JPS58225181A - Heat storage material - Google Patents

Abstract

PURPOSE:To obtain a latent heat-type heat storage material, capable of reducing the degree of supercooling during its solidification, by adding, as nucleating agent(s), sodium tetraborate and/or borax to disodium hydrogenphosphate. CONSTITUTION:The objective heat storage material can be obtained by adding to (A) disodium hydrogenphosphate (Na2PO4.12H2O), (B) pref. 0.5-10 (especially 1-5)wt% of sodium tetraborate (Na2B4O7) and/or borax (Na2B4O7.10H2O).

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat storage material. More specifically, the present invention relates to a latent heat type heat storage material that reduces the degree of supercooling during solidification.

Water and crushed stone have traditionally been used as heat storage materials, but these have low heat storage density (1cnt/g4eg
(below), a fairly large heat storage device is required for practical use. 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.

In response, research and development on applying latent heat during melting and solidification of substances to heat storage has become active in recent years. 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 10aIVg.

By the way, with recent advances in solar heat utilization technology and waste heat recovery technology, temperatures of 30 to 50 degrees Celsius have been used as a heat source for hot water supply and space heating.
Heat storage at relatively low temperatures is attracting attention. Organic substances such as paraffin and inorganic hydrates are attracting attention as latent heat type heat storage materials for storing heat at such low temperatures.

Although organic materials as latent heat storage materials have good stability during melting and solidification, they have problems in absorbing and releasing heat because the material itself has poor thermal conductivity. 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 1.5 to 2.0 degrees, 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 humidity.

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.

Disodium hydrogen phosphate (N a 2HPOa ・12
H20) has a melting temperature of 35°C and a latent heat of 49c.
m/g (measured by differential scanning calorimeter), it is very promising as a latent heat storage material for hot water supply and space heating, but supercooling phenomena are also observed in the case of this inorganic hydrate. That is,
Once melted, disodium hydrogen phosphate does not solidify even if it is left at room temperature around 25°C. This is because the solidification start temperature of disodium hydrogen phosphate is 21°C,
This is because supercooling corresponding to a temperature difference of 14° C. occurs after all. Therefore, in order to effectively extract the latent heat of this inorganic hydrate, it is necessary to use water as cold as 10-odd degrees Celsius.
In fact, it could not be used as a super-cleaning material.

As a result of various studies in search of a nucleating agent that can reduce the degree of supercooling of disodium hydrogen phosphate, the present inventor found sodium tetraborate (Na 2 B 407 ) and borax (Na2B40.・1oH2o ). was found to be very effective.

Therefore, the present invention relates to a latent heat type heat storage material that reduces the degree of supercooling, and this heat storage material is made by adding one or two of sodium tetraboron and borax to disodium phosphate.

The degree of supercooling reduction depends on the addition ratio of the nucleating agent used, but adding too much of the nucleating agent will not produce the expected effect, so disodium hydrogen phosphate is generally used. It is used at a ratio of about 0.5 to 10% by weight, preferably about 1 to 5% by weight.

The degree of supercooling reduction is indicated by the difference ΔTsc between the melting temperature of the heat storage device and the solidification start temperature.
It is possible to reduce the value of sc to about % of that without additives. In addition, the time required to return to the melting temperature is also shortened (see graph), allowing for more efficient heat storage.

Next, the present invention will be described in detail with reference to examples.

Example A predetermined proportion of sodium tetraborate or borax was added to disodium hydrogen phosphate, and their △T
The value of sc was measured according to the following method.

10 'II' of disodium hydrogen phosphate is placed in a 20-capacity glass container, a predetermined amount of nucleating agent is added thereto, and the container is tightly sealed. This was left in a constant temperature bath at 70°C for about 1 hour.
Allow to completely thaw. Next, the glass container containing the molten sample mixture is placed in 10° C. water and cooled while stirring with a magnetic tank and a stirrer. The sample mixture is supercooled to a certain temperature, leading to solidification.

The humidity change during this temperature drop was measured using a thermal lightning pair, and the degree of supercooling ΔGa was determined. I looked into it. The results obtained are shown in Table 1 below.

Table 1 1 None 142 Sodium tetraborate 0.5
103 1
．． 0 84 /I
5.0
75 10.0
6 Borax 1.0 The graph shows the change in humidity over time during the cooling process for A1 and A3.

Comparative Example Various other nucleating agents were added to phosphorous disodium hydrogen in an amount of 1% by weight, and Tea was added to the degree of supercooling.
was measured. The results obtained are shown in Table 2 below.

Table 2 Nucleating agent △
T80 (deg)1 Cryolite (1Ja3AI!F6)
132 Activated carbon 3 Strontium hydroxide [Sr(OH)2.8H2
0]124 Barium nitrate (Ba(No,)2]
13

[Brief explanation of the drawing]

The drawing is a graph showing changes in humidity over time during the cooling process for Examples A1 and 3. Representative Patent Attorney Yoshi 1) Toshio Time

Claims (1)

[Claims] 1. Disodium hydrogen phosphate-(Na2apo, .12
A latent heat type heat storage material made by adding one or both of sodium tetraborate (Na2B40.) and borax (Na2B40y40H20) to H20). 2. The latent heat type heat storage material according to claim 1, wherein sodium tetraborate and/or borax are added in a proportion of about 0.5 to 10% by weight based on disodium hydrogen phosphate. 3. A latent heat type heat storage material according to claim 1, which is used for heating purposes.