KR940005189B1 - Heat sink material for using carboxymethyl celluolose - Google Patents

Abstract

This is a new latent heat storage material using carboxymethyl cellulose which inhibits phase separation phenomenon and super cooling. The latent heat storage material is manufactured by forming a network structured gel by mixing carboxymethyl cellulose and inorganic hydrate in the presence or nonpresence of nucleation agent such as potassium sulfate. The above hydrate is one of acetates. Carboxymethyl cellulose has so good enhancing property of viscosity that it prevents the heat storage material from phase separation.

Description

Latent Heat Storage Materials Using Carboxymethyl Cellulose

The present invention relates to a latent heat storage material used for energy storage, and more specifically, to prevent phase separation by using carboxymethyl cellulose (carboxymethyl celluolose), as well as providing an accompanying heat storage material that can suppress the supercooling phenomenon. It is about.

If there is a time or quantity discrepancy in supply-demand between the supply and use of energy, much energy is wasted inefficiently. To prevent this, the excess energy is temporarily stored, and when the energy supply is insufficient, the stored energy can be recovered and used to use the energy more efficiently.

There are several methods for storing energy, and the most widely used method is a thermal storage method in which energy is stored in the form of heat and then recovered and used in the form of heat, and the heat storage method is a heat capacity of a heat storage medium. It is divided into sensible heat storage method using the latent heat storage method using the latent heat accompanying the phase change of the storage medium. The latent heat storage method has been studied a lot because the energy storage capacity per unit volume and unit weight is larger than the sensible heat storage method, and has developed and used a latent heat storage material in which a phase change occurs in the temperature range depending on the required temperature range.

Hydrates such as magnesium chloride, calcium chloride, sodium sulfate, sodium phosphate, and acetate are mainly used as the low temperature latent heat storage agent having a phase change below 100 ° C, and phase separation and supercooling are important issues for the use of the hydrate.

The phase separation phenomenon refers to a phenomenon in which the anhydrous salt separates and precipitates as the latent heat material repeatedly melts and solidifies. An important cause of the phase separation is that the heat storage material has an unharmonized melting point. Materials with unharmonized melting points do not dissolve all anhydrous salts in the crystallized water at the melting point, and undissolved anhydrous salts settle down due to their high density, and as the melting and solidification is repeated, the amount of precipitation increases and eventually the heat storage capacity decreases. do. In order to prevent the phase separation phenomenon, a material having a harmonic melting point at which the melting point anhydrous salt is dissolved in all of the crystallized water can be selected and used.However, there are not many hydrates having a harmonic melting point. There is almost no heat storage material that satisfies the requirements of the latent heat storage material.

Therefore, if the phase change in the required temperature range and the latent heat amount is large, even a material having an unharmonized melting point should be used as a latent heat material by a method of preventing phase separation.

Methods for solving the phase separation problem include a method using a phase balance, physical stirring, a method of adding a thickener to the heat storage material, and a method of micro-encapsulation of the heat storage material. The most widely used of these, a convenient method is to use a thickener to prevent phase separation.

As an example, SB Marks's paper, An Investigation of the Thermal Energy Storage Capacity of Glauber's Salt with respect to Thermal Cycling, Soalt Energe, 25 (3), 255-258 (1980), describes atapol for phase separation. The use of jitter clay as a thickener has been described, which is difficult to use as the material continues to decrease with repeated cycles. US Pat. No. 4,423,85 has been proposed to reduce the moisture of peat moss to 10% and to use it as a thickener with a particle size of 1-3 mm. US Pat. No. 4,494,313 is used for acrylic or carboxyl water-soluble polymers. It is proposed to use an insoluble hydrogel obtained by reacting a polyvalent metal of magnesium or aluminum as a thickener, but there is a disadvantage in that the amount of the polymer to be added is large and a polyvalent metal should be used. Max's research paper, The Effect of Crystal Size on the Thermal Enerhy Capacity of Thickened Glauber's Salt, Solar Energy, 38 (1), 45-49 (1980), describes acrylamide and acrylic acid, which reduce the crystal size of heat storage materials. It is proposed to use polycarboxylic acid as a thickener with the copolymer of but it does not completely prevent phase separation.

In addition, starch, sawdust, etc. may be used as a thickener, but preservatives should be added to suppress the growth of bacteria and the like. Korean Patent No. 5551 proposes a method for solving the phase separation problem of inorganic hydrates using a super absorbent polymer. According to this method, the superabsorbent polymer is very effective in the case of inorganic crystal salts having a high crystal content such as forget-me-not, phosphate, etc. In small cases, it does not effectively thicken. Most of the inorganic hydrates with high crystal counts have low melting point and thus have low energy quality.

