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염한길(Han Kil Yeom),이승우(Seung Woo Lee),박길종(Kil Jong Park) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.5
Thermally induced errors of machine tools could be reduced by oil cooler. For precise temperature control, both cooling and heating should be implemented. There are three major control methods of thermal errors. The on-off method has the largest market share as a result of its lower price, although the accuracy of temperature control is relatively lower, while the inverter method is mostly offered as an option for high precision machine tools due to its high control accuracy. But this method has complicated control system and high price. The hot gas by-pass method, which offers a compromise between the two method. In this study, we tested on-off and hot gas by-pass control methods and analyzed performance and economic efficiency.
600kJ급 SMES용 전도냉각시스템의 냉각특성 (Ⅱ)
염한길(Han-Kil Yeom),홍용주(Yong-Ju Hong),고득용(Deuk-Yong Koh),김효봉(Hyo-Bong Kim),박성제(Seong-Je Park) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.10
The characteristic of the superconducting magnetic energy storage (SMES) system is more fast response, long life time, more economical, and environment-friendly than other uninterruptible power supply (UPS) using the battery. So, the SMES system can be used to develop methods for improving power quality where a short interruption of power could lead to a long and costly shutdown. Recently, cryogen free SMES is developed briskly on BSCCO wire. We fabricated and tested the conduction cooling system for the 600 kJ class HTS SMES. The experiment was accomplished for dummy coils. The dummy coils were made of aluminium, and have inner and outer coil diameters of 460 ㎜ and 728 ㎜ and coil height of 237 ㎜. The mass of coil is 171.6 kg, it is equivalent to thermal mass of 600 kJ HTS SMES coil. The coil is cooled with two GM coolers through the copper conduction bar. In this paper, we report that the test results of cool-down and heat loads characteristics of the dummy coils.
홍용주(Yong-Ju Hong),염한길(Han-Kil Yeom),박성제(Seong-Je Park),김효봉(Hyo-Bong Kim),고득용(Deuk-Yong Koh) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
SMES systems need cryogenic cooling systems. Conduction cooling system has more effective, compact structure than cryogen. In general, 2 stage GM cryocoolers are used for conduction cooling of HTS SMES system. 1st stages of cryocoolers are used for the cooling of current leads and radiation shields, and 2nd stages of cryocoolers for HTS coil. For the effective conduction cooling of the HTS SMES system, the temperature difference between the cryocooler and HTS coil should be minimized. In this paper, a cryogenic conduction cooling system for HTS SMES is analyzed to evaluate the performance of the cooling system. The analysis is carried out for the steady state with the heat generation of the HTS coil and effects of the thermal contact resistance. The results show the effects of the heat generation and thermal contact resistance on the temperature distribution.
홍용주(Yong-Ju Hong),염한길(Han-Kil Yeom),박성제(Seong-Je Park),김효봉(Hyo-Bong Kim),고득용(Deuk-Yong Koh) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
A SMES system stores the energy in the cryogenically cooled superconducting coils to reduce the losses. A SMES system has coils, refrigeration systems and a cryostat. Conduction cooling methods without liquid cryogen have a lower cooling cost, simple and reliable structure of the system. The HTS SMES coil has composite structure, which consists of several filaments of Bi, Ag and epoxy film. It has complex thermal characteristics due to the composition and geometry. To reduce cooling costs, the temperature difference of the coil and heat load to the cryocooler should be minimized. In this study, the detail thermal analysis on the cooling system of the HTS SMES system was performed. The thermal conduction analyses of HTS coil were performed to determine the anisotropic thermal conductivity of the composite. The results show the effective thermal conductivity of the composite and temperature difference of the HTS SMES system.