JP4953116B2 - Lubricating oil for compressor of cooling or heating equipment using carbon dioxide as working fluid - Google Patents

Description

  The present invention relates to a lubricating oil for a compressor of an apparatus that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle.

  A cooling and heating device using a refrigeration cycle (heat pump cycle) based on a Carnot reverse cycle includes a compressor, a gas cooler, an expander, and an evaporator. After the working fluid is adiabatically compressed by the compressor, the gas cooler Condensed and dissipated, the fluid to be heated (air or water) is heated with this heat. Next, the working fluid adiabatically expands in the expander, then evaporates in the evaporator, absorbs the heat necessary for this evaporation from the fluid to be cooled, and again goes to the compressor to perform adiabatic compression, isothermal heat dissipation, heat insulation. Repeat expansion and isothermal endotherm.

  As the working fluid of the refrigeration cycle, hydrofluorocarbons and the like have been conventionally used instead of chlorofluorocarbons and hydrochlorofluorocarbons from the viewpoint of protecting the ozone layer. Hydrofluorocarbons are also a cause of global warming. For this reason, in recent years, natural fluids such as hydrocarbons, ammonia, carbon dioxide and the like have attracted attention as working fluids to replace them. Of these, hydrocarbons have flammability problems and ammonia has odor and toxicity problems, while carbon dioxide has no such problems, and is expected as a particularly promising working fluid.

  However, when carbon dioxide is used as a working fluid, carbon dioxide reaches 353 to 413 K and 10 to 20 MPa in the adiabatic compression process, and is in a so-called supercritical state. Since carbon dioxide in the supercritical state has a high ability to dissolve substances and the lubricating oil of the compressor is easily dissolved in carbon dioxide passing through the compressor, the carbon dioxide in which the lubricating oil is dissolved may circulate as a working fluid. . In this case, there is a possibility that the lubricating oil dissolved in carbon dioxide may condense during cooling, and heat exchange performance may be reduced due to the retention of the lubricating oil in the gas cooler and the evaporator.

For example, Patent Documents 1 and 2 listed below relate to a lubricating oil suitable for a compressor of a refrigeration cycle (heat pump cycle) using carbon dioxide as a working fluid.
In Patent Document 1, a 10% distillation point by a gas chromatographic distillation method is 400 ° C. or more, an 80% distillation point is 600 ° C. or less, a kinematic viscosity at 100 ° C. is ² to 30 mm ² / s, and a viscosity index is 100 or more. It is described that a lubricating oil composition mainly composed of a certain lubricating base oil is suitable. Specific examples include those containing polyalphaolefin or polyalkylene glycol as the main component. The polyalkylene glycol represented by _{CH 3 (PO) m (EO} ) n CH 3, are mentioned those wherein m / n = 8/2.

Patent Document 2 describes that any one or mixed oil of poly-α-olefin, paraffinic mineral oil, naphthenic mineral oil, or alkylbenzene, which is incompatible with the carbon dioxide working fluid, is suitable.
In addition, as a lubricant for a compressor when the working fluid is hydrofluorocarbon, for example, a main component of a polyalkylene glycol represented by the following formula (2) (“SUNICE P” manufactured by Nippon San Oil Co., Ltd.) -56 (product name) ").

JP 2001-294886 A JP 2003-336916 A

However, the lubricating oils described in Patent Documents 1 and 2 have room for further improvement as a lubricating oil for a compressor of a refrigeration cycle (heat pump cycle) using carbon dioxide as a working fluid.
The present invention is suitable as a lubricating oil for a compressor of a refrigeration cycle (heat pump cycle) using carbon dioxide as a working fluid. “It is difficult to dissolve in carbon dioxide in a supercritical state, and temperature dependency and pressure dependency of density and kinematic viscosity. It is an object of the present invention to provide a device that cools in a refrigeration cycle or heats in a heat pump cycle, which can operate satisfactorily without deteriorating the lubrication characteristics of the compressor by specifying a low-performance lubricant.

The present invention is a lubricating oil for a compressor of a device that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle. (1) For a compressor of a cooling or heating apparatus characterized by containing, as a main component , polyethylene glycol , polyethylene glycol monomethyl ether, and polyethylene glycol dimethyl ether represented by the formula, wherein n = 4 to 6 Provide lubricating oil.

