• Korean Membrane Journal
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• v.9 no.1
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• pp.34-42
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• 2007

A perovskite-type ($La_{0.6}Sr_{0.4}Ti_{0.2}Fe_{0.8}O_{3-{\delta}}$) dense ceramic membrane was prepared by polymerized complex method, using citric acid as a chelating agent and ethylene glycol as an organic stabilizer. Effect of Ti addition on lanthanum-strontium ferrite mixed conductor was investigated by evaluating the thermal expansion coefficient, the oxygen flux, the electrical conductivity, and the phase stability. The thermal expansion coefficient in air was $21.19\;{\times}\;10^{-6}/K$ at 473 to 1,223 K. At the oxygen partial pressure of 0.21 atm ($20%\;O_2$), the electrical conductivity increased with temperature and then decreased after 973 K. The decrement in electrical conductivity at high temperatures was explained by a loss of the lattice oxygen. The oxygen flux increased with temperature and was $0.17\;mL/cm^2{\cdot}min$ at 1,223 K. From the temperature-dependent oxygen flux data, the activation energy of oxygen ion conduction was calculated and was 80.5 kJ/mol at 1,073 to 1,223 K. Also, the Ti-added lanthanum-strontium ferrite mixed conductor was structurally and chemically stable after 450 hours long-term test at 1,173 K.

• Journal of the Korean Ceramic Society
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• v.34 no.3
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• pp.289-295
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• 1997

Effect of ceramic processing was investigated on the microstructure and electronic properties of low loss Mn-Zn ferrite. Addition of CaO and SiO2 to calcined powder rather than to raw materials mixtured resulted in finer-grained microstructure. Higher oxygen pressure during sintering caused microstructural inhomogeneity and the increase in power loss and disaccommodation factor. Relatively low power loss was found for sintering up to 130$0^{\circ}C$ from powders calcined at high temperature and milled shortly. It was caused by slow densification rate and normal grain growth up to 130$0^{\circ}C$. Calcination at low temperature and prolonged milling enhanced den-sification, which gave a fine grained microstructure and low powder loss at sintering temperture below 120$0^{\circ}C$. Sintering temperature above 125$0^{\circ}C$, however, showed abnormal grain growth.

• Journal of computational fluids engineering
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• v.21 no.2
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• pp.90-98
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• 2016

A numerical study is conducted on thermal performance of a large-area hot plate specially designed as a heating and cooling tool for thermal nanoimprint lithography process. The hot plate has a dimension of $240mm{\times}240mm{\times}20mm$, in which a series of cartridge heaters and cooling holes are installed. The material is stainless steel selected for enduring the high molding pressure. A numerical model based on the ANSYS Fluent is employed to predict the thermal behavior of the hot plate both in heating and cooling phases. The PID thermal control of the device is modeled by adding user defined functions. The results of numerical computation demonstrate that the use of cartridge heaters provides sufficient heat-up performance and the active liquid cooling in the cooling holes provides the required cool-down performance. However, a crucial technical issue is raised that the proposed design poses a large temperature non-uniformity in the steady heating phase and in the transient cooling phase. As a remedy, a new hot plate in which heat pipes are installed in the cooling holes is considered. The numerical results show that the installation of heat pipes could enhance the temperature uniformity both in the heating and cooling phases.

• Journal of the Korean Society for Heat Treatment
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• v.14 no.2
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• pp.103-109
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• 2001

Plasma nitrocarburising and post oxidation were performed on SM45C steel using a plasma nitriding unit. Nitrocarburising was carried out with various methane gas compositions with 4 torr gas pressure at $570^{\circ}C$ for 3 hours and post oxidation was carried out with 100% oxygen gas atmosphere with 4 torr at different temperatures for various times. It was found that the compound layer produced by plasma nitrocarburising consisted of predominantly ${\varepsilon}-Fe_{2-3}(N,C)$ and a small proportion of ${\gamma}-Fe_4(N,C)$. With increasing methane content in the gas mixture, ${\varepsilon}$ phase compound layer was favoured. In addition, when the methane content was further increased, cementite was observed in the compound layer. The very thin oxide layer on top of the compound layer was obtained by post oxidation. The formation of Oxide phase was initially started from the magnetite($Fe_3O_4$) and with increasing oxidation time, the oxide phase was increased. With increasing oxidation temperature, oxide phase was increased. However the oxide layer was split from the compound layer at high temperature. Corrosion resistance was slightly influenced by oxidation times and temperatures.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.21 no.1
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• pp.1-10
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• 2011

