A copper alloy / silicon nitride composite capillary core for a loop heat pipe and a preparation method thereof

Abstract

The present invention relates to a copper alloy / silicon nitride composite capillary core for a loop heat pipe and a preparation method thereof. The copper alloy / silicon nitride composite capillary core for the loop heat pipe comprises: a porous silicon nitride ceramic capillary core matrix, and a porous metal layer connected to the porous silicon nitride ceramic capillary core matrix; the material of the porous metal layer is a copper alloy.

Description

Technical Field

[0001] The present invention relates to a metal / ceramic composite capillary wick, and particularly to a copper alloy / silicon nitride composite capillary wick for a loop heat pipe and a preparation method thereof, belonging to the technical field of thermal control. Background Art

[0002] As a device with high heat transfer efficiency and active temperature control characteristics, the loop heat pipe has a wide range of applications in the field of thermal control. As a porous material, the capillary action of the capillary wick inside the loop heat pipe evaporator provides the driving force for the circulation of the two-phase working fluid in the pipeline. In addition, the thermal conductivity of the capillary wick skeleton has an important influence on the evaporation of the working fluid. Therefore, the material and pore structure design of the capillary wick are crucial for the heat transfer efficiency of the loop heat pipe.

[0003] Traditional capillary wicks with single pore size distribution and double pore size distribution are difficult to meet the heat dissipation requirements of high heat flux density heat sources. The new type of capillary wick requires that the part close to the heat source has the characteristics of high thermal conductivity and high permeability to meet the higher heat transfer and steam overflow efficiency; while the part far from the heat source has the characteristics of low thermal conductivity and large capillary force to achieve small heat leakage and large working fluid pumping capacity. Therefore, the gradient structure design of the capillary wick has become a research hotspot.

[0004] Traditional gradient structure capillary wicks are mainly composed of a single material, but a single material is difficult to meet the thermal conductivity requirements of each part of the capillary wick. Therefore, the composite design of different types of materials is very important for preparing a capillary wick that meets the functional requirements of each part. Summary of the Invention

[0005] Aiming at the above problems, the purpose of the present invention is to provide a metal-ceramic composite capillary wick for a loop heat pipe and a preparation method thereof, specifically a copper alloy / silicon nitride composite capillary wick. This capillary wick is a composite capillary wick of porous copper alloy and porous silicon nitride. The copper alloy has a high thermal conductivity, while the porous silicon nitride ceramic has a relatively small thermal conductivity and can maintain sufficient strength at a high porosity.

[0006] On the one hand, the present invention provides a copper alloy / silicon nitride composite capillary wick for a loop heat pipe, including: a porous silicon nitride ceramic capillary wick matrix, and a porous metal layer connected to the porous silicon nitride ceramic capillary wick matrix; the material of the porous metal layer is copper alloy.

[0007] Preferably, the mass ratio of copper element to other metal elements in the copper alloy is at least 1:0.5, preferably 1:(0.1 - 0.3); preferably, the copper alloy is a copper-zinc alloy, a copper-silver alloy, or a copper-zinc-silver alloy.

[0008] Preferably, the porosity of the porous silicon nitride ceramic capillary core matrix is 55% to 75%. The porosity of the porous metal layer is 50% to 80%.

[0009] Preferably, the total porosity of the copper alloy / silicon nitride composite capillary core for the loop heat pipe is 55% to 78%.

[0010] On the other hand, the present invention provides a method for preparing a copper alloy / silicon nitride composite capillary core for a loop heat pipe, including: fixing a porous silicon nitride ceramic capillary core matrix in a mold and filling copper powder or copper alloy powder around it;

[0011] After the filled mold is vibrated and compacted on a vibrating table, it is then subjected to hot press sintering to obtain a copper alloy / silicon nitride composite capillary core for a loop heat pipe.

