• Title/Summary/Keyword: Liquid Nitrogen

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Lubrication Effect of Liquid Nitrogen in Cryogenic Machining Friction on the Tool-chip Interface

  • Jun Seong-Chan
    • Journal of Mechanical Science and Technology
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    • v.19 no.4
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    • pp.936-946
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    • 2005
  • The liquid nitrogen as an environmentally safe coolant has been widely recognized in cryo­genic machining, its function as a lubricant is plausible due to its chemical inertness, physical volatility and low viscosity. Since a reduced friction is a direct witness of the lubrication effect from a tribological viewpoint, this paper presents an evaluation of the apparent friction coefficient on the tool-chip interface in cryogenic cutting operations to prove and characterize the lubricity of LN2 in cryogenic machining. The cryogenic cutting technology used in this study is based on a cooling approach and liquid nitrogen delivery system which are intended to apply liquid nitrogen in well-controlled fine jets to selectively localized cutting zones and to penetrate liquid nitrogen to the tool-chip interface. It has been found that the apparent friction coefficient can be significantly reduced in cryogenic machining, depending on the approach of liquid nitrogen delivery.

Larvicidal Action of Liquid Nitrogen against. Metacercariae of Clonorchis sinensis (액화질소에 의한 간흡충 피낭유충의 살충에 대한 연구)

  • 송수복
    • The Korean Journal of Parasitology
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    • v.25 no.2
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    • pp.123-128
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    • 1987
  • The author investigated the larvicidal action of liquid nitrogen against the metacercariae of Clonorchis sinensis, with an observation on the freshness and change of taste in the flesh of fishes. The results obtained were as follows: 1. The metacercariae in the mesh of Pseudorasbora parve, which were treated with liquid nitrogen ($-192^{\circ}C$), were not killed within 10 seconds, but completely killed over 30 seconds. In comparison, the metacercariae in the flesh of p. parka kept in a refrigerator ($-12^{\circ}C$) were killed only in 84% in 10-hour exposure group. 2. The freezing speed of fishes by liquid nitrogen was 4 min.(') and 15 seconds(") for Cyprinus carpio, 1'22" for Carassius carassius and only $30^{\circ}C$ for Pseudorasbora larva. 3. As for the freshness and taste of raw fresh water fishes, they were not deteriorated after the treatment with liquid nitrogen. 4. In animal infection experiment of C. sinensis metacercariae after freezing, they were found not infective after they were treated with liquid nitrogen. From the results, it is inferred that the treatment of fresh water fishes for longer than 30 seconds with liquid nitrogen is helpful to reduce the possibility of C, sinensis infection without alteration of the freshness and taste of fishes.

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Shape and Dielectric Strength of Thermal Bubbles in Liquid Nitrogen (액체질소 중 열기포 형상 및 절연 특성)

  • Baek, Seung-Myeong;Kim, Hae-Jong
    • 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.

A study on the discharge characteristics of liquid nitrogen using at cryogenic cable (극저온 전력케이블을 액체질소에 대한 방전특성에 관한 연구)

  • 이현동;주재현;박원주;이광식;이동인
    • Proceedings of the Korean Institute of IIIuminating and Electrical Installation Engineers Conference
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    • pp.125-129
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    • 1996
  • This study describes that electrical breakdown of liquid nitrogen which is influenced with bubble has been investigated as liquid nitrogen is used coolant of high temperature(T/sub c/) superconductivity. In order to investigate breakdown of liquid nitrogen, we formed electrode system of parallel and vertical configuration toward gravitutional direction. In case of changing with electrode configuration of equal electrode and gap spacing in uniform and nonuniform electric field bubble behavior is changed. In result of that, breakdown voltage is changed. Therefore, this study proved that electrode configuration must be formed the smallest existing probability of bubble between two electrodes in order to increase breakdown strength of liquid nitrogen at atmosphere pressure.

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Preservation of Toxoplasma gondii (RH strain) in liquid nitrogen for 5 years (톡소플라즈마원충(原蟲)(RH주(株))의 5년간 동결보존시험)

  • Jeon, Yeong;Jang, Hwan
    • Korean Journal of Veterinary Research
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    • v.33 no.2
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    • pp.285-287
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    • 1993
  • Toxoplasma gondii frozen by the method of very slow cooling ($-30^{\circ}C/3hrs.{\rightarrow}\;-60^{\circ}C/lhr.{\rightarrow}\;-196^{\circ}C$ of liquid nitrogen)were inoculated mice after storage in the liquid nitrogen for 5 years. The results obtained were as follows; 1. Toxoplasma gondii was detected in mice 4~5th day after intraperitoneal inoculation of organisms stored in the liquid nitrogen once a year for 5 years. 2. Toxoplasma gondii could be preserved longer than 5 years in liquid nitorgen being evidenced by the in vivo test.

