• Journal of the Korean Society for Precision Engineering
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• v.11 no.1
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• pp.44-53
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• 1994

We experimented on cutting characteristics-cutting force, behavior of cutting temprature, surface foughness, behavior of chips-under low tempdeature, which generated by liquid nitrogen (77K). The workpieces were freezed to -195 .deg. C and liquid nitrogen was also sprinkled on cutting area in order to increase the efficiency of machining in low temperature. The workpiece was became to -195 .deg. C in 5 minutes, and cutting temperature in CC was lower about 170 .deg. C than NC. The cutting force trended to increase slighty in cooled cutting, but chip thickness was decreased, shear angle was however increased. The form of chips was in good conditions of long or short tubular chips in CC. In CC surface roughness of workpiece was better than NC. In NC surface hardness of chips trended to increase according to increasing of cutting speed, but in CC it trended to decrease. The power spectrum of vertical cutting force trended to increase according to increasing of feed, and in CC it was higher than NC.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2002.02a
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• pp.77-81
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• 2002

The helium recondensing type cryostat with 4 K GM cryocooler is fabricated in order to keep cryogenic state of two saddle type superconducting magnet opposite to each other designed maximum 0.3 T magnetic field, and 1270 mm diameter open bore. The current leads which consist of metal current leads made for brass sheet and HTS current leads made in American Superconductor$^{TM}$ intermediate cool down with cryocooler Thus , the cryocooler for helium recondensing is a 1.5W/4.2 K GM SUMITOMO cryocooler. While superconducting magnet is working of 1600 gauss to 200 A, the cryostat keep constantly the level of liquid helium at 0.05 bar gauge pressure.e.

• Journal of Plant Biotechnology
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• v.35 no.3
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• pp.195-201
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• 2008

A simplified technique that cryoprotects zygotic embryos by desiccation was developed for germplasm conservation of wild yam species(Dioscorea spp.) in Korea. Comparative studies with three other cryogenic techniques were conducted. The maximum survival of zygotic embryos were achieved at a frequency of 96.6% when embryos were cryopreserved by the desiccation method. For the successful cryopreservation of yam zygotic embryos, those that were excised from immature/mature seeds were dried in the air stream of a laminar flow cabinet for 30 min at room temperature and then directly immersed in liquid nitrogen.

• Journal of Korean Society for Atmospheric Environment
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• v.13 no.3
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• pp.221-229
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• 1997

Wax is a protectant for floors that is used widely in Korea and is considered an emission source of volatile organic compounds (VOCs) in the indoor environment. This study examined the concentration change of indoor VOCs due to waxing and also due to wiping the floor with an oiled dustcloth. VOCs were identified using a cryogenic concentration/thermal desorption system with capillary GC that utilized a liquid nitrogen cryostat and induction heating. The major components emitted from the waxing were nonane, decane, undecane, $C_2$-benzene, and $C_3$-benzene. The concentrations of nonane were 1,276 $\mu\textrm{g}$/㎥ an hour after wax applications, 832 $\mu\textrm{g}$/㎥ after 3 days, and less than 10$\mu\textrm{g}$/㎥) after 15 days. Another emission source of VOCs in indoor was the oiled dustcloth used for cleaning the floor. The oiled dustcloth gave VOCs concentrations three times higher than the normal undusted floor.

• Proceedings of the KIEE Conference
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• 1992.07b
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• pp.850-853
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• 1992

A cryogenic electron cyclotron resonance plasma etching system has been built to study wafer-temperature in the silicon etching characteristics. The wafer temperature was controlled from -150 to +30 $^{\circ}C$ during etching using the liquid nitrogen cooled helium gas. Although silicon was etched isotropically in $SF_6$ plasma at room temperatures, we found that it is possible to suppress the etch undercut in Si by reducing a substrate temperature without side wall passivation. In addition, the selectivity of silicon to photoresist was improved considerably at a low wafer temperature. Etch rates, anisotropy and selectivity to photo resist are measured as a function of the wafer temperature in the region of -125 $\sim$ 25$^{\circ}C$ and rf bias power of 20W $\sim$ 80W.

• 한국가스학회:학술대회논문집
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• 2001.10a
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• pp.35-44
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• 2001

Analytical and experimental studies have been performed to investigate the strength of the membrane and the reaction force at the anchor point. Using nonlinear FEM code and experiments, the stress analysis of the corrugated membrane related the cryogenic liquid pressure and thermal loading is performed to ensure the stability and fatigue strength of the membrane. This paper reports on the FEM results of membrane.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.3
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• pp.333-339
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• 2004

For an electrical insulation design of HTS cable, it is important to understand the dielectric characteristics of insulation materials in L$N_2$ and the insulation type. Generally, the electrical insulation of HTS Cable is classified into two types of the composite insulation and solid insulation type. In this research, we selected the insulation paper/L$N_2$ composite insulation type for the electric insulation of a HTS cable, and studied electric insulation characteristics of synthetic Laminated Polypropylene Paper(LPP) in liquid nitrogen(L$N_2$) for the application to high temperature superconducting(HTS) cable. Furthermore, we compared the breakdown characteristics of the butt gap and bended mini-model cable. It is necessary to understand the winding parameter of insulation paper/LN2 composite insulation.

• Journal of the Korean Institute of Gas
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• v.6 no.4 s.18
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• pp.47-52
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• 2002

Analytical studies have been performed to investigate the strength of the membrane and the reaction force at the anchor point. Using nonlinear FEM code and experiments, the stress analysis of the corrugated membrane related the cryogenic liquid pressure and thermal loading is performed to ensure the stability and fatigue strength of the membrane. This paper reports on the FEM results of membrane.

• Journal of Energy Engineering
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• v.23 no.4
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• pp.215-222
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• 2014

A theory-based methodology for describing the thermodynamic properties of molecular nitrogen is presented. The results obtained indicate a successful application of a fully consistent statistical method for the description of a molecular system in different phase states. The method employs a density of states equation for solid nitrogen and a perturbation potential for gaseous and liquid nitrogen. The main characteristics of the calculation method include the need for a minimal number of initial data and the absence of fitting parameters. The adequacy of the physical model that is the basis for the method allows a description of existing experimental data and the peculiarities of the thermodynamic properties.

• Progress in Superconductivity and Cryogenics
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• v.6 no.4
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• pp.51-54
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• 2004

A 1 MV A single phase high temperature superconducting (HTS) transformer was manufactured. In order to reduce AC loss generated in the HTS winding, winding was concentrically arranged. Operation temperature is set at 65K to increase the critical current and reduce the amount of HTS tape usage and the volume. The cryogenic system which consists of main cryostat with the windings and secondary cryostat with 2 GM coolers and cryopump on top and heat exchanger inside is also designed and the cooling performance is simulated with Fluent. Temperature distribution of the windings is investigated whether the windings are kept under designed operation temperature.