JPS6340457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a solar pond using hydrogel as a new heat storage material.

A solar pond is a pond that can absorb and store sunlight in the form of heat.

The heat collection and storage feature of conventional solar ponds is to suppress heat radiation by forming a non-convection layer that prevents convection. Heat radiation can be suppressed by creating a salt concentration gradient, and by using the density difference caused by this concentration gradient to prevent density differences caused by temperature differences, convection due to buoyancy can be prevented. If convection is prevented, heat radiation is suppressed and long-term heat storage becomes possible.

However, saline water solar ponds have the following drawbacks. To create a concentration gradient, fresh water is forced into the upper layer of a concentrated salt solution to forcibly form a concentration gradient, resulting in a dilute salt solution in the upper layer.Convection occurs in the upper layer and fresh water is constantly flowing. Therefore, maintenance and management costs and effort are required. This salt water pond requires a considerable number of days to form a salt water gradient and several months to start storing heat. In addition, even a small amount of water leakage results in highly concentrated salt water, so it cannot be used in areas where salt damage is fatal, such as when hatching or cultivating fish. Furthermore, since convection cannot be prevented unless the concentration of salt water is 20% or more, a large amount of salt is required, which is economically disadvantageous.
Some salts, such as sodium borate, have the disadvantage that if used for a long period of time, the salt will settle and the bottom will turn white. Also, the amount of heat stored is expressed as the product of specific heat, temperature, and mass, but the specific heat of water is the largest, and since salts are relatively small, the amount of heat stored in water alone is the largest, and decreases as the concentration of salts increases. do. The calorific value of a salt solar pond determined by the density gradient method is a concentrated salt aqueous solution, so compared to a low concentration salt aqueous solution, a low concentration salt aqueous solution is larger at the same temperature and mass. Therefore, concentrated salt water solar ponds can be said to be an inefficient method. Furthermore, if algae, mud, or sand is mixed in, there are drawbacks such as the large amount of concentrated salt water that causes salt damage and cannot be dumped. Lastly, I will write about the most important issue, heat collection. Conventional heat collection has used a concentration gradient method in which fresh water exists in the upper layer and the concentration of salt gradually increases with depth, but sunlight is in the visible light range of 300 nm to 800 nm. Although transparent fresh water and salt water absorb almost no light, they have been used in a state where no light is absorbed. In addition, commercially available pigments and dyes are not light-resistant to sunlight and easily fade, so they cannot be used in cases where they are exposed to sunlight for a long period of time, such as in solar ponds. Therefore, salt water solar ponds have traditionally been used without being colored and with poor heat collection efficiency.

The present invention takes into consideration the above-mentioned drawbacks, and as a result of intensive research into a heat storage material for solar ponds that can collect and store a large amount of heat, the present invention uses a completely non-fading material in a gel-like material as a completely new heat storage material for solar ponds. The inventors have discovered that the object can be achieved by doing so, and based on this knowledge, the present invention has been achieved.

In the present invention, an aqueous solution of iron hydroxide sol dissolved in silicate is neutralized with acid and ion exchange resin to produce a colored gel-like substance, which is used as a heat storage material for solar ponds, and is used for heat collection and storage. The present invention provides a heat storage material whose efficiency is greatly improved over conventional salt water solar ponds.

The heat storage material of the present invention will be described in more detail. First, the silicates, sodium silicate, potassium silicate, and lithium silicate, can be used in the form of powder or concentrated solution (candy-like). For iron hydroxide sol, an iron hydroxide sol aqueous solution is prepared by adding an iron chloride solution to boiling water, and this solution is added to a silicate aqueous solution. Acids that can be used as neutralizing agents include inorganic acids such as hydrochloric acid, sulfuric acid, and nitric acid, as well as acetic acid, succinic acid, citric acid,
such as fumaric acid. The ion exchange resin used as the neutralizing agent may be any weakly acidic or strongly acidic cation exchange resin.

The reaction conditions for gel production and the optimal conditions for use as a heat storage material are as follows: After dissolving the silicate, the gel is produced by adding an aqueous iron hydroxide sol solution, and then neutralizing it by adding acid or ion exchange resin. , a colored hydrogel containing a large amount of water and containing iron hydroxide sol is produced. Economically, it is desirable to have a concentration of silicate that provides a quick gelation time and does not cause fluidity at low concentrations. The optimal silicate concentration commonly used is 0.1% to 10%.

It is better to color the encapsulated water gel so that it absorbs light more easily, but this problem was solved by using iron ions, which have extremely low fading properties. An iron hydroxide sol aqueous solution can be created by dropping a ferric chloride aqueous solution into boiling water and slowly cooling it.
This solution exhibits acidity and can also be used as a neutralizing agent for silicate, thereby saving the amount of neutralizing acid and ion exchange resin. The concentration of ferric chloride dropped into boiling water can be any concentration below the concentration of a saturated solution. The optimum amount of ferric chloride to be dropped into the boiling water is 0.01% to 9% based on the weight of the boiling water.