Examples of the polyethylene glycol represented by the formula (1) and n = 4 to 13 and derivatives thereof include those shown in Table 1 and Table 2 below.
Since these substances are difficult to dissolve in carbon dioxide in the supercritical state and the temperature and pressure dependence of density and kinematic viscosity are small, lubrication for compressors in refrigeration cycles (heat pump cycles) using carbon dioxide as the working fluid Suitable as the main component of oil. One of these substances may be used as the main component, or a mixture of two or more types may be used as the main component.
Even in the case of polyethylene glycol represented by the above formula (1) and derivatives thereof, compounds having n of 14 or more are remarkably high in viscosity or solid at the operating temperature of the cooling or heating device described above. There is a risk that the performance required for the lubricating oil may not be obtained, or the lubricating oil may remain in the working fluid circulation path.

Among these, those containing tetraethylene glycol or a derivative thereof where n = 4 as a main component are preferable, and those containing tetraethylene glycol as a main component are particularly preferable.
The present invention also provides a lubricating oil for a compressor of a device that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle. represented by the (1 ') wherein the polyethylene glycol is n =. 4 to 6, to provide a compressor lubricating oil cooling or heating device, characterized in that it contains as a main component.

R3 and R4 are hydrogen, a methyl group, or an oleyl group, and may be the same as or different from each other.
Even in the case of polyethylene glycol represented by the above formula (1 ′) and derivatives thereof, a compound having n of 14 or more has a significantly high viscosity or a solid at the operating temperature of the cooling or heating device described above. There is a possibility that the performance required as the lubricating oil may not be obtained, or the lubricating oil may stay in the circulation path of the working fluid.

Usually, the lubricating oil for compressors contains an antioxidant, an extreme pressure agent, and a stabilizer as additives in addition to the main components.
Examples of the antioxidant added to the lubricating oil for compressors of the present invention include 2,6-di-tertiary butylphenol, 2,6-di-tertiary butylhydroxytoluene, 2,6-phenol, which are phenolic antioxidants. Examples include di-tertiary butyl-4-ethylphenol, 2,2′-methylene bis (4-methyl-6-tertiary butyl phenol), 2,2′-methylene bis (4-ethyl-6-tertiary butyl phenol), and the like. .

Examples of the extreme pressure agent added to the compressor lubricating oil of the present invention include a phosphate ester extreme pressure agent and a phosphite ester extreme pressure agent.
Examples of the phosphate ester extreme pressure agent include triphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, triethylphenyl phosphate, trialkyl (C = 1 to 10) phosphate, and the like.

  Phosphite extreme pressure agents include dipentyl phosphite, tridipentyl phosphite, dihexyl phosphite, trihexyl phosphite, dioctyl phosphite, trioctyl phosphite, dinonyl phosphite, trinonyl phosphite, dioleyl Examples thereof include phosphite, trioleyl phosphite, dicresyl phosphite, tricresyl phosphite and the like.

Examples of the stabilizer added to the compressor lubricating oil of the present invention include an epoxy compound and a carbodiimide compound.
Epoxy compounds include pentyl glycidyl ether, hexyl glycidyl ether, 2-ethylhexyl glycidyl ether, decyl glycidyl ether, phenyl glycidyl ether, cresyl glycidyl ether, neopentyl glycol glycidyl ether, 1,6-hexanediol glycidyl ether, glycerin triglycidyl Ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, pentanoic acid glycidyl ester, hexanoic acid glycidyl ester, 2-ethylhexanoic acid glycidyl ester, neodecanoic acid glycidyl ester, Benzoic acid glycidyl ester etc. It is.
As the carbodiimide compound, N, N′-diphenylcarbodiimide, N, N′-ditoluylcarbodiimide, N, N′-dixylenylcarbodiimide, N, N′-di (2,6-tertiarybutylphenyl) carbodiimide, N, N′-dialkylcarbodiimide and the like can be mentioned.

The present invention is also a compressor of an apparatus that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle. Provided is a compressor characterized by being lubricated with a machine lubricant.
The present invention is also an apparatus that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle. Provided is a cooling or heating device characterized in that the compressor is lubricated with oil.

