JP7760815B2 - Heat storage material composition - Google Patents

Description

The present invention relates to a heat storage material composition.

Heat storage materials (latent heat storage materials, sensible heat storage materials, heat storage materials, etc.) that store heat (absorb heat) and release heat (release heat) by utilizing a phase change between solid and liquid (solid-liquid phase change) within a specified temperature range have been known for some time. Heat storage materials are widely used in a variety of fields, for example, in heating and cooling equipment for buildings (homes, office buildings, etc.) that require large amounts of cold or hot heat, and in waste heat recovery equipment for factories.

As a technology related to heat storage materials, for example, Japanese Patent Application Laid-Open No. 11-323319 (Patent Document 1) discloses a latent heat storage material composition that combines sodium acetate trihydrate with hydrophilic fumed silica, hydrophilic fumed alumina, and calcium salt as phase separation inhibitors. This prevents phase separation even when subjected to repeated melting-freezing heat cycles over a long period of time.

Japanese Patent Laid-Open Publication No. 2000-63810 (Patent Document 2) discloses a latent heat storage material composition comprising 100 parts by weight of calcium chloride hydrate having the general formula CaCl ₂ ·nH ₂ O (where n is 4.5 to 6.5), 10 to 35 parts by weight of a polyhydric alcohol, 1 to 30 parts by weight of one or more alkali metal or alkaline earth metal halides (excluding strontium chloride and barium chloride), and 0.1 to 20 parts by weight of strontium chloride and/or barium chloride, and, if necessary, 0.1 to 20 parts by weight of one or more fibrous minerals such as attapulgite, wollastonite, or sepiolite. This composition has a relatively low freezing point (5 to 25°C) and is therefore suitable for use as a heat storage material in air conditioning heating and cooling systems.

In addition, Japanese Patent Application Laid-Open Publication No. 2015-218212 (Patent Document 3) discloses a latent heat storage material composition containing a latent heat storage material (A) as the main component, and a melting point adjuster (B), a phase separation inhibitor (C) with microcrystal formation, supercooling prevention, and thickening properties, and/or a melting point adjuster (B') with microcrystal formation properties, and a supercooling inhibitor (D) blended in predetermined amounts as essential ingredients. The latent heat storage material composition is obtained by blending the latent heat storage material, melting point adjuster, phase separation inhibitor, and supercooling inhibitor in predetermined amounts, melting, mixing, and cooling. This composition is composed primarily of aggregates of fine particles that are flexible and fluid at room temperature and pressure, and does not undergo phase separation or supercooling, allowing for excellent, stable repeated heat storage and heat release. It is also said to be usable as a flowable heat transfer medium.

Furthermore, Japanese Patent Laid-Open Publication No. 2016-108535 (Patent Document 4) discloses a heat storage material composition containing a sugar alcohol and a supercooling stabilizer, wherein the supercooling stabilizer is (i) a salt that has a solubility of 9 g or more in 100 mL of water at 20°C and is a monovalent anion, (ii) a polymer whose monomer is a salt, or (iii) a polymer with a molecular weight of 7,000 to 4,000,000 and whose monomer is an alcohol that has a solubility of 9 g or more in 100 mL of water at 20°C. This is said to enable the supercooled state to be stably maintained at room temperature or a temperature close to room temperature.

For example, in International Publication No. 2007/099798 (Patent Document 5), the present applicant discloses a heat storage material composition containing calcium chloride as the main component, strontium chloride and barium chloride as nucleating agents, and a cellulose-based material as a thickener. This makes the composition resistant to deterioration and provides high durability and heat resistance, even when repeatedly exposed to high temperatures above room temperature.

Furthermore, in Japanese Patent Laid-Open Publication No. 2019-137854 (Patent Document 6), the present applicant discloses a heat storage material composition containing a solid-liquid phase change material that undergoes a phase change between solid and liquid within a specified temperature range, water, a nucleating material whose main component is strontium chloride, and graphite powder. This is said to achieve a rapid solid-liquid phase change and enable repeated use.

