• Progress in Superconductivity and Cryogenics
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• v.18 no.4
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• pp.25-29
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• 2016

The high temperature superconducting (HTS) contra-rotating propulsion (CRP) systems comprise two coaxial propellers sited on behind the other and rotate in opposite directions. They have the hydrodynamic advantage of recovering the slipstream rotational energy which would otherwise be lost to a conventional single-screw system. However, the cooling systems used for HTS CRP system need a high cooling power enough to maintain a low temperature of 2G HTS material operating at liquid neon (LNe) temperature (24.5 - 27 K). In this paper, a single thermo-syphon cooling approach using a Gifford-McMahon (G-M) cryo-cooler is presented. First, an optimal thermal design of a 1.5 MW HTS motor was conducted varying to different types of commercial 2G HTS tapes. Then, a mono-cryogenic cooling system for an integration of two 1.5 MW HTS motors will be designed and analyzed. Finally, the 3D finite element analysis (FEA) simulation of thermal characteristics was also performed.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.3
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• pp.25-37
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• 2005

For pump-fed rocket propulsion system, the temperature of LOX to be supplied to turbopump inlet should be satisfied with pump inlet temperature requirement during all operating stages, as excessive temperatures can result in cavitation due to reduction in NPSH, thus either damaging the pump or adversely affecting pump performance rise. So exact estimation of LOX temperature rise is absolutely needed for developing reliable propulsion system. This paper presents systematic analysis scheme for estimating inner process of cryogenic propellant tank which is needed for LOX temperature rise. And this paper presents LOX temperature rise and thermal stratification for all rocket operating stages including cooling, filling, waiting, pre-pressurization and firing, with the application of buoyancy driven boundary layer theory.

• Aerospace Engineering and Technology
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• v.10 no.1
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• pp.79-88
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• 2011

A fill-drain valve is operated by provided control gas at the ground for liquid propellant feeding system of space launch vehicle, which fills or drains on-board propellant tanks with a cryogenic oxidizer. We have analyzed and modified the data of fill-drain valve designed by Yuzhnoye. The simulation model of fill-drain valve is designed by using the AMESim code to predict and evaluate the dynamic characteristics and pneumatic behavior of valve. In this study, we performed a dynamic characteristic simulation on design parameter. And we could predict opening/closing time and pressures, operating performances on design parameters. This study will serve as one of reference guides to enhance the developmental efficiency of fill-drain valves with the various operating requirements, which shall be used in the Koreanized Space Launch Vehicle.

• Transactions of the Korean hydrogen and new energy society
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• v.33 no.4
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• pp.391-399
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• 2022

Hydrogen is one of the energy carriers and has high energy efficiency relative to mass. It is an eco-friendly fuel that makes only water (H₂O) as a by-product after use. In order to use hydrogen conveniently and safely, development of production, storage and transfer technologies is required and attempts are being made to apply hydrogen as an energy source in various fields through the development of the technology. For transporting and storing hydrogen include high-pressure hydrogen gas storage, a type of storage technologies consist of cryogenic hydrogen liquid storage, hydrogen storage alloy, chemical storage by adsorbents and high-pressure hydrogen storage containers have been developed in a total of four stages. The biggest issue in charging high-pressure hydrogen gas which is a combustible gas is safety and the backfire prevention device is that prevents external flames from entering the tank and prevents explosion and is essential to use hydrogen safely. This study conducted a numerical analysis to analyze the performance of suppressing flame propagation of 2, 3 inch flame arrestor. As a result, it is determined that, where the flame arrestor is attached, the temperature would be lowered below the temperature of spontaneous combustion of hydrogen to suppress flame propagation.

• Korean Chemical Engineering Research
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• v.61 no.4
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• pp.550-554
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• 2023

Fossil energy sources are limited in their sustainable use and expansion due to global warming caused by carbon dioxide emissions. Hydrogen is considered as a promising alternative to traditional fossil fuels. To ensure the stable long-term storage, it is necessary to accurately predict its thermodynamic properties at cryogenic temperatures. Therefore, this study aimed to investigate thermodynamic properties, such as saturated vapor pressure and density, enthalpy, and entropy of liquid and gas, using cubic equations of state that demonstrate relatively simple relationships. Among the three types of equations of state (Redlich-Kwong (RK), Soave-Redlich-Kwong (SRK), and Peng-Robinson (PR)), the SRK model exhibited relatively accurate prediction results for various physical properties.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.876-880
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• 2015

In 2016, the IMO's new rules for an 80% reduction in NOx emissions in newly built ships will necessitate the use of LNG as a clean fuel. So far, the developed European countries have led the development of LNG bunkering ships and related facilities. An LNG bunkering system stores LNG in a horizontal or vertical IMO "C"-Type tank insulated with perlite powder, and a vacuum in the annular space between the double walls, like the cryogenic liquid nitrogen tank. Current storage tanks have high heat leakage, evaporating over 2.0% daily, and are difficult to build with the required vacuum. A more efficiently insulated storage tank could reduce the evaporation rate. This research carried out thermal analysis on a new effective insulation method that separates high vacuum in the annular space between two tanks with a solid insulation material, such as urethane foam, lining the outer vessel. This highly efficient insulation system obtained an evaporation rate of 0.03% per day under a $10^{-3}torr$ vacuum, and an evaporation rate of 0.11% at $10^{-45}torr$. Even if the space loses its vacuum, the new insulation system showed a lower evaporation rate of 4.12% than the present perlite system of 4.9%. This newly developed tank can increase the efficiency of LNG storage tank and may help keep LNG bunkering systems safe.

