JPH0372675B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat storage material that is effective for utilizing solar heat, factory waste heat, etc. When using solar heat and factory waste heat, so-called latent heat storage materials, which store the energy as latent heat when melting a substance and release it during solidification, have a large energy storage density and are not very effective in terms of energy utilization. be. Calcium chloride (hexahydrate, melting point 29.2°C) is the most widely known heat storage material. This calcium chloride has a melting point of 30°C or less, so it is used as a heat source for heat pumps. Sodium thiosulfate (Na ₂ S ₂ O ₃ .5H ₂ O, melting point 48.5°C) is used to directly use the heat released from the heat storage material for heating. This sodium thiosulfate has a large heat storage capacity and is inexpensive, so it can be stored using solar heat and waste heat, and used to heat air or water as an auxiliary heat source for space heaters and water heaters. . However, when using a heat storage material as a heat source for generating fluorocarbon steam in a Rankine engine that uses solar heat, a high temperature heat storage material with a melting point of 80°C or higher is required.
As a relatively inexpensive heat storage material that satisfies this requirement,
Ammonium alum ( _AlNH4) with a melting point of 93.5℃
(SO ₄ ) ₂・12H ₂ O). However, this ammonium alum has the drawback of exhibiting large supercooling of 30°C or more during solidification, and there is currently no countermeasure to overcome this drawback. In view of the above, the present invention aims to provide a heat storage material that prevents overcooling of ammonium alum and stores and releases heat at a predetermined temperature. Moreover, it is characterized in that an organic compound having a crystal plane with a low molecular density is added as a nucleating material. In general, the phase change from liquid to solid can be divided into a crystal nucleus generation stage and a crystal growth stage centered on the nucleus. Nuclear generation requires a large amount of energy, and it is known that the supercooling phenomenon occurs due to the energy barrier. Therefore, a method of adding nuclear material is being used to prevent overcooling. In this case, the nuclear substance exists undissolved in the liquid phase, the interfacial energy with the newly generated crystal on the interface is small, and the nucleus has a certain critical radius (1 to
It is also known that it is necessary to have a size of 100 μm or more. In addition, crystal growth occurs on crystal planes with low molecular density, such as 100, 110,
It is known that crystal growth tends to occur on 111 planes, and that crystals grow in the form of step movement. As examples of such nucleating materials, the nucleating effect of barium hydroxide and strontium hydroxide on calcium chloride (hexahydrate) has been recognized. However, this strontium hydroxide becomes an insoluble salt (BaSO ₄ .SrSO ₄ ) and precipitates in an aqueous sulfate solution, so it loses its effectiveness as a nucleating material.
In other words, substances that cause chemical reactions with heat storage substances are not suitable as nucleating materials. Based on the above theoretical viewpoint, the present inventor conducted experiments and research on nucleating materials for ammonium alum (AlNH ₄ (SO ₄ ) _{2.12H 2} O) and found that it cleaves at a melting point of 93.5°C or higher. It is sufficient to use as a nucleating material an organic compound crystal that has a property and is sublimable, or an organic substance that dissolves in trace amounts in water or an aqueous solution of ammonium alum but does not cause a chemical reaction with ammonium alum. I found out. Furthermore, it was found that the effect as a nucleating material is particularly large when the specific gravity of the nucleating material is in the range of ±0.3 with respect to the specific gravity of ammonium alum (1.64±0.3=1.34 to 1.94). It is known that the above-mentioned cleavable crystal has a weak bonding force at the cleavage plane. For example, when atoms are arranged two-dimensionally to form a flaky crystal, the bonds between the planes of the flakes tend to form weak cleavage planes. This cleavage plane is a low energy plane (low density plane), and it is considered that crystals are likely to grow on this plane. Furthermore, the fact that the density of the nucleating material is close to that of the heat storage material has the effect of uniformly dispersing crystal nuclei in the salt solution (heat storage material) to be crystallized and promoting the growth of crystals at various locations within the solution. Furthermore, the fact that the nucleating material sublimes or dissolves in a small amount in water and aqueous salt solutions is thought to be due to the fact that the crystal surface is dissolved and removed in a small amount to clean it and form a surface suitable for crystal growth. Ammonium alum belongs to the equiaxed crystal system, but the crystal form of the nucleating material does not necessarily have to be equiaxed;
If the crystal has a crystal face such as 110 or 111, or if the crystal face is exposed by cleavage, it is considered that the crystal grows on that face. Specific examples of this type of nucleating material include the following organic compounds. That is, as monoclinic organic compounds, picric acid, picramide, dambose, salicylic acid fumarate, cyanuric acid, O-chlorobenzoic acid, dulcitrate, 3.5 dinitrobenzoic acid, melamine, oxamide, P-oxybenzoic acid, thianthrene, P - Contains nitrobenzoic acid and gallic acid,
In addition, phthalic anhydride and orthorhombic anhydride are organic compounds.
There is succinic anhydride. The effect of the above nucleating material is recognized even when added in small amounts, but in practical terms, 0.01
% (weight) or more. The upper limit of its addition is 10% (by weight), although there is no reason to limit it in terms of function and effect, but adding a large amount will reduce the heat storage density.
It is practical to limit the amount to a certain extent. These nucleating materials may be added directly to the ammonium alum, but if necessary, the nucleating material may be held by a suitable support and interposed in the ammonium alum. In this example, the heat storage and heat dissipation conditions of a heat storage material made by adding phthalic anhydride as a nucleating material to ammonium alum (AlNH ₄ (SO ₄ ) _{2.12H 2} O) as a nucleating material are evaluated. A comparison with water as a heat storage material is shown in FIG. 1, where the solid line shows the case in which the nucleating material is added, the broken line shows the case in which the nucleating material is not added, and the dashed line shows the case in which water is used. This figure shows that when no nucleating material is added, when cooling after melting at 93.5°C or higher, the temperature rises to 45°C due to supercooling.
It does not solidify until it reaches 45°C and radiates heat as shown by the dashed line 1' (CD), creating a thermal history cycle shown by ACDFA. On the other hand, the heat storage material of this example to which 0.1% of phthalic anhydride was added releases heat at 90°C as shown by the solid line 2' (BE), which shows the thermal history cycle of heat absorption and heat release of ABEFA. Note that the arrow direction in the figure indicates the direction of heat storage amount change, 1' and 2' indicate heat radiation, and 2 indicates heat absorption. Comparing the amount of heat stored per unit volume of ammonium alum, it is approximately 97.8 kcal/at 93.5℃, while that of water at the same temperature (80 to 93.5℃) shown by the dashed-dotted line 3 Since the amount of heat storage is 13.5kcal/, it is clear that ammonium alum is excellent as a heat storage material. Next, an example will be described. Figure 2 shows a model experimental device, in which a heat storage tank 1 in which a temperature sensor 4b is inserted is housed in a water tank 2 in which a stirrer 3 and a temperature sensor 4a are inserted, and both tanks 1 and 2 are placed in a container 5. It is constructed by storing it in.
A heat storage material, that is, ammonium alum (AlNH ₄ (SO ₄ ) _{2.12H 2} O) to which 0.05% of the nucleating material shown in Table 1 was added was placed in the heat storage tank 1, and the temperature was heated to 20 to 105°C.
The melting-solidification characteristics of the heat storage material were measured by repeatedly heating and cooling within the range of . The results are shown in Table 1.