[0012] Preferably, the copper alloy powder is composed of copper and other metals, and the other metals are at least one of zinc and silver; preferably, the mass ratio of copper element to other metal powder in the copper alloy powder is 1:(0 to 0.5) (the content of other metal elements is not 0), preferably 1:(0.1 to 0.3).

[0013] Preferably, the particle size of the copper powder or copper alloy powder is 100 μm to 400 μm.

[0014] Preferably, the vibration frequency of the vibrating table is 100 to 300 Hz, the vibration height is 0 to 4 mm, and the vibration time is 2 to 10 minutes; preferably, the vibration height is 1 mm to 2 mm.

[0015] Preferably, the atmosphere of the hot press sintering is an inert atmosphere, the sintering temperature is 450 to 950 °C, the hot press pressure is 0.05 MPa to 1 MPa, and the heat preservation time is 1 hour to 3 hours; preferably, the inert atmosphere is an argon atmosphere, and the heating rate of the hot press sintering is 1 to 5 °C per minute.

[0016] Beneficial effects:

[0017] The present invention successfully prepares a copper alloy / silicon nitride composite capillary wick for a loop heat pipe. The porous copper alloy has a relatively high thermal conductivity and pore size, which can provide a relatively fast capillary wick framework heat conduction and steam overflow; the porous silicon nitride has a relatively low thermal conductivity and pore size, which can provide a relatively large capillary force and effectively reduce heat leakage. In addition, compared with most ceramic materials, porous silicon nitride, as a ceramic material with high strength, can maximize the capillary pumping performance of the capillary wick with a porosity that can be achieved under the same strength index. The copper alloy / silicon nitride composite capillary wick can meet the functional requirements of the capillary wick, with a controllable size ratio between the porous metal layer and the porous ceramic layer, relatively low processing difficulty, and relatively low cost. Most importantly, the present invention utilizes the synergistic effect of porous copper alloy and silicon nitride to reduce the evaporator thermal resistance and improve the heat transfer efficiency of the loop heat pipe. Description of the Drawings

[0018] Figure 1 Schematic diagram of the filling of copper alloy mixed powder;

[0019] Figure 2 Schematic diagram of the hot pressing of the copper alloy / silicon nitride composite capillary wick;

[0020] Figure 3 Schematic diagram of the copper alloy / silicon nitride composite capillary wick;

[0021] Among them, 1 - stainless steel shell, 2 - copper alloy powder, 3 - porous silicon nitride ceramic, 4 - pressing head, 5 - porous copper alloy. Detailed Embodiments

[0022] The present invention is further illustrated by the following embodiments. It should be understood that the following embodiments are only used to illustrate the present invention and do not limit the present invention.

[0023] In the present disclosure, a copper alloy / silicon nitride composite capillary wick for a loop heat pipe is successfully prepared. The porous copper alloy layer near the heating surface of the evaporator has the characteristics of relatively high thermal conductivity and relatively large pore size, which helps the heat conduction of the capillary wick framework and the steam overflow; the porous silicon nitride layer far from the heat source has relatively low thermal conductivity and pore size, which can effectively reduce the heat leakage from the evaporator to the reservoir while ensuring sufficient capillary force. These characteristics are expected to improve the heat transfer efficiency and operating stability of the loop heat pipe.

[0024] The following examples illustrate the preparation method of the copper alloy / silicon nitride composite capillary wick provided by the present invention.

[0025] In an alternative embodiment, silicon nitride powder, a sintering aid, a binder, a dispersant, and absolute ethanol are uniformly mixed by ball milling. Among them, the content of α-Si3N4 in the silicon nitride powder is greater than 90%. The sintering aid can be at least one of Y2O3, Al2O3, MgO, Yb2O3, and Lu2O3, and the addition amount is preferably 0.2-6 wt% of the silicon nitride powder, more preferably 2-4 wt%. The binder can be polyvinyl butyral, and the addition amount is preferably 0.5-8 wt% of the silicon nitride powder, more preferably 2-4 wt%. The dispersant can be polyethylene glycol, and the addition amount is preferably 0.5-8 wt% of the silicon nitride powder, more preferably 0.5-2 wt%. The addition amount of absolute ethanol is preferably 80-160 wt% of the silicon nitride powder. The ball milling speed is preferably 150-350 r / min, and the ball milling time is preferably 5-24 h.

