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X-선 회절법에 의한 철-질소 화합물층의 ε과 γ'상 분율 해석
김윤기,Kim, Yoon-Kee 한국재료학회 2006 한국재료학회지 Vol.16 No.2
The fraction of $\varepsilon\;and\;\gamma$'-iron nitride in compound layer is predicted by x-ray diffraction using direct comparison method. The validity of formulation models was checked by comparing calculated results with metallographic analysis of iron nitride compound layer grown on steel S45C by gas nitriding. The fraction of $\varepsilon$ calculated by the three phase model, porous-$Fe_3N$/ dense-$Fe_3N$/ mixed layer with $Fe_3N\;and\;Fe_4N$, is 80 percent of that analyzed by etching technique. The $\varepsilon$ fraction predicted by mixed layer model is 122 percent of that measured by microscope.
수치해석 기법을 이용한 차량 내부 유동 가시화 및 응용연구
김윤기(Yoon Kee Kim),양장식(Jang Sik Yang),김경천(Kyung Chun Kim),지호성(Ho Seong Ji) 한국자동차공학회 2010 한국자동차공학회 부문종합 학술대회 Vol.2010 No.5
To investigate detailed flow characteristics under recirculation cool vent-mode inside automotive passenger’s compartment related with HVAC system, quantitative flow visualization study is carried out using numerical method. Through pre-study on simplified passenger’s compartment, the variation of flow structure is investigated with respect to grid and timestep change. Advanced study based on real vehicle and human FE model is also carried out under real operational condition. To simulate initial cool down process in a hot sunny day, initial condition is set as 60℃. And thermal condition at every timestep is monitored to evaluate thermal comfort for overall cooling process. Through the numerical study, flow inside passengers compartment shows various complex flow pattern. The flow momentum observed in front of panel vent and its structure is continuously delivered to back seat. Since the exhaust vent is located at the right side with respect to center plane, asymmetrical velocity field is formed around passengers compartment and temperature distribution is known to be nonuniform. Through PMV(predicted mean vote) analysis, cooling effect at each passengers seat is closely discussed . Brief-study on defrost mode is also mentioned in this paper. Conclusively, flow characteristic inside passengers compartment is quantitatively analyzed using numerical method, and this results will be provided as useful fundamental data with related to additional study.
펄스직류방전과 유도결합방전의 복합에 의한 SCM440강의 이온질화
김윤기(Yoon-Kee Kim) 한국표면공학회 2010 한국표면공학회지 Vol.43 No.2
SCM440 steels were nitrided using pulsed dc plasma combined with inductively coupled plasma (ICP) generated by 13.56 ㎒ rf power in order to enhance case hardening depth. The case hardening depth was increased with rf power. The effective case-depth with ICP at 900 watt was as 1.6 times as that nitrided without ICP. The hardening depth was also increased up to 1.45 times. The compound layers formed on top surface were dense and thin when pulsed dc plasma was combined with ICP.
김윤기(Yoon Kee Kim),양장식(Jang Sik Yang),김경천(Kyung Chun Kim),지호성(Ho Seong Ji) 한국가시화정보학회 2009 한국가시화정보학회 학술발표대회 논문집 Vol.2009 No.11
The new methods of modernization, higher efficiency, and system control of HVAC system are constantly introduced, however it is still important to investigate the thermal comfort inside the vehicle. Thermal comfort of passenger is affected by many environmental thermal conditions and it is closely related to the flow characteristic inside the vehicle. Many numerical studies have been carried out, however thermal and flow characteristic inside the vehicle did not fully investigated. In this paper, the flow characteristic was studied numerically under re-circulation cool-vent mode using CFX 12.0. Rear model and human FE model was introduced in this study for more reasonable CFD results. Several spatial distribution of velocity at different air vent was investigated, visualized and through flow analysis, passenger’s comfort at different seat was predicted.
자동차 내부 쾌적성 평가를 위한 수치해석적 유동특성 연구
김윤기(Yoon Kee Kim),양장식(Jang Sik Yang),김경천(Kyung Chun Kim),지호성(Ho Seong Ji) 한국자동차공학회 2009 한국자동차공학회 학술대회 및 전시회 Vol.2009 No.11
Thermal comfort of passengers inside the compartment is one of the important issue in automotive engineering. Circulating airflow for thermal comfort inside the automotive compartment is closely related with the thermal-fluid characteristics. Thermal-fluid inside the compartment was evaluated using CFX code based on FVM and FEM. The temperature of inlet airflow was calculated under re-circulation cool-vent mode. Radiant heat flux from cabin ceiling, and sides wall were also considered. 3-D simulation for several thermal conditions was carried out after timestep and grid optimization procedure. Each result was evaluated in PMV(Predicted Mean Value) and times processed to the temperature of the steady state inside a vehicle.
