JPS594677A - Cold accumulating material and its preparation - Google Patents

Abstract

PURPOSE:To provide a cold accumulating material consisting of an aqueous suspension of hydrated crystals of an organic compound having low boiling point and a specific critical decomposition point, and capable of accumulating cold efficiently without lowering the rate of heat transfer in crystallization because of its characteristics of precipitating crystals by cooling itself by its own latent heat of evaporation. CONSTITUTION:An organic compound having a boiling point of <=30 deg.C and capable of forming a hydrate having a critical decomposition point of 5-18 deg.C by reacting with water (preferably Flon 12 or a mixture of Flon 11 and Flon 12) is added to water (e.g. water or an aqueous solution of sodium chloride, sodium sulfate, etc.) in liquid phase, and a part of the organic compound is evaporated from the resultant mixture to cool the mixture by its own heat of evaporation precipitating the hydrated crystal of the organic compound. EFFECT:The material can be prepared at an extremely low cost, and the organic compound can be liquefied after use and recycled for the formation of the hydrate. USE:It is suitable as a cold source of 5-15 deg.C for the air-conditioning in summer season.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low-temperature heat storage material and a method for producing the same, and more specifically, a low-temperature heat storage material that is suitably used with a cold heat source in the range of 5°C to 15°C, and a heat storage material raw material that is used as a refrigerant. This invention relates to a simple manufacturing method for heat storage materials, which is also used for the production of heat storage materials.

Conventionally, ice has been used as a latent heat storage material for cold heat. However, the following drawbacks have been pointed out to ice for use as a low-temperature heat storage material in air conditioning facilities for residences, offices, etc., and it has not yet been put into practical use.

(1) It is not necessary for the cold source in an air conditioning facility to have a temperature below O''CC, and a cold source with a temperature range of 5°C to 15°C is sufficient for cooling in the summer.

(2) In a low-temperature heat storage tank consisting of a group of heat transfer tubes or an ice capsule, when ice crystallizes, there is supercooling and a delay in the generation of crystal nuclei, which results in an increase in the energy required for heat storage. Decrease heat storage efficiency.

(3) Since ice crystals grow from the heat transfer interface, as they grow, convection on the heat transfer surface is obstructed and the heat transfer rate decreases, and as the ice crystals crystallize, the volume expands, so there is no need for extra space. This makes it difficult to design a high-performance heat storage tank.

Therefore, the present invention has been made to solve these drawbacks and develop a low-temperature heat storage material that can replace ice.It is suitable for use in summer cooling applications, and it cools itself using its own latent heat of vaporization to precipitate crystals. Since the heat transfer rate is not hindered during crystallization, it has features such as being able to store cold heat with high performance.

That is, the low-temperature heat storage material of the present invention is characterized by comprising hydrate crystals of an organic compound having a boiling point of 30°C or less suspended in water, provided that the hydrate crystal has a critical decomposition point of 5°C.
~18°C. In addition, in the method for producing such a low-temperature heat storage material, an organic compound having a boiling point of 30°C or less and capable of reacting with water to form a hydrate with a critical decomposition point of 5°C to 18°C is prepared in a liquid state in water. A part of the organic compound is evaporated from the resulting mixture, and the mixture is cooled by the heat of evaporation to precipitate hydrate crystals of the organic compound.

The low-temperature heat storage material of the present invention is one in which hydrate crystals of an organic compound capable of forming a hydrate are suspended in water. Here, organic compounds usually include methane halides and propane, and are so-called low-boiling compounds whose boiling point is 30°C or less, and whose hydrate crystals have a critical decomposition point of 5°C to 18°C. °C.

Table 1 below shows examples of typical low boiling point compounds and the properties of their hydrates.

(Margins below this page) As is clear from Table 1, the precipitation temperatures (critical decomposition point temperatures) of hydrate crystals of these organic compounds are all higher than the freezing point of 0°C, which is the precipitation temperature of ice. temperature, i.e. in the temperature range from 5°C to 18°C, and the heat of formation of these hydrates is 70 to 90 CaI/, and the heat of crystallization of ice B □ K (Jl!/, It is about the same level.

