• Progress in Superconductivity and Cryogenics
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• v.15 no.1
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• pp.45-50
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• 2013

Closed-loop J-T (Joule-Thomson) refrigeration cycle is advantageous compared to common open loop $N_2$ decompression system in terms of nitrogen consumption. In this study, two closed-loop pure $N_2$ J-T refrigeration systems with sub-atmospheric device for cooling High Temperature Superconductor (HTS) power cable are investigated. J-T cooling systems include 2-stage compressor, 2-stage precooling cycle, J-T valve and a cold compressor or an auxiliary vacuum pump at the room temperature. The cold compressor and the vacuum pump are installed after the J-T valve to create sub-atmospheric condition. The temperature of 67 K is possible by lowering the pressure up to 24 kPa at the cold part. The optimized hydrocarbon mixed refrigerant (MR) J-T system is applied for precooling stage. The cold head of precooling MR J-T have the temperature from 120 K to 150 K. The various characteristics of cold compressor are invstigated and applied to design parameter of the cold compressor. The Carnot efficiency of cold compressor system is calculated as 16.7% and that of vacuum pump system as 16.4%. The efficiency difference between the cold compressor system and the vacuum pump system is due to difference of enthalpy change at cryogenic temperature, enthalpy change at room temperature and different work load at the pre-cooling cycle. The efficiency of neon-nitrogen MR J-T system is also presented for comparison with the sub-atmospheric devices. These systems have several pros and cons in comparison to typical MR J-T systems such as vacuum line maintainability, system's COP and etc. In this paper, the detailed design of the subcooled $N_2$ J-T systems are examined and some practical issues of the sub-atmospheric devices are discussed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.9
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• pp.175-181
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• 2019

In the case of a conventional single stage decompression regulator used for large depressurization in the hydrogen fuel cell system of a fuel cell electric vehicle (FCEV), problems can arise, such as pulsation, slow response, hydrogen brittleness, leakage, high weight, and high cost due to high decompression. Most of these problems can be overcome easily using two decompression mechanisms (two-stage structures). In addition, a wide outlet-pressure control range can be secured if an electronic solenoid is applied to the second decompression. Accordingly, it is necessary to improve the precision of the outlet pressure of a two-stage pressure-reducing regulator and develop techniques, such as leakage prevention, durability, light weight, and price reduction. Therefore, to improve the outlet pressure accuracy and prevent leakage, the structural part before and after decompression to improve the air tightness were divided and the analysis was carried out assuming that the valve part was closed (open ratio: 0%) after each initial internal pressure application.

• Transactions of Materials Processing
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• v.12 no.8
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• pp.702-709
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• 2003

In the automotive industry hydroforming of sheet metal pairs have received special attention because materials for various sheet metal components of vehicles have changed into the high strength steel, aluminum, and titanium blank having low formability. Uniform deformation over the whole region is a main advantage in the sheet hydroforming process. Because upper and lower parts could be produced simultaneously with one tool, hydroforming of sheet metal pairs is competitive in reducing the lead-time and development cost. In this paper, the multi-stage hydroforming process of sheet pair is proposed in order to increase the formability of a structural part like the oil pan shape. The upper die for forming oil pan shape is divided into two parts which can move separately. By the finite element simulation, the design parameters such as geometry of the tool and detailed specification of hydraulic pump were calculated and verified. For the strict comparison of the proposed process, the blank holding force is kept to a constant value during deformation by hydraulic valve. The deformed shape and strain distribution of the manufactured parts with the proposed process are compared with the results of simulation. In the multi-stage hydroforming process, maximum thickness strain was improved by more than 30 percent.

• Journal of Chest Surgery
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• v.38 no.12 s.257
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• pp.856-859
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• 2005

A male neonate was referred to our hospital with facial cyanosis and tachypnea at 19 days of age. Two-dimensional echocardiography showed type B interrupted aortic arch, posterior malalignment ventricular septal defect and valvular aortic stenosis. A new surgical repair was done with biventricular repair and neo-aortic arch reconstruction. Left ventricular outflow track (LVOT) was consisted of aortic valve and pulmonic valve. Right ventricular outflow (RVOT) track was reconstructed with extracardiac conduit. Postoperative two-dimensional echocardiography showed no stenosis and turbulency flow on LVOT and RVOT.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.4
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• pp.328-333
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• 2006

In this paper, we developed a pressure measurement apparatus with the parallel structure to improve the measurement efficiency of pressure sensors by reducing the measurement time of pressure. The developed system has two parallel positions for loading Silicon pressure sensor and has a dual valve structure. The semiconductor pressure sensors prepared by Copal Electronics were used to confirm the performance of the developed measurement system. Two stage differential amplifier circuit was employed to amplify the weak output signal and the amplified output signal was improved utilizing a low-pass filter. New apparatus shows the measurement time of pressure two times shorter than that of conventional one with the serial structure, while both structures show the similar linear output versus pressure characteristics.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.8
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• pp.425-432
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• 2009

In this study, the improvement of cooling capacity by applying gas injection technique in a two-stage heat pump using R410A was experimentally investigated. A twin rotary type compressor with gas injection was applied to the heat pump system. The optimum refrigerant charge for the injection and the non-injection cycles was selected to achieve the maximum COP at the cooling standard condition. The injection cycle showed less optimum refrigerant charge than that of the non-injection cycle. The cooling performances of the injection and the non-injection cycles were measured and compared by varying compressor frequency from 40 to 90 Hz. The cooling capacity of the gas injection cycle was 1.6% -11.3% higher than that of the non-injection cycle. The COP of the gas injection cycle was 13.7% to 28.9% higher than that of the non-injection cycle at the same cooling capacity. The heat pump system showed stable operation after 30% of the injection valve opening.

