JP2020070979A - heat pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat pipe which is low cost, lightweight and excellent in long-term reliability. A heat pipe of the present invention is a heat pipe including a container base material having a cavity and a wick structure arranged therein, and a working fluid enclosed in the cavity. The wick structure contains SiO2 as a main component, the total content of Li, Na, Mg, K, Ca, and Ba is 0.01% by mass or more, and the total content of Li, Na, K, Ca, and Ba is 1. It is a glass material having a mass% or less and a Mg content of 10% by mass or less, and the working fluid is characterized by containing water. [Selection diagram] Fig. 1

Description

  The present invention relates to a heat pipe that is lightweight and has excellent reliability.

  In recent years, the amount of heat generated has increased with the miniaturization of electric and electronic devices and the increase in current, and cooling thereof has become an important issue. A heat pipe is used as one of cooling methods for electric and electronic devices.

  The heat pipe has a container base material and a wick structure. Further, the heat pipe is mainly made of copper, which is excellent in heat transfer performance. Here, there is an increasing demand for weight reduction of heat pipes for mobile devices and products installed in vehicles. On the other hand, application of a glass material to the wick structure has been studied from the viewpoint of reducing the weight of the heat pipe, and various techniques have been proposed.

  As a technique of using a wick structure made of a glass material, for example, a first capillary structure having a net structure attached to an evaporation portion in a chamber and an axially arranged portion from the evaporation portion to the condensation portion are knitted and woven. A heat pipe having a wick structure composed of a second capillary structure composed of a braided cord, wherein the first capillary structure and the second capillary structure are made of glass or the like is proposed (for example, See Patent Document 1).

  A micro heat pipe in which a working liquid and capillaries or filaments are filled in a free state or in a restrained state leaving an appropriate space inside a decompression thin tube closed at both ends, and water is used as a working fluid. However, there is disclosed a capillary or filament that uses an inorganic glass such as quartz glass or boric acid glass (see, for example, Patent Document 2).

  Furthermore, the outer wall side of the hollow glass is formed as a dense glass layer of dense glass, and the inner wall side of the hollow glass is a heat pipe with a porous glass layer in which both end portions of the hollow glass are communicated by pores. A device using water is disclosed (for example, see Patent Document 3).

Utility model registration No. 3194101 JP-A-63-226595 JP, 2008-122024, A

  However, when glass is used as the wick structure, there is a problem that alkali is eluted from the glass of the wick structure into water used as a working fluid due to long-term use of the heat pipe. In a closed environment such as a heat pipe, the alkaline component is concentrated in the working fluid and the pH is increased. Due to this increase in pH, the glass matrix phase is etched, the shape of the wick structure is impaired, the wick performance is degraded, that is, the thermal performance of the heat pipe is degraded, and long-term reliability may not be obtained. In addition, the melted glass component may be recrystallized at another place to deteriorate the wick performance.

  The present invention has been made in view of the above, and an object of the present invention is to provide a heat pipe that is low in cost, lightweight, and excellent in long-term reliability.

In order to solve the above-mentioned problems and achieve the object, a heat pipe according to the present invention has a cavity, and a container base material in which a wick structure is arranged, and a working fluid enclosed in the cavity. And a wick structure comprising SiO ₂ as a main component, the total content of Li, Na, Mg, K, Ca, and Ba being 0.01% by mass or more, and Li, A glass material having a total content of Na, K, Ca, and Ba of 1.0 mass% or less and a Mg content of 10 mass% or less, wherein the working fluid contains water. .

  Further, the heat pipe according to the present invention is characterized in that, in the above-mentioned invention, the wick structure is glass fiber.

  Further, the heat pipe according to the present invention is characterized in that, in the above invention, the wick structure is a yarn in which a plurality of glass fibers are bundled.

  In the heat pipe according to the present invention, in the above invention, the wick structure is a glass fiber cloth in which glass fibers are woven in a cloth shape.

  Further, the heat pipe according to the present invention is characterized in that, in the above invention, the wick structure is a nonwoven fabric of glass fiber.

  Further, the heat pipe according to the present invention is characterized in that, in the above-mentioned invention, the glass fiber has a diameter of 2 to 10 µm.

  Further, the heat pipe according to the present invention is characterized in that, in the above-mentioned invention, the thickness of the wick structure is 0.01 to 0.2 mm.

  Further, in the heat pipe according to the present invention, in the above invention, the material constituting the container base material mainly contains any one of aluminum, magnesium, titanium, copper, stainless steel, or aluminum, magnesium, titanium, and copper. It is an alloy.

