JPS58117277A - Thermal energy storage material - Google Patents

Abstract

PURPOSE:To provide a thermal energy storage material which facilitates nucleation during solidification, can prevent supercooling over a long period of time, and is economical and stable, by blending a specified nucleating agent with Na2 SO4.10H2O. CONSTITUTION:A thermal energy storage material is obtd. by blending at least one member selected from saccharin sodium, vanadate salts such as sodium vanadate, alkaline earth metal ethylenediamine-tetraacetates, such as barium ethylenediamine-tetraacetate, MgO and Mg(OH)2 as a nucleating agent with Na2SO4.10H2O. By adding the nucleating agent, nucleation is facilitated during the solidification of Na2SO4.10H2O. Further, since supercooling can be prevented over a long period of time, it becomes possible to provide an energy storage system using an economical, stable thermal energy storage material.

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 increasing momentum for the effective use of waste heat and solar heat.As a heat storage method that requires a wide time range, sensible heat using water, rocks, etc. There are seven possible methods, such as a latent heat method using hydrated salt, paraffin, etc., 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 a heat storage material because it is inexpensive and has a melting point near room temperature11, but it has not been put into practical use because it has a noticeable supercooling phenomenon. 1. The supercooling phenomenon in which when the temperature of sodium sulfate decahydrate is gradually lowered from its molten state, it does not crystallize and does not release heat even after passing the phase change temperature (32°C). This means that no heat can be taken out at a certain temperature, even if the temperature is low.In order to use sodium sulfate decahydrate as a heat storage material, it is essential to suppress this supercooling phenomenon.

In order to eliminate these 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 heat dissipation crystallization of sodium sulfate decahydrate. Based on the discovery of an effective nucleating agent, sodium sulfate decahydrate is a colorless monoclinic crystal with a specific gravity of 1.46 and a peritectic point of 32.4°C.
Heat can be recovered from heat sources that fluctuate widely, such as comparatively low-temperature waste heat or solar heat, and can be stored and reused.

The heat of fusion of sodium sulfate decahydrate is approximately 60 cd/f.
, the heat of fusion per unit volume is approximately 93 dl/d, which is a fairly large heat of fusion, and the present inventors have focused on the fact that it is an extremely suitable compound as a heat storage material. We investigated various nucleating agents to prevent the problem of supercooling. Nucleating agents for sodium sulfate decahydrate have conventionally used sodium salts such as Na2B407, barium salts such as barium hydroxide, barium chloride, and barium nitrate, and strontium salts such as strontium hydroxide, strontium chloride, and strontium nitrate. Although a number of proposals have been made regarding the use of nucleating agents, they still have problems when used continuously, and cannot be said to be effective nucleating agents. As a result of various studies on nucleating agents for heat storage agents based on sodium sulfate decahydrate, the present inventors found that certain sodium salts, acetate salts, propylbenzene derivatives, magnesium compounds, etc. The present invention was achieved based on the discovery that one or more types of nucleating agents are extremely effective nucleating agents.

That is, the present invention combines sodium sulfate decahydrate 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. The present invention relates to a heat storage material made of.

The sodium sulfate 1O hydrate used in the present invention does not have to be exactly V-containing to the 10-hydrate; it may be in the form of a composition close to that of the 10-hydrate, and is not in the form of crystals, but in the form of an aqueous solution or slurry close to that of the 10-hydrate. It includes everything such as. ′
Vanadate salts used as nucleating agents include sodium vanadate and ammonium vanadate, and alkaline earth metal salts of ethylenediaminetetraacetic acid include &MCa salt, M2 salt, Ba salt, etc. .

By adding at least one of these nucleating agents, it is possible to easily generate nuclei during solidification of sodium sulfate 1O hydrate, and to prevent long-term overcooling and overcooling. This makes it possible to create an energy storage system using a reliable and stable heat storage material. 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 1% by weight or more is added, the effect will not improve depending on the amount added. It is difficult to see, and it is not economically advisable. Therefore, the preferred range of the amount of nucleating agent added is 0.01 to 1% by weight relative to sodium sulfate decahydrate, and since it is a small amount, it does not have any adverse effect on the essential physical properties of sodium sulfate decahydrate. , which 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 detail using examples.

Example 1 30 grams of sodium sulfate decahydrate (containing 0.62 sodium polyacrylate) sealed in a glass container A
and the same sodium sulfate 1° hydrate 302 (contains 0.62 sodium polyacrylate) and saccharin sodium o, 1st (based on sodium sulfate decahydrate 0.5 weight ratio)
Sample B was prepared by adding, thoroughly mixing, and sealing (thermocouples were inserted in both samples)5.Both samples were first immersed in a constant temperature water bath at 50°C until the internal temperature reached 50°C.
After heating to ℃, both mice were transferred to a separately prepared constant temperature water bath (/c) and the internal temperature was measured. By repeating this heating-cooling cycle, the temperature at which solidification started, The supercooling temperatures are shown in Table 1. In A, which does not contain a nucleating agent, no solidification occurs as a result of supercooling, making it completely unsuitable as a heat storage material, while in B, which contains a nucleating agent, there is only a slight amount of supercooling and no solidification occurs. occurs.
ing,.

Table 1 Also, in FIG. 1, the solidification start temperature (1) and supercooling temperature (2) of B in Table 1 are shown in a line graph.

As is clear from these results, when a nucleating agent is added, the supercooling becomes slighter than that of i/, and its properties hardly change even after repeated use, making it practical as a heat storage material.

FIG. 2 shows the internal temperature when the heat storage material is heated to 50° C. only once and left as it is. The difference between curves A and B in this figure is that they contain nucleating agents. In A, which does not contain a nucleating agent, only sensible heat can be used, whereas in B, which contains a nucleating agent, latent heat is released during solidification in the flat part.

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 2-6. Comparative Examples 1 to 3 In the same manner as in Example 1, sodium vanadate hexahydrate, barium ethylenediaminetetraacetate, likunin, magnesium oxide, and magnesium hydroxide were used as nucleating agents, and sodium nitrate, ammonium acetate, and calcium hydroxide were used as comparative examples. 0.151i' each (for sodium sulfate 1
The solidification start temperature and supercooling temperature were measured by adding 0.5 hydrated salt (by weight)5. The results are shown in Table 2, and the supercooling was slight in all of Examples 2 to B. The solidification temperature showed almost no change and could withstand repeated use over a long period of time. On the other hand, none of Comparative Examples 1 to 5 solidified, and latent heat could not be recovered.

[Brief explanation of the drawing]

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, then cooled repeatedly. FIG. 2 is a graph (relationship between temperature and time) showing nine states of temperature drop for similar samples and samples to which no nucleating agent was added. Agents 1) Akira Agent Ryo Hagiwara - February 1980/, P-day Commissioner of the Patent Office Haruki Shimada 1, Indication of the case 1982 Patent Application No. 6,0 2, Name of the invention Thermal storage material 3 , Relationship with the person making the amendment 1'- Patent applicant 1i: +'li 525 Okiube, Ube City, Yamaguchi Prefecture
3 No. 1 (Name (220) Central Glass Co., Ltd. and (fl Representative Miyoshi Ito Z subject of amendment (1) Contents of -8 amendment to "Detailed Description of the Invention" of the specification (No. 11 of the specification) 7th page F to 4th line to 3rd line r jJI
This shows the internal temperature when heated and left as is. '' has been corrected to ``Indicates the internal temperature when heated and then transferred to constant temperature water m at 20°C.''

Claims (1)

[Claims] A heat storage material comprising sodium sulfate decahydrate mixed 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.