WO2015072503A1

WO2015072503A1 - Heat accumulator

Info

Publication number: WO2015072503A1
Application number: PCT/JP2014/080049
Authority: WO
Inventors: 裕昭桐木; 明旭韓; 久保　修一
Original assignee: イビデン株式会社
Priority date: 2013-11-15
Filing date: 2014-11-13
Publication date: 2015-05-21
Also published as: JP2017036841A

Abstract

A heat accumulator (10) comprises: piping (1); a powdered/granular body in which the piping is buried and the principal component of which is graphite (2); and a vessel (3) that houses the piping (1) and the powdered/granular body. As a result, the powdered/granular body that has graphite as a principal component accumulates heat, and the graphite is thereby inherently able to transfer heat without relying on convection, and mechanisms of heat accumulation and heat transfer are unchanged from low temperatures to high temperatures. The present invention can therefore accumulate heat independent of temperature. Further, because the powdered/granular body that has graphite as a principal component accumulates heat, and because the material thereof is highly heat resistant and does not easily deteriorate, the present invention can be used even at high temperatures and, in addition, can be used over long periods of time.

Description

Heat accumulator

The present invention relates to a heat accumulator.

Thermal accumulators are widely used in fields that handle heat, such as air conditioning systems and refrigerators.
Patent Document 1 discloses a heat storage system that stores water by freezing water in a heat storage tank with a refrigerant that flows through the circulation pipe disposed in the heat storage tank, and each of the circulation pipes is connected to each of the circulation pipes. A heat storage system is described, wherein the bent portions are continuously bent so as to be located in a zigzag shape in a parallel plane, and the refrigerant flow directions of adjacent circulation pipes are reversed. Yes.

A structure that bends continuously so as to be zigzag in a plane is also called a serpentine structure, and it is widely used as a method of arranging pipes that deliver heat within a limited area, such as air conditioners and automobile radiators. Has been.

Japanese Utility Model Publication No. 1-78835

However, the heat storage system described in Patent Document 1 maintains the liquid (water) in the heat storage tank at a predetermined temperature by exchanging heat through a pipe. Since the heat storage body (liquid in the heat storage tank) is a liquid, heat transfer is premised on convection. For this reason, when the viscosity increases in the temperature range to which the heat storage body is exposed, or when solidification or boiling occurs, the heat storage performance is significantly lowered, and in some cases, the heat storage device is damaged.
For this reason, the temperature range in which the heat accumulator can be used is greatly affected by the type of the heat accumulator used.

An object of the present invention is to provide a heat accumulator that can be used in a wide range of temperature, has little deterioration in performance even at low temperatures, can be used at high temperatures, has high heat transfer performance, and has little performance deterioration. And

The heat accumulator of the present invention for solving the above problems is composed of a pipe, a granular material mainly composed of graphite in which the pipe is embedded, a container for accommodating the pipe and the granular material.
According to the heat accumulator of the present invention, since the granular material mainly composed of graphite stores heat, the graphite itself can transfer heat without convection, and the mechanism of heat storage and heat transfer does not change from low temperature to high temperature. . For this reason, heat can be stored without depending on temperature.
According to the heat accumulator of the present invention, since the granular material mainly composed of graphite stores heat, it is a material that has high heat resistance and is not easily deteriorated. Can be used for use.

Furthermore, the following aspect is desirable for the heat accumulator of the present invention.
(1) The granular material contains silicon carbide.
Silicon carbide is a hard ceramic, and graphite is a soft ceramic. By coexisting with each other, silicon carbide polishes the graphite by friction between particles constituting the granular material due to vibration, thermal deformation, etc. during repeated use, increasing the contact area and facilitating heat conduction. .

(2) The pipe has a serpentine structure.
When the pipe of the heat accumulator of the present invention further has a serpentine structure, deformation of the pipe at the time of temperature rise or temperature drop occurs at various places, and friction between particles constituting the granular material is generated at that place. It tends to occur. Moreover, since the part with a large thermal deformation by thermal expansion and contraction is also a part with a large heat flow around a pipe, the heat storage to a heat storage body can be performed efficiently.

(3) The pipe has a plurality of serpentine structures facing each other, and a graphite plate is embedded between the plurality of serpentine structures.
The heat accumulator of the present invention has a plurality of serpentine structures in which the pipes face each other, and a graphite plate is embedded between the plurality of rows of serpentine structures, thereby forming two substantially parallel graphite plates. The pipes constituting the serpentine structure are arranged in the space, and the pipes are arranged to be embedded in the powder particles.

