JPH021195B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat storage material for air conditioning, and is used to promote the coagulation of acetic acid (CH ₃ COOH) or a composition in which acetic acid is added to acetic acid and to prevent overcooling during solidification. A nucleating agent is added.

Pure acetic acid solidifies at a temperature of 16.7℃, while industrial acetic acid containing impurities solidifies at a constant temperature of 14.5℃ or higher.
It is known that it is used as a heat storage material because it melts and releases and absorbs latent heat. However, when acetic acid is sealed in an airtight container, it is overcooled by 6 to 10°C, and heat storage and heat radiation cannot be carried out at a predetermined temperature. The cause of this is not clear, but when acetic acid is poured into an open container, evaporation of acetic acid occurs from the surface, and as the heat of vaporization is removed, acetic acid crystals precipitate, which become nuclei. This is thought to be due to the progress of coagulation.

Even in a composition in which acetate is dissolved in acetic acid, supercooling does not occur in an open state, but in a sealed state, supercooling of 6 to 10 °C occurs, as in the case of acetic acid.
Heat storage - heat dissipation is difficult to achieve at a predetermined temperature.

The purpose of the present invention is to prevent supercooling of acetic acid or a composition obtained by adding an acetic acid salt to acetic acid, and to provide a heat storage material particularly suitable for use in air conditioning, which can smoothly store and release heat at a constant temperature determined by the composition of the substance. Our goal is to provide the following.

In general, the phase change from liquid to solid can be divided into a crystal nucleus generation stage and a crystal growth stage centered on the nucleus. Nuclear generation requires a large amount of energy, and it is known that supercooling occurs due to this energy barrier. For this reason, methods are being used to prevent overcooling by adding nuclear material.

In this case, the nuclear material exists undissolved in the liquid phase,
It is also known that the interfacial energy with the newly formed crystal on the interface is small, and that the nucleus needs to have a size larger than a certain critical radius (the critical radius is 1 to 100 μm). In addition, crystal growth is caused by crystal planes with low molecular density (100, 110, and 111 planes in cubic crystals).
It is known that this is likely to occur.

An example of such a nucleating agent is calcium chloride6.
The effects of barium hydroxide and strontium hydroxide on water salts have been recognized. However, since barium hydroxide and strontium hydroxide produce barium acetate and strontium acetate in acetic acid and dissolve in acetic acid, such basic inorganic substances cannot serve as nucleating agents. Furthermore, since acetic acid reacts with most organic compounds, many organic compounds cannot serve as nucleating agents. Therefore, as a result of investigating the nucleation effect of oxidized and neutral inorganic substances, it was found that anhydrous calcium chloride exhibits a remarkable nucleation effect.

Calcium chloride (CaCl ₂ ) and acetic acid are
CaCl ₂ 4CH ₃ COO ₄ (melting point 73℃) is generated and dissolved in acetic acid, but near the freezing point of acetic acid, the solubility of CaCl ₂ decreases and crystals of CaCl ₂ precipitate, and this CaCl ₂ becomes a nucleus and dissolves in acetic acid. , or crystals of acetic acid with dissolved salts precipitate. Such nucleation also causes Ca,
It has been found that this is commonly observed in halides (anhydrides) of Sr and Ba.

The heat storage material of the present invention includes acetic acid or a composition in which acetic acid is added with an acetate, and as a nucleating agent anhydrous calcium chloride, anhydrous calcium bromide, anhydrous calcium iodide, anhydrous strontium chloride, anhydrous strontium bromide, anhydrous strontium iodide, One or more substances selected from the group of anhydrous barium chloride, anhydrous barium bromide, and anhydrous barium iodide (anhydrous halides of Ca, Ba, and Sr) are added.

Among these halides of Ca, Sr, and Ba, calcium chloride (anhydrous) has the greatest nucleating effect. Therefore, the case where calcium chloride anhydride is added as a nucleating agent will be explained below.

Figure 1 shows the cooling curve of pure acetic acid (99.5%), curve a.
Curve b is the case in which no nucleating agent is added, and curve b is the case in which 0.1% by weight of anhydrous calcium chloride is added as the nucleating agent. In curve a, there is supercooling of 8°C before solidification starts, solidification starts at 7.5°C, the temperature rises accordingly, reaches 15.5°C, and is maintained at this temperature until solidification is completed. On the other hand, in curve b, the supercooling before the start of solidification is 0.5°C, which is extremely small compared to curve a. In this case as well, the temperature rises with the start of solidification and curve a
Similarly, it is kept at 15.5℃ until solidification is complete.

