JPS6111985B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a refrigeration composition used in an absorption refrigerator.

In general, an absorption refrigerating machine is formed into a closed cycle consisting of a generator containing a refrigeration composition, a condenser, an evaporator, and an absorber. When the liquid refrigerant is evaporated in the evaporator, heat is taken from the outside, and the evaporation Latent heat is used for freezing. The refrigerant vapor evaporated in the evaporator is contacted and absorbed by the refrigeration composition with a low refrigerant concentration sent from the generator in the absorber, and is returned to the generator as a refrigeration composition with a high refrigerant concentration. The refrigerant-rich refrigeration composition is heated by an external heat source in a generator to generate refrigerant vapor, which is condensed in a condenser and sent back to the evaporator as liquid refrigerant.

Conventionally, the refrigeration composition used in absorption refrigerators consisting of such a cycle uses water (H ₂ O) as a refrigerant and lithium bromide (LiBr) as an absorbent for many commercial absorption refrigerators. The frozen composition is
Furthermore, refrigeration compositions containing ammonia (NH ₃ ) as a refrigerant and water (H ₂ O) as an absorbent have been used for a long time for low-temperature absorption refrigerators.

However, since H ₂ O-LiBr-based refrigeration compositions use water as a refrigerant, the evaporation temperature cannot be set below 0°C, and therefore they cannot be used for purposes other than air conditioning. air cooling of the condenser is difficult due to limited solubility in water, the vapor pressure is too low and a significant negative pressure must be maintained in the equipment, and the corrosive nature of the solution makes it difficult to air cool the equipment. There are drawbacks such as restrictions on the materials used to form the film.

In addition, since NH ₃ -H ₂ O-based refrigeration compositions have a fairly high vapor pressure, the equipment must be designed to withstand high pressure, and ammonia gas is explosive and toxic, making it dangerous to handle. Not suitable as a frozen composition. Therefore, a system has been proposed in which alcohols such as methanol and ethanol are used as refrigerants to obtain temperatures below 0°C, and halides such as lithium bromide (LiBr) and zinc bromide (ZnBr ₂ ) are used as absorbents. being researched.

However, in this system, the solubility of halides in alcohol is low, and halide crystals often precipitate in the low concentration range, resulting in a narrow operating concentration range and the power required for liquid circulation due to the high viscosity of the solution. It has been pointed out that there are disadvantages such as the liquid film of the concentrated absorbent solution in the absorber becoming thicker and the alcohol absorption rate decreasing.

In view of the above-mentioned problems with refrigeration compositions, studies have recently been conducted on systems that use various fluorocarbon compounds as refrigerants and various organic solvents that dissolve these fluorocarbon compounds as absorbents. . However, there are many possible combinations of these systems, and the current situation is that sufficient research has not yet been done on each individual combination. Dimethyl ether ( _CH3O
Refrigeration compositions using (C ₂ H ₄ O) ₄ CH ₃ ) as an absorbent have attracted attention, but their vapor pressure is as high as that of the NH ₃ --H ₂ O system.

In view of the various drawbacks of such conventional refrigeration compositions, the present invention provides safe handling, vapor pressure near atmospheric pressure, high solubility of refrigerant in absorbent, and no problems such as crystal precipitation. Furthermore, it was developed with the aim of providing a refrigeration composition that is less corrosive to equipment, and as a result of intensive research, dichlorotrifluoroethane was used as a refrigerant, and N-methyl-2-
The inventors have discovered that a refrigeration composition using pyrrolidone as an absorbent is an excellent refrigeration composition that is well suited to the above-mentioned purpose, leading to the present invention.

That is, the present invention is a refrigeration composition for an absorption refrigerator that uses dichlorotrifluoroethane as a refrigerant and N-methyl-2-pyrrolidone as an absorbent.

Dichlorotrifluoroethane used as a refrigerant in the present invention has three isomers with different structural formulas, namely CHCl ₂ -CF ₃ (R123), CHClF-
CClF ₂ (R123a) and CHF ₂ -CCl ₂ F R123b exist, but since their physical properties are almost similar, either isomer can be used in the same way.
Therefore, in the following explanation, the case where R123a is used as dichlorotrifluoroethane will be exemplified and explained.

In Figure 1, (R123a) is used as a refrigerant, and N-
A temperature-vapor pressure diagram using the absorbent concentration as a parameter of the refrigeration composition of the present invention using methyl-2-pyrrolidone as an absorbent is shown.

In general, a refrigeration cycle that uses fluorocarbons as a refrigerant involves the generation of fluorocarbon gas from a dilute absorbent solution (a solution with a high concentration of fluorocarbons), the condensation of the generated fluorocarbon gas, the evaporation (vaporization) of liquefied fluorocarbons, and the evaporation (vaporization) of a concentrated absorbent solution (a solution with a low concentration of fluorocarbons). This is achieved by repeating processes such as absorption of fluorocarbon gas into a solution), but the concentration of the absorbent dilute solution and concentrated solution depends on the operating conditions of the refrigerator,
In other words, the heating temperature of the absorbent dilute solution (temperature inside the generator), the evaporation temperature of liquefied CFC (temperature inside the evaporator)
and the absorption temperature of the fluorocarbon gas (temperature inside the absorber).

