Refrigeration system using hydrofluorocarbon refrigerant

Abstract: A refrigerant which contains hydrofluorocarbon as a main ingredient is circulated in a circuit comprising a compressor (1), a condenser (2), and an evaporator (4). Oil (6) is stored in the compressor (1) to lubricate moving parts and to seal a compression chamber. Lubricating oil which flows out of the compressor circulates with the refrigerant but is separated from the refrigerant, being insoluble with the refrigerant at liquid phase in the circuit. The oil has low viscosity and small specific gravity.

Description: This invention relates to refrigeration devices such as a refrigerant compressor, a refrigerator and a refrigerating air conditioner, which uses a refrigerant of which a main ingredient is hydrofluorocarbon. In a conventional refrigeration unit a flon containing chlorine element (e.g. chloro-difluorocarbon CFC12) is used as a refrigerant, and mineral oils or synthesis oils, such as alkyl benzene oil, which are soluble with the refrigerant are used as a lubricating oil. Recently, however, it has been known the flon refrigerants containing chlorine element destroy the ozone layer in the atmosphere. Therefore, it is demanded that the flon containing chlorine element is replaced by a flon containing hydrogen such as hydrofluorocarbon HFC134a which will not affect the environment. One example of a conventional refrigeration unit in which the hydrofluorocarbon HFC134a is used as a refrigerant is shown in FIG. 8. As disclosed by the publication "Tribologist" vol. 35, No. 9 (1990), pp 621-626, in the case where a refrigeration unit is formed by using the hydrofluorocarbon refrigerant, namely, HFC134a refrigerant, the mutual solubility of the refrigerant and a refrigerating machine oil is one of the important factors. That is, since mineral oils or synthesis oils which are used as a lubricating oil in the conventional refrigeration device using the CFC12 refrigerant are insoluble with the HFC134a refrigerant, these mineral oils and synthesis oils have not been used in a refrigeration unit in which the HFC134a refrigerant is used. Therefore, PAG (polyoxyalkyleneglycol) or ester group refrigerating machine oil which are soluble with the HFC134a refrigerant has been employed. FIG. 8 shows a refrigeration unit which uses an HFC134a refrigerant. In FIG. 8, reference numeral 1 designates a compressor for compressing a refrigerant gas; 2, a condenser for condensing a high pressure refrigerant gas discharged from the compressor 1; 3, a capillary tube; 4, an evaporator; 5, an accumulator having a function of adjusting the amount of refrigerant; and 6, a refrigerating machine oil pooled in the compressor 1, for lubrication of the slide parts of the compressor 1 and sealing of the compressor chamber. The refrigerating machine oil 6 is PAG 6a or ester group refrigerating machine oil 6b. The behavior of the oil in the refrigeration unit will be described. The refrigerant compressed by the compressor 1 is supplied to the condenser 2. In the case of a compressor with a high pressure container, although a larger part of the lubricating oil 6, which is used for sealing the compression chamber for instance, is separated from the refrigerant, the lubricating oil 6 which is of the order of 0.5 to 1.0% by weight of the refrigerant is discharged from the compressor 1 together with the refrigerant. The lubricating oil 6 thus discharged, being soluble with the refrigerant, is high in fluidity, and is therefore returned through the condenser 2, the capillary tube 3, the evaporator 4 and the header 5 to the compressor 1. Hence, the lubricating oil 6 is present in the compressor 1 at all times; that is, the lubrication is carried out suitably at all times. Furthermore, even when the compressor 1 is not operated for a long time; that is, even when the refrigerant is held still, it can not be prevented from being foamed. The conventional refrigeration unit using HFC134a refrigerant is constructed as described above. The PAG 6a has 10 7 to 10 10 Ω·cm in volume resistivity, and about 25000 ppM in saturated water content; and the ester group refrigerating machine oil has 10 12 to 10 14 Ω·cm, and about 1500 ppM. However, they are much lower in electrical insulation and in hygroscopicity than a refrigerating machine oil used with a CFC12 refrigerant which has about 10 15 Ω·cm in volume resistivity and about 500 ppM in saturated water content. The electrical insulation greatly affects the long-range reliability of the compressor. On the other hand, it is rather difficult to suitably deal with the hygroscopicity, because in order to suitably handle the components of the compressor, or the compressor itself, the