Although the concentration and amount of neutralizing conditions vary depending on the type of acid and ion exchange resin, the normal neutralizing condition is a hydrogen ion concentration of 6 to 8. The so-called gelation time, when the solution becomes gel-like, is determined by the hydrogen ion concentration; for example, at 20℃
When a solution containing 2% sodium silicate and 2% iron hydroxide sol was neutralized with 50% sulfuric acid to a hydrogen ion concentration of 7.5, gelation started in 1 hour and the temperature increased from 2 to 2.
Complete in 3 hours. The acid and ion exchange resin used for gelation can be selected according to the required gelation rate, and a large amount of colored hydrogel can be easily produced.

The colored hydrogel produced by the above method is economically inexpensive because it is produced from low concentrations of silicate and iron hydroxide and can be used as a heat storage material.

Since the colored hydrogel is neutral, it is completely harmless even if water leaks from the pond. Because the colored hydrogel holds a large amount of water, it can prevent water convection, thereby suppressing heat radiation and effectively storing heat. In addition, the specific heat, which is a measure of calorific value, is almost the same as the specific heat of water because it is a dilute solution containing a small amount of silicate and iron hydroxide. Because it is used for water, its specific heat is small, and if the same temperature and mass are used, the colored encapsulated water gel pond will accumulate a much larger amount of heat. The above points are the most advantageous features of the present invention.

Next, the present invention will be explained in detail by examples.
The present invention is not limited to the following examples unless it exceeds the gist thereof.

Example 1 After dissolving 25 g of powdered sodium silicate in 500 ml of water, 50 ml of 40% ferric chloride solution was added to 300 ml of boiling water to create iron hydroxide sol, and then added to the silicic acid solution. Added with stirring. A solution of 5.0g of sulfuric acid dissolved in 20ml of water was added to the silicate.
It was added dropwise to the iron hydroxide sol solution while stirring, and neutralized to a hydrogen ion concentration of 7.5. After neutralization, water was added to bring the volume to 1. When I poured 750ml of the solution into the thermos flask (inner diameter 90mm, depth 230mm), the solution started to gel after about an hour, so after 3 hours I gently poured 250ml of water to separate the gel phase and aqueous phase. de1
And so. On the other hand, pour 750ml of 25% sodium chloride into the same thermos flask, and then gently pour in 250ml of water.
And so.

Place two thermos bottles directly under the 500W tungsten light bulb.
I installed them side by side. The distance between the bulb and the thermos was 300 mm from the opening of the thermos to the bulb glass surface, and the amount of light measured by the pyranometer was 0.804 cal cm ^-2 min ^-1 .
The temperature was measured using a thermocouple placed 190 mm from the opening of each thermos flask and a recorder. Light irradiation was achieved by repeatedly turning on a light bulb for 6 hours and then turning it off for 18 hours to make it almost the same as the solar radiation. When we measured this blinking process over a long period of time, we found that when we compared the temperature rise of the hydrogel and the salt, the hydrogel always maintained a higher temperature than the salt. That is, when comparing the highest temperature immediately after 6 hours of lighting and the lowest temperature immediately after 18 hours had passed after the lights were turned off, the water encapsulation gel had a higher temperature than the salt. The minimum temperature after 82 hours, which is about 4 days, was 5.2°C higher for the hydrogel, and the maximum temperature after 92 hours was 8.5°C higher for the hydrogel.

Claims (1)

[Scope of Claims] 1. A solar pond characterized by using a composite hydrogel which is a reaction product obtained by neutralizing an aqueous solution of silicates and iron hydroxide with an acid. 2. Claim 1 states that one or more of alkali salts and alkaline earth salts such as sodium silicate, potassium silicate, and lithium silicate are used as the silicates from which the hydrogel is produced. The capsule water gel solar pond. 3. The hydrogel solar pond according to claim 1, wherein the iron hydroxide present in the hydrogel is an iron hydroxide sol. 4. The acid used as a neutralizing agent for the mixed solution of silicate and iron hydroxide sol that produces the hydrogel is hydrochloric acid, sulfuric acid, nitric acid, or one of organic acids such as acetic acid, succinic acid, citric acid, fumaric acid, etc. The water-encased gel solar pond according to claim 1, in which two or more types are used. 5. A patent claim in which one or more of weakly acidic and strongly acidic cation exchange resins are used as the ion exchange resin as a neutralizing agent for a mixed solution of silicate and iron hydroxide sol that produces a hydrogel. The hydrogel solar pond according to item 1 in the scope of .