[0026] In an alternative embodiment, the uniform ceramic slurry is placed in an oven for drying and then sieved. Among them, the drying temperature is preferably 50-120 °C, and the drying time is preferably 8-24 h; the mesh number of the sieve is preferably 30-120 meshes.

[0027] In an alternative embodiment, the sieved ceramic powder is filled into a mold for pre-pressing. After demolding, the formed green ceramic body is subjected to cold isostatic pressing. Among them, the pre-pressing pressure is preferably 5-20 MPa, and the pressure holding time is preferably 5-30 s; the cold isostatic pressing pressure is preferably 40-120 MPa, more preferably 60-100 MPa, and the pressure holding time is preferably 2-5 min.

[0028] In an alternative embodiment, the green ceramic body after secondary pressing is placed in a muffle furnace and heated in an air atmosphere, and then cooled with the furnace after the heating program ends. Among them, the heating rate is preferably 0.5-5 °C / min, more preferably 1-3 °C / min, the holding temperature is preferably 450-750 °C, and the holding time is preferably 1-5 h.

[0029] In an alternative embodiment, the debonded green ceramic body is placed in a sintering furnace and sintered in a nitrogen atmosphere, and then cooled with the furnace after the sintering process ends. Among them, the nitrogen gas pressure is preferably 0.05-0.4 MPa, the heating rate is preferably 1-10 °C / min, the holding temperature is preferably 1690-1750 °C, and the holding time is preferably 2-4 h.

[0030] In an alternative embodiment, the sintered silicon nitride capillary core is processed, and then the processed silicon nitride capillary core is fixed in a special mold. Subsequently, copper alloy powder is filled around the silicon nitride capillary core. After filling, the mold is placed on a vibrating table to compact the copper alloy powder. The process of filling and compacting the copper alloy powder is as Figure 1As shown in the figure. Among them, the vibration frequency of the vibration table is preferably 100-300 Hz, the vibration height is preferably 0-4 mm, more preferably 1-2 mm, and the vibration time is preferably 2-10 min; the particle size of the copper alloy powder is 100-400 μm, and the alloy powder is composed of copper and other metals. The other metals are at least one of zinc and silver. The mass ratio of copper to other metal powders in the alloy powder is preferably 1:(0-0.5); more preferably 1:(0.1-0.3).

[0031] In an alternative embodiment, the mold after tamping the copper alloy powder is placed in a hot pressing furnace and sintered in an argon atmosphere. After the sintering process is completed, it is cooled with the furnace. The process of hot pressing and sintering is as Figure 2 shown. Then, the composite capillary wick is demolded and processed according to the designed dimensions. The copper alloy / silicon nitride composite capillary wick is as Figure 3 shown. Among them, the sintering temperature can preferably be 450-950 °C, the hot pressing pressure can be 0.05-1 MPa. The heating rate can be 1-5 °C / min. The holding time can be 1-3 h.

[0032] In the present invention, the porosity of the capillary wick is measured by the Archimedes drainage method.

[0033] The following further illustrates the present invention with examples. It should be understood that the following examples are only used to further illustrate the present invention and cannot be construed as limiting the protection scope of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention fall within the protection scope of the present invention. The specific process parameters and the like in the following examples are only an example within a suitable range, that is, those skilled in the art can make selections within a suitable range through the description in this article, rather than being limited to the specific values in the following examples.

