JPH1135931A - Cold storage material utilizing latent heat - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a cold storage material utilizing latent heat comprising an aqueous solution of sodium chloride which is protected from supercooling phenomenon, has a freezing point approximated closely to the phase transition temperature of the aqueous solution of sodium chloride as much as possible and is also free from deactivation phenomenon by incorporating graphite into the aqueous solution of sodium chloride. SOLUTION: A cold storage medium employed is an aqueous solution of sodium chloride. The concentration of sodium chloride is not limited so far as it forms an aqueous solution and is preferably 5-30 wt.%, more preferably 15-27 wt.%. The purity of sodium chloride is preferably 99% or higher. Graphite employed as a supercooling preventing agent has a purity of 99.0% or higher and there can be exemplified natural graphite (graphite, diamond, etc.), artificial graphite (including flake graphite). The amount of graphite employed is 0.1-10 pts.wt. based on 100 pts.wt. of an aqueous solution of sodium chloride. A water- absorbent resin can be added if required. The cold storage material utilizing latent heat exhibits a phase transition phenomenon preferably at -40 deg.C-2 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a latent heat storage material using an aqueous solution of sodium chloride as a refrigerant (main agent). More specifically, the present invention relates to a latent heat storage material in which graphite is added as a supercooling inhibitor to a cold storage material containing an aqueous solution of sodium chloride.

[0002]

2. Description of the Related Art Various efficient storage methods of electric power energy have been studied and developed for the purpose of utilizing surplus electric power. For example, development of a latent heat storage material utilizing absorption heat accompanying a phase change such as melting and solidification of a substance serving as a heat medium is one of them. A heat storage material is a material that accumulates heat or cold in a substance and effectively uses the flow of heat when necessary. Particularly, a material utilizing heat generation / endothermic reaction mainly due to a phase change of a substance is referred to as a latent heat storage material, and more particularly, a case in which cold heat is stored in advance and then cooled when necessary is referred to as a latent heat storage material. There is no clear distinction. Among the latent heat storage materials, those using inorganic materials such as inorganic salts and inorganic hydrated salts as the refrigerant storage medium have higher thermal conductivity, larger latent heat, smaller volume change, and nonflammability than organic materials. Among them, an aqueous solution of sodium chloride has further advantages that it is less toxic, has low reactivity, is easily available, has an appropriate solubility, and has a eutectic temperature close to the frozen food storage temperature. Therefore, these regenerative materials can be particularly suitably used for refrigeration of foods, cold preservation at the time of delivery, refrigeration of chemicals and pharmaceuticals, and cooling processes in food factories and the like.

[0003]

However, a latent heat storage material using an inorganic material such as sodium chloride as a refrigerant storage medium,
There is a problem of causing a supercooling phenomenon. The term “supercooling” means that when a substance is cooled, the phenomenon of the transition does not appear even when the temperature of the phase transition from a liquid to a solid is exceeded. For example, 23.
A 3% by weight aqueous solution of sodium chloride has a phase transition temperature of -21.
Despite the temperature, the phase transition may not actually occur unless the temperature is lowered to around -30 ° C. In other words, to cause the supercooling phenomenon, it is necessary to prepare a refrigerator capable of cooling to a temperature lower than the temperature to be actually used (the freezing point of the regenerative material). There is also a problem that extra energy is required, such as an increase in running cost due to a decrease in operation efficiency due to operation (3% decrease every 1 ° C. decrease).

[0004] In order to alleviate this supercooling, a substance (supercooling inhibitor) which becomes a core of the refrigerant storage during solidification is added. For example, JP-A-5-331457
Japanese Patent Application Laid-Open Publication No. H11-146, discloses that carbon black having a DBP oil absorption of 100 or more is added to an inorganic heat storage medium such as NH ₄ Cl or NaCl. Also, Japanese Patent Application Laid-Open No. 2-929
No. 87 discloses an aqueous solution of potassium nitrate, sodium silicate, sodium carbonate, magnesium sulfate, ammonium dihydrogen phosphate and potassium chloride containing activated carbon and / or
Alternatively, a regenerator material composition containing graphite is disclosed. However, the regenerator material containing a supercooling inhibitor has a so-called deactivation phenomenon in which the supercooling prevention effect disappears when the temperature is higher than (the melting point of the coagulant + 30) ° C (WATANABE et al. A).
CS Symp. Ser. D438 (1990) p395). In other words, during the cold storage / cooling cycle, at the time of the next cold storage in which the cold storage material temperature has exceeded the certain temperature for some reason,
A phenomenon appears in which the supercooling inhibitor does not work effectively and the degree of supercooling increases. In this case, once re-solidified, it may not be usable as it is,
In some cases, it can be used continuously.

