JP7284988B2 - Heat pipe manufacturing method - Google Patents

Description

The present invention relates to a heat pipe in which a working fluid is sealed and a heat pipe manufacturing method.

2. Description of the Related Art In recent years, as electronic devices and medical devices have become smaller and have higher performance, cooling of high-heat-generating electronic components has become one of the important techniques in designing electronic devices (see Patent Document 1, for example).

In particular, smartphones and tablet PCs have limited space for cooling devices, making it difficult to use electronic elements with high heat generation density, which is an obstacle to achieving higher performance.

JP 2015-59683 A

The present invention has been made in view of the above problems, and an object thereof is to provide a heat pipe that is compact and has excellent heat transport performance, and a heat pipe manufacturing method.

In order to achieve the above object, a heat pipe according to the present invention comprises a container in which a working fluid is enclosed, and a wick provided on the inner wall surface side of the container and forming a liquid flow path for the working fluid, The wick is characterized by being formed of a nanoparticle layer for forming the liquid channel.

Further, a heat pipe manufacturing method according to the present invention includes a container in which a working fluid is enclosed, and a wick provided on an inner wall surface side of the container and forming a liquid flow path for the working fluid, the wick comprising: A method for manufacturing a heat pipe formed of a nanoparticle layer for forming the liquid flow path, the nanoparticle layer adhering to the inner wall surface of the container, the pipe constituting the container The nanoparticle layer is formed by immersing the inside of the pipe portion in a silica nanofluid and causing nucleate boiling inside the pipe portion.

Another heat pipe manufacturing method according to the present invention includes a container in which a working fluid is enclosed, and a wick provided on an inner wall surface side of the container and forming a liquid flow path for the working fluid, the wick is a method for manufacturing a heat pipe that is formed of a nanoparticle layer for forming the liquid flow path and has a nanoparticle layer-attached mesh having the nanoparticle layer on the surface thereof on the inner wall side of the container. Then, the mesh with the nanoparticle layer is manufactured by placing the mesh in a constant temperature bath and immersing it in silica nanofluid.

ADVANTAGE OF THE INVENTION According to this invention, the heat pipe which is small and excellent in heat-transporting performance, and a heat pipe manufacturing method can be provided.

(a) is a partial side sectional view showing the configuration of the heat pipe according to the first embodiment, and (b) is a partial enlarged view of part A shown in (a). FIG. 10 is a photograph showing a mesh (that does not form nanoparticles) used in Experimental Examples. FIG. 3 is a photograph showing a mesh (on which nanoparticles are formed) used in an experimental example. It is a schematic diagram explaining forming a nanoparticle layer in a copper pipe inner wall in an experimental example. In an experimental example, a heat pipe having a nanoparticle layer formed on the inner wall surface thereof is cut along the longitudinal direction of the pipe and photographed from the inner wall surface side of the pipe. It is a schematic diagram explaining measuring performance using a heat pipe in an experimental example. 5 is a graph showing the relationship between the amount of heat transported and the temperature difference between the evaporating section and the condensing section in Experimental Example 1. FIG. FIG. 5 is a graph showing the relationship between heat transport amount and thermal resistance in Experimental Example 1; 9 is a graph showing the relationship between the amount of heat transported and the temperature difference between the evaporator and the condenser in Experimental Example 2. FIG. FIG. 10 is a graph showing the relationship between the amount of heat transported and the thermal resistance in Experimental Example 2;

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The embodiments shown below are examples for embodying the technical idea of the present invention, and the materials, shapes, structures, arrangements, etc. of the components are not limited to those described below. The embodiments of the present invention can be modified in various ways without departing from the scope of the invention.

[First embodiment]
In FIG. 1, (a) is a partial side sectional view of the heat pipe according to the first embodiment, and (b) is a partial enlarged view of (a).

The heat pipe HP according to the first embodiment includes a container C made of copper in which a working fluid (not shown) is enclosed, and a liquid flow path (not shown) for the working fluid provided on the inner wall surface side of the container C. a forming wick (capillary structure, not shown); The wick is formed of a nanoparticle layer NL for forming liquid channels. In this embodiment, the nanoparticle layer NL adheres to the inner wall surface of the container C over the entire surface.

