• Journal of Ocean Engineering and Technology
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• v.28 no.6
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• pp.517-526
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• 2014

The leakage of cryogenic LNG through cracks in the insulation membrane of an LNG carrier causes the hull structure to experience a cold spot as a result of the heat transfer from the LNG. The hull structure will become brittle at this cold spot and the evaporated natural gas may potentially lead to a hazard because of its flammability. This paper presents a computational model for the LNG flow and heat diffusion in an LNG insulation panel subject to leakage. The temperature distribution in the insulation panel and the speed of gas diffusion through it are simulated to assess the safety level of an LNG carrier subject that experiences a leak. The behavior of the leaked LNG is modeled using a multiphase flow that considers the mixture of liquid and gas. The simulation model considers the phase change of the LNG, gas-liquid multiphase interactions in the porous media, and accompanying rates of heat transfer. It is assumed that the NO96-GW membrane storage is composed of glass wool and plywood for the numerical simulation. In the numerical simulation, the seepage, heat diffusion, and evaporation of the LNG are investigated. It is found that the diffusion speed of the leakage is very high to accelerate the evaporation of the LNG.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.9
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• pp.717-724
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• 2020

We study the closing characteristics of a self-sustainable poppet valve which serves as a main oxidizer shut-off valve for liquid rocket engines. Numerical analysis for predicting closing transient responses are presented and the calculated results have been verified by a comparison with experimental data. The effective area of a pilot gas discharge system and the pressure distribution of passage flow around the valve moving part are shown to be main parameters in determining the closing characteristics for dry and cryogenic conditions, respectively. Moreover, it is presented that the passage flow pressure at the valve closing moment as well as the valve closing velocity can be effectively adjusted by the appropriate employment of the pilot gas.

• ETRI Journal
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• v.24 no.5
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• pp.349-359
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• 2002

With Ni/Au and Pd/Au metal schemes and low temperature processing, we formed low resistance stable Ohmic contacts to p-type GaN. Our investigation was preceded by conventional cleaning, followed by treatment in boiling $HNO_3$:HCl (1:3). Metallization was by thermally evaporating 30 nm Ni/15 nm Au or 25 nm Pd/15 nm Au. After heat treatment in $O_2$ + $N_2$ at various temperatures, the contacts were subsequently cooled in liquid nitrogen. Cryogenic cooling following heat treatment at $600^{\circ}C$ decreased the specific contact resistance from $9.84{\times}10^{-4}$ ${\Omega}cm^2$ to $2.65{\times}10^{-4}$ ${\Omega}cm^2$ for the Ni/Au contacts, while this increased it from $1.80{\times}10^{-4}$ ${\Omega}cm^2$ to $3.34{\times}10^{-4}$ ${\Omega}cm^2$ for the Pd/Au contacts. The Ni/Au contacts showed slightly higher specific contact resistance than the Pd/Au contacts, although they were more stable than the Pd contacts. X-ray photoelectron spectroscopy depth profiling showed the Ni contacts to be NiO followed by Au at the interface for the Ni/Au contacts, whereas the Pd/Au contacts exhibited a Pd:Au solid solution. The contacts quenched in liquid nitrogen following sintering were much more uniform under atomic force microscopy examination and gave a 3 times lower contact resistance with the Ni/Au design. Current-voltage-temperature analysis revealed that conduction was predominantly by thermionic field emission.

• Progress in Superconductivity and Cryogenics
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• v.17 no.1
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• pp.44-47
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• 2015

High voltage superconducting apparatuses have been developed presently around the world under AC and DC sources. In order to improve electrical reliability of superconducting apparatuses with AC and DC networks, a study on the DC as well as the AC electrical breakdown characteristics of cryogenic insulations should be conducted for developing a high voltage superconducting apparatus. Recently, a sub-cooled liquid nitrogen cooling system is known to be promising method for developing a high voltage superconducting apparatus. A sub-cooled liquid nitrogen cooling system uses gaseous nitrogen to control the pressure and enhance the dielectric characteristics. However, the dielectric characteristics of gaseous nitrogen are not enough to satisfy the grade of insulation for a high voltage superconducting apparatus. In this case, the application of solid insulating barriers is regarded as an effective method to reinforce the dielectric characteristics of a high voltage superconducting apparatus. In this paper, it is dealt with a barrier effect on the DC and AC dielectric characteristics of gaseous nitrogen with respect to the position and number of solid insulating barriers. As results, the DC and AC electrical breakdown characteristics by various barrier effects is verified.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.19 no.8
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• pp.144-149
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• 2005

