JPS6356915B2 - - Google Patents

Description

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

In general, absorption refrigerators are formed with 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 The heat is used for freezing. The refrigerant vapor evaporated in the evaporator is absorbed in the absorber by the refrigeration composition containing a high concentration of absorbent sent from the generator, and is returned to the generator as a refrigeration composition containing a low concentration of absorbent. . The refrigeration composition containing a low concentration of absorbent is heated in a generator with an external heat source to release refrigerant vapor, which is condensed in a condenser and sent back to the evaporator.

Conventional refrigeration compositions used in absorption refrigerators consisting of such cycles include those using water (H ₂ O) as a refrigerant and lithium bromide (LiBr) as an absorbent, and those using ammonia (NH ₃ ) as an absorbent. Refrigeration compositions using a refrigerant and water (H ₂ O) as an absorbent have been put into practical use.

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 so a significant negative pressure must be maintained in the equipment, and corrosion control is required due to the corrosive nature of the solution. There are drawbacks such as restrictions on the addition of agents and materials for equipment.

In addition, NH ₃ - H ₂ O-based refrigeration compositions have a considerably high vapor pressure, so the equipment must be designed to withstand high pressure, and ammonia gas is explosive and toxic, making it dangerous to absorb. Currently, it is hardly used for type refrigerators. 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 tend to precipitate in low concentration ranges, resulting in a narrow operating concentration range.The viscosity of the solution is high, which increases the power required for liquid circulation. Disadvantages have been pointed out, 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. , some of which are disclosed in Japanese Patent Application Laid-open Nos. 54-55849 and 1983.
- Proposed in Publication No. 79175, etc. but,
There are many possible combinations of systems in which a fluorocarbon compound is used as a refrigerant and an organic solvent is used as an absorbent, and the current situation is that sufficient research has not yet been conducted on individual combinations. 22) etc. as a refrigerant,
Refrigeration compositions using tetraethylene glycol dimethyl ether 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 problems of the refrigeration compositions used in conventional absorption refrigerators, the present invention provides a refrigeration composition that is particularly safe to handle, does not have a very high vapor pressure, and is less corrosive to equipment. As a result of intensive research, a refrigeration composition containing chlorotrifluoroethane as a refrigerant and N,N'-dimethylformamide as an absorbent was found to be well suited to the above purpose and is an excellent refrigeration composition. This discovery led to the present invention. That is, in the present invention, chlorotrifluoroethane is used as a refrigerant, N,
This is a refrigeration composition for absorption refrigerators that uses N'-dimethylformamide as an absorbent.

Chlortrifluoroethane used as a refrigerant in the present invention has three isomers with different structural formulas, namely CHClF-CHF ₂ (R133), CH ₂ Cl-CF ₃
(R133a) and CClF ₂ --CH ₂ F (R133b) exist, but since their physical properties are almost similar, either isomer can be used. Therefore, in the following explanation, chlorotrifluoroethane is used as
The case where R133a is used will be explained as an example.

In Figure 1, R133a is used as a refrigerant, and N, N′-
A temperature-vapor pressure diagram using the absorbent concentration as a parameter for the refrigeration composition of the present invention using dimethylformamide 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,
i.e. the heating temperature of the dilute absorbent solution (temperature inside the generator);
It is arbitrarily set according to the evaporation temperature of liquefied fluorocarbon (temperature inside the evaporator) and the absorption temperature of fluorocarbon gas (temperature inside the absorber). In a refrigeration cycle using such CFCs as a refrigerant, as in the present invention, CFCs are used as refrigerants.
When R133a is used and N,N'-dimethylformamide is used as an absorbent, the evaporation temperature of liquefied R133a is approximately 0°C, the absorption temperature is approximately 40 to 53°C, and the absorbent dilute solution concentration is approximately 50% by weight. (Hereinafter, in this specification, % represents weight % unless otherwise specified.) It is appropriate to set the concentration of the concentrated solution to about 60%.