Japanese Patent Application Publication No. 11-323319 Japanese Patent Application Laid-Open No. 2000-63810 Japanese Patent Application Laid-Open No. 2015-218212 Japanese Patent Application Laid-Open No. 2016-108535 International Publication No. 2007/099798 Japanese Patent Application Laid-Open No. 2019-137854

The heat storage material compositions that utilize the solid-liquid phase change process described above typically have low overall thermal conductivity, making it difficult to quickly store heat from or release heat to the surrounding environment, resulting in the problem that heat storage and release take a long time.

The applicant is attempting to shorten the heat storage and heat release time by adding graphite powder, which has high thermal conductivity, to the heat storage material composition, as described in Patent Document 6.

However, although graphite powder has good thermal conductivity, its specific gravity is higher than that of water. Therefore, even if graphite powder is added to a heat storage material composition, the graphite powder settles to the bottom of the heat storage material composition, leaving no graphite powder in the upper part of the heat storage material composition, which makes it difficult to improve the overall thermal conductivity of the heat storage material composition. The technologies described in Patent Documents 1-6 above cannot solve these problems.

The present invention was made to solve the above problems, and aims to provide a heat storage material composition that enables rapid heat storage and release and can be used repeatedly and stably.

The heat storage material composition of the present invention contains a solid-liquid phase change material that undergoes a phase change between solid and liquid within a specified temperature range, water, a nucleating material, graphite powder, and a fine powder that has a specific gravity close to that of water, is resistant to water wetting, and has high thermal conductivity.

This invention enables rapid heat storage and release, and allows for stable, repeated use.

1 is a table showing ingredients of heat storage material compositions of Example 1 and Comparative Examples 1 and 2. 1 is a graph showing the temperature changes of the heat storage material compositions of Example 1 and Comparative Example 1-2 during the fifth heat cycle. 1 is a table showing ingredients of the heat storage material compositions of Examples 2-3 and Comparative Example 1. 1 is a graph showing the temperature changes of the heat storage material compositions of Example 2-3 and Comparative Example 1 during the sixth heat cycle. 1 is a table showing ingredients of the heat storage material compositions of Examples 3-4 and Comparative Example 1. 1 is a graph showing the temperature changes of the heat storage material compositions of Examples 3-4 and Comparative Example 1 during the sixth heat cycle. 1 is a table showing ingredients of the heat storage material compositions of Examples 4 to 7 and Comparative Example 1. 1 is a graph showing the temperature changes of the heat storage material compositions of Examples 4-7 and Comparative Example 1 during the third heat cycle.

The following describes an embodiment of the present invention with reference to the accompanying drawings to aid in understanding the present invention. Note that the following embodiment is an example of a specific embodiment of the present invention and is not intended to limit the technical scope of the present invention.

The inventors have confirmed that in a heat storage material composition containing a solid-liquid phase change material that undergoes a phase change between solid and liquid within a specified temperature range, water, a nucleating material, and graphite powder, the rate of heat storage and heat release is improved to a certain extent due to the high thermal conductivity of the graphite powder (the thermal conductivity of graphite is approximately 2000 W/(m·K), while the thermal conductivity of copper is approximately 400 W/(m/K)). Here, graphite refers to graphite.

However, the specific gravity of the heat storage material composition (aqueous solution) is approximately 1.5, while the specific gravity of the graphite powder is approximately 2.0. Because the specific gravity of graphite powder is higher than that of water, the graphite powder settles to the bottom of the heat storage material composition, leaving no graphite powder in the upper part of the heat storage material composition, which has proven difficult to achieve in improving the overall thermal conductivity of the heat storage material composition.

The inventor has been researching the above-mentioned heat storage material composition for many years, and has focused on fine powders that have a specific gravity close to that of water, are resistant to water wetting, and have high thermal conductivity. Based on the examples described below, he has completed the present invention.