In this paper, insulations characteristics by temperature changes($+30{\sim}-40[^{\circ}C]$) of $SF_6$ gas in the experimental chamber were studied. From this result, The breakdown characteristics classify the vapor stage of $SF_6$ according the Paschen's law, the gas & liquid coexisted stage of voltage value increases & much deviation and the VB low stage as the interior of chamber gets filled with mixture of $SF_6$ that are not liquefacted and remaining air which couldn't be ventilated. In addition the ability of insulation of liquid $SF_6$ was higher than that of the highly pressurized $SF_6$ gas. In this research, we want to provide the base data on designing insulation of high-temperature superconductor and the cryogenic equipments by investigating the insulation characteristics of $SF_6$.

• Journal of the Korean Society of Propulsion Engineers
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• v.22 no.1
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• pp.1-6
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• 2018

Temperatures of cryogenic nitrogen jet inside an injector and at three different downstream positions (0.9, 10.6, and 28.1d) were measured with thermocouples in sub- and supercritical states. The jet temperature decreased while cooling the supply line and injector. The jet experienced from flash boiling, boiling and then no boiling according to decreasing temperature. As an analogy to flash-boiling at the subcritical state, pseudo-flash boiling has been assumed considering the existence of pseudo-boiling at the supercritical state. By showing an area where the temperature did not increase downstream, the plausibility of pseudo-flash boiling is proposed.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.2
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• pp.110-118
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• 2021

In a liquid rocket engine system, the flow of oxidizer into the combustion chamber is controlled by the main oxidizer shut-off valve. When the valve is closed, the oxidizer flows via the recirculation line, not into the combustion chamber. In this situation, the measured pressure could be much higher than a design value because of the water hammer phenomenon. In this paper, the experiments on the water hammer in the recirculation line with different initial conditions were conducted in order to study the pressure wave produced in each case. According to the experimental results, characteristics of the pressure wave in the recirculation line depend on the initial condition. To be specific, the pressure surge is maximized in case that the shock is condensation-oriented in the end of the recirculation line.

• Journal of Plant Biotechnology
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• v.8 no.1
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• pp.43-50
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• 2006

The goal of this research was to develop an efficient cryopreservation protocol for germplasms of yam (Diosorea batatas), that were cultivated in Korea. Comparative studies with four other cryogenic techniques and subsequent experiments for shoot regrowth were conducted. in vitro-grown shoot-apices of the D. batatas were successfully cryopreserved by encapsulation-dehydration. The maximum survival of shoot-apices could be achieved when the precultured (with 0.3 M of sucrose for one day) and encapsulated (with a 3%(w/v) Na-alginate solution) apices were dehydrated for $3.5{\sim}4\;h$ prior to direct immersion in LN (liquid nitrogen). The frequency of regrowth rate of cryopreserved apices was not decreased during 3-month storage period. The thawing method markedly affected survival of the cryopreserved apices, and thawing at $40^{\circ}C$ for 3 min produced the best results. When cryopreserved apices were post-cultured on the post-culture medium (MS), supplemented with $0.2mgl^{-1}$ of BA ($N_6$-benzyladenine) and $0.2mgl^{-1}$ of kinetin, they showed direct shooting without callusing.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.191-195
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• 2005

Propellant remains as outage at engine shutdown contributes no useful impulse to the rocket and produces an unwanted increase in burnout weight. Minimization of outage, is therfore is a basic consideration in attaining the maximum performance capability of my bipropellant liquid rocket. This paper present the calculation procedures of outage and optimum loading propellant mass. And some control methods and measurement techniques for outage are presented.

• Progress in Superconductivity and Cryogenics
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• v.7 no.1
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• pp.42-46
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• 2005

The resistive type high temperature superconducting fault current limiter (HTSFCL) limits the fault current using the resistance generated by fault current. The generated resistance by fault current makes large pulse power which makes the operation of HTSFCL unstable. So, the cryogenic cooling system of the resistive type HTSFCL must diffuse and eliminate the pulse energy very quickly. Although the best way is to make wide direct contact area between HTS winding and coolant as much as possible, HTS winding also needs the impregnation layer which fixes and protects it from electromagnetic force. This paper deals with the thermal conductivity and dielectric strength of some epoxy compounds for the impregnation of high temperature superconducting (HTS) winding in liquid nitrogen. The measured data can be used in the optimal design of impregnation for HTS winding. Aluminar filling increased the thermal conductivity of epoxy compounds. Hardener also affected the thermal and electric characteristic of epoxy compounds.