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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.
GM형 맥동관 냉동기의 저온부 방향에 따른 성능저하 억제 방안 연구
김효봉(Hyobong Kim),고준석(Junseok Ko),고득용(Deuk-Yong Koh),홍용주(Yong-Ju Hong),염한길(Hankim Yeom),강인수(In-Su Kang),이청수(Chung-Soo Lee),박성제(Seong-Je Park) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
This paper describes experimental study on GM-type pulse tube refrigerator(PTR). A PTR has no moving part in its cold part and thus, it has advantages of simple configuration, low vibration and high reliability. It generates refrigeration effect by gas expansion work inside pulse tube in which gas displacer roles sold displacer of GM cryocooler. The pulse tube is only filled with working gas and there exists natural convection due to large temperature difference between cold-end and warm-end. The stability of secondary flow is affected by orientation of cold-head and thus, cooling performance is deteriorated by gas mixing due to secondary flow. In this study, a single stage orifice type pulse tube is fabricated and tested. The cooling performance of the fabricated PTR is measured as varying cold-head orientation angle. The screen mesh is installed inside pulse tube to suppress the performance degradation due to secondary flow inside pulse tube. From experimental results with several size of screen mesh, fine mesh shows the effective suppression of performance degradation for the large orientation angle, but the degradation of cooling performance for the small orientation angle.
SSD에서의 TRIM 명령어 처리 성능 분석 및 Ext4 파일 시스템으로의 적용
손효봉(Hyobong Son),이영재(Youngjae Lee),김용석(Yongserk Kim),김진수(Jin-Soo Kim) 한국정보과학회 2015 정보과학회 컴퓨팅의 실제 논문지 Vol.21 No.1
본 논문에서는 SSD의 TRIM 명령어 처리 성능을 LBA 범위의 특성 및 개수에 따라 분석하고, 그 결과를 바탕으로 Ext4 파일 시스템에서의 TRIM 명령어 처리 성능을 개선하였다. 대부분의 SSD에서 LBA 범위의 크기가 크고, 섹터 번호가 정렬 및 연속되어 있으며, 하나의 TRIM 명령어로 다수의 LBA 범위 정보를 전달할수록 TRIM 명령어의 처리 성능이 증가하는 것으로 나타났다. 한편, 기존의 Ext4 파일 시스템은 이와 같이 다수의 LBA 범위 정보를 전달할 때 그 성능이 더 높음에도 불구하고, 하나의 TRIM 명령어 당 하나의 LBA 범위 정보만 전달하는 문제점을 가지고 있다. 이를 해결하기 위해 하나의 TRIM 명령어로 최대 64개의 LBA 범위 정보를 전달하도록 Ext4 파일 시스템을 개선하였고, Filebench를 이용한 성능 평가에서 파일 삭제 성능이 최대 35% 증가하는 것을 확인하였다. In this paper, we analyze the performance of the TRIM commands on various SSDs and, based on our analysis results, we enhance the performance of these TRIM commands in the Ext4 file system. We observed that the performance of the TRIM commands improves as the size of the LBA-range increases, the sector number is aligned and continuous or more LBA-ranges are notified via a single TRIM command. However, although the performance is better when multiple LBA-ranges are informed by a single TRIM command, the Ext4 file system issues a single TRIM command for every LBA-range. In this paper, we modify the Ext4 file system to convey at most 64 LBA-ranges per TRIM command. Evaluations through Filebench show that the performance of file deletion operations is improved by up to 35%.