JPS6251991B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a heat storage material that utilizes latent heat accompanying phase transformation of sodium sulfate 10 hydrate or its eutectic. The need for heat storage is increasing from the standpoint of heating and cooling by utilizing solar heat or waste heat, and reducing the load on air conditioners for the purpose of alleviating power peaks. A heat storage method that utilizes the latent heat of a substance has the advantage of having a relatively high heat storage density and being able to transfer a large amount of heat in and out with a small temperature difference. On the other hand, heat storage materials are required to be inexpensive, available in large quantities, non-toxic, non-flammable and non-corrosive. Materials that meet these objectives include sodium sulfate decahydrate and its eutectic. Sodium sulfate decahydrate has a melting point of 32℃ and 60Cal/g.
It has a latent heat of The melting point of sodium sulfate decahydrate can be changed by making a eutectic; for example, in a eutectic mixture of 1 mole of sodium sulfate decahydrate and 1 mole of potassium chloride, the melting point can be changed to about 4°C. It can be lowered. Generally, there are two problems when using a hydrate as a heat storage material. One of these is the so-called supercooling phenomenon in which the material does not solidify even if the temperature drops below the freezing point during cooling. In the case of sodium sulfate decahydrate and its eutectic, US Pat. No. 2,667,664 discloses that the problem can be solved by adding sodium tetraborate decahydrate (borax) as a nucleating material. . Another problem is that sodium sulfate decahydrate and its eutectic exhibit anharmonic melting. That is, when it is melted at the melting point, the solubility of sodium sulfate anhydride is low, so it does not completely dissolve in crystal water, and a portion remains in the solution, and because of its high density, it precipitates. When such a mixture is cooled and solidified in a static state, the dissolved sodium sulfate or its eutectic forms a decahydrate and returns to the state before melting, but only the surface of the precipitated anhydrous sodium sulfate remains. Ten
It becomes aqueous salt, and some remains as anhydrous sodium sulfate. Therefore, when such a system is subjected to repeated cycles of heat storage and heat release of melting and solidification, the amount of heat storage decreases because the remaining anhydrous sodium sulfate does not participate in phase transformation. As a solution to this problem, a method has been proposed that prevents precipitation of anhydrous sodium sulfate and uniformly disperses and maintains it in a solution.
Specifically, the solution is mixed with an organic polymer compound such as sawdust, wood bulb, methylcellulose, starch, organic alginate, ionic bond crosslinked product of polyacrylic acid with polyvalent metal ions (Japanese Patent Application Laid-open No. 16387/1987), Attempts have also been made to thicken the solution into a so-called gel state by using inorganic thickeners such as silica gel, diatomaceous earth, finely powdered silica, and attapulgide clay (US Pat. No. 3,986,969). However, even when precipitation of anhydrous sodium sulfate is prevented by such a method, crystal particles of anhydrous sodium sulfate grow due to repeated cycles of melting and solidification, and only the surface of the particles forms hydrates during solidification. The center of the particle will remain anhydrous. As a result, even in a system in which precipitation of anhydride due to gelation is prevented, the amount of heat storage decreases with each cycle. The present inventors have previously developed a heat storage material using sodium sulfate decahydrate and its eutectic by adding at least one of sodium oleate, potassium oleate, and lithium oleate to repeat the cycle of melting and solidification. It has already been proposed that the deterioration of heat storage properties due to The present invention was made with the aim of further improving the above-mentioned heat storage material and reducing the deterioration of heat storage properties due to repeated melting and solidification. In heat storage materials using a copolymer of an olefinic carboxylic acid having an active carbon-carbon double bond as a thickening agent and a polyalkenyl polyether of a polyhydric alcohol, lithium oleate and sodium oleate are used as a thickening agent. The effect of the addition of potassium oleate, etc. on properties is particularly remarkable, and compared to when added to heat storage materials using thickeners such as fumed silica and carboxymethyl cellulose, the properties can be improved with the addition of low concentrations. We have discovered that it is possible. The effect of improving the properties of the heat storage material according to the present invention was also confirmed in the heat storage material whose main component is sodium sulfate decahydrate; however, the following examples were carried out using a eutectic product of sodium sulfate decahydrate as an example. The effect will be explained using an example. <Example> Na ₂ SO ₄ 33 parts by weight H ₂ O 42 〃 NaCl 6.8 〃 NH ₄ Cl 6.2 〃 Borax 3 〃 Hibiswako 104 (trade name) 2 〃 NaOH 0.8 〃 To the mixture of raw materials in the above ratio, Sodium oleate 0, 0.01, 0.05, respectively
Samples were prepared in which 0.80 and 0.1% by weight were added. Hibiswako used here as a thickening agent
104 is manufactured by Wako Pure Chemical Industries, Ltd. and is a copolymer of acrylic acid and polyalkenyl polyether containing polyalkylene glycol as the polyhydric alcohol. These samples were repeatedly heated and cooled at 40°C and -30°C, and their heat storage properties were measured. The change in heat storage amount of each sample before and after the cycle was as shown in the table below.