[0034] Example 1:

[0035] 100 g of Si3N4 powder, 4 g of Y2O3, 2 g of polyvinyl butyral, 1 g of polyethylene glycol, 100 g of absolute ethanol and 207 g of silicon nitride balls were ball-milled and mixed at 300 r / min for 4 h to obtain a uniform ceramic slurry. The ceramic slurry was placed in an oven at 60 °C and dried for 12 h, and then sieved through a 100-mesh sieve. The obtained powder was pre-pressed at 18 MPa with a holding time of 10 s; then cold isostatically pressed at 60 MPa with a holding time of 2 min to obtain a ceramic green body. The debinding system of the ceramic green body was heated to 550 °C at a rate of 1 °C / min, held for 2 h, and cooled with the furnace. The sintering system of the debound ceramic was heated to 1700 °C at a rate of 3 °C / min, held for 2 h, with a nitrogen gas pressure of 0.1 MPa, and cooled with the furnace. Around the processed porous silicon nitride ceramic wick, a copper-zinc mixed powder was filled, where the mass ratio of copper to zinc was 1:0.1, the average particle size was 200 μm, and the total mass was 200 g. After filling, the mold was placed on a vibrating table to vibrate and compact the copper-zinc mixed powder. Among them, the vibration frequency of the vibrating table was 120 Hz, the vibration height was 2 mm, and the vibration time was 6 min. Subsequently, the mold after vibrating and compacting the copper-zinc mixed powder was placed in a hot press furnace and sintered under an argon atmosphere. The sintering temperature was 490 °C, the heating rate was 2 °C / min, the holding time was 2 h, and the hot press pressure was 0.1 MPa. After the sintering system ended, it was cooled with the furnace. After processing the sintered wick, a copper / water loop heat pipe was assembled to test the evaporator thermal resistance. The porosity of the copper alloy / silicon nitride wick prepared in Example 1 was 65%; compared with a single silicon nitride ceramic wick, the evaporator thermal resistance of the composite wick was reduced by 15%.

[0036] Example 2:

[0037] The preparation process of the wick in this Example 2 refers to Example 1, the difference being that: the mass ratio of copper / zinc is 1:0.3. The porosity of the copper alloy / silicon nitride wick prepared in this Example 2 was 61%; compared with a single silicon nitride ceramic wick, the evaporator thermal resistance of the composite wick was reduced by 12%.

[0038] Example 3:

[0039] The preparation process of the wick in this Example 3 refers to Example 1, the difference being that: the mass ratio of copper / zinc is 1:0.5. The porosity of the copper alloy / silicon nitride wick prepared in this Example 3 was 58%; compared with a single silicon nitride ceramic wick, the evaporator thermal resistance of the composite wick was reduced by 8%.

[0040] Example 4:

[0041] In Example 4, the preparation process of the wick refers to Example 1, with the difference that the mass ratio of copper / silver is 1:0.3. The porosity of the copper alloy / silicon nitride wick prepared in this Example 4 is 62%; compared with a single silicon nitride ceramic wick, the thermal resistance of the composite wick evaporator is reduced by 14%.

[0042] Example 5:

[0043] In Example 5, the preparation process of the wick refers to Example 1, with the difference that the mass ratio of copper / silver is 1:0.1. The porosity of the copper alloy / silicon nitride wick prepared in this Example 5 is 66%; compared with a single silicon nitride ceramic wick, the thermal resistance of the composite wick evaporator is reduced by 17%.

[0044] Example 6:

[0045] In Example 6, the preparation process of the wick refers to Example 1, with the difference that the average particle size of the copper-zinc mixed powder is 100 μm. The porosity of the copper alloy / silicon nitride wick prepared in this Example 6 is 57%; compared with a single silicon nitride ceramic wick, the thermal resistance of the composite wick evaporator is reduced by 7%.

[0046] Example 7:

[0047] In Example 7, the preparation process of the wick refers to Example 1, with the difference that the average particle size of the copper-zinc mixed powder is 400 μm. The porosity of the copper alloy / silicon nitride wick prepared in this Example 7 is 70%; compared with a single silicon nitride ceramic wick, the thermal resistance of the composite wick evaporator is reduced by 18%.

