• 태양에너지
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• 제17권4호
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• pp.23-33
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• 1997

본 연구에서는 Rankine 사이클을 이용한 해양 온도차 발전 시스템을 컴퓨터로 모사했고 작동유체를 변화시켜 가면서 그 성능을 비교하였다. 증발기와 응축기는 UA(총괄열전달계수$\times$전열면적)와 LMTD(대수평균온도차) 방법으로 모사하였으며 터빈과 펌프는 등엔트로피 효율로 모사하였다. 작동유체로는 R22, R290, R1270, R134a, R125, R143a, R32, R410A 그리고 암모니아 등을 사용하였다. 모사 결과 OTEC 발전 시스템의 효율은 작동유체에 상관없이 거의 일정한 것으로 드러났다. 한편 증발기 출구에서의 과열도와 응축기 출구에서의 과냉도는 시스템의 성능에 거의 영향을 미치지 않는 것으로 나타났지만 터빈의 효율과 열교환기의 크기는 시스템 성능에 큰 영향을 미치는 것으로 나타났다. 마지막으로 따뜻한 표층수와 차가운 심해수 사이의 온도차가 $20^{\circ}C$이상일 때 실제로 전기를 생산할 수 있다는 사실을 확인했다.

• 유기물자원화
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• 제11권4호
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• pp.49-56
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• 2003

토양미생물인 Ralstonia eutropha JMP134는 세균의 염색체상의 페놀분해경로를 통하여 삼염화에틸렌(TCE)을 분해하는 특징이 있다. 이전의 실험에서 본 세균으로부터 분리된 페놀분해효소가 단독으로 삼염화에틸렌을 분해하는 것을 밝힌바 있다. 본 실험에서는 페놀분해효소를 생성하는 유전자를 유전자 재조합방법을 통하여 plasmid에 cloning한 유전자 재조합세균 R. eutropha AEK301을 대상으로 TCE의 분해능을 실험하였다. AEK301은 페놀에 의한 유도작용 없이도 여러 유기물의 존재하에서 TCE를 분해하는 것으로 나타났다. 본 세균은 0.05%의 에탄올이 유일한 탄소원으로 제공된 배양액에서 TCE의 농도 $200{\mu}M$ 까지 거의 분해하였으며 농도 $400{\mu}M$에서는 약 70%까지 제거하는 특성을 보여주었다.

• 생명과학회지
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• 제27권5호
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• pp.567-574
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• 2017

본 연구는 막걸리로부터 ${\gamma}$-amino butyric acid (GABA) 생성 유산균을 분리 및 동정하고 최적 GABA 생산조건을 확립하는데 그 목적이 있다. 막걸리로부터 64균주의 유산균은 MRS 배지에서 성장된 집락의 색과 모양의 특성에 따라 분리하였다. 분리균주의 GABA 생산은 1% MSG가 첨가된 MRS 액체배지에서 배양하여 TLC와 HPLC 방법에 의해 평가되었다. B-134 균주는 GABA생성을 위한 우수균주로 선발하였다. 16S rRNA 유전자 및 glutamate decarboxylase B (gadB) 유전자의 염기서열분석을 통하여, B-134 균주는 Lactobacillus plantarum subsp. plantarum B-134 균주로 명명하였다. GABA 생성을 위한 온도, pH, NaCl 및 MSG 농도를 달리하여 최적배양조건을 조사하였다. 그 결과 B-134 균주의 최적배양 조건은 온도 $37^{\circ}C$, pH 5.7, NaCl 농도 0% (w/v), 그리고 MSG 농도 3% (w/v)로 결정되었으며 본 조건에서 48시간 배양시 25 mM의 GABA를 생산하였다. 이러한 결과로부터 B-134 균주는 GABA함유 건강기능식품개발을 위한 유용한 균주로 판단된다.

• 대한기계학회논문집B
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• 제30권12호
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• pp.1203-1210
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• 2006

The filmwise condensation heat transfer coefficients of R-134a on the horizontal copper and stainless steel tubes were measured and analyzed. The outside diameter of the tubes was 15.88 mm, and the tube thickness ranged from 0.89 to 1.65 mm. The polished stainless steel tube had an RMS surface roughness($R_q$) of 0.37 $\mu$m, and commercial stainless steel tubes had an surface roughness($R_q$) of 1.855 $\mu$m. The tests were conducted at the saturation temperatures of 20 and $30^{\circ}C$, and the liquid wall subcoolings from 0.4 to $2.1^{\circ}C$. The measured condensation heat transfer coefficients were significantly lower than the predicted data by the Nusselt analysis. This trend in the stainless steel tube was explained by the effects of thermal resistance of tube material and surface roughness. Based on the experimental data with respect to wall thickness and surface roughness, it was suggested that the existing correlation on external condensation should be modified by considering material and surface roughness factors. The revised correlation was developed by introducing the effects of wall thickness and surface roughness into the Nusselt equation. The average deviation of the revised correlation was 13.0 %.

• 설비공학논문집
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• 제14권8호
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• pp.617-625
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• 2002

In this study, effects of refrigerant and oil charges on the performance of a refrigeration system simulating an automobile air conditioner have been experimentally investigated using R134a and PAG oil. Measurements were taken in a breadboard type refrigeration test unit with a compressor used for a commercial automobile air-conditioner under a set of condition imposed upon normally to automobile air conditioners. Both the COP and capacity decreased rapidly as the oil charge increased because of the decrease in vapor pressure of the circulating refrigerant/oil mixture. The excess oil left in the evaporator also caused heat transfer degradation resulting in a decrease in capacity and in turn COP. It was found that there is an optimum refrigerant charge at which the COP becomes the maximum. Below this optimum charge, both the capacity and COP increased as the refrigerant charge increased and above the optimum charge, both of them remained almost constant. Hence, the COP seems to be the most important factor in determining the optimum refrigerant charge. When the system was undercharged, the refrigerant at the condenser exit lost subcooling and showed a sign of poor miscibility.

