JPS5942238B2 - Cold storage heat material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cold storage material used in a cold storage heating and cooling system.

There are two methods of cold storage type air conditioning and heating equipment: a method in which a cold storage heat tank is installed in the conditioned air flow path of a heat pump type air conditioning system, and heat is exchanged with the cold storage heat material using air; There is a method of exchanging heat with a cold heat storage material using a refrigerant, and the former method has been extensively researched in the United States and has even been put into practical use.

The present invention relates to a cold storage heat material used in the latter type of system. The latter system will be explained using FIG.

Figure 1 is an explanatory diagram of the main parts of a cold storage heat type air conditioning system that incorporates a cold storage heat tank into the refrigerant circuit, in which 1 is a compressor, 2 is a refrigerant passage pipe,
3 is an outdoor heat exchanger, 4 and 5 are expansion valves, and 6 is a cold storage heat tank, the inside of which is filled with a cold storage heat material □. 8 is an indoor heat exchanger, and 9 to 14 are pulps.

Cold storage, heat storage, cooling, and heating operations using this method are performed by the following mechanism. (c) Cold storage operation: With pulp 1 mouth, 11, 13, and 14 closed, the refrigerant gas discharged from the compressor 1 reaches the outdoor heat exchanger 3 via the refrigerant passage pipe 2, where it is condensed. After passing through the pulp 9 and the expansion valve 4, it reaches the cold storage heat tank 6, where it is evaporated and the surrounding cold storage heat material 7
Capture more heat.

In this case, the cold storage heat material □ in the cold storage heat storage tank 6 is in a liquid phase at room temperature, but as the refrigerant absorbs heat, it gradually cools down and begins to solidify, and finally solidifies completely and becomes a solid phase. On the other hand, the evaporated refrigerant is returned to the absorption side of the compressor 1 via the pulp 12. (2) Cooling operation using cold storage source: Pulp 9, 11, 12
and 13 are closed, the refrigerant gas discharged from the compressor 1 reaches the outdoor heat exchanger 3 via the refrigerant passage pipe 2,
After being condensed here, it passes through the pulp 10 and reaches the cold storage heat storage tank 6, where it releases heat to the cold storage heat material 7.

In this case, the cold storage heat material 1 becomes solid and
It is in a state of liquid coexistence. The cold storage heat material 1, which absorbs heat from the refrigerant, gradually warms up and begins to melt near the peritectic point temperature, and finally becomes completely liquid. The liquefied refrigerant passes through the expansion valve 5 and the pulp 14 and reaches the indoor heat exchanger 8, where it takes away the heat in the room, that is, cools the room, and the evaporated refrigerant is returned to the suction side of the compressor 1. . (3) Heat storage operation: valves 10, 11,
13 and 14 are closed, the refrigerant gas discharged from the compressor 1 passes through the refrigerant passage pipe 2a, passes through the valve 12, and reaches the cold storage heat tank 6, where it is condensed and cooled in a solid-liquid coexistence state. Heat is released to the heat material 7.

In this case, the cold storage heat material 7 absorbs this heat, stores it, and enters a liquid phase state. On the other hand, the condensed refrigerant passes through the expansion valve 4 and the valve 9 and reaches the outdoor heat exchanger 3, where the refrigerant evaporates and absorbs heat from the outside air and returns to the compressor 1. (4) Heating operation using heat storage source: With the valves 9, 10, 12, and 13 closed, the refrigerant gas discharged from the compressor 1 reaches the indoor heat exchanger 8 via the refrigerant passage pipe 2a, where it is heated. It exchanges heat with indoor air and heats the room.

The condensed refrigerant passes through the valve 14 and the expansion valve 5 and reaches the cold storage heat storage tank 6, where it is transferred to the cold storage heat storage material 7 that has been stored with heat during the heat storage operation.
The refrigerant that has absorbed more heat and evaporated is returned to the compressor 1 via the valve 11. The following materials have been put into practical use or have been reported in research as cold heat storage materials used in such systems, but each of them has the following drawbacks.