In other words, the heat storage material composition of the present invention contains a solid-liquid phase change material that undergoes a phase change between solid and liquid within a specified temperature range, water, a nucleating material, graphite powder, and a fine powder that has a specific gravity close to that of water, is resistant to water wetting, and has high thermal conductivity. This enables rapid heat storage and release, as well as stable, repeated use.

In other words, by adding fine powder, the fine powder does not settle to the bottom of the heat storage material composition, but rather remains at the top of the heat storage material composition and is uniformly dispersed, increasing the thermal conductivity of the upper portion of the heat storage material composition. On the other hand, by adding graphite powder to the heat storage material composition, the graphite powder remains at the bottom of the heat storage material composition and is uniformly dispersed, increasing the thermal conductivity of the lower portion of the heat storage material composition. In this way, the combination of graphite powder and fine powder can increase the overall thermal conductivity of the heat storage material composition, thereby making it possible to speed up the heat storage and heat release rate of the heat storage material composition.

Furthermore, even if the heat storage material composition repeatedly melts and solidifies during a heat cycle in which the temperature is lowered from a high temperature to a low temperature and then raised back to a high temperature, the graphite powder and fine powder act as a medium for heat conduction to the solid-liquid phase change material, ensuring stable heat storage and release by the heat storage material composition and suppressing supercooling. This allows for repeated use over long periods of time.

The type of solid-liquid phase change material is not particularly limited, but examples include calcium chloride, sodium acetate, and sodium hydrogen phosphate. Calcium chloride is a component that changes phase in the thermal storage material composition between calcium chloride hexahydrate crystals (solid) and calcium chloride water liquid (liquid) as the temperature of the surrounding environment changes. The calcium chloride in the thermal storage material composition can be anhydrous (CaCl ₂ ) or its hydrate (CaCl ₂ ·nH ₂ O (n = 1 to 6)). Calcium chloride dihydrate is particularly preferred because it is relatively easy to obtain. The amount of water added to the thermal storage material composition is the amount required to generate calcium chloride hexahydrate, and although this may vary slightly depending on the amount of water added due to the addition of other components, it is approximately 6 moles per mole of CaCl ₂ . When a hydrate is used as calcium chloride, the amount of water is approximately 6 moles, including the water of crystallization in the hydrate.

Note that other solid-liquid phase change materials also undergo a phase change similar to that of calcium chloride within a specified temperature range, although the temperature range for the phase change is different. These types of solid-liquid phase change materials may be combined as appropriate.

The type of _nucleating material is not particularly limited, and examples thereof include barium chloride ( _BaCl2 ), strontium chloride ( _SrCl2 ), sodium dihydrogen phosphate ( _NaH2PO4 ), and barium sulfide (BaS). Since barium chloride, strontium chloride, sodium dihydrogen phosphate, and barium sulfide form hydrates, for example, their anhydrides or hydrates of these compounds may be used. Other _nucleating materials such as disodium _hydrogen phosphate dodecahydrate ( _{Na2HPO4.12H2O} ) and fly ash may also be included.

Now, there are no particular limitations on the type of graphite in the graphite powder, but examples include flaky graphite, amorphous graphite, artificial graphite, coke, expanded graphite, spherical graphite, specially treated graphite, spherical graphite, carbon fiber, carbon nanotubes, etc. Furthermore, it is preferable that the graphite powder be subjected to a hydrophilic surface treatment to improve dispersibility in an aqueous solution containing a solid-liquid phase change material. These types of graphite powder may also be combined as appropriate.

Furthermore, there are no particular limitations on the average particle size of the graphite powder, but, for example, an average particle size of 5 μm to 20 μm is preferred, and an average particle size of 5 μm to 15 μm is even more preferred.

Here, there are no particular limitations on the type of fine powder, but carbon black is one example. Carbon black has the same components as graphite powder, is resistant to water, and has excellent thermal conductivity. Although the specific gravity of carbon black is approximately 1.8 to 1.9, the apparent specific gravity of carbon black in fine powder form is extremely low, at approximately 0.04 to 0.08. Therefore, when carbon black is added as a fine powder to a heat storage material composition, the carbon black remains in the upper part of the heat storage material composition and is uniformly dispersed, thereby increasing the thermal conductivity of the upper part of the heat storage material composition.