[0048] Comparative Example 1

[0049] In this Comparative Example 1, the preparation process of the wick refers to Example 1, with the difference that the average particle size of the copper-zinc mixed powder is 50 μm. The porosity of the copper alloy / silicon nitride wick prepared in this Comparative Example 1 is 49%; compared with a single silicon nitride ceramic wick, there is no obvious reduction in the thermal resistance of the composite wick evaporator.

[0050] Comparative Example 2

[0051] In this Comparative Example 2, the preparation process of the wick refers to Example 1, with the difference that the average particle size of the copper-zinc mixed powder is 500 μm. The porosity of the copper alloy / silicon nitride wick prepared in this Comparative Example 2 is 74%, and the strength of this wick cannot meet the assembly requirements of the evaporator.

[0052] Comparative Example 3

[0053] In this Comparative Example 3, the preparation process of the wick refers to Example 1, with the difference that the mass ratio of copper / zinc is 1:0. There are gaps at the interfaces between the copper alloy / silicon nitride wicks prepared in this Comparative Example 3; in addition, under these process conditions, the sintering performance of the porous copper is poor.

[0054] Table 1 shows the performance parameters of the copper alloy / silicon nitride capillary wick prepared by the present invention:

[0055] Porosity / % Reduction ratio of evaporator thermal resistance Silicon nitride capillary wick 57％ - Example 1 65％ 15％ Example 2 61％ 12％ Example 3 58％ 8％ Example 4 62％ 14％ Example 5 66％ 17％ Example 6 57％ 7％ Example 7 70％ 18％ Comparative Example 1 49％ 0 Comparative Example 2 74％ - Comparative Example 3 - - 。

Claims

1. A preparation method of a copper alloy / silicon nitride composite capillary wick for a loop heat pipe, characterized in that, The copper alloy / silicon nitride composite wick for the loop heat pipe includes: a porous silicon nitride ceramic wick matrix, and a porous metal layer connected to the porous silicon nitride ceramic wick matrix; the material of the porous metal layer is copper alloy; the copper alloy is copper-zinc alloy, copper-silver alloy, or copper-zinc-silver alloy; the mass ratio of copper element to other metal elements in the copper alloy is (0.1-0.3); the preparation method includes: Fix the porous silicon nitride ceramic wick matrix in a mold and fill copper alloy powder around it; the mass ratio of copper element to other metal powder in the copper alloy powder is 1:(0.1-0.3); the particle size of the copper alloy powder is 100μm-400μm; After the mold filled with copper alloy powder is vibrated and compacted on a vibrating table, hot press sintering is carried out to obtain the copper alloy / silicon nitride composite wick for the loop heat pipe.

2. The preparation method according to claim 1, characterized in that, The porosity of the porous silicon nitride ceramic wick matrix is 55-75%.

3. The preparation method according to claim 1, characterized in that, The porosity of the porous metal layer is 50-80%.

4. The preparation method according to claim 1, wherein The total porosity of the copper alloy / silicon nitride composite wick for the loop heat pipe is 55%-78%.

5. The preparation method according to claim 1, wherein, The vibration frequency of the vibrating table is 100-300Hz, the vibration height is 0-4mm, and the vibration time is 2-10 minutes.

6. The preparation method according to claim 5, characterized in that, The vibration height of the vibrating table is 1mm-2mm.

7. The preparation method according to any one of claims 1-6, characterized in that, The atmosphere of the hot press sintering is an inert atmosphere, the sintering temperature is 450-950°C, the hot press pressure is 0.05MPa-1MPa, and the holding time is 1 hour-3 hours.

8. The preparation method according to claim 7, characterized in that, The inert atmosphere is argon atmosphere, and the heating rate of the hot press sintering is 1-5°C / minute.

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