Even if an organic compound has the ability to form a hydrate, if the boiling point of the organic compound exceeds 30°C or the critical decomposition point of the hydrate exceeds 5
If the temperature is outside the range of °C to 18 °C, the pressure inside the heat storage tank will be low, requiring expensive equipment for the compressor to condense and liquefy the compounds evaporated in the tank, and also requiring expensive equipment for cooling. The appropriate cold source temperature is between 5°C and 15°C, and in order to use the hydrate suspension as a cold source for air conditioning,
The cooling effect is low at heat storage temperatures of 8°C or higher, and
Below this, the power of the freezing tank increases, which is not preferable.

The water in which the hydrate crystals are suspended may be an aqueous solution of water-soluble inorganic salts or organic compounds, such as common salt, sodium sulfate, alcohol, etc. These aqueous solutions are used to lower the pressure and temperature at the decomposition point, and these aqueous solutions are preferably used for compounds that exhibit a high critical decomposition point.

The low-temperature heat storage material of the present invention is produced by using a low-boiling organic compound itself as a refrigerant. That is, a low boiling point organic compound capable of reacting with water to form a hydrate, as described above, is mixed in liquid form into water or water containing an inorganic salt or an organic compound as described above. and,
While a portion of this organic compound is evaporated, the remaining organic compound is reacted with water to form a hydrate of the organic compound. Then, the reaction system is cooled by the heat of evaporation due to evaporation of the organic compound, and hydrate crystals precipitate and become suspended in water, yielding a low-temperature heat storage material. That is, the low boiling point organic compound precipitates its own hydrate crystals by acting as a refrigerant. Therefore, in the method for producing a low-temperature heat storage material of the present invention, there is no need for a group of heat transfer tubes or a cooling capsule, which is required, for example, in the production of ice, which is a typical conventional low-temperature heat storage material.

In other words, in the present invention, the reaction system is not cooled from a specific interface, but the entire system is uniformly cooled, so the heat transfer rate is not hindered by hydrate crystals as in the past, and the cold heat is transferred to the cold water. It is possible to store heat with high performance through sensible heat and the heat of formation of hydrate crystals.

The mixing ratio with a low-boiling organic compound can be determined as appropriate as long as hydrate crystals can be precipitated by the heat of vaporization of this organic compound, and although it varies depending on the type of organic compound and its heat of vaporization, it is usually C. Non-flammable Freon 11. Freon 12. Freon 21. Freon 22, preferably 7on1, whose critical decomposition point temperature and pressure are in the range where heat storage operation is easy, i.e. 11.8°C and 3,340m7rLHg.
2. It is a mixture of Freon 11 and Freon 12.

The production method of the present invention can be carried out using, for example, Freon 12 (CCl2F2-heat of hydrate formation = 70
c'a to 6! To specifically show the case where ) is used, Freon 12 is mixed in liquid form in water, and Freon 12 is mixed in water.
While evaporating a part of the mixture, the mixture is cooled by the heat of evaporation, and a cold heat storage operation is performed at a vapor temperature of 8°C until the hydrate crystal content reaches 40%, and the hydrate crystals of Freon 12 are suspended in water. A low-temperature heat storage material was obtained. The amount of heat stored in this heat storage material is calculated by setting the available cold heat temperature (maximum heat dissipation temperature) to 11°C, which is close to the hydrate decomposition temperature of Freon 12, 11.8°C, and calculating the total amount of heat stored per 1 kg of suspension. When calculated, it is 30.0 c
m! / to (cold water sensible heat 1,8 cal + hydrate formation heat 2
8.21:c-Il). Also, the amount of heat storage per 1 m8 is 31.5 x 103KQII (the specific volume of the suspension is 0.954 x 10'm"Ag). This amount of cold heat storage is 3 x IQ"
This corresponds to approximately 10 times that of Kail (calculated assuming a temperature difference of 3°C in the use of cold energy).

As mentioned above, the low temperature heat storage material of the present invention has a critical decomposition point of 5.
Since it is made by suspending organic compound hydrate crystals at a temperature of 18°C to 18°C in water, the heat of formation of this hydrate can be used to
It can be used directly as a circulating fluid for air conditioning in air conditioning facilities with a temperature range of 15° C., or it can be used to produce cold water using a heat exchanger and use this cold water as a circulating fluid for cooling.

Moreover, the heat storage material of the present invention does not require any special organic compound as a raw material, and can be easily obtained as a commercially available product, and can be manufactured at an extremely low cost because it simply forms a hydrate.

However, in the production of the heat storage material of the present invention, the organic compound itself acts as a refrigerant and cools the reaction system by accumulating heat, so there is no need to use a separate refrigerant, which reduces the production cost of the heat storage material. be able to.