• 설비공학논문집
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• 제29권5호
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• pp.231-238
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• 2017

HFO refrigerants have recently come to be regarded as promising alternatives to R134a for use in turbo chillers. This study provides results from experiments evaluating the film condensation heat transfer characteristics of HFO refrigerants R1234ze(E) and R1233zd(E) on smooth horizontal laboratory tubes. The experiments were conducted at a saturation vapor temperature of $38.0^{\circ}C$ with surface sub-cooling temperatures in the range of $3{\sim}15^{\circ}C$. We observe that the film condensation heat transfer coefficient decreases as surface sub-cooling temperatures increase. In the case of laboratory tubes with a diameter of 19.05 mm, the film condensation heat transfer coefficients of R1234ze(E) and R1233zd(E) were approximately 11% and 20% lower than those of R134a, respectively. Furthermore, our investigation of the effect of tube diameter on film condensation heat transfer coefficients, demonstrates an inverse relationship where the film condensation heat transfer coefficient increases as laboratory tube diameter decreases. We propose experimental correlations of Nusselt number for R1234ze(E) and R1233zd(E), which yield a ${\pm}20%$ error band.

• 설비공학논문집
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• 제18권12호
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• pp.971-976
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• 2006

The objectives of this paper are to study the characteristics of pool boiling heat transfer for enhanced tubes used in the evaporator of turbo chiller and to provide a guideline for optimum design of an evaporator using HFC134a. Three different enhanced tubes are tested at 4 different saturation temperatures. The wall super heated temperature difference ranges from $0.5^{\circ}C\;to\;3.5^{\circ}C$. The refrigerant, HFC134a evaporates on the outside of the tube while the chilled water flows inside the tube. This study provides experimental heat transfer coefficients for evaporation on the enhanced tubes. It is found that the turbo-II tube provides the highest heat transfer coefficient.

• KSBB Journal
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• 제31권2호
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• pp.134-143
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• 2016

Lycii fructus has been traditionally used as a preventive and therapeutic medicine to treat enervation and diverse chronic diseases. In this study, we investigated whether fermentation of Lycii fructus extract (LE) increases the enzymatic activity of the alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH). The fermentation of LE by Bacillus subtilis subsp. subtilis and Saccharomyces cerevisiae IFO 2376 was shown to increase the enzymatic activity of ADH and ALDH. TLC analysis of LE and fermented LE (FLE) showed that ADH and ALDH activities increased in different spots. Fraction No. 66 of LE and fraction No. 68 of FLE by Silica gel chromatography showed increased ADH activity of 129.1% and 148.9%, respectively. Fractions No. 128 of LE and FLE by Silica gel chromatography showed increased ALDH activity of 134.1% and 148.1%, respectively. The fraction No. 68 of FLE obtained by HPLC showed new peaks at $R_t$ 11.938min, $R_t$ 22.072min and $R_t$ 28.842min, indicating that ADH activity was increased. The LE and FLE fractions with the greatest increases in ADH activity peaked at the same time ($R_t$ 13min),whereas the LE and FLE fractions with the greatest increases in ALDH activity peaked at different times ($R_t$ 16.307min and $R_t$ 36.640min, respectively).

• 해양환경안전학회지
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• 제27권6호
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• pp.839-845
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• 2021

본 연구에서는 CO₂ 가스 배출 저감 및 선박 폐열 회수 증대를 목적으로 선박 배기로 버려지는 폐열을 전기로 변환하는 ORC(Organic Rankine Cycle) 발전에 대해 시뮬레이션을 통한 냉매별 효율을 보여주고 있다. 상대적으로 고온인 배기가스의 폐열과 상대적으로 저온인 냉각해수를 이용하여 Aspen HYSYS 11을 이용하여 시뮬레이션을 수행하였다. 해수냉각 ORC 발전시스템의 시뮬레이션 결과, 작동유체 효율은 R717 냉매가 2.86 %로 가장 높았고, 다음 순으로 R152a, R134a, R143a, R125a로 나타났다.

• 태양에너지
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• 제18권1호
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• pp.69-79
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• 1998

This paper is concerned about the performance of HCFC22 alternative refrigerants used in heat pumps and industrial chillers. A water-to-water breadboard heat pump with counter-current heat exchangers and a hermetic compressor was built to carry out the experiments with various refrigerants. For each test, more than 40 temperatures, 4 pressures, power input, mass flow rates of the heat transfer fluids were measured. Refrigerants tested were HCFC22, R290(Propane), an azeotrope of 45%Propane/55%R134a mixture, and a nonazeotropic mixture of Calor 50. All tests were conducted under ARI test A condition. It is found that the COP and capacity of propane were 18% and 2.5% higher than those of HCFC22 while the COP and capacity of 45%Propane/55%R134a mixture were 3.5% and 5.3% higher than those of HCFC22 respectively. Also the COP and capacity of Calor 50 were 17% and 7.8% higher than those of HCFC22. Compressor discharge temperatures of alternative refrigerants were roughly $35^{\circ}C$ lower than that of HCFC22 indicating that these refrigerants are good from the view point of compressor reliability. The charging amounts for the alternative refrigerants were reduced by 40-60% as compared to that of HCFC22. Overall, it can be said that hydrocarbon containing alternative refrigerants are excellent in thermodynamic performance but should be used with considerable care due to their flammability.