(1) Water: Although it has been put into practical use, only sensible heat in the liquid state can be used for heating purposes, so the cold storage tank has a large capacity, but the phase change temperature is too low for cooling purposes, resulting in low efficiency. A good heat pump cannot be found at any time. (2) Tetrahydrofuran hydrate: It is put into practical use exclusively for cooling.

It has a low melting point of 4°C and cannot be used for heating. Also, it has a high vapor pressure and is flammable, so it must be completely sealed. (3) Paraffin (Cl4-Cl6): latent heat per volume is 25-30
Kca is as small as 1/l, and the cold storage heat tank has a large capacity.

Furthermore, there is a problem in heat exchangeability due to large shrinkage during solidification. (4)
Inorganic salt hydrates: In general, inorganic salts have a large hydration enthalpy value, so research into hydrates such as sulfates, thiosulfates, phosphates, and chlorides is active in order to take advantage of this. Since inorganic salt hydrates generally have a high degree of supercooling, a compressor with a large capacity is required, which is disadvantageous from the viewpoint of energy conservation.

Furthermore, since phase separation development occurs, heat exchange efficiency is poor, and reproducibility of the amount of cold storage heat cannot be obtained under conditions where the amplitude of the cold storage heat temperature and the cold collection heat temperature is narrow. Moreover, most of them are highly corrosive to heat exchanger metals. In order to provide a cold storage material for a cold storage air conditioning system that does not have the above-mentioned drawbacks, the present inventors investigated the phase diagram of coexistence systems with water, hydration enthalpy values, and their physical and chemical properties for various substances. As a result of considering the characteristics of
HCOONa is added to the binary system of sodium formate (HCOONa) and water, which has a small degree of supercooling and does not cause phase separation.
Substances with a lower affinity for water, such as NaNO3
The present invention was achieved by discovering that a three-component system containing the following as the third component is optimal as a cold storage heat material for the system.

That is, the present invention uses a 40.0 to 50.0% by weight HCOONa aqueous solution of 85 to 90% by weight and a substance having a lower affinity for water than HCOONa by 15 to 10% by weight as a cold storage material for a cold storage heat type air conditioning system. It is characterized by the use of a mixture of

As the cold storage heat material of the present invention, 44 to 45% by weight of HCOONa
- an aqueous sodium formate solution consisting of 55-56% by weight of water;
Or HCOONa:water-1:1 (weight) 85~
90% by weight - NaNO31O to 15% by weight, especially HCO
ONa:water:NaNO3-45:45:10% by weight is preferred.

First, the behavior of the sodium formate-water two-component system will be explained based on the schematic phase change diagram of the two-component system shown in FIG.

If the summer bath temperature is about 30'C, for example, 50% by weight HCO
In an ONa aqueous solution, when the temperature is lowered by heat exchange, precipitation of dihydrate should start at 25°C since this concentration is the saturated concentration at 25°C, but in reality, the temperature is lowered further. The dihydrate does not precipitate even if the solution is heated to a higher temperature, and the liquid remains supersaturated (as shown by the broken line in Figure 2).

This is called supercooling phenomenon A. When the temperature further decreases, precipitation of a solid phase begins as crystal nuclei are generated. Due to the heat generated due to solid phase precipitation, the relationship between the liquid composition and temperature of the cold storage material returns to the solid-liquid phase equilibrium curve as shown in FIG. As cooling continues, the cold heat storage material precipitates dihydrate B (2
When hydrate 1y precipitates, sodium formate in the liquid phase becomes 0.
667 and 0.357 water is consumed), and the liquid phase composition decreases along the equilibrium curve. Liquid phase composition is 44.2
When the weight percentage is reached, trihydrate C precipitates thereafter. The point at which the crystal type changes in this way is called the peritectic point. Also, at this peritectic point, the precipitated crystal type may not change and the equilibrium relationship may move toward the extension of the dihydrate precipitation line; in this case, after a certain amount of movement, the equilibrium relationship changes to trihydrate precipitation. Moving toward the line, the amount of trihydrate precipitated decreases by the amount of dihydrate precipitated in excess. If we now lower the temperature of the cold storage heat material to 5℃, there will be approximately 33% by weight of HCOONa in the cold storage heat material.
There will be an aqueous solution and precipitated dihydrate and trihydrate crystals. From here, the melting behavior D when the temperature of the cold storage heat material is increased is that if the temperature is increased slowly (by matching the solvation rate and the temperature increase rate), the phase equilibrium will reach the same level as shown in Figure 3A. However, substances with large cohesive energy have a slow solvation rate at temperatures below the melting point of the substance; for example, the trihydrate has a 17
Since it remains in a solid phase up to ℃, a phase equilibrium movement occurs as shown in FIG. 3B.

