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최덕규(Deok-Gyu Choi),판 탄 호앙(Thanh-Hoang Phan),박성호(Sung-Ho Park),김동현(Dong-Hyun Kim),박원규(Warn-Gyu Park) 한국전산유체공학회 2021 한국전산유체공학회지 Vol.26 No.2
Understanding cavitation dynamics considering thermodynamic effect is critical to handle specific cavitation phenomena such as high temperature fluid flow or cryogenic fluid flow. In this study, a numerical analysis has been performed to investigate a the Venturi nozzle cavitation characteristic at 5 different points; 4 0℃, 50℃, 65℃, 80℃ and 95℃. A compressible homogeneous mixture model is applied, which is based on a dual-time preconditioning method. The results show that the evolution of cavitation in the Venturi nozzle and its cyclic motion can be described by re-entrant jet behavior, which is formed at a moment when high stagnation pressure occurs at the end of the cavity. After the re-entrant jet cuts off the head of the leading part, cloud shedding cavitation detaches from the main body of the cavity and it starts a vortex motion. In addition, increasing fluid temperature from 50℃ to 80℃ makes thermal effects dominant, which suppress and interrupt further development of cavitation due to the decrease of the local vapor pressure as cavitation occurs. Nonetheless, the 95℃ case, which is almost close to the boiling point of water, induces a thick and long cavity due to its higher saturated vapor pressure value when compared to others.
이상희(Sang Hee Lee),김원경(Won-Kyung Kim),어재원(Jae Won Eo),이상봉(Sang Bong Lee),최덕규(Deok Gyu Choi),박석호(Seok Ho Park),강연구(Youn Koo Kang),천창욱(Chang Uk Cheon) 유공압건설기계학회 2024 드라이브·컨트롤 Vol.21 No.3
This study aimed to evaluate the impact of mechanizing onion harvesting on labor reduction and work efficiency in Shinan Area. The mechanized harvesting system comprised a stem cutter, digging harvester, and collector. The field tests showed that the average residual stem length after using the stem cutter was 13.22±5.01 cm, with a stem cutting ratio of 91.3% and a damage ratio of 0%. The digging harvester achieved a digging ratio of 100% and a damage ratio of 1.2%, while the collectors damage ratio was 4.1%, loss ratio was 2.7%, and debris mixing ratio was 3.2%. The total working capacity of the mechanized system was 2.3 h/10a, significantly reducing 97.2% of labor time compared to manpower. These results indicate that the mechanization of onion harvesting can effectively reduce labor costs and increase work efficiency. Future research should include performance verification in various environments and an economic analysis of the mechanized system.