JPS5827300B2 - Refrigerant for absorption refrigerators - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a refrigerant used in an absorption refrigerator, and particularly relates to a refrigerant that has a large latent heat of vaporization, a large vapor pressure drop rate when combined with an absorbent, and a low crystallization point and viscosity. .

Absorption refrigerators generally have a basic circuit configuration as shown in FIG. a condenser that cools a refrigerant into a liquid refrigerant; 3 is the condenser 2;
An evaporator 5 obtains a desired cooling function by reducing the pressure of the liquid refrigerant in a pressure reducer 4 and vaporizing it by dispersing it under low pressure conditions. absorber that enables continuous cooling operation in
6 is a heat exchanger for exchanging heat between the concentrated absorption liquid from which the refrigerant is separated in the generator 1 and sent to the absorber 5f, and the diluted absorption liquid returned from the absorber 5 to the generator 1; 7 is a heat exchanger for the absorption liquid; It is a circulation pump, and the composition of the refrigerant and absorption liquid used in such an absorption refrigerator is such that even if the heating temperature in the generator 1 is not very high, the refrigerant is separated from the absorption liquid and the cooling in the condenser 2 is maintained. It is preferable that the refrigerant liquefies even if the temperature is not very low.

For example, the heating temperature required in generator 1 is 80
If the refrigerant is separated from the absorption liquid at temperatures between 120°C and 120°C, it becomes possible to drive the generator relatively easily using solar heat as a heat source.
In addition, if the refrigerant can be liquefied at a condensation temperature of 40 to 60°C, an air-cooled condenser can function sufficiently as a condenser, and the latent heat of vaporization allows the refrigerant to vaporize at a temperature of 5 to 10°C while satisfying such conditions. If a refrigerant with a high refrigerant temperature could be obtained in a form that poses less harm to the human body, the range of applications for small-sized absorption refrigerators would be extremely widened.

For example, in a refrigerant-absorbing liquid system using water or methyl alcohol as a refrigerant, the latent heat of vaporization of the refrigerant is large and the coefficient of performance tends to be large, but lithium halides (LiBr, LiC1, etc.) are usually selected as the absorbent. Crystallization of the absorbent becomes a problem.

Furthermore, when ammonia is used as a refrigerant, the toxicity of ammonia is an obstacle to the widespread use of absorption refrigerators, and there are still no other known refrigerant absorption liquid systems that satisfy all of the above conditions. Not obtained.

In view of these points, the present invention employs a refrigerant having the characteristics of high vapor pressure drop rate, high latent heat of vaporization, and low viscosity in an absorption refrigerator. A certain trifluoroethanol (CF3CH20H) is used as a refrigerant,
N-methyl-2-pyrrolidone (
Vapor pressure temperature diagrams at various concentrations using t- (self≧HO)t- are shown.

In the figure, line A indicates the saturated vapor pressure of trifluoroethanol at each temperature, and line B1. B2. B3 is N-methyl-2-pyrrolidone trifluoroethanol 60
Based on the values obtained by measuring the vapor pressure at each temperature for wt% solution, 70wt% solution, and g□wt% solution (However, a small amount of water (B20) is added to suppress corrosion of equipment. Although not shown in the figure, it was also confirmed that the boiling point of trifluoroethanol is 75°C and the boiling point of N-methyl-2-pyrrolidone is 202°C.

Absorption refrigerants made from trifluoroethanol and N-methyl-2-pyrrolidone do not produce crystals or absorb liquid under normal operating conditions, compared to lithium halide aqueous solutions widely used in the absorption refrigerating machine field. The heat storage property of solidification is low, and therefore the absorption refrigeration cycle can be circulated under various absorbent concentration conditions.

When the absorption refrigeration cycle shown in Fig. 1 is operated with a 64% mixed solution (absorption liquid) containing trifluoroethanol as a refrigerant and N-methyl-2-pyrrolidone as an absorbent, it is approximately indicated by a thick solid line. It was experimentally confirmed that the absorption refrigerator could be operated as shown.

That is, in the generator 1, a 64% solution of N-methyl-2-pyrrolidone (hereinafter referred to as dilute absorption solution) diluted with trifluoroethanol and flowing in [point a in Figure 2] is about 12% diluted with trifluoroethanol.
The trifluoroethanol is vaporized and separated by heating to 5°C [point b] and sent to the condenser 2, while the N-
Methyl-2-pyrrolidone (hereinafter referred to as absorption solution) is cooled through a heat exchanger 6 and supplied to the absorber 5 [point C].

Trifluoroethanol flowing into condenser 2 has a temperature of approximately 50°C.
It is cooled to liquefy and passed through the pressure reducing device 4 to about 19 mmHg.
The evaporator 3 is supplied to the evaporator 3 at a pressure of about 5° C., and when vaporized there, it cools the objects around the evaporator 3 to about 5° C.

