• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2006년도 춘계학술논문 발표대회 제6권1호
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• pp.35-38
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• 2006

This study investigated fundamental properties of lightweight foamed concrete using cement kiln dust (CKD) and both fly ash(FA) and stability agent. Test results showed that concrete incorporating more amounts of admixture decreased slump flow and it caused increase of superplasiticizer in order to secure the fluidity performance. In addition concrete adding stability agent showed stable flow state, resisting segregation of materials and decreasing bleeding capacity. Sinking depth of concrete incorporating 20% of CKD and adding 0.002% of stability agent was indicated at 0mm. For the properties of hardened concrete. compressive strength of concrete incorporating CKD declined due to a lower appearance density, compared with other specimens. The difference of that was not very significant and the value of ail specimen was higher than KS range. Moreover strength of concrete incorporating CKD was even higher at curing temperature $5^{\circ}C$. Tensile strength ratio of concrete incorporating CKD was indicated between 0.50 to 0.59, which is higher value than control concrete. Heat conductivity of concrete incorporating FA was under the KS range while concrete incorporating 20% of CKD was satisfied in KS. Concrete adding stability agent improved insulation performance due to the lower heat conductivity. In conclusion, it is possible that concrete incorporating 20% of CKD and adding 0.002% of stability agent can secure high quality of lightweight foamed concrete.

• 대한치과기공학회지
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• 제23권1호
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• pp.9-19
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• 2001

Microstructure and phase transformation of Ti-Ni-Cu alloy powders produced by using attrition milling method were studied. Mixed powders of Ti-(50-X)Ni-XCu ($X=0{\sim}20$ at%) in composition range were mechanically alloyed for maximum 20 hours by using SUS 1/4" ball in argon atmosphere. Ball to powder ratio was 50: 1 and impeller speed was 350rpm. Mechanically alloyed with attrition millimg method. powder was heat treated at the temperature up to $850^{\circ}C$ for 1 hour in the $10^{-6}$ torr vacuum. Ti-Ni-Cu alloy powders have been fabricated by attrition milling method. and then phase transformation behaviours and microstructual properties of the alloy powders were investigated to assist in improving the the high damping capacity of Ti-Ni-Cu shape memory alloy powders. The results obtained are as follows: 1. After heat treating of fully mechanically alloyed powder at $850^{\circ}C$ for 1hour. most of the B2 and B 19' phases was formed and $TiNi_3$ were coexisted. 2. The B 19' martensite were formed in Ti-Ni-Cu alloy powders whose Cu-content is less than 5a/o. where as the B19 martensite in those whose Cu-content is more than 10at%. 3. The powders of as-milled Ti-Ni-Cu alloys whose Cu-contents is less than 5at% are amorphous. whereas those of as-milled Ti-Ni-Cu alloys whose Cu-content is more than 10at% are crystalline. This means that Cu addition tends to suppress amorphization of Ti-Ni alloy powders.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3224-3229
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• 2007

This study aims to analyse the influence of steam injection on the performance of hybrid systems combining a solid oxide fuel cell and a gas turbine. The steam is generated by recovering heat from the exhaust gas. Two system configurations, with difference being the operating pressure of the SOFC, are examined and effects of steam injection on performances of the two systems are compared. Two representative gas turbine pressure ratios are simulated and a wide range of both the fuel cell temperature and the turbine inlet temperature is examined. Without steam injection, the pressurized system generally exhibits better system efficiency than the ambient pressure system. Steam injection increases system power capacity for all design cases. However, its effect on system efficiency varies much depending on design conditions. The pressurized system hardly takes advantage of the steam injection in terms of the system efficiency. On the other hand, steam injection contributes to the efficiency improvement of the ambient pressure system in some design conditions. A higher pressure ratio provides a better chance of efficiency increase due to steam injection.

• 한국분말재료학회지
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• 제16권6호
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• pp.389-395
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• 2009

A Si-CuO-graphite composite was prepared by a mechanical alloying (MA) method. The Si-CuO composite has a mixture structure, where CuO is homogeneously dispersed in Si. Also, $Cu_2O$ and $Cu_3Si$ phases were formed during MA and heat treatment. Graphite with the Si-CuO composite was mixed in the same mill for 30 minutes with weight ratio of Si-CuO composite and graphite as 1:1. The Si-CuO composite was homogeneously covered with graphite. SiC phase was not formed. Electrochemical tests of the composite have been investigated, and the first charge and discharge capacities of the material were about 870mAh/g and 660mAh/g, respectively. Those values are about 76% of the first cycle efficiency. The cycle life of the composite showed that the initial discharge capacity of 660 mAh/g could be maintained up to 92% after 20 cycles.

