JPH1135930A - Cold storage material utilizing latent heat - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively prevent supercooling by incorporating sodium borate in a specific ratio into an aqueous solution of sodium chloride. SOLUTION: The amount of sodium borate is preferably 0.1-5 pts.wt. based on 100 pts.wt. of an aqueous solution of sodium chloride and the concentration of sodium chloride is preferably 5-30 wt.%. The phase transition temperature of a cold storage material utilizing latent heat obtained is preferably -40 to -2 deg.C. For an aqueous solution of sodium chloride as a cold storage medium is employed sodium chloride having a purity of 99% or higher. As sodium borate employed as a supercooling preventing agent, there can be exemplified borax, anhydrous sodium borate, sodium borate dihydrate, etc., and among these borax is preferable. Sodium borate prevents the supercooling phenomenon of a cold storage material utilizing latent heat comprising sodium chloride as a cold storage medium and makes the freezing point close to the phase transition temperature of the aqueous solution of sodium chloride. To this material may be added a water-absorbent resin, attapulgite clay, gelatin, agar, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a latent heat storage material using an aqueous solution of sodium chloride as a refrigerant (main agent). More specifically, the present invention relates to a latent heat storage material in which borax is added as a supercooling inhibitor to a cold storage material containing an aqueous solution of sodium chloride.

[0002]

2. Description of the Related Art Various efficient storage methods of electric power energy have been studied and developed for the purpose of utilizing surplus electric power. For example, development of a latent heat storage material utilizing absorption heat accompanying a phase change such as melting and solidification of a substance serving as a heat medium is one of them. A heat storage material is a material that accumulates heat or cold in a substance and effectively uses the flow of heat when necessary. Particularly, a material utilizing heat generation / endothermic reaction mainly due to a phase change of a substance is referred to as a latent heat storage material, and more particularly, a case in which cold heat is stored in advance and then cooled when necessary is referred to as a latent heat storage material. There is no clear distinction. Among the latent heat storage materials, those using inorganic materials such as inorganic salts and inorganic hydrated salts as the refrigerant storage medium have higher thermal conductivity, larger latent heat, smaller volume change, and nonflammability than organic materials. Among them, the aqueous sodium chloride solution has further advantages that it is less toxic, has low reactivity, is easily available, is inexpensive, has an appropriate solubility, and its eutectic temperature is close to the frozen food storage temperature. Therefore, these regenerative materials can be particularly suitably used for refrigeration of foods, cold preservation at the time of delivery, refrigeration of chemicals and pharmaceuticals, and cooling processes in food factories and the like.

[0003]

However, a latent heat storage material using an inorganic material such as sodium chloride as a refrigerant storage medium,
There is a problem of causing a supercooling phenomenon. The term “supercooling” means that when a substance is cooled, the phenomenon of the transition does not appear even when the temperature of the phase transition from a liquid to a solid is exceeded. For example, 23.
A 3% by weight aqueous solution of sodium chloride has a phase transition temperature of -21.
Despite the temperature, the phase transition may not actually occur unless the temperature is lowered to around -30 ° C. In other words, to cause the supercooling phenomenon, it is necessary to prepare a refrigerator capable of cooling to a temperature lower than the temperature to be actually used (the freezing point of the regenerative material). There is also a problem that extra energy is required, such as an increase in running cost due to a decrease in operation efficiency due to operation (3% decrease every 1 ° C. decrease).

[0004] In order to alleviate the supercooling, a substance (supercooling inhibitor) which becomes a core of the refrigerant during solidification is added to the refrigerant. As such a supercooling inhibitor, for example, JP-A-6-80956 discloses the use of a crystalline nucleating agent having a particle size of 1 to 200 μm. However, the refrigerant storage material of the cold storage material disclosed in this publication has a phase transition temperature of 7 to 8 ° C., such as sodium sulfate decahydrate, calcium chloride hexahydrate, and sodium acetate trihydrate.
None has a low phase transition temperature of about −20 ° C.
In the cold storage material, the lower the temperature is, the more the problem of supercooling becomes large in terms of cooling efficiency.

