JPH0571073B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a latent heat storage agent composition containing sodium sulfate decahydrate or its eutectic as a main component. There is little decrease in the amount of latent heat stored due to
It is extremely useful as a latent heat storage agent. [Conventional technology] Sodium sulfate decahydrate or its eutectic product has been used for heating and cooling using solar heat, waste heat, or late-night electricity because of its large latent heat of fusion and melting point of around 30°C. It is known as a useful latent heat storage agent. However, there are two problems when using sodium sulfate decahydrate or its eutectic as a heat storage agent. One of these is the occurrence of a so-called supercooling phenomenon in which the material does not solidify even if the temperature drops below its freezing point during cooling. This supercooling phenomenon is a fatal drawback as a heat storage agent for ordinary heating because when heat is radiated, the latent heat of fusion is not released at the set temperature, and the temperature decreases while it remains a liquid. As a means to prevent supercooling, it is described in US Pat. No. 2,667,664 that the problem can be solved by adding a so-called nucleating substance, such as sodium tetraborate decahydrate, and various substances have been used since then. known to play a role. Another problem is that sodium sulfate decahydrate or its eutectic may undergo anharmonic melting. That is, when sodium sulfate decahydrate is melted, it separates into two phases: a saturated aqueous solution of sodium sulfate and a solid sodium sulfate, and the solid sodium sulfate precipitates at the bottom of the container because it has a higher density than a saturated aqueous solution. When the separated system is cooled, crystals of sodium sulfate decahydrate are formed on top of the precipitated solid sodium sulfate, forming a barrier, and the solid sodium sulfate combines with water to form a sulfuric acid Prevents the formation of sodium decahydrate. Therefore, solid sodium sulfate is precipitated by repeating melting and solidification, that is, heat storage and heat radiation, and does not participate in heat storage, so that the amount of heat storage decreases. To solve this problem, we used wood pulp, methylcellulose, starch, alginate, polyacrylic acid bonded cross-linked polyvalent metal ions (Japanese Patent Laid-Open No. 54-16387), carboxymethyl cellulose (Japanese Patent Laid-Open No. 16387), 60-11575), a combination of natural gelling agents such as guar gum, locust bean gum, and carrageenan with polyhydric alcohols (Japanese Patent Application Laid-Open No. 1983-1157)
Attempts have been made to increase the viscosity by adding various thickening agents such as silica gel and attapulgite clay (US Pat. No. 3,986,969) to create a so-called gelled state. Further, as another method, it has been proposed to add an alkali metal salt of lauric acid (Japanese Patent Application Laid-Open No. 60-79088) or an alkali metal salt of oleic acid (Japanese Patent Application Laid-Open No. 57-200482). [Problems to be Solved by the Invention] The method of adding the various thickening agents described above can prevent the precipitation of sodium sulfate in the initial stage, but it can prevent sodium sulfate crystals from gradually growing due to repeated melting and solidification. There is no ability to prevent this, and the amount of heat storage will still decrease due to crystal growth. In addition, it is recognized that the above-mentioned method of adding an alkali metal salt of lauric acid or an alkali metal salt of oleic acid has the effect of dispersing sodium sulfate particles to some extent and preventing crystal growth.
Alkali metal salts of lauric acid have the disadvantage of poor dispersibility and poor compatibility due to their high melting point, while alkali metal salts of oleic acid have the disadvantage that dispersed particles tend to become coarse. However, since oleic acid has unsaturated bonds in its molecule, it also has the disadvantage of thermal deterioration when used for a long period of time, and neither of these is satisfactory. Accordingly, an object of the present invention is to provide a latent heat storage agent composition in which the amount of heat stored in sodium sulfate decahydrate or its eutectic decreases less when melting and solidifying are repeated. [Means for Solving the Problems] The present invention achieves the above object by adding at least one kind of alkali metal salt of isostearic acid to a latent heat storage agent composition containing sodium sulfate decahydrate or its eutectic seismic acid as a main component. This has been achieved by a latent heat storage agent composition characterized by containing the following. The latent heat storage agent composition of the present invention will be described in detail below. As the sodium sulfate decahydrate or its eutectic product used in the present invention, sodium sulfate decahydrate or a eutectic product obtained by adding a known melting point regulator such as sodium chloride, amminium chloride, potassium chloride, etc. Can be mentioned. Isostearic acid constituting the salt used in the present invention is liquid at room temperature, has an appropriate viscosity (1650 cps/20°C), and is thermally stable. Suitable alkali metals constituting the salt with the isostearic acid include sodium, potassium, and lithium. The above alkali metal salts of isostearic acid are
It is a transparent liquid at room temperature, has an appropriate viscosity, and has excellent compatibility and dispersion with the above-mentioned sodium sulfate decahydrate or its eutectic. In addition, the above-mentioned alkali metal salt of isostearic acid has a smaller amount of foaming than the alkali metal salts of oleic acid and lauric acid in sodium sulfate decahydrate or its eutectic, and is superior in this respect as well. . The above alkali metal salt of isostearic acid is preferably added in an amount of 0.1 part by weight or more per 100 parts by weight of sodium sulfate decahydrate or its eutectic; Since there is no change in the effect of suppressing weight loss, it is sufficient to add up to about 5 parts by weight, and it is particularly preferable to add 0.5 to 2 parts by weight. The latent heat storage agent composition of the present invention includes, in addition to the essential components sodium sulfate decahydrate or its eutectic and an alkali metal salt of isostearic acid, a thickening agent such as xanthan gum, locust bean gum, guar gum, Natural gums such as carrageenan and alginates, synthetic gums such as carboxymethyl cellulose, polyacrylates, polyvinyl alcohol, and alkyl cellulose, inorganic thickeners such as fumed silica, or the previously known various thickeners mentioned above. The effect can be further enhanced by using agents. Further, the latent heat storage agent composition of the present invention may contain a conventionally known nucleating substance (nucleating agent) as described above to prevent supercooling, or may not contain a nucleating agent. Supercooling may be maintained until some kind of shock is applied. [Example] Examples and comparative examples of the present invention are shown below, but the present invention is not limited thereto. Example 1 Sodium sulfate decahydrate 94.0 parts by weight Borax (nucleating agent) 3.5 parts by weight invention). In addition, for comparison, a latent heat storage agent composition (conventional product) having the above-mentioned composition and without adding sodium isostearate was obtained. These latent heat storage agent compositions were heated to 50°C for 1 hour and cooled in a 10°C water bath for 30 minutes as one cycle.
The change in heat storage amount of each latent heat storage agent composition after repeating 300 times is shown in Table 1 below, which shows that the latent heat storage agent composition of the present invention containing sodium isostearate has an effect of suppressing a decrease in heat storage amount. .

