JPS60243188A - Heat storage material - Google Patents

Abstract

PURPOSE:A heat storage material for reducing the degree of supercooling during coagulation, showing stabilized performance gainst long-period heat cycle, obtained by blending sodium acetate trihydrate with sodium bromate, or sodium iodate as a nucleating agent. CONSTITUTION:(A) Sodium acetate trihydrate is blended with (B) 0.01-20wt% (preferably 0.05-10wt%) sodium bromate and/or sodium iodate as a nucleating agent, to give the aimed heat storage material. EFFECT:Capable of making a cluster exist stably even in a temperature environment >=20 deg.C higher than the melting point of the component A.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to heat storage materials. More specifically, the present invention relates to a heat storage material that reduces the degree of supercooling during solidification and exhibits stable performance over long-term thermal cycles.

[Conventional technology]

Traditionally, water and crushed stone have been used as heat storage materials, but these have low heat storage density (1m/g-eLeg).
? (L) 1. In practical use, a fairly large heat storage device is required. Furthermore, as the heat is dissipated, the temperature inside the heat storage device gradually decreases, so it is technically quite difficult to obtain stable thermal energy.

As a result of this, there has been an increase in research and development in recent years on the application of latent heat during the melting and solidification of materials to heat storage. A feature of such a latent heat type heat storage material is that it can stably absorb and release thermal energy at a constant temperature corresponding to the melting temperature of the material at a high heat storage density of several tens of cubic meters.

By the way, with recent advances in solar heat utilization technology and waste heat recovery technology, 50 to 60
Heat storage at relatively low temperatures such as °C is attracting attention.

Organic substances and inorganic hydrates such as paraffin wax and higher fatty acids are attracting attention as latent heat type heat storage materials for storing heat at such low temperatures.

Although organic substances as latent heat type heat storage materials have good stability during melting and solidification, 1. Due to the poor thermal conductivity of the material itself, there are problems in absorbing and releasing heat. Furthermore, since the specific gravity is small, the heat storage device is also relatively large.

On the other hand, inorganic hydrates have about twice the thermal conductivity as organic heat storage materials, and have a high specific gravity of about 1.5 to 2.0, so the heat storage device can also be made smaller.

However, inorganic hydrates generally exhibit a so-called supercooling phenomenon in which the solidification initiation temperature becomes lower than the melting temperature.

This phenomenon occurs when inorganic hydrates are used as heat storage materials.
This significantly impairs the feature of the latent heat storage material, which is to stably absorb and release thermal energy at a constant temperature.

Sodium acetate trihydrate OH,0OONa-3H20
has a melting temperature of 58°C and a latent heat of 51 ayl/
g (as measured by a differential scanning calorimeter), making it very promising as a latent heat storage material for hot water supply, space heating, and even air conditioning as a constant temperature. A phenomenon is observed.

That is, once melted sodium acetate trihydrate does not solidify even if it is left at room temperature of about 15°C. This means that the solidification initiation temperature of sodium acetate trihydrate is approximately -
This is because supercooling corresponding to a temperature difference of nearly 80° C. occurs after all.

Therefore, since heat absorption and release at 58° C. are not performed smoothly at all, it cannot be used alone as a heat storage material.

However, sodium acetate trihydrate with a melting point of 58°C is
When melted by heating to 0°C, it may solidify when cooled to room temperature. The cause is not clear, but
According to the inventor's opinion, although sodium acetate trihydrate melted near its melting point appears to be melted, fine crystal nuclei (clusters) of it still exist in the melt. This cluster becomes unstable as the temperature rises, and can exist in this state at temperatures above 60°C. Therefore, it is thought that even if it is cooled, it will not nucleate, and the melt will be in a supercooled state.

Therefore, when a certain substance is added as a nucleating agent to sodium acetate trihydrate, the clusters can exist stably even at relatively high temperatures, and when the melt is solidified, supercooling is prevented. The extent of this can be reduced as a result. Here, solidification treatment refers to solidifying a melt of sodium acetate trihydrate to which a nucleating agent has been added.
It refers to a process in which solidification is caused once by cooling to 0°C or below to solidify, or by adding a small amount of sodium acetate trihydrate or anhydride powder. For this reason, the above-mentioned cluster One way to evaluate the performance of a nucleating agent is to determine how stably it can exist even at high temperatures, or in other words, how much the degree of supercooling can be reduced.

[Problems to be solved by the invention] [As a result of various studies on nucleating agents that can reduce the degree of supercooling of sodium acetate trihydrate, the present inventor found that sodium salt of phosphoric acid or carbonate It was previously discovered that sodium is very effective (Japanese Patent Application Nos. 58-12458 and 58-260).
No. 83).

Therefore, the present inventor focused on the fact that these i-nucleating agents are nonmetallic sodium oxyoxides, and
A new finding is that sodium salts of halogen-based oxyacids exhibit nucleation activity equivalent to or superior to sodium salts tested for performance as nucleating agents.

[Means for Solving the Problem] and [Operation] Therefore, the present invention relates to a heat storage material, and the heat storage material is made of acetic acid.
Sodium bromate Ma as a nucleating agent in Jum trihydrate
The degree of supercooling reduction depends on the addition ratio of the nucleating agent used, but even if too much nucleating agent is added, it is not expected. Not only is it not as effective as possible, but it also causes deterioration of the material, so it is generally used in a proportion of 0.01 to 20% by weight, preferably 0.05 to 10% by weight, based on sodium acetate trihydrate. used in

The degree of supercooling reduction is indicated by the difference ΔTsa between the melting temperature Tm and the solidification start temperature Tm' of the heat storage material. , ΔTsc can be significantly reduced. 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 thermal cycle tests, allowing for more efficient heat storage.