• Progress in Superconductivity and Cryogenics
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• v.8 no.1
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• pp.59-64
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• 2006

A closed-loop cryogenic cooling system for high field magnets is presented. This design is motivated by our recent development of cooling system for 21 tesla Fourier Transform ion Cyclotron Resonance (FT-ICR) superconducting magnets without any replenishment of cryogen. The low temperature superconducting magnets are immersed in a subcooled 1.8 K bath, which is connected hydraulically to the 4.2 K reservoir through a narrow channel. Saturated liquid helium is cooled by Joule-Thomson heat exchanger and flows through the JT valve, isenthalpically dropping its pressure to approximately 1 6 kPa, corresponding saturation temperature of 1.8 K. Helium gas exhausted from pump is now recondensed by two-stage cryocooler located after vapor purify system. The amount of cryogenic Heat loads and required mass flow rate through closed-loop are estimated by a relevant heat transfer analysis, from which dimensions of JT heat exchanger and He II heat exchanger are determined. The detailed design of cryocooler heat exchanger for helium recondensing is performed. The effect of cryogenic loads, especially superfluid heat leak through the gap of weight load relief valve, on the dimensions of cryogenic system is also investigated.

• Journal of Chest Surgery
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• v.11 no.4
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• pp.481-487
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• 1978

Seventeen patients of the congenital pulmenic stenosis were operated at the department of Thoracic Surgery, Seoul National University Hospital. There were thirteen male and four females, and ranging from six to thirty years of age. And it's incidence was 2.7% of congenital heart disease cases that were operated on. (Total 628) Seven case of trilogy of Fallot were excluded. Two cases of bacterial endocarditis were found. Right heart catheterization was done in all patients. Average right ventricular pressure was $121{\pm}35.8$mmHg, pulmonary artery $20{\pm}6.8$mmHg, and RV-PA pressure gradient $98{\pm}34.5$mmHg. The preoperative average time interval of A2-P2 which was checked at phonocardiography was $0.08{\pm}0.016$second, and was reduced to $0.03{\pm}0.009$second postoperatively. One was operated by Varco's procedure, another one was done by Brock's procedure, and fifteen patients were done by open heart surgery with heart-lung machine. Pure valvular stenosis was found in sixteen and infundibular stenosis in one case. And the combining anormalies were two patent ductus arteriosus, two patent foramen ovale, and one tricuspid valve hypoplasia. Two expired postoperatively at the begining stage of cardiac surgery in this Department. The remaining fifteen showed excellent operative results.

• Journal of Drive and Control
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• v.17 no.2
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• pp.55-62
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• 2020

There are two types of IMV for MCV, the spool type and the poppet type. The spool type is used in the existing excavator MCV and easily meets large-capacity flow conditions, but has a flow force problem which affects the spool control. The poppet type stably blocks the flow and has excellent rapid response. However, the larger the capacity, the larger the diameter of the poppet needed, requiring a strong spring to withstand the oil pressure. In this study, a bi-directional three-stage IMV for MCV that can be used in medium and large hydraulic excavators was proposed. This is a poppet type, enabling bi-directional flow control and resolves the problem of proportional solenoid suction force limitation. To investigate the validity of the proposed valve, the system was mathematically modeled and the static and dynamic characteristics were investigated through the simulation using commercial software. It has been concluded that the reverse flow is possible in a regeneration circuit and that the proposed IMV can be used to perform various excavation modes.

• Journal of Chest Surgery
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• v.25 no.4
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• pp.406-411
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• 1992

Thirty-four patients were received bidirectional cavopulmonary shunt[BCPS] from Aug. 1989 to Apr. 1991 at Sejong General Hospital, Puchon, Korea. Their ages were from 43 days to 21 years old with 19 cases of infant, 10 from 1 to 5 years old and 5 cases above 6 years old. Their diagnoses were as follows: 13 cases with uni-ventricular heart, 9 tricuspid atresia, 6 double outlet of right ventricle, 4 pulmonary atresia with intact ventricular septum, and 2 transposition of great arteries with pulmonary stenosis. Among them, 10 patients had received other palliative operations before. The BCPS operations were performed under the cardiopulmonary bypass and 10 patients who had bilateral superior vena cava received bilateral BCPS. Other associated procedures were 9 cases of takedown of Blalock-Taussig shunt, 3 pulmonary artery angioplasty, 1 unifocalization, 1 repair of total anomalous pulmonary venous return, 1 Damus procedure, 1 relief of sub-aortic stenosis, 1 right ventricular outflow tract reconstruction and one case of tricuspid valve obliteration. There were 3 operative deaths[8.8%] and two late deaths. The remainders show good postoperative state and their oxygen saturation was increased significantly. Conclusively, the bidirectional cavopulmonary shunt is very effective and safe palliative or pre-Fontan stage operation for the many complex congenital anomalies with low pulmonary blood flow especially for the patients who have the risk of Fontan repair.