• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.31 no.7
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• pp.45-52
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• 2002

1991년에 Maryland 대학에 Dr. Reinhard Rader-macher에 의해 환경에너지공학연구소(CEEE)가 설립되었다. 이 연구소는 환경 및 경제적인 관점에서 에너지 변환 시스템을 개발하는데 선두적인 역할들 수행해왔다. 환경 에너지 공학 연구소는 산업체, 정부,및 연구소에서 지원 받는 컨소시엄 형태의 연구 센터이다. 대체 냉매, $CO_2$초월임계 사이클에 관한 연구를 1993년에 시작한 이래, 현재 세계적으로 40여 개의 회사가 지원을 하고 있다. 2단 압축 $CO_2$ 사이클 최적화, 초월 임계 사이클에서의 오일에 따른 열전달 영향, 초월$CO_2$임계 시스템에서의 오일 정체, $CO_2$압축기 모델링, 자동차에서의 $CO_2$기후 조절 시스템, $CO_2$냉매를 이용한 에어컨, $CO_2$저온 냉동 시스템 등에 관한 연구를 수행하고 있다. CEEE는 향후 연구로 구성요소 및 시스템 최적화, 효율향상, 시스템 적용확대에 관한 연구를 할 예정이다. 센터는 보고서, 컨소시엄 미팅. 워크샵, 교과목 개설, 당문 연구자 초청들을 통해 산업계 및 기술을 전달하고 있다. 본 고에서는 환경에너지 공학 연구소에서 $CO_2$ 초월임계 사이클에 초점을 맞추어 연구소의 연구활동을 기술한다.

• 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.

• Journal of Energy Engineering
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• v.18 no.3
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• pp.203-211
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• 2009

Vapor pressure of HFC-404a and polyol ester system were measured at 56 points from 263.15 to 323.15 K and from 0 to 90 mass %polyol ester. It was found that below 273.15 K, the effect of the polyol ester on the vapor pressure was negligible up to 30 mass % polyol ester. The vapor pressure of the system significantly decreased as the mass fraction of polyol ester increased over 50 percent. Raoult's model and Flory-Huggins model were tested for data reduction. Empirical vapor pressure equations were obtained in terms of temperature and mass fraction of polyol ester.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.125-130
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• 2008

The main components of the KSTAR helium refrigeration system (HRS) can be classified into the warm compression system (WCS) and the cryogenic devices according to the operating temperature levels. The WCS itself consists of the compressor station (C/S) and the oil removal system (ORS). The process helium is compressed from 1 bar to 22 bar maximum in the C/S and downstream, the ORS removes the oil mixed in the helium to less than 10 ppbw as per the operation criteria of the cryogenic devices of the KSTAR HRS. After the installation, the pre-commissioning and commissioning activities were started on July, 2007. Before the start-up of the C/S, vibration measurement and the skid reinforcement jobs were performed for stable operation of the C/S. The results of the WCS performance tests met the requirements of the KSTAR HRS but satisfied the vibration level criteria only at the compressors' full load condition.

• Journal of Energy Engineering
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• v.11 no.1
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• pp.1-9
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• 2002

The purpose of this study is to maintain high efficiency and reasonable use of cool thermal storage systems operated in the domestic building sector. As the result of efficiency test from the five types of operated cool storage systems on the condition that COP ranges are 2.6 to 3.4 during the day time and 2.1 to 3.0 during the night time and it decreased by more than 30% of rated COP given 3.8 to 3.0. The Analysis of cool storage rate shows that only 3 (21.4%) systems out of 15 buildings hold to over 40% capacity for its total capacity. To prevent the decrease in operating efficiency, it should correct the malfunction of 3-way valve and expansion valve and the mistake of control values for schedule program and increase cooling tower capacity. In order to improve piping line, it needs bypass brine line off refrigerator, separation of chilled water line with Ice Slurry system at day and night time and speed control of chilled and warm water pumps. This study does require the more studies on improving difficulty of increasing cooling load with Ice on Coil system, waterproofing with Ice Ball system, COP drop during the night time with Ice Lens, low operating temperature during the day time with Ice Slurry and increasing of Power loss due to hot gas de-icing with Ice Harvest in the future.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.3
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• pp.175-181
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• 1994

This paper deals with the correlation of absorption rate in absorber and evaporation rate in evaporator. The evaporator consists of a copper tube of 10mm dia, and 600mm long and chilled water flowing through the tube is fed by the chilled water circulator. The flowrate of LiBr-water solution in the absorber plays a significant role in determining the magnitude of the heat transfer rate from chilled water to refrigerant There exists a flowrate of solution which has a maximum value of heat transfer. It is interesting to note that the absorption rate of absorber increases with increasing the heat transfer rate of the evaporator. Also, absorption rate increases with evaportation rate, and the ratio(the former/the other) depends on the inlet temperature of LiBr-water solution in the absorber. The heating capacity in the absorber is higher than the refrigerating capacity in the evaporator.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.8
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• pp.1129-1136
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• 2009

The paper presents the performance characteristics for a cooling system using EEV. The water cooler was used to reduce thermal deformation and contraction due to high speed of machine tools and the EEV was used for capacity control for water cooler. The apparatus was designed for hot-gas bypass system which a hot-gas can flows from outlet of compressor to the inlet of evaporator. This experiment is the intermediary study for precise temperature control through PID control. The results show that the evaporator pressure increased and refrigeration capacity decreased as the EEV opening step of hot-gas bypass increased. These results can be used as basic data for the design of effective water cooler.

• Journal of the Korean Society of Food Science and Nutrition
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• v.42 no.12
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• pp.2012-2018
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• 2013

The objective of this research was to investigate the quality characteristics of the spirits by different distillation and filtrations. The contents of alcohol, total acids, and amino acids in rice mash were 15%, 0.25 g/100 mL, and 0.15 g/100 mL, respectively. The soluble content was $10^{\circ}Brix$, and pH was 4.6 in the rice mash. Lactic acid was the most prominent organic acid found in rice mash. The rice spirit distilled by a multi stage distiller showed the highest amounts of aroma compounds, such as fusel oil and esters. However, the filtration did not affect the amounts of total aroma compounds. It is suggested that a multi stage distiller may influence taste and flavor positively by enhancing the aroma and removing the impurities in rice spirits.

• Journal of the Korean Society of Food Science and Nutrition
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• v.37 no.4
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• pp.505-511
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• 2008

This study was carried out to investigate the antioxidative effect of Kochujang seasoning sauce with the addition of fruit and vegetable extract (FVE) for pork Bulgogi, as well as to establish the optimum mixture ratio of ingredients using mixture experimental design (MED). During 5 months of storage at $-25^{\circ}C$, the thiobarbituric acid (TBA) values of the seasoned pork containing soy sauce (control), Kochujang added group (KG) and Kochujang and FVE added group (KFVEG) were remarkably lower than that of unseasoned pork. Among the seasoned porks, the antioxidative effect of KG was much higher than the control. Moreover, TBA values of KFVEG were significantly lower than those of KG. Therefore, the lipid oxidation stability of seasoned pork Bulgogi was improved by the addition of Kochujang, red pepper powder and FVE into the seasoning sauce. When Kochujang was used in seasoning sauce, the preference scores of pork Bulgogi increased with the increasing amount of red pepper powder and FVE. The optimum mixture ratios of seasoning sauce for pork Bulgogi established by the MED were Kochujang 0.04, red pepper powder 0.20, FVE 0.39 and water 0.37.