• Transactions of the Korean Society of Mechanical Engineers B
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• v.37 no.1
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• pp.87-93
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• 2013

The selection of the temperature sensor in a cryogenic system depends on the temperature range, shape, and accuracy. An accurate temperature sensor is essential for improving the reliability of an experiment. We have developed a calibration system for cryogenic temperature sensors using a two-stage cryocooler. To reduce the heat load, a thermal shield is installed at the first stage with multiple layer insulation (MLI). We have also developed a sensor holder for calibrating more than 20 sensors simultaneously in order to save time and reduce costs. This system can calibrate sensors at variable temperatures via temperature control using a heater. In this paper, we present the design and fabrication of the temperature sensor calibration system and a representative experimental result.

• Journal of Ocean Engineering and Technology
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• v.36 no.4
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• pp.217-231
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• 2022

Reinforced polyurethane foam (R-PUF), a material for liquefied natural gas cargo containment systems, is expected to have different mechanical properties depending on its stacking position of foaming as the glass fiber reinforcement of R-PUF sinks inside R-PUF under the influence of gravity. In addition, since R-PUF is not a homogeneous material, it is also expected that the coordinate direction within this material has a great correlation with the mechanical properties. So, this study was conducted to confirm this correlation with the one between the mechanical properties and the stacking position. In particular, in this study, R-PUF of 3 different densities (130, 170, and 210 kg/m³) was used, and tensile, compression, and shear tests of this material were performed under 5 temperatures. As a result of the tests, it was confirmed that the strength and modulus of elasticity of the material increased as the temperature decreased. Specifically, the strength and modulus of elasticity in the Z direction, which was the lamination direction, tended to be lower than those in the other directions. Finally, the strength and elastic modulus of different specimens of the material found at the bottom of their lamination compared to the specimens with these properties found at positions other than their lamination bottom were evaluated. Further analysis confirmed that as the temperature decreased, hardening of R-PUF occurred, indicating that the strength and modulus of elasticity increased. On the other hand, as the density of R-PUF increased, a sharp increase in strength and elastic modulus of R-PUF was observed.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.153-160
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• 2010

A magnetocardiogram (MCG) is a recording of the biomagnetic signals generated by cardiac electrical activity. Biomagnetic instruments are based on superconducting quantum interference devices (SQUIDs). A liquid cryogenic Dewar flask was used to maintain the superconductors in a superconducting state at a very low temperature (4 K). In this study, the temperature distribution characteristics of the liquid helium in the Dewar flask was investigated. The Dewar flask used in this study has a 30 L liquid helium capacity with a hold time of 5 d. The Dewar flask has two thermal shields rated at 150 and 40 K. The temperatures measured at the end of the thermal shield and calculated from the computer model were compared. This study attempted to minimize the heat transfer rate of the cryogenic Dewar flask using an optimization method about the geometric variable to find the characteristics for the design geometric variables in terms of the stress distribution of the Dewar flask. For thermal and optimization analysis of the structure, the finite element method code ANSYS 10 was used. The computer model used for the cryogenic Dewar flask was useful to predict the temperature distribution for the area less affected by the thermal radiation.

• Journal of the Korean Vacuum Society
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• v.13 no.4
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• pp.139-144
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• 2004

Recently, the importance of clean vacuum and partial pressure measurement of gas species has been increased in the vaccum process. In this study, the partial pressures of $H_2$, He, C, N, $O_2$, $H_2O $, Ar/2, $N_2$(CO), Ar, $CO_2$ were measured by residual gas analyzer according to temperature of cryogenic pump which is used to clean vacuum generation and compared. The experimental results showed that the cryopanel temperature was reached to 12K after 72 minutes of pumping and after 25hours, the partial pressures in percent were 24.9 %, 6.6%, 5.5 %, 2.2 %, 3.8%, 30.7%, 6.5%, 6.1 %, 5.5%, 8.2% for $H_2$, He, C, N, $O_2$, $H_2O $, Ar/2, $N_2$, Ar, $CO_2$ respectively. The dominant gases were $H_2$ and $H_2O $, and the partial pressures were relatively high compare to other gases.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.17 no.3 s.106
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• pp.239-248
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• 2006

In this paper, the cryogenically cooled low noise amplifier module for radio telescope receiver front-end using pHE-MT MMIC is designed and fabricated. In the selection of MMIC, the MMIC fabricated with the pHEMTS providing successful cryogenic operation are chosen. They are mounted in the housing using the thin film substrate. In the design of the housing, the absorber and the elimination of the gap between the carrier and the housing as well removed the unnecessary oscillations by its structure. The mismatch is improved by ribbon-tuning to provide the best performance at room temperature. The fabricated module shows the gain of $35dB{\pm}1dB$ and the noise figure of $2.37{\sim}2.57dB$ at room temperature over $21.5{\sim}23.5GHz$. In the cryogenic temperature of $15^{\circ}K$ cooled by He gas, the measured gain was above 35 dB and flatness ${\pm}2dB$ and the noise temperatures of $28{\sim}37^{\circ}K$.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.477-480
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• 2011

The stress analyses of the 'U'-shaped multi-ply reinforced gimbal bellows under high pressure and rotational displacement loadings are performed at the room and cryogenic temperatures. The bellows are used for the Lox pipe line which connects the combustion chamber with the turbopump of a liquid rocket engine. The distributions of the stress, the strains and the contact pressures are obtained from the finite element analysis considering the geometric non-linearities of the contacts between the plies and the material one of the isotropic plasticity. Those are compared with the stress results from EJMA (Expansion Joint Manufacturing Association) standard. Also, the effects of the operating temperature and the reinforcing ring on the stresses are investigated.

