• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.281-286
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• 2001

The radial turbine has been successfully applied to the systems which request relatively small output compared with the axial turbine, and has low manufacturing cost due to it's small size and simple structure. Recently, the researches on the development and the efficiency maximization of the radial turbine are in progress corresponding with the trend toward miniaturization in turbo machinery and the development of small dispersed power generation systems. The radial turbine is to be applied to our turbo refrigerator of which engine speed is 26,000 rpm and turbine efficiency is $88\%$. Also, as a heat exchanger is accepted instead of a combustor in our turbo refrigerator, the design of radial turbine has been performed to be appropriate to the circumstance of low temperature air, not high temperature combustor gas, into the turbine inlet . This radial turbine is being developed in consideration with not only the aero-dynamic performance but also the simplification of manufacturing and integration, and the durability at operating condition. This paper refer to the performance evaluation about the radial turbine design by comparison with consulting from Russia and the our evaluation about various design factors which are considered in aero-dynamic design process.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.320-325
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• 2010

A multiphase CFD analysis is performed to investigate the effect of near-wall grid for simulating a subcooled boiling flow in vertical tube. The multiphase flow model used in this CFD analysis is the two-fluid model in which liquid(water) and vapor(steam) are considered as continuous and dispersed fluids, respectively. A wall boiling model is also used to simulate the subcooled boiling heat transfer at the heated wall boundary. The diameter and heated length of tube are 0.0154 m and 2 m, respectively. The system pressure in tube is 4.5 MPa and the inlet subcooling is 60 K. The near-wall grid size in the non-dimensional wall unit ($y_{w}^{+}$) was examined from 64 to 172 at the outlet boundary. The CFD calculations predicted the void distributions as well as the liquid and wall temperatures in tube. The predicted axial variations of the void fraction and the wall temperature are compared with the measured ones. The CFD prediction of the wall temperature is shown to slightly depend on the near-wall grid size but the axial void prediction has somewhat large dependency. The CFD prediction was found to show a better agreement with the measured one for the large near-wall grid, e.g., $y_{w}^{+}$ > 100.

• 한국전산유체공학회지
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• 제15권3호
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• pp.24-31
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• 2010

boiling flow in vertical tube. The multiphase flow model used in this CFD analysis is the two-fluid model in which liquid(water) and gas(vapour) are considered as continuous and dispersed fluids, respectively. A wall boiling model is also used to simulate the subcooled boiling heat transfer at the heated wall boundary. The diameter and heated length of tube are 0.0154 m and 2 m, respectively. The system pressure in tube is 4.5 MPa and the inlet subcooling is 60 K. The near-wall grid size in the non-dimensional wall unit for lqiuid phase ($y^+_{w,l}$) was examined from 101 to 313 at the outlet boundary. The CFD calculations predicted the void distributions as well as the liquid and wall temperatures in tube. The predicted axial variations of the void fraction and the wall temperature are compared with the measured ones. The CFD prediction of the wall temperature is shown to slightly depend on the near-wall grid size but the axial void prediction has somewhat large dependency. The CFD prediction was found to show a better agreement with the measured one for the large near-wall grid, e.g., $y^+_{w,l}$ > 300 at the tube exit.

• 한국세라믹학회지
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• 제41권3호
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• pp.242-246
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• 2004

화염분무열분해(FSP) 공정을 이용하여 결정질의 좁은 입도분포를 가지는 $\alpha$-알루미나 나노입자를 제조하였다. 초미분의 액적을 형성시키기 위해 전구체 용액으로서 연료인 등유를 연속상으로 하고 산화제인 알루미늄 질산염 수용액을 분산상으로 하는 유중수적(W/O)형의 마이크로에멀전을 제조하였다 0.5M 농도의 알루미늄 질산염 수용액을 10vol%, 등유 80vol%, 그리고 유용성 유화제 10vol%를 혼합하여 안정한 분산상태를 가지는 마이크로에멀전을 제조한 후, 이류체 노즐 분무기를 사용하여 0.03㎫의 공기 압력으로 분무하여 화염에 직접 노출시켰다. 제조된 생성물은 20에서 30 나노미터의 균일한 크기를 가지는 $\alpha$-알루미나 상으로 확인되었다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 춘계 학술대회논문집
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• pp.47-50
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• 2005

The Grid'[1] means the collaboration of computing and experimental resources in dispersed organizations by high-speed network. It has been paid much attention for an unlimited number of potential resources available and the easiness to build collaborative environments among multiple disciplines. However, the difficulty in establishing the environments and accessing and utilizing the resources has prevented application scientists from conducting Grid computing. Thus, the present study focuses on building PSE(Problem Solving Environment) which assists application researchers to easily access and utilize the Grid. The Cactus toolkit, originally developed by astrophysicists, is used as a base frame for Grid PSE. Some modules are newly developed and modified for CFD(Computational Fluid Dynamics) analysis. Simultaneously, a web portal, Grid-One portal, is built for remote monitoring/control and job migration. Cactus frame through the web portal service has been applied to various CFD problems, demonstrating that the developed PSE is valuable for large-scaled applications on the Grid.