saturated water content should as less as possible. Furthermore, in assembling a refrigerator, the production suffers from a number of problems in handling the machine oil; for instance, it is necessary to shorten the period of time for which the refrigeration circulation system is open. On the other hand, when a large quantity of water gets in the refrigeration circulation system, it is tend to form sludge, or freeze the water in the circulation system so as to clog up the capillary tube, thus impairing the refrigerating action. Furthermore, if, in the conventional refrigeration unit using HFC134a refrigerant, the oil is high in hygroscopicity it will suffer from the following difficulties: That is, it is rather difficult to prevent the components of the compressor from rusting. Ice may be formed in the capillary tube and the expansion valve of the refrigeration unit, to clog up them. Hydrolysis of the ester oil is accelerated by the water content, resulting in formation of sludge. In addition, hydrolysis of a polyethylene-terephthalate material employed as an insulation material for the motor is accelerated, thus resulting in formation of sludge. In order to eliminate the above-described difficulties, in the manufacture of the refrigeration unit using HFC134a, it is necessary to remove water from the machine oil and the refrigerant circuit more carefully than the refrigeration unit using CFC12 refrigerant. That is, it is necessary to increase the water removing ability of a dryer in the refrigerant circuit. For this purpose, it is necessary to use a dryer larger in water catching capacity. On the other hand, a conventional refrigerating unit using HFC134a refrigerant is disadvantageous in the following point: When the compressor is stopped, the liquid-phase refrigerant is returned into the container of the compressor through its suction inlet. When it is started again, the lubricating oil in the compressor is led into the refrigerant circular system together with the liquid-phase refrigerant. Since the HFC134a refrigerant is low in solubility with the lubricating oil, it is difficult for the lubricating oil thus led to return into the compressor until its flow rate reaches a certain value. That is, the lubricating oil is not sufficiently supplied to the compressor, so that the latter may become out of order. SUMMARY OF THE INVENTION Accordingly, an object of this invention is to eliminate the above-described difficulties. More specifically, an object of the invention is to provide a refrigeration device which is operated satisfactorily with the oil applied to the electric motor provided for the compressor, the oil impregnated into the sintered components, and the oil used in assembling the compressor improved in hygroscopicity, and which is high in electrical insulation; a refrigeration device in which low temperature fluidity is established for the oil in the evaporator and the header, and the oil film formed on the inner wall of the evaporator is small in thickness, thus preventing the reduction in heat-exchange efficiency; and a refrigeration device which is excellent in electrical insulation and in hygroscopicity, and in which the refrigerating machine oil is smoothly and positively returned to the compressor so that the refrigeration device is high in reliability. EP-A-0 485 979 and WO-A-90 05172 both teach that a lubricating oil which is insoluble with the refrigerant should not be used. The present invention provides a refrigeration system comprising: a refrigerating circuit in which a compressor, a condenser, and an evaporator are connected by pipes; a refrigerant, which contains hydrofluorocarbon as a main ingredient, being circulated in the refrigerating circuit; a lubricating oil being contained in the compressor to lubricate movable members of the compressor and to seal a compression chamber of the compressor; and the lubricating oil circulating with the refrigerant in the refrigerating circuit if the oil flows out of the compressor to the refrigerating circuit; characterised in that the lubricating oil is insoluble with the refrigerant at liquid phase in the refrigerating circuit so that the oil is separated from the refrigerant, the lubricating oil is low in viscosity, the oil being 2000 cSt or less in viscosity at the evaporation temperature of the system or being 200 cSt or less in viscosity at operating ambient temperature of the system or being of the order of 10 to 22 cSt at 40°C, and the lubricating oil has a smaller specific gravity than the refrigerant at liquid phase. Preferably, alkyl benzene or poly-α-olefin oil is employed as the lubricating oil, which is applied to parts of the compressor and used in assembling the