• 한국대기환경학회지
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• 제10권1호
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• pp.41-48
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• 1994

A monitoring system for atmospheric CFC-12 and CFC-11 has been established at Mt. Kwan-Ak, Seoul National University (SNU) since July, 1991. The concentrations showed quite a large variation ranging from 495 to 37600 pptv (pptv=part per trillion, 10$^{-12}$ , v/v) for CFC-12 and from 233 to 12100 pptv for CFC-11 due to many local sources. However, monthly medians show rather limited ranges ; 553~765 pptv for CFC-12 and 301~431 pptv for CFC-11. Furthermore minimum concentrations could be defined relatively well during the whole period of observation. The regional background concentrations in 1993 near SNU wer estimated as 533 pptv for CFC-12 and 293 pptv for CFC-11. These values are very comparable to global averages in Northern Hemisphere, 523 pptv for CFC-12 and 287 pptv for CFC-11, reflecting the fast atmospheric mixing processes within the hemisphere. Examinations with meteorological parameters such as wind speed and direction suggest the possible measurement-window at SNU, appropriate for regional monitoring. Studies for improving the monitoring capability of the SNU station such as automation of the analysis system along with correlation with other meteorological parameters, are in progress at the present time.

• 설비공학논문집
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• 제10권5호
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• pp.569-580
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• 1998

In this study, condensation heat transfer coefficients(HTCs) of a plain tube, low fin tube, and Turbo-C enhanced tube for CFC-11, HCFC-123, CFC-12, HFC-l34a are measured and compared against each other. All data are taken at the vapor temperature of 39$^{\circ}C$ with a wall subcooling temperature 3~8$^{\circ}C$. Test results show that HTCs of a low vapor pressure refrigerant, HFC-123, for a plain, low fin, and Turbo-C tubes are 10.5~20.5%, 8.2~12.2%, 16.5~19.2% lower than those of CFC-11, respectively. On the other hand, HTCs of a medium vapor refrigerant, HFC-l34a, for a plain, low fin, and Turbo-C tubes are 20.6~31.8%, 0.0~8.0%, 13.2~20.9% higher than those of CFC-12, respectively. For all refrigerants tested, HTCs of Turbo-C tube are the highest among the three tubes showing almost 8 times increase in HTCs as compared to those of a plain tube. Nusselt's prediction equation for a plain tube yielded 12% deviation for all plain tube data while Realty and Katz's prediction equation for a low fin tube yielded 20% deviation for all low tube data.

• 대한기계학회논문집B
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• 제21권6호
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• pp.830-840
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• 1997

In this study, condensation heat transfer coefficients(HTCs) of CFC-11, HCFC-123 and HCFC-141b are measured, which are used/or considered as working fluids in centrifugal chillers. The main objectives of this study are to measure and compare the HTCs of various refrigerants on plain and low fin tubes and also to find out the optimum fin density of the low fin tubes. To accomplish these goals, HTCs of three refrigerants are measured for the plain tube as well as 4 types of low fin tubes. All measurements are carried out at the vapor temperature of 39.deg. C with the wall temperature difference of 3 .deg. C ~ 8.deg. C. For all the refrigerants tested, a low fin tube of 28 fins per inch yielded the best performance among all the tubes tested. For the plain tube, the HTCs of CFC-11 and HCFC-141b were very similar and those of HCFC-123 were 10% lower than those of CFC-11.Thus, it can be concluded that HCFC-123 and HCFC-141b are acceptable as alternative refrigerants for CFC-11 from the view point of condensation heat transfer.

• 설비공학논문집
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• 제6권4호
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• pp.365-379
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• 1994

Pool boiling experiments were carried out to study the effect of electric field on nucleate boiling heat transfer. CFC-11 and its alternative HCFC-123 were used as working fluids. Boiling on both single tube and a bundle of five tubes was investigated. Heat flux varied from 5 to $25kW/m^2$ while the applied voltage changed from 0 to 1kV. The results showed that at low heat flux where boiling was not present or very weak, electric field-induced forced convection helped increase the heat transfer coefficients of CFC-11 and HCFC-123 significantly(4-15 times increase). However, at higher heat flux, nucleate boiling of CFC-11 which is a highly dielectric fluid, was not affected significantly by the application of electric field. In contrast to CFC-11, even at high heat flux, nucleate boiling of CFC-11 which has a relatively larger electric conductivity than CFC-11, was vigorously increased up to 2-4 times. The additional power required to apply the electric field was 1-2% of the total power consumption by the heater. The increase in overall heat transfer coefficient of evaporators with HCFC -123 was about 40%, suggesting a considerable reduction in evaporator size with EHD technique.