Figure 2 shows the cooling curve of a composition prepared by adding and dissolving 5% by weight of sodium acetate (CH ₃ COONa) and 5% by weight of potassium acetate (CH ₃ COOK) in acetic acid. Curve a is the cooling curve when no nucleating agent is added, curve b is is 0.1% calcium chloride anhydrous as a nucleating agent.
This is the case when it is added by weight%. In curve a, there is supercooling of 6°C before solidification starts, solidification starts at 1.5°C, the temperature rises accordingly, reaches 7.5°C, and is maintained at this temperature until solidification is completed.

On the other hand, in curve b, the supercooling before the start of solidification is 0.3
℃, it is extremely small compared to curve a. In this case as well, the temperature rises as the solidification begins and is maintained at 7.5°C until the solidification is completed, as in curve a.

A common method of using heat storage materials is to melt the heat storage material, send a heat medium such as low-temperature water or air around the heat storage tank, and heat it with the heat released when the heat storage material solidifies. , this heat is being utilized. If the heat storage material is supercooled below the temperature of the heat medium at this time, the latent heat of solidification cannot be effectively extracted. Generally, when a heat storage material is used for heating or cooling, it is efficient to set the difference between the solidification/melting temperature of the heat storage material and the temperature of the heat medium before heat exchange to be 2 to 4°C.

For this reason, the presence of a slight amount of supercooling greatly affects heat utilization efficiency.

Examples of the present invention will be described below.

(1) A heat storage material prepared by adding 0.01% by weight of calcium chloride anhydride as a nucleating agent to industrial acetic acid (melting point 15.0°C) was heated to 40°C and then cooled to 0°C, repeating the cycle 20 times to develop a heat storage material. A temperature-time curve was recorded.

In this case, the supercooling each time was 0.5°C or less, and the solidification temperature and degree of supercooling did not change at all after 20 repetitions. Furthermore, in the heating and cooling experiments of acetic acid without nucleating material conducted at the same time, overcooling of 8 to 10°C occurred each time.

(2) A composition prepared by adding 5% by weight of sodium acetate and 3% by weight of potassium acetate to industrial acetic acid (freezing point: 8
Calcium chloride anhydrous as nucleating agent at 0.01 °C)
A cycle of heating the heat storage material to which % by weight was added to 25°C and then cooling it to -5°C was repeated 20 times, and the temperature-time curve of the heat storage material was recorded. In this case, each round of supercooling was 0.4°C or less, and the solidification temperature and degree of supercooling did not change at all after 20 repetitions. In addition, in the heating and cooling experiments of the same composition of acetic acid and acetate without a nucleating agent, which were conducted at the same time, each time
Supercooling of 5.5-6°C occurred.

As explained above, according to the present invention, acetic acid,
Alternatively, it is possible to prevent supercooling of a composition obtained by adding acetate to acetic acid, and to obtain a heat storage material particularly suitable for use in air conditioning, in which heat storage and heat release are performed smoothly at a constant temperature determined by the composition of the substance. In addition, it is possible to reduce the difference between the solidification temperature of the heat storage material and the temperature of the heat medium (water, air, etc.) to be heat exchanged, thereby facilitating thermal design.

[Brief explanation of drawings]

Figure 1 is a temperature-time curve during cooling of pure acetic acid, where curve a shows the case without a nucleating agent and curve b shows the case where 0.1% by weight of calcium chloride anhydride is added as a nucleating agent.
Figure 2 shows the temperature-time curve during cooling of a composition in which 5% by weight of sodium acetate (CH ₃ COONa) and 5% by weight of potassium acetate (CH ₃ COOK) were added to acetic acid (CH ₃ COOH). Curve b shows the case where 0.1% by weight of anhydrous calcium chloride was added as a nucleating agent without a nucleating agent.

Claims (1)

[Claims] 1. Acetic acid (CH ₃ COOH) or a composition in which acetic acid is added with an acetate salt selected from the group of anhydrous halides of calcium (Ca), strontium (Sr), and barium (Ba). A heat storage material characterized by being made by adding one or more kinds of substances. 2. The heat storage material according to claim 1, characterized in that anhydrous calcium chloride (CaCl ₂ ) is added to acetic acid (CH ₃ COOH) or a composition in which an acetate is added to acetic acid.