Here, carbon black refers to a finely powdered, spherical or chain-like conductive substance produced by the gas-phase thermal decomposition or incomplete combustion of natural gas or hydrocarbon gas. There are no particular limitations on the type of carbon black, but examples include acetylene black, furnace black, thermal black, and channel black. These types of carbon black may also be combined as appropriate.

While there are no particular limitations on the average particle size of carbon black, it is preferable for the average particle size to be 10 to 100 nm, and more preferably 20 to 90 nm. Here, the average particle size of carbon black can be measured using, for example, photon correlation spectroscopy (dynamic light scattering) or laser diffraction/scattering (static light scattering).

Furthermore, there are no particular limitations on the dibutyl phthalate (DBP) oil absorption of carbon black, but the DBP oil absorption is preferably 30 ml/100 g to 200 ml/100 g, and more preferably 50 ml/100 g to 150 ml/100 g. The DBP oil absorption of carbon black can be measured, for example, in accordance with JIS K 6217-4.

In addition to carbon black, the fine powder may be, for example, carbon fiber that has been crushed and then surface-treated to make it water-repellent. It may also be plastic or metal that has been crushed and then surface-treated to make it water-repellent.

Furthermore, a higher total concentration of graphite powder and fine powder is preferable because the graphite powder and fine powder in the heat storage material composition come into contact with each other, forming a network of graphite powder and fine powder, and increasing the thermal conductivity of the entire heat storage material composition. However, if the total concentration of graphite powder and fine powder is too high, it will interfere with the melting and solidification of the solid-liquid phase change material. Therefore, for example, the total concentration of graphite powder and fine powder is preferably 1% to 10% by weight of the total heat storage material composition, and more preferably 2% to 8% by weight of the total heat storage material composition.

The concentration of the graphite powder is not particularly limited, but is preferably within the range of 0.5% to 5.0% by weight of the total heat storage material composition. The concentration of the fine powder is not particularly limited, but is preferably within the range of 0.5% to 5.0% by weight of the total heat storage material composition. The mixing ratio of the graphite powder to the fine powder is not particularly limited, but is preferably within the range of 1.0:0.2 to 1.0:5.0 by weight, and more preferably 1.0:0.5 to 1.0:2.5 by weight. The concentration of the fine powder is preferably equal to or greater than the concentration of the graphite powder.

It is also preferable to add a hydrophilic thickener to the heat storage material composition. Adding a hydrophilic thickener increases the viscosity of the heat storage material composition as a whole, and even if there is a slight difference in the specific gravity of the heat storage material composition, the specific gravity of the graphite powder, and the specific gravity of the fine powder, it is possible to suppress segregation of the graphite powder and fine powder in the heat storage material composition, uniformly disperse the graphite powder at the bottom of the heat storage material composition, and fix the fine powder in a uniformly dispersed state at the top of the heat storage material composition. This makes it possible to maintain a high thermal conductivity of the entire heat storage material composition, accelerate the solid-liquid phase change of the solid-liquid phase change material, and increase the rate of melting and solidification of the solid-liquid phase change material.

Here, the type of hydrophilic thickener is not particularly limited, but examples include water-soluble copolymers such as PEG/PPG, hydroxyethylcelluloses such as carboxymethylcellulose and hypromellose (methylhydroxyethylcellulose), hydroxypropylmethylcellulose, cellulose ether, cellulose derivatives, cellulose nanofiber, polyethylene glycol, carboxyvinyl polymer, acrylic acid/alkyl methacrylate copolymer, cross-linked acrylic acid-based water-soluble polymers such as polyacrylates, xanthan gum, diutan gum, polysaccharides, sodium polyacrylate, finely powdered silica, silica flour, diatomaceous earth fine powder, glycerin, agar, etc. These types of thickeners may also be combined as appropriate.