As in the present invention, dichlorotrifluoroethane is used as the refrigerant and N-methyl-2 as the absorbent.
- When using pyrrolidone, if the evaporation temperature of the liquid refrigerant is approximately 0°C and the absorption temperature is approximately 44 to 53°C, the concentration of the dilute absorbent solution is approximately 44% by weight (% is not specified hereinafter). % by weight), it is appropriate to set the concentration of the concentrated solution to about 54%.

When the operating conditions are set to a value other than the above, the dilute solution concentration and concentrated solution concentration conditions of the absorbent can be changed accordingly. In addition, the refrigeration composition of the present invention absorbs heat from the outside air in the evaporator by changing the operating conditions and solution concentration in the same way as the above-mentioned refrigeration cycle.
It can also be applied to an absorption heat pump cycle in which heat is released indoors using a condenser or absorber.

Next, an example of the operation of an absorption refrigeration cycle using the refrigeration composition of the present invention will be explained based on the flow sheet of FIG. 2 and the refrigeration cycle diagram of FIG. 3. The refrigeration cycle diagram in Figure 3 is R123a in Figure 1.
- Diagrams with pure R123a and N-methyl-2-pyrrolidone concentrations of 44% and 54% are extracted from the temperature-vapor pressure diagram of the N-methyl-2-pyrrolidone-based frozen composition. .

First, a 44% dilute solution of N-methyl-2-pyrrolidone (point A in Figure 3) in which R123a is dissolved as a refrigerant is heated in the generator 1 at a constant pressure from about 88°C to about 98°C using the external heat source 3. Approximately 1100mm when heated below
R123a with pressure of Hg (indicates absolute pressure. The same applies below)
Gas is generated and the 44% dilute solution is concentrated to a 54% concentrated solution (point B in Figure 3). Next, this R123a gas is introduced into condenser 2 and cooled down to approximately 40°C through cooling pipe 4.
It condenses and liquefies at (the temperature at the point where the extension line from B→A intersects the line R123a). Next, the pressure of the liquid R123a is reduced by the pressure reducing valve 5 and introduced into the evaporator 3. When the temperature in the absorber 4 is set at approximately 44 to 53°C, the pressure inside the evaporator 3 is reduced to approximately 230 mmHg, which corresponds to the vapor pressure, and liquid R123a is sprayed from the nozzle 6 and evaporates at approximately 0°C. The latent heat of vaporization is then taken away from the brine flowing through the pipe 7 to cool it and use it for refrigeration.

Next, the evaporated R123a gas is introduced into the absorber 4,
The mixture is cooled from the generator 1 through the heat exchanger 8 and absorbed into a 54% concentrated N-methyl-2-pyrrolidone solution (point C in Figure 3) at about 53°C which is sprayed from the nozzle 9.
10 is a cooling pipe for adjusting the temperature inside the absorber 4 within a predetermined range.

The concentrated solution that absorbed R123a gas was diluted to a 44% dilute solution of N-methyl-2-pyrrolidone (3.
After exchanging heat with the concentrated solution sent from the generator 1 to the absorber 4 via the heat exchanger 8 and being heated, it is introduced into the generator 1 by the pump 11 (point A in Figure 3). , and then repeat the same cycle.

In the above example, the case where the evaporation temperature of liquefied R123a in the evaporator 3 was 0°C was explained, but the above operating conditions may be selected and implemented as appropriate depending on the degree or speed of freezing or cooling required. be able to.

As explained above, according to the refrigeration composition of the present invention which uses dichlorotrifluoroethane as a refrigerant and N-methyl-2-pyrrolidone as an absorbent, as is clear from the refrigeration cycle diagram, the vapor during operation is Approximately 1100mmHg in the generator where the pressure is highest
is lower than conventional chlorodifluoromethane-tetraethylene glycol dimethyl ether-based or ammonia-water-based refrigeration compositions, while compared to lithium bromide-water-based or lithium bromide-alcohol-based refrigeration compositions. It can be operated at almost atmospheric pressure, and the pressure-resistant structure of the refrigerator can be significantly relaxed.

Also, 90% N-methyl-2-pyrrolidone of R123a
Small pieces of steel, stainless steel, and copper were separately immersed in 5 ml of each concentrated solution and heated under reflux at 200°C for 10 days. Since no deterioration was observed at all, it was found that the frozen composition of the present invention also has excellent corrosion resistance and thermal stability.

Furthermore, dichlorotrifluoroethane has a high solubility in N-methyl-2-pyrrolidone, and there is no risk of crystallization that occurs in lithium bromide-water systems or lithium bromide-alcohol systems, so it can be operated in a wide concentration range. It has been demonstrated that the composition has extremely favorable properties as a composition for isossorption refrigerators.

[Brief explanation of the drawing]

Figure 1 shows dichlorotrifluoroethane
Temperature-vapor pressure diagram with various concentrations of absorbent as parameters for the refrigeration composition of the present invention using R123a as a refrigerant and N-methyl-2-pyrrolidone as an absorbent, Figure 2 is an absorption refrigeration diagram. Cycle flow sheet, FIG. 3 shows an example of a refrigeration cycle diagram using the refrigeration composition of the present invention. 1... Generator, 2... Condenser, 3... Evaporator,
4... Absorber, 5... Pressure reducing valve, 8... Heat exchanger,
11...Pump.

Claims (1)

[Claims] 1 dichlorotrifluoroethane as a refrigerant, N
- A refrigeration composition for an absorption refrigerator, characterized in that methyl-2-pyrrolidone is used as an absorbent.