• Transactions of the Korean hydrogen and new energy society
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• v.23 no.6
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• pp.670-677
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• 2012

Perovskite-type oxides such as doped barium zirconate ($BaZrO_3$) show high proton conductivity and chemical stability when they are exposed to hydrogen and water vapour containing atmospheres, thus it can be applicable to the hydrogen separation and the fuel cell electrolyte membranes. However the high temperature ($1700-1800^{\circ}C$) and long sintering times (24h) are generally required to prepare the fully densified $BaZrO_3$ pellets. These sintering conditions lead to the limitation of the grain size growth and the degradation of conductivity due to the acceleration of BaO evaporation at $1200^{\circ}C$. Here we demonstrate NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ with lower calcination and sintering temperature, less experimental procedure and lower process cost than the conventional mixing method. The stoichiometry of $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ was optimized by the control of excess amount of Ba (5mol%) to minimized BaO evaporation. We found that the crystal size of NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ was increased with increase of calcination temperature from XRD analysis. NiO-doped $BaZr_{0.85}Y_{0.15}O_{3-{\delta}}$ powder was calcined at $1000^{\circ}C$ for 12h when its showed the highest conductivity of $3.3{\times}10^{-2}s/cm$.

• Transactions of the Korean hydrogen and new energy society
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• v.22 no.4
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• pp.534-545
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• 2011

This paper describes the evaluation of kinetic parameters for pyrolysis and carbon char oxidation of residual oil. The non-isothermal pyrolysis of residual oil was carried out with TGA (Thermo-Gravimetric Analyzer) at heating rate of 2, 5, 10 and $20^{\circ}C/min$ up to $800^{\circ}C$ under N2 atmosphere. The first order and nth order pyrolysis models were used to fit the experimental data, and the nth order model was turned out to follow the experimental data more precisely than the first order model. For carbon char oxidation experiment, TGA and four heating rates used in pyrolysis experiment were also adapted. The kinetic parameters for the residual carbon char particle were obtained with three char oxidation model, that is, volume reaction, grain and random pore model. Among them, the random pore model described the char oxidation behaviour quite well, compared to other two models. The non-linear regression method was used to obtain kinetic parameters for both pyrolysis and carbon char oxidation of residual oil.

• International Journal of Korean Welding Society
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• v.2 no.2
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• pp.26-31
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• 2002

Considering the fuel consumption of car, a light structure of aluminum alloys is desired fer car body nowadays. However, fusion welding of aluminum alloys has some problems of reduction of joint efficiency, porosity formation and hot cracking. In the present work, investigation to improve the joint performance of laser welded joint has been carried out by addition of Cu, Ni, and Zr to A6NO 1 alloy welds. Aluminum alloy plate of 2.Omm in thickness with filler metal bar was welded by twin beam Nd: YAG laser facility (total power: 5kW). The filler metals were prepared by changing the chemical compositions for adding the elements into the weld metal. Thirteen filler metal bars were prepared and pre-placed into the base metal before welding. Ar gas shielding with a flow rate of 10 1/min was used. The defocusing distance is kept at 0 mm. At travel speeds off 3 to 9 and at laser power of 5kW (front beam 2kW rear beam 3kW), full penetration welds were obtained, whereas at travel speeds of 12 to 18 m/min and same power, partial penetration was observed. The joint efficiency of laser-welded joint was improved by the addition of Cu, Ni, and Zr due to the solid solution hardening, grain refining and precipitation hardening. The type of hardening has been further considered by metallurgical examination.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.820-824
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• 2010

The purpose of this study is to develop basic technology of hybrid rocket vehicle by constructed and launched. This small hybrid rocket using HDPE/LN2O and Aluminium steel for its body (weight : 12.5 kg, diameter : 114 mm, height : 1.8 m) was designed. The fuel grain and injector were designed for 50 kgf thrust and burning time 2.5 sec. This rocket was loaded the data acquisition device for obtaining data of pressure and velocity during its flying and equiped an automatic ejector system using spring/motor and timer to collect the rocket more safely after launching. It was launched successfully, but found some problem that the rocket's weight was heavier than expected and the thrust was not enough to reach the designed altitude and analyzed its flight path way.

