JPS6342957B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel heat storage material for solar ponds, and more particularly, to an excellent solar pond made of a hydrogel-like material that is free from salt damage, inexpensive, and capable of storing a large amount of heat. The present invention relates to heat storage materials for use.

In recent years, with the depletion of petroleum resources, research into alternative energy sources has been actively conducted, and the use of solar energy is attracting particular attention.

Solar ponds are attracting attention as one means of utilizing solar energy. A solar pond is a pond that can absorb sunlight in the form of heat and store it.The huge amount of heat stored in this solar pond can be used for regular purposes such as agriculture, heating and cooling of buildings, and power generation. It can be supplied as an energy source.

By the way, as the heat storage material used in the solar pond, an aqueous salt solution has conventionally been used.
By forming a concentration gradient in this aqueous salt solution, preventing convection and increasing the heat insulation effect, and suppressing heat radiation, it is possible to store heat over a long period of time.

The concentration gradient in this salt aqueous solution varies in magnitude depending on the type and concentration of the salt used, but is usually formed by injecting fresh water into a concentrated salt aqueous solution. When a concentration gradient is formed, a density gradient is formed accordingly, and this density gradient prevents the occurrence of density differences due to temperature differences, and furthermore, prevents the occurrence of convection due to buoyancy, thereby suppressing heat radiation. Long-term heat storage becomes possible.

However, when an aqueous salt solution is used as a heat storage material for a solar pond, there are the following drawbacks. In other words, (1) in order to forcibly form a concentration gradient, it is necessary to flow a large amount of fresh water into the upper layer of the concentrated salt aqueous solution, which requires a lot of cost and effort for maintenance; forming a concentration gradient,
It takes several months to start storing heat; (3) there is a risk of salt damage due to water leakage, so it cannot be used in areas where salt damage is fatal, such as during fish hatching or aquaculture; (4) the concentration of the salt aqueous solution. (5) Of the salts, borax settles when used for a long time, and magnesium chloride and calcium chloride are expensive. It is more than 10 times more powerful than table salt. (6) The amount of heat storage is expressed as the product of specific heat, temperature, and mass. Therefore, concentrated salt aqueous solutions have a low specific heat and have a poor heat storage effect. (7) When algae, mud, sand, etc. are mixed in. However, since it is a large amount of concentrated salt aqueous solution, there are disadvantages such as the fact that it cannot be dumped because it would cause salt damage.

The inventors of the present invention have conducted intensive research to overcome these drawbacks and provide a heat storage material for solar ponds that can collect and store a large amount of heat. The inventors discovered that the obtained hydrogel-like substance could achieve the objective, and based on this knowledge, they completed the present invention.

That is, the present invention provides a solution obtained by neutralizing an aqueous solution of an inorganic salt capable of forming a gel-like substance upon neutralization or an aqueous solution of the inorganic salt to which a coloring agent has been added with an acid, a salt, or an ion exchange resin. The present invention provides a heat storage material for solar ponds made of a hydrogel-like substance.

The inorganic salt used in the heat storage material of the present invention is one that can form a gel-like substance by neutralization, and is, for example, an alkali metal silicate such as sodium silicate, potassium silicate, lithium silicate, or Silicates of alkaline earth metals are preferably used. These inorganic salts may be in the form of powder or concentrated solution (candy-like), and may be used alone or in combination of two or more.

In the present invention, the acid used for neutralizing the inorganic salt aqueous solution preferably includes inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, and organic acids such as acetic acid, succinic acid, citric acid, and fumaric acid. These acids may be used alone or in combination of two or more.

In addition, examples of salts include magnesium chloride, calcium chloride, manganese chloride, aluminum chloride, cuprous chloride, cupric chloride, ferrous chloride,
Metal chlorides such as ferric chloride and nickel chloride, nitrates such as magnesium nitrate, calcium nitrate, and aluminum nitrate, sulfates such as magnesium sulfate, calcium sulfate, and aluminum sulfate, and acetates such as magnesium acetate, calcium acetate, and aluminum acetate. , or succinate, citrate, or fumarate of magnesium or calcium. These salts may be used alone or in combination of two or more.

Furthermore, the ion exchange resin may be either a commercially available weakly acidic cation exchange resin or a strongly acidic cation exchange resin, and these may be used alone or in a mixture of two or more.

The concentration of the inorganic salt aqueous solution in the present invention is such that the gel-like substance formed by neutralization contains a large amount of water,
It is desirable that the concentration is such that no flow occurs;
A range of 0.5 to 10% by weight is preferred.

Next, neutralization conditions vary depending on the type of acid, salt, ion exchange resin, etc. used as the neutralizing agent, but the pH is usually within the range of 6 to 8. In addition, the time required for gelation depends on the pH and the type of neutralizing agent; for example, at a temperature of 20°C,
If a 2.5% by weight aqueous sodium silicate solution is neutralized to pH 7 with 50% by weight sulfuric acid, it will gel in 5 minutes. On the other hand, when aluminum chloride is used as a neutralizing agent, gelation occurs immediately upon addition to the aqueous sodium silicate solution.

