JPH0482037B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a latent heat storage material and a method for producing the same. Conventional technology Generally, materials used as heat storage materials have a large specific heat or exhibit abnormal specific heat phenomena due to evaporation, melting, crystal transition, etc. of the material, and are used as heat storage materials in a certain temperature range. It is preferable to use a substance that exhibits an abnormal specific heat phenomenon, and attempts have been made to utilize a change in specific heat due to crystal transition because it is particularly easy to handle.
There is a strong demand for heat storage materials that can store heat in the temperature range of 180 to 240 degrees Celsius and utilize the heat dissipation. In particular, there are not many cases in which the crystal transition of substances can be used, but one example is the crystal transition of pentaerythritol (188℃).
There is a known example of using
Publication No.). For inorganic compounds, there is a possibility of heat storage based on crystal transition in this temperature range (approximately 30
If there is a latent heat of [J/g] or more, it can be used), Electronic Technology Research Institute Investigation Report (No. 196,
According to June 1973), NH ₄ Cl, KHF ₂ ,
Descriptions of NH ₄ BF ₆ , CsOH, WCl ₆ , and Na ₂ O ₂ are found. Furthermore, KOH−NaOH, LiOH−NaOH,
NaCN−NaOH, NaClO ₃ , KOH−LiOH, KCl
−KOH−LiOH, LiOH−NaNO ₃ −NaOH,
A combined composition of NaNO ₂ -NaOH is also known (Industrial Materials, vol.32No.5P-64 1984). Problems to be Solved by the Invention However, when using pentaerythritol as a heat storage material that can be used in the temperature range of 180 to 240 degrees Celsius, since it is an organic substance, it does not have sufficient heat resistance and deteriorates during long-term use. and become unable to achieve their goals. Furthermore, since decomposition gas is generated, it is difficult to have a sealed structure, and oxygen from outside the system is involved, making it difficult to take measures to stabilize it. In order to avoid these problems, it was necessary to strictly suppress the upper limit temperature in practical use. For this reason, it has been particularly difficult to apply it to places where the temperature of the supplied heat source fluctuates significantly above its crystal transition temperature. In the case of inorganic substances,
NH ₄ Cl and WCl ₆ evaporate easily, and the vapor can corrode equipment. KHF ₂ , NH ₄ BF ₆ are deleterious substances.
CsOH and the like are expensive and therefore not suitable for use as heat storage materials. Combination compositions of other alkali metal hydroxides have extremely high hygroscopicity, and safety is also problematic because they are combined with deleterious substances. In addition, when putting a heat storage material into practical use, it is necessary to combine it with a heat storage device, and as this design greatly affects the heat exchange rate, there is a problem that the inherent performance of the heat storage material cannot be used more effectively. It was hot too. Means for Solving the Problems In order to solve the above-mentioned problems, the present invention provides anhydrous sodium sulfate with an element belonging to Group A of the Periodic Table of Elements (alkali metal) or an element belonging to Group A (alkali metal). By coexisting at least one compound of an earth metal (earth metal) and an element belonging to group A (halogen group) to form a heat storage material, the change in specific heat due to crystal transition inherent in anhydrous sodium sulfate is almost completely eliminated. Its endothermic transition temperature (248℃) and exothermic transition temperature (226
℃), and the objective of the present invention is 180~240℃
The purpose of the present invention is to provide a heat storage material that can be used in a temperature range of Effect The various heat storage materials generally known at present have a large amount of change in specific heat (also referred to as heat storage amount) due to crystal transition, but they have various problems in practical use. focused on anhydrous sodium sulfate (Na ₂ SO ₄ ), which is stable against large fluctuations in the supply heat source and does not cause any major problems in handling, and investigated ways to lower its crystal transition temperature. , mixing at least one compound of an element belonging to Group A (alkali metal) or an element belonging to Group A (alkaline earth metal) and an element belonging to Group A (halogen group) of the Periodic Table of Elements; It has been found that the object of the present invention can be satisfied by heating and melting them and making them coexist. The crystal transition temperature of anhydrous sodium sulfate on its endothermic side and exothermic side can be lowered by compounds of the above-mentioned alkali metals and halogen groups (alkali metal halogen compounds) or compounds of alkaline earth metals and halogen groups (alkaline earth metals). Compounds of the same halogen group that are metal elements in the same period in the periodic table (for example, KCl and
CaCl ₂ , NaBr, MgBr, etc.) give almost identical results. The amount of decrease in crystal transition temperature varies depending on the type of alkali metal halide compound or alkaline earth metal halide compound coexisting with anhydrous sodium sulfate, that is, the type of metal element, and the amount of decrease in crystal transition temperature varies depending on the halogen element. If the temperature range up to F is relatively narrow,