• Korean Journal of Environmental Agriculture
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• v.36 no.4
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• pp.256-262
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• 2017

BACKGROUND: Seed of perilla (Perilla frutescens var. japonica Hara) is short-lived in conventional storage conditions. For long-term conservation of plant species, cryopreservation is the method currently available. This study was performed to find out reliable methods for a long-term storage of seeds of perilla as a genetic resource. METHODS AND RESULTS: Using seeds of 9 perilla cultivars, the effects of desiccation, aging, and cryopreservation on seed germinability and ascorbate peroxidase activity in the seeds were investigated. Initial germinability of the seeds was various, and dry seeds of all cultivars survived cryopreservation without loss of viability. The highest germination was achieved at 4-5% moisture content, and stimulatory effect of cryogenic temperature on the seed germination was observed in some cultivars. Accelerated aging of perilla seeds led to reduction in germination and ascorbate peroxidase activity, and the susceptibility of seeds to aging was different among the tested cultivars. No significant difference in germination was observed for the aged seeds of control and liquid nitrogen exposed. CONCLUSION: The results of this study suggest that cryopreservation at 4-5% moisture content would be a suitable method for long-term conservation of perilla seeds without detrimental effects on germination.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.4
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• pp.141-147
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• 2010

Liquefied natural gas(LNG) is natural gas that has been converted temporarily to liquid form for ease of storage and transport it. Natural gas is the worlds cleanest burning fossil fuel and it has emerged as the environmentally preferred fuel of choice. In Korea, the demand of this has been increased since the first import from the Indonesia in 1986. LNG takes up about 1/600th the volume of natural gas in the gaseous state by cooling it to approximately $-162^{\circ}C(-260^{\circ}F)$. The reduction in volume therefore makes it much more cost efficient to transport and store it. Modern LNG storage tanks are typically the full containment type, which is a double-wall construction with reinforced concrete outer wall and a high-nickel steel inner tank, with extremely efficient insulation between the walls. The insulation will be installed to LNG outer tank for the isolation of cryogenic temperature. The insulation will be installed in the base slab, wall and at the roof. According to the insulation's arrangement, the different aspects of temperature transmission is shown around the outer tank. As the result of the thermal & stress analysis, by the installing cellular glass underneath the perlite concrete, the temperature difference is greatly reduced between the ambient temperature and inside of concrete wall, also reducing section force according to temperature load.

• Journal of Korean Tunnelling and Underground Space Association
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• v.21 no.1
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• pp.31-48
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• 2019

The artificial ground freezing (AGF) method is a groundwater cutoff and/or ground reinforcement method suitable for constructing underground structures in soft ground and urban areas. The AGF method conducts a freezing process by employing a refrigerant circulating through a set of embedded freezing pipes to form frozen walls serving as excavation supports and/or cutoff walls. However, thermal expansion of the pore water during freezing may cause excessive deformation of the ground. On the other hand, as the frozen soil is thawed after completion of the construction, mechanical characteristics of the thawed soil are changed due to the plastic deformation of the ground and the rearrangement of soil fabric. This paper performed a field experiment to evaluate the freezing rate of marine clay in the application of the AGF method. The field experiment was carried out by circulating liquid nitrogen, which is a cryogenic refrigerant, through one freezing pipe installed at a depth of 3.2 m in the ground. Also, a piezo-cone penetration test (CPTu) and a lateral load test (LLT) were performed on the marine clay before and after application of the AGF method to evaluate a change in strength and stiffness of it, which was induced by freezing-thawing. The experimental results indicate that about 11.9 tons of liquid nitrogen were consumed for 3.5 days to form a cylindrical frozen body with a volume of about $2.12m^3$. In addition, the strength and stiffness of the ground were reduced by 48.5% and 22.7%, respectively, after a freezing-thawing cycle.

• Journal of the Korean Society of Food Science and Nutrition
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• v.44 no.10
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• pp.1492-1503
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• 2015

This study evaluated the combination effect of various freezing and thawing techniques on the quality and nutritional aspects of onions. Onions were frozen by natural air convection freezing (NCF), air blast freezing (ABF), and liquid nitrogen freezing (LNF). Onions were frozen for 76 min by NCF, 9 min by ABF, and 9 min by LNF. The freezing treatment was stopped when the core temperature reached $-12^{\circ}C$ for NCF and ABF, and $-120^{\circ}C$ for LNF. Frozen samples were thawed through natural air convection thawing, running water thawing, sonication thawing (ST), or microwave thawing. The quality and nutritional aspects of frozen-thawed onions were evaluated by measuring thawing loss, pH, texture, water content, color, and SEM image. ST was found to cause the least loss in onion sample among the tested thawing methods, whereas the freezing methods did not cause any significant loss. In our experiment, thawing is found to be a more critical technique when compared to that of freezing. There were no clear quantifications or trends of pH and water content among different freezing and thawing techniques. The highest total color difference (${\Delta}E$) was observed in the NCF sample. For morphological observation, ABF gave the smallest ice crystal size, as well as minimum cell collapse. Loss of vitamin C, free sugar, and organic acid content was lower in the ABF and ST sample, when compared to other trials. In our study, we found that combination of ABF and ST could preserve the quality and nutritional aspects of frozen-thawed onions better than other methods.