According to the present invention, it is suitable as a lubricating oil for a compressor of a refrigeration cycle (heat pump cycle) using carbon dioxide as a working fluid, “it is difficult to dissolve in carbon dioxide in a supercritical state, and the temperature dependence of density and kinematic viscosity and Lubricants with low pressure dependency are provided.
Moreover, the lubrication characteristic of a compressor becomes favorable by using this lubricating oil. Accordingly, a device that cools in the refrigeration cycle or a device that heats in the heat pump cycle can operate well without impairing the lubrication characteristics of the compressor.

Hereinafter, embodiments of the present invention will be described.
FIG. 1 is a schematic configuration diagram showing a cooling and heating apparatus corresponding to an embodiment of the present invention.
This apparatus is a cooling and heating apparatus using a refrigeration cycle and a heat pump cycle, and includes a compressor 1, a gas cooler 2, a heat exchange unit 3, an expansion valve (expander) 4, an evaporator 5, an oil separator 6, and heat exchange. Part 7 is provided. Also, a working fluid pipe 12 connecting the compressor 1 and the gas cooler 2, a working fluid pipe 25 connecting the gas cooler 2 and the evaporator 5, a working fluid pipe 56 connecting the evaporator 5 and the oil separator 6, and oil separation The working fluid piping 61 which connects the container 6 and the compressor 1 is provided. Furthermore, an oil recovery pipe 8 that connects the working fluid pipe 61 and the oil separator 6 is provided.

The heat exchanging unit 3 includes a portion 25a in which the working fluid piping 25 is formed in a coil shape, and a blower fan 31 installed in the vicinity of the coiled portion 25a. The heat exchanging unit 7 includes a portion 61a in which the working fluid piping 61 is formed in a coil shape, and a blower fan 71 installed in the vicinity of the coiled portion 61a.
Carbon dioxide was used as the working fluid, and the lubricating oil for the compressor 1 was mainly composed of tetraethylene glycol.

In this cooling and heating apparatus, after the working fluid is adiabatically compressed by the compressor 1, the working fluid is condensed from the working fluid pipe 12 toward the gas cooler 2 and radiated. The working fluid exiting from the gas cooler 2 to the working fluid piping 25 heats the air around the coiled portion 25a. The heated air is supplied to the outside of the heat exchange unit 3 by the rotation of the blower fan 31.
Next, the working fluid is adiabatically expanded by the expansion valve 4, evaporates toward the evaporator 5, and enters the working fluid pipe 61 through the oil separator 6. The heat necessary for this evaporation is absorbed from the air around the coiled portion 61a. The air cooled by the heat absorption is supplied to the outside of the heat exchanging unit 7 by the rotation of the blower fan 71. The working fluid in the working fluid piping 61 is again directed to the compressor 1 and repeats adiabatic compression, isothermal heat dissipation, adiabatic expansion, and isothermal heat absorption.

  Since the lubricating oil of the compressor 1 is dissolved in the carbon dioxide that has become a supercritical state in the adiabatic compression process, the carbon dioxide in a state in which the lubricating oil is dissolved enters the working fluid pipe 12 from the compressor 1, and this “lubricating oil” + Carbon dioxide "circulates through the working fluid piping 12, 25, 56, 61. Then, when this “lubricating oil + carbon dioxide” enters the oil separator 6 from the working fluid piping 56, the carbon dioxide and the lubricating oil are separated due to the difference in density, and the gaseous carbon dioxide rises and the working fluid piping 61. The lubricating oil accumulates at the bottom of the oil separator 6. Lubricating oil that has traveled to the working fluid piping 61 together with carbon dioxide is recovered by the oil recovery piping 8 in the lower portion (oil sump) of the oil separator 6.

  In this cooling and heating apparatus, a lubricating oil mainly composed of tetraethylene glycol is used as a lubricating oil for the compressor 1. Tetraethylene glycol is difficult to dissolve in carbon dioxide in a supercritical state, and has little temperature and pressure dependence of density and kinematic viscosity. Therefore, it is considered that this cooling and heating device can operate satisfactorily without impairing the lubrication characteristics of the compressor 1.