This results in a gradual broadening of Cl, Br, and I.
Furthermore, the alkaline earth halogen compound coexisting with anhydrous sodium sulfate provides the same effect as the alkali metal halogen compound at about 1/10 or less of the amount of the alkali metal halogen compound.
Here, the elements belonging to Group A that are allowed to coexist in anhydrous sodium sulfate are Li, Na, K, Rb, Cs, and Fr, and the effects of these halogen compounds are the same. However, in view of practical availability and economy, halogen compounds of Li, Na, K, and Rb are more preferable. The elements belonging to Group A are Be, Mg, Ca, Sr, Ba, and Ra, and the effects of these halogen compounds are the same. However, halogen compounds of Mg, Ca, and Ba are more preferable in terms of toxicity, availability, and economy. Further, the halogen group is located in Group A of the periodic table, and F, Cl, Br, I, and At belong to this group. In particular, when the above-mentioned compounds are allowed to coexist with anhydrous sodium sulfate under heating, the composition change of I, At compounds becomes large due to decomposition or scattering, resulting in fluctuations in the crystal transition temperature. preferable. When the anhydrous sodium sulfate used in the present invention coexists with an alkali metal or alkaline earth metal and a halogen compound, it is easier to use an anhydride during the melting process, but it is easier to use it in the melting process. Sodium sulfate (Na ₂ SO ₄・10H ₂ O) and Na ₂ SO ₄・7H ₂ O, which have 10 crystal waters called
Even if it is heated and melted, it becomes an anhydride (Na ₂ SO ₄ 10H ₂ O converts to an anhydride at 32.4℃)
Therefore, there is no problem in providing the heat storage agent of the present invention. Furthermore, the object of the present invention is satisfied by the coexistence of at least one type of an alkali metal halogen compound and an alkaline earth metal halogen compound with respect to anhydrous sodium sulfate, but the coexistence of two or more of both types also reaches the crystal transition temperature This is effective as a means of adjusting the area. The method for producing the heat storage material of the present invention includes adding at least one of an alkali metal halogen compound or an alkaline earth metal halogen compound to anhydrous sodium sulfate or Glauber's salt.
As a means of making more than one type coexist, these compounded materials are mixed in the form of a mere mixture, such as heating and mixing below the melting temperature, dissolving and mixing in mutually soluble solvents such as water, and then evaporating and separating the solvent. However, a coexistence system of at least one type of alkali metal halogen compound or alkaline earth metal halogen compound with respect to the crystal unit of anhydrous sodium sulfate cannot be formed at the crystal unit level, and the desired effect of the present invention is not achieved. This cannot be expected, and the heat storage material of the present invention can only be provided by heating and melting. The heat storage material of the present invention can store heat by heating itself and can utilize heat radiation energy. In practical use, the heat storage material of the present invention has a slightly smaller amount of heat storage than conventionally known materials, so it is necessary to use a larger amount. is always present. The quality of this design greatly affects heat exchange efficiency, so as a method to eliminate this influence and more effectively utilize the inherent performance of the heat storage material, the heat storage material of the present invention is impregnated with a fluid that does not mix with it. By doing so, it is possible to reduce the amount used by improving heat exchange efficiency and making effective use possible. The fluid used here needs to exhibit fluidity in a temperature range where the heat storage material of the present invention can absorb and release heat without any problem due to crystal transition. A fluid that satisfies these conditions is a hydrocarbon-based or silicon-based heat medium, or wax. Examples Examples will be shown below. (Example 1) Anhydrous sodium sulfate (molecular weight 142.04) 90 mol%
LiCl (molecular weight 42.39), NaCl (molecular weight
58.44), KCl (molecular weight 74.56), RbCl (molecular weight 110.99)
Weigh out 50 g of each in a quartz glass test tube to give a total concentration of 10 mol%, heat and melt, let it cool, take it out from the test tube, crush it in a mortar, and place it in a differential scanning calorimeter ( Shimadzu DT−
30B type), the crystal transition start temperature, end temperature, and heat absorption amount [J/g] on the endothermic side and the crystal transition start temperature, end temperature, and heat release amount [J/g] on the exothermic side were measured. The results shown in Table 1 were obtained by comparing the measured values. The heat storage materials of the present invention obtained by heating and melting were white opaque crystalline powders in all compositions. Furthermore, when the chloride content was changed to 40 mol% relative to anhydrous sodium sulfate, the endothermic crystal transition temperature showed the change shown in FIG.