[0005] In addition, regarding what kind of supercooling inhibitor to use, there is a theory that it is better to use a material having the same crystal structure and lattice constant as the heat storage medium. Some have a high supercooling prevention effect,
At present, what kind of supercooling inhibitor is suitable for a specific heat storage medium is trial and error.

It is an object of the present invention to provide a latent heat storage material which suppresses the supercooling phenomenon of a latent heat storage material using an aqueous solution of sodium chloride as a heat storage medium and has a freezing point as close as possible to the phase transition temperature of the aqueous solution of sodium chloride. is there.

[0007]

Under these circumstances, the present inventors have conducted various studies. As a result, when sodium borate is used as a supercooling inhibitor for an aqueous solution of sodium chloride, supercooling is particularly effectively suppressed. The inventors discovered for the first time that they were effective, and completed the present invention. That is, the present invention provides (1) a latent heat storage material containing an aqueous sodium chloride solution and sodium borate, and (2) an amount of sodium borate is 0.1 to 5 parts by weight based on 100 parts by weight of the aqueous sodium chloride solution. (1) The latent heat storage material according to (3), -40 ° C to -2 ° C
(1) or (2), wherein the phase change phenomenon occurs in the temperature range of (1) or (2), and (4) the concentration of sodium chloride is 5 to 30% by weight. And a latent heat storage material according to (1).

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The refrigerant storage medium used in the present invention is an aqueous sodium chloride solution. The concentration of sodium chloride is not particularly limited as long as an aqueous solution is formed. Above all, 5-30
% By weight, more preferably 15 to 27% by weight. When the content of sodium chloride is 5 to 30% by weight, the temperature difference at the time of solidification and melting becomes small, and the cold storage / cooling temperature becomes close to constant, which is desirable as a cold storage material. Although the purity of sodium chloride is not particularly limited, it is usually 99%.
The above is preferably used.

Sodium borate used as a supercooling inhibitor includes borax (sodium borate decahydrate), anhydrous sodium borate, sodium borate dihydrate, sodium borate tetrahydrate, and borate. Sodium pentahydrate can be used, and among them, borax is preferable. The amount of sodium borate used is 0.1 to 5 parts by weight, preferably 2 to 4 parts by weight, based on 100 parts by weight of the aqueous sodium chloride solution. If the amount is less than 0.1 part by weight, the expected effect of preventing supercooling cannot be obtained. May be

In addition to the essential components, other components that may be added to the latent heat storage material of the present invention include water-absorbing resins, thickening agents such as attapulghai clay, gelatin, agar, and silica gel. However, the composition of the present invention does not contain carbon black.

The latent heat storage material of the present invention is preferably
40 ° C to -2 ° C, more preferably -30 ° C to -15 ° C
It is preferable that a phase transition phenomenon occurs in the above temperature range.

The method of producing the regenerator material is not particularly limited. For example, sodium chloride is gradually added to pure water or ion-exchanged water in a container while gradually stirring to a predetermined amount, and the mixture is sufficiently mixed. The borax, which is an agent, is gradually added to a predetermined amount while stirring, and mixed well, and other additives are added simultaneously or after this, followed by stirring and mixing.
There is a method of pouring an aqueous solution in which sodium chloride, borax and the like are mixed in advance on the resin. The order of adding sodium chloride, borax and other additives is optional.
It is also possible to heat to about 50 ° C. to promote dissolution. After mixing sodium chloride and borax, the mixture may be added to pure water or ion-exchanged water.

Although the form of the cold storage material is not particularly limited, it is usually a form in which the above-mentioned cold storage material is packaged with a corrosion-resistant metal or inorganic material and / or an organic material such as polyethylene or other plastics. Examples of the shape include a lump, a plate, and a sheet. As a place where such a cold storage material is arranged, as it is in a cold storage room,
Alternatively, it is conceivable to place it in a heat exchange section.

