JPH0443951B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a latent heat storage material mainly composed of sodium acetate trihydrate. Conventional Structures and Problems There are generally known heat storage materials that utilize the sensible heat of substances and those that utilize latent heat. Heat storage materials that use latent heat have a larger amount of heat storage per unit weight than heat storage materials that use sensible heat, and only a small amount is required to store the required amount of heat, making it possible to downsize heat storage devices. becomes possible. Furthermore, a heat storage material that uses latent heat has the characteristic that unlike a heat storage material that uses sensible heat, the temperature does not drop with heat radiation, and instead releases heat at a constant temperature at a transition point. In particular, heat storage materials that utilize the latent heat of fusion of inorganic hydrated salts are known to have a large amount of heat storage per unit volume. By the way, sodium acetate trihydrate (CH ₃ CO ₂ Na・3H ₂ O, melting point: approximately 58°C) has traditionally had a large amount of heat storage among inorganic hydrated salts, and was considered to be a promising heat storage material for heating, for example. . But CH ₃
Once CO ₂ Na・3H ₂ O is melted, it tends to become supercooled, and the molten liquid is usually -20
Supercooling cannot be broken unless it is cooled to about ℃. The supercooled state is a phenomenon in which the latent heat of fusion is not released even if the material is cooled to the freezing point, and the material is cooled below that temperature, which is a fatal drawback for heat storage materials that utilize the latent heat of fusion. Purpose of the Invention The present invention aims to prevent the supercooling phenomenon of sodium acetate trihydrate, and to provide a heat storage material that is inexpensive, has stable heat absorption and radiation performance, and has a large amount of heat storage per unit weight or unit volume. be. Structure of _{the Invention The main feature of the present invention is that the main component is sodium acetate trihydrate (CH 3 CO 2 Na・3H 2 O ) , and the} Lithium fluoride (LiF), sodium fluoride (NaF), sodium hydrogen fluoride (NaHF ₂ ), strontium fluoride (SrF ₂ ), potassium titanium fluoride (K ₂ TiF) are used as crystal nucleation materials to prevent cooling. ₆ ),
The present invention is characterized in that it contains at least one selected from the group of compounds consisting of manganese fluoride (MnF ₂ ) and cobalt fluoride (CoF ₃ ). By the way, FIG. 1 shows a phase diagram of the CH ₃ CO ₂ Na-H ₂ O system. According to this figure, a system consisting of 60.3% by weight of CH ₃ CO ₂ Na and 39.7% by weight of H ₂ O is CH ₃ CO ₂
This corresponds to the Na.3H ₂ O composition, and it can be seen that with this composition, melting and solidification occur at about 58°C unless supercooling occurs. Also, from this phase diagram, CH ₃ CO ₂
Add water to Na・3H ₂ O to increase the concentration of CH ₃ CO ₂ Na.
It can be seen that when the content is reduced below 60.3% by weight, the amount of latent heat decreases significantly. Therefore, CH ₃ CO ₂ Na・3H ₂ O
It is not preferable to add water to the heat storage material because it will greatly reduce the amount of heat stored in the heat storage material.
Furthermore, in heat storage materials in which H ₂ O is added to CH ₃ CO ₂ Na and 3H ₂ O to reduce the concentration of CH ₃ CO ₂ Na in the heat storage material, fluorides such as lithium fluoride are used as crystal nucleation materials. Even if it is added, if melting and crystallization are repeated, the effect of the crystal nucleation agent will gradually be lost, and the range of supercooling will become larger. Therefore, from this point of view as well, when CH ₃ CO ₂ Na.3H ₂ O is used as a heat storage material, it is not desirable to add water. The content of crystal nucleation material is CH ₃ CO ₂ Na・3H ₂ O.
Approximately 1 part by weight per 100 parts by weight is sufficiently effective, and even if it is contained more than that, it is naturally effective. However, when using the heat storage material according to the present invention in a heat storage device for air conditioning, etc.,
It is considered normal to use around 1000Kg.
In such a case, even when the CH ₃ CO ₂ Na・3H ₂ O crystal is in a molten state, the whole is not uniform,
A low concentration solution of CH ₃ CO ₂ Na is present in the upper part, and a precipitate of crystal nucleation material and a high concentration solution of CH ₃ CO ₂ Na are present in the lower part. Therefore, even if the amount of crystal nucleation material mixed is much smaller than the minimum amount required to form a homogeneous solution, the crystal nucleation material will not dissolve in the heat storage material and will not function as a crystal nucleation material. act. The minimum amount of the crystal nucleation material necessary for crystal nucleation, that is, the lower limit of the mixing amount, is the CH ₃ used.
Since it depends on the amount of CO ₂ Na and 3H ₂ O and the shape of the container housing the heat storage material, it can be determined according to the usage pattern. However, adding too much crystal nucleation material is not preferable as a heat storage material, and leads to a decrease in the amount of heat storage when viewed as a whole of the heat storage material.
Therefore, in practice, the mixing ratio of the crystal nucleation material is 40 parts by weight of CH ₃ CO ₂ Na・3H ₂ O to 100 parts by weight.
It is desirable not to exceed parts by weight. Description of Examples 1000 g of CH ₃ CO ₂ Na.3H ₂ O and 10 g of the crystal nucleation material shown in Table 1 were placed in a beaker and heated to 75°C in a water bath to form CH ₃ CO ₂ Na.3H. ₂ O
all melted. This mixture was placed in a cylindrical container with an inner diameter of 100 mm and a length of 100 mm, and the container was sealed with a stopper equipped with a thermocouple insertion tube. The container was placed in a water bath and heated and cooled continuously between 76°C and 40°C. Figure 2 shows the change in the degree of supercooling, that is, the difference between the solidification temperature and the temperature at which supercooling breaks down, when a heat storage material using lithium fluoride as a crystal nucleation material is repeatedly heated and cooled 100 times. This shows the situation. The horizontal axis of the figure shows the number of repetitions of the heating/cooling cycle on a logarithmic scale, and the vertical axis shows the degree of supercooling (°C). From this figure, the heat storage material of this example shows that even after repeated heating and cooling 100 times,
It can be seen that the degree of supercooling is stable in the range of 3 to 4°C, and the supercooling prevention function is working effectively without deterioration.

