• Journal of the Korean Solar Energy Society
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• v.36 no.3
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• pp.63-74
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• 2016

The nanofluids are the fluids with excellent thermal property, it is expected as a working fluid of the next generation. The nanofluids are well known that if it is used in the boiling heat transfer system, the critical heat flux is enhanced up to 200%, and the thermal conductivity is increased up to from 10 to 160%. However, the fouling phenomenon can be occurred that nanoparticles of nanofluids are deposited on the heat transfer surface. Therefore, to investigate relation between nanofluid and fouling, this study is carried out using oxidized graphene nanofluid. Also it compared and analyzed the critical heat flux and the boiling heat transfer coefficient. As the result, in case of oxidized graphene deposition for fouling, the critical heat flux is increased up to 20% more than oxdized graphene nanofluid. However, the boiling heat transfer coefficient is decreased down to about $6kW/m^2K$ at $1,000kW/m^2$ more than pure water.

• Korean Journal of Poultry Science
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• v.22 no.2
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• pp.117-128
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• 1995

Vitarnin A levels of egg yolk from hens fed diets supplemented with vitamin A increased slowly up to Week 4, while the values rapidly increased thereafter. The highest value(360% of initial value) was observed at Week 8 in birds fed 64,000 IU of vitamin A/kg diet. On the other hand, the contents of vitamin E in egg yolk rapidly increased in the first 2 weeks of the experiment and then stabilized up to Week 8. However, the efficiency of egg transfer decreased(P<0.05) as dietary vitamins A and E levels increased. It took at least 4 weeks for the increased levels of vitamin A and E in eggs from hens fed diets supplemented with each vitamin to recover the normal levels. Vitamin E levels of egg yolk in hens fed the vitamin A supplemented diets decreased as dietary vitamin A level increased (P<0.05). On the other hand, a slightly reduced levels of vitamin A levels of egg yolks from hens fed the vitamin E supplemented diet for 4 weeks of experiment was recovered back to control level at Week 8(P<0.05). Supplemental vitamin A markedly decreased the yolk deposition of vitamin F when two vitamins were supplemented simultaneously. The yolk deposition of vitamin A decreased as high level of vitamin B was supplemented, suggesting an antagonistic interactions between the two vitamins.

• Nuclear Engineering and Technology
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• v.52 no.10
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• pp.2353-2360
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• 2020

An anodic electrophoretic deposition (EPD) technique is used to create a uniform TiO₂ thin film coating on boiling thin steel plates (1.1 mm by 90 mm). All of the effective parameters except time of the EPD method are kept constant. To investigate the effect of gamma irradiation on the critical heat flux (CHF), the test specimens were irradiated in a gamma cell to different doses ranging from 100 to 300 kGy, and then SEM and BET analysis were performed. For each coated specimen, the contact angle and capillary length were measured. The specimens were then tested in a boiling pool for CHF and boiling heat transfer coefficient. It was observed that irradiation significantly decreases the maximum pore diameter while it increases the porosity, pore surface area and pore volume. These surface modifications due to gamma irradiation increased the CHF of the nano-coated surfaces compared to that of the unirradiated surfaces. The heat transfer coefficient (HTC) of the nano-coated surfaces irradiated at 300 kGy increased from 83 to 160 kW/(㎡ K) at 885 kW/㎡ wall heat flux by 100%. The CHF of the irradiated (300 kGy) and unirradiated surfaces are 2035 kW/㎡ and 1583 kW/㎡, respectively, an increase of nearly 31%.

• 한국연소학회:학술대회논문집
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• 2015.12a
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• pp.197-200
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• 2015

Understanding the slag flow behavior is important in an entrained coal gasifier for its influence of ash discharge and wall heat transfer rate. This study presents a new model to predict the transient behavior of the liquid and solid slag layers. Unlike the previous steady-state model, the solid slag layer was included in solving the governing equations in order to identify the temporal and spatial transformation between the solid-liquid slag, rather than treating the solid region as a boundary condition of the liquid layer. The performance of the new model was evaluated for changes in the slag deposition rate (${\pm}10%$) and gas temperature (${\pm}50K$) in a simple cylindrical gasifier. The results show that the characteristic times to reach a new steady-state ranged between 80 s to 180s for the changes in the two parameters. Because the characteristic times of the gasifier temperature and slag deposition rate by changes in the coal type and/or operating conditions would be almost instantaneous, the time-scale for the slag thickness at the bottom of the gasifier to stabilize was much larger.

• Journal of the Korean Institute of Telematics and Electronics
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• v.27 no.10
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• pp.113-123
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• 1990

Tungsten film was deposited on the single crystal silicon wafer in a low pressure chemical vapor deposition reactor from silane and tungsten hexafluoride in the temperature range of $250-400^{\circ}C$ Deposition rate was found to be determined by the mass transfer rate of reactants from the gas phase to the safter surface. It was found out that tungsten films deposited contained about 3 atomic $\%$ of silicon and that the crystallinity and the grain size increased as the deposition temperature was increased. The resistivity of the film was measured to be in the range of $7~25{\mu}{\Omega}-cm$ and decreased with increasing deposition temperature. The adhesion of the tungsten film on a silicon surface was measured by the tape peel off test and it was improved with increasing deposition temperature. From the analysis of the gas composition, the reaction pathway to form $SiF_{4}$ and $H_{2}$ was found to be more favorable than HF formation.