In addition, although this cooling heating apparatus is provided with the coil-shaped parts 25a and 61a as an internal heat exchanger, these internal heat exchangers may or may not be provided depending on the situation.
It was confirmed by the following method that the lubricating oil mainly composed of tetraethylene glycol was suitable as the lubricating oil for the compressor 1 of this cooling and heating apparatus.
In this method, the apparatus shown in FIG. 2 was used. This apparatus is capable of simultaneously examining the kinematic viscosity, liquid phase density, and carbon dioxide content of “carbon dioxide + lubricating oil” at high temperature and high pressure.

The apparatus shown in FIG. 2 includes an air thermostat 104 in which an equilibrium cell 109, a density meter 111, a viscometer 112, and the like are arranged, and an introduction unit that introduces carbon dioxide and lubricating oil into the equilibrium cell 109 in the air thermostat 104. And a carbon dioxide content measuring unit arranged outside the air thermostat 104.
The introduction unit includes a carbon dioxide cylinder 101, a high-pressure injector 102, a high-performance liquid chromatograph pump 103, and pipes 121, 122, and 123. The pipe 121 directs the carbon dioxide gas from the carbon dioxide cylinder 101 to the high-pressure injector 102. The high-pressure injector 102 includes a rotary handle 102a. The piping 122 directs the liquid carbon dioxide from the high pressure injector 102 to the equilibrium cell 109. The pipe 123 directs the lubricating oils 91 and 92 that have entered the high-performance liquid chromatograph pump 103 to the equilibrium cell 109.

An on-off valve 121 a is attached to the pipe 121, and an on-off valve 122 a is attached to the pipe 122. The on-off valve 122 a of the pipe 122 is attached to a position outside the air thermostat 104. A pressure sensor 105 is attached at a position inside the air thermostat 104 of the pipe 122.
The equilibrium cell 109 installed in the air thermostat 104 is made of SUS316, has a pressure resistant window, has a volume of 500 cm ³ , and can withstand a pressure of 25 MPa at 423K. A platinum resistor 106 and a heater 107 for temperature measurement are attached to the equilibrium cell 109. In addition, a stirrer 108 that stirs the liquid phase part of the equilibrium cell 109 and a thermometer 119 that measures the temperature of the liquid phase part are provided.

A gas-phase circulation path is formed in the air thermostat 104 by the pipes 131 and 132 and the circulation pump 110A. The pipe 131 extends from the gas phase part of the equilibrium cell 109 to the liquid phase part, but the lower end of the pipe 132 exists in the gas phase part of the equilibrium cell 109.
In the air thermostat 104, a liquid phase circulation path is formed by a density meter 111, a viscometer 112, a sampling cylinder 113, pipes 133 to 137, and a circulation pump 110B. The liquid in the equilibrium cell 109 is moved in the order of the pipe 137, the pipe 136, the density meter 111, the pipe 135, the viscometer 112, the pipe 134, the sampling cylinder 113, and the pipe 133 by the operation of the circulation pump 110B. Return to the inner liquid phase.

The density meter 111 is a high pressure vibrating tube density meter “512P” manufactured by Anton Paar. The sampling cylinder 113 is a portable cylinder “304L-HDF2-40” made by Swagelok having a volume of about 40 cm ³ .
The viscometer 112 is a dynamic viscometer “SPC-501” manufactured by Cambridge Applied System. This kinematic viscometer is provided with an electromagnetic piston that moves in a direction perpendicular to the flow path, and determines the kinematic viscosity by measuring the period when the piston reciprocates once. Here, the standard viscosity liquid “S60” manufactured by Cannon Instrument was used for calibration of the viscometer, and the relationship between the cycle and the kinematic viscosity was determined from 6.9 to 16.1 mm ² / s at 344.3 to 377.6K. Obtained.

The carbon dioxide content measuring unit is equipped with a sampling cylinder 113 that is removed from the liquid-phase circulation path of the air thermostat 104, a container 141 that releases the gas in the sampling cylinder 113, a metering valve 114, and an air A sealed container 116, a wet integrating flow meter 115, and pipes 142 and 143 are provided. The pipe 142 once extends upward from the container 141, then bends sideways, and further bends downward toward the sealed container 116 and extends to the lower part in the sealed container 16. The pipe 143 extends upward from the upper part in the sealed container 116 and is connected to the wet integrating flow meter 115.
The wet integrated flow meter 115 is an integrated flow meter “W-NK-05” made by Shinagawa with a resolution of 0.1 cm ³ . Further, as an apparatus for measuring the mass of the sampling cylinder 113, an EXACT direct balance “AV1581” having a minimum sensitivity of 0.1 mg was prepared.