The thickener has an affinity with the water in the heat storage material composition, forming a network and increasing viscosity, so it is effective even at low concentrations. However, if the thickener concentration is too high, it will interfere with the melting and solidification of the solid-liquid phase change material. Therefore, for example, the thickener concentration is preferably 0.1% to 3.0% by weight of the total heat storage material composition, and more preferably 0.1% to 2.0% by weight. Here, if the fine powder is carbon black, the carbon black itself has a thickening effect, so it is not necessary to add a hydrophilic thickener.

Furthermore, a melting point adjuster may be appropriately added to the heat storage material composition. Here, the melting point adjuster refers to a lowering material that lowers the freezing point (melting point) of the solid-liquid phase change material and changes the latent heat generation temperature. Examples include ammonium bromide (NH ₄ Br) and ammonium chloride (NH ₄ Cl). Specifically, the latent heat generation temperature of calcium chloride hexahydrate is approximately 30°C, which is its freezing point. However, depending on the intended use of the heat storage material, it may be desirable to lower the freezing point to a temperature lower than approximately 30°C, such as around 20°C. In such cases, by adding a melting point adjuster to the heat storage material composition, the freezing point of the solid-liquid phase change material of the heat storage material composition can be intentionally lowered to suit the intended use of the heat storage material. The concentration of the melting point adjuster is not particularly limited, and is set, for example, to 1.0% by weight to 20.0% by weight of the total heat storage material composition.

Furthermore, there are no particular limitations on how the heat storage material composition can be used, but one example is to fill a container with the heat storage material and seal it, and use the resulting product as a heat storage material. Because the heat storage material composition has high thermal conductivity, there are no particular limitations on the shape of the container, and the design can be modified appropriately to suit the application, such as into a plate or cylinder.

Furthermore, there are no particular limitations on the uses of the heat storage material composition, and it can be used, for example, as a heat storage material in air conditioning and heating equipment, factory exhaust heat recovery equipment, agricultural equipment such as greenhouses, electronic devices such as terminal devices and mobile terminal devices, and location identification devices used in automobiles and buses. The heat storage material can be used to effectively utilize thermal energy by storing heat from the surrounding environment during the day and releasing it into the surrounding environment at night.

The following provides a detailed explanation of examples and comparative examples of the present invention, but the application of the present invention is not limited to these examples.

Example 1
A heat storage material composition was produced by adjusting the solid-liquid phase change material (calcium chloride _dihydrate ) ( _CaCl2.2H2O ) to 54.0 wt%, the melting point adjuster (ammonium bromide) ( _NH4Br ) to 10 wt%, the water to 25.5 wt%, the nucleating material to 4.5 wt%, the graphite powder to 2.5 wt%, the carbon black to 2.5 wt%, and the hydrophilic thickener to 1.0 wt%. By adding the melting point adjuster, the freezing point (melting point) of the heat storage material composition was set to 18°C.

Here, the nucleating material was a mixture of barium chloride dihydrate ( _BaCl2.2H2O ), strontium chloride dihydrate ( _SrCl2.2H2O ), and sodium _dihydrogen phosphate ( _{NaH2PO4 )} in appropriate proportions. The graphite powder used was flaky graphite with an average particle size of 10.3 μm _. Furnace black was used as the carbon black. The hydrophilic thickener used was a mixture of cellulose ether and polyethylene glycol in appropriate proportions. This manufactured heat storage material composition was designated Example 1.

<Comparative Example 1>
A heat storage material composition was produced in the same manner as in Example 1, except that the graphite powder, carbon black, and hydrophilic thickener were not added and the amount of water added was adjusted in the heat storage material composition of Example 1. This produced heat storage material composition was designated Comparative Example 1.

<Comparative Example 2>
A heat storage material composition was produced in the same manner as in Example 1, except that no carbon black was added and the amount of water added was adjusted in the heat storage material composition of Example 1. This produced heat storage material composition was designated Comparative Example 2. Note that Figure 1 shows ingredient tables for the heat storage material compositions of Example 1 and Comparative Examples 1-2.