• 한국응용과학기술학회지
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• 제29권1호
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• pp.63-70
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• 2012

자성유체 유체씰에 사용할 수 있는 마그네타이트를 공침법에 의하여 합성하였다. 마그네타이트의 평균입자크기는 동적광산란 측정장치(DLS)에 의해 약 10-12 nm 로 측정되었다. XRD 측정결과, $NH_4OH$ 의 농도가 증가함에 따라 마그네타이트의 결정화도가 증가하였다. 수중 분산된 자성유체의 제타전위는 -49.3 mV 에서 -26.2 mV 까지 DLS에 의하여 측정되었다. 입자의 형상은 구형이었고, 수상과 유상 자성유체에서 스파이킹 효과를 확인하였다.

• 한국시뮬레이션학회논문지
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• 제6권2호
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• pp.1-14
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• 1997

The characteristics of the flow and energy conversion in OMACON liquid-metal MHD system are investigated. Numerical simulation of two-phase flow in the OMACON system without magnetic field was carried out by the Phoenics code and the energy conversion characteristics are studied in association with the fact that the mechanical energy loss at the nozzle of the OMACON system are to be converted into electrical energy. In this system, working fluid (gas) is injected through the mixer located at the bottom of the riser, and is mixed with hot liquid metal. Therefore in the riser two-phase flow is developed under the influence of the gravity. In this study, the interaction between the gas and liquid is considered by the use of IPSA(InterPhase Slip Algorithm) where standard drag coefficient has been used. It has been assumed that in the flow regime the liquid is continuous and the gas is dispersed. For the liquid and gas, the continuity equations, momentum equations and energy equations are solved respectively in association with void fraction in the flow field. In order to calculate the energy conversion efficiency, firstly the ratio of the mechanical energy loss of liquid metal flow at the nozzle to the input thermal energy is considered. Secondly flow pattern of liquid metal in the generator has been analyzed, and the characteristics of the conversion of the mechanical energy into the electrical energy has been investigated. For an representative case where Hartmann number is 540 and magnetic field is 0.35 T, the present analysis shows that the energy conversion efficiency is 0.653. This result is considered to be reasonable in comparison with published experimental results.

• 설비공학논문집
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• 제21권9호
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• pp.483-495
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• 2009

Feedwater heaters of many nuclear power plants have recently experienced severe wall thinning damange, which will increase as operating time progresses. Several nuclear power plants in Korea have experienced wall thinning damage in the area around the impingement baffle-installed downstream of the high pressure turbine extraction stream line-inside number 5A and 5B feedwater heaters. At that point, the extracted steam from the high pressure turbine is two phase fluid at high temperature, high pressure, and high speed. Since it flows in reverse direction after impinging the impingement baffle, the shell wall of the number 5 high pressure feedwater heater may be affected by flow-accelerated corrosion. This paper describes operation of experience and numerical analysis composed similar condition with real high pressure feedwater heater. This study applied squared, curved and new type impingement baffle plates to feedwater heater same as previous study. In addition, it shows difference of pressure distribution and value between single phase and two phase based on experience and numerical analysis.

• 한국자기학회지
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• 제5권5호
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• pp.819-823
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• 1995

The oil-based magnetic fluids were sysnthesized using ultra-fine $Fe_{3}O_{4}$ powder dispersed in hydrocarbon oil. To synthesize ultra-fine $Fe_{3}O_{4}$, we carried out the experiments varying the pH of reacting medium and the initial concentration of $Fe^{2+}$. We also investigated the amount of oleic acid to obtain a stable dispersion and the proper base oil of MF for loudspeaker application. The limits of adsorbed amount of oleic acid on the $Fe_{3}O_{4}$ surface were approximately 35~40 percents of the total magnetite weight. As the $Fe_{3}O_{4}$ content increased from 0.1g/cc to 0.6g/cc, the viscosity of oil-based magnetic fluid increased from 1,063cP to 1,828cP, and its saturation magnetization at 10kOe increased from 66G to 242G. When we tested the MF sample to a commercial speaker, improvements were noted.

• 지구물리와물리탐사
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• 제18권3호
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• pp.143-153
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• 2015

탄화수소 생산에서 화학공법은 폴리머 용액을 저류층에 주입함으로써 탄화수소의 생산량을 증대시키는 방법이다. 화학공법의 유용성을 파악하기 위해서는 저류층 내 폴리머 용액의 거동 양상을 모니터링하는 것이 매우 중요하다. 저류층 내 폴리머 용액과 유체 변화에 대한 모니터링의 가능성을 확인하기 위해, 저류층을 구성하고 있는 암석 및 유체의 종류, 포화도 등의 매개변수에 따른 탄성파 및 전기비저항 암석물리모델을 구성하고, 폴리머 주입에 따른 탄성파 및 EM 토모그래피의 반응을 계산하였다. 특히 전기비저항 암석물리모델 구성에서는 순수사암, 셰일질 사암, 사암셰일박리층 3가지의 서로 다른 저류층 암석을 고려하였다. 폴리머 용액의 농도는 가장 일반적으로 이용되는 2 wt%로 하고 담수를 이용한 경우와 염수를 이용한 경우로 나누어 분석하였다. 더 나아가, 화학공법에 대한 중성자검층 민감도 분석을 수행하였다. 이 논문에서 다루는 기법들은 탄화수소 저류층뿐만 아니라 지열 저류층 등의 모니터링에 있어서도 중요하게 적용될 것이다.