JPH0212270B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid composition useful as a heat absorber for solar water heaters and heat collectors. The object of the present invention is to provide a liquid for absorbing solar heat that can be stably used.

It is conventionally known to expose a black liquid to the sun's rays to absorb solar heat, and then use heat exchange to raise the temperature of ordinary tap water for use in domestic or industrial applications. As such liquid heat absorbers, black dyes dissolved in water or black pigments dispersed in water are used, but those using dyes are resistant to long-term light exposure. It is not practical due to poor stability. On the other hand, products using black pigments such as carbon black have excellent stability against light, but for long-term use, for example, carbon black dispersed in water with a dispersant may be used in water heaters and heat collectors. When tap water is poured into a pipe to absorb solar heat and then heated by a heat exchanger, the dispersed carbon black deposits on the inner surface of the pipe, reducing the heat absorption rate, etc. Dispersion stability deteriorates due to repeated temperature changes and the influence of sunlight, resulting in precipitation of carbon black, which has the disadvantage of losing its performance as a heat absorber.

As a result of intensive research to solve the drawbacks of conventional heat-absorbing liquids as described above, the present inventors selected a specific material as a heat-absorbing black material, and used a specific dispersant and dispersion medium in combination. The present invention was completed based on the finding that by doing so, a heat-absorbing liquid that solved the drawbacks of the above-mentioned prior art could be obtained.

That is, the present invention provides a solar heat absorbing liquid comprising a dispersion medium, a dispersant, and a black material,
The dispersion medium is a mixture of glycerin and water or a mixture of glycerin, propylene glycol and water, and the dispersant is polyvinylpyrrolidone and/or
Alternatively, it is a liquid for absorbing solar heat, which is caramel, and the black material is powdered activated carbon.

Next, to explain the present invention in more detail, the proportion of the components constituting the liquid composition of the present invention is about 0.001 to 10 parts by weight of powdered activated carbon, preferably about 0.01 parts by weight, based on 100 parts by weight of the liquid composition. -2 parts by weight, and if the amount is below the lower limit of this range, absorption of solar heat will be insufficient, while if it exceeds the upper limit, solar rays will not reach the interior of the liquid and heat absorption will be insufficient. The dispersant is used in an amount of about 0.001 to 30 parts by weight, preferably about 0.5 to 10 parts by weight, and if the amount is below the lower limit of this range, the dispersion stability of the activated carbon powder will decrease. On the other hand, if the upper limit is exceeded, the viscosity becomes too high and the efficiency of heat exchange decreases. The dispersion medium is mainly powdered activated carbon and the remaining parts by weight of the dispersant, and is used in an amount of about 70 parts by weight or more, preferably about 93 parts by weight or more. Below the lower limit of this range, the viscosity and concentration of the resulting endothermic liquid will become too high, resulting in reduced heat exchange efficiency and insufficient heat absorption rate, as described above.

The activated carbon used in the present invention is obtained by carbonizing organic substances, and has conventionally been used for decolorization, deodorization, adsorption, catalysts, etc., and it can also be used as a coloring agent or filler. Carbon black differs in its particle structure. Such activated carbon may be produced by any method such as the zinc chloride method or the steam method, but its particle size must be about 10 μm or less, preferably about 5 μm or less. Such powdered activated carbon can be easily obtained by pulverizing commercially available powdered activated carbon or powdered activated carbon using a normal pulverizer, or by grinding it at the same time as dispersion and adjusting the particle size. be able to.

The dispersant used in the present invention is polyvinylpyrrolidone or caramel or a mixture thereof. Regarding polyvinylpyrrolidone, various types having an average molecular weight of about 5,000 to about 500,000 are known, and any of these known polyvinylpyrrolidones can be used in the present invention. Such polyvinylpyrrolidone has been well known as a dispersant (protective colloid) for pigments, etc., but it can be used to stably disperse activated carbon powder in a mixture of glycerin and water or a mixture of glycerin, propylene glycol, and water. It is not known as a dispersant that can cause According to detailed research by the present inventors, when the above-mentioned dispersion medium contains a relatively small amount of water, polyvinylpyrrolidone with a relatively low molecular weight shows excellent dispersion stability; It has been found that polyvinylpyrrolidone, which has a relatively high molecular weight, exhibits excellent dispersion stability when it contains a relatively large amount of water.

