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고Si DP980강 스폿 용접 특성에 미치는 Phosphorus (P) 및 in-situ 후열처리 펄스 조건의 영향
최두열(Du-Youl Choi) 대한용접·접합학회 2015 대한용접·접합학회지 Vol.33 No.6
Recently, application of UHSS(Ultra High Strength Steels) whose tensile strength is over 1000MPa to car body structure are growing due to great needs for light weighting and improved crash worthiness. However, their poor weldability is one of obstacles to expand selecting to car body. In this study, effect of Phosphorus contents on resistance spot weldability of high elongation DP980 steel whose Si content is over 1% was investigated. The cross tension strength (CTS) was decreased showing partial interface fracture as Phosphorus content increase because of solidification segregation of Phosphorus. In order to improve resistance spot weldability by modification of welding condition, in-situ post-weld heating pulse was introduced after main pulse. The optimum cooling time between main and post pulse and post-pulse current condtion were determined through FEM welding simulation and DOE tests. The CTS was increased about 1.5 time showing plug fracture. The decrease of Phosphorus segregation was found to be a major reason for weld ductility and CTS improvement.
다중효용 담수설비용 열압축기의 디퓨져 형상에 관한 연구
최두열(Du-youl Choi),정한식(Han-shik Chung),정효민(Hyo-min Jeong),김진화(Zhen-hua Jin),김필환(Pil-hwan Kim) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.10
A thermocompressor is the equipment which compresses a vapor to a desired discharge pressure. Since it was first used as the evacuation pump for a surface condenser, it has been widely adopted for energy saving systems due to its high working confidence. In the present study, the geometrical analysis of the shape between the jet nozzle and the diffuser inlet, the drag force was calculated by means of the integrated equation of motion and the computational fluid dynamic (CFD) package called FLUENT. The computer simulations were performed to investigate the effects by the various suction flow rates, the distance from jet nozzle outlet to the diffuser inlet and the dimensions of the diffuser inlet section through the iterative calculation. In addition, the results from the CFD analysis on the thermocompressor and the experiments were compared for the verification of the CFD results. Furthermore, in this study, a special attention was paid on the performance of the thermocompressor by varying the diffuser convergence angle of 0.0°, 0.5°, 1.0°, 2.0°, 3.5° and 4.5°. With the increase of the diffuser convergence angle, the suction capacity was improved up to the degree of 2.0° while it was decreased over the degree of 2.0°.
Tube-bundle형 열교환기의 액막 유동에 관한 시뮬레이션
김필환(Pil-Hwan Kim),최두열(Du-Youl Choi),우주식(Ju-Sik Woo),정효민(Hyo-Min Jeong),정한식(Han-Shik Chung),김경석(Kyeong-Seok Kim) 대한설비공학회 2009 대한설비공학회 학술발표대회논문집 Vol.2009 No.-
Seawater amounts to 70% of the earth and represents a quite unlimited resource for the production of fresh water by desalination processes and for the extraction of dissolved salts present in it. Recently, the falling film evaporation has increased in interest as an efficient method for seawater desalination system. In the desalination system, the flow characteristics of the falling film is very important issue to make highly efficient system. So, this study is taken to investigate numerically the falling film thickness on the inlet Renold Number ranges are 400 to 700. Numerical simulations are performed using FLUENT6.3.26, a commercial CFD code.
최순호(Soon-Ho Choi),송영호(Young-Ho Song),윤정오(Jeong-Oh Yun),김경석(Kyong-Suk Kim),최두열(Du-Youl Choi) 대한기계학회 2009 대한기계학회 춘추학술대회 Vol.2009 No.11
Traditionally, Middle East area is suffered from the lack of water. In addition, as growing the global industrialization, human is faced with the shortage of water resource at present, which makes the desalination system the promising business. Recently, many domestic engineering companies focus on the desalination plant market because it will be promising business in the next few decades. This study was performed to evaluate the theoretical heat balance calculation for multi-stage evaporating type desalination system, especially Multi-Effect Desalination (MED). In MED system, the steam evaporated in the first stage is used for the heating source of the second stage and this process is repeated for the next stage. Therefore, this heat balance calculation method from this study will be highly useful to design the MED system.