By adopting such an arrangement, when a serpentine-structured pipe is deformed due to thermal expansion or contraction, its movement is constrained by two substantially parallel graphite plates and powder particles, and the powder particles around the pipe A strong frictional force is generated on the body. For this reason, the contact area between the particles constituting the granular material is increased, heat can be easily transferred between the particles constituting the granular material, and the heat transfer performance can be enhanced.

(4) The space formed by the particles of the granular material is filled with a phase change material.
A phase change material absorbs or releases a lot of heat with a phase transition. Therefore, when holding the granular material which is a heat storage body at the temperature more than a phase transition temperature, a temperature fall can be suppressed. Moreover, when holding the granular material which is a heat storage body at the temperature below a phase transition temperature, a temperature rise can be suppressed. In addition, since heat transfer is performed by powder particles without using a phase change material, there is little deterioration in performance even at low temperatures, and it can be used at high temperatures, providing a heat accumulator with high heat transfer performance and low performance deterioration. be able to.

According to the present invention, since the granular material having graphite as a main component stores heat, the graphite itself can transfer heat without convection, and the mechanism of heat storage and heat transfer does not change from low temperature to high temperature. For this reason, heat can be stored without depending on temperature.
According to the heat accumulator of the present invention, since the granular material mainly composed of graphite stores heat, it is a material that has high heat resistance and is not easily deteriorated. Can be used for use.

Fig.1 (a) is a top view of the external appearance of the thermal accumulator of Embodiment 1 which concerns on this invention, FIG.1 (b) is the side view. 2A is a cross-sectional view taken along line AA ′ of FIG. 1A, FIG. 2B is a cross-sectional view taken along line BB ′ of FIG. 1A, and FIG. FIG. 2 is a cross-sectional view taken along the line CC ′ of FIG.

The heat accumulator of the present invention is composed of a pipe, a granular material mainly composed of graphite in which the pipe is embedded, a container that accommodates the pipe and the granular material.
According to the heat accumulator of the present invention, since the granular material mainly composed of graphite stores heat, the graphite itself can transfer heat without convection, and the mechanism of heat storage and heat transfer does not change from low temperature to high temperature. . For this reason, heat can be stored without depending on temperature.
According to the heat accumulator of the present invention, since the granular material mainly composed of graphite stores heat, it is a material that has high heat resistance and is not easily deteriorated. Can be used for use.

The material and thickness of the pipe of the present invention are not particularly limited. Among these, the material of the pipe is preferably a metal, and for example, stainless steel, iron, copper, aluminum and the like can be used.
The powder is not particularly limited as long as graphite is a main component. Any kind of graphite such as natural graphite, artificial graphite, quiche graphite, and expanded graphite can be used.

In the present specification, “a granular material containing graphite as a main component” means that 50 to 100% by weight of the granular material is graphite. The weight of graphite contained in the granular material is desirably 70 to 100% by weight of the granular material. If 50% by weight or more of the granular material is graphite, the graphite is likely to be worn by friction, and if it is 70% by weight or more, it is more likely to be worn. When the graphite is worn, the contact area between the particles increases, and the heat transfer performance in the heat storage body can be improved.

The form of the granular material is not particularly limited. For example, the following forms are mentioned.
(A) The form of the granular material formed by mixing graphite and another substance.
(B) The form of the granular material formed by partially converting the surface of the graphite particles into another substance.
(C) The form of a granular material in which other substances are present inside the graphite particles.
The “other substance” is not particularly limited, but may be, for example, silicon carbide.

The measuring method about content of the graphite in a granular material is demonstrated.
Unlike other ceramics, graphite is a gas such as carbon dioxide or carbon monoxide that is a reaction product with oxygen and does not form a film. For this reason, it can remove by heating in air | atmosphere. For this reason, by pulverizing the graphite surface to be exposed and burning in the air, the weight change before and after heating can be measured, and the graphite content can be measured.

In the heat accumulator of the present invention, the container for storing the granular material is not particularly limited. For example, a ceramic container, a metal container, or the like can be used. In addition, when using a thermal accumulator at the temperature over 600 degreeC, it is preferable to be sealed so that it may not contact external air.

The average particle diameter of the granular material of the regenerator of the present invention is not particularly limited. It can be fine or coarse. Among these, the average particle size of the desirable powder is 1 to 50 mm. When the average particle diameter is 1 mm or more, the number of contacts between the particles can be reduced, so that the heat transfer performance between the powder particles can be increased. When the average particle diameter is 50 mm or less, the heat transfer performance can be improved because the pipes inside the heat accumulator can be contacted at many places.
Further, the particle size distribution of the granular material is not particularly limited, but preferably has a plurality of peaks. When the particle size distribution of the granular material is a particle size distribution having a plurality of peaks, fine particles can enter the gaps between the coarse particles, so that the heat transfer performance can be further improved and the heat storage capacity can be increased.