<Evaluation method>
For the heat storage material compositions of Example 1 and Comparative Example 1-2, the ambient temperature of each heat storage material composition was lowered from approximately 35°C to approximately 5°C over a predetermined time (cooling), and then again raised from approximately 5°C to 35°C (heating), and this heat cycle was repeated a predetermined number of times to measure the temperature change of each heat storage material composition.

<Evaluation results>
Figure 2 shows a graph of the temperature changes of the heat storage material compositions of Example 1 and Comparative Example 1-2 during the fifth heat cycle. As shown in Figure 2, it can be seen that during cooling in the heat cycle, the heat storage material composition of Example 1 had a higher cooling temperature per unit time and a faster cooling rate than the heat storage material composition of Comparative Example 1-2.

On the other hand, it can be seen that during heating in the heat cycle, the heat storage material composition of Example 1 had a higher heating temperature per unit time, a faster heating rate, and a faster rise in the graph compared to the heat storage material composition of Comparative Example 1-2.

Example 2
A heat storage material composition was produced in the same manner as in Example 1, except that the concentration of graphite powder was 1.0 wt %, the concentration of carbon black was 1.0 wt %, and the amount of water added was adjusted in the heat storage material composition of Example 1. This produced heat storage material composition was designated Example 2.

Example 3
A heat storage material composition was produced in the same manner as in Example 1, except that in the heat storage material composition of Example 1, the graphite powder concentration was set to 5.0 wt%, the carbon black concentration was set to 1.0 wt%, and the amount of water added was adjusted. This produced heat storage material composition was designated Example 3. Note that Figure 3 shows the ingredient tables of the heat storage material compositions of Examples 2-3 and Comparative Example 1. Examples 2-3 and Comparative Example 1 were also evaluated using the same evaluation methods as described above.

<Evaluation results>
Figure 4 shows a graph of the temperature changes of the heat storage material compositions of Example 2-3 and Comparative Example 1 during the sixth heat cycle. Also shown in Figure 4 are photographs of the ambient temperature and the appearance of the heat storage material composition of Example 2-3. As shown in Figure 4, it can be seen that during cooling in the heat cycle, the heat storage material composition of Example 2-3 had a higher cooling temperature per unit time and a faster cooling rate than the heat storage material composition of Comparative Example 1.

On the other hand, it can be seen that during heating in the heat cycle, the heat storage material composition of Example 2-3 had a higher heating temperature per unit time, a faster heating rate, and a faster rise in the graph compared to the heat storage material composition of Comparative Example 1. Furthermore, it can be seen that no separation of water was observed in any of the heat storage material compositions of Example 2-3, and that the water was uniformly dispersed.

Furthermore, the heat storage material composition of Example 3 had a higher cooling temperature per unit time and a faster cooling rate than the heat storage material composition of Example 2. Furthermore, the heat storage material composition of Example 3 had a higher heating temperature per unit time and a faster heating rate than the heat storage material composition of Example 2. In other words, it was found that the cooling rate and heating rate improved as the concentration of graphite powder increased.

Example 4
A heat storage material composition was produced in the same manner as in Example 1, except that in the heat storage material composition of Example 1, the graphite powder concentration was 1.0 wt %, the carbon black concentration was 5.0 wt %, and the amount of water added was adjusted. This produced heat storage material composition was designated Example 4. Note that Figure 5 shows ingredient tables for the heat storage material compositions of Examples 3-4 and Comparative Example 1. Examples 3-4 and Comparative Example 1 were also evaluated using the same evaluation methods as described above.

<Evaluation results>
Figure 6 shows a graph of the temperature changes of the heat storage material compositions of Examples 3-4 and Comparative Example 1 during the sixth heat cycle. Figure 6 also shows the ambient temperature and a photograph of the appearance of the heat storage material composition of Example 4. As shown in Figure 6, it can be seen that during cooling in the heat cycle, the heat storage material compositions of Examples 3-4 had a higher cooling temperature per unit time and a faster cooling rate than the heat storage material composition of Comparative Example 1.