[Table] (Example 2) For 85 mol% of anhydrous sodium sulfate, NaF
(molecular weight 41.99), LiBr (molecular weight 86.85), KBr (molecular weight 119.01), and NaI (molecular weight 149.89), respectively.
The mixture was mixed at 15 mol %, treated and measured in the same manner as in Example 1, and the results shown in Table 2 were obtained. The heat storage material of the present invention obtained by heating and melting was a white opaque crystalline powder in all compositions, but after being left for 24 hours, decomposition and sublimation of iodine was observed in the heat storage material using NaI. The inside of the polyethylene bag used to enclose and preserve the product was colored purple.

[Table] (Example 3) Glauber's salt (Na ₂ SO ₄ 10H ₂ O, molecular weight 322.04) was treated in the same manner as in Example 1 so that 90 mol % of KCl was 10 mol %. Got the results. When this result was compared with the results of Example 1, it was found that the result was almost the same as that of the heat storage material of the present invention obtained using anhydrous sodium sulfate as a starting material.

[Table] (Example 4) MgCl ₂ for 99.4 mol% of anhydrous sodium sulfate
(molecular weight 95.21), CaCl ₂ (molecular weight 110.99), BaCl ₂ .
2H ₂ O (molecular weight: 244.28) was treated in the same manner as in Example 1 to give a concentration of 0.6 mol %, and the results shown in Table 4 were obtained.

[Table] (Example 5) KCl6.7 for 92.0 mol% of anhydrous sodium sulfate
Treatment was carried out in the same manner as in Example 1 so that CaCl ₂ was 1.3 mol %, and the results shown in Table 5 were obtained.

[Table] (Example 6) For 90 mol% of anhydrous sodium sulfate
Completely dissolve 10 mol% NaCl in an appropriate amount of water at room temperature and raise the temperature to 100℃.
The results of differential scanning calorimetry measurements of the material evaporated to dryness at temperatures below showed the results in Table 6. This matter is almost not significantly different from the comparative example shown in Example 1, and it shows that only a mixture of independent crystals of each component was formed and no coexistence state could be formed. be.

[Table] (Example 7) Heat storage material of the present invention obtained in Example 1 (Na ₂ SO ₄ :
KCl = 90: 10 mol%) is crushed and the particle size is 100 μm to 30 μm.
Sample 3 was prepared by pressing and filling an aluminum container with a lid with a thickness of 3 mm, a diameter of 50 mm, and a depth of 25 mm at a pressure of 500 kg/cm ² so that the tip of the CA thermocouple was located in the center. Next, add 30% by weight of silicone oil (KF965 manufactured by Shin-Etsu Chemical Co., Ltd.) to 70% by weight of the same heat storage material.
Sample 2 was prepared by filling a slurry-like mixture of the following into the container so that the tip of the CA thermocouple was located in the center. These samples were placed in an air circulation heating tank and heated from 25°C, and the temperature rise curve of the heat storage material was measured when the ambient temperature was maintained at 250°C and is shown in Figure 2. From this result, it is clear that the sample in which the thermal medium is impregnated with the heat storage material can transfer heat more efficiently than the sample in which the heat storage material is simply filled with powder. Effects of the Invention As explained above, the present invention enables the use of anhydrous sodium sulfate as a heat storage material that utilizes the crystal transition of a substance that can be used in the temperature range of 180 to 240°C by significantly lowering its inherent crystal transition temperature. It is possible to match the temperature range to the purpose, eliminate deterioration of the heat storage material due to continuous use as seen in the use of pentaerythritol, and eliminate the need to control the upper limit temperature of the heat source. It is possible to improve the evaporation and scattering of substances during use, strong hygroscopicity, handling safety, and corrosiveness of heat storage devices, and in addition, extremely low prices can be achieved. Furthermore, when the heat storage material of the present invention is put into practical use, by impregnating the heat storage material with an insoluble heat medium, the inherent performance of the heat storage material can be effectively utilized with high efficiency.

[Brief explanation of the drawing]

FIG. 1 is a curve diagram showing a change in crystal transition start temperature on the endothermic side based on measurement by a differential scanning calorimeter due to a change in the composition of the heat storage material according to the present invention. FIG. 2 is a curve diagram showing the effect of temperature increase due to atmospheric heating in the heat storage material of the present invention, depending on whether or not the heat medium is impregnated.

Claims (1)

[Claims] 1. Anhydrous sodium sulfate containing an element (alkali metal) belonging to Group A of the Periodic Table of Elements or Group A
A heat storage material comprising at least one compound of an element belonging to Group A (alkaline earth metal) and an element belonging to Group A (halogen group). 2 The elements belonging to group A of the periodic table of elements are Li,
The heat storage material according to claim 1, which is Na, K, and Rb. 3 The elements belonging to group A of the periodic table of elements are Mg,
The heat storage material according to claim 1, which is Ca or Ba. 4 The elements belonging to group A of the periodic table of elements are F,
Claims 1 and 2 are Cl and Br.
The heat storage material described in Section 1 or Section 3. 5. The heat storage material according to claim 1, which is impregnated with an insoluble heat medium. 6 Anhydrous sodium sulfate in group A of the periodic table of elements
A method for producing a heat storage material, in which at least one compound of an element belonging to Group A or an element belonging to Group A and an element belonging to Group A is mixed and heated and melted to coexist.