• Progress in Superconductivity and Cryogenics
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• v.17 no.3
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• pp.51-56
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• 2015

Cryogenic cooling system for HTS electric power devices requires a reliable and efficient high-capacity cryocooler. A Striling cryocooler with a linear compressor can be a good candidate. It has advantages of low vibration and long maintenance cycle compared with a kinematic-driven Stirling cryocooler. In this study, we developed dual-opposed linear compressor of 12 kW electric input power with two 6 kW linear motors. Electrical performance of fabricated linear compressor is verified by experimental measurement of thrust constant. The developed Stirling cryocooler has gamma-type configuration. Piston and displacer are supported with flexure spring. A slit-type heat exchanger is adopted for cold and warm-end, and the generated heat is rejected by cooling water. In cooling performance test, waveforms of voltage, current, displacement and pressure are obtained and their amplitude and phase difference are analysed. Moreover, temperatures of cooling water, housing and linear motor are recorded and electric power parameters of driving circuit are also obtained. The developed Stirling cryocooler reaches to 47.8 K within 23.4 min. with no-load. From heat load tests, it shows cooling capacity of 440 W at 78.1 K with 6.45 kW of electric input power and 19.4 of % Carnot COP.

• 한국지구물리탐사학회:학술대회논문집
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• 2003.11a
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• pp.238-243
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• 2003

As there are many advantages on underground caverns, such as safety and operation, they can also be used for gas storage purpose. When liquefied gas is stored underground, the cryogenic temperature of the gas will affect the stability of the storage cavern. In order to store the liquefied gas successfully, it is essential to estimate the exact temperature distribution of the rock mass around the cavern. In this study, an analytic solution and a conceptual model that can estimate three-dimensional temperature distribution around the storage cavern are suggested. When calculating the heat transfer within a solid, it is likely to consider the solid as the intersection of two or more infinite or semi-infinite geometries. Therefore heat transfer solution for the solid is expressed by the product of the dimensionless temperatures of the geometries, which are used to form the combined solid. Based on the multi-dimensional transient heat transfer theory, the analytic solution is successfully derived by assuming the cavern shape to be of simplified geometry. Also, a conceptual model is developed by using the analytic solution of this study. By performing numerical experiments of this multi-dimensional model, the temperature distribution of the analytic solution is compared with that of numerical analysis and theoretical solutions.

• Journal of Welding and Joining
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• v.32 no.3
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• pp.89-94
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• 2014

AISI 304 austenitic stainless steel is widely used for LNG pipes for LNG transmission thanks to its good metallurgical and mechanical properties. In the present research, impact toughness of a gas tungsten arc welded AISI 304 stainless steel pipe was evaluated between room and liquid nitrogen ($-196^{\circ}C$) test temperatures. In addition, a comparative study was made of the fracture behavior of FCC crystal structured stainless steel weldments and BCC crystal structured mild steels(A-grade and SS400). The results showed a slight decrease in the impact energy of the AISI 304 base metal, heat affected zone(HAZ), and welded zone with decreasing test temperature. In addition, the welded metal has the highest absorbed impact energy, followed by HAZ and the base metal.

• Progress in Superconductivity and Cryogenics
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• v.15 no.2
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• pp.1-8
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• 2013

This paper reviews the development status of magnetic refrigeration system for hydrogen liquefaction. There is no doubt that hydrogen is one of most important energy sources in the near future. In particular, liquid hydrogen can be utilized for infrastructure construction consisting of storage and transportation. Liquid hydrogen is in cryogenic temperatures and therefore high efficient liquefaction method must be studied. Magnetic refrigeration which uses the magneto-caloric effect has potential to realize not only the higher liquefaction efficiency > 50 %, but also to be environmentally friendly and cost effective. Our hydrogen magnetic refrigeration system consists of Carnot cycle for liquefaction stage and AMR (active magnetic regenerator) cycle for precooling stages. For the Carnot cycle, we develop the high efficient system > 80 % liquefaction efficiency by using the heat pipe. For the AMR cycle, we studied two kinds of displacer systems, which transferred the working fluid. We confirmed the AMR effect with the cooling temperature span of 12 K for 1.8 T of the magnetic field and 6 second of the cycle. By using the simulation, we estimate the total efficiency of the hydrogen liquefaction plant for 10 kg/day. A FOM of 0.47 is obtained in the magnetic refrigeration system operation temperature between 20 K and 77 K including LN2 work input.