compressor. Furthermore, a compressor of high pressure container type may be employed. Furthermore, a mechanism for preventing a back flow from the compressor to the evaporator may be provided. In assembling the refrigerant compressor the control of water content can be achieved similarly as in the case of the conventional CFC 12 refrigerant compressor. The refrigeration system of the present invention is excellent in electrical insulation and in hygroscopicity. The oil returns smoothly to the compressor. Its viscosity is such that it has sufficient fluidity to return to the compressor within a predetermined time period even if much oil flows out and such that only a thin film of oil is formed on the inner wall of the evaporator. In a refrigerating air condition in accordance with the invention, the oil employed is improved in volume resistivity and is less in hygroscopicity when compared with the ester oil or PAG oil. Therefore, the refrigerating air conditioner is equivalent to the conventional one using a CFC12 refrigerant in the control of water content when assembled. With the refrigerating air conditioner, in assembling the compressor the control of water content can be performed similarly as in the case of the conventional CFC12 refrigerant compressor. Furthermore, in the refrigerating air conditioner, low temperature fluidity is established for the oil in the evaporator and the header, and the oil film formed on the inner wall of the evaporator is small in thickness, which prevents a reduction in heat-exchange efficiency. Thus, its cooling capacity is substantially equal to that provided when an oil soluble in the refrigerant is used. With the refrigerating air conditioner of the invention, the quantity of refrigerant can be reduced as much as 10% to 20% by weight of the quantity of oil sealed in it when compared with that provided when an oil soluble in the refrigerant is used. Furthermore, in the refrigerating air conditioner of the invention, the refrigerating machine oil is positively returned to the compressor without being detained in the header, and an excess of refrigerant can be saved depending on the conditions of the refrigeration load. In the refrigerating air conditioner, a difficulty is eliminated that, when the compressor is stopped, the gas leaks from the high pressure side to reach the header and the evaporator through the suction pipe to increase the temperature of the latter. This contributes to a reduction of the power consumption. In the refrigerating air conditioner, the capillary tube is prevented from being clogged up by the oil. Thus, the refrigerating air conditioner is high in reliability. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the arrangement of a refrigeration unit using a refrigerant compressor, which constitutes one embodiment of this invention. FIG. 2 is a graphical representation indicating viscosities of a hard alkyl benzene oil with attainable temperatures of an evaporator. FIG. 3 is a diagram showing an refrigeration circuit in a refrigerator, which constitutes another embodiment of the invention. FIG. 4 is a diagram showing a part of the refrigeration circuit in the refrigeration in more detail. FIG. 5 is a diagram showing the arrangement of a refrigerating air conditioner, which constitutes another embodiment of the invention. FIG. 6 is a graphical representation indicating oil return times of the refrigerating air conditioner with oil viscosities at an operating ambient temperature thereof. FIG. 7 is a graphical representation indicating refrigeration chamber temperatures of a refrigerating air conditioner, which constitutes another embodiment of the invention, with oil viscosities at an evaporation temperature thereof. FIG. 8 is a diagram showing the arrangement of a refrigeration unit using a conventional refrigerant compressor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of this invention will be described with reference to FIG. 1. In FIG. 1, reference numeral 11 designates a closed container; 12, an electric motor driving a rotary compressor 1; and 13, an insulated wire in the motor 12. A hard alkyl benzene oil applied to improve the slidability of the wire, thereby to achieve the wire winding operation with higher efficiency. A cylinder 16 forming the compressor chamber, and sintered components such as bearings 17 are impregnated with the hard alkyl benzene oil. In assembling the slide parts of the compressor, the hard alkyl benzene oil is applied. In a refrigeration unit using an HFC134a refrigerant as shown in FIG. 1, the aforementioned hard alkyl benzene oil is employed as the refrigerating machine oil 6 in the compressor 1. In the refrigerant compressor 1 constructed as described