• Progress in Superconductivity and Cryogenics
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• v.22 no.3
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• pp.20-24
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• 2020

The purpose of this analytic study is to design and examine an efficient hydrogen liquefaction cycle by using a pre-cooler. The liquefaction cycle is primarily comprised of a pre-cooler and a refrigerator. The fed hydrogen gas is cooled down from ambient temperature (300 K) to the pre-cooling coolant temperature (either 77 K or 120 K approximately) through the pre-cooler. There are two pre-cooling methods: a single pre-coolant pre-cooler and a cascade pre-cooler which uses two levels of pre-coolants. After heat exchanging with the pre-cooler, the hydrogen gas is further cooled and finally liquefied through the refrigerator. The working fluids of the potential pre-cooling cycle are selected as liquid nitrogen and liquefied natural gas. A commercial software Aspen HYSYS is utilized to perform the numerical simulation of the proposed liquefaction cycle. Efficiency is compared with respect to the various conditions of the heat exchanging part of the pre-cooler. The analysis results show that the cascade method is more efficient, and the heat exchanging part of the pre-coolers should have specific UA ratios to maximize both spatial and energy efficiencies. This paper presents the quantitative performance of the pre-cooler in the hydrogen liquefaction cycle in detail, which shall be useful for designing an energy-efficient liquefaction system.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.7
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• pp.252-257
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• 2018

In this paper, we propose a mean time to failure (MTTF) to improve the solution for a cryogenic cooler, which is an important part of a cooled thermal device. Common electronic devices have a high possibility of failure due to various environmental factors, such as temperature and humidity. But some special devices (such as thermal devices) are designed to overcome environmental factors. The most affected part of a cooled thermal device's MTTF is the cryogenic cooler. The MTTF of a cryogenic cooler is affected by the device's internal heat. Therefore, if the device's internal heat is reduced, the cryogenic cooler's MTTF increases. From the present device's internal heat simulation, we analyze the improvement method of the device. The proposed improvement method's effectiveness is verified by simulation and MTTF calculation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.5
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• pp.605-609
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• 2010

In modern surveillance equipment, infrared (IR) sensors are essential for detection and observation. The IR sensor is connected to a miniature cryogenic cooler to maintain the temperature at very low levels, i.e., temperatures as low as 77 K. However, the quality of the image captured by the sensor is degraded by the transmission of vibration disturbances from the cooler. Therefore, to maintain high image quality, the compressor vibration and the force transmitted to the sensor have to be mitigated. For the compressor vibration isolating system, a tuned dynamic vibration absorber, combined with a passive isolator, is proposed. A cryogenic compressor bracket and springs are designed to allow the absorber mass to mitigate the vibration jitter in the axial direction. The system design is analyzed and evaluated in terms of the dynamic suppression of the harmonic force at the operating frequency of the cooler.

• Journal of Power System Engineering
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• v.14 no.2
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• pp.28-33
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• 2010

In this research, cascade liquefaction process was simulated using two-staged direct expansion with inter-cooler. Evaporated gaseous refrigerant which has low pressure and temperature from the inter-cooler is mixed with gaseous refrigerant from outlet of 1st compressor, and flows into 2nd compressor. Therefore this prevents superheating compression. Compressor work of process which includes inter-cooler to all cycles shows the lowest value of 338.68 MW and it is lower 16.34% than that of basic process. Refrigeration capacity shows decreasing tendency as applied inter-cooler and that of process which includes inter-cooler to all cycles shows the lowest value of 449 MW. COP was increased when the inter-cooler was applied, and process which includes inter-cooler to all cycles shows highest value of 1.33. It shows that COP was increased because decrement of compressor work by applying inter-cooler was higher than decrement of refrigeration capacity.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2001.04a
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• pp.731-734
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• 2001

A cryogenic stirling cooler is currently under development at Korea Institute of Industrial Technology(KITECH). Cryocooler has many kinds of types. The stirling cooler is the most appropriate one for under 80K with the trait of long life cycle and small size. The stirling cooler uses helium as a working fluid. Helium is pressurized by the linear compressor which is driver by linear motor. In this paper, the change of pressure and volume is studied by the isothermal analysis method. It is necessary to investigate the optimized pressure to meets the highest COP. The compressor's piston and expender's displacer interact according to the working fluid's pressure level and the phase difference. This paper presents the relation between the initial pressure and the work of cryocooler. By that results, we can predict the performance of linear compressor.