In this embodiment, when manufacturing the heat pipe HP, the inside of the copper tube P is immersed in silica nanofluid (not shown), and nucleate boiling is caused inside the copper tube P, so that it adheres to the inner wall surface of the copper tube P. Then, a nanoparticle layer NL is formed. Thus, when a solid heated to a high temperature is immersed in a nanofluid, a nanoparticle layer NL is formed on the surface of the solid. When nucleate boiling is performed, the nanoparticle layer NL can be efficiently formed by directing the copper tube P vertically. Nanofluids other than silica nanofluids can also be used to form nanoparticle layers other than silica (eg, alumina nanoparticle layers).

Then, a working fluid (for example, pure water) is put into the copper pipe P and both ends of the copper pipe P are closed to manufacture the heat pipe HP according to the first embodiment.

In this embodiment, a wick that forms a liquid flow path for the working fluid is provided on the inner wall surface side of the container C. As shown in FIG. The wick is formed of a nanoparticle layer NL for forming liquid channels. That is, the heat pipe HP according to this embodiment is a nanoparticle-layer pre-coated heat pipe.

The nanoparticle layer NL is extremely thin and has strong capillary forces. Therefore, due to the wick of the nanoparticle layer NL, when the working fluid is liquid, the speed at which the working fluid moves with the wick (the speed at which the working fluid moves from the condensing portion to the evaporating portion) is remarkably faster than before. Therefore, a heat pipe HP that is small and has excellent heat transport performance is realized.

In addition, by using pure water as the working fluid, it is possible to use a substance (pure water) that is inexpensive and extremely easy to handle as the working fluid, compared to the case of using a nanofluid.

In addition, since the nanoparticle layer NL can be formed at a low cost, by using the nanoparticle layer NL as a wick for the heat pipe HP as in this embodiment, the cooling device can be made smaller, have higher performance, and be less expensive. In particular, it is possible to achieve higher performance of mobile devices such as smartphones.

[Second embodiment]
A heat pipe according to the second embodiment includes a nanoparticle layer-attached mesh LM (see FIG. 3) having a nanoparticle layer NL on its surface.

In this embodiment, a mesh LM with a nanoparticle layer is manufactured by placing a mesh (for example, a brass mesh BM (see FIG. 2, bare mesh) in a constant temperature bath and immersing it in a silica nanofluid).

Then, by putting this nanoparticle layer-attached mesh LM (see FIG. 3) and a working fluid (for example, pure water) into the copper pipe P (see FIG. 1) and closing both ends of the copper pipe P, Manufacture heat pipes.

In this embodiment, unlike the first embodiment, the mesh LM with a nanoparticle layer can be manufactured in advance and arranged on the inner wall surface side of the container (copper tube). Therefore, it is not necessary to cause nucleate boiling inside the copper tube as in the first embodiment. Therefore, the work process during manufacturing can be simplified.

Further, by forming the nanoparticle layer NL on the mesh, the capillary force is improved, so that the heat pipe HP having excellent heat transport performance can be realized.

<Experimental example>
The inventor conducted experiments to investigate the performance of various heat pipes.

(Experimental example 1)
(1) Formation of nanoparticle layer on screen mesh A cylindrical brass screen mesh with a roughness of 120 meshes, a length of 100 mm and a width of 30 mm was placed in a constant temperature bath and heated in an atmosphere of 800°C for 5 minutes, and the particle concentration was 0.4. immersed in kg/m ³ of silica (AEROXOIDE 90 G) nanofluid. This operation was repeated three times to form a nanoparticle layer over the mesh.

Then, the screen mesh on which the nanoparticle layer is formed in this way (an example of the mesh LM with the nanoparticle layer, see FIG. 3) is inserted into a copper tube having an outer diameter of 8 mm, a thickness of 0.5 mm, and a length of 100 mm. A heat pipe was fabricated by enclosing a working fluid (pure water or silica nanofluid) and closing both ends. The loading of nanoparticles (including the mass of oxides) was 12-14 g/m ² . The screen mesh (an example of the mesh BM described in the second embodiment) before forming the nanoparticle layer is shown in FIG. 2, and the screen mesh after forming the nanoparticle layer is shown in FIG.