Incidentally, when the operating conditions are set to other than the above, the dilute solution concentration and concentrated solution concentration conditions of the absorbent can be changed accordingly. Furthermore, the refrigeration composition of the present invention uses a refrigeration cycle similar to the above, and a heat pump cycle (not shown) configured in a system in which an evaporator absorbs heat from outside air and a condenser or absorber releases heat. ) can also be applied as is.

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 operating cycle diagram of FIG. 3. The operating cycle diagram in Figure 3 is R133a in Figure 1.
- From the temperature-vapor pressure diagram of the N,N'-dimethylformamide-based refrigeration composition, pure R133a and N,
N′-dimethylformamide concentration is 50% and 60%
This is an excerpt of the diagram.

First, a 50% dilute solution of N,N'-dimethylformamide in which R133a was dissolved as a refrigerant (point A in Figure 3)
The external heat source 3 is heated inside the generator 1 at a temperature of about 96°C and a pressure of about 2500 mmHg (absolute pressure, the same applies hereinafter).
The 50% dilute solution is concentrated to a 60% concentrated solution (point B in Figure 3) by heating to about 113° C. using a 300° C., during which time R133a gas corresponding to a pressure of 2500 mmHg is generated. Next, this R133a gas is introduced into condenser 2 and cooled through cooling pipe 4 to approximately 40°C (the extension line from B to A is
It condenses and liquefies at the temperature at the point where it intersects the R133a line. Next, the pressure of the liquid R133a 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 40 to 53°C, the pressure inside the evaporator 3 is reduced to approximately 600 mmHg, which corresponds to the vapor pressure, and liquid R133a is sprayed from the nozzle 6 and evaporates at approximately 0°C. The heat of evaporation is then taken away from the brine flowing through the pipe 7 to cool it and use it for refrigeration.

Next, the evaporated R133a gas is introduced into the absorber 4,
It is cooled from the generator 1 through the heat exchanger 8 to the nozzle 9.
It is absorbed into a 60% concentrated solution of N,N'-dimethylformamide (point C in Figure 3) at about 53°C, which is sprayed from a source. 10 is a cooling pipe for adjusting the temperature inside the absorber 4 within a predetermined range. The concentrated solution that has absorbed the R133a gas is diluted to become a 50% dilute solution of N,N'-dimethylformamide (point D in Figure 3), which is sent from the generator 1 to the absorber 4 via the heat exchanger 8. After being heated by exchanging heat with the concentrated solution, it is introduced into the generator 1 by the pump 11 (point A in Figure 3),
The same cycle is repeated thereafter.

In the above example, the case where the evaporation temperature of liquid R133a 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 chlorotrifluoroethane as a refrigerant and N,N'-dimethylformamide as an absorbent, as is clear from the above-mentioned operation cycle, the vapor during operation is Approximately 2500mmHg in the generator with the highest pressure
The vapor pressure is considerably lower than that when using methane-based fluorocarbons, and the pressure-resistant structure of the refrigerator can be significantly relaxed.

Also, R133a N,N'-dimethylformamide 95
Small pieces of steel, stainless steel, and copper were separately immersed in 5 ml of each % concentrated solution and heated under reflux at 180°C for 3 days. Since no deterioration was observed at all, the refrigeration composition of the present invention was found to have excellent corrosion resistance and thermal stability, and was demonstrated to have extremely favorable characteristics as a refrigeration composition for absorption refrigerators. .

[Brief explanation of the drawing]

Figure 1 shows chlorotrifluoroethane
Temperature-vapor pressure diagram with various concentrations of the absorbent as parameters for the refrigeration composition of the present invention using R133a as the refrigerant and N,N'-dimethylformamide as the absorbent, Figure 2 shows absorption refrigeration. Cycle flow sheet, FIG. 3 is an operating cycle diagram using the refrigeration composition of the present invention. DESCRIPTION OF SYMBOLS 1... Generator, 2... Condenser, 3... Evaporator, 4... Absorber, 5... Pressure reducing valve, 8... Heat exchanger, 11... Pump.

Claims (1)

[Claims] 1 Using chlorotrifluoroethane as a refrigerant, N,
A refrigeration composition for an absorption refrigerator, characterized in that N'-dimethylformamide is used as an absorbent.