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Hankil Yeom,Seung Woo Lee 제어로봇시스템학회 2008 제어로봇시스템학회 국제학술대회 논문집 Vol.2008 No.10
In accordance with the trend for high-speed and multi-axes of machine tools, thermal deformation has become an important factor in the accuracy of machine tools. It was analyzed that thermal deformation error accounts for about 70% of all errors made with machine tools. For precise temperature control, both cooling and heating should be done. A hot gas by-pass type of cooling method has a simplified structure and temperature control accuracy to with in ±0.1 °C. In this study, the operational characteristics of the thermal error controller, including temperature controllability according to hot gas flow and preset temperature sustainability according to heat load, were tested. It is expected that this study will contribute to the development and performance assessment of thermal error controllers, which could minimize thermal errors and improve the quality of semiconductor equipment, precision injection molds, and precision machine tools.
염한길(Hankil Yeom),홍용주(Yong-Ju Hong),고준석(Junseok Ko),김효봉(Hyobong Kim),고득용(Deuk-Yong Koh),박성제(Seong-Je Park),인세환(Sehwan In),김혜림(Hye-Rim Kim) 대한기계학회 2013 대한기계학회 춘추학술대회 Vol.2013 No.12
The SFCL (Superconducting Fault Current Limiter) must be cooled to below the critical temperature of HTS(High Temperature Superconductor) modules. In general, they are submerged in sub-cooled liquid nitrogen because of their thermal stability. To cool and maintain the target temperature and pressure the cryostat should be designed well with a cryocooler and a circulation devices. There are two operation modes in SFCL. One is the standby mode, there exist steady heat load due to heat invasion through current lead, heat invasion from surroundings and heat generation by AC loss. Their heat loads are removed by the cryocooler. Another is the quench mode, when the HTS modules are quenched with the event of high current, it instantaneously generates large amount of heat. This heat is removed by the liquid nitrogen’s latent heat of evaporation, so the generated nitrogen gas should be exhausted from the cryostat. In this paper, we designed the cryostat and cooling method for the stable operation of the SFCL. To achieve this objective sizing and structural analysis of the cryostat, and design the cooling method as cool in sub-cooled liquid nitrogen.
〈학술논문〉고온초전도 전력케이블용 극저온냉각시스템 개발현황
염한길(Hankil Yeom),고득용(Deuk-Yong Koh),박성제(Seong-Je Park),홍용주(Yong-Ju Hong),고준석(Junseok Ko),김효봉(Hyobong Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.5
기존에 진행되고 있는 대표적인 국내외 초전도 전력케이블 개발 및 케이블에 적용된 극저온냉각 시스템에 대한 현황을 소개하였다. 현재 초전도 전력케이블은 1 ㎞ 이상 장선화가 진행됨에 따라 수 십 ㎾ 용량의 냉각시스템을 필요로 하고 있다. 지난 10년간 프론티어사업을 통해 초전도케이블은 선진국과 대등한 수준이거나 일부 앞서가는 분야도 있다. 이제는 극저온 냉동기 등의 핵심부품 국산화 개발을 통해 저렴하고 신뢰성 있는 극저온냉각시스템을 갖춤으로서 초전도케이블시스템이 시장에서 경쟁력을 갖출 수 있는 기반을 마련해야 할 때임을 상기해야 할 것이다. Cryogenic cooling is necessary for HTS power cables to perform their intended function. In the cooling process, sub-cooled liquid nitrogen is circulated by a pump to absorb and dissipate the heat generated in the cable and introduced from outside. For successful cooling, the thermal loads of cable systems and the hydraulic characteristics of the cooling passage of the cable should be well investigated to design the long length cables. The cooling capacity of the cable system is decided by evaluating the thermal load. The pressure drop in the cable is an important design parameter, because the pressure drop decides the length of the cable, size of the coolant circulation pump and circulation pressure, etc. Recently, demonstrative and practical researches of the HTS power cable and the cryogenic system are has been actively going. In this paper, the domestic and international current state of this field is described.
경부하 성능향상을 위한 가스바이패스형 오일쿨러에 관한 연구
염한길(Hankil Yeom),이승우(Seung Woo Lee),하승한(Seung Han Ha) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Oil cooler is a temperature controller using oil. The gas by-pass type can provide both acceptable performance and economy with excellent accuracy of temperature control and an economic price. But this type has a problem in low load state. Because traditional gas by-pass type oil cooler has capillary tube expansion device which is restricted the by-passed hot gas. In this study, we recommend the modified control method that can be applied to the gas by-pass type oil cooler. The capillary tube is replaced by an electronic expansion device. There are two dynamic expansion devices in modified oil cooler. One controls liquid refrigerant at condenser outlet and another controls by-passed hot gas at compressor outlet. This cooler can be adapted to low load state by linked controlling of two electronic expansion devices. In test results, modified oil cooler was more effective than traditional cooler.
Kim, Hyobong,Yeom, Hankil,Choo, Sangyoon,Kim, Jongwoo,Park, Jiho,In, Sehwan,Hong, Yong-Ju,Park, Seong-Je,Ko, Junseok 한국초전도저온공학회 2020 한국초전도저온공학회논문지 Vol.22 No.4
This paper describes the real operation of 2 kW class reverse-Brayton refrigeration system with neon as a working fluid. The refrigeration cycle is designed with operating pressure of 0.5 and 1.0 MPa at low and high pressure side, respectively. Compressor package consists of several helium scroll compressors witch are originally used for driving GM cryocooler. Three segments of plate heat exchanger are adopted to cover the wide temperature range and the refrigeration power is produced by turbo expander. The developed refrigeration system is successfully operated at its target temperature of 77 K. In experiments, all parameters such as pressure, temperature, mass flow rate and valve opening are measured to investigate characteristics during cool-down process and normal state. The difference between design and real operation is discussed with measured experimental data. At normal state of 77 K operation, the developed reverse-Brayton refrigeration system shows 1.83 kW at 68.2 K of cold-end temperature.
Development of high capacity stirling cryocooler
Ko, Junseok,Yeom, Hankil,Kim, Hyobong,Hong, Yong-Ju,In, Sehwan,Park, Seong-Je The Korea Institute of Applied Superconductivity a 2015 한국초전도저온공학회논문지 Vol.17 No.3
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.
In, Sehwan,Yeom, Hankil,Ko, Junseok,Hong, Yong-Ju,Kim, Hyobong,Park, Seong-Je,Koh, Deuk-Yong,Kim, Hye-Rim Institute of Electrical and Electronics Engineers 2015 IEEE transactions on applied superconductivity Vol.25 No.3
<P>It is one of important design issues in the high-temperature superconducting fault current limiter (HTS-FCL) to estimate how much liquid nitrogen vaporizes during its quench process. This paper describes the small scale experiment about the vaporization of subcooled liquid nitrogen by instantaneous heat generation corresponding to the quench in HTS-FCL. In the experiment, the heat is given liquid nitrogen by Joule heating of the stainless steel strip for the short time of about 100 ms. The time variations of temperature and pressure in the liquid nitrogen test chamber are measured for different subcooling conditions of liquid nitrogen and various heat flux conditions. In addition, the amount of vaporization of liquid nitrogen is calculated from experimental results according to the subcooling of liquid nitrogen. The experimental results show that the vaporization of liquid nitrogen strongly depends on heat flux and subcooling conditions. The amount of vaporization linearly decreases with the increase in the subcooling of liquid nitrogen. The calculation results about the amount of vaporization suggest that the subcooling of more than 20 K is necessary to suppress bubble generation for the heat flux condition of 46 W/cm<SUP>2</SUP> or more.</P>