  According to the present invention, it is possible to obtain a heat pipe which is low in cost, lightweight and excellent in long-term reliability.

FIG. 1 is a sectional view perpendicular to the axial direction of a heat pipe according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments described below. Further, in the description of the drawings, the same or corresponding elements are appropriately assigned the same reference numerals.

(Embodiment)
FIG. 1 is a cross-sectional view perpendicular to the axial direction of a heat pipe 10 according to an embodiment of the invention. The heat pipe 10 includes a cavity 4 and a container base material 1 in which the wick structure 2 is arranged, and a working fluid 3 enclosed in the cavity 4 of the container base material 1.

  The container base material 1 is a thin tube having a circular cross section perpendicular to the axial direction. The sectional shape is not limited to the circular shape, and may be a rectangular shape, an elliptical shape, or the like. Further, the thin tube may be L-shaped or the like in addition to being linear. Further, the shape of the heat pipe may be formed by laminating a plate material and a foil material in addition to the tube material. The material forming the container base material 1 is aluminum, magnesium, titanium, copper, stainless steel, or an alloy mainly containing any one of aluminum, magnesium, titanium, and copper. From the viewpoint of weight reduction, aluminum, magnesium, titanium, or an alloy mainly containing any one of aluminum, magnesium, and titanium is preferable. Here, "mainly containing" means that the proportion of any one of aluminum, magnesium, and titanium is 50% by mass or more.

  The wick structure 2 is arranged inside the container substrate 1. The wick structure 2 is arranged from the axial length of the container base material 1, for example, from one end which is an evaporation part where the working fluid is vaporized to the other end which is a condensation part where the working fluid is liquefied. In FIG. 1, the wick structure 2 is arranged on the entire inner wall surface of the container base material 1, but may be arranged so as to cover a part of the inner wall surface.

The wick structure 2 contains SiO ₂ as a main component, and the total content of Li, Na, Mg, K, Ca, and Ba is 0.01 mass% or more, and the total content of Li, Na, K, Ca, and Ba. Is 1% by mass or less and the content of Mg is 10% by mass or less. A glass material containing SiO ₂ as a main component generally has good wettability with water and is suitable as the wick structure 2. Further, when the total content of Li, Na, Mg, K, Ca, and Ba, which are alkaline components in the glass material, is 0.01% by mass or more, the melting point of the glass material is lowered, so that the production is easy. Therefore, increase in manufacturing cost can be suppressed.

  Further, when a glass material having a total content of Li, Na, K, Ca, and Ba of 1% by mass or less is used as the wick structure 2 of the heat pipe 10, Li, Na, K in water as the working fluid 3 is used. , Ca, and Ba are less eluted, it is possible to prevent an increase in the pH of the working fluid and a reduction in the mass of the wick structure 2. The total content of Li, Na, K, Ca, and Ba is preferably 0.5% by mass or less, and particularly preferably 0.2% by mass or less.

  Furthermore, when a glass material having a Mg content of 10 mass% or less is used as the wick structure 2 of the heat pipe 10, the elution amount of Mg into water, which is the working fluid 3, is small, so that the pH of the working fluid increases and It is possible to prevent the mass reduction of the wick structure 2. Since Mg has a low solubility in water, its content in the glass material may be 10 mass% or less, but 5 mass% or less is preferable, and 1 mass% or less is particularly preferable.

  A glass material having a total content of Li, Na, Mg, K, Ca, and Ba in the above range is a glass material having a total content of Li, Na, Mg, K, Ca, and Ba in the above range. Is used as the wick structure 2. Moreover, by removing Li, Na, Mg, K, Ca, and Ba by acid-treating a glass material whose total content of Li, Na, Mg, K, Ca, and Ba exceeds the upper limit of the above range. It is also possible to use acid-treated glass having a total content of Li, Na, Mg, K, Ca, and Ba in the above range. When the acid-treated glass is used as the wick structure 2, it is preferable to use a glass matrix that has been densified by heat treatment at a high temperature after the acid treatment.

  As a technique for suppressing the elution of alkali from the glass material, there is also a bloom treatment (sulfur treatment) using ammonium sulfate, sulfurous acid gas, anhydrous sulfur dioxide, concentrated sulfuric acid, or the like. In the bloom treatment, the amount of the alkali component contained in the entire glass substrate needs to be controlled because the alkali component only near the glass surface layer is removed and the alkali is gradually eluted from the inner layer in which the alkali remains.

