JPH0134476B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat storage material used in latent heat type heat storage devices and the like. As is well known, in order to cope with the deterioration of the energy situation in recent years, there is a growing momentum for the effective use of waste heat and solar heat, and as a heat storage method that requires a wide time range, sensible heat using water, rocks, etc. The method and
Although a latent heat method using hydrated salt, paraffin, etc. can be considered, the present invention utilizes hydrated salt as a latent heat type heat storage material. Among hydrated salts, sodium carbonate decahydrate has long been known as an inexpensive heat storage material with a melting point near room temperature, but it has not been put into practical use due to its remarkable supercooling phenomenon. Not yet. The supercooling phenomenon in which when the temperature of sodium carbonate decahydrate is gradually lowered from its molten state, it does not crystallize and does not release heat even after the phase change temperature (32℃) This means that heat cannot be extracted, and in order to use sodium carbonate decahydrate as a heat storage material, it is essential to suppress this supercooling phenomenon. In order to eliminate such drawbacks, the present invention modifies sodium carbonate decahydrate to make it a heat storage material that can withstand long-term use. This is based on the discovery of a nucleating agent. In other words, sodium carbonate decahydrate is a colorless monoclinic crystal with a specific gravity of 1.44 and a peritectic point of 32°C. can be reused. In addition, the heat of fusion of sodium carbonate decahydrate is approximately
59 cal/g, heat of fusion per unit volume is approximately 85 cal/
The inventors of the present invention have focused on the fact that this compound has a fairly large heat of fusion of cm ³ and is extremely suitable as a heat storage material. Various agents were investigated. Conventional nucleating agents for sodium carbonate decahydrate include strontium salts such as strontium hydroxide, strontium chloride, and strontium nitrate; barium salts such as barium hydroxide, barium chloride, and barium nitrate; calcium hydroxide, calcium chloride; Various proposals have been made, including those using calcium compounds such as calcium nitrate, but they still have problems when used continuously and cannot be said to be effective nucleating agents. The present inventors investigated various nucleating agents for heat storage materials based on sodium carbonate decahydrate, and found that one or more of the previously unknown specific aluminum compounds, sodium salts, and acetates are extremely effective. The present invention was developed based on the knowledge that it is a nucleating agent. That is, the present invention includes sodium carbonate decahydrate, aluminum hydroxide, alkali metal bisulfite, alkali metal sulfite, azide salt,
The present invention relates to a heat storage material containing at least one salt selected from the group consisting of vanadates and alkaline earth metal salts of ethylenediaminetetraacetic acid. Sodium carbonate decahydrate, which is the main ingredient used in the present invention, does not need to be in the form of decahydrate, nor does it need to be in the form of crystalline powder. It may be of a composition close to that of sodium carbonate decahydrate, and may be an aqueous solution, slurry, or crystal, as long as its composition is close to that of decahydrate. Specific compounds of the nucleating agent include sodium bisulfite and potassium bisulfite as alkali metal bisulfites, and sodium sulfite and potassium sulfite as alkali metal sulfites. Azide salts include sodium azide and lead azide; vanadate salts include sodium vanadate and ammonium vanadate; alkaline earth metal salts of ethylenediaminetetraacetic acid include Ca salt, Mg salt, Ba salt, and Sr salt. Examples include salt. Adding at least one of these nucleating agents facilitates nucleation during solidification of sodium carbonate decahydrate and prevents overcooling over a long period of time, making it economical and An energy storage system using stable heat storage material becomes possible. The amount of these nucleating agents used in the present invention is at least 0.01% by weight based on sodium carbonate decahydrate.
The above is preferable, and even if 1% by weight or more is added, no improvement in effect commensurate with the amount added is seen, and it is not economically advisable. Therefore, the preferred range of the amount of nucleating agent added is 0.01 to 1.0% by weight based on sodium carbonate decahydrate.
Since it is present in a small amount, it does not have any adverse effect on the essential physical properties of sodium carbonate decahydrate and can be effectively used as a heat storage material. In addition, since the nucleating agent and some sodium carbonate anhydrous salt exist as solids during melting, mica was added to prevent these from separating from the liquid phase and to increase the rate of transition to decahydrate during solidification. A small amount of a thickening agent such as powder, sodium alginate, sodium polyacrylate or gelatin may be added. The present invention will be explained in more detail with reference to Examples below. Example 1 30 g of sodium carbonate decahydrate (containing 0.6 g of sodium polyacrylate) sealed in a glass container A and 30 g of the same sodium carbonate decahydrate (containing 0.6 g of sodium polyacrylate) were hydroxylated. Aluminum 0.15g (for sodium carbonate decahydrate)
Sample B was prepared by adding 0.5% by weight), thoroughly mixing and sealing (a thermocouple was inserted in both samples).
Both samples were first immersed in a constant temperature water bath at 50°C until the internal temperature reached
After heating to 50°C, both samples were transferred to a separately prepared thermostatic water bath at 20°C, and the internal temperature was measured.
After repeating this heating-cooling cycle, the solidification start temperature and supercooling temperature are shown in Table 1.A, which does not contain a nucleating agent, does not solidify as a result of supercooling and is completely unsuitable as a heat storage material. In B containing the nucleating agent, supercooling was slight and solidification occurred.

[Table] Figure 1 also shows the solidification start temperature of B in Table 1.
(1) and supercooling temperature (2) are shown in a line graph. As is clear from these results, by adding a nucleating agent, supercooling becomes slight, and its properties hardly change even after repeated use, making it practical as a heat storage material. Figure 2 shows the temperature at 20℃ after heating the heat storage material once to 50℃.
Indicates the internal temperature when transferred to a constant temperature water bath at °C. The difference between curves A and B in this figure is that in curve A, which does not contain a nucleating agent, only sensible heat can be utilized, whereas in curve B, which contains a nucleating agent, latent heat is released during solidification at the flat part. It is something to do. Since latent heat is significantly larger than sensible heat, it is advantageous in miniaturizing the device, and since latent heat is released at a constant temperature, it is advantageous in terms of device operation. Examples 2 to 6, Comparative Examples 1 to 3 In the same manner as in Example 1, sodium bisulfite, sodium sulfite, sodium azide, sodium vanadate hexahydrate, and barium ethylenediaminetetraacetate were added as nucleating agents, and as a comparative example, 0.15 g of each of aluminum chloride, sodium metavanadate, and strontium acetate 1/2 hydrate (0.5% by weight of sodium carbonate decahydrate) were added, and the solidification initiation temperature and supercooling temperature were measured. The results are shown in Table 2. All of Examples 2 to 6 showed slight supercooling, almost no change in solidification temperature, and were able to withstand repeated use over a long period of time. Further, in Comparative Examples 1 to 3, no solidification occurred and latent heat could not be recovered.

【table】 [Brief explanation of drawings]

Figure 1 is a graph showing the state of supercooling when a sample of sodium carbonate decahydrate added with a thickener and a nucleating agent is heated and melted and then cooled repeatedly. (Relationship between temperature and number of operations)
FIG. 2 is a graph (relationship between temperature and time) showing the state of temperature drop for a similar sample and a sample to which no nucleating agent was added.

Claims (1)

[Claims] 1 Sodium carbonate decahydrate as a nucleating agent, aluminum hydroxide, alkali metal bisulfite, alkali metal sulfite, azide, vanadate,
A heat storage material containing at least one type of salt selected from the group consisting of alkaline earth metal salts of ethylenediaminetetraacetic acid.