• Progress in Superconductivity and Cryogenics
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• v.8 no.3
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• pp.1-4
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• 2006

The characteristics of Bi2212 round wire was systematically studied depending on different heat treatment conditions. Initial wire was drawn after routine PIT (Powder In Tube) process. The wire was divided into 3 pieces with 10 cm in length and 2.5 mm in diameter. 3 wires were pre-heat treated separately by different heat treatment schedules, heated in air and nitrogen atmosphere and centrifugally melted. Pre-heated wires were annealed at $845^{\circ}C$ for 40 hours in oxygen atmosphere. SEM results indicate that all pre-heated wires showed highly oriented microstructure. However the wire by centrifugally melted process showed higher density and better electric properties as compared with 2 other wires pre-heated in air and nitrogen atmosphere. The critical current of a centrifugally melted wire was about 18 A in 77 K.

• Journal of the Korean Society of Combustion
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• v.15 no.4
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• pp.1-8
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• 2010

Mild combustion is considered as a promising combustion technology for energy saving and low emission of combustion product gases. In this paper, the controllability of reaction region in mild combustion is examined by using co-axial air nozzle. For this purpose, numerical approach is carried out. Propane is considered for fuel and air is considered for oxidizer and the temperature of air is assumed 900K slightly higher than auto ignition temperature of propane. But unlike main air, the atmospheric condition of co-axial air is considered. Various cases are conducted to verify the characteristics of Co-Axial air burner configuration. The use of coaxial air can affect reaction region. These modification help the mixing between fuel and oxidizer. Then, reaction region is reduced compare to normal burner configuration. The enhancement of main air momentum also affects on temperature uniformity and reaction region. The eddy dissipation concept turbulence/chemistry interaction model is used with two step of global chemical reaction model.

• Proceedings of the SAREK Conference
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• 2006.06a
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• pp.953-958
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• 2006

Perimeter zone has been reinforced by active systems, such as fan-coil units, because it causes an increase in heating and cooling loads, dew condensation in winter, or discomfort with cold-draft to residents in buildings, through poor insulation by light-weighed skin due to progressing multi-storied buildings and skyscrapers. However, because these active systems raise Its capacity so that fossil fuel is used as much as they are added, and ultimately, greenhouse effect is urged, we proposed BIPV system functioned as solar collector which can substitute active system. As an early stage, heat balance equation in steady-state by Fortran was used not only for pre-heating effect and electric power capacity during the day in winter, but also for electric power capacity during day in slimmer and sky radiation effect during night in summer. Especially, we should have considered shading on PV, since even a little bit of it makes the efficiency too low for the PV to work. Still, when the flux of pre-heated air was increased to make air-barrier, its temperature was not enough to make it because the speed of heat exchange was too fast to warm up the air, thus the capacity to meet the condition was evaluated, and electric power from PV was made used for it.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.103-108
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• 2003

The control of flame shapes in a laminar pre-mixed flame has been experimentally investigated for propane/air pre-mixed laminar flames. Flames of different size and shapes are observed with heated wires or by controlling the equivalence ratio and flow rate of a mixture. The characteristics of the partitioning of a flame or the merge of flames are analyzed and explained by considering the balance between laminar flame speed and upstream mixture velocity. A combustor might be sized down while maintaining its heat production rate the same by partitioning a flame established in it. When the equivalence ratio of mixture is decreased, individual flames are merged together and the upstream mixture velocity can be practically decreased on a nozzle having opening ratio less than unity. As a result, the flame shape is to he adjusted until the newly established balanced condition is satisfied, and then. the stable combustion can be achieved again.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.105-112
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• 2007

Recently developed raised floor heating system is not only capable of basic function to reduce noise between floors, but also is a multi-functional floor heating system enabling natural ventilation. The procedure of this system for natural ventilation is to import outdoor air through bottom space of the floor heating system, circulate indoor space and discharge it out of ceiling. In winter, powerless natural ventilation is possible with buoyancy effect caused by temperature difference between outdoor and indoor. And it also allows saving of energy by importing pre-heated air in bottom space of the floor heating system. To evaluate ventilation performance of this system, on-site measurement was conducted in 2 test laboratories, and the nominal air change rate was satisfied as 0.4$\sim$0.8 h-1 under the condition of outdoor temperature $5^{\circ}C{\sim}-5^{\circ}C$, which was evaluated as highly possible to be applied as a natural ventilation system in multi-family houses.