• Journal of Ecology and Environment
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• v.29 no.4
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• pp.405-410
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• 2006

Landscape changes for 20 years between 1981 and 2001 in the Wangsuk stream basin located on the central Korea were investigated on the basis of physiognomic vegetation map made from the aerial photograph interpretation and field check. Changes of landscape structure were noticeable in agricultural field and forest landscape elements. Changes in the agricultural fields due to transformation of agricultural pattern into the institutional agriculture dominated landscape change, although urbanization also contributed to such change. The former change due to change of food production structure originated from socio-economic development during this period and the latter to the overpopulation of Seoul. As energy sources for heating and cooking, fertilizer, and fodder for livestock transform from plant materials to fossil fuel, manufactured one, and grain, succession of forest escaped from direct human disturbance dominated change of landscape structure in forested land. Differently from the positive landscape change in the upper area, change in the lower area deteriorated landscape quality by increasing artificial land. It was estimated that such landscape deterioration in the Wangsuk stream basin would influence water quality of the stream. In order to realize sustainable land-use against such environmental degradation, systematic environmental management based on landscape ecological perspective such as "an eco-plan for creating riparian vegetation belt," which is under preparation by Ministry of Environment, was recommended.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.3
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• pp.512-521
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• 2017

This paper reports development process of a university-based sounding rocket using simplified hybrid rocket propulsion system for low-altitude flight application. A hybrid propulsion system was tried to be designed with as few components as possible for more economical, simpler and safer propulsion system, which is essential for the small scale sounding rocket operation as a CanSat carrier. Using blow-down feeding system and catalytic ignition as combustion starter, 250 N class hybrid rocket system was composed of three components: a composite tank, valves, and a thruster. With a composite tank filled with both hydrogen peroxide($H_2O_2$) as an oxidizer and nitrogen gas($N_2$) as a pressurant, the feeding pressure was operated in blowdown mode during thruster operation. The $MnO_2/Al_2O_3$ catalyst was fabricated for propellant decomposition, and ground test of propulsion system showed the almost theoretical temperature of decomposed $H_2O_2$ at the catalyst reactor, indicating sufficient catalyst efficiency for propellant decomposition. Auto-ignition of the high density polyethylene(HDPE) fuel grain successfully occurred by the decomposed $H_2O_2$ product without additional installation of any ignition devices. Performance test result was well matched with numerical internal ballistics conducted prior to the experimental propulsion system ground test. A sounding rocket using the developed hybrid rocket was designed, fabricated, flight simulated and launch tested. Six degree-of-freedom trajectory estimation code was developed and the comparison result between expected and experimental trajectory validated the accuracy of the developed trajectory estimation code. The fabricated sounding rocket was successfully launched showing the effectiveness of the simplified hybrid rocket propulsion system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1648-1653
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• 2009

Fossil fuel causes the greenhouse effect by emitting $CO_2$, and an estimated amount of oil deposits are also limited. Therefore, people have been interested in alternative energies. Vegetable oil which is one of the alternative energies is eco-friendly renewable energy source and has similar properties like diesel oil with high efficiency. Also, vegetable oil has been well recognized as one of solutions to reduce the greenhouse effect caused by $CO_2$release. In this study, we chose Waste vegetable oil(WVO) to solve the problems of high price of grain and lack of food. Impurities and sediments from WVO were removed by separation process using sieves of $15{\mu}m$pore size. Blending was performed in Homo-mixer by 5000 rpm for 10 min. We investigated viscosities and Iodine values in different compositions of WVO and diesel oil blends. Finally, we could find out blended oils have some possibility to be used in the diesel engine.

