• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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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.

• 한국산학기술학회논문지
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• 제13권4호
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• pp.1440-1446
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• 2012

본 논문은 수평 마이크로핀관내 초임계 $CO_2$와 PAG 혼합물의 열전달과 압력강하 특성에 대해서 실험적으로 연구한 것이다. $CO_2$와 PAG 혼합물의 열전달계수는 압력이 10 MPa이고, 질량유속은 520 kg/$m^2s$이며, PAG 오일 농도는 0.06~2.26%에서 측정하였다. PAG 오일농도가 0.3%인 경우, $CO_2$와 PAG 혼합물의 열전달계수와 압력강하는 순수 $CO_2$ 냉매의 열전달계수와 동일한 경향을 나타내었다. 그리고 PAG 질량농도가 2.26%인 경우, 초임계 온도근처에서 측정한 열전달계수는 순수 $CO_2$의 열전달계수 보다 약 50%정도 낮게 나타났다. 마찰압력강하는 $60^{\circ}C$의 $CO_2$ 평균온도에서 순수 $CO_2$의 압력강하보다 약 1.6배 더 높게 나타났다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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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.

• 설비공학논문집
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• 제19권3호
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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 $CO_2/PAG$.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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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.

• 설비공학논문집
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• 제20권5호
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• pp.357-363
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• 2008

In order to investigate $CO_2$ heat transfer coefficient and pressure drop by PAG oil concentration during $CO_2$ evaporation, the experiment on evaporation heat transfer characteristics in a horizontal micro-fin tube was performed. The experimental apparatus consisted of a test section, a DC power supply, a heater, a chiller, a mass flow meter, a pump and a measurement system. Experiment was conducted for various mass fluxes($400{\sim}1200\;kg/m^2s$), heat fluxes($10{\sim}30\;kW/m^2$) and saturation temperatures ($-5{\sim}5^{\circ}C$), and PAG oil concentration($0{\sim}5\;wt%$). The variation of the heat transfer coefficient was different in accordance with the oil concentration. With the increase of the oil concentration, the evaporation heat transfer coefficient decreased and the delay of dryout by oil addition was found. Pressure drop increased with the increase of the oil concentration and heat flux, and the decrease of saturation temperature.

• 한국산림과학회지
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• 제102권3호
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• pp.331-337
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• 2013

Formate dehydrogenase(FDH)는 포름산이온을 이산화탄소로 산화하는 반응을 촉매하는 효소로서, 건조와 저온 그리고 병원균 감염 등에 반응하는 스트레스 단백질로 알려져 있다. 본 연구에서는 현사시나무에서 FDH의 cDNA를 분리하여 구조와 발현 특성 등을 조사하였다. 현사시나무의 FDH cDNA(PagFDH1)는 1,499개의 염기쌍으로 이루어져 있으며, 388개의 아미노산으로 구성되는 예상 분자량 42.5 kDa의 단백질을 암호화한다. PagFDH1 단백질은 미토콘드리아 신호펩티드와 $NAD^+$ 결합부위를 가지고 있다. PagFDH1은 현사시나무의 염색체에 1 copy가 존재하며, 배양세포에서 가장 높게 발현되고 뿌리와 꽃 그리고 잎에서도 발현되었다. 현탁배양세포의 생장주기에서 유도기와 초기 지수생장기에 높게 발현하였다. PagFDH1은 건조와 염 스트레스에 반응하여 ABA를 경유한 신호전달경로에 의해 발현이 유도되는 것으로 나타났다. 본 연구결과는 FDH 유전자의 도입과 발현조절을 통한 환경 스트레스 저항성나무의 개발에 도움을 줄 것으로 생각된다.

• 설비공학논문집
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• 제19권10호
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• pp.718-725
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• 2007

In the general vapor-compression refrigeration system, refrigeration lubricant circulates in refrigeration system with refrigerant. Knowledge of the amount of circulating lubricant is very important to exactly calculate capacity of the refrigeration system. An experimental study was conducted to estimate the oil concentration of a flowing $CO_2/Oil$ mixtures. POE and PAG oil are considered as test lubricants in this study. Performance tests were conducted under simulated liquid conditions for $CO_2/POE$ oil mixture in oil concentration of 0 to 10 weight-percent and $CO_2/PAG$ oil mixture in oil concentration of 0 to 6 weight-percent in the temperature ranges of $-5^{\circ}C\;to\;15^{\circ}C$. The results obtained indicate specific gravity of $CO_2/Oil$ mixture is increased as oil concentration is increased and as temperature of mixture is decreased. Oil concentration correlation of $CO_2/POE$ oil mixture and $CO_2/PAG$ oil mixture is suggested, based on the measurement of specific gravity and temperature. This correlation enable to predict the oil concentration without extraction of the mixture and can be applied for $CO_2/POE$ mixtures and $CO_2/PAG$ mixtures.

• 설비공학논문집
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• 제23권1호
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• pp.73-79
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• 2011

A portion of oil for lubrication of compressor flows together with refrigerant in the refrigeration system. If the oil discharge from a compressor is increased in the refrigeration system, not only pressure drop is increased in other components, such as evaporator and gas cooler, but also heat transfer coefficient in the heat exchangers is decreased. Oil discharge rate from a compressor may strongly depend on operating conditions of a compressor. In this study, one stage single rotary compressor is employed for measuring oil circulation ratio(OCR). Carbon dioxide and PAG oil are used as refrigerant and lubricant. Using a U-tube densimeter, mixture density is measured. Oil circulation ratio(OCR) can be estimated by measured mixture density. The results obtained indicate that the oil circulation ratio(OCR) is increased as the suction temperature or compressor operating frequency is increased. Oil circulation ratio(OCR) correlation of the compressor is also suggested.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2007년도 동계학술발표대회 논문집
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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.