• Current Industrial and Technological Trends in Aerospace
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• v.7 no.2
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• pp.48-58
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• 2009

Since 1960s, cryogenic cooling technologies has been adopted in the development of spacecraft with components that must be cooled to cryogenic temperatures of 2 to 150 K. In recent years this technology has been a substantial growth in the emerging number of programs that include such spacecraft to service scientific, military, and weather observation missions. The cooling of optics and detectors to reduce signal noise in infrared (IR) telescopes is the principal applications of cryogenic cooling technologies. The choice of cooling technologies depends on the desired temperature level, the amount of heat to be removed, and the required operating life. This paper will present the status of modern cryogenic cooling technologies especially for space application.

• Journal of Aerospace System Engineering
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• v.18 no.2
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• pp.71-78
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• 2024

During the initial thermal design process, determining the thermal effect of various design variables in a complex orbital thermal environment is time-consuming. To save time in the initial design phase, it is necessary to quickly derive optimal design parameters and predict the temperature. To address these challenges, Veritrek, a software specialized in optimal design using a reduced-order model (ROM), was released in 2018. In this paper, we utilized the Veritrek software to build a reduced-order model, conduct sensitivity analysis, and perform optimal design analysis for a graphite sheet-based cryogenic cooler thermal control system. The goal was to determine the optimal design values for the number of graphite sheet layers, radiator area, and thickness that would meet the allowable temperature of the cryogenic cooler.

• Progress in Superconductivity and Cryogenics
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• v.5 no.1
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• pp.133-135
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• 2003

Cryogenic systems are requirement for the operation of HTS power cables. In general, HTS power cables require temperature below 77K, a temperature that can be achieved from the liquid nitrogen at latm or sub-cooled LN2 above latm. HTS power cable needs sufficient refrigeration to overcome its low temperature heat loading. This loading typically cones in two forms : (1) heat leaks from the surroundings and (2) internal heat generation. This paper explains the cooling test system of 10m HTS power cable. This system is composed of storage dewar, auto fill system, core cryostat and cold-box. Storage dewar is a LN2 storage tank and auto fill system is a LN2 supply device to the sub-cooler, Core cryostat is a LN2 flow line. Cold box is a control unit of temperature and flow rate. It is composed of control valve, flow meter, sub-cooler and circulation pump, etc..

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.127-131
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• 2003

Foil gas bearing is a noncontact bearing operated by coupled interaction between hydrodynamic pressure of viscous fluid and elastic deformation of foil structure. It has valuable advantages, such as low power loss, long life, oilless environment and low vibration, over conventional bearings for the high speed applications. A high speed BLDC motor adopting the foil bearing has been developed. It is designed to have 38㎾ power at 100,000 RPM for a cryogenic cooler whose operating fluid is neon. In this paper, structural development details especially for the foil gas bearing and rotordynamics are presented.

• Progress in Superconductivity and Cryogenics
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• v.24 no.4
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• pp.71-77
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• 2022

Sub-Kelvin cooling has been generally demanded for the fields of low temperature physics, such as physical property measurements, astronomical detection, and quantum computing. The refrigeration system with a small size can be appropriately introduced when the measurement system does not require a high cooling capacity at sub-Kelvin temperature. The dilution refrigerator which is a common method to reach sub-Kelvin, however, must possess a large ³He circulation equipment at room temperature. As alternatives, a sorption refrigerator and a magnetic refrigerator can be adopted for sub-Kelvin cooling. This paper describes those coolers which have been developed by various research groups. Furthermore, a cold-cycle dilution refrigerator of which the size of the ³He circulation system is minimized, is also introduced. Subsequently, a new concept of dilution refrigerator is proposed by our group. The suggested cooler can achieve sub-Kelvin temperature with a small size since it does not require any recuperator and turbo-molecular vacuum pump. Its architecture allows the compact configuration to reach sub-Kelvin temperature by integrating the sorption pump and the magnetic refrigerators. Therefore, it may be suitably utilized in the low temperature experiments requiring low cooling capacity.