Furthermore, since the organic compound used as a raw material in the present invention has a boiling point of 30° C. or lower, it is extremely easy to liquefy it after being used as a cold heat source and recirculate it to form a hydrate.

Furthermore, during the production of heat storage materials, the reaction system is not cooled from a specific interface, but the entire system is uniformly cooled, so the conduction of heat is not inhibited by hydrate crystals, and the cold heat is cooled by the cold water. Heat can be stored with high efficiency as heat and the heat of formation of hydrate crystals.

Hereinafter, the present invention will be explained in detail based on examples.

The example diagram shows an example of the course of a cold heat storage operation using Freon 12 as a low-boiling organic compound, as shown by a broken line in a phase equilibrium diagram of a water-Freon 12 system.

In the figure, line segment 1 indicates the condensation line of Freon 12, line segments 2 and 6 indicate hydrate production lines, and intersection point 4 of these lines indicates the critical decomposition point of hydrate.

This critical decomposition point 4 differs depending on the type of low-boiling organic compound, and for Freon 12, it is at 11.8°C and 3,3401 RmHg as shown in Table 1 above. Zone 5 is a region where water, the gas phase of Freon 12, and hydrate coexist, Zone 6 is a region where the liquid phase of Freon 12 and hydrate coexist, and Zone 7 is a region where water, the floor, and the liquid phase of Freon 12 coexist. , Area 8 is water and Freon 12
The regions in which the gas phases coexist are shown. When Freon 12 is directly mixed in liquid form into the water in the low-temperature heat storage tank and the Freon 12 liquid is evaporated, the temperature and pressure inside the tank will decrease according to the broken line 9 in the figure due to the heat of evaporation, and the relationship between the temperature and pressure is as follows. Enter zone 5 where hydrates are formed. Then, after passing through a supercooled state of 2°C to 3°C below the hydrate decomposition temperature, for example, point 1
0 (temperature 9°C), hydrate crystals begin to precipitate. Furthermore, add Freon 12 liquid and continue the crystallization operation of hydrate crystals while evaporating it, and when the crystal content reaches about 40%,
For example, when the injection of fluorocarbon liquid is stopped at point 11 (temperature 8°C) and the remaining fluorocarbon liquid is evaporated and recovered, the temperature and pressure inside the tank reach point 12 on hydrate formation m (line segment 2). End the cold heat storage operation.

The heat dissipated from the cold heat of the suspension of hydrate crystals obtained by such cold heat storage operation is due to the decomposition of a part of the hydrate crystals due to external heat input, and the heat of decomposition (=heat of formation) and water. The pressure and temperature inside the tank rise along line segment 2 in the figure as the hydrate decomposes. Then, the hydrate crystal in the thick part is decomposed, and the temperature inside the tank is close to the hydrate decomposition point temperature of 11.8°C, for example, point 15 (11
'c), the low boiling point organic compound is again injected in liquid form, the pressure inside the tank is raised to a point 14 near the condensation line 1, and the cold heat storage operation is started. In this case, undecomposed hydrate crystals remain in the tank, so there is no need for supercooling or waiting time to generate crystal nuclei, and as the low-boiling organic compounds evaporate, the hydrate crystals Crystals precipitate quickly. Then from point 14 to point 11 and then point 12-! In j,
Cold heat storage operation can be performed in the same manner as above. Further, at point 16, if there is continued heat input from the outside, it is possible to perform the cold heat storage operation and the cold heat dissipation simultaneously.

[Brief explanation of drawings]

The figure shows an example of the method for manufacturing a low-temperature heat storage material of the present invention.
It is a phase equilibrium diagram of Freon 12 (CCf2F2). Temperature (C)

Claims (1)

[Claims] 1. A low-temperature heat storage material comprising hydrate crystals of an organic compound having a boiling point of 30° C. or lower suspended in water. However, the critical decomposition of the hydrate crystal is between 5°C and 18°C.
It is °C. 2. From the mixture obtained by mixing an organic compound with a boiling point of 30°C or less and which can react with water to form a hydrate with a critical decomposition point of 5°C to 18°C into water, A method for producing a low-temperature heat storage material, characterized in that a part of the organic compound is evaporated, and the mixture is cooled by the heat of evaporation to precipitate hydrate crystals of the organic compound.