  Further, the glass material used for the wick structure 2 may contain Al, Cu, Ni, Ti, Zr, or the like. A glass material containing Al, Cu, Ni, Ti, Zr or the like can enhance the water resistance of the glass matrix phase.

  The shape of the wick structure 2 is not particularly limited, but it is preferable to use glass fiber from the viewpoint of wick performance and handling. For the wick structure 2, a yarn in which a plurality of glass fibers are bundled, a glass fiber cloth in which glass fibers are woven in a cloth shape, or a nonwoven fabric of glass fibers can be preferably used, and they can also be used in combination. it can.

  The wire diameter of the glass fiber used for the wick structure 2 is not particularly limited, but if it is too thin, it may cause tears during production, and the handling property decreases, and if it is too thick, flexibility decreases. Handleability deteriorates. Therefore, the wire diameter of the glass fiber is preferably 2 to 10 μm, and particularly preferably 4 to 8 μm.

  The thickness when using a glass fiber cloth or a non-woven fabric as the wick structure 2 is not particularly limited, but if it is too thin, it may be torn during manufacturing, and if it is too thick, the heat pipe 10 can be made lighter and smaller. Besides being disadvantageous, a part of the air remains in the wick structure 2, which may deteriorate the heat pipe performance. The thickness of the wick structure 2 is preferably 0.01 mm to 0.2 mm, particularly preferably 0.02 mm to 0.1 mm.

  The wick structure 2 may be one in which the glass material described above is used at least in part, and the other portion may use a conventional metal material. If at least a part is made of a glass material that does not elute alkali, the heat pipe 10 can be lightweight and has excellent long-term reliability.

  The working fluid 3 is a fluid containing water. Water has a large latent heat of vaporization, is advantageous for heat transport, has no environmental load, and is easy to manage. Therefore, water can be suitably used as the working fluid 3. Depending on the use environment, a pH adjuster may be added, or alcohol, ethylene glycol, propylene glycol, etc. may be added for the purpose of preventing freezing of the working fluid 3, but at least 50% by mass or more of water may be contained. preferable.

  By adopting the above configuration, it is possible to obtain the heat pipe 10 that can be manufactured at low cost, is lightweight, and has excellent long-term reliability. In addition, although the metal material is used as the container base material 1 in the above-mentioned embodiment, a glass material used for the wick structure 2 without alkali elution can also be used.

  The heat pipe 10 seals one end of the container base material 1 from which dirt has been washed, arranges the wick structure 2 on the container base material 1, injects the working fluid 3, and then degasses the inside of the container base material. It can be manufactured by sealing the other end of the container base material 1. Before the sealing, the shape of the sealing portion (both ends of the container material 11) may be appropriately adjusted by drawing or the like. When a plate material or a foil material is laminated to form a container, the portion other than the injection port is sealed before the working fluid 3 is injected, the working fluid 3 is injected, and the part of the injection port is sealed after deaeration. .. Further, the heat pipe may be adjusted to a desired shape by performing flattening or bending between the respective steps.

  It is preferable to clean the dirt and the like adhering to the surface of the container base material 1 since it may lead to a decrease in heat transfer ability after being made into a heat pipe. Cleaning may be performed by a general method, for example, solvent degreasing, electrolytic degreasing, etching, oxidation treatment, or the like.

  The method for sealing the container base material 1 is not particularly limited, but a general method such as TIG welding, resistance welding, thick welding, soldering, or the like may be used. The method of installing the wick structure 2 inside the container base material 1 is not particularly limited, and the wick structure 2 having a cross shape is provided along the inner surface of the container base material 1, the yarn is installed inside the container base material 1, and the like. It can be installed by the appropriate method. If necessary, the container base material 1 may be used for fixing.

<Manufacture of test sample>
One end of a straight tube of an oxygen-free copper tube having an outer diameter of 8 mm, a thickness of 0.3 mm, and a length of 220 mm was sealed by TIG welding, and a glass cloth having the components shown in Table 1 below was placed along the inner surface. . Then, deionized water was poured, and after deaeration by heating deaeration, the deaeration port was sealed by TIG welding to obtain a heat pipe test sample. The glass cloth having a thickness of 0.01 to 0.2 mm was appropriately selected and used. The working fluid in the heat pipe was adjusted to about 1.8 g.