[Table] By the way, Figure 3 shows the degree of supercooling when sodium fluoride is used as the crystal nucleation material.
Figure 5 shows the case when sodium hydrogen fluoride is used, Figure 5 shows the case when strontium fluoride is used, Figure 6 shows the case when titanium potassium fluoride is used, Figure 7 shows the case when manganese fluoride is used, and Figure 8 shows the case when manganese fluoride is used. The figure shows the case using cobalt fluoride. The heat storage materials of these Examples are all very stable at a degree of supercooling of around 3 to 4°C. Example 2 500 kg of CH ₃ CO ₂ Na・3H ₂ O and 500 g of the crystal nucleation material shown in Table 1 were placed in an inner cylindrical container with an inner diameter of 80 cm and a height of 90 cm and equipped with a heater. It was sealed with a stopper with a pair of insertion tubes. All of the CH ₃ CO ₂ Na.3H ₂ O was melted by a heater inside the container. Then, when the heater was stopped and cooled, it was found that lithium fluoride, sodium fluoride, sodium hydrogen fluoride, strontium fluoride, potassium titanium fluoride, manganese fluoride, and cobalt fluoride were used as the crystal nucleation material. Also,
Supercooling breaks down around 55℃, and the temperature inside the container reaches 58℃.
It rose to After that, heating and cooling were repeated 50 times, but the supercooling was broken stably when the degree of supercooling reached around 3°C, confirming that the heat storage material of this example was functioning sufficiently as a heat storage material. Ta. Comparative Example 1 1000g of CH ₃ CO ₂ Na・3H ₂ O was stored in the same container as in Example 1, and heated to 76°C to form CH ₃ CO 2 Na・3H ₂ O.
All of the 3H ₂ O was melted. When the mixture was then cooled, CH ₃ CO ₂ Na.3H ₂ O did not crystallize even when the temperature reached room temperature. Comparative Example 2 500 kg of CH ₃ CO ₂ Na・3H ₂ O was stored in the same container as in Example 2, and CH ₃ CO ₂ was heated using a heater inside the container.
Heating Na・3H ₂ O to 70℃, CH ₃ CO ₂ Na・
All of the 3H ₂ O was melted. After that, when I stopped heating with the heater and cooled it down, even though it reached room temperature.
CH ₃ CO ₂ Na.3H ₂ O did not crystallize. Comparative Example 3 1000 g of CH ₃ CO ₂ Na・3H ₂ O and 10 g of niobium fluoride (NbF ₅ , t _n =75.5°C) were stored in the same container as in Example 1, heated to 76°C, and CH ₃ CO ₂ Na・3H ₂
All O was melted. At that time, niobium fluoride also melted. After cooling,
Even when the temperature reached room temperature, CH ₃ CO ₂ Na.3H ₂ O did not crystallize. Effects of the invention As shown in the examples above, the heat storage material of the present invention
It is a heat storage material made of CH ₃ CO ₂ Na・3H ₂ O containing a specific fluoride as a crystal nucleation material that does not melt or decompose at temperatures below 80℃, so it will not melt even after repeated melting and crystallization. It has stable heat absorption and heat dissipation performance with almost no supercooling, is inexpensive, and has a large amount of heat storage. In the examples, cases are shown in which these crystal nucleation materials are used alone, but equivalent effects can be obtained even if a plurality of them are used in combination. The heat storage material of the present invention can be applied not only to heat storage devices for air conditioning, but also to all fields that utilize heat storage, such as heat storage type heat insulators.

[Brief explanation of the drawing]

FIG. 1 is a phase diagram of the sodium acetate-water system. FIGS. 2 to 8 show how the degree of supercooling changes when the heat storage material according to the embodiment of the present invention is repeatedly heated and cooled 100 times.

Claims (1)

[Claims] 1 Sodium acetate trihydrate (CH ₃ CO ₂ Na・3H ₂
O), lithium fluoride (LiF), sodium fluoride (NaF), sodium hydrogen fluoride (NaHF ₂ ), strontium fluoride (SrF ₂ ), potassium titanium fluoride (K ₂ TiF ₆ ) as crystal nucleation materials. , manganese fluoride (MnF ₂ ), cobalt fluoride (CoF ₃ )
A heat storage material containing at least one selected from the following in an amount of 0.1 part by weight or more but not exceeding 40 parts by weight.