〔Effect of the invention〕

The heat storage material according to the present invention can be produced in a temperature environment that is 20°C or more higher than the melting point of sodium acetate trihydrate by using sodium bromate, sodium io, -mono-uride, or a mixture thereof as a nucleating agent. Even in this case, the clusters can be stably present, which has the effect of reducing the degree of supercooling. Moreover, this supercooling prevention effect is always stably exhibited even when the heat storage material is used repeatedly over a long period of time.

〔Example〕

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

Examples 1 to 2, Comparative Example 1 0.1 g of each of sodium bromate, sodium iodate, or sodium chlorate was added to 10 liters of sodium acetate trihydrate, and the mixture was placed in a 20-volume glass container. Seal tightly. This is left in a constant temperature bath at 80° C. for 4 hours to completely melt the sample, and then left at room temperature.

The sample line undergoes supercooling and remains in a liquid state even after reaching room temperature.

Add a small amount of acetic acid to this supercooled melt.
Addition of trihydrate causes solidification.

The sample subjected to assimilation treatment in this way was heated at 70 to 85℃.
The mixture was left in a constant temperature bath for 2 hours to heat and melt. Thereafter, the melt was air-cooled to room temperature, and the solidification state of each of the five samples was evaluated according to the following criteria. The results obtained are shown in Table 1.

O: Entirely nucleates △D Partially does not nucleate ×: Does not nucleate at all Table 1 75 0 0 x 77.5 0 0 x 80 Q Δ x 82h5 Δ ×゛× ss x x x Example 3 A predetermined proportion of sodium bromate trihydrate was added as a nucleating agent, and the ΔTsc values thereof were measured according to the following method.

Acetic acid) IJium trihydrate 10 g Total 5M 20 m
Place it in a glass container, add a nucleating agent to it, and
Seal tightly. This was placed in a constant temperature bath and heated within the range of upper limit temperature 75°C and lower limit temperature 15°C at a temperature increase rate of 1°C/min, and the temperature of the mixture was raised above the melting temperature (Tm). After increasing the temperature, the material is cooled at a cooling rate of 1°C/min, and a heat cycle test is repeated until it supercools to a certain temperature (Tm') and solidifies, and the temperature change at that time is measured with a thermocouple. and the degree of supercooling ΔTso (Tm −Tm'
) was investigated. The results obtained are shown in Table 2 below.

Table 2 The effect of preventing supercooling must be demonstrated stably over a long period of time. The results in Table 2 above are the values at the 20th cycle, but the effect has not changed from the first time.
It is stable even after 0 cycles. Addition ratio is 20
If the amount exceeds the weight percent, the melting temperature of IJium trihydrate (Tm) as a heat storage material will be significantly lower than the original melting temperature (Tm), and the required temperature range of 50 to 60°C will not be satisfied. Become. Based on these results, the upper limit of the addition ratio is about 20% by weight.

In addition, thermal cycle test (20th time) in the case of A5
The temperature change over time is shown in the graph of FIG.

Example 4 In Example 3, sodium iodate was used in place of sodium bromate. The degree of supercooling in the 2o cycle is shown in Table 3 below.

Table 3 ノ(addition amount (weight%) △Tsc(dog) Tm(C
Top 1 0 78 58 2 0.05 6 3 0.1 4 p 4 0.5 3 1 557 7 10 56' 8 20 53

[Brief explanation of drawings]

FIG. 1 is a graph showing the temperature change over time in the thermal cycle test (20th time) in the case of A5 of Example 3. Representative Patent Attorney Yoshi 1) Toshifuo1 Figure Male A Time (/l龜3匈2 Procedural amendment (0劃劃1) Display of the case 1982 Patent Application No. 99562 2 Name of the invention Thermal storage material 3 Make the amendment Relationship with the case Patent applicant name (438) Japan Oil Seal Industry Co., Ltd. 4 Agent (105) Address 501 Ato Building, 1-2-7 Shiba Daimon, Minato-ku, Tokyo
No. 5 Column 6 for Detailed Description of the Invention in the Specification Subject to Amendment Contents of the Amendment (1) "Therefore, it can be reduced." on page 4, lines 15 to 19 is corrected as follows. "On the other hand, if a certain substance is added to sodium acetate trihydrate as a nucleating agent, and the heat storage material to which this nucleating agent is added is assimilated, the clusters will exist stably even at relatively high temperatures. Therefore, even if the heat storage material is placed in a high-temperature environment, the clusters that stably exist in the melt will reproduce nucleation during cooling, thereby reducing supercooling. (2) On page 5, lines 8-9, change ``To what extent can the degree of supercooling be reduced?'' to ``To what extent can the reproducibility of nucleation during cooling be Can it be maintained?”・

Claims (1)

[Claims] 1. Sprinkle with vinegar) IJum trihydrate with at least 7 sodium bromate and sodium iodate as a nucleating agent,
A heat storage material made by adding seeds. diacetic acid) 0.01-20 for 13um trihydrate
The heat storage material according to claim 1, wherein a nucleating agent is added in a proportion of 1% by weight.