• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2000.04b
• /
• pp.64-67
• /
• 2000

Element distribution analysis and degradation characteristics of the ZnO varistors fabricated at the ambient sintering-process is investigated in this study. ZnO varistors made of Matsuoka's composition were fabricated by standard ceramic techniques. The ambient sintering-process is performed at the special electrical-furnace which is equipped with the vacuum system. The Gases of injection at sintering- process were oxygen, air, nitrogen and argon respectively. Element and quantitative analysis in the microstructure of ZnO varistors made use of EPMA equipment. Degradation characteristics were showed by DC degradation tests at $115{\pm}2\;^{\circ}C$ for period up to 13 h. From above analysis, it is found that at the DC degradation test the ZnO varistor sintered in oxygen atmosphere showed the excellent prop properties among them and these results could be explain by element and quantitative analysis in ZnO microstructure.

• Journal of Advanced Marine Engineering and Technology
• /
• v.29 no.8
• /
• pp.907-914
• /
• 2005

Experiments at the Japan Microgravity Center (JAMIC) have investigated the interaction between diffusion flames and solid surfaces Placed neat flames The fuel for the flames was $C_{2} H_{4}$ The surrounding oxygen concentration was 35$\%$ with surrounding air temperatures of $T_{a}$ : 300K. Especially, the effect of wall temperature on soot deposition from a diffusion flame Placed near the wall has been studied by utilizing microgravity environment, which can attain very stable flame along the wall. Cylindrical burner with fuel injection was adopted to obtain two dimensional soot distributions by laser extinction method. In the experiment two different wall temperatures. $T_{w}$=300, 800 K, were selected as test conditions The results showed that the soot distribution between flame and burner wall was strong1y affected by the wall temperature and soot deposition increases with decrease in wall temperature. The comparison among the values lot two different wall temperatures suggests that the change in thermophoretic effect is the most dominant factor to give the change in soot deposition characteristics.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.5 no.4
• /
• pp.70-83
• /
• 1997

We made a selection of engine operating conditions in the natural aspiration type diesel engine as load and speed. The effects on the power, smoke emission and cylinder pressure characteristics of these variations in operating conditions were observed experimentally. Also, the smoke emission was predicted by using the Arrhenius equation and empirical equation of the smoke emission was made. At the same time, the correlations, between the combustion and smoke emission characteristic were examined. From the above results, it is clear that to prevent power dropping and to decrease exhaust fume whin the conditions are changed, one should improve the intake system. To do this, the best way is to lower the air-fuel mixing ratio. We found that the parameters of the indicated mean effective pressure, maximum pressure and its location and combustion duration, etc. change the motion in accordance with the conditions described above. Also, we found that the variation of the pressure cycle comes from an amplified variation of the early part of process. From the analysis of comparing combustion and exhaust fume, the exhaust fume is produced at the latter time of combustion and decreased when the combustion ratio is higher. Also, we developed a special formula which can predict the exhaust fume value according to the engine load and speed.

• Journal of Biomedical Engineering Research
• /
• v.34 no.3
• /
• pp.117-122
• /
• 2013

Hyaluronic acid(HA) microbeads were synthesized by dropping the sodium hyaluronate(Streptococcus) solutions in NaOH into a solution mixture of divinyl sulfone(DVS) in 2-methyl-1-propanol, followed by stirring, cleaning and drying process at room temperature. The initial experimental conditions are crosslinking time(CLTi) of 5 h, crosslinking temperature(CLTe) of room temperature, injection air pressure(IAPr) of 5 psi, and DVS concentration( DVSc) of 0.2 vol%, respectively. Then, parametric studies were performed by varying the parameters to investigate the morphology, the porosity, the swelling ratio and the size of the beads. The microbead size pattern was not regular to function of the degree of crosslink. It was observed that the swelling ratio, the degree of crosslink, and the pore size can be controlled by adjusting the CLTi, CLTe and DVSc. Among the parameters investigated, the smallest bead size can be achieved by varying the CLTi parameter. The lowest swelling ratio, as an indication of the highest degree of crosslink, can be obtained by varying CLTe.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2005.11a
• /
• pp.201-206
• /
• 2005