• 대한기계학회논문집
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• 제19권9호
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• pp.2316-2327
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• 1995

Experimental results from nucleate pool boiling heat transfer with various finned tubes in CFC11, HCF123 and HCFC141b are reported. One plain tube and four low fin tubes of various fin densities were tested in an attempt to find out the optimum fin density in the heat flux range of 10-60 kW/m$^{[-992]}$ at near atmospheric pressure. The results indicated that CFC11 showed the highest heat transfer coefficients. Its alternatives, HCFC123 and HCFC141b, showed 3-5% lower heat transfer coefficients than those of CFC11 at the same heat flux. As the fin density increases, so does the heat transfer surface area. Measured heat transfer coefficients, however, do not necessarily always increase as the fin density increases. This unique phenomenon seems to be caused by the coalescence of the bubblers that prevent the cool liquid from entering into the fin valleys. For all the refrigerants tested, the optimum fin density yielding the highest performance was 28 fins per inch confirming the previous results by other researchers.

• 대한설비공학회지:설비저널
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• 제28권5호
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• pp.389-395
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• 1999

냉동공조설비, 발전설비, 화학플랜트설비 등에 사용되는 응축기는 주로 증기가 관의 외부에서 응축을 하고 냉각수가 관 내부로 흐르는 쉘-튜브(shell and tube)형 태를 취하고 있다. 초기투자비용 및 운전비용을 줄이기 위해서는 응축기의 열교환 성능을 향상시키는 일이 필수적이며 이를 위해 코팅 표면(coated surfaces), 거친 표면(rough surfaces), 코일 튜브(coiled tubes), 선회 흐름장치(swirl flow), 전열면적을 넓힌 낮은 핀관과 3차원 형상을 갖는 열전달 촉진관의 사용이 제시되고 있다.

• 한국고분자학회지:고분자과학과기술
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• 제2권2호
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• pp.99-104
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• 1991

• Bulletin of the Korean Chemical Society
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• 제22권11호
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• pp.1273-1276
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• 2001

• 한국지하수토양환경학회지:지하수토양환경
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• 제8권2호
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• pp.1-8
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• 2003

Chlorofluorocarbons(CFCs) 조사를 위한 지하수 시료 채취 방법 중 cold-welded copper tube method(구리관법)과 flame-sealed borosilicate glass ampule method(유리앰퓰법)의 두 방법을 비교하고 검토하였다. 구리관법에 의해 채취된 시료의 CFCs 농도는 중복시료간에 재현성이 불량한 반면, 유리앰퓰법은 상대표준오차가 5％ 이내로 좋은 재현성을 보여주었다. 이것은 구리관법을 적용할 때, 관정의 출수구와 구리관의 연결의 밀봉성이 좋지 않았기 때문인 것으로 추정된다. 또한 구리관법에 의한 CFCs 농도는 전체적으로 유리앰퓰에 의한 값보다 높았으며 이러한 특징은 CFC-11이 CFC-12보다 더 두드러졌다. 구리관법의 경우에 플라스틱 관이나 관정에 설치된 출수구에 포함된 고무 패킹 등이 시료를 CFCs로 오염시켰을 것으로 평가된다. 유리앰퓰법을 적용했을 때에는 이러한 가능성을 제거하기 위해 stainless steel과 nylon 재질만을 이용하고, 시료채취장비를 관정의 주배수관에 직접 연결하였다. 인위적인 공급원에 의한 CFCs가 없을 것으로 예상되는 시료에서 유리앰퓰법에 의해 매우 낮은 수준의 CFCs농도가 측정됨으로써 이 시료채취과정의 유효성이 검증되었다.

• 한국가스학회지
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• 제9권1호
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• pp.16-20
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• 2005

LNG저장탱크용 경질 폴리우레탄 폼의 발포에 많이 사용되어온 것은 CFC-11이었으며 현재 사용되고 있는 것은 HCFC-l4lb이다. 하지만 CFC-11과 이의 대안으로 사용되고 있는 HCFC-l4lb는 성층권에 존재하는 오존층(ozone layer)을 파괴하기 때문에, 선진국의 경우 CFC-11은 1996년부터 사용이 금지되어 왔으며 HCFC-141b도 2005년부터 사용이 금지될 예정이다. 이러한 국제적 제약으로 인해 이들 발포제를 대체할 차세대 발포제와 이를 이용한 폴리우레탄 폼에 대한 연구가 활발히 진행되고 있다. 본 논문에서는 HFC계 발포제를 사용하여 합성한 경질폴리우레탄 폼의 물리적, 기계적 특성을 측정하였으며 이 결과를 HCFC-l4lb를 사용하여 합성한 경질폴리우레탄 폼의 특성과 비교하였으며 이로부터 LNG저장탱크용 단열재에 있어서 HFC계 발포제의 HCFC-l4lb대체가능성에 대하여 검토하였다.