• Progress in Superconductivity and Cryogenics
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• v.23 no.4
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• pp.56-60
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• 2021

The microwave Radar used for special purposes in the past is being applied in various areas due to the technological advancement and cost reduction, and is particularly applied to autonomous driving in the automobile field. The FMCW (Frequency Modulated Continuous Wave) Radar can acquire level information of liquid in vessel based on the beat frequency obtained by continuously transmitting and receiving signals by modulating the frequency over time. However, for cryogenic fluids with small impedance differences between liquid medium and gas medium, such as liquid nitrogen and liquid hydrogen, it is difficult to apply a typical Radar-based level meter. In this study, we develop an 80 GHz FMCW Radar for level measurement of cryogenic fluids with small impedance differences between media and analyze its characteristics. Here, because of the low intrinsic impedance difference, most of the transmitted signal passes through the liquid nitrogen interface and is reflected at the bottom of the vessel. To solve this problem, a radar measurement algorithm was designed to detect multiple targets and separate the distance signal to the bottom of the vessel in order to estimate the precise position on the liquid nitrogen interface. Thereafter, performance verification experiments were performed according to the liquid nitrogen level using the developed radar level meter.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2000.02a
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• pp.48-51
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• 2000

The behavior of cryogenic liquid stored in a closed cryogenic tank has been studied at various liquid levels, as a function of pressure and temperature on time, assuming heat leak(NER) is 0.7%/day. The pressure depends, as expected, on the liquid-vapor ratio in a tank. The calculation shows that if liquid level is as high as 90%,much higher than the critical volume ration, in a closed tank of designed pressure 11 bar, it takes 5.4 to 15days for the entire volume of the tank to be filled with liquid and 11 to 22 days for the tank to be exploded. If a closed tank is full of liquid, it is extremely dangerous because of abrupt pressure increase so that the safety devices are necessary to vent out pressurized gas. These phenomena can be explained with the liquid heat capacity, latent heat and compressibility.

• Transactions of the Korean hydrogen and new energy society
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• v.35 no.1
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• pp.34-39
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• 2024

Korea government is trying to supply liquid hydrogen from another country to domestic The research for liquid hydrogen transportation and liquefaction plant of hydrogen underway for several years, and empirical research is also planned in the future. Along with the development of liquid hydrogen transport ship/liquefaction plant technology, the development of liquid hydrogen reception base technology must be carried out. In this study, a concept level liquid hydrogen receiving terminal is constructed based on the process of the LNG receiving terminal. Based on this, a study is conducted on the development of analysis technology for the amount of BOG (pipe, tank) generated during cooldown and unloading in the liquid hydrogen unloading line (loading arm to storage tank). The research results are intended to be used as basic data for the design and liquid hydrogen receiving terminal in the future.

• Tribology and Lubricants
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• v.28 no.4
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• pp.167-172
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• 2012

The turbo pump of a liquid rocket engine is composed of three main parts: the oxidizer pump, fuel pump, and turbine. Liquid oxygen ($LO_X$) is the working fluid in the cryogenic environment in the oxidizer pump, but tests are usually performed using liquid nitrogen ($LN_2$), which has a boiling point similar to that of $LO_X$ but is comparatively safer and easier to use for the test. In this study, a bearing test rig is developed and its performance is evaluated using a cryogenic ball bearing with $LN_2$ as the working fluid. Verifying the performance of the bearing test rig is crucial for ensuring correct working of the turbo pump unit in the liquid rocket engine. A stable test rig for the bearing in a cryogenic environment makes the bearing technology enhance its reliability. The test results show that the system operates stably and the requirement of performance time of 500 s is met. The test results of temperature, motor speed, and torque are discussed. The developed cryogenic bearing test rig is expected to help in widening knowledge and expanding research on ball bearings in the future.

• 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.

• Progress in Superconductivity and Cryogenics
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• v.20 no.3
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• pp.28-33
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• 2018

With the continuous performance improvement and commercialization of HTS wires, there have been many efforts to commercialize HTS power cables recently. Unlike conventional power cables, a cryogenic cooling system is required for a HTS power cable and a cryogenic pump is one of the essential components to circulate subcooled liquid nitrogen and cool the HTS power cable. Especially, the development of a reliable and high-efficiency cryogenic pump is an important issue for the commercialization of HTS power cables of several kilometers or more. In this study, we designed and fabricated a cryogenic pump for subcooled liquid nitrogen with a mass flow rate of 1.2 kg/s, a differential pressure of 5 bar, and evaluated the hydraulic performance of the pump. Impeller design was conducted to meet the target design performance with 1 D analysis model and CFD analysis. The pump performance parameters such as pressure heads, mass flow rates, and efficiencies in accordance with rotating speeds were assessed using a laboratory's performance evaluation system.

• Progress in Superconductivity and Cryogenics
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• v.9 no.3
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• pp.72-82
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• 2007

This paper relates to reducing the temperature of a cryogenic liquid by contacting it with gas bubbles, which can be characterized by diffusion-driven evaporative cooling, The characteristic of diffusion-driven evaporative cooling is thoroughly examined by theoretical. analytical and experimental methods specifically for the case of helium injection into liquid oxygen. The results reveal that if the gaseous oxygen partial pressure in helium bubbles is lower than the liquid oxygen vapor pressure, cooling occurs autonomously due to diffusion mass transfer. The method of lowering the injected helium temperature turns out to be very effective for cooling purpose.

• Transactions of the Korean hydrogen and new energy society
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• v.34 no.6
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• pp.615-622
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• 2023

In this study, the theoretical analysis focused on the quantity of liquid hydrogen required for cooling down to 20 K, as well as the generation of boil-off gas (BOG) from the cooling process of the cryogenic components. The study involved calculating the amount of liquid hydrogen needed to achieve the desired temperature for the cryogenic components and subsequently determining the resulting BOG production at various reference temperatures. It was shown that it was important to efficiently lower the temperature of cryogenic parts through preliminary cooling. As a result, the reference temperature and pressure had an influence on the BOG generation on the cooling of cryogenic components using liquid hydrogen.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.4
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• pp.391-397
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• 2010

Performance tests of a liquid-oxygen pump were carried out using liquid nitrogen (LN2) as a working fluid in a cryogenic turbopump test facility in Korea Aerospace Research Institute (KARI). The tests were performed at 30-55% of the design rotational speed, and the results were compared with those from a water test. The experimental results confirmed the similarity of the hydraulic performance, which allows the prediction of the pump performance at a design rotational speed of 20,000 rpm. The overall cavitation performance of the pump in the cryogenic environment was better than that in the water environment for all ranges of flow rates and rotational speeds. Critical cavitation number at the design flow rate was determined as 0.012 from the cryogenic test, and as 0.024 from the water test. The improved cavitation performance is due to the thermodynamic effect in cryogenic fluids.

• Journal of computational fluids engineering
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• v.18 no.2
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• pp.17-25
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• 2013

The process of flow through porous media is of interest a wide range of engineering fields and areas, and the importance of fluid flow with a change in phase arises from the fact that many industrial processes rely on these phenomena for materials process, energy transfer. Especially, the flow phenomena of cryogenic liquid subjected to evaporation is of interest to investigate how the cryogenic liquid behaves in the porous structure. In this study, thermo physical properties, morphological properties of the glass wool with different bulk densities in terms of its temperature-dependence and permeability behaviors under different applying pressure are discussed. Using the experimentally determined properties, characteristics of two main experimental results are investigated. In addition, simulation results are used to realize the cryogenic liquid's flow in porous media, and are compared with experimental results. By using the experimentally determined properties, more reasonable results can be suggested in dealing with porous media flow.