The effect of internal liquid flow on spray plume characteristics was performed experimentally in subsonic crossflows. The injector internal flow was classified as three modes such as a normal, cavitation, and hydraulic flip. The objectives of the research are to investigate the effect of internal liquid flow on the spray plume characteristics and compare the trajectory of spray plume with previous works. The results suggest that the trajectory of spray plume can be correlated as a function of liquid/air momentum flux ratio(q), injector diameter and normalized distance from the injector exit(x/d). It's also found that the injector internal turbulence influences the spray plume characteristics significantly.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.584-587
• /
• 2011

An internal flow aerodynamic test was performed for a Mach 5 scramjet engine. The test was done without fuel injection, as a preliminary test for the combustion test. Test engine is an engineering model with intake cross-section of $70mm{\times}200mm$ and total length of 1.7m. Test facility is a blowdown-type, high enthalpy, hypersonic facility. 19 pressures were measured through the holes on the model surface along the engine internal flow passage. It was found that the facility start is possible, and also supersonic flow is maintained inside the engine.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.05a
• /
• pp.395-399
• /
• 2009

Advanced afterburner used in the most modernized gas turbine has new designing paradigm to cope with reinforced power density. The most distinct change is the designing trend to integrate fuel injectors and flame holder in order to manage higher temperature of inlet air. F414 and F110-GE-132 engine adopted this methodology and installed a variable nozzle utilizing CMC(Ceramic Matric Composite) material and active cooling of nozzle flap with ejector nozzle in order to enhance the life cycle of engine components and an economical aspect. These technological trends can be utilized for an advanced ramjet engine and combined cycle engine like TBCC.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2009.05a
• /
• pp.83-87
• /
• 2009

Ramjet engine is weak for low frequency combustion instability because of their long air flow passage. A model combustor which has fuel injector and V-gutter shaped flame holder was designed and fabricated in order to simulate a combustion mechanism of ramjet engine, and it could demonstrate combustion instability which might occur in ramjet combustor. The frequency of the instability was very similar to that of acoustic resonance frequency of combustor, and it proved that a typical combustion instability by thermo-acoustic coupling occurred.

• JSTS:Journal of Semiconductor Technology and Science
• /
• v.15 no.4
• /
• pp.454-461
• /
• 2015

Light enhancement of GaN based light emitting diodes (LEDs) have been investigated by texturing the top p-GaN surface. Nano-textured LEDs have been fabricated using self-assembled Ni nano mask during dry etching process. Experimental results were further compared with simulation data. Three types of LEDs were fabricated: Conventional (planar LED), Surface nano-porous (porous LED) and Surface nano-cluster (cluster LED). Compared to planar LED there were about 100% and 54% enhancement of light output power for porous and cluster LED respectively at an injection current of 20 mA. Moreover, simulation result showed consistency with experimental result. The increased probability of light scattering at the nano-textured GaN-air interface is the major reason for increasing the light extraction efficiency.

• Journal of ILASS-Korea
• /
• v.12 no.1
• /
• pp.11-17
• /
• 2007

The swirl spray for direct-injection spark-ignition (DISI) engines was investigated using a nozzle whose exit surface shape was cut with a certain tapered angle. The reason for the change in spray's characteristics at various tapered angles was explained by the data correlating the taper and flow angles. The spray tended to shift its characteristics from the symmetric to asymmetric when the tapered angle was increased; furthermore, the spray penetration and spray cone angle were also increased. When the tapered angle was greater than the $90^{\circ}$ minus flow angle, an opened hollow cone spray was formed because of the fuel impingement against the tapered surface area of the nozzle exit. This behavior indicates that the reduction in the air pressure difference between the inner and outer spray of the spray can be achieved. This behavior also promises the potential use of the tapered nozzle for the case where the independence of the spray performance from atmospheric pressure and fuel temperature is desired.