The apparatus of FIG. 2 is operated and used in the following procedure.
First, after the inside of the equilibrium cell 109 is deaerated with a vacuum pump, the high-performance liquid chromatograph pump 103 is operated to introduce the lubricating oil 91 or 92 into the equilibrium cell 109 through the pipe 123. Next, the on-off valve 122 a of the pipe 122 is closed, and carbon dioxide is introduced from the carbon dioxide cylinder 101 through the pipe 121 into the cooled high-pressure injector 102. Next, the on-off valve 121 a of the pipe 121 is closed, the on-off valve 122 a of the pipe 122 is opened, and carbon dioxide liquefied in the high-pressure injector 102 is introduced into the equilibrium cell 109 through the pipe 122.

  Next, the agitator 108 is operated to mix the lubricating oil and carbon dioxide in the equilibrium cell 109, and the circulation pumps 110A and 111B are operated. As a result, the “lubricating oil + carbon dioxide” in the equilibrium cell 109 is in an equilibrium state between the gas phase and the liquid phase. In this state, the “lubricating oil + carbon dioxide” is balanced by the circulation pump 110A in the gas phase circulation path. The return from the gas phase portion in the cell 109 to the liquid phase portion is repeated. In the liquid phase circulation path, “lubricating oil + carbon dioxide” is fed from the liquid phase portion in the equilibrium cell 109 through the density meter 111, the viscometer 112, and the sampling cylinder 113 by the circulation pump 110 </ b> B. Repeat returning to the department.

When the platinum resistance temperature detector 106 and the pressure sensor 105 confirm that the temperature and pressure are constant, the stirring by the stirrer 108 and the circulation by the circulation pumps 110A and 111B are stopped, and the density and kinematic viscosity are determined by the density meter 111 and the viscosity. Measurement is performed using a total 112.
Next, the valves 113 a and 113 b at both ends of the sampling cylinder 113 are closed, the sampling cylinder 113 is removed from the pipes 133 and 134, and the mass (W _b ) of the sampling cylinder 113 is measured outside the air thermostat 104. To do. By measuring the empty mass (W ₀ ) of the sampling cylinder 113 in an empty state in advance, the value obtained by subtracting the mass (W ₀ ) of the empty cylinder from the measured value (W _b ) is the sampling cylinder 113. It is obtained as the mass W _m (= W _b −W ₀ ) of “lubricating oil + carbon dioxide” sampled inside.

  Next, after attaching the sampling cylinder 113 to the container 141 of the carbon dioxide content measurement unit, the valve 113a on the container 141 side is opened to release the carbon dioxide in the sampling cylinder 113 into the container 141. The carbon dioxide released into the container 141 enters the sealed container 116 through the pipe 142 and pushes the air in the sealed container 116 to the pipe 143. The volume (v) of air passing through the pipe 143 is measured by the wet integrating flow meter 115.

The volume v (liter) of the extruded air, the room temperature t (K), the atmospheric pressure: 1 (atm), the gas constant R = 8.314 J / mol · K, and the gas state equation “PV = nRT” It is substituted into, and calculates the number of moles n _a of the air through the pipe 143. Since the number of moles n _{a of} this air is equal to the number of moles of carbon dioxide released into the container 141 and entering the sealed container 116, the value obtained by multiplying the number of moles n _a by the molecular weight of carbon dioxide 44.01. Is the mass of carbon dioxide (W _CO2 ) contained in the sampling cylinder 113. A value obtained by dividing W _CO2 by W _m is the carbon dioxide content in “lubricating oil + carbon dioxide” contained in the sampling cylinder 113.

The accuracy of temperature and pressure measured using this apparatus is 0.1K and 0.01 MPa, respectively. Based on the minimum sensitivity of the balance used for mass measurement of the sampling cylinder 113 and the resolution of the gas integrating flow meter 115, the measurement accuracy of the carbon dioxide content is estimated to be 0.01 mass%, and the density and kinematic viscosity are respectively Presumed to be 0.01 kg / m ³ and 0.1 mm ² / s.