In the heat accumulator of the present invention, the powder body mainly composed of graphite preferably contains silicon carbide.
Silicon carbide is a hard ceramic, and graphite is a soft ceramic. The coexistence of these allows silicon carbide to polish the graphite by friction between the particles constituting the granular material due to vibration, thermal deformation, etc., increasing the contact area and facilitating heat conduction.

In addition, when a granular material contains graphite and silicon carbide, the form of a granular material is "other substances" in the form (a), (b), or (c) of the granular material mentioned above. It is desirable that the granular material is silicon carbide.
Such a method for producing a granular material when the granular material contains graphite and silicon carbide is exemplified below.
(A) When a granular material is a form formed by mixing graphite and silicon carbide, the granular material can be obtained, for example, by mixing graphite particles and silicon carbide particles.
(B) When the granular material is in a form in which the surface of the graphite particle is partially converted to silicon carbide, the surface of the granular material reacts due to the action of SiO gas or the like in a high temperature atmosphere of 1500 ° C. or higher. It can be obtained by pulverizing the converted graphite lump.
(C) When the powder is in a form in which silicon carbide is present inside the graphite particles, the powder is mixed with, for example, silicon carbide powder in coke, which is a raw material of graphite, and a binder such as pitch is added. It can be obtained by further pulverizing the graphite material obtained by kneading, press molding, firing and graphitization. Such a granular material has a structure in which silicon carbide particles are uniformly dispersed inside graphite.

A preferable content of silicon carbide is 20 to 30% by weight. When the silicon carbide content is in the range of 20 to 30% by weight, the ratio of silicon carbide as the abrasive to the polished graphite is appropriate, and the contact area between the particles tends to increase due to wear.

The pipe of the regenerator of the present invention preferably has a serpentine structure.
When the pipe of the regenerator of the present invention has a serpentine structure, deformation of the pipe when the temperature rises occurs at various places, and friction between the particles constituting the granular material easily occurs at that place. Moreover, since the part with a large thermal deformation by thermal expansion and contraction is also a part with a large heat flow around a pipe, the heat storage to a heat storage body can be performed efficiently.

The serpentine structure is a state where a snake-like bent structure is formed, and a linear object is alternately folded back to form a surface.
Since the serpentine structure can diffuse a linearly flowing fluid in a planar shape, heat can be transmitted to more powder particles by using it as a heat storage body.

The pipe of the regenerator of the present invention preferably has a plurality of serpentine structures facing each other, and a graphite plate is embedded between the plurality of serpentine structures.

The heat accumulator of the present invention has a plurality of serpentine structures in which the pipes face each other, and a graphite plate is embedded between the plurality of rows of serpentine structures, thereby forming two substantially parallel graphite plates. The pipes constituting the serpentine structure are arranged in the space, and the pipes are arranged to be embedded in the powder particles.

By adopting such an arrangement, when a serpentine-structured pipe is deformed due to thermal expansion or contraction, its movement is constrained by two substantially parallel graphite plates and powder particles, and the powder particles around the pipe A strong frictional force is generated on the body. For this reason, the contact area between the particles constituting the granular material is increased, heat can be easily transferred between the particles constituting the granular material, and the heat transfer performance can be enhanced.
In addition, since the pipe has a plurality of serpentine structures facing each other, the fluid flowing linearly can be spread to every corner of the granular material inside the heat accumulator.

It is preferable that the space formed by the granular material of the present invention is filled with a phase change material.
A phase change material absorbs or releases a lot of heat with a phase transition. Therefore, when holding the granular material which is a heat storage body at the temperature more than a phase transition temperature, a temperature fall can be suppressed. Moreover, when holding the granular material which is a heat storage body at the temperature below a phase transition temperature, a temperature rise can be suppressed.
In addition, heat transfer is performed by powder and granular material without depending on phase change material, so there is little deterioration in performance even at low temperatures, it can be used at high temperatures, and it should be a heat storage device with high heat transfer performance and low performance deterioration. Can do.

As the phase transition material, sodium nitrate, potassium nitrate, etc. can be used. Since these substances have a melting point in the temperature range that can be used in the regenerator of the present invention, the high temperature can be maintained for a longer time when heated exceeding the melting point. Moreover, when it cools below melting | fusing point, it can maintain low temperature for a long time.

Since the heat storage body of the present invention is composed of a granular material containing graphite as a main component, it can be used at a high temperature. For example, it can be suitably used as a heat storage body that stores the heat of solar thermal power generation. When used for solar thermal power generation, it is preferable to maintain a higher temperature. Moreover, it is preferable not to use a phase change substance or to use sodium nitrate etc., for example. These phase change materials can be used stably up to a temperature exceeding 380 ° C., and can be used without degrading the performance of the regenerator.