승용차의 제상 및 성에 제거 성능 평가를 위한 수치해석적 연구
김윤기(Yoon Kee Kim),양장식(Jang Sik Yang),김경천(Kyung Chun Kim),지호성(Ho Seong Ji) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.2
HVAC(Heating, Ventilating, Air Conditioning) 시스템은 승객실 내부의 열환경을 제어하여 쾌적성을 향상시키거나 전면 유리창에 생성된 성에를 제거하여 운전자의 가시영역을 확보하는 등 차량의 성능과 관련된 매우 중요한 기능을 담당한다. 본 연구에서는 CFX 를 사용하여 HVAC 시스템의 기능 중 제상 덕트의 성능과 관련된 수치해석적 연구를 수행하였다. 제상덕트의 해석결과, 출구에서의 유량배분특성 및 유동구조는 일반적인 설계주안점에 부합된 양호한 결과를 얻었다. 외부온도 -18℃ 하에서 물의 잠열인 3.37×105[J/kg]을 고려한 상변화 과정을 수치적으로 모사하기 위하여 열용량법을 사용하였고, 시간에 따른 제상패턴 해석을 위해 얼음과 유리의 고체도메인에 대한 추가적인 격자 생성 작업이 필요하였다. 유동해석 결과, 전면유리 근처의 유동구조, 유적선, 온도장 해석결과는 본 연구에서 수행한 제상덕트 모델이 우수한 성능으로 제상기능을 수행할 수 있음을 보였으며, 수치해석적 결과는 실험적 결과와 비교하여 제상패턴이 잘 일치함을 확인하였다. 또한 전면유리 상의 4 개의 지점에서 얻어진 온도, 물분율, 엔탈피의 시간에 따른 변화를 통해 상변화 과정을 정량적으로 파악하였다. The heating, ventilating, air conditioning (HVAC) system is a very important part of an automotive vehicle: it controls the microclimate inside the passenger’s compartment and removes the frost or mist that is produced in cold/rainy weather. In this study, the numerical analysis of the defrost duct in an HVAC system and the de-icing pattern is carried out using commercial CFX-code. The mass flow distribution and flow structure at the outlet of the defrost duct satisfied the duct design specification. For analyzing the de-icing pattern, additional grid generation of solid domain of ice and glass is pre-defined for conductive heat transfer. The flow structure near the windshield, streakline, and temperature fields clearly indicate that the de-icing capacity of the given defrost duct configuration is excellent and that it can be operated in a stable manner. In this paper, the unsteady changes in temperature, water volume fraction, and static enthalpy at four monitoring points are discussed.
노즐홀더의 형상변경을 통한 탱크세정기의 성능개선에 관한 수치해석적 연구
김윤기(Yoon Kee Kim),이진오(Jin O Lee),김창묵(Chang Muk Kim),안주하(Joo Ha An),김경천(Kyung Chun Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.5
This paper is a numerical study on shape optimization for performance improvement of tank cleaning machine(TCM). TCM is used for cleaning the inner part of the tanker like VLCC(Very large Crude oil Carrier). Therefore, dynamic pressure at nozzle exit of TCM is very important performance index. Since the conventional TCM has been proven to have low performance, we investigated which parameter cause so large pressure drop in tank cleaning machiner. As a result, large pressure drop in nozzle holder is revealed to be main reason of low performance. Prior to the shape modification, numerical simulation on conventional model is carried out and is compared to the experimental value for reliability of CFD code. After several step of consideration, two type of improvement scheme is drawn out. A final decision is made from CFD analysis and a prototype is prepared according to the modified drawing. The experimental results illustrate the new-designed model showed 50% increased performance compared to conventional model.
김윤기(Yoon-Kee Kim),김상권(Sang Gweon Kim) 한국표면공학회 2011 한국표면공학회지 Vol.44 No.3
Growth behaviors of iron-nitride on S45C steels at low pressure gas nitriding were examined. Surfaces of the steels covered with fine and porous oxide during the pre-oxidation using N₂O gas. Well faceted particles connected with them were observed after 1 min nitriding. They grew steadily and filled inter-pores during additional nitriding process. From the X-ray diffraction analysis, γ'-iron nitride was dominantly formed at the initial stage but the amount of ε-iron nitride was rapidly increased as nitriding treatment time. The porous layer was formed on the particles and thickened up to half of nitride layer after 60 min nitriding. The observed growth behaviors were discussed in internal stress related with volume expansion involved in transforming from iron to iron-nitrides.