Using this apparatus, the air constant temperature bath 104 is maintained at 377.6K, and the pressure in the equilibrium cell 109 is changed to change the "carbon dioxide (CO ₂ ) + polyalkylene glycol-based lubricant (PAG)" and "dioxide dioxide". Regarding “carbon (CO ₂ ) + tetraethylene glycol (TEG)”, the relationship between pressure and carbon dioxide content, the relationship between pressure and density, and the relationship between pressure and kinematic viscosity were examined. The results are shown graphically in FIGS.

As PAG, “Sunice P-56 (trade name)” manufactured by Nippon San Oil Co., Ltd. was used. The nominal molecular weight of “SUNICE P-56” is 1180 g / mol, and the density at 288 K is 1015.0 kg / m ³ . A TEG having a purity of 99.0% was prepared. Also, decane having a purity of 99.0% was prepared.
First, to examine the soundness of the data, the density of TEG under atmospheric pressure at 377.6K and the carbon dioxide content in “decane + carbon dioxide” at 2.96-15.33 MPa and “decane + The liquid density of “carbon dioxide” was measured. As a result, values consistent with the literature values were obtained, so the data obtained from this device was considered sound.

FIG. 3 is a graph showing the relationship between pressure and carbon dioxide content. From this graph, it can be seen that “CO ₂ + TEG” has a smaller change in CO ₂ content with respect to a change in pressure than “CO ₂ + PAG”. The CO ₂ content of “CO ₂ + PAG” tends to increase linearly at 10 MPa or more. On the other hand, in “CO ₂ + TEG”, the CO ₂ content tends to reach a peak from around 15 MPa.

FIG. 4 is a graph showing the relationship between pressure and density (standardized density). From this graph, it can be seen that “CO ₂ + TEG” is smaller in density change with respect to pressure than “CO ₂ + PAG”. In either case, the density tends to decrease with increasing pressure, and the tendency is more conspicuous in “CO ₂ + PAG”. On the other hand, in “CO ₂ + TEG”, the degree of decrease in density decreases from around 12 MPa.

FIG. 5 is a graph showing the relationship between pressure and kinematic viscosity. From this graph, it can be seen that the change in kinematic viscosity with respect to the change in pressure is smaller in “CO ₂ + TEG” than in “CO ₂ + PAG”. In either case, the kinematic viscosity decreases monotonously with increasing pressure, but the degree of “CO ₂ + PAG” is greater.
Lubricating oil for compressors of refrigeration cycle (heat pump cycle) using carbon dioxide as working fluid, “Less soluble in carbon dioxide in the supercritical state and less temperature and pressure dependence of density and kinematic viscosity” Oil is suitable. Therefore, from the above results, it can be seen that TEG is more suitable than PAG as compressor lubricating oil for a refrigeration cycle (heat pump cycle) using carbon dioxide as a working fluid.

  For each of the lubricating oils Nos. 1 to 6 shown in Table 3 below, the viscosity of “carbon dioxide + lubricating oil” was examined using the apparatus shown in FIG. 6 while changing the pressure.

  No. 1 is tetraethylene glycol, No. 4 is hexaethylene glycol monomethyl ether, and No. 5 is pentaethylene glycol monooleyl ether represented by the following formula (3). Nos. 2 and 3 are not pure substances, but are mixtures of polyethylene glycols having different degrees of polymerization.

In the apparatus of FIG. 6, the pressure vessel 11 is disposed in the oil bath 13, and the entire pressure vessel 11 is immersed in the oil 13a. The pressure vessel 11 is provided with a stirrer composed of a stirring bar 14b with a propeller 14a at the tip and a motor 14c for rotating the stirring bar 14b. Further, the pressure vessel 11 is provided with a temperature sensor 15 for detecting the internal temperature and a viscometer 16 for measuring the viscosity.
A pipe 17 for introducing carbon dioxide into the pressure vessel 11 and a pressure sensor 18 for detecting the internal pressure are attached to the upper portion of the pressure vessel 11. A valve 17 a for adjusting the opening degree is attached to the pipe 17. Although not shown in the figure, the pressure vessel 11 is provided with a liquid introduction pipe for introducing the lubricating oil 93 therein and a vacuum pump for discharging the gas inside.