Embodiment 1 of the present invention will be described below with reference to the drawings.
Fig.1 (a) is a top view of the external appearance of the thermal accumulator of Embodiment 1 which concerns on this invention, FIG.1 (b) is the side view.
2A is a cross-sectional view taken along line AA ′ of FIG. 1A, FIG. 2B is a cross-sectional view taken along line BB ′ of FIG. 1A, and FIG. FIG. 2 is a cross-sectional view taken along the line CC ′ of FIG.
The cross section along the line AA ′ is a cross section at the position of the pipe, and the cross section along the line BB ′ is a cross section at the position of the graphite plate.

As shown in FIGS. 1A and 1B, the heat accumulator 10 according to the first embodiment is accommodated in a container 3 made of a rectangular parallelepiped stainless steel having outer dimensions of a length of 1412 mm, a height of 798 mm, and a width of 1400 mm. A heat insulating material having a thickness of 50 mm is attached to the upper surface, the lower surface, and the side surface of the inside of the container 3. The heat insulating material is made of alumina.
At both ends in the length direction of the container 3, there are joints 4 connected to the internal pipe 1. The opening of the joint 4 has an inner diameter of φ150 mm. The pipe 1 is bent so that the inside of the heat accumulator 10 has a serpentine structure. The thickness of the pipe 1 is φ30 mm. The pipe 1 having such a serpentine structure has five rows so as to be connected in parallel to the joints 4 at both ends, and a graphite plate 5 of 448 × 360 × 10 mm is formed between the surfaces formed by the pipe having the serpentine structure. Each is inserted. The pipe 1 and the graphite plate 5 having a serpentine structure are filled with a granular material 2 mainly composed of graphite. The void formed by the particles of the granular material is further filled with a phase change material made of sodium nitrate.

The granular material 2 is obtained as follows, for example. The graphite mass is placed in an environment of 1500 to 2200 ° C., and SiO gas is introduced. Thereby, silicon carbide is formed on the surface of the graphite particles by the reaction shown in the following (formula 1).
2C + SiO → SiC + CO ↑ (Formula 1)
By pulverizing the graphite lump in which silicon carbide is formed, a granular material whose main component is graphite, in which part of the surface is made of particles converted to silicon carbide, is obtained. When the starting material is graphite and converted to silicon carbide with SiO gas, the proportion of graphite converted from graphite before reaction to silicon carbide can be calculated stoichiometrically from the weight change W ′ due to the reaction. .

That is, the ratio C of the weight of graphite converted to silicon carbide and the weight of graphite before reaction (C = weight of graphite converted to silicon carbide / weight of graphite before reaction) is defined as the atomic weight of carbon (graphite) being 12. When the atomic weight of silicon is 28, it can be expressed by the following (formula 2).
C = 3 × (W′−1) / 2 (Formula 2)
For example, if there is no weight increase due to the reaction (the weight of the reaction product after the reaction is the same as the original weight: W ′ = 1), there will be no graphite converted into silicon carbide.
If the weight increase due to the reaction is 66.7% (W ′ = 1.667), all the graphite has been converted to silicon carbide.
If the weight increase due to the reaction is 22% (W ′ = 1.22), 33% of the pre-reaction graphite has been converted to silicon carbide.

According to the heat accumulator of this embodiment, the heat accumulating material is composed of a granular material mainly composed of graphite and a phase change material. The phase change material can be used stably if it is 380 ° C. or lower. The heat accumulator can transfer heat without convection and can be used in a wide temperature range.
In addition, since the granular material contains silicon carbide, the contact area of the granular material can be gradually increased by friction between graphite and silicon carbide during use, and therefore a heat storage device having high heat transfer performance is provided. Can do.

DESCRIPTION OF SYMBOLS 1 Pipe 2 Granule 3 Container 4 Joint 5 Graphite plate 10 Regenerator

Claims

Pipes,
A granular material mainly composed of graphite embedded in the pipe;
A heat accumulator comprising the pipe and a container for accommodating the powder and granular material.
The heat storage device according to claim 1, wherein the granular material contains silicon carbide.
The regenerator according to claim 1, wherein the pipe has a serpentine structure.
The regenerator according to claim 3, wherein the pipe has a plurality of serpentine structures facing each other, and a graphite plate is embedded between the plurality of serpentine structures.
The heat accumulator according to any one of claims 1 to 4, wherein a gap formed by the particles of the granular material is filled with a phase change material.