• 유체기계공업학회:학술대회논문집
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• 2001.11a
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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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• 2010.05a
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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.

• Journal of computational fluids engineering
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• v.15 no.3
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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.

• Journal of the Korean Ceramic Society
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• v.41 no.3
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• pp.242-246
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• 2004

Nano-sized a-alumina with a narrow distribution was prepared by using Flame Spray Pyrolysis (FSP). The microemulsion of water in oil (W/O) was prepared to make ultrafine droplets for FSP process. Kerosene (fuel) as a continuos phase and Al(NO$_3$)$_3$$.$9$H_2O$ (oxidizer) aqueous solution as a dispersed phase were prepared for microemulsification. The microemulsion with dispersion stability was obtained by adjusting the composition of 80 vol% kerosene, 10 vol% aqueous solution, and 10 vol% emulsifying agent. Microemulsion was sprayed onto the flame by using two-fluid nozzle spray gun under the condition of 0.03 ㎫ air pressure. The synthesized products were $\alpha$-alumina phase with the size of 20 to 30 nm.

• 한국전산유체공학회:학술대회논문집
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• 2005.04a
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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.

• Journal of the Korean Applied Science and Technology
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• v.29 no.1
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• pp.63-70
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• 2012

Magnetite in the use of magnetic fluid seal was synthesized by coprecipitation method. Mean particle size of magnetite was measured about 12 nm by using dynamic light scattering(DLS). As a result of XRD test, along with the $NH_4OH$ concentration was increased, the crystallinity of magnetite was increased. The zeta potential of dispersed ferrofluid in water was measured in the range from -49.3 mV to -26.2 mV by DLS. The shape of magnetite particle was sphere form, and the spiking effect of aqueous and oily ferrofulid was confirmed.

• Journal of the Korea Society for Simulation
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• v.6 no.2
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.9
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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.

• Journal of the Korean Magnetics Society
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• v.5 no.5
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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.

• Geophysics and Geophysical Exploration
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• v.18 no.3
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• pp.143-153
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• 2015

Polymer flooding for enhancing hydrocarbon production injects into a reservoir polymer solution that is viscous. It is very important to monitor the behavior pattern of the polymer solution in order to evaluate the effectiveness of polymer flooding. To monitor the distribution of polymer solution and thus fluid substitution within the reservoir, we first construct seismic and resistivity rock physics models (RPMs), which are functions of reservoir parameters such as rocks and type of fluid, fluid saturation. For the seismic and resistivity RPMs, responses of seismic and electromagnetic (EM) tomography are numerically simulated as polymer injection, using two dimensional (2D) staggered-grid finite difference elastic modeling and 2.5D finite element EM modeling algorithms, respectively. In constructing RPM for EM tomography, three different reservoir rocks are considered: clean-sand, dispersed shale-sand, and sand-shale lamination rocks. The polymer solution is assumed to have 2 wt% of polymer as normally generated, while water is freshwater or saltwater. Further, neutron logging is also considered to check its sensitivity to polymer flooding. The techniques discussed in the paper are important in monitoring not only hydrocarbon but also geothermal reservoirs.