<Evaluation method>
(1) pH of working fluid
In order to simulate alkali elution from the glass wick structure when the heat pipe was used for a long period of time, the produced test sample was subjected to an accelerated test under the condition of 150 ° C. × 185 h, and the pH of the working fluid after the heat treatment was measured. When the pH after heat treatment was 8 or less, it was evaluated as ⊚, when 8.5 or less was evaluated as ◯, when 9 or less was evaluated as Δ, and when it was more than 9, it was evaluated as x.
(2) Change in mass of wick structure In order to simulate the dissolution of the glass wick structure in the working fluid when the heat pipe is used for a long period of time, the prepared test sample is subjected to an acceleration test under the condition of 150 ° C. × 185 h, and before and after heat treatment. The change in the mass of the wick structure was measured. The mass change of the wick structure is calculated by the following formula. The case where the mass change rate after the durability test was 5% or less was evaluated as ⊚, the case of 10% or less was evaluated as ◯, the case of 15% or less was evaluated as Δ, and the case of greater than 15% was evaluated as x.
Mass change = (mass before durability test−mass after durability test) / (mass before durability test)
(3) Cost The manufacturing cost was evaluated according to the degree of difficulty of manufacturing the glass material. When the manufacturing cost was low, it was evaluated as ◯, and when the manufacturing cost was high, it was evaluated as x.

  Table 1 shows the evaluation results of the above (1) to (3) for the test sample of the manufactured heat pipe.

  In each of Examples 1 to 7 and Comparative Example 5, a glass material having an alkali component reduced by heat treatment after acid treatment was used as a wick structure. As shown in Table 1, as the alkaline component in the glass material became thicker, the pH after durability increased and the mass change increased.

  In Examples 8 to 11 and Comparative Example 1, a glass material having a reduced amount of alkali added was used as the wick structure. As shown in Table 1, as the alkali component became thicker, the pH after endurance increased and the mass change increased.

  In Comparative Example 2, E glass was used as the wick structure. Although E glass is known as non-alkali glass, it has a high Ca content of 13 mass%. In the wick structure using E glass, the pH after endurance increased and the change in mass also increased. Even E glass, which is expected to have water resistance in conventional applications, cannot obtain long-term reliability in a heat pipe environment.

  In Comparative Example 3, the E glass of Comparative Example 2 was subjected to bloom treatment, and the glass from which the alkaline component in the surface layer was removed was used as the wick structure. The bloom treatment also increased the pH after endurance and increased the mass change. It is known that blooming can suppress alkali elution in conventional applications, but long-term reliability cannot be obtained in a heat pipe environment. In order to obtain long-term reliability in a heat pipe environment, it is not enough to remove the alkaline component of the glass surface layer, and it is necessary to reduce the alkaline component of the entire mother phase.

  In Comparative Example 4, Pyrex (registered trademark) glass used in general water resistant applications was used as the wick structure. After the endurance, the pH increased and the change in weight also increased. Even for Pyrex glass, which is expected to be water resistant in conventional applications, long-term reliability cannot be obtained in a heat pipe environment.

  In Reference Example 1, quartz glass was used as the wick structure. Quartz glass contains almost no alkali component and there is no concern of alkali elution. However, since it does not contain alkali component, it has a high melting point, which increases the difficulty of production and increases the cost.

  In the present invention, since the glass material contains an alkali component in an amount of 0.01% by mass or more, the glass material can be manufactured at a relatively low cost, and results similar to those of quartz glass are obtained in pH and mass change after endurance.

1 Container Base Material 2 Wick Structure 3 Working Fluid 4 Cavity 10 Heat Pipe

Claims (8)

A heat pipe comprising a container base material having a hollow portion, in which a wick structure is arranged, and a working fluid sealed in the hollow portion,
The wick structure contains SiO ₂ as a main component, and the total content of Li, Na, Mg, K, Ca, and Ba is 0.01 mass% or more, and the total content of Li, Na, K, Ca, and Ba. Is 1% by mass or less and the content of Mg is 10% by mass or less.
The heat pipe, wherein the working fluid includes water.   The heat pipe according to claim 1, wherein the wick structure is glass fiber.   The heat pipe according to claim 1, wherein the wick structure is a yarn in which a plurality of glass fibers are bundled.   The heat pipe according to claim 1, wherein the wick structure is a glass fiber cloth in which glass fibers are woven in a cloth shape.   The heat pipe according to claim 1, wherein the wick structure is a non-woven fabric of glass fiber.   The heat pipe according to claim 2, wherein the glass fiber has a diameter of 2 to 10 μm.   The heat pipe according to claim 1, wherein the wick structure has a thickness of 0.01 to 0.2 mm.   The material forming the container base material is aluminum, magnesium, titanium, copper, stainless steel, or an alloy mainly containing any one of aluminum, magnesium, titanium, and copper. The heat pipe according to any one.

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