• Proceedings of the SAREK Conference
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• 2008.06a
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• pp.271-276
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• 2008

The oil trap in oil separator is one of the most important characteristics for normal operation of compressor. In this study, oil separation characteristics has been investigated for $CO_2$/PAG mixture using a gravity type of oil separator. The experimental study has been carried out in the range of oil concentration 0 to 5 weight-percent and the mixture temperature range of $0^{\circ}C$ to $15^{\circ}C$. The results obtained indicate that oil separation ratio in oil separator is increased with an increase in the oil concentration and mixture temperature.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.386-391
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• 2005

An experimental study was conducted to analyze the thermal stability and to estimate the lifetime of refrigerating lubricants. PAG and POE oil are considered as a test fluids in this study. The viscosity of PAG and POE oil was measured by the vibration type viscometer while temperature is varied periodically in the range of $0^{\circ}C{\sim}100^{\circ}C$. The results indicate that the reduction rates of viscosity of PAG and POE oil were less than 5% after 510 cycles. In order to estimate lifetime of PAG and POE oil with temperature, the viscosity was measured while the temperature of oils was maintained at 180, 200 and $220^{\circ}C$. It is found that the lifetimes of PAG oil were shown to be 244, 177 and 89 hours at the temperature of 180, 200 and $220^{\circ}C$, respectively. Also the lifetimes of POE oil were estimated to be 1,744, 1,007 and 334 hours at the temperature of 180, 200 and $220^{\circ}C$, respectively. The lifetime correlations of PAG and POE oil are suggested in this paper.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.646-651
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• 2007

This study has been conducted to select the suitable refrigeration oil for a $CO_2$ refrigeration system. The oil return is one of the most important characteristics for refrigeration oils. PAG and POE oils are considered as a test fluids in this study. An evaporator model is employed to simulate the evaporator of a $CO_2$ refrigeration system. Oil return characteristics has been investigated for $CO_2$/PAG and $CO_2$/POE mixtures in the range of oil concentration 0 to 5 weight-percent and the mixture temperature range of $0^{\circ}C$ to $15^{\circ}C$. The results obtained indicate that oil return is decreased with an increase in the oil concentration and mixture temperature for both POE and PAG oils. It is also found that POE oil is seen to be superior than PAG oil in terms of oil return in an evaporator of a $CO_2$ refrigeration system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.20 no.6
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• pp.388-393
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• 2008

This study has been conducted to select the suitable refrigeration oil for a $CO_2$ refrigeration system. Non-hygroscopic property of refrigeration oils is one of the most important properties for refrigeration oils. PAG and POE oils are considered as test oils in this study. Transient variation of water content of PAG and POE oils was measured for 3 different vessels in the environmental conditions, such as in the range of temperature $25^{\circ}C$ to $40^{\circ}C$ and relative humidity 40% to 85%. The results obtained that water content of both POE and PAG is increased with an increase in the contact area with ambient for 3 different vessels. It is also found that water content of both POE and PAG is increased as the ambient temperature and relative humidity is increased. Non-hygroscopic property of POE oil is found to be much superior than that of PAG oil.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.131-136
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• 2008

The oil separation in an oil separator is one of the most important characteristics for proper compressor operation. In this study, a gravity type of oil separator is used. Oil separation characteristics has been investigated for $CO_2$/PAG mixture in the range of oil concentration 0 to 5 weight-percent and the mixture temperature range of $5^{\circ}C$ to $15^{\circ}C$ and $70^{\circ}C$ to $90^{\circ}C$. The results obtained indicate that the oil separation is increased with an increase in the oil concentration. It is also found that the oil separation in liquid state is increased with an increase in the mixture temperature while the oil separation in gas state is decreased.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.19 no.3
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• pp.213-219
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• 2007

An experimental apparatus was constructed to obtain vapor-liquid equilibrium data for $CO_2/oil$ mixtures using mass analysis method with sample cylinder. Lubricants employed were POE (poly-ol ester) and PAG (poly alkylene glycol). The phase equilibria of $CO_2/oil$ mixtures prevailed in an equilibrium cell were observed through a couple of sight glasses at the opposite ends. Data were obtained over the temperatures $-10^{\circ}C,\;-5^{\circ}C,\;0^{\circ}C,\;5^{\circ}C,\;10^{\circ}C,\;25^{\circ}C,\;40^{\circ}C,\;60^{\circ}C,\;and\;80^{\circ}C$ under pressures up to 14 MPa and then mole fractions were calculated, respectively In general, more solubility of $CO_2$ is observed in POE than in PAG. Miscibility gap is closed for $CO_2/POE$ mixture but not for $CO_2/PAG$.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.652-657
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• 2007