• Korean Journal of Materials Research
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• v.15 no.11
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• pp.705-710
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• 2005

NIL (nanoimprint lithography) technique has demonstrated a high potential for wafer size definition of nanometer as well as micrometer size patterns. During the replication process by NIL, the stiction between the stamp and the polymer is one of major problems. This stiction problem is moi·e important in small sized patterns. An antistiction layer prevents this stiction ana insures a clean demolding process. In this paper, we were using a TCP (transfer coupled plasma) equipment and $C_4F_8$ as a precursor to make a Teflon-like antistiction layer. This antistiction layer was deposited on a 6 inch silicon wafer to have nanometer scale thicknesses. The thickness of deposited antistiction layer was measured by ellipsometry. To optimize the process factor such as table height (TH), substrate temperature (ST), working pressure (WP) and plasma power (PP), we were using a design of experimental (DOE) method. The table of full factorial arrays was set by the 4 factors and 2 levels. Using this table, experiments were organized to achieve 2 responses such as deposition rate and non-uniformity. It was investigated that the main effects and interaction effects between parameters. Deposition rate was in proportion to table height, working pressure and plasma power. Non-uniformity was in proportion to substrate temperature and working pressure. Using a response optimization, we were able to get the optimized deposition condition at desired deposition rate and an experimental deposition rate showed similar results.

• Korean Chemical Engineering Research
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• v.45 no.5
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• pp.506-514
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• 2007

To select the best oxygen carrier particle for syngas fueled chemical-looping combustor, the reduction reactivity and carbon deposition characteristics were determined in a thermogravimetric analyzer. Four kinds of oxygen carrier particles (NiO/bentonite, $NiO/LaAl_{11}O_{18}$, $Co_xO_y/CoAl_2O_4$, $NiO/NiAl_2O_4$) were tested with the simulated syngas (30% $H_2$, 10% $CO_2$, 60% CO) as a reduction gas. With each of these particles, the maximum conversion and oxygen transfer capacity increase with increasing the reduction temperature At the given experimental range, the optimum operating temperature to maximize oxygen transfer rate is found to be $900^{\circ}C$ and carbon deposition on the particles could avoid at the temperature above $800^{\circ}C$. Among four kinds of oxygen carrier particles, the NiO-based particles exhibits better reactivity than the CoO-based particle. Moreover, the NiO/bentonite particle produces the best reactivity based on the oxygen transfer rate and the degree of carbon deposition. The measured oxygen transfer rate increases as the metal oxide content in NiO/bentonite particle is increased thereby higher metal oxide contents could provide stable operation of chemical-looping combustor.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2881-2892
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• 2024

Annular flow refers to a special type of two-phase flow pattern in which liquid flows as a thin film at the periphery of a pipe, tube, or conduit, and gas with relatively high velocity flows at the center of the flow section. This gas also includes dispersed liquid droplets. The liquid film flow rate continuously changes inside the tube due to two processes-entrainment and deposition. To determine the liquid holdup, pressure drop, the onset of dryout, and heat transfer characteristics in annular flow, it is important to have proper knowledge of flow characteristics. Especially a better understanding of entrainment fraction is important for the heat transfer and safe operation of two-phase flow systems operating in an annular two-phase flow regime. Therefore, the objective of this work is to develop a computational model for the simulation of the annular two-phase flow regime and assess the various existing models for the entrainment rate. In this work, Computational Fluid Dynamics (CFD) in ANSYS FLUENT has been applied to determine annular flow characteristics such as liquid film thickness, film velocity, entrainment rate, deposition rate, and entrainment fraction for various gas-liquid flow conditions in a vertical upward tube. The gas core with droplets was simulated using the Discrete Phase Model (DPM) which is based on the Eulerian-Lagrangian approach. The Eulerian Wall Film (EWF) model was utilized to simulate liquid film on the tube wall. Three different models of Entrainment rate were implemented and assessed through user-defined functions (UDF) in ANSYS. Finally, entrainment for fully developed flow was determined and compared with the experimental data available in the literature. From the simulations, it was obtained that the Bertodano correlation performed best in predicting entrainment fraction and the results were within the ±30 % limit when compared to experimental data.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.6
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• pp.403-407
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• 2015

Generally, MWCNT, with thermal, chemical and electrical superiority, is manufactured with CVD (chemical vapor deposition). Using MWCNT, it is comonly used as gas sensor of MOS-FET structure. In this study, in order to repeatedly detect gases, the author had to effectively eliminate gases absorbed in a MWCNT sensor. So as to eliminate gases absorbed in a MWCNT sensor, the sensor was applied heat of 423[K], and in order to observe how the applied heat was diffused within the sensor, the author interpreted the diffusion process of heat, using COMSOL interpretation program. In order to interpret the diffusion process of heat, the author progressed modeling with the structure of MWCNT gas sensor in 2-dimension, and defining heat transfer velocity($u={\Delta}T/{\Delta}x$), accorded to governing equation within the sensor, the author proposed heat transfer mechanism.

• Proceedings of the Polymer Society of Korea Conference
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• 2006.10a
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• pp.232-232
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• 2006

Intramolecular energy transfer in heteroleptic red phosphorescent dopant materials with mixed ligand units in one molecule was studied. 1-phenylisoquinoline(piq) and phenylpyridine(ppy) moieties were introduced as ligands for Ir based phosphorescent dopants and light emission mechanism was investigated. Intramolecular energy transfer from ppy ligand to piq ligand resulted in pure red emission without any green emission from ppy. Current efficiency of red devices was improved from 4 cd/A to 4.8 cd/A by using mixed ligand structures and deposition temperature of red dopant could be lowered by introducing ppy ligand.