(2) Formation of nanoparticle layer on inner wall of copper tube FIG. 4 is a schematic diagram illustrating formation of a nanoparticle layer on the inner wall of a copper tube in an experimental example.

A nichrome wire heater 30 is wound around the copper pipe P, and a heat-resistant polyimide tape 32 and a fluorine tape 34 are used for electrical insulation and heat insulation.

Then, after being immersed in silica nanofluid with a particle concentration of 0.4 kg/m ³ , a bolt slider (not shown) is used to adjust the AC power supplied to the nichrome wire heater 30 to 180 kW/m ² , and the copper tube P Nucleate boiling was caused on the inner surface of the container, and a nanoparticle layer NL (see FIG. 5) was formed over the entire inner wall surface of the container. The deposition amount of nanoparticles produced by this method was 1.5-2.0 g/m ² .

FIG. 5 shows the inner surface of the copper pipe P on which the nanoparticle layer NL is formed. Note that the part that looks white in FIG. 5 is due to the reflection of light.

(3) Heat Transfer Characteristic Experiment FIG. 6 shows an outline of an experimental apparatus for conducting a heat transfer characteristic experiment of the heat pipe HP. The heat pipe HP was manufactured using a circular copper tube having an outer diameter of 8 mm, a thickness of 0.5 mm, and a length of 100 mm.

The portion of the heat pipe HP on the left side of the paper surface of FIG. The portion of the heat pipe HP on the right side of the paper surface of FIG. Grease with high thermal conductivity is filled between the fins 46 and the heat pipe HP. The temperature was measured at 9 points (positions T1 _{to T9} in FIG. 6) at 5, 15, 25, 40, 50, 60, 75, 85, and 95 mm from the left end of the heat pipe HP shown in FIG. Each is done with a spot-welded K-type thermocouple. The input power Q to the heat pipe HP is tested in the range of 3 to 25 W using the bolt slider 50 . The thermal resistance R of the heat pipe HP in the steady state is defined by the following equation using the heat transfer amount (that is, input power) Q of the heat pipe HP, the evaporator temperature Te, and the condenser temperature Tc.

R=(Te-Tc)/Q (Formula 1)
(4) Experimental results (4-1) Heat transport amount (a) Heat pipes made of copper pipe without nanoparticle layer (Bare), mesh without nanoparticle layer (Bare), and pure water (Water) are BBW
(b) Copper tube without nanoparticle layer (Bare), mesh without nanoparticle layer (Bare), heat pipe made of silica nanofluid (particle concentration 0.2 kg/m ³ ) (Nano) for BBN
(c) Copper tube without nanoparticle layer (Bare), mesh with nanoparticle layer (Nano), and heat pipe made of pure water (Water) are BNW
(d) NXW heat pipe made of copper tube with nanoparticle layer (Nano), no mesh (X), and pure water (Water)
(e) Copper tube with nanoparticle layer (Nano), mesh without nanoparticle layer (Bare), and heat pipe made of pure water (Water) are NBW
called. where BBW is a commercial product and BBN was previously used in existing studies. The other BNWs, NXWs, and NBWs are unprecedented and the first to examine their heat transport performance.

Using the five types of heat pipes described above, the input power Q was gradually changed, and the temperature difference ΔT between the evaporator and the condenser when a steady state was reached was experimentally investigated. FIG. 7 shows the obtained relationship between Q and ΔT. Here, ΔT is the value of (Te-Tc).

First, comparing BBW and BBN, BBN has a smaller ΔT overall, confirming the effectiveness of using nanofluids as working fluids for heat pipes. Next, in BNW with a nanoparticle layer formed on the screen mesh, the temperature difference ΔT is almost the same as BBN when the input heat is 3-9W, but the ΔT is rather large when the input heat is 9-25W. The main reason for this is considered to be that the performance of conveying the working fluid deteriorated due to clogging of the mesh.