This paper is an interim report on the investigation of thermodynamic properties of $CO_2$/oil mixture refrigerant. First, liquid density of POE (poly-ol ester) and PAG (poly alkylene glycol) were measured and expressed as a function of temperature. Then, a solubility equation was developed which enables us to calculate the weight fraction of $CO_2$ for the mixture in a liquid state. An experimental apparatus with a cell was constructed to measure P-$\upsilon$-T-$\chi$ data for $CO_2$/oil mixture. The volume of the cell was determined using a certain formula considering change in volume as a function of temperature and pressure. Then, experimental data were obtained over the temperatures $40^{\circ}C$, $50^{\circ}C$, $60^{\circ}C$, $70^{\circ}C$ and $80^{\circ}C$ with various mole fractions. Finally, assuming a primitive model of ideal gas, the volume of $CO_2$/oil mixture was predicted with a relatively larger error of 5.05% for $CO_2$/PAG and 8.81% for $CO_2$/POE. The volume of $CO_2$/oil mixtures would be better predicted using an appropriate equation of state, of which results will be reported soon.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.2
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• pp.78-83
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• 2007

An experimental study has been carried out to analyze the thermal stability and to estimate the lifetime of refrigerating lubricants. PAG and POE oil are considered as test oils in this study. The viscosity of PAG and POE oil was measured by the vibration type viscometer while temperature is varied periodically in the range of $0^{\circ}C{\sim}100^{\circ}C$. In order to estimate lifetime of PAG and POE oil with temperature, the viscosity was measured while the test temperature of oils was maintained continuously at $180,\;200\;and\;220^{\circ}C$. The lifetime of oils is estimated as the decrease in viscosity change by 15%. The results indicate that the reduction rates of viscosity of PAG and POE oil are less than 5% after 510 temperature variation cycles. However, when the oils are kept at high temperature, it is found that the lifetimes of PAG oil is seen to be 244, 177 and 89 hours at the test temperature of $180,\;200\;and\;220^{\circ}C$, respectively, where as the lifetimes of POE oil are estimated to be 1,744, 1,007 and 334 hours at the temperature of $180,\;200\;and\;220^{\circ}C$, respectively. Thus, the lifetime of POE oil is found to be much longer than that of PAG oil. The lifetime correlations of PAG and POE oil are also obtained by Arrhenius's equation method in this paper.

• International Journal of Air-Conditioning and Refrigeration
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• v.17 no.3
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• pp.88-93
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• 2009

Lubricant oil is needed in air conditioning and refrigeration system because the compressor requires oil to prevent surface to surface contact between its moving parts, to remove heat, to provide sealing, to keep out contaminants, to prevent corrosion, and to dispose of debris created by wear. Thus, the oil separation in an oil separator is one of the most important characteristics for proper compressor operation. In this study, a gravity type of oil separator is used. Oil separation characteristics have been investigated for $CO_2$/PAG mixture in the range of oil concentration 0 to 5 weight-percent and the mixture temperature range of $0^{\circ}C$ to $15^{\circ}C$ at 50 bar and $70^{\circ}C$ to $90^{\circ}C$ at 80 bar. The results obtained indicate that the oil separation is increased with an increase in the oil concentration. It is also found that the oil separation in liquid state is increased with an increase in the mixture temperature while the oil separation in gas state is decreased.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.380-385
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• 2005

An experimental apparatus was constructed to obtain vapor-liquid equilibrium data for $CO_2$/oil mixtures using mass analysis method with sample cylinder. Lubricants employed were POE(Polyol Ester) oil and PAG(Poly Alkylene Glycol) oil. The phase equilibria of $CO_2$/oil mixtures formed in high pressure equilibrium cell are observed through sight glasses at the opposite ends. Data were measured over the temperature range from -10 to $10^{\circ}C$ with $5^{\circ}C$ intervals under pressures up to 14 MPa. Mole fractions were calculated for $CO_2$/oil and $CO_2$/PAAG, respectively and were compared with each other.