Therefore, for example, the saturation temperature for a composition of 46% by weight is approximately 2
Although the temperature was 0°C, 2 precipitated unless the temperature was raised to 25°C.
Hydrates are difficult to dissolve, and the saturation temperature for a 40% composition is about 13°C, but trihydrates are difficult to dissolve unless the temperature reaches 17°C. As mentioned above, sodium formate hydrate is
The phase equilibrium shifts very slowly with respect to temperature rise, and the hydrate crystal hardly dissolves even when it comes into contact with an unsaturated solution, and dissolves all at once at around the hexaperitectic point temperature. That is, they behave as if they have a melting point, so sodium formate trihydrate does not melt until around 17°C, and sodium formate dihydrate remains in a solid phase until around 25°C. Therefore, near the upper limit of the operating temperature range (6°C to 25°C), the thermal conductivity of the solid phase of the cold storage heat material is extremely low, making it difficult to completely dissolve sodium formate dihydrate, so the melting behavior If we focus only on sodium formate 4, only sodium formate trihydrate precipitates as a solid phase.
The reproduced energy storage value is higher when using a composition of 4.2% by weight, in other words, a saturated composition at 17°C.
That is, focusing on material 17, if a composition of 44.2% by weight or more is used, a dihydrate will precipitate until the liquid phase composition reaches 44.2% by weight. For example, if a composition of 50 tonne weight is used, the liquid phase composition will be 50 wt% HCOONa → 44.2 wt%
During the formation of HCOONa, 0.2747 hydrates per 17 of the material precipitate, so the remaining amount is 0.7267.If the dihydrate remains undissolved and only the trihydrate dissolves, from the beginning 4
If a composition of 4.2% by weight is used, 1 part of the material will work effectively, but if a composition of 50% by weight is used, only 0.7267 parts will work effectively. On the other hand, supercooling during solidification differs greatly depending on this composition.

This is because, as is clear from FIG. 2, the hydration numbers of the crystal nuclei are different. If a composition higher than 44.2% by weight of sodium formate is used, dihydrate will precipitate as primary crystals, resulting in less supercooling and solidification at the lower limit of the operating temperature range;
After the phase equilibrium reaches the peritectic point of dihydrate and trihydrate due to hydrate precipitation, dihydrate precipitation tends to continue;
As a result, the dihydrate precipitates excessively and the amount of trihydrate precipitated decreases, thereby reducing the amount of stored energy. This excessively produced dihydrate settles and forms a strong solid phase, but since its thermal conductivity is low, the heat exchange surface must be brought into direct contact with the solid phase, or the solid phase must be brought into contact with the solid phase to the extent that the solid phase is crushed. If measures such as strong stirring are not taken, undissolved phase separation will occur at the upper limit of the operating temperature range.
wake up Conversely, when using a composition of 44.2% by weight or less of sodium formate, it is necessary to add a core material such as sodium formate anhydride. The difference in the degree of supercooling between the formulation in which the dihydrate precipitates as a primary crystal and the formulation in which the trihydrate precipitates as a primary crystal is due to the wetting of the crystal surface by the solution due to the difference in cohesive energy of both primary crystals. This is thought to be due to the difference in the remaining state of the molecular aggregate based on the difference in properties or the difference in the properties of both crystals in the molten state.

