• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 제39회 하계학술대회
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• pp.1663-1664
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• 2008

Many years ago, most of thermal power plants built in this country were of subcritical pressure, of medium or small size, of constant pressure operations and of drum type steam generators with circulation type boilers. But, nowadays almost all of them were of high efficiency, of supercritical pressure, of big capacity, of sliding pressure operations, and of once through type steam generators. Presently built once through boilers introduce turbine bypass systems to variable pressure operation which eliminates unexpected materials in boiler tube during startup, minimizes fuel loss by short startup period and eventually improve both total efficiency and power system stability.

• 대한수학회논문집
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• 제16권1호
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• pp.137-152
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• 2001

Steady two-dimensional flows due to an applied pressure distribution in water of finite depth are considered. Gravity is included in the dynamic boundary condition. Gravity is included in the dynamic boundary condition. The problem is solved numerically by using the boundary integral equation technique. It is shown that, for both supercritical and subcritical flows, solutions depend on three parameters: (i) the Froude number, (ii) the magnitude of applied pressure distribution, and (iii) the span length of pressure distribution. For supercritical flows, there exist up to two solutions corresponding to the same value of Froude number for positive pressures and a unique solution for negative pressures. For subcritical flows, there are solutions with waves behind the applied pressure distribution. As the Froude number decreases, these waves when the Froude numbers approach the critical values.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1997년도 추계학술대회 논문집 학회본부
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• pp.238-241
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• 1997

The recent trend toward increased use of the once-through supercritical boiler worldwide is mainly due to its rapid response. The transient behavior of the steam generator are essential in the study of the system performance of power plants as well as for the design of their appropriate control systems. In this paper, a mathmatical model of the once-through supercritical pressure boiler is obtained by simulating a set of nonlinear differential and algebraic equations.

• Bulletin of the Korean Chemical Society
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• 제19권12호
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• pp.1351-1355
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• 1998

A simple apparatus for adding a modifying solvent to supercritical CO2 extractant was described. Small, fixed volumes (typically 100 μL) of liquid modifying solvents were delivered during the extraction process by use of an in-line high pressure loop injector and an air pump. Without disconnecting the extraction cell from the supercritical fluid extraction system, the modifying solvent was repeatedly delivered. The solvent modification device was optimized during the extraction of carbaryl and bis(acetylacetonato) copper(Ⅱ). Extraction recoveries from spiked filter paper and soil samples ranged between 22% and 109%, depending on the analyte and matrix components. The addition of polar modifying solvents were necessary to improve the extractability of the nonpolar CO2.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2011년도 제36회 춘계학술대회논문집
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• pp.103-108
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• 2011

초임계환경에서 작동하는 케로신/액체산소 동축와류형 분사기의 혼합특성을 수치적으로 연구하였다. 케로신 물성치를 계산하기 위하여 써로게이트 모델이 적용되었다. 난류모델은 LES를 기반으로 하였고, 초임계영역의 상태량을 계산하기위해 SRK 상태방정식, 점성계수와 열전도도에 대하여 Chung이 제안한 고압상태 혼합물에 대한 방정식, 확산계수에 대하여 Fuller 이론에 Takahashi가 제안한 고압상태의 특징을 고려한 식을 적용하였다. 연소실 압력변화에 따른 분사기와 연소실에서의 열역학적 물성치와 혼합특성을 관찰하였다. 또한 분사기의 압력섭동 스펙트럼밀도를 분석하였다.

• 생명과학회지
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• 제13권5호
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• pp.569-575
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• 2003

초임계 이산화탄소를 이용하여 saw palmitto로부터 전립선 비대증 치료를 위한 유효성분을 효율적으로 추출하기 위하여 초임계 유체의 압력(22, 30 Mpa), 온도 $(35^{\circ}C,\; 60^<\circ}C)$, 및 보조용매의 농도, 및 추출시간에 다른 효율을 조사하였다. 보조 용매로는 메탄올보다는 에탄올이 효과적이었고. 보조용매의 농도가 증가할수록 유효성의 추출 효율은 증가하였고 15% 에탄올 농도에서 효율이 가장 높았다. 15%에탄올 농도에서 초임계유체의 최적 추출조건은 압력은 30 Mpa, 온도는$60^<\circ}C$이였고, 추출시간에 따른 추출효율은 추출시간이 증가할수록 완만하게 증가하는 경향을 나타내었다. 초임계 이산화탄소의 추출조건으로 saw palmitto로부터 전립선 비대 치료를 위한 유효물질을 추출할 수 있다.