Next, NXW and NBW have a 15 to 40% reduction in ΔT compared to BBW and BBN, indicating an improvement in heat transport performance. That is, by forming the nanoparticle layer NL over the entire inner wall surface of the container C, that is, over the entire inner surface of the heat pipe, compared to simply using a nanofluid as the working fluid, the It is recognized that the heat transfer performance is improved. Therefore, it can be said that an improvement in heat transport performance can be expected by forming a nanoparticle layer on the inner wall of the tube. In particular, it is interesting that even NXW, which does not have a mesh, exhibits performance that surpasses BBW and BBN.

(4-2) Thermal Resistance FIG. 8 shows the result of converting the relationship between the input heat quantity (that is, input power) Q and the thermal resistance R for each heat pipe from Equation (1). Focusing on NXW and NBW, under low heat transfer conditions of Q = 3 to 9 W, R shows a higher value than existing specifications such as BBW and BBN, but high heat transfer of Q = 9 to 25 W Under these conditions, a heat resistance reduction effect of about 13 to 32% is obtained.

(5) Summary Under the condition of 3 to 25 W of input heat, we investigated the heat transport performance of a heat pipe manufactured using a screen mesh with a nanoparticle layer and a copper tube with a nanoparticle layer on the inner wall. compared to pipes. The main conclusions obtained are summarized below.

(5-1) In the heat pipe in which the nanoparticle layer was formed on the screen mesh, the thermal resistance decreased by about 2 to 8% at an input heat amount of 3 to 9W.

In addition, under the conditions of 9 to 25 W, the thermal resistance rather increased. One of the reasons for the increase in thermal resistance is thought to be that the transport of the working fluid is inhibited by the nanoparticle layer or the oxide layer formed when heated to a high temperature.

(5-2) In a heat pipe with a nanoparticle layer formed on the inner wall of a copper tube, the thermal resistance increased when the input heat amount was 3 to 9 W, but the thermal resistance was reduced by about 13 to 32% when the input heat amount was 9 to 25 W. . In particular, the fact that better heat transfer performance than the existing specification was obtained even without installing a mesh is considered to be useful in developing a small heat transport device.

(Experimental example 2)
In Experimental Example 2, similar to Experimental Example 1 using the experimental apparatus of FIG. We conducted an experiment on the heat transfer characteristics of Here, BNW and NBW were produced by the same production method as in Experimental Example 1.

The relationship between Q and ΔT obtained in Experimental Example 2 is shown in FIG. FIG. 10 shows the result of converting the relationship between Q and ΔT into the relationship between Q and R.

As shown in FIG. 10, in BNW, the value of R is significantly smaller than that in BBW (about 50% on average). That is, by forming a nanoparticle layer on the mesh, it is recognized that the capillary force is improved and the heat transport performance is improved.

In NBW, the value of R does not change significantly from that in BBW, but a decrease in the value of R is observed under conditions where Q is large.

BM Mesh C Container HP Heat pipe LM Nanoparticle layer mesh NL Nanoparticle layer P Copper tube 30 Nichrome wire heater 32 Heat resistant polyimide tape 34 Fluorine tape 40 Evaporator 42 Nichrome wire heater 44 Condenser 46 Fin 48 Fan 50 Bolt slider

Claims (4)

a container containing a working fluid;
a wick provided on the inner wall surface side of the container and forming a liquid flow path for the working fluid;
with
the wick is formed of a nanoparticle layer for forming the liquid flow path;
The nanoparticle layer is attached to the inner wall surface of the container,
The inside of the pipe portion that constitutes the container is immersed in silica nanofluid, and the nanoparticle layer is formed by nucleate boiling inside the pipe portion,
A method for manufacturing a heat pipe, wherein the pipe portion is oriented vertically during the nucleate boiling. a container containing a working fluid;
a wick provided on the inner wall surface side of the container and forming a liquid flow path for the working fluid;
with
the wick is formed of a nanoparticle layer for forming the liquid flow path;
A mesh with a nanoparticle layer having the nanoparticle layer on the surface is provided on the inner wall surface side of the container,
A heat pipe manufacturing method, wherein the mesh with the nanoparticle layer is manufactured by placing the mesh in a constant temperature bath and immersing it in silica nanofluid. 3. The method of manufacturing a heat pipe according to claim 1, wherein the working fluid is pure water or nanofluid. The heat pipe manufacturing method according to any one of claims 1 to 3, wherein the container is made of copper.

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