On the other hand, it can be seen that during heating in the heat cycle, the heat storage material composition of Examples 3-4 had a higher heating temperature per unit time, a faster heating rate, and a faster rise in the graph compared to the heat storage material composition of Comparative Example 1. It can also be seen that the heat storage material composition of Example 4 did not show any separation of water and was uniformly dispersed. In other words, it was found that, as with graphite powder, the cooling rate and heating rate improved as the concentration of carbon black increased.

Example 5
A heat storage material composition was produced in the same manner as in Example 1, except that in the heat storage material composition of Example 1, the concentration of graphite powder was 2.5% by weight, the carbon black was thermal black, the carbon black concentration was 2.5% by weight, no hydrophilic thickener was added, and the amount of water added was adjusted. This produced heat storage material composition was designated Example 5.

Example 6
A heat storage material composition was produced in the same manner as in Example 1, except that in the heat storage material composition of Example 1, the concentration of graphite powder was 5.0% by weight, the carbon black was thermal black, the concentration of carbon black was 1.0% by weight, no hydrophilic thickener was added, and the amount of water added was adjusted. This produced heat storage material composition was designated Example 6.

Example 7
A heat storage material composition was produced in the same manner as in Example 1, except that in the heat storage material composition of Example 1, the concentration of graphite powder was 1.0 wt%, the carbon black was thermal black, the concentration of carbon black was 5.0 wt%, no hydrophilic thickener was added, and the amount of water added was adjusted. This produced heat storage material composition was designated Example 7. Note that Figure 7 shows the ingredient tables of the heat storage material compositions of Examples 4-7 and Comparative Example 1. Examples 4-7 and Comparative Example 1 were also evaluated using the same evaluation methods as described above.

<Evaluation results>
Figure 8 shows a graph of the temperature changes of the heat storage material compositions of Examples 4-7 and Comparative Example 1 during the third heat cycle. The ambient temperature is also shown in Figure 8. As shown in Figure 8, it can be seen that during cooling in the heat cycle, the heat storage material compositions of Examples 4-7 had a higher cooling temperature per unit time and a faster cooling rate than the heat storage material composition of Comparative Example 1.

On the other hand, it can be seen that during heating in the heat cycle, the heat storage material compositions of Examples 4-7 had a higher heating temperature per unit time, a faster heating rate, and a faster rise in the graph compared to the heat storage material composition of Comparative Example 1. In other words, it was found that regardless of the type of carbon black, the combination of graphite powder and carbon black resulted in good cooling and heating rates. Furthermore, due to the thickening effect of the carbon black itself, uniform dispersion was possible without the addition of a hydrophilic thickener.

This shows that adding graphite powder and carbon black to the heat storage material composition enables rapid heat storage and release, as well as stable repeated use.

In the examples and comparative examples of the present invention, evaluations were performed by adding ammonium bromide as a melting point adjuster so that the freezing point (melting point) of the heat storage material composition was 18°C. However, the same effects were achieved even without adding a melting point adjuster. Furthermore, the same effects were achieved even when the phosphorus graphite in the graphite powder was replaced with a different type of graphite powder.

As described above, the heat storage material composition of the present invention is useful as a heat storage material in a variety of fields, enabling rapid heat storage and release, and is effective as a heat storage material composition that can be stably used repeatedly.

Claims (2)

a solid-liquid phase change material that changes phase between solid and liquid in a temperature range of 5°C to 35°C ;
Water and
a nucleating material;
Graphite powder,
A fine powder with a specific gravity close to that of water, which is resistant to water wetting and has high thermal conductivity.
Contains
The fine powder includes carbon black.
Heat storage material composition. The concentration of the graphite powder is in the range of 0.5% by weight to 5.0% by weight based on the total heat storage material composition;
The mixing ratio of the graphite powder to the carbon black is within a range of 1.0:0.2 to 1.0:5.0 by weight.
The heat storage material composition according to claim 1 .