[Table] In the sample to which sodium oleate was not added, the initial heat storage amount was 42.3 cal/g, but after 60 cycles, the heat storage amount decreased by 6%.
In the sample containing 0.01% by weight, the decrease in heat storage remained at 1.8% even after 60 cycles. On the other hand, in the sample containing 0.1% by weight of sodium oleate, the initial amount of heat storage is small, and the amount of heat storage after 60 cycles is also smaller than that of the sample without additives. Therefore, the preferred addition amount is in the range of 0.01% by weight or more and 0.08% by weight. Similar results were also obtained when similar experiments were conducted using potassium oleate and lithium oleate instead of sodium oleate. In addition, when using ``Carbopol'' manufactured by Gutudoritsu in the United States, which uses polyalkenyl polyether made from sucrose, which is one of the oligosaccharides, as the polyhydric alcohol for the thickening agent, the results are different from when using Hivis Wako. Got the same good results. That is, the thickening agent for the heat storage material of the present invention may be a copolymer of an olefinic carboxylic acid having an active carbon-carbon double bond and a polykenyl polyether of a polyhydric alcohol. The oleic acid to be added preferably contains at least 0.01% by weight of at least one of lithium oleate, sodium oleate, and potassium oleate. As described above, a copolymer of a polyalkenyl polyether of an olefinic carboxylic acid and a polyhydric alcohol, which has sodium sulfate decahydrate or its eutectic as a main component and has an active carbon-carbon double bond as a thickening agent. The heat storage material contains at least 0.01% by weight, preferably 0.01% by weight of at least one of lithium oleate, sodium oleate, and potassium oleate.
Addition in a range of 0.08% by weight or less has a remarkable effect on improving the deterioration of heat storage characteristics.

Claims (1)

[Scope of Claims] 1. A polyalkenyl polyether of an olefinic carboxylic acid having an active carbon-carbon double bond and a polyhydric alcohol, the main component being sodium sulfate decahydrate or its eutectic. A heat storage material comprising a copolymer and further comprising at least one of lithium oleate, sodium oleate, and potassium oleate. 2. The heat storage material according to claim 1, which contains at least one of lithium oleate, sodium oleate, and potassium oleate in a range of 0.01% by weight or more and 0.08% by weight or less. 3. The heat storage material according to claim 1 or 2, wherein the thickening agent is a copolymer of acrylic acid and polyalkel polyether of polyhydric alcohol. 4. The heat storage material according to claim 1 or 2, wherein the polyhydric alcohol is an oligosaccharide. 5. The heat storage material according to claim 1 or 2, wherein the polyhydric alcohol is sucrose. 6. The heat storage material according to claim 1 or 2, wherein the polyhydric alcohol is polyalkylene glycol.