JPH0134477B2 - - 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 sensible heat methods using water, rocks, etc. are the methods of heat storage that require a wide time range. Alternatively, a latent heat method using hydrated salt, paraffin, etc. can be considered, but the present invention utilizes hydrated salt as a latent heat type heat storage material. Among hydrated salts, sodium sulfate 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 because of its pronounced supercooling phenomenon. . sodium sulfate 10
The supercooling phenomenon in which when the temperature of aqueous salt 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 the supercooling phenomenon cannot be extracted, and in order to use sodium sulfate 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 sulfate decahydrate to make it a heat storage material that can withstand long-term use, and promotes the generation of crystal nuclei during the heat dissipation crystallization of sodium sulfate decahydrate. This is based on the discovery of an effective nucleating agent. In other words, sodium sulfate decahydrate is a colorless monoclinic crystal with a specific gravity of 1.46.
It has a peritectic point of 32.4°C, and can recover heat from relatively low-temperature exhaust heat or heat sources with large fluctuations such as solar heat, store it, and reuse it. Also, the heat of fusion of sodium sulfate decahydrate is approximately
60cal/g, heat of fusion per unit volume is approximately 93cal/
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. Conventionally, sodium salts such as Na ₂ B ₄ O ₇ are used as nucleating agents for sodium sulfate decahydrate;
Various proposals have been made, including those using barium salts such as barium hydroxide, barium chloride, and barium nitrate, and strontium salts such as strontium hydroxide, strontium chloride, and strontium nitrate, but they still have problems when used continuously and are ineffective. It cannot be said to be a typical nucleating agent. As a result of various studies on nucleating agents for heat storage agents based on sodium sulfate decahydrate, the present inventors found that a specific sodium salt, acetate, a propylbenzene derivative, or a magnesium compound, which had not been previously known, was used as a nucleating agent. We have found that the above is an extremely effective nucleating agent, and have arrived at the present invention. That is, the present invention provides sodium sulfate decahydrate,
The present invention relates to a heat storage material containing at least one selected from the group consisting of saccharin sodium, vanadate, ethylenediaminetetraacetic acid alkaline earth metal salt, lignin, magnesium oxide, and magnesium hydroxide as a nucleating agent. The sodium sulfate decahydrate used in the present invention is 10
It does not have to be in the form of aqueous salt; it may have a composition close to that of decahydrate, and includes not only crystals but also aqueous solutions and slurries similar to decahydrate. Vanadate salts used as nucleating agents include sodium vanadate and ammonium vanadate, and alkaline earth metal salts of ethylenediaminetetraacetic acid include Ca salt,
Examples include Mg salt and Ba salt. Adding at least one of these nucleating agents facilitates nucleation during solidification of sodium sulfate decahydrate and prevents overcooling over a long period of time, resulting in economical and stable heat storage. An energy storage system using materials becomes possible. The amount of these nucleating agents used in the present invention is preferably at least 0.01% by weight or more based on sodium sulfate decahydrate, and even if they are added at least 1% by weight, no improvement in effect commensurate with the amount added is observed. It's not economically advantageous either. Therefore, the preferred range of the amount of nucleating agent added is 0.01 to 1% by weight based on sodium sulfate decahydrate.
Since the amount is small, it does not have any adverse effect on the essential physical properties of sodium sulfate decahydrate and can be effectively used as a heat storage material. Since the nucleating agent and some sodium sulfate anhydride exist as solids during melting, mica powder 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 thickener such as sodium alginate, sodium polyacrylate or gelatin may be added. Hereinafter, the present invention will be explained in more detail with reference to Examples. Example 1 30 g of sodium sulfate decahydrate (containing 0.6 g of sodium polyacrylate) sealed in a glass container A, and 30 g of the same sodium sulfate decahydrate (containing 0.6 g of sodium polyacrylate) containing saccharin Sodium 0.15g (vs. sodium sulfate 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 and heated until the internal temperature reached 50°C, and then heated to a separately prepared 20°C water bath.
Both samples were transferred to a constant temperature water bath and the internal temperature was measured. After repeating this heating-cooling cycle, the solidification start temperature and supercooling temperature are shown in Table 1. As a result of supercooling, A, which does not contain a nucleating agent, does not solidify 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 The same procedure as in Example 1 was carried out using sodium vanadate hexahydrate, barium ethylenediaminetetraacetate, lignin, magnesium oxide, magnesium hydroxide as a nucleating agent, and sodium nitrate and acetic acid as comparative examples. 0.15 each of ammonium and calcium hydroxide
g (0.5% by weight of sodium sulfate decahydrate) was added, and the solidification initiation temperature and supercooling temperature were measured. The results are shown in Table 2, and the samples of Examples 2 to 6 all showed slight supercooling, almost no change in solidification temperature, and could withstand repeated use over a long period of time. On the other hand, in Comparative Examples 1 to 3, none solidified, 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 prepared by adding a thickener and a nucleating agent to sodium sulfate decahydrate 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 sulfate decahydrate is blended with at least one member selected from the group consisting of saccharin sodium, vanadate, alkaline earth metal salt of ethylenediaminetetraacetic acid, lignin, magnesium oxide, and magnesium hydroxide as a nucleating agent. Heat storage material.