JP2800039B2 - Latent heat storage material - Google Patents

Description

The present invention relates to a latent heat storage material. More specifically, the present invention relates to a latent heat type heat storage material that reduces the degree of supercooling during solidification and exhibits stable performance over a long-term heat cycle.

[Conventional technology]

Conventionally, water and crushed stone have been used as heat storage materials, but since they have a low heat storage density (1 cal / g · deg or less), a considerably large heat storage device is required in practical use. In addition, since the temperature inside the heat accumulator gradually decreases with the heat radiation, it is technically very difficult to obtain stable thermal energy.

On the other hand, in recent years, research and development for applying the latent heat at the time of melting and solidifying a substance to heat storage have been actively conducted. A characteristic of such a latent heat type heat storage material is that it can stably absorb and release heat energy at a constant temperature corresponding to the melting temperature of the material at a high heat storage density of several tens cal / g.

By the way, heat storage at a relatively high temperature, such as about 90 ° C., has been attracting attention as a heat source for hot water supply with recent advances in solar heat utilization technology and waste heat recovery technology. As a latent heat storage material for performing heat storage at such a high temperature, an inorganic hydrate has attracted attention.

However, the inorganic hydrate generally exhibits a so-called supercooling phenomenon in which the solidification start temperature is lower than the melting temperature. Such a phenomenon significantly impairs the characteristic of the heat storage material that stably absorbs and releases thermal energy at a constant temperature when the inorganic hydrate is used as the heat storage material.

Potassium alum KAl (SO ₄ ) ₂・ 12H ₂ O has a melting temperature of 9
1 ℃, latent calorie 55 cal / g (by differential scanning calorimeter)
Therefore, it is very promising as a latent heat type heat storage material for hot water supply and the like, but a supercooling phenomenon is also observed in the case of this inorganic hydrate. That is, once melted potassium alum is about 15
It does not solidify even when left at room temperature around ℃. This is because the solidification start temperature of potassium alum is about -25 ° C,
This is because supercooling corresponding to a temperature difference of 116 degrees is generated. Therefore, the absorption and release of heat at 91 ° C. are not performed at all smoothly, so that it cannot be used alone as a heat storage material.

[Problems to be solved by the invention]

An object of the present invention is to provide a potassium alum-based latent heat type heat storage material in which the degree of supercooling is reduced.

[Means for solving the problem]

The latent heat storage material of the present invention for achieving the above object is obtained by adding cesium sulfate Cs ₂ SO ₄ or cesium chloride CsCl as a nucleating agent to potassium alum, or manganese carbonate monohydrate MnCO _3. After adding 1H ₂ O or manganese ammonium sulfate hexahydrate (NH ₄ ) ₂ Mn (SO ₄ ) ₂ .6H ₂ O, solidification is once experienced.

The degree of supercooling reduction depends on the proportion of nucleating agent added, but not only does not obtain the expected effect even if too much nucleating agent is added, but also causes deterioration of the material. It is generally used in a proportion of about 0.05-20% by weight, preferably about 0.1-10% by weight, based on potassium alum.

Of these nucleating agents, manganese salts do not exhibit a nucleating effect by simply adding them, and do not solidify even at room temperature, but by some treatment of potassium alum to which the nucleating agent is added. For the first time, it will exert its nucleating effect. In other words, the supercooled melt of potassium alum is cooled to about -30 ° C to solidify it, or a small amount of potassium alum is added to this melt and solidified. The effect is exhibited, and a stable supercooling prevention effect is exhibited even for a long-term heat cycle.

〔The invention's effect〕

The degree of supercooling reduction exhibited by such nucleation action is determined by the difference ΔT between the melting temperature Tm of the heat storage material and the solidification start temperature Tsc.
As indicated by sc, the value of ΔTsc can be significantly reduced by adding the nucleating agent in the above proportion to potassium alum. In addition, the time required to return to the melting temperature is shortened, and stable performance is exhibited over a long period of time in the heat cycle test, so that a more efficient heat storage action can be performed.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 A mixture obtained by adding 0.4 g of Cs ₂ SO _{4 to 10} g of KAl (SO ₄ ) ₂ .12H ₂ O was sealed in a polyethylene container having a capacity of 20 ml.
Upon heating at 0 ° C., it melted at 91 ° C. When the melted sample was cooled at a cooling rate of 1 ° C./min, solidification started at 75 ° C. The coagulation initiation temperature was within the range of ± 2 ° C. even if the melting-coagulation was repeated 20 times. Therefore, by adding this nucleating agent, the difference (ΔTsc) between the melting temperature and the solidification starting temperature can be reduced to about 16
The degree of supercooling was greatly reduced. The ΔTsc when Cs ₂ SO ₄ was added in the range of 0.05 to 20% by weight was about 16 degrees.

Example 2 In Example 1, when 0.2 g of CsCl was used instead of 0.4 g of Cs ₂ SO ₄ , the solidification starting temperature at that time was 76 ° C.
Even when coagulation was repeated 20 times, it was within the range of ± 2 ° C. Therefore, by adding this nucleating agent, ΔTsc becomes 116
It became about 15 degrees from the degree, and supercooling was able to be greatly reduced.

The ΔTsc when CsCl was added in the range of 0.05 to 20% by weight was about 15 degrees.

Example 3 A mixture obtained by adding 0.1 g of MnCO ₃ .1H ₂ O to ₁₀ g of KAl (SO ₄ ) ₂ .12H ₂ O was sealed in a polyethylene container having a capacity of 20 ml, and the mixture was heated at 100 ° C. and melted at 91 ° C. did. This sample was once cooled to -30 ° C to be solidified, and then heated to 100 ° C again to be melted. When the melted sample was cooled at a cooling rate of 1 ° C./min, solidification started at 78 ° C. The coagulation initiation temperature was within the range of ± 2 ° C. even if the melting-coagulation was repeated 20 times. Therefore, by adding this nucleating agent, the difference (ΔTsc) between the melting temperature and the solidification starting temperature becomes approximately 13 degrees from 116 degrees when the nucleating agent is not added, and the supercooling is greatly reduced. Was completed.

The ΔTsc when MnCO ₃ .1H ₂ O was added in the range of 0.05 to 20% by weight was about 13 degrees.

Example 4 In Example 3, (NH ₄ ) was used instead of 0.1 g of MnCO ₃ .1H ₂ O.
_When 0.4 g of ₂ Mn (SO ₄ ) ₂ .6H ₂ O was used, the solidification onset temperature at that time was 80 ° C., and the temperature was within ± 2 ° C. even when melting-solidification was repeated 20 times. Therefore, by adding this nucleating agent, ΔTsc was changed from 116 degrees to about 11 degrees, and supercooling was significantly reduced.

(NH ₄ ) ₂ Mn (SO ₄ ) ₂ .6H ₂ O is 0.05 to 20% by weight.
ΔTsc when added within the range was approximately 11 degrees.

Claims (2)

(57) [Claims] 1. A latent heat storage material obtained by adding cesium sulfate or cesium chloride as a nucleating agent to potassium alum. 2. A latent heat storage material obtained by adding manganese carbonate monohydrate or manganese ammonium sulfate hexahydrate as a nucleating agent to potassium alum and then allowing it to solidify once.