• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2206-2210
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• 2007

As a power transmission line supplying power to a densely populated city, the high temperature superconducting (HTS) cable is expected to one of the most effective cables with a compact size because of its high current density. The verification of HTS power cable system have been progressed by KEPRI. A cooling system for a 3-phase 100m HTS power cable with 22.9kV/1.25kA was installed and tested at KEPCO's Gochang power testing center in Korea. The system consists of a liquid nitrogen decompression cooling system with a cooling capacity of 3kW and a closed circulation system of subcooled liquid nitrogen. Several performance tests of the cable system with respect to the cooling such as cooling capacity, heat load and temperature stability, were performed at several temperatures. Thermal cycle test, cool-down to liquid nitrogen temperature and warm-up to room temperature, was also performed to investigate thermal cycle influences. The outline of the installed cooling system and performance test results are presented in this paper.

• Design & Manufacturing
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• 제17권4호
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• pp.63-71
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• 2023

In order to increase the extrusion production speed of aluminum, extrusion die cooling technology using liquid nitrogen has recently attracted a lot of attention. Increasing the extrusion speed increases the temperature of the bearing area of extrusion dies and the extrusion profile, which may cause defects on the surface of extruded profile. Extrusion die cooling technology is to directly inject liquid nitrogen through a cooling channel formed between the die and the backer inside the die-set. The liquid nitrogen removes heat from the die-set, and gaseous nitrogen at the exit of the channel, covers the extrusion profile of an inert atmosphere reducing the oxidation and the profile temperature. The aim of this study is to evaluate the cooling capacity by applying die cooling to extrusion of Al-Mn-based aluminum alloy flat tubes, and to investigate the effects of die cooling on the change in extrusion characteristics of flat tubes. Cooling capacity was confirmed by observing the temperature change of the extrusion profile depending on whether or not die cooling is applied. To observe changes in material characteristics due to die cooling, surface observation is conducted and microstructure and precipitate analysis are performed by FE-SEM on the surface and longitudinal cross section of the extruded flat tubes.

• 설비공학논문집
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• 제30권1호
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• pp.24-32
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• 2018

In this paper, analytical studies were conducted to obtain optimal design factors and analysis parameters of liquid nitrogen cooling exchanger applied in cryogenic refrigerator. The target value of heat transfer rate was more than 1 kW and pressure drop was less than 40 kPa. Design factors of cryogenic heat exchanger included width of channel and configuration of paths. Analytical factors of liquid nitrogen cooling exchanger included temperatures of coolant header surface and inlet liquid nitrogen. The width and number of channels in the design parameters were 0.0050~0.0150 m and 4~8, respectively. The configuration of channel path was 4 ways. Temperatures of coolant header surface and inlet liquid nitrogen in analytical parameters were 74 to 78K and 82 to 86K, respectively. As result, the design factor and analysis parameter satisfying the target values were obtained. The biggest heat transfer rate was 1.36 kW with pressure drop of 32.26 kPa.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.170-173
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• 2007

본 연구에서는 액체로켓엔진 내부에 라이너를 설치하고 기체 질소를 이용한 막냉각 방법을 사용하여, 라이너의 막냉각 특성을 살펴보았다. 고온 가스는 액체로켓 연소가스와 액체질소를 혼합하여 사용하였다. 기존의 액체로켓엔진 시험 설비에 추가적으로 라이너 냉각 기체를 공급 설비를 구축하였으며, 라이너 및 냉각 기체 공급부를 제작하였다. 10초 연소 실험을 통해 라이너 내부 고온 가스의 온도와 라이너 외부 벽면 온도를 측정하였으며, 기체 질소에 의한 라이너 냉각 특성을 확인하였다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.147-150
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• 2007

본 연구에서는 액체로켓엔진의 연소 가스에 액체 질소를 혼합하여 연소 가스의 냉각 특성을 알아보고자 하였다. 이를 위해 기존에 사용되던 액체로켓 연소실 후단에 액체 질소 분사용 분사기를 설계/제작하여 장착하였으며, 두 가스의 혼합 가스의 안정화를 위한 연소실과 노즐을 질소 분사링 뒤에 장착하였다. 액체질소 분사에 의한 상류 점화/연소 상태의 영향을 살펴보기 위한 시험이 먼저 수행되었으며, 이후 10초 연소 실험을 성공적으로 수행하였다. 따라서 기존의 액체로켓엔진에 액체질소를 분사함으로써, 연소 가스의 온도를 저하시킬 수 있음을 확인하였다.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 추계학술대회 논문집
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• pp.281-283
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• 2003

High temperature superconducting power cable requires forced flow cooling. Liquid nitrogen is circulated by a pump and cooled back by cooling system. Typical operating temperature range is expected to be between 65K and 80K. Subcooler heat exchanger uses saturated liquid nitrogen boiling on the shell side to subcool the circulating liquid nitrogen stream that cools the HTS cable. The paper describes performance tests of the cooling system. The test items are heat exchanging performance of subcooler. pressure drop between supply and return lines, heat transfer coefficient inside former, cable cryostat heat leak and simulation of electrical load of HTS cable.