Generally, the tire curing process is the process in which the sulfur is added and subsequently the tire is heated to give the tire elasticity. In this process, all kinds of the chemicals in the tire are emitted with a lot of heat. The chemical fume and heat aggravate the work environment. To solve this problem, 92 local exhaust ventilators and 8 gravity ventilators were used, but not satisfactory yet. Preliminary survey showed that the temperatures in the process were very high: 30.3, 32.9 and $37.2^{\circ}C$ at 2, 4 and 6m above the ground level, respectively in the winter (outside temperature was $2^{\circ}C$). It can be imagined that the process is severely hot in the summer time. The higher temperature distribution in the higher space tells us that the hot plume could not be removed with the existing ventilation systems. Therefore, in this study, some alternative ventilation systems were designed. The partitions were used to contain the hot plume to increase the capture efficiency. The gravity ventilators were newly designed to improve the extraction efficiency of hot fume. To satisfy the balance of pressure in the curing process, some supply air system was introduced by renewing the existing air conditioning system. Many alternative solutions were evaluated by using computational fluid dynamics modelling. The best and applicable solution was selected and the existing ventilation system was modified. After implementing the new ventilation system, the hot environment was much improved. The temperature reduction in the curing process was about $6.4^{\circ}C$.

• Proceedings of the Materials Research Society of Korea Conference
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• 2011.10a
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• pp.31.2-31.2
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• 2011

We studied a method of manufacturing an anode to restrict contraction in reducing NiO/YSZ by uniformly mixing. In order to mix Ni and YSZ, a sub-micron Ni core surface was coated at high-speed by a mixture of nano-sized YSZ and a spherical core-shell was subsequently formed. The micron-sized core-shell anode powder was then heat treated at $400{\sim}1,450^{\circ}C$ in an air atmosphere and Ni was extruded and synthesized in nano-size. Subsequently, when the nano-sized mixture of the anode was heat treated and maintained at a temperature of $1,450^{\circ}C$, the anode was manufactured, where Ni and YSZ were uniformly distributed with the nano-structure. According to the nano-sized anode powder synthesis process, Ni particles were oxidized at $400{\sim}500^{\circ}C$ and became spherical by surface tension. In the case of the spherical core Ni powder, the heat treatment temperature rose to $1,250^{\circ}C$ and then a gap between the internal and external pressures occurred due to thermal and tensile stresses. A crack subsequently appeared on the surface, and the heat treatment temperature was increased continuously to increase the pressure gap and then the core Ni extruded as a nano-sized powder, Ni and YSZ uniformly distributed. It was found that the anode of 50~200 nm with a consistent structure obtained in this study has electric conductivity that is approximately 3 times larger than that of a commercial anode.

• Journal of Energy Engineering
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• v.12 no.1
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• pp.1-10
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• 2003

Pressurized fluidized bed combustion unit is operated at pressures of 1~1.5 MPa with combustion temperatures of 850~87$0^{\circ}C$. The pressurized coal combustion system heats steam, in conventional heat transfer tubing, and produces a hot gas supplied to a gas turbine. Gas cleaning is a vital aspect of the system, as is the ability of the turbine to cope with some residual solids. The need to pressurize the feed coal, limestone and combustion air, and to depressurize the flue gases and the ash removal system introduces some significant operating complications. The proportion of power coming from the steam : gas turbines is approximately 80:20%. Pressurized fluidized bed combustion and generation by the combined cycle route involves unique control considerations, as the combustor and gas turbine have to be properly matched through the whole operating range. The gas turbines are rather special, in that the maximum gas temperature available from the FBC is limited by ash fusion characteristics. As no ash softening should take place, the maximum gas temperature is around 90$0^{\circ}C$. As a result a high pressure ratio gas turbine with compression intercooling is used. This is to offset the effects of the relatively low temperature at the turbine inlet.