• Tribology and Lubricants
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• 제37권3호
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• pp.99-105
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• 2021

In this study, for a high-pressure turbine (HPT) of 800 MW class supercritical thermal-power plant, considering aerodynamic cross-coupling, we performed a rotordynamic logarithmic decrement (LogDec) stability analysis with various tilting pad journal bearing (TPJB) designs, which several steam turbine OEMs (original equipment manufacturers) currently apply in their supercritical and ultra-supercritical HPTs. We considered the following TPJB designs: 6-Pad load on pad (LOP)/load between pad (LBP), 5-Pad LOP/LBP, Hybrid 3-Pad LOP (lower 3-Pad tilting and upper 1-Pad fixed), and 5-Pad LBPs with the design variables of offset and preload. We used the API Level-I method for a LogDec stability analysis. Following results are summarized only in a standpoint of LogDec stability. The Hybrid 3-Pad LOP TPJBs most excellently outperform all the other TPJBs over nearly a full range of cross-coupled stiffness. In a high range of cross-coupled stiffness, both the 6-Pad LOP and 5-Pad LOP TPJBs may be recommended as a practical conservative bearing design approach for enhancing a rotordynamic stability of the HPT. As expected, in a high range of cross-coupled stiffness, the 6-Pad LBP TPJBs exhibit a better performance than the 5-Pad LBP TPJBs. However, contrary to one's expectation, notably, the 5-Pad LOP TPJBs exhibit a slightly better performance than the 6-Pad LOP TPJBs. Furthermore, we do not recommend any TPJB design efforts of either increasing a pad offset from 0.5 or a pad preload from 0 for the HPT in a standpoint of stability.

• Preventive Nutrition and Food Science
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• 제16권3호
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• pp.261-266
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• 2011

Supercritical $CO_2$ pretreatment before dehydration leads to a faster dehydration rate. The best supercritical $CO_2$ pretreatment conditions for the most effective dehydration were $45^{\circ}C$, 25 MPa and $55^{\circ}C$, 25 MPa. Increasing pressure of the supercritical $CO_2$ pretreatment system tended to accelerate the dehydration rate more than increasing temperature did. Samples pretreated at higher temperatures and pressures showed greater shrinking and pore distribution on scanning electron microscopy. Control samples maintained their cell walls, whereas samples pretreated at higher temperatures and pressures showed more cell disruption, and more pores were observed. Pore sizes of control and pretreated samples were about 100 and $70{\sim}80\;{\mu}m$, respectively. Samples pretreated at higher temperatures and pressures had smaller pores and a denser distribution.

• Nuclear Engineering and Technology
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• 제40권2호
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• pp.107-116
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• 2008

The present paper describes the preliminary compilation, assessment and examination of the supercritical heat transfer(SCHT) database. The availability and reliability of the SCHT data are discussed. Similarities in thermodynamic supercritical properties and SCHT behaviour of water, $CO_{2}$ and R-134a have been examined and some tentative conclusions are made. Finally, the future experimental and analytical program at the University of Ottawa is described.

• 한국세라믹학회지
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• 제37권7호
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• pp.625-631
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• 2000

In this study, the characteristics and sinterablities of TiO2 powders which were fabricated on sol-gel process and supercritical fluid process were examined. The powders fabricated on sol-gel process were amorphous. The particle size and shape were changed with the amount of water used for hydrolysis of titanium ethoxide. The powders were changed from amorphous to crystalline by heating at 400℃. The crystalline anatase TiO2 powders were directly prepared in ethanol supercritical fluid condition that temperature was 270±3℃ and pressure was 7.3 MPa. It's primary crystalline size was 20 nm and agglomerated as spherical shape whose size was 0.7∼1㎛. The powders prepared on sol-gel process were not sintered densely at 900℃ because of abnormal grain growth. However, the powders which prepared on supercritical fluid process were sintered densely at the comparatively low temperature of 800℃ by ideal growth of grain, which are fired at 900℃.