However, inorganic hydrochlorides having a small number of crystals have a higher melting point compared to hydrates having a large number of crystals, that is, a relatively high temperature in the low temperature latent heat storage material, so that heat can be stored and recovered at a higher temperature. And the quality of energy is excellent. Therefore, the prevention of phase separation of inorganic salts with small number of crystals is very important in terms of energy utilization.

The supercooling phenomenon is a phenomenon in which no phase change occurs and no latent heat is released even when the temperature is lowered below the melting point, which is an obstacle to efficiently recovering and using the stored heat. The method mainly used to prevent the supercooling phenomenon is to use a nucleating agent. The nucleating agent is a substance having a similar atom size compared to that of the latent heat material. When the nucleus is used as the nucleus, the crystallization of the latent heat material is promoted, thereby suppressing the supercooling phenomenon.

However, since the nucleating agent is more dense than the melt of the latent heat material and can be precipitated, it is effective to use it with a thickener.

In addition to the above problems, most commercialized latent heat storage systems are encapsulating the heat storage material. It is very difficult to encapsulate latent heat accumulators, which have been thickened by thickeners, that is, whose viscosity has risen sharply, during the manufacturing process of the capsule. Therefore, it is necessary to adjust the appropriate viscosity to facilitate encapsulation without inhibiting the phase separation prevention function of the thickener.

It is an object of the present invention to provide a new latent heat storage material in which these problems are solved.

These and other objects of the present invention are achieved by the latent heat storage material of the present invention, which is characterized by mixing with or without carboxymethyl cellulose and a hydrate nucleating agent to form a gel.

In achieving the object of the present invention, carboxymethyl cellulose is a white or milky white powder having a strong absorbency and easily soluble in water, thus exhibiting viscosity, and thus is suitable as a thickener for heat storage material, and the ion of latent heat storage material solution has a uniform network with carboxymethyl. It causes a structural bond and gelates.

Since carboxymethyl cellulose is added to the hydrate completely dissolved above the melting point to form a homogeneous network to form a gel, even if the solidification of the hydrate having a non-harmonic melting point is repeated, the anhydrous salt that is not dissolved does not precipitate, thereby causing phase separation. It can be prevented completely.

In particular, while the superabsorbent polymer has no effect on the thickening of inorganic hydrate salts having low hydrates, carboxymethyl cellulose has an excellent thickening effect even on inorganic hydrate salts having low hydrates, thereby effectively inhibiting phase separation of heat storage materials.

In addition, in the case of using the nucleating agent, even if a large nucleating agent having a specific gravity is dispersed in a stable state in the gel, the nucleating agent may not be separated and precipitated even after repeated melt solidification, thereby effectively suppressing the supercooling phenomenon.

The present invention will be described in more detail with reference to Examples.

Example 1

95 g of sodium acetate trihydrate (CH ₃ COONa.3H ₂ O)) was heated to a melting point or higher, and 3 g of carboxymethyl cellulose was mixed in the resulting melt to form a network gel.

When the carboxymethyl cellulose was added, the mixture was sufficiently stirred to uniformly disperse the anhydride precipitated in the melt in the gel state.

The latent heat storage material produced by the above method did not show phase separation even after repeated 500 times of solidification of melting, and ₂ g of calcium sulfate (K ₂ SO ₄ ) was added as a nucleating agent, and the supercooling was performed at 15-20 ° C. to 2-3 ° C. Suppressed. In addition, when only carboxymethyl cellulose is used as the thickener, the viscosity is too high, making it difficult to encapsulate in a spherical or cylindrical container. However, when 2% by weight of carboxymethyl cellulose is added as a thickener and 1% by weight of horizontal lubricating polymer, the viscosity can be lowered without phase separation of the heat storage material, so that encapsulation is easy. Phase separation and subcooling of acetate in industrial as well as reagents was completely solved by the above method.

Example 2

93 g of sodium thiosulfate pentahydrate (NA ₂ S ₂ O ₃ 5H ₂ O) was heated to a melting point or higher, and then 3 g of carboxymethyl cellulose was mixed to form a network gel in the same manner as in Example 1. The latent heat storage material produced by the above method did not show phase separation even after 500 times of melt solidification. When ₄ g of strontium sulfate (SrSO ₄ ) was added as a nucleating agent, the supercooling of about 20 ° C. was suppressed to within 3-5 ° C. Can be.

Claims (5)

A latent heat storage material comprising carboxymethyl cellulose and an inorganic hydrate, and having a gel-like network structure. The latent heat storage material according to claim 1, further comprising a nucleating agent. The latent heat storage material according to claim 1 or 2, further comprising a super absorbent polymer. The latent heat storage material according to claim 1 or 2, wherein the inorganic hydrate is a hydrate of acetate and the nucleating agent is calcium sulfate. The latent heat storage material according to claim 1 or 2, wherein the inorganic hydrate is a hydrate of thiochloride chloride and the nucleating agent is strontium sulfate.