• 한국초전도ㆍ저온공학회논문지
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• 제19권2호
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• pp.1-8
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• 2017

Recently, Research and development activity of HTS (High Temperature Superconducting) power application is very progressive worldwide. Especially, HTS cable system and HTSFCL (HTS Fault current limiter) system are proceeding to practical stages. In such system and equipment, cryogenic cooling system, which makes HTS equipment cooled lower than critical temperature, is one of crucial components. In this article, cryogenic cooling system for HTS application, mainly cable, is reviewed. Cryogenic cooling system can be categorized into conduction cooling system and immersion cooling system. In practical HTS power application area, immersion cooling system with sub-cooled liquid nitrogen is preferred. The immersion cooling system is besides grouped into open cycle system and closed cycle system. Turbo-Brayton refrigerator is a key component for closed cycle system. Those two cooling systems are focused in this article. And, each design and component of the cooling system is explained.

• 한국초전도학회:학술대회논문집
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• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
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• pp.7-11
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• 1999

The recent progress in new cooling techniques of the high Tc superconductor(HTS) systems is reported and discussed with some practical examples. At the beginning stage of the HTS development in research laboratories, liquid nitrogen(LN$_2$) is the standard medium for an effective cooling. The success of HTS in many different application areas, however, has required a variety of need in the cooling temperature and the cooling capacity with specific design restrictions. While the utilization of alternative liquid cryogens such as liquid neon (LNe) or liquid hydrogen (LH$_2$) has been tired in some of them, even solid cryogens such as solid nitrogen (SN$_2$) or solid hydrogen (SH$_2$) may be another option in special applications. The gaseous helium cooled by a cryogenic refrigerator has also been a good candidate in many cases. One of the best cooling methods for the HTS is the direct conduction-cooling by a closed-cycle refrigerator with no cryogen at all. The refrigeration may be based on Joul-Thomson, Brayton, Stirling, Gifford-McMahon, or pulse tube cycles. The pros and cons of the newly proposed cooling methods are described and some significant design issues are presented.

• 한국정밀공학회지
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• 제34권4호
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• pp.247-251
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• 2017

Titanium alloy has been widely used in the aerospace industry because of its high strength and good corrosion resistance. During cutting, the low thermal conductivity and high chemical reactivity of titanium generate a high cutting temperature and accelerates tool wear. To improve cutting tool life, cryogenic machining by using a liquid nitrogen (LN2) jet is suggested. In cryogenic jet cooling, evaporation of LN2 in the tank and transfer tube could cause pressure fluctuation and change the cooling rate. In this work, cooling uniformity is investigated in terms of liquid nitrogen jet pressure in cryogenic jet cooling during titanium alloy turning. Fluctuation of jet spraying pressure causes tool temperature to fluctuate. It is possible to suppress the fluctuation of the jet pressure and improve cooling by using a phase separator. Measuring tool temperature shows that consistent LN2 jet pressure improves cryogenic cooling uniformity.

• 한국추진공학회지
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• 제22권6호
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• pp.142-148
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• 2018

발사체 연료 케로신은 발사체의 성능 향상을 위해 고밀도화 과정을 거치게 된다. 고밀도화 방법 중 액체질소 주입 냉각법은 시스템이 간단하고 비용이 저렴한 효과적인 방법이다. 하지만 냉각과정 중 질소가 케로신에 용해되어 물성을 변화시키는 원인이 되기도 한다. 따라서 냉각 후 케로신 내 용존질소의 양을 측정하고 제거하는 작업이 필수적이다. 본 연구에서는 케로신 내 용존질소 함유량을 측정할 수 있는 진공추출 원리를 소개하였다. 또한 질소 샘플링 장치를 설계/제작하여 수행한 실험 결과를 설명하였다. 실험결과로부터 질소 샘플링 장치와 용존질소 측정법/제거법의 유효성을 입증하였다.