From [Table], it was confirmed that the heat storage material according to the present invention is stable as a heat storage material because it has little supercooling and solidifies and melts at a constant temperature. In addition, 1 nucleating material from Table 1
A similar effect was obtained when adding %. As explained above, according to the present invention, it is possible to obtain a heat storage material that prevents overcooling of ammonium alum and stores and releases heat at a predetermined temperature.

[Brief explanation of drawings]

FIG. 1 is a diagram comparing the heat storage and heat release states of the heat storage material of the present invention, the heat storage material without addition of nucleating material, and water, and FIG. 2 is a sectional view of a model experimental device.

Claims (1)

[Claims] 1. Ammonium alum (AlNH ₄ (SO ₄ ) ₂ .
12H ₂ O), with a melting point of 93.5℃ or higher as a nucleating material,
1. A heat storage material comprising a monoclinic or orthorhombic organic compound having a specific gravity in the range of 1.47 to 1.8 and having a cleavage plane. 2 The nucleating material includes picric acid, picramide, danbose, fumaric acid, salicylic acid, cyanuric acid,
Consists of one or more from the group of O-chlorobenzoic acid, dulcitrate, 3.5 dinitrobenzoic acid, melamine, oxamide, P-oxybenzoic acid, thianthrene, P-nitrobenzoic acid, gallic acid, phthalic anhydride, and acid anhydride. The heat storage material according to claim 1, characterized in that: 3. Claim 1 or 2, characterized in that the amount of the nucleating material added is 0.01 to 10% by weight.
Heat storage material as described in section.