• 한국수소및신에너지학회논문집
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• 제22권3호
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• pp.402-408
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• 2011

Organic Rankine cycles (ORC) can be used to produce power from heat at different temperature levels available as geothermal heat, as biogenic heat from biomass, as solar or as waste heat. In ORC working fluids with relatively low critical temperatures and pressures can be compressed directly to their supercritical pressures and heated before expansion so as to obtain a better thermal match with their heat sources. In this work thermal performance of ORC with and without an internal heat exchanger is comparatively investigated in the range of subcritical and transcritical cycles. R134a is considered as working fluid and special attention is paid to the effect of turbine inlet pressure on the characteristics of the system. Results show that operation with supercritical cycles can provide better performance than subcritical cycles and the internal heat exchanger can improve the thermal efficiency when the temperature of heat source becomes higher.

• 청정기술
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• 제12권2호
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• pp.53-61
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• 2006

생분해성 고분자인 Poly(lactide-co-glycolide) (PLGA)와 약물 단백질로 약물 중합체를 만들기 위하여 초임계 나노 입자 제조 공정중 하나인 PGSS법을 이용하여 연구를 수행하였다. 초임계 이산화탄소에 의해서 고분자 PLGA의 유리전이온도($T_g$)를 강하시켜 가소화시키면서 단백질을 용기 내에서 혼합하였다. 고분자 PLGA에 캡슐화 된 단백질의 입자를 얻기 위해 고압 용기에 들어있는 시료를 노즐을 통하여 대기압으로 이산화탄소를 분사시켰다. 입자의 형태, 입자 크기 그리고 크기 분포에 대한 영향을 알아보기 위해서 고압 용기 안에서 초임계 이산화탄소를 이용하여 공정변수들을 조작함으로서 PGSS 실험을 하였다. 입자는 거칠고 불규칙하며 표면에 기공이 생성되었음을 확인하였다. 제조된 입자의 크기와 크기분포는 과포화도, 핵 생성시간 등으로 설명하였다. 제조된 입자 내의 protein의 활성도 저하는 거의 없었다.

• 대한기계학회논문집B
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• 제41권11호
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• pp.699-707
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• 2017

본 연구에서는 아홉 종류의 작동유체를 고려하여 저온 열원으로 구동되는 아임계 및 초월임계 유기 랭킨 사이클의 열역학적 성능 특성을 비교 해석한다. 터빈입구압력, 열원온도 및 작동유체가 열교환기 내 온도분포와 핀치포인트, 작동유체의 유량, 시스템 출력 및 열효율 등 시스템의 성능에 미치는 영향을 분석한다. 해석 결과는 작동유체의 압력이 아임계 영역에서 초임계 영역으로 높아지면 열교환기에서 열원과 작동유체 사이의 온도 불균일 정도가 감소하면서 시스템 출력이나 열효율 등은 증가하나 시스템의 단위출력당 터빈 크기는 작아짐을 보여준다.

• 한국응용과학기술학회지
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• 제31권2호
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• pp.231-237
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• 2014

최근 자원과 에너지를 절약하고 효과적으로 사용하여 환경 훼손을 줄이고 청정에너지를 이용할 수 있는 기술의 연구가 활발하게 진행되고 있다. 이와 관련 하여, 친환경적이고 경제적이며 독성이 거의 없는 초임계 유체가 물질의 합성과 프로세스에 많이 응용되고 있다. 이산화탄소는 낮은 임계온도와 압력, 가격 경쟁력 그리고 무독성 등의 장점을 가짐으로써 초임계 공정에 많이 사용되고 있는 용매중에 하나이다. 그러나 분자량이 높은 고분자들에게는 낮은 용해력이 단점으로 있어서 사용에 제한적이다. 따라서, 분자량이 높은 고분자를 용해하기 위해선 하이드로카본 계열의 용매를 사용하여야 한다. 본 연구에서는, 초임계 유체를 이용하여 Poly (methyl methacrylate)/클레이 나노 복합체 제조에 관한 연구를 진행 하였다. 또한, 초임계 유체 내에서 분산성을 극대화 할 수 있도록 $Na^+$-MMT 클레이 표면을 플로린 계열의 surfactant로 개질 시키어 복합체 제조에 응용 하였다. 개질된 클레이를 이용하여 제조 된 복합체는 neat Poly (methyl methacrylate)보다 향상된 기계적, 열적 특성을 보였으며, 제조 된 복합체는 X-ray 회절 방법, 열적 안정성 그리고 TEM 으로 나노 클레이의 분산성을 분석 하였다.

• 한국고분자학회:학술대회논문집
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• 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
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• pp.210-211
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• 2006

A series of L-LA polymerizations initiated by $Sn(Oct)_{2}\;([LA]_{0}/[Sn]_{0}=200)$ were carried out in scR22 at $130^{\circ}C$ and 300 bar, where $[LA]_{0}$ is the initial L-lactide concentration and $[Sn]_{0}$ is the initial $Sn(Oct)_{2}$ concentration. The reaction time dependences of monomer conversion and PLLA MW improved. The monomer conversion and PLLA MW increased with increasing reaction time. The effect of temperature on monomer conversion and PLLA MW was investigated in a series of polymerizations conducted at temperatures ranging from 90 to $150^{\circ}C$ and at a constant pressure of 200 bar. In all of these experiments, the ratio of monomer to R22 concentration was held constant at 12.4 wt.-%. Increasing the reaction temperature from 90 to $130^{\circ}C$ resulted in increased monomer conversion from 11.5 to 72.2 %.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2011년도 춘계학술논문집 1부
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• pp.306-309
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• 2011