Using this device, first, a predetermined amount of lubricating oil 93 is introduced into the pressure vessel 11 and then the vacuum pump is operated to discharge the internal air. Next, carbon dioxide in the liquid phase is introduced into the pressure resistant container 11 from the pipe 17, and the pressure is kept constant at a plurality of points in the range of 0 to 10 MPa while maintaining the temperature in the pressure resistant container 11 at 100 ° C. Viscosity measurement was performed. The results are shown graphically in FIG.
From this graph, it can be seen that the change in viscosity with respect to the change in pressure is smaller when the lubricating oil No. 1 to 5 included in the present invention is used than when the PAG No. 6 is used. In either case, the viscosity monotonously decreases with increasing pressure, but the degree is greater when PAG is used.

  Lubricating oil for compressors of refrigeration cycle (heat pump cycle) using carbon dioxide as working fluid, “Less soluble in carbon dioxide in the supercritical state and less temperature and pressure dependence of density and kinematic viscosity” Oil is suitable. Therefore, from the above results, as a lubricating oil for compressors of a refrigeration cycle (heat pump cycle) using carbon dioxide as a working fluid, No. 1-5 lubricating oil (n is 4-6) It can be seen that polyethylene glycol, hexaethylene glycol monomethyl ether, pentaethylene glycol monooleyl ether) are preferred.

  Further, as shown in Table 3, the No. 5 lubricating oil having a structure with an oleyl group has a larger volume resistivity than the No. 1 to 4 lubricating oil and is excellent in electrical insulation. In a hermetic compressor such as a water heater, since the motor is included in the compressor, high electrical insulation is required for the refrigerant and the lubricating oil. Therefore, among the No. 1 to No. 5 lubricating oils, No. 5 lubricating oil is preferable as the lubricating oil for the hermetic compressor. In the lubricating oil of No. 1 to 4, the carbon number of R4 in the formula (1 ′) is 0 to 1, whereas in the lubricating oil of No. 5 the carbon number of R4 in the formula (1 ′) is 18 Many.

  In the polyethylene glycol represented by the formula (1 ′) and derivatives thereof, generally, R3 and R4 are hydrocarbon groups having a hydrocarbon group or a substituent, and the volume resistivity is higher as the number of carbon groups is larger. Although large, the viscosity tends to increase and the low temperature fluidity tends to decrease. Therefore, it is necessary to select the lubricating oil used in the compressor as appropriate in consideration of the requirement for insulation performance and other performance.

It is a schematic block diagram which shows the cooling heating apparatus corresponded to one Embodiment of this invention. It is a schematic block diagram which shows the apparatus which can investigate simultaneously the kinematic viscosity, liquid phase density, and carbon dioxide content rate of "carbon dioxide + lubricating oil" at high temperature and high pressure. Measuring “carbon dioxide (CO ₂ ) + polyalkylene glycol-based lubricating oil (PAG)” and “carbon dioxide (CO ₂ ) + tetraethylene glycol (TEG)” by changing the pressure using the apparatus of FIG. It is a graph which shows the relationship between the pressure and carbon dioxide content rate which were obtained by this. Measuring “carbon dioxide (CO ₂ ) + polyalkylene glycol-based lubricating oil (PAG)” and “carbon dioxide (CO ₂ ) + tetraethylene glycol (TEG)” by changing the pressure using the apparatus of FIG. It is a graph which shows the relationship between the pressure and the density which were obtained by this. Measuring “carbon dioxide (CO ₂ ) + polyalkylene glycol-based lubricating oil (PAG)” and “carbon dioxide (CO ₂ ) + tetraethylene glycol (TEG)” by changing the pressure using the apparatus of FIG. It is a graph which shows the relationship between a pressure and kinematic viscosity obtained by (3). It is a schematic block diagram which shows the apparatus used in order to investigate the viscosity of "carbon dioxide + lubricating oil" in an Example, changing a pressure. Measuring “carbon dioxide (CO ₂ ) + polyalkylene glycol-based lubricating oil (PAG)” and “carbon dioxide (CO ₂ ) + tetraethylene glycol (TEG)” by changing the pressure using the apparatus of FIG. It is a graph which shows the relationship between the pressure and the viscosity which were obtained by (3).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor 2 Gas cooler 3 Heat exchange part 4 Expansion valve (expander)
DESCRIPTION OF SYMBOLS 5 Evaporator 6 Oil separator 7 Heat exchange part 8 Oil recovery piping 11 Pressure-resistant container 12 Working fluid piping 13 Oil bath 13a Oil 14a Propeller 14b Stirring rod 14c Motor 15 Temperature sensor 16 Viscometer 17 Piping 17a Valve 18 Pressure sensor 25 Working fluid Piping 25a Coiled portion of working fluid piping 31 Blower fan 56 Working fluid piping 61 Working fluid piping 61a Coiled portion of working fluid piping 71 Blower fan 91, 92, 93 Lubricating oil 101 Carbon dioxide cylinder 102 High pressure injector 102a Handle 103 High speed Liquid chromatograph pump 104 Air constant temperature bath 105 Pressure sensor 106 Platinum resistor 107 Heater 108 Stirrer 109 Equilibrium cell 110A Circulation pump 110B Circulation pump 111 Density meter 112 Viscometer 113 Sampling cylinder 114 Metering valve 115 Wet total flow meter 116 Sealed container with air 119 Thermometer 121 Pipe 121a Open / close valve 122 Pipe 122a Open / close valve 123 Pipe 131, 132 Pipe 133-137 Pipe 136, 137 Pipe 141 Container 142, 143 Pipe