• Korean Journal of Food Science and Technology
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• v.31 no.6
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• pp.1583-1588
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• 1999

Garlic pieces without peeling were subjected to hot air heating at $60{\sim}90^{\circ}C$ for 30 min. and microwave oven heating for 10 sec to reduce the strength of garlic flavor. Volatile compounds of the treated garlic were decreased, as the heating temperature was raised. Garlic heated at 70, 80 and $90^{\circ}C$ had 20%, 31% and 49% less volatile compounds, respectively, compared to those of the control. Microwave oven heating revealed a similar trend to those heated at $60{\sim}80^{\circ}C$. As the heating temperature was raised, glucose, fructose and fructooligosaccharide contents in the heated garlic were decreased. Pyruvic acid contents in garlic, a degradation product of alliin, was decreased as the heating temperature was raised, but contents of the other organic acids were not affected. Arginine, the main amino acid in garlic was decreased by the hot air heating, but was not affected by the microwave heating. Glutamic acid and tyrosine contents were decreased in all the treated garlic samples.

• International Journal of Automotive Technology
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• v.5 no.3
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• pp.155-164
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• 2004

The direct injection gasoline spray-wall interaction was characterized inside a heated pressurized chamber using various visualization techniques, including high-speed laser-sheet macroscopic and microscopic movies up to 25,000 frames per second, shadowgraph, and double-spark particle image velocimetry. Two hollow cone high-pressure swirl injectors having different cone angles were used to inject gasoline onto a heated plate at two different impingement angles. Based on the visualization results, the overall transient spray impingement structure, fuel film formation, and preliminary droplet size and velocity were analyzed. The results show that upward spray vortex inside the spray is more obvious at elevated temperature condition, particularly for the wide-cone-angle injector, due to the vaporization of small droplets and decreased air density. Film build-up on the surface is clearly observed at both ambient and elevated temperature, especially for narrow cone spray. Vapor phase appears at both ambient and elevated temperature conditions, particularly in the toroidal vortex and impingement plume. More rapid impingement and faster horizontal spread after impingement are observed for elevated temperature conditions. Droplet rebounding and film break-up are clearly observed. Post-impingement droplets are significantly smaller than pre-impingement droplets with a more horizontal velocity component regardless of the wall temperature and impingement angle condition.

• Smart Structures and Systems
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• v.19 no.5
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• pp.553-565
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• 2017

Structural modeling of unencapsulated ionic polymer metal composite (u-IPMC) actuators that are used for flapping the insect scale-flapping wing of micro air vehicles (FMAV) in dry environmental conditions is carried out. Structural modeling for optimization of design parameters for retention of water, maximize actuation performance and to study the influence of water activity on the actuation characteristics of u-IPMC is explored for use in FMAV. The influence of equivalent weight of Nafion polymer, cations, concentration of cations, pre-treatment procedures on retention of water of u-IPMCs and on actuation parameters, flapping angle, flexural stiffness and actuation displacement are investigated. IPMC designed with Nafion having equivalent weight 900-1100, pre-heated at $30^{\circ}C$ and with sodium as the cations is promising for optimum retention of water and actuation performance. The actuation parameters while in operation in dry and humid environment with varying water activity can be tuned to desirable frequency, deflection, flap angle and flexural stiffness by changing the water activity and operational temperature of the environment.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.16 no.2
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• pp.142-148
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• 2017

The objective of this study is to investigate the cooling characteristics of a heat sink for an LED headlight used in passenger cars. To this end, this study conducts the experimental and numerical analysis of the heat sink heated at constant heat fluxes without air flow applied. In the experiments, heat was transferred at a constant heat flux through the bottom of a heat sink. The measured temperature on pre-selected locations of the heat sink was in good agreement with the numerically predicted one. The experimental and numerical results indicate that the convective heat transfer coefficient for the natural convection mode was decreased by increasing the heat flux applied to the bottom of heat sink, lowering the cooling capabilities.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.315-318
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• 1999

Bi$_{2}Sr_{2}CaCu_{2}O_{\delta}$ superconducting films were rapidly fabricated on copper tape by liquid reaction between a Cu-free precursor and Cu tape (LiReac-PreCu) method. Those thick films were well oriented along the c-axis. The precursor was made by melt-quenched technology using twin roller. The melt-quenched films were transparent and glossy yellow in appearance. These films which were the compostion of Bi$_2SrCaO_y$, Bi$_3Sr_2CaO_z$ were placed on copper tape and then heated at various temperatures for several minutes in air. They were analyzed using X-ray powder diffraction, SEM, a DC four-probe method. The mechanism of superconducting phase formation . from the melt-quenched precursor on Cu tape was studied