above, the hard alkyl benzene oil is employed as a coating oil, impregnating oil, and assembling oil, for the components. The alkyl benzene oil is low in hygroscopicity. Therefore, the components of the compressor can be handled similarly as in the case of those of the conventional compressor using CFC12 refrigerant. Further, the hard alkyl benzene oil employed as the refrigerating machine oil is high in electrical insulation (10 15 to 10 16 Ω·cm in volume resistivity). Therefore, countermeasures against the electric leakage may be the same as in the compressor using CFC12 refrigerant. Furthermore, in the refrigeration unit using HFC134a refrigerant as shown in FIG. 1, a hard alkyl benzene oil low in viscosity (hereinafter referred to as "a low viscosity hard alkyl benzene oil", when applicable) can be employed as the lubricating oil of the compressor 1. The low viscosity hard alkyl benzene oil is lower in viscosity than a hard alkyl benzene oil employed, as lubricating oil, in a conventional CFC12 refrigerant compressor. Heretofore, a refrigeration unit such as a refrigerator equipped with a rotary compressor employs a lubricating oil which is around 31 cSt in viscosity at a temperature of 40°C; however, in the evaporator 4, the lubricating oil is of the order of 1000 to 5000 cSt with the solubility of the refrigerant taken into account. Hence, in order to allow a low viscosity hard alkyl benzene oil in which the HFC134a refrigerant is insoluble to have the same viscosity in the evaporator, the viscosity should be of the order of 10 to 22 cSt at a temperature of 40°C. In the case where, as was described above, the lubricating oil in the evaporator 4 is held the same in viscosity, the fluidity and the thickness of the oil film on the inner wall of the evaporator can be substantially the same as those in the conventional case where the CFC12 refrigerant is employed. FIG. 2 shows relationships between the viscosity of the hard alkyl benzene oil at a temperature of 40°C and the attainable temperature of the evaporator 4 provided when the compressor of the refrigeration device is operated continuously. With the oil 10 cSt in viscosity at a temperature of 40°C, the attainable temperature is substantially equal to that in the case of the ester oil 32 cSt at a temperature of 40°C; that is, the cooling capacity is sufficiently high. On the other hand, the viscosity of the oil at the slide parts inside the compressor 1 depends whether or not the oil is soluble in the refrigerant. However, the solubility of the CFC12 refrigerant in the oil at the slide parts inside the compressor 1 is substantially equal to the solubility of the CFC12 refrigerant in the evaporator 4. Hence, when the above-described low viscosity oil is used in the atmosphere of HFC134a refrigerant, then even at the slide parts the viscosity and the lubrication can be substantially equal to those in the case of the lubrication oil 6c in the CFC12 refrigerant compressor. It should be noted that usage of the low viscosity hard alkyl benzene oil will not adversely affect the assembling work at all. In FIGS. 3 and 4, reference numeral 1 designates a compressor for compressing a refrigerant gas; 2, a condenser for condensing a high pressure refrigerant gas discharged from the compressor 1; 3, a capillary tube; 4, an evaporator; 5, an accumulator as a refrigerant pool having a function of adjusting the amount of refrigerant; and 6, a lubricating oil which is held in the compressor 1, lubricating slide parts of the latter and sealing the compression chamber. The lubricating oil is a hard alkyl benzene oil 6a which is insoluble with an HFC134a refrigerant. The upper end portion of the accumulator 5 is connected to the outlet of the evaporator 4, and the lower end portion is connected to the suction side of the compressor 1, the suction pipe 7 of which is inserted into the accumulator 5 in such a manner that it is extended upwardly. The suction pipe 7 has an oil return hole 8 in its side wall. More specifically, the hole 8 is formed in the side wall of the upper portion of the suction pipe 7. Since the hard alkyl benzene oil is insoluble with the HFC134a refrigerant and has a smaller specific gravity than the HFC134a refrigerant, the HFC134a refrigerant is detained in the lower part of the accumulator 5 while the hard alkyl benzene oil is detained upper part of the accumulator 5. Therefore, the oil detained at the upper portion is returned to compressor 1 by the oil return hole 8 which is formed at the side wall of the suction pipe 7 which is inserted into the accumulator 5 form below. Accordingly, it can be prevented the oil in the compressor from decreasing due to detaining much of the oil in the