The types of acids, salts, and ion exchange resins used for gelation are appropriately selected depending on the desired gelation rate, and by using these, a large amount of hydrogel can be easily produced.

Furthermore, in the present invention, in order to absorb sunlight more efficiently, it is preferable to add a black dye such as Japanese ink, sulfur black, diamond black, or naphthol brown black as a coloring agent to the inorganic salt aqueous solution. These colorants may be used alone or in combination of two or more.

Since the hydrogel-like substance of the present invention is obtained from a small amount of inorganic salt such as sodium silicate, it is economically advantageous as a heat storage material for solar ponds, and since it is neutral, it does not corrode equipment and can be used as a heat storage material for solar ponds. Even if water leaks, it is completely harmless.

Since this hydrogel-like substance holds a large amount of water, it stores heat extremely effectively by preventing water convection and suppressing heat radiation. In addition, since the concentration of solid matter is low, the specific heat is almost the same as that of water. Therefore, compared to a solar pond using an aqueous salt solution as a heat storage material, a solar pond using the hydrogel-like substance of the present invention has the same It can store much more heat at the same temperature and mass. Furthermore, it has features such as no algae growth and no deterioration.

Further, repair work for a solar pond using the hydrogel-like substance of the present invention is extremely simple. For example, if a hydrogel-like substance is dried in the sun as it is, it becomes silica gel, which is as harmless as sand and easy to handle, making it easy to carry out repair work. Note that if the silica gel is dried at a temperature of 100° C. or higher, it can also be used as a desiccant.

Next, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples unless the gist thereof is exceeded.

Example After dissolving 25 g of powdered sodium silicate in 955 ml of water, a solution of 4.5 g of sulfuric acid dissolved in 20 ml of water was added dropwise to the above sodium silicate solution while stirring to neutralize it to pH 7. did. 750 ml of this neutralized sodium silicate solution was poured into a thermos bottle (inner diameter 90 mm, depth 230 mm). The sodium silicate aqueous solution gelled in about 10 minutes to form a hydrogel. Next, 250 ml of water was gently injected to make the gel phase and aqueous phase equal to 1.

On the other hand, pour 750ml of a 25% by weight sodium chloride aqueous solution into the same thermos bottle, and then gently pour 250ml of water into the same thermos bottle.
ml was poured to bring the volume to 1.

Each thermos bottle was placed directly under a 500W tungsten light bulb. The distance between the light bulb and the thermos bottle is 300 mm from the opening of the thermos bottle to the surface of the light bulb glass.
mm. The amount of light measured by the pyranometer at this distance is
It was 0.804 Cal・cm ^-2・min ^-1 . Temperature measurements are made using thermocouples at a depth of 190 mm for each thermos bottle.
At the same time, the indoor temperature was measured and recorded with a thermocouple.

By blinking a light bulb, it was made to mimic the solar radiation from the sun. In other words, we repeated the process of turning on the light bulb for 6 hours and turning it off for 18 hours, and measured it over a long period of time.
It was always kept at a higher temperature than the saline thermos. In addition, when comparing the highest temperature immediately after turning on for 6 hours and the lowest temperature just before turning on 18 hours after turning off the light, the water gel thermos bottle is better.
Always stayed at a higher temperature for a longer time than a thermos of saline solution. The lowest temperature after 82 hours, which was about 4 days, was 5.0°C higher for the hydrogel, and the highest temperature after 92 hours was 8.2°C higher for the hydrogel.

Claims (1)

[Scope of Claims] 1. A solution obtained by neutralizing an aqueous solution of an inorganic salt capable of forming a gel-like substance upon neutralization, or an aqueous solution of the inorganic salt to which a coloring agent has been added, with an acid, a salt, or an ion exchange resin. A heat storage material for solar ponds made of water-enclosed gel-like material. 2. The heat storage material according to claim 1, wherein the inorganic salt capable of forming a gel-like substance upon neutralization is at least one selected from silicates of alkali metals or alkaline earth metals. 3 The acid used for neutralization is hydrochloric acid, sulfuric acid, nitric acid, acetic acid,
The heat storage material according to claim 1, which is at least one selected from succinic acid, citric acid, and fumaric acid. 4. The salt used for neutralization is at least one selected from magnesium, calcium, manganese, aluminum, copper, iron, nickel chlorides, or metal salts of nitric acid, sulfuric acid, acetic acid, succinic acid, citric acid, and fumaric acid. The heat storage material according to claim 1, which is a seed. 5. The heat storage material according to claim 1, wherein the ion exchange resin used for neutralization is at least one selected from weakly acidic cation exchange resins and strongly acidic cation exchange resins. 6. The heat storage material according to claim 1, wherein the colorant is ink or at least one selected from sulfur black, diamond black, and naphthol brown black dyes.