Since the vaporized trifluoroethanol is absorbed by the concentrated absorption solution sprayed in the absorber 5, the inside of the evaporator 3 is maintained at approximately 197nr/LHg, and the trifluoroethanol gas is absorbed and diluted [point d] ] The dilute absorption solution exchanges heat with the concentrated absorption solution flowing into the absorber 5 in the heat exchanger 6 to raise its temperature, and then flows into the regenerator 1 again [point a].

A very characteristic feature of the present invention is that the operating pressure of the absorption refrigerator is approximately 250 mmH9 on the high pressure side where the generator 1 is located.
On the low pressure side where the evaporator 3 is located, the pressure is approximately 20 mmHg, which is lower than atmospheric pressure in all parts, and the operating pressure is 10 to 20 kg/m2 on the high pressure side, as in conventional ammonia-water systems and Freon-tetraethylene glycol dimel ether systems. Unlike refrigerant systems that operate under high pressure conditions of approximately 5 kg/m2 even on the side, there is no risk of liquid or gas leaking from the absorption chiller, and the strength of the chiller components is reduced and maintenance management is simplified. It can also be measured.

Furthermore, when N-methyl-2-pyrrolidone or an absorption liquid as described below is used as an absorbent, there is no crystallization of the absorption liquid under normal operating conditions of an absorption refrigerator, and there is no extreme increase in viscosity. , it will not become impossible to drive in cold regions, and
Since the condenser 2 and absorber 3 can be air-cooled, conventional water
This eliminates the need for water cooling mechanisms or cooling towers like those for lithium bromide systems, making it possible to operate absorption chillers in areas with poor water conditions.

In the above explanation, the difference in concentration between a dilute absorption solution and a concentrated absorption solution of N-methyl-2-pyrrolidone used in combination with the refrigerant of the present invention was explained as an experimental result of 8%. The differences in concentration and concentration are just examples, and it can be easily confirmed from the diagram in FIG. 2 that the same operation can be performed with other concentrations.

In addition to trifluoroethanol, the refrigerant of the present invention includes monofluoroethanol [CFH2
CH20H], difluoroethanol [CF2HCH2
0H], trifluoropropanonol [CF3CH2C
H20H], monochlorodifluorooroethanol [CC
There are lower alcohols having a halogen atom such as 1F2CH20H], and some of their properties are as follows.

Example I TFE in a composition with a concentration of 30% by weight of TFE and 70% by weight of organic compounds of various absorbents shown in Table 1 below
The reflux boiling point of Nakamoto was measured and shown in Table 1.

As is clear from Table 1, it can be seen that alkanolamine-based, amide-based, ether-based, and other compounds form complexes with TFE and significantly raise the boiling point of TFE.

In other words, due to complex formation, these compounds have been shown to have significantly superior TFE absorption ability.

It was confirmed that this boiling point increase was not due to azeotropy but to complex formation.

Example 2 65% by weight of 2-pyrrolidone and 35% of various fluorinated alcohols
The reflux boiling points of various fluorinated alcohols in the weight percent composition were measured and shown in Table 2.

As is clear from this result, these fluorinated alcohols* show a significant increase in boiling point in 2-pyrrolidone and form a complex.

It was confirmed that the boiling point increase in this case was not due to azeotropy but due to complex formation.

In addition, as an absorbent, in addition to N-methyl-2-pyrrolitone (self?ro), diethylene glycol monomethyl ether [CH30CH2CH20CH2CH20H
], N, N-dimethylacetamide [(CH3)2NC
OCH3], N,N-dimethylformamide [(CH3
)2NCOH], diethylene glycol dimethyl ether [CH30CH2CH20CH2CH20CH3], monoethanolamine [H2NCH2CH20H], butyrolactone [[2]\], etc. were experimentally confirmed to be effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic cycle of an absorption refrigerator, and FIG. 2 is a diagram of vapor pressure and temperature at various concentrations of an absorption liquid using the refrigerant of the present invention. 1 - generator, 3 - evaporator, 5 - absorber.

Claims (1)

[Scope of Claims] 1. A refrigerant for an absorption refrigerator that uses ethanol or propatool containing fluorine atoms as a refrigerant and is used in combination with an absorbent that absorbs the refrigerant in a refrigeration cycle. 2. A refrigerant for an absorption refrigerator, wherein the ethanol having a fluorine atom according to claim 1 is a compound having a boiling point of 120° C. or lower, such as trifluoroethanol, monofluoroethanol, difluoroethanol, or monochlorodifluoroethanol. 3. A refrigerant for an absorption refrigerator, wherein the fluorine atom-containing propazole according to claim 1 is a compound having a boiling point of 120° C. or lower, such as trifluoropropatol.