• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.28 no.5
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• pp.326-331
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• 2015

In this paper, we study the insulating properties of the liquid nitrogen(LN2) including the thermal bubbles. The shape of the thermal bubbles in accordance with the current change was observed in the 77 K and 65 K LN2. According to the temperature of liquid nitrogen, bubbles were generated differently. The round shape of the bubble is occurred in 77 K LN2. But the layer shape of bubble is occurred in 65 K LN2. When the bubbles present, the dielectric strength of liquid nitrogen is low. However, the breakdown patterns were different according to the electrode arrangement. AC breakdown voltage(BDV) was lower than the DC BDV due to the influence of bubbles. Therefore, the design of a high-voltage superconducting equipments should consider the bubbles.

• Progress in Superconductivity and Cryogenics
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• v.4 no.2
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• pp.1-4
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• 2002

Electrical properties of liquid nitrogen ($LN_2$) and gaseous nitrogen($GN_2$) have become of great interest again since the discovery of high temperature superconductors . It is very important from a point of superconducting apparatus protection to elucidate breakdown characteristics in $LN_2$ and $GN_2$ at atmospheric and pressurized conditions Therefore. this paper studies the effect of pressure on the breakdown characteristics in $LN_2$ and $GN_2$. Af high voltage is applied to electrode system with uniform and non-unform field in various gap length. And Breakdown voltages of $LN_2$ and $GN_2$ are investigated under AC voltage for Pressure ranging from 0 and 0.5 MPa. This research presented basis information of electrical insulation design for liquid nitrogen immersed HTS power apparatus.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.2
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• pp.177-182
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• 2000

Composite insulation system of liquid nitrogen and solid spacer is widely applied in high temperature superconduction power machine. This study has three step procedure. As follow, first step is composition of parallel deposited electrode and vertically deposited electrode along the direction of immersion in liquid nitrogen(LN2). Second step is investigation into surface flashover voltage of solid spacer under partially immersed in LN2, and last step is comparison the result of this research with that of fully immersed in LN2 and at cryogenic temperature gaseous nitrogen(GN2). This result presented that surface flashover voltage along solid spacer half immersed in LN2 was almost the same as that of fully immersed spacer when the thickness of spacer(t) was t<10mm. In the case of t> 10mm, however, spacer flashover voltage was equal to that obtained in GN2 at cryogenic temperature. And the immersed direction functions as role of deciding the difference of surface flashover voltage.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.4
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• pp.490-496
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• 2020

A styrofoam box is used as a simple and easy freezing method to preserve animal semen as a livestock genetic source. This study optimized the methods of freezing chikso brindled cattle semen. To test the freezing box, the motility of spermatozoa was compared between two box sizes (length×width×heigh) with the dimensions of 23.5×30.5×22.5 cm and 25.5×46.5×26.5 cm. The motility of thawed sperm from brindled Korean bulls was used to confirm the efficiency of the freezing boxes. The box having a larger inner space with larger horizontal and height measurements supported better motility after thawing (60.4±5.3% vs 67.2±3.1%) with 10 min of exposure time in liquid nitrogen vapor. The optimized freezing space is estimated to be an essential element for successful freezing results and the larger box could be used for production of more than 60 frozen semen straws. These properties are also helpful to optimize the cryopreservation techniques that would control the quality and quantity of semen straws according to different animal species.

• Journal of the Korean Chemical Society
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• v.43 no.2
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• pp.167-171
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• 1999

An investigation of the interaction of Co(II), Ni(II), Cu(II), Zn(II), Cd(II), Pb(II) and Ag(I) with two N,N'-dibenzylated nitrogen-oxygen mixed donor macrocyclic ligands, has been carried out. Tle log K values for the respective complexes in 95% methanol have been determined potentiometrically. Both ligands have formed stable complex with only Cu(II) and Ag(I) ion. Transport measurements in a bulk liquid membrane system exhibited a very high selectivity of Ag(I) ion over the other metal ions used.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.3
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• pp.66-73
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• 2005

The pressurization system in a liquid rocket propulsion system provides a controlled gas pressure in the ullage space of the vehicle propellant tanks. It is advantage to employ a hot gas heat exchanger in the pressurization system to increase the specific volume of the pressurant and thereby reduce over-all system weight. A significant improvement in pressurization-system performance can be achieved, particularly in a cryogenic system, where the gas supply is stored inside the cryogenic propellant tank. In this study liquid nitrogen was used instead of liquid oxygen as a simulant. The temperature characteristic of cryogenic pressurant is very important to develop some components in pressurization system. Numerical modeling and test data were studied using SINDA/FLUINT Program and PTF(Propellant-feeding Test facility).

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.25-28
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• 2003

The bearing/sealing test (BST) facility is intended for tests of bearing and seal for turbopump of liquid rocket engine (LRE) in various media (water, liquid nitrogen, liquid oxygen). The bearing test for serviceability is fulfilled with the estimation of the flow rate of cooling medium through the test bearing separator and with the simulation of axial and(or) radial loading. The purpose of seals test is the determination of magnitude of leakages through the seal and a time variation of this magnitude.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.82-85
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• 2009

In the development of Liquid Rocket Engine(LRE) systems, it is essential to understand the spray characteristics which influence mainly the performance and the stability of combustion. The injectors for this study have a recessed Liquid-swirl/Gas-centered jet coaxial type. For the similarity with actual conditions, the experimental conditions are calculated by using the momentum ratio as a matching parameter, and the stimulants of fuel and oxidizer are gaseous nitrogen and water respectively. The spray fields were measured by means of a photographic technique. Moreover, an effect of the momentum ratio has been investigated.

• Membrane Journal
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• v.27 no.3
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• pp.226-231
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• 2017

1-Butyl-3-methylimidazolium tetrafluoroborate ($BMIM^+BF_4{^-}$) and $Al_2O_3$ as metal oxide for preparation of composite membrane were utilized for the $CO_2$ separation. When 13 nm $Al_2O_3$ nanoparticles were incorporated into ionic liquid $BMIM^+BF_4{^-}$, the separation performance for composite membrane showed the selectivity ($CO_2/N_2$) of 30.5 and $CO_2$ permeance of 45.7 GPU. The enhanced separation performance was attributable to the increased $CO_2$ solubility by both oxide layer of $Al_2O_3$ and abundant free ions of ionic liquid. In particular, $Al_2O_3$ nanoparticles acted as obstacles to nitrogen gas, resulting in the decrease of permeability of nitrogen gas. As a result, the carbon dioxide separation performance could be enhanced.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.6
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• pp.802-808
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• 2011

One of the important mechanical properties of cryogenic temperature structure material is fracture toughness. Research on normalization of fracture toughness test method is becoming very important issue with development of cryogenic structural elements. Specially, mechanical properties estimation by each micro-structure of welding department is important because it can cause unstable fracture when use under cryogenic environment in case of welding department. In this study, fracture toughness estimation test was carried out to unloading compliance method and sensitization heat-tread minimized test specimen at liquid nitrogen (77K), liquid helium (4K), 293K temperature to STS-316L base metal and weld metal.