Claims (9)

A lubricating oil for a compressor of a device that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle,
Compression of a cooling or heating apparatus characterized by containing, as a main component , polyethylene glycol , polyethylene glycol monomethyl ether, and polyethylene glycol dimethyl ether represented by the following formula (1), where n = 4 to 6 Lubricant for machine.

A lubricating oil for a compressor of a device that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle,
A lubricating oil for a compressor of a cooling or heating apparatus characterized by containing polyethylene glycols represented by the following formula (1 ′) and n = 4 to 6 as a main component.

R3 is hydrogen, and R4 is any one of hydrogen, a methyl group, and an oleyl group. A compressor of an apparatus that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle;
It is characterized by being lubricated with a lubricating oil containing , as a main component , polyethylene glycol , polyethylene glycol monomethyl ether, and polyethylene glycol dimethyl ether represented by the following formula (1), where n = 4 to 6: Compressor.

A compressor of an apparatus that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle;
A compressor characterized by being lubricated with a lubricating oil containing , as a main component, polyethylene glycols represented by the following formula (1 ′) and n = 4 to 6 .

R3 is hydrogen, and R4 is any one of hydrogen, a methyl group, and an oleyl group.
A device that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle,
The compressor is lubricated with a lubricating oil containing any one of polyethylene glycol , polyethylene glycol monomethyl ether, and polyethylene glycol dimethyl ether represented by the following formula (1) and n = 4 to 6 as a main component. A cooling or heating device characterized by that.

A device that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle,
A cooling or heating apparatus characterized in that the compressor is lubricated with a lubricating oil which is represented by the following formula (1 ′) and contains polyethylene glycols having n = 4 to 6 as a main component.

R3 is hydrogen, and R4 is any one of hydrogen, a methyl group, and an oleyl group. A lubricating oil for a compressor of a device that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle,
Indicated by (1 ') below, n =. 4 to polyethylene glycol is 6, the compressor lubricant cooling or heating device, characterized in that it contains as a main component.

R3 and R4 are hydrogen, a methyl group, or an oleyl group, and may be the same as or different from each other. A compressor of an apparatus that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle;
Is indicated by (1 ') below, n =. 4 to the compressor, characterized in that it is lubricated with a lubricating oil containing as a main component 6 in which polyethylene glycols.

R3 and R4 are hydrogen, a methyl group, or an oleyl group, and may be the same as or different from each other. A device that uses carbon dioxide as a working fluid, includes a compressor, a gas cooler, an expander, and an evaporator, and cools in a refrigeration cycle or heats in a heat pump cycle,
A cooling or heating device characterized in that the compressor is lubricated with a lubricating oil containing , as a main component, polyethylene glycols represented by the following formula (1 ') and n = 4 to 6 .

R3 and R4 are hydrogen, a methyl group, or an oleyl group, and may be the same as or different from each other.

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