Caramel, which is used in place of the above polyvinylpyrrolidone or mixed in any proportion, is a substance obtained by heat-treating sugars such as glucose and sugar. It is also called scorched sugar, and has traditionally been widely used as a natural coloring agent. For example, powder caramel made from glucose, liquid caramel made from glucose, liquid caramel made from sugar, powdered caramel, special liquid caramel, solid caramel, etc. are manufactured by Senba Toka Kogyo.
It is widely commercially available from companies such as Co., Ltd. As a result of extensive research into dispersants for uniformly and stably dispersing powdered activated carbon in the medium described below, the present inventor found that
It has been discovered that such caramel is optimal together with the above-mentioned polyvinylpyrrolidone.

As mentioned above, the dispersion medium used in the present invention is a mixture of glycerin and water or a mixture of glycerin, propylene glycol, and water, and in such a dispersion medium, the powdered activated carbon becomes uniform and stable due to the dispersant. This is the result of the discovery that it can be dispersed into Glycerin and/or propylene glycol serve as a dispersion medium as well as a dispersion aid and antifreeze agent for winter use; these vehicles contain at least about 15% by weight of glycerin, or glycerin and propylene. There should be a mixture with glycols. When the amount of glycerin or a mixture of glycerin and propylene glycol is less than about 15%, the dispersion stability of the powdered activated carbon decreases and the freezing point of the medium increases, which may cause freezing problems in winter.

The essential components of the endothermic liquid of the present invention are as described above, and in addition, various water-soluble polymer emulsifiers,
Various additives such as stabilizers, preservatives, and rust preventives can be added as necessary.

The endothermic liquid of the present invention blends the above-mentioned components,
This can be easily prepared by dispersing it using a conventional dispersing machine such as a ball mill, homomixer, attritor, sand mill, colloid mill, roll, or the like. The heat-absorbing liquid of the present invention thus obtained is a uniform black liquid and is useful as a heat-absorbing liquid for solar water heaters and heat collectors. In other words, in such applications, the temperature is raised and lowered countless times over a long period of time, and is constantly exposed to sunlight (during the day). Good dispersion stability can be maintained for a long period of time. Furthermore, when conventional carbon black is used, the carbon black tends to deposit on the inner surfaces of circulation equipment such as pipes of water heaters and heat collectors, significantly reducing heat absorption and heat exchange performance. On the other hand, the endothermic liquid of the present invention hardly exhibits this tendency. Such performance was completely unexpected in view of the original physical properties of activated carbon. Furthermore, since the heat-absorbing liquid of the present invention does not contain ionic components, it does not corrode metal parts of water heaters and heat collectors.

Next, the present invention will be explained in more detail with reference to Examples. Note that parts and percentages in the text are based on weight.

Example 1 Activated carbon (manufactured by Nimura Chemical Industry Co., Ltd., trade name Taiko K) 5
1 part, 5 parts of polyvinylpyrrolidone (manufactured by BASF, trade name: Kollidon 30), 20 parts of glycerin, and 70 parts of water were mixed and dispersed in a sand mill to prepare a dispersion in which the particle size of activated carbon was 5 μm or less.

One part of this dispersion, 58 parts of water, 40 parts of glycerin, and 1 part of polyvinylpyrrolidone (manufactured by BASF, trade name: Kollidon 90) were uniformly mixed and stirred to obtain an endothermic liquid of the present invention having a freezing point of -16°C. This liquid at 80℃
After continuous heat treatment for several months, the dispersibility of the activated carbon was examined using a microscope, and it was found that the dispersibility of the activated carbon was as good as before heating.

Example 2 Activated carbon (manufactured by Nimura Chemical Industry Co., Ltd., trade name Taiko M) 5
1 part, 5 parts of glucose powder caramel (manufactured by Senba Toka Kogyo Co., Ltd., trade name S-W), 30 parts of glycerin, 20 parts of propylene glycol, and 40 parts of water, and dispersed in a ball mill until the particle size of activated carbon became 5μ or less. Then, a dispersion was prepared.