accumulator 5. In the conventional refrigeration device as shown in FIG. 8, the lower end portion of the accumulator 5 is connected to the outlet of the evaporator 4, and the upper end portion is connected to the suction side of the compressor 1, and the pipe inserted into the accumulator from below forms a refrigerant pooling section. Therefore, in the case of an ester oil soluble in the HFC134a refrigerant being employed, the ester oil is dissolved in the refrigerant, and therefore it is not detained in the accumulator 5; that is, it is returned to the compressor 1; and in the case of the hard alkyl benzene oil insoluble in the HFC134a refrigerant being employed, the hard alkyl benzene oil is detained in the accumulator 5, so the quantity of oil in the compressor 1 is decreased as much, whereby the slide parts in the compressor are not sufficiently lubricated, and the compression chamber is not sufficiently sealed. On the other hand, in the embodiment, as was described above, the upper end portion of the accumulator 5 is connected to the outlet of the evaporator 4, and the lower end portion is connected to the suction side of the compressor 1, and the oil return hole 8 is formed in the side wall of the suction pipe 7 which is inserted into the accumulator 5 from below. Hence, even if the oil not dissolved in the refrigerant, the oil is returned to the compressor 1; that is, it will never be detained in the accumulator 5. As was described above, the oil return hole 8 is formed in the upper portion of the pipe 7. Therefore, the oil, being smaller in specific gravity than the HFC134a refrigerant, returns to the compressor 1. And in the accumulator 5, the refrigerant is collected below the oil return hole 8. Thus, the function of adjusting the variation in load of the refrigerator is performed satisfactorily; that is, the cooling operation is suitably achieved with high efficiency. The alkyl benzene oil is not soluble in the HFC134a refrigerant, and therefore the quantity of refrigerant is less both in absolute value and in the rate of change which is dissolved in the oil 6 in the compressor 1 when the ambient temperature or the load condition of the refrigerator changes. This results in the following advantages: The accumulator 5 for adjusting the quantity of refrigerant can be miniaturized. The difficulty is eliminated that the cooling operation is not suitably carried out because of an improper quantity of refrigerant. That is, the refrigeration unit operates with high efficiency. In the case where a high pressure container type rotary compressor is employed, the quantity of refrigerant in it can be reduced by 10% to 20% of the quantity of oil therein. In the above-described embodiments, the HFC134a refrigerant and the hard alkyl benzene oil are employed. However, the same effects can be obtained by using any other combination of refrigerant and oil which are not soluble with each other. A second embodiment of the invention will be described. In the second embodiment, a hard alkyl benzene oil is employed as a refrigerating machine oil. It has been confirmed through experiments that, in the case where an oil is used for a refrigerator which is smaller than 200 cSt in viscosity at an operating ambient temperature and is soluble in a given refrigerant, it will return to the compressor even when it flows out excessively to close the capillary tube of the refrigerator. FIG. 5 shows an experiment apparatus used for investigation of the above-described fact, and FIG. 6 indicates the results of investigation. In the apparatus shown in FIG. 5, an oil pool 19 is provided on the high pressure side of the refrigerant circuit of a refrigeration device, and the oil is removed from its compressor 1, and an HFC134a refrigerant 18 is held in the latter 1. Under this condition, the compressor 1 is started, for investigation of the behavior of the oil. When the compressor is started in this way, the refrigerant 18 is compressed, and the discharge pressure is gradually increased. However, as is apparent from FIG. 6, as the oil viscosity increases and the ambient temperature decreases, the rate of return of the oil to the compressor 1 is decreased. As is seen from FIG. 6, when the oil viscosity is more than 200 cSt at a given ambient temperature, the oil, clogging up the capillary tube 3, will not return for at least 240 minutes. In the case where the oil viscosity is smaller than 200 cSt, then the oil will returned in several tens of minutes; that is, the oil will not clog up the capillary tube. Hence, by setting the oil viscosity to less than 200 cSt at an operating ambient temperature, a refrigeration unit can be formed in which the oil is positively returned to