[Table] Example 2 Sodium sulfate decahydrate 84.0 parts by weight Sodium chloride 10.0 parts by weight Borax 3.5 parts by weight . For these products of the present invention and conventional products, heating and cooling were repeated under the same conditions as in Example 1, and changes in heat storage amount were measured. The change in heat storage amount before and after the repetition was as shown in Table 2 below.

【table】

[Table] As is clear from the results shown in Table 2 above, when the amount of sodium isostearate added is 0.1 parts by weight or more, there is an effect of suppressing a decrease in the amount of heat storage. More preferably, the suppressing effect is high at 0.5 parts by weight or more, and 5 parts by weight only lowers the initial latent heat, and it is considered that addition of more than this is not practically necessary. Example 3 A product of the present invention and a conventional product were obtained using the same formulation as in Example 2, except that potassium isostearate and lithium isostearate were used in the amounts shown in Table 3 below in place of sodium isostearate. These inventive and conventional products were repeatedly heated and cooled under the same conditions as in Example 1, and changes in heat storage amount were measured. The change in heat storage amount before and after the repetition was as shown in Table 3 below.

[Table] As is clear from the results shown in Table 3 above, it can be seen that potassium isostearate and lithium isostearate also have the effect of suppressing the decrease in heat storage amount due to repeated use, similar to sodium isostearate. Example 4 A product of the present invention and a conventional product were obtained using the same formulation as in Example 2, except that fumed silica was used instead of xanthan gum as a thickening agent. For these products of the present invention and conventional products, heating and cooling were repeated under the same conditions as in Example 1, and changes in heat storage amount were measured. The changes in geothermal energy before and after the repetition are shown in Table 4 below.

[Table] As is clear from the results shown in Table 4 above, even when the thickening agent was replaced with an inorganic substance, the latent heat storage agent composition of the present invention similarly exhibited the effect of suppressing the decrease in heat storage amount. Comparative example Sodium oleate and sodium laurate were used in place of sodium isostearate in Table 5 below.
Conventional products were obtained using the same formulation as in Example 2 except that the amounts shown were used. These conventional products were repeatedly heated and cooled under the same conditions as in Example 1, and changes in heat storage amount were measured. The change in heat storage amount before and after the repetition was as shown in Table 5 below.

【table】

〔Effect of the invention〕

The latent heat storage agent composition of the present invention is extremely useful as a latent heat storage agent because the amount of heat storage of sodium sulfate decahydrate or its eutectic decreases little even after repeated melting and solidification.

Claims (1)

[Claims] 1. A latent heat storage agent composition containing sodium sulfate decahydrate or a eutectic thereof as a main component, which is characterized by containing one or more types of alkali metal salts of isostearic acid.