1 part of this dispersion, 50 parts of glycerin, 10 parts of propylene glycol, 4 parts of the above glucose powder caramel
1 part and 35 parts of water were mixed and stirred to obtain an endothermic liquid. Even when this endothermic liquid was forced to circulate in a glass tube at 80°C for 6 months, its dispersion stability was excellent. Further, no deposit of activated carbon was observed on the inner wall of the glass tube.

Example 3 1 part of the dispersion of Example 1, 1 part of polyvinylpyrrolidone (manufactured by BASF, trade name Kollidon 90), 20 parts of glycerin, 30 parts of propylene glycol, and 48 parts of water.
The components were mixed uniformly to obtain an endothermic liquid with a freezing point of -20°C. This endothermic liquid was put into a flexible tube with an inner diameter of 5 mm, both ends of which were sealed with rubber stoppers, and the mixture was irradiated for 1000 hours in a fade meter at a temperature of 63℃.The dispersibility of activated carbon was examined using a microscope. The properties were as good as the properties, and there was no precipitation of activated carbon on the inner wall of the glass tube.

Example 4 1 part of the dispersion of Example 1, 3 parts of polyvinylpyrrolidone (manufactured by BASF, trade name Kollidon 30), powdered glucose caramel (manufactured by Senba Toka Kogyo Co., Ltd., trade name S)
-W) 2 parts 60 parts of glycerin, 0.1 part of sodium hexametaphosphate, 0.1 part of disodium phosphate and 33.8 parts of water were uniformly mixed and stirred to obtain an endothermic liquid with a freezing point of -35°C. After continuously heating this liquid at 80° C. for 6 months, the dispersibility of the activated carbon was examined using a microscope, and it was found that the dispersibility of the activated carbon was as good as before heating.

Example 5 The same procedure as in Example 1 was performed except that the same amount of glucose powder caramel (manufactured by Senba Toka Kogyo Co., Ltd., trade name S-W) was used in place of polyvinylpyrrolidone in Example 1, and the same results were obtained. The results were obtained.

Example 6 The endothermic liquids of Examples 1 to 5 were placed in a solar water heater and subjected to an exposure test for 6 months while being forced to circulate.The endothermic liquids were then diluted 25 times with water and tested using a spectrophotometer (Hitachi, Ltd.). As shown in the drawing, the transmittance was measured using a liquid (Model 25) before exposure.
The transmittance curve almost matched the transmittance curve of the liquid (diluted twice), and there was no agglomeration of activated carbon even after exposure, and the liquid remained stable.

Comparative Example 1 Except that 5 parts of soybean lecithin was used as a dispersant instead of 5 parts of polyvinylpyrrolidone in Example 1,
A dispersion was prepared in the same manner as in Example 1, and 1 part of this dispersion, 58 parts of water, 40 parts of glycerin, and 1 part of soybean lecithin were uniformly mixed and stirred to obtain an endothermic liquid with a freezing point of -16°C. .

As a result of continuous heat treatment of this liquid at 80°C, the activated carbon coagulated and precipitated over 3 days.

Comparative Example 2 A dispersion was prepared in the same manner as in Example 2, except that 5 parts of sucrose fatty acid ester was used as a dispersant instead of 5 parts of the glucose powder caramel in Example 2, and 1 part of this dispersion, 50 parts of glycerin, 10 parts of propylene glycol, 4 parts of fatty acid ester of sucrose, and 35 parts of water were mixed and stirred to obtain an endothermic liquid.

As a result of continuous heat treatment of this liquid at 80°C, the activated carbon coagulated and settled in 3 days.

[Brief explanation of drawings]

The figure is a diagram showing the light transmittance of an endothermic liquid before and after exposure.

Claims (1)

[Claims] 1 In a solar heat absorbing liquid consisting of a dispersing medium, a dispersing agent, and a black material, the dispersing medium is a mixture of glycerin and water, or a mixture of glycerin, propylene glycol, and water, and the dispersing agent is polyvinylpyrrolidone and/or caramel. A liquid for absorbing solar heat, characterized in that the black material is powdered activated carbon.