• 한국신재생에너지학회:학술대회논문집
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• 2011.05a
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• pp.179.1-179.1
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• 2011

Pretreatment of cellulosic biomass is necessary before enzymatic saccharification and fermentation. The objective of this study was to evaluate the effect of combined aqueous ammonia-dilute sulfuric acid treatment on cellulosic biomass. Miscanthus was pretreated using aqueous ammonia and dilute sulfuric acid solution under high temperature and pressure conditions to be converted into bioethanol. Aqueous ammonia treatment was performed with 15 %(w/w) ammonia solution at $150^{\circ}C$ of reaction temperature and 20 minutes of reaction time. And then, dilute sulfuric acid treatment was performed with 1.0 %(w/w) sulfuric acid solution at $150^{\circ}C$ of reaction temperature and 10 minutes of reaction time. The compositional variations of this combined aqueous ammonia-dilute sulfuric acid treatment resulted in 68.0 % of cellulose recovery and 95.7 % of hemicellulose, 81.3 % of lignin, 89.1 % of ash removal respectively. The enzymatic digestibility of 90.5 % was recorded in the combined pretreated Miscanthus sample and it was 14.7 times higher than the untreated sample. The ethanol yield in the Simultaneous Saccharification and Fermentation was 90.4 % of maximum theoretical yield based on cellulose content of the combined pretreated sample and it was about 98 % compared to the ${\alpha}$-cellulose ethanol yield.

• Journal of Powder Materials
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• v.23 no.5
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• pp.384-390
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• 2016

Tri-isotropic (TRISO) coatings on zirconia surrogate beads are deposited using a fluidized-bed vapor deposition (FB-CVD) method. The silicon carbide layer is particularly important among the coated layers because it acts as a miniature pressure vessel and a diffusion barrier to gaseous and metallic fission products in the TRISO-coated particles. In this study, we obtain a nearly stoichiometric composition in the SiC layer coated at $1400^{\circ}C$, $1500^{\circ}C$, and $1400^{\circ}C$ with 20 vol.% methyltrichlorosilane (MTS), However, the composition of the SiC layer coated at $1300-1350^{\circ}C$ shows a difference from the stoichiometric ratio (1:1). The density decreases remarkably with decreasing SiC deposition temperature because of the nanosized pores. The high density of the SiC layer (${\geq}3.19g/cm^2$) easily obtained at $1500^{\circ}C$ and $1400^{\circ}C$ with 20 vol.% MTS did not change at an annealing temperature of $1900^{\circ}C$, simulating the reactor operating temperature. The evaluation of the mechanical properties is limited because of the inaccurate values of hardness and Young's modulus measured by the nano-indentation method.

• Transactions of the Korean Society of Automotive Engineers
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• v.15 no.2
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• pp.1-7
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• 2007

The effect of injector geometries including the injection angle and number of nozzle holes on homogeneous charge compression ignition (HCCI) engine combustion has been investigated in an automotive-size single-cylinder diesel engine. The HCCI engine has advantages of simultaneous reduction of PM and NOx emissions by achieving the spatially homogenous distribution of diesel fuel and air mixture, which results in no fuel-rich zones and low combustion temperature. To make homogeneous mixture in a direct-injection diesel engine, the fuel is injected at early timing. The early injection guarantees long ignition delay period resulting in long mixing period to form a homogeneous mixture. The wall-impingement of the diesel spray is a serious problem in this type of application. The impingement occurs due to the low in-cylinder density and temperature as the spray penetrates too deep into the combustion chamber. A hole-type injector (5 holes) with smaller angle ($100^{\circ}$) than the conventional one ($150^{\circ}$) was applied to resolve this problem. The multi-hole injector (14 holes) was also tested to maximize the atomization of diesel fuel. The macroscopic spray structure was visualized in a spray chamber, and the spray penetration was analyzed. Moreover, the effect of injector geometries on the power output and exhaust gases was tested in a single-cylinder diesel engine. Results showed that the small injection angle minimizes the wall-impingement of diesel fuel that results in high power output and low PM emission. The multi-hole injector could not decrease the spray penetration at low in-cylinder pressure and temperature, but still showed the advantages in atomization and premixing.