However, when a small amount of a third component is added to a two-component system of sodium formate and water, the phase change behavior becomes different from that of the original two-component system. By adding a substance with a lower affinity for water than sodium formate as the third component, the melting point of the dihydrate can be lowered without significantly changing the phase equilibrium relationship of the original two-component system. The present invention focuses on this point, and due to the effect of lowering the melting point, supercooling is small (primary crystals of the dihydrate are precipitated) and phase separation does not occur (the upper limit of the predetermined temperature (The dihydrate completely melts at 25°C.) A well-balanced cold storage heat material can be prepared. For example, an outline of the phase change when sodium nitrate is added as the third component is shown in FIGS. 4 and 5. Figure 4 shows water-HC
The phase diagram of the OONa-NaNO3 ternary system is shown.

In the figure, A is the dihydrate precipitation region, B is the trihydrate precipitation region, C is the NaNO3 precipitation region, D is the melting point, and E is the ternary eutectic point. In the figure, if equilibrium movement between the curves connected by arrows is used, the intersection with each peritectic line (in the case of dihydrate, the point where the movement line is extended and intersects with the peritectic line) is the point of intersection of each crystal. It is the melting point.
The above FIG. 2 corresponds to the phase diagram of the water-HCOONa line (base) in FIG. 4, and in the present invention, water-HCOONa and NaNO3
The composition used as a ternary system of water and HCOONa appears on the line connecting the point of the soil and the apex (NaNO3), and
FIG. 5 is a projected cross-sectional view taken along a line connecting the 50% by weight point and the apex on the COONa line. Figure 5 shows the weight ratio [HCOO
Na]:[H2O]:[NaNO3]-0,45:0.
This shows how the phase equilibrium moves due to temperature changes when using a blending composition of 45:0.10.
The melting points of the trihydrate and dihydrate melted at 25°C are determined by the line Ab representing the locus of the liquid phase composition in equilibrium with the precipitated solid phase or its extrapolation and the peritectic line (dihydrate). hydrate A, trihydrate B
), which are 13°C and 21°C, respectively, 4°C lower than the original two-component system, and the upper limit of the set temperature is 25°C.
Completely liquefies at ℃, no phase separation occurs (C: saturation point,
D: supercooling, E: solidification curve, F: melting). Furthermore, in the range of addition of 10 to 17% by weight of sodium nitrate, dihydrate precipitates as primary crystals, and supercooling is small, and the melting point of dihydrate is /+12a lower than that of the two-component system, and 25 Complete liquefaction is possible at ℃.

In addition, the cold storage heat material according to the present invention undergoes phase separation when the concentration of sodium formate increases due to water evaporation, so it has strong water repellency.
Approximately 2 to 3 layers of paraffin oil, such as Suniso 351 oil, whose specific gravity is smaller than that of the cold storage heat material, is used. It is used by floating the cold heat storage material on soil and sealing it to prevent water evaporation. By using the cold heat storage material of the present invention, the following effects can be achieved.

(1) There is little supercooling and no phase separation occurs.

(2) The amount of energy stored varies depending on the temperature that the cold storage material reaches after solidification starts, but up to 9°C is 40Kca1//?
, 45Kcal/l can be accumulated up to 6°C. (3)
Poisoning and corrosion of heat exchanger metals are not a problem.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the main parts of a cold storage heat type air conditioning system in which a cold storage heat tank is incorporated into the refrigerant circuit, and Figure 2 is an explanatory diagram of the main parts of a cold storage heat type air conditioning system that incorporates a cold storage heat tank into the refrigerant circuit.
This is a schematic diagram of the phase change of the component system, and FIG. 3 shows the phase change diagram of water-HCOONa.
Figure 4 is a phase equilibrium transfer diagram depending on the temperature of water-HCO
FIG. 5 is a state diagram of a three-component system of ONa-NaNO, and FIG. 5 is a projected cross-sectional view of a three-component system of water-HCOONa-NaNO.

Claims (1)

[Claims] 1 Add HCOO to 40-50% by weight HCOONa aqueous solution.
Substances with a lower affinity for water than Na should be added to 10~10% of the total solution.
A cold storage heat material for a cold storage type air conditioning system, which is added at a concentration of 15% by weight.