A lattice model based molecular clusters is presented to improve a classical equation of state(EOS) for volumetric properties in the critical region. The term is based on the two assumptions: (1) The Helmholtz energy is individually divided into classical and long-range density fluctuation contribution (2) All molecules form cluster near the critical region due to long-range density fluctuation. To formulate such molecular cluster, we extended the Veytsman statistics originally developed for the cluster due to hydrogen bonding. The probability function in the statistics is modified to represent the characteristics of long-range density fluctuation vanishing far from critical region. The proposed fluctuation contribution was incorporated into the Sanchez-Lacombe EOS and the combined model with 6 adjustable parameters has been tested against experimental VLE data for pure compounds. The combined model is found to well represent flatten critical isotherm for methane and top of the coexistence curve for the tested components.

• 한국산학기술학회:학술대회논문집
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• 한국산학기술학회 2010년도 춘계학술발표논문집 2부
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• pp.961-964
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• 2010

A semi-empirical fluctuation term is presented to improve a classical equation of state (EOS) for volumetric properties in the critical region. The term is based on the two assumptions: (1) The Helmholtz energy is individually divided into classical and long-range density fluctuation contribution (2) All molecules form cluster near the critical region due to long-range density fluctuation. To formulate such molecular cluster, we extended the Veytsman statistics originally developed for the cluster due to hydrogen bonding. The probability function in the statistics is modified to represent the characteristics of long-range density fluctuation vanishing far from critical region. The proposed fluctuation contribution was incorporated into the Sanchez-Lacombe EOS and the combined model with 6 adjustable parameters has been tested against experimental VLE data. The combined model is found to well represent flatten critical isotherm for methane and top of the coexistence curve for the tested components. The prediction results for caloric data are in good agreement with the experimental data.

• 산업기술연구
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• 제18권
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• pp.267-275
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• 1998

Continuous thermodynamics has been applied for modeling of phase equilibria in multicomponent mixtures, to avoid disadvantages of the pseudo-component and key-component method. In this paper continuous thermodynamic relations formulated by using the Pate-Teja equation of state were adopted for calculations of phase equilibria in natural gas mixtures, crude oil mixtures and mixtures extracted by supercritical $CO_2$ fluids. Calculations of phase equilibria were performed by two procedures ; a moment method coupled with the beta distribution function and a quadrature method combined with Gaussian-Legendre polynomials. Calculated results were compared with experimental data. It was showed that continuous thermodynamic frameworks considered in this paper were well-matched to experimental data.

• Nuclear Engineering and Technology
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• 제52권9호
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• pp.2107-2118
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• 2020

The nuclear reactor coupled with supercritical carbon dioxide (S-CO₂) Brayton cycle has good prospects in generation IV reactors. Turbomachineries (turbine and compressor) are important work equipment in circulatory system, whose performances are critical to the efficiency of the energy conversion system. However, the sharp variations of S-CO₂ thermophysical properties make turbomachinery performances more complex than that of traditional working fluids. Meanwhile, almost no systematic analysis has considered the effects of turbomachinery efficiency under different conditions. In this paper, an in-house code was developed to realize the geometric design and performance prediction of S-CO₂ turbomachinery, and was coupled with systematic code for Brayton cycle characteristics analysis. The models and methodology adopted in calculation code were validated by experimental data. The effects of recompressed fraction, pressure and temperature on S-CO₂ recompression Brayton cycle were studied based on detailed design of turbomachinery. The results demonstrate that the recompressed fraction affects the turbomachinery characteristic by changing the mass flow and effects the system performance eventually. By contrast, the turbomachinery efficiency is insensitive to variation in pressure and temperature due to almost constant mass flow. In addition, the S-CO₂ thermophysical properties and the position of minimum temperature difference are significant influential factors of cyclic performance.

• 한국응용과학기술학회지
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• 제25권4호
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• pp.446-458
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• 2008

Essential fatty acids (EFA) are fatty acids that must be obtained from the diet because they can not be biosynthesized by human or animals. Gamma fatty acids contain gamma-linolenic acid (GLA, 18:3n-6) and dihomo-gamma-linolenic acid (DHGLA, 20:3n-6) as intermediate metabolites of linoleic acid (LA, 18:2n-6), which is an EFA found in vegetable oils. GLA is an important essential fatty acid that is required by human and animals to function normally. Recently, studies have indicated that GLA may be an essential component of the cell membrane, as well as an active component of dietary supplements and medicine. GLA must beadministered through the diet because it is converted into DHGLA in the body quickly and completely. DHGLA is a key material involved in the metabolism of LA. GLA is biosysthesized by the rate limiting step of ${\Deltac}^6$-desaturase, which is an enzyme that desaturates LA, there by allowing it to be converted into DHGLA via chain elongation. In addition, DHGLA exerts bioactive effects via action as a precursor of eicosanoid series 1. Breast milk contains an abundant amount of GLA; however, GLA is also available directly in evening primrose oil, black currant seed oil, borage oil and hemp seed oil. In addition, GLA enriched animal and plant can be produced using biotechnology, and highly pure GLA can be extracted using supercritical fluids, such as supercritical carbon dioxide, which will allow economically feasible production of GLA for use in medicines.