• Journal of Korean Medical classics
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• v.20 no.3
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• pp.49-56
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• 2007

The "Somun Jogyongron(素問 調經論)" describes excess and deficiency syndromes. The study suggests that excess syndrome(實證) is caused by vigorous pathogenic fire(火邪)(the spirit(神)), pathogenic dryness(燥邪)(Gi(氣)), pathogenic wind(風邪)(blood(血)), pathogenic dampness(濕邪)(physique(形)) or pathogenic coldness(寒邪)(will(志)). When pathogenic fire is dominant within the body, Gi and blood becomes excessive and come out of the body, but the body cannot take them back, leading to the symptom in which the patient cannot stop laughing. When pathogenic dryness prevails, the lung(肺) cannot function properly. This means that the convergence(收斂) function of the clearing the lung and descending Gi(肅降) is deteriorated, and the patient shows symptoms of dyspnea and cough. Strong pathogenic wind increases the ascencling Gi in the liver(肝氣) and fuel angry emotion when the patient becomes upset. When pathogenic dampness is dominant, spleen(脾) function drops due to lumping effects, and the patient will experience abdominal distention(腹脹), which will disturb urination and defecation. When pathogenic coldness prevails, abdominal distention occurs due to condensating effects, and Yang Gj(陽氣) in the kidney(腎) is disturbed, leading to digestion disorders and eventually water-grain dysentery. Deficiency syndrome is caused by the lack of essential Gi(精氣) in the five viscera(五藏). Deficiency of sprit means the lack of Gi in the heart(心氣), so the patient becomes vulnerable to sadness. Deficiency of Gi means the lack of Gi in the lung(肺氣), so the patient may have breathing disorders. Deficiency of blood means the lack of Gi in the Liver(肝氣), so the patient can be easily scared. Deficiency of physique means the lack of Gi in the spleen(脾氣), making it difficult to use arms and legs. Deficiency of will means the lack of Gi in the kidney(腎氣), so Gowl syndrome(厥證) can ensue.

• Journal of Aerospace System Engineering
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• v.15 no.3
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• pp.87-92
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• 2021

In this study, a numerical approach was utilized to observe the phenomena in the ground combustion test of a gas generator for a ducted rocket with a plunger-type flow control device. The design factors were also identified through the analysis. It was observed that the pressure increase without the adhesion of the combustion product at the discharge pipe was quite similar to the analysis assuming a cone-shaped erosive burning effect. The pressure increase in most cases was similar to the analysis results when assuming the change in discharge pipe area due to the adhesion of combustion products. Moreover, it was also established that for a given grain shape and discharge flow area, the effect of the adhesion of combustion products has a significant effect on the combustion chamber pressure for cases over n=0.45.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.207-213
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• 2019

Corrosion and mechanical behavior of the hot-rolled 0.5%Gd-0.8%B-stainless steel to develop a spent nuclear fuel storage material was studied in a simulated nuclear waste treatment condition with rolling condition. The austenite and ferrite phases of the 0.5%Gd-0.8%B-stainless steels are about 88:12. The average austenite and ferrite grain size of the plane normal to rolling, transverse and normal directions of the hot rolled specimens are about 5.08, 8.94, 19.35, 23.29, 26.00 and 18.11 [${\mu}m$], respectively. The average micro-hardness of the as-cast specimen is 200.4 Hv, whereas, that of the hot-rolled specimen are 220.1, 204.7 and 203.5 [$H_v$] for the plane normal to RD, TD and ND, respectively. The UTS, YS and elongation of the as-cast and the hot-rolled specimen are 699, 484 [MPa], 34.0%, and 654, 432 [MPa] and 33.3%, respectively. The passivity was observed both for the as-cast and the hot rolled specimens in a simulated nuclear waste solution. The corrosion potential and corrosion rate of the as-casted specimens are $-343[mV_{SHE}]$ and $3.26{\times}10^{-7}[A/cm^2]$, whereas, those of the hot rolled specimens with normal to ND, RD and TD are -630, -512 and -620 [$mV_{SHE}$] and $6.12{\times}10^{-7}$, $1.04{\times}10^{-6}$ and $6.92{\times}10^{-7}[A/cm^2]$, respectively. Corrosion tends to occur preferentially Cr and B rich area.