the compressor even under ultimate conditions. In the case where a refrigeration unit employs an oil whose viscosity is smaller than 2000 cSt at an evaporation temperature thereof, its cooling performance is equivalent to that in the case where it employs an oil soluble in the refrigerant. FIG. 7 indicates relationships between oil viscosity and cooling performance in the case where a refrigerator is operated continuously. As is apparent from FIG. 7, in the case where the oil viscosity is smaller than 2000 cSt at the evaporation temperature, the ultimate temperature can be obtained which is substantially equal to that which is obtained when the ester oil is used. In the invention, the oil is not soluble in the refrigerant. Therefore, in the case where a high pressure container type compressor is employed, the phenomenon scarcely takes place that the refrigerant becomes larger or smaller in quantity than required because the quantity of refrigerant dissolved in the oil 6 in the compressor 1 changes with the ambient temperature. For the same reason, the quantity of refrigerant to be used can be reduced as much as it is not soluble in the oil 6. More specifically, in the refrigeration unit, the quantity of refrigerant corresponding to 10% to 20% by weight of the quantity of oil can be reduced when compared with the case where an oil soluble in the refrigerant is used. In Fig. 3, reference numeral 20 designates a check valve, which is set between the compressor 1 and the evaporator 4. The refrigerant is separate from the refrigerant oil, and its viscosity is lower than the viscosity of the solution formed by dissolution of the refrigerant and the oil. Therefore, when the compressor 1 is stopped, the refrigerant flows well, as a result of which the refrigerant is increased in quantity which tends to flow back to the evaporator 4 through the gap of the slide parts of the compressor 1, so that the temperature of the evaporator 4 is increased, and the power consumption of the refrigeration unit is increased. In order to eliminate this difficulty, the check valve 20 is provided between the compressor 1 and the evaporator 4, to prevent the back flow of the refrigerant thereby to prevent the temperature rise of the evaporator. The check valve 20 may be replaced by a back-flow preventing mechanism having the same function. In the above-described embodiment, the hard alkyl benzene oil is employed as the refrigerator oil 6. However, the same effects can be obtained by using one or some of the refrigerator oils such as a soft alkyl benzene oil, poly-α-olefin, paraffin mineral oil, and naphthene mineral oil, which are excellent in low temperature fluidity. The above-described refrigerator oils may be used satisfactorily as they are, without additives. However, their characteristics such as wear resistance, load resistance and thermal stability may be improved by adding one or some of the additives such as an oxidation inhibitor, extreme pressure additive, wear preventing agent, thermal stability improving agent, and deforming agent. The oxidation inhibitor is of a hinderd phenol group, amine group, or sulfur group. Examples of the oxidation inhibitor are 2, 6-di-t-butyl-4-methylphenol; 4, 4'-methylenebis (2, 6-di-t-butylphenol); 2, 2'-thio-bis (4-methyl-6-t-butylphenol); trimethyl hydroquinone; p, p'-diactyl-diphenylamine; 3, 7-diactylphenthiazine; alkylphenothiazine-1-carboxylate; phenyl-2-naphthylamin; 2, 6-di-t-butyl-2-dimethyl-p--cresol; 5-ethyl-10, 10'-diphenylphenazaline, and alkyl disulfide, each of which is used as much as 0.2 to 5% by weight. Examples of the extreme pressure additive and the wear preventing agent are ester phosphate, ester phosphite, alkyl- or aryl-phosphorothionate, halogeno-hydrocarbon, halogenated carbonic acid, dialkyl- or diaryl-dithiophosphate metallic acid, dialkyldithiocalbamic acid metallic salt, and oil-soluble molybdenum sulfide containing compound, each of which is used as much as 1 to 30% by weight. An example of the thermal stability improving agent is an epoxy compound, which is used as much as 0.2 to 5% by weight. Examples of the deforming agent are dimethyl polysiloxane, and carboxylic metal salt, each of which is used as much as 0.001 to 0.1% by weight. In the refrigerant compressor using an HFC134a refrigerant, according to the present invention, an oil applied to components of the compressor and used in assembling the compressor is insoluble in the refrigerant. Therefore, the refrigerant compressor can be readily assembled, and the components can be also readily handled. Further, the refrigerating machine oil is employed for the compressor which is insoluble in the refrigerant. Hence, the refrigeration unit is high in