until the copper powder fully fills the gap. During filling, shake the mold appropriately to ensure that the copper powder is filled evenly.

[0045] A graphite sheet of the same size as the base plate 9 is placed on the surface of the outer frame 6 and clamped with a fixture, and then placed in a vacuum sintering furnace for sintering. The sintering process includes four stages: (1) evacuating the sintering furnace and introducing a reducing or inert gas as a protective gas to prevent powder oxidation; (2) raising the temperature from room temperature to 900℃ within 180 min and holding it for 30 min; (3) raising the temperature from 900℃ to 950℃ within 30 min and holding it for 180 min to fully sinter the copper powder on the surface of the base plate 9; (4) allowing the furnace to cool naturally to room temperature, demolding to obtain the base plate 9 with sintering liquid channels 2 and sintering Tesla microchannels, as shown. Figure 1 As shown.

[0046] Step 3, working fluid injection and sealing:

[0047] After aligning the cover plate 8 with the base plate 9, a sealed cavity is formed around the sealing edges. Sealing methods include, but are not limited to, adhesive bonding and welding. A vacuum is drawn into the working fluid circulation channel through the injection port 7, and then a liquid working fluid is injected. In this embodiment, deionized water is used as the working fluid. Finally, the injection port 7 is sealed using ultrasonic welding, cold welding, or argon arc welding to obtain a loop heat pipe with a copper powder sintered Tesla valve evaporation end.

[0048] The loop heat pipe described in this invention ensures directional flow of the working fluid within the loop heat pipe by incorporating Tesla valves with directional flow characteristics at both the evaporation and condensation ends. Simultaneously, the use of a sintered porous structure in both the evaporation end and the liquid channel enhances the liquid supply at the evaporation end through capillary suction, resulting in excellent working fluid circulation. This results in a loop heat pipe with a copper powder sintered Tesla valve evaporation end. Furthermore, the high hydrophilicity of the porous medium at the evaporation end increases the capillary effect on the liquid surface, enhancing local rewetting and significantly strengthening thin-film evaporation. Finally, a low-cost sintering method enables efficient, low-cost, and robust fabrication of enhanced heat transfer structures within microscale channels, effectively overcoming the shortcomings of traditional methods for processing enhanced heat transfer structures.

Claims

1. A loop heat pipe with a porous Tesla valve evaporator end, characterized in that: It includes an evaporation end, a gas passage, a condensation end, and a liquid passage arranged sequentially along the working fluid circulation direction; Both the evaporation end and the liquid channel are filled with a first solid medium, and the condensation end is filled with a second solid medium. A first Tesla microchannel is provided in the first solid medium of the evaporation end, and a second Tesla microchannel is provided in the second solid medium of the condensation end. The first Tesla microchannel and the second Tesla microchannel cooperate to enable the working fluid to flow in one direction. The first solid medium is a porous thermally conductive medium, which is used to draw the liquid working fluid from the condensation end to the evaporation end through capillary action and increase the evaporation efficiency of the liquid working fluid at the evaporation end.

2. The loop heat pipe according to claim 1, characterized in that: The first solid medium is formed by sintering metal powder.

3. The loop heat pipe according to claim 2, characterized in that: The metal powder is spherical or irregular in shape, with a particle size of 25~150μm.

4. The loop heat pipe according to claim 2 or 3, characterized in that: The metal powder includes copper powder, nickel powder, and aluminum powder.

5. The loop heat pipe according to claim 1, characterized in that: The first solid medium in the liquid channel, the first solid medium at the evaporation end, and the first Tesla microchannel are manufactured using a one-piece molding process.

6. The loop heat pipe according to claim 1, characterized in that: The second solid medium is made of dense metal.

7. The loop heat pipe according to claim 1, characterized in that: Multiple first Tesla microchannels are arranged parallel to the working fluid flow direction, and multiple second Tesla microchannels are arranged parallel to the working fluid flow direction.

8. The loop heat pipe according to claim 1, characterized in that: It also includes a base plate and a cover plate that are arranged opposite to each other, as well as an inner frame and an outer frame that are fixedly arranged between the base plate and the cover plate. The enclosed space formed by the base plate, the cover plate, the inner frame and the outer frame is a working fluid circulation channel.

9. The loop heat pipe according to claim 8, characterized in that: The outer frame is provided with an injection port for injecting working medium into the working medium circulation channel.

10. A method for manufacturing a loop heat pipe according to any one of claims 1-9, characterized in that, Includes the following steps: Second Tesla microchannel fabrication: A second solid medium is set at the condensation end, and a second Tesla microchannel is fabricated on the second solid medium; First Tesla microchannel processing: A Tesla microchannel mold is set at the evaporation end, the Tesla microchannel mold being a positive mold with the shape of a Tesla microchannel; metal powder is filled into the liquid channel and the evaporation end, and a sintering process is used to form a first solid medium in the liquid channel and the evaporation end, and a first Tesla microchannel is formed in the first solid medium at the evaporation end, and then the Tesla microchannel mold is removed; Working fluid injection and sealing: After completing the processing of the first Tesla microchannel and the second Tesla microchannel, the working fluid is injected into the working fluid circulation channel composed of the evaporation end, the gas channel, the condensation end and the liquid channel and then sealed.

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