• 한국정밀공학회지
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• 제23권3호
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• pp.47-55
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• 2006

Laser welding of dissimilar metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research is to investigate the influence of the process parameters, such as the welding for SM45C and STS304 with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the dissimilar welding, the welding quality of the cut section, stress-strain behavior and the hardness of the welded metal are investigated. From the results of the investigation, it has been shown that the optimal voiding condition without defects in the vicinity of the welded area and with a good welding quality is 1600W of the laser power, 0.85m/min of welding speed and $4{\ell}/min$ of pressure for shielding gas.

• 한국초전도ㆍ저온공학회논문지
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• 제2권1호
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• pp.19-23
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• 2000

We are developing a small-sized superconducting magnetic energy storge ($\mu$SMES) magnet with the storage capacity of a few megajoules, which provides electric power with high quality to sensitive electric loads. A kA class superconductor with a high coppe $r^erconductor ratio was selected as a candidate conductor. The superconductor was tested in two points of view, which are basic and important in development of the $\mu$SMES magnet. First, stabilities of the superconductor against localized disturbances such as wire motions were estimated by using a wire heater. Second, the quench current characteristics for different charge rates were also tested. The stability data showed that the short heat pulses made the conductor more unstable. The superconductor had relatively high recovery currents ranging between 40% and 50% of its critical currents. The quench tests indicated that the quench currents of the conductor were independent of current ramp rates up to 3000 A/s and nearly equal to its cuitical current data.ta.

• 한국세라믹학회지
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• 제42권7호
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• pp.503-508
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• 2005

A simple and effective method for the synthesis of LiMn$_{2}$O$_{4}$ powder as a cathode material for lithium secondary battery is reported. Micrometer size LiMn$_{2}$O$_{4}$ was prepared by combustion synthesis technique employing initial mixture of l.l LiNO$_{3}$ -1.3Mn-0.7MnO$_{2}$-1NaCl composition. Parametric study of the combustion process including molar ratio of Mn/MnO$_{2}$ and NaCl concentration were carried out under air atmosphere. The combustion products obtained were additionally heat treated at the temperature 900$^{\circ}C$ and the washed by distilled water. The results of charging-discharging characteristics revealed that LiMn$_{2}$O$_{4}$ cell synthesized in the presence of NaCl had a high capacity and much better reversibility than one formed without NaCl An approximate chemical mechanism for LiMn$_{2}$O$_{4}$ formation is proposed.

• 한국태양에너지학회 논문집
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• 제34권4호
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• pp.111-122
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• 2014

The purpose of this study is to understand daily variation of short-wave radiation trends according to the state of surface and observation of atmosphere conditions in downtown and suburban observation area. The followings are main results from this study. 1) We found out daily air temperature variation of downtown is less than that of suburban area because of bigger heat capacity of artificial elements such as massive buildings and pavements. 2) It is more effective to estimate of air condition by water vapor pressure than relative humidity in the atmosphere. 3) The difference of solar radiation ratio between downtown and suburban area is dependant on different atmosphere conditions at two observation stations.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2006년도 춘계학술대회 논문집
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• pp.17-18
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• 2006

Laser welding of metals has been widely used to improve a wear resistance and a corrosion resistance of the industrial parts. The objective of this research works is to investigate the influence of the process parameters, such as the welding for metals with CW Nd:YAG lasers. The bead-on-plate welding tests are carried out for several combinations of the experimental conditions. In order to quantitatively examine the characteristics of the butt welding, the welding quality of the cut section, stain-stress behavior and the hardness of the welded part are investigated. From the results of the investigation, it has been shown that the optimal welding condition without defects in the vicinity of the welded area and with a good welding quality is 1400W of the laser power, 0.8m/min, 0.9m/min of welding speed and $4{\ell}$ in of pressure for shielding gas.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2008년도 추계학술대회 논문집
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• pp.372-374
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• 2008

Korea classified into a development country when UNFCCC was concluded in 1995. So Korea doesn't have a GHG reduction duty until 2012. As the UNFCCC is strengthened, recently there is a growing interest in renewable energy and energy usage efficiency improvement for reducing GHG emission. It is associated with CES and renewable energy. CES is a total energy (heat, cooling and power)supplier in aggregated demand zone like a hotel, building, hospital and redevelopment district using CHP and it improves energy usage efficiency. At present, renewable energy is needed for GHG reduction duty but renewable energy doesn't have economic feasibility. So renewable energy is needed various support system to popularize which is a FIT and RPS. Especially RPS is carrying out instead of FIT in many advanced country and it will be inroduced in Korea. RPS is a duty which electricity service provider must guarantee renewable energy as much as specific ratio of total capacity. Therefore this study conducts an economic feasibility estimation of CES considering renewable energy when RPS will introduced in the future.