[0014]

The present invention will be described below in more detail with reference to examples. However, the present invention is not limited to the following examples. Example 1 Temperature drop rate: 1 ° C./min→−
Hold at 45 ° C. for 20 minutes → heating rate 2 ° C./min→5.0 wt%, 10.0 wt%, 1 wt% under the program of −10 ° C.
100% aqueous solution was added to 5.0% by weight, 20.0% by weight and 23.3% by weight aqueous sodium chloride solution, respectively.
By adding 3 parts by weight of borax to parts by weight to obtain a cold storage material,
The solidification start temperature of the cold storage material was measured. Table 1 shows the results.

Comparative Example 1 The solidification start temperature of each concentration of sodium chloride aqueous solution was measured in the same manner as in Example 1 except that borax was not used. Table 1 shows the results.

[0016]

[Table 1]

Example 2 2 parts by weight of borax was added to an aqueous solution of sodium chloride having a concentration of 23.3% by weight based on 100 parts by weight of the aqueous solution to obtain a regenerator material, and the solidification start temperature of the regenerator material was measured. The measurement was performed in the same manner as in Example 1.

Example 3 The solidification start temperature of the regenerator material was measured in the same manner as in Example 2 except that the amount of borax was changed to 1 part by weight with respect to 100 parts by weight of the aqueous sodium chloride solution.

Comparative Example 2 A regenerator material was obtained by using a supercooling inhibitor shown in Table 2 in a 23.3% by weight aqueous sodium chloride solution, and the solidification start temperature of each regenerator material was set in the same manner as in Example 1. Was measured by DSC. Table 2 shows the results of Examples 2 and 3 and Comparative Example 2 together with the results of the cold storage material using the 23.3% by weight aqueous sodium chloride solution of Example 1 and the results of the 23.3% by weight aqueous sodium chloride solution of Comparative Example 1. Shown in "Degree of supercooling" refers to the difference between the melting temperature of the aqueous sodium chloride solution and the solidification start temperature of the cold storage material when no supercooling inhibitor is added.

[0020]

[Table 2]

Example 4 A sample (a borax was added to an aqueous 23.3% by weight sodium chloride solution, and a sodium chloride aqueous solution 1 was placed in a heat-resistant glass beaker)
(3 parts by weight with respect to 00 parts by weight) was added, and the container was plugged with a silicon stopper to prevent evaporation, and a stainless sheath T-type thermocouple was placed in the liquid for temperature measurement. The sample container was placed in a low-temperature freezer, cooled from room temperature to -40 ° C, and the solidification onset temperature was measured. The results are shown in Table 3 together with the degree of supercooling.

Comparative Example 3 The solidification starting temperature of sodium chloride was measured in the same manner as in Example 2 except that borax was not used. The results are shown in Table 3 together with the degree of supercooling.

[0023]

[Table 3]

From the results of the above Examples and Comparative Examples, the latent heat storage material of the present invention has an effect of preventing supercooling of 10 ° C. or more as compared with the case where no supercooling inhibitor is used. It has been found that a remarkably good result can be obtained as compared with the case where a compound used as a supercooling inhibitor is used in a cold storage material using another main ingredient.

[0025]

The cold storage material of the present invention is an economically effective cold storage material that can effectively prevent supercooling of an aqueous solution of sodium chloride and has high safety, and thus has a problem in keeping cold food such as ice cream. Available without.

Claims (4)

[Claims] 1. A latent heat storage material containing an aqueous sodium chloride solution and sodium borate. 2. The latent heat regenerator according to claim 1, wherein the amount of sodium borate is 0.1 to 5 parts by weight based on 100 parts by weight of the aqueous sodium chloride solution. 3. The latent heat storage material according to claim 1, wherein a phase transition phenomenon occurs in a temperature range of −40 ° C. to −2 ° C. 4. The concentration of sodium chloride is 5 to 30% by weight.
The latent heat storage material according to claim 1, wherein