electrical insulation. Furthermore, alkyl benzene or poly-α-olefin oil is employed as the oil which is applied to the parts of the compressor, and used in assembling the latter. Therefore, the compressor can be readily assembled, and the components can be handled with ease. The oil employed is less in hygroscopicity than the ester oil or PAG oil. Thus, the control of water content can be achieved similarly as in the case of the conventional refrigerating air conditioner using a CFC12 refrigerant. In the refrigeration device, the refrigerating machine oil is employed which is 2000 cSt or less in viscosity at an evaporation temperature of the refrigeration device. Hence, low temperature fluidity is established for the oil in the evaporator, and the oil film formed on the inner wall of the evaporator is small in thickness, which prevents a reduction in heat-exchange efficiency. Thus, its cooling capacity is substantially equal to that provided when an oil soluble in the refrigerant is used. Since the refrigeration device employs the compressor of high pressure container type, the quantity of refrigerant can be reduced as much as 10 to 20% by weight of the quantity of oil sealed in it when compared with that provided when an oil soluble in the refrigerant is used. In the refrigeration device, the refrigerant is allowed to flow downwardly in the header, and the end portion of the lower piper is inserted into the header. Therefore, the refrigerating machine oil is positively returned to the compressor without being excessively detained in the header, and an excess of refrigerant can be saved depending on the conditions of the refrigeration load. In the refrigeration device, the mechanism for preventing the back flow from the compressor to the evaporator is provided between the compressor and the evaporator. Hence, the difficulty is eliminated that, when the compressor is stopped, the gas leaks from the high pressure side to reach the header and the evaporator through the suction pipe to raise the temperature of the latter. This will contribute to a reduction of the power consumption. In the refrigeration device, the refrigerating machine oil is employed which is 200 cSt or less in viscosity at an operating ambient temperature of the refrigerating air conditioner. Hence, the capillary tube is prevented from being clogged up by the oil. Thus, the refrigerating air conditioner is high in reliability.

Claims: A refrigeration system comprising: a refrigerating circuit in which a compressor (1), a condenser (2), and an evaporator (4) are connected by pipes; a refrigerant, which contains hydrofluorocarbon as a main ingredient, being circulated in the refrigerating circuit; a lubricating oil (6) being contained in the compressor (1) to lubricate movable members of the compressor and to seal a compression chamber of the compressor; and the lubricating oil circulating with the refrigerant in the refrigerating circuit if the oil flows out of the compressor to the refrigerating circuit; characterised in that the lubricating oil is insoluble with the refrigerant at liquid phase in the refrigerating circuit so that the oil is separated from the refrigerant, the lubricating oil is low in viscosity, the oil being 2000 cSt or less in viscosity at the evaporation temperature of the system or being 200 cSt or less in viscosity at operating ambient temperature of the system or being of the order of 10 to 22 cSt at 40°C, and the lubricating oil has a smaller specific gravity than the refrigerant at liquid phase. A refrigeration system as claimed in claim 1, in which a driving means (12) for driving the compressor (1) is provided in the housing (11) of the compressor. A refrigeration system as claimed in claim 1 or 2, in which the compressor (1) is a rotary compressor. A refrigeration system as claimed in any of claims 1 to 3, in which the lubricating oil is alkyl benzene oil or poly-α-olefin oil.

Inventors: KAWAGUCHI SUSUMU, KONISHI HIROSHIGE, MARUYAMA HITOSHI, MASUDA NOBORU, OGASAWARA SHINOBU, SHIMIZU TATSUAKI, SUMIDA YOSHIHIRO, TOYAMA SATORU, KAWAGUCHI, SUSUMU, KONISHI, HIROSHIGE, MARUYAMA, HITOSHI, MASUDA, NOBORU, OGASAWARA, SHINOBU, SHIMIZU, TATSUAKI, SUMIDA, YOSHIHIRO, TOYAMA, SATORU, KAWAGUCHI, SUSUMU, C/O MITSUBISHI DENKI K.K., KONISHI, HIROSHIGE, C/O MITSUBISHI DENKI K.K., MARUYAMA, HITOSHI, C/O MITSUBISHI DENKI K.K., MASUDA, NOBORU, C/O MITSUBISHI DENKI K.K., OGASAWARA, SHINOBU, C/O MITSUBISHI DENKI K.K., SHIMIZU, TATSUAKI, C/O MITSUBISHI DENKI K.K., SUMIDA, YOSHIHIRO, C/O MITSUBISHI DENKI K.K., Toyama, Satoru, c/o Mitsubishi Denki K.K.
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1992
Main classification: F25B31
IPC codes: C10M171, F25B31, F25B43, F04B39