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An Analysis of Heat Transfer and Pressure Drop Characteristics for Optimum Design of Cryogenic Heat Exchanger used for Liquid Nitrogen Cooling (액체질소 냉각용 극저온 열교환기의 최적설계를 위한 열전달 및 압력강하 특성 분석)

  • Ko, Ji Woon;Jeon, Doong Soon
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.30 no.1
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    • pp.24-32
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    • 2018
  • In this paper, analytical studies were conducted to obtain optimal design factors and analysis parameters of liquid nitrogen cooling exchanger applied in cryogenic refrigerator. The target value of heat transfer rate was more than 1 kW and pressure drop was less than 40 kPa. Design factors of cryogenic heat exchanger included width of channel and configuration of paths. Analytical factors of liquid nitrogen cooling exchanger included temperatures of coolant header surface and inlet liquid nitrogen. The width and number of channels in the design parameters were 0.0050~0.0150 m and 4~8, respectively. The configuration of channel path was 4 ways. Temperatures of coolant header surface and inlet liquid nitrogen in analytical parameters were 74 to 78K and 82 to 86K, respectively. As result, the design factor and analysis parameter satisfying the target values were obtained. The biggest heat transfer rate was 1.36 kW with pressure drop of 32.26 kPa.

Experimental Study of Liquid Nitrogen Pool Spreading with Continuous Spill (연속적으로 누출되는 액체질소 풀의 확산에 관한 실험적 연구)

  • Choi, Jaewhan;Kim, Myungbae;Choi, Byungil;Kim, Taehoon
    • Journal of Energy Engineering
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    • v.23 no.3
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    • pp.174-180
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    • 2014
  • Experimental study of liquid nitrogen pool spread is carried out when it is continuously released. The liquid nitrogen spreads over a cement mortar plate with continuous release. Evaporation rate per unit area of the liquid nitrogen is measured using a digital balance, and a spreading distance of the liquid pool is measured by thermocouples. It is discovered that the evaporation rate per unit area of liquid nitrogen tends to decrease as the liquid pool spreads.

Analysis of Partial Discharge Characteristics at Cryogenic Temperature below 77K (77K 이하 극저온 상에서의 부분방전 특성 분석)

  • Lee, Sang-Hwa;Kim, Bok-Yeol;Shin, Woo-Ju;Lee, Bang-Wook;Koo, Ja-Yoon
    • Proceedings of the KIEE Conference
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    • pp.1562-1563
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    • 2011
  • Partial discharge measurement is one of the effective diagnostic techniques to predict abnormal high voltage dielectric insulation conditions of the electric equipments. Recently partial discharge diagnostic techniques were also utilized to evaluate the cryogenic dielectric insulation of high temperature superconducting electric equipment in liquid nitrogen. Generally, liquid nitrogen at 77 K is used used as the cryogenic and dielectric media for many high temperature superconducting high voltage applications. When a quench in the superconductor occurs, bubbles are generated which can affect the dielectric properties of the liquid nitrogen. So in order to reduce the bubble formation, subcooled nitrogen was also employed for this purpose. In this work, investigation of partial discharge characteristics of subcooled liquid nitrogen were conducted in order to clarify the retardation of partial discharge initiation voltage according to the different subcooling temperature of liquid nitrogen. And also the relation of partial discharge phenomena and the activities of bubbles were analyzed. It was observed that PD inception voltages shows rather different characteristics according to the decrease of subcooling temperature and the activities of bubbles were strongly influenced by temperature of the subcooled liquid nitrogen.

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Construction of High-Pressure Pressurized Liquid Nitrogen Supply Facilities (고압의 가압식 액체질소 공급 설비 구축)

  • Shin, Minkyu;Oh, Jeonghwa;Kim, Seokwon;Ko, Youngsung;Chung, Yonggahp
    • Journal of Aerospace System Engineering
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    • v.14 no.5
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    • pp.26-32
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    • 2020
  • In this study, a facility was constructed to supply liquid nitrogen to simulate combustion instability in a liquid rocket combustor. The pressurization and supply performances were predicted and verified through different experiments. The liquid nitrogen supply system was composed of a pressurized supply system, and a dome regulator was used to adjust the pressure of the pressurant. A cavitation venturi was used to control the mass flow rate of liquid nitrogen. The condition of liquid nitrogen supply was a mass flow rate of 2.55 kg/s and the venturi inlet pressure was above 100 bar. Based on the initial experiment, it was observed that the predicted amount of the pressurant was not sufficiently supplied and the target pressure was not supplied due to a drop in tank pressure. Through the modification of the established facilities, the target mass flow rate was successfully supplied and the cryogenic liquid nitrogen supply facility was verified.

Thermal diffusion experiment of impulsive heat in subcooled liquid nitrogen (과냉 액체질소 내에서 순간적 열확산 실험)

  • Choi, J.H.;Ha, J.C.;Byun, J.J.;Chang, H.M.;Kim, H.M.;Ko, T.K.
    • Progress in Superconductivity and Cryogenics
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    • v.8 no.1
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    • pp.65-70
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    • 2006
  • Transient heat transfer caused by an impulsive heating in subcooled liquid nitrogen is investigated experimentally. This study is part of out ongoing efforts directed to a stable cryogenic cooling system lot superconducting fault current limiters (SFCL). A thin heater attached by epoxy on one surface of a GFRP plate is immersed in liquid-nitrogen bath at temperatures between 77 K and 55 K. A strong heat flux up to $150W/cm^2$ is generated lot 100 ms, and the temperature of the heater sulfate is measured as a function of time. The behavior of bubbles on the heating surface can be explained by comparing the measured temperature history for vertical and two horizontal (up and down) orientations. It is concluded that the subcooling of liquid nitrogen below 70 K is very effective in suppressing bubbles, resulting in better thermal protection and faster recovery from an impulsive heat.