[0005] In addition, regarding what kind of supercooling inhibitor to use, there is a theory that it is better to use a material having the same crystal structure and lattice constant as the heat storage medium. Some have a high supercooling prevention effect,
At present, what kind of supercooling inhibitor is suitable for a specific heat storage medium is trial and error.

An object of the present invention is to suppress the supercooling phenomenon of a latent heat storage material using an aqueous solution of sodium chloride as a heat storage medium, to bring the freezing point as close as possible to the phase transition temperature of the aqueous solution of sodium chloride, and to deactivate it. It is to provide a latent heat storage material without a phenomenon.

[0007]

Under these circumstances, the inventors of the present invention have conducted various studies. As a result, when graphite was used as a supercooling inhibitor for an aqueous solution of sodium chloride, the effect of suppressing supercooling was particularly effective. We discovered for the first time and completed the present invention. That is, the present invention provides (1) a latent heat storage material containing an aqueous sodium chloride solution and graphite, and (2) a graphite having a purity of 9%.
(1) or (2), wherein the latent heat storage material according to (1) is 9% or more, and (3) the amount of graphite is 0.1 to 10 parts by weight with respect to 100 parts by weight of the aqueous sodium chloride solution. (4) The latent heat storage material according to any one of (1) to (3), wherein a phase transition phenomenon occurs in a temperature range of -40 ° C to -2 ° C, and (5) the concentration of sodium chloride. Is 5 to 30% by weight of the latent heat storage material according to any one of the above (1) to (4).

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The refrigerant storage medium used in the present invention is an aqueous sodium chloride solution. The concentration of sodium chloride is not particularly limited as long as an aqueous solution is formed. Above all, 5-30
% By weight, more preferably 15 to 27% by weight. When the content of sodium chloride is 5 to 30% by weight, the temperature difference at the time of solidification and melting becomes small, and the cold storage / cooling temperature becomes close to constant, which is desirable as a cold storage material. Although the purity of sodium chloride is not particularly limited, it is usually 99%.
The above is preferably used.

The graphite used as the supercooling inhibitor preferably has a purity of 99.0% or more, and includes, for example, natural graphite (graphite, diamond, etc.) and artificial graphite (including flake graphite). Can be

[0010] The amount of graphite used is 1
0.1 to 10 parts by weight, preferably 1 to 100 parts by weight
４4 parts by weight. When the amount is less than 0.1 part by weight, the expected effect of preventing supercooling cannot be obtained. On the other hand, when the amount exceeds 10 parts by weight, the amount of latent heat is reduced, and a residue of the solution is observed. May be

In addition to the essential components, the components that may be added to the latent heat storage material of the present invention include water-absorbing resins, thickening agents such as attapulghai clay, gelatin, agar, and silica gel.

The latent heat storage material of the present invention is preferably-
40 ° C to -2 ° C, more preferably -30 ° C to -15 ° C
It is preferable that a phase transition phenomenon occurs in the above temperature range.

The method for producing the regenerator material is not particularly limited. For example, sodium chloride is gradually added to pure water or ion-exchanged water contained in a container to a predetermined amount while gradually stirring the mixture, and the mixture is sufficiently mixed. Charge the graphite as a premixing agent up to a predetermined amount while stirring, mix well and add other additives at the same time or after, stirring and mixing, sodium chloride, graphite, etc. on the resin And a method of pouring an aqueous solution obtained by premixing the components in advance. In addition, sodium chloride,
The order of charging graphite and other additives is arbitrary, and heating to about 50 ° C. is possible to promote dissolution. After mixing sodium chloride and graphite, the mixture may be added to pure water or ion-exchanged water.

Although the form of the cold storage material is not particularly limited, it is usually a form in which the above-mentioned cold storage material is packaged with a corrosion-resistant metal or inorganic material and / or an organic material such as polyethylene or other plastics. Examples of the shape include a lump, a plate, and a sheet. As a place where such a cold storage material is arranged, as it is in a cold storage room,
Alternatively, it is conceivable to place it in a heat exchange section.

[0015]

The present invention will be described below in more detail with reference to examples. However, the present invention is not limited to the following examples. Example 1 A 23.3% by weight aqueous sodium chloride solution was added to the aqueous solution 10
0 parts by weight of artificial graphite (purity 99.9%, shape:
(Sphere, average particle size: about 5 μm) was added to obtain a regenerator material. The solidification start temperature of the obtained regenerator material was determined by DSC (differential scanning calorimeter) at a temperature lowering rate of 1 ° C./min→held at −45 ° C. for 20 minutes → a temperature increasing rate of 2 ° C./min→+10° C. as one cycle
The measurement was repeated seven times. Further, even when the temperature of the obtained regenerator material was raised to 10 ° C., the deactivation phenomenon did not appear remarkably.

Example 2 Instead of artificial graphite, natural graphite (purity 99.9%, shape:
Example 1 except that granular, average particle size: 10 μm) was used.
A regenerator material was obtained in the same manner as described above, and the solidification start temperature was measured.

Comparative Example 1 The solidification starting temperature of a 23.3% by weight aqueous sodium chloride solution (without using a supercooling inhibitor) was measured in the same manner as in Example 1.

Comparative Example 2 Ketjen Black (purity 99.3) was used instead of artificial graphite.
%, Shape: particle aggregate, average particle size: 30 nm), and a regenerator material was obtained in the same manner as in Example 1, and the solidification start temperature was measured.

Comparative Example 3 In place of artificial graphite, acetylene black (purity 99.7)
%, Shape: particle aggregate, average particle size: 50 nm), and a regenerator material was obtained in the same manner as in Example 1, and the solidification start temperature was measured. Table 1 and FIG. 1 show the results of Examples 1 and 2 and Comparative Examples 1 to 3.

[0020]

[Table 1]

From the results of the above Examples and Comparative Examples, the latent heat storage material of the present invention has an effect of preventing supercooling of 10 ° C. or more as compared with the case where no supercooling inhibitor is used. It can be seen that considerably better characteristics are obtained as compared with the results of black.

[0022]

The regenerator material of the present invention is an economically effective regenerator material which can effectively suppress supercooling of an aqueous solution of sodium chloride and does not show a deactivation phenomenon. It can be used for keeping food cool.

[Brief description of the drawings]

FIG. 1 shows the solidification start temperature of the cold storage materials of Examples 1 and 2 and Comparative Examples 1 to 3. The vertical axis indicates the solidification start temperature, and the horizontal axis indicates the number of cycles (times).

[Explanation of symbols]

a shows the solidification onset temperature of the sample of Example 1. b Shows the solidification onset temperature of the sample of Example 2. c Shows the solidification start temperature of the sample of Comparative Example 1. d shows the solidification start temperature of the sample of Comparative Example 2. e shows the solidification start temperature of the sample of Comparative Example 3. f shows the melting temperature of an aqueous 23.3% by weight sodium chloride solution (-21.1 ° C, without supercooling).

Claims (5)

[Claims] 1. A latent heat storage material containing an aqueous sodium chloride solution and graphite. 2. The latent heat storage material according to claim 1, wherein the graphite has a purity of 99% or more. 3. The amount of graphite is 10% aqueous sodium chloride solution.
3. The latent heat storage material according to claim 1, wherein the amount is 0.1 to 10 parts by weight relative to 0 parts by weight. 4. The latent heat storage material according to claim 1, wherein a phase transition phenomenon occurs in a temperature range of −40 ° C. to −2 ° C. 5. The concentration of sodium chloride is 5 to 30% by weight.
The latent heat storage material according to any one of claims 1 to 4, wherein