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현열교환용 사류형 열교환소자의 성능에 대한 수치해석 연구
최종락(Jongrak Choi),허남건(Nahmkeon Hur),김내현(Nae-Hyun Kim) 대한설비공학회 2012 대한설비공학회 학술발표대회논문집 Vol.2012 No.6
Inclined-flow heat exchanger element is an air to air heat exchanger which recuperate sensible heat as well as latent heat. In the present study, 3-D incompressible steady flow in enthalpy exchanger was investigated by changing the angle of flow array. To compare the overall performance of heat exchanger, ε-NTU method was performed. The results of sensible heat transfer showed good agreements with the relation of effectiveness-number of transfer units. To enhance the sensible heat transfer of the inclined-flow heat exchanger, the effects of the angle of flow inclination was investigated. The present numerical analysis can provide useful information such as the performance of the inclined-flow heat exchanger for various heat exchanger applications.
자동차 도장 건조 공정의 건조 성능 향상을 위한 수치해석 연구
최종락(Jongrak Choi),허남건(Nahmkeon Hur),김동철(Dongchoul Kim),김희수(Hee-Soo Kim) 대한설비공학회 2012 설비공학 논문집 Vol.24 No.12
In the present study, three-dimensional transient numerical simulations were carried out to improve the performance of a vehicle paint drying process. In order to describe the movement of a vehicle, the techniques of moving boundary condition and multiple reference flames (MRF) were used. For the validation of the numerical analysis, the predicted temperature on the surface of a vehicle was compared to the experimental data, and a good agreement was achieved. With validated numerical procedure, various operating conditions of the temperature and the flow rate of the supply air were investigated to improve the drying performance of the facility. It is shown that the optimization of the operating condition can lead to energy savings and faster line speed of the production.
최종락(Jongrak Choi),허남건(Nahmkeon Hur) 대한기계학회 2020 대한기계학회 춘추학술대회 Vol.2020 No.12
Blood is damaged by hemolysis of red blood cells in transporting the blood driven devices in various medical conditions, leading to blood hemoglobinemia. A hemolysis phenomenon methodology is vital to design in-vitro medical devices, including the cannular, the blood pump, and the oxygenator. In this study, the Eulerian based hemolysis model was developed by comparing the previous experimental results of hemolysis. To cover the short exposure time and high shear stress in the turbulent flow near the blood pumps rotor, a profile of the hemolysis index is adopted by solving the passive scalar transport equation. A good agreement with the modified hemolysis index was obtained in the cannula and FDA blood pump. This method for the hemolysis prediction can be helped the designer of the blood pump with a low computational cost.
최종락(Jongrak Choi),허남건(Nahmkeon Hur) 대한기계학회 2020 大韓機械學會論文集B Vol.44 No.9
기어는 동력 전달의 중요한 구성 요소 중 하나이며, 처닝(churning) 손실은 부하 없이 작동하는 기계 시스템의 효율을 결정하는 중요한 요소이다. 실험의 경험식을 통한 처닝 손실이 오랫동안 분석되어 왔지만, 최근 계산 성능 향상을 통한 3D CFD(전산 유체역학) 해석이 가능해졌다. 본 연구에서는 3차원 CFD 해석을 이용하여 기어의 처닝 손실 예측을 수행하였다. 미끄럼 격자 방법과 다중 좌표계(multiple reference frames) 방법을 이용하여 기어의 회전을 모사하였다. 또한, 계면 유동을 예측을 위한 VOF(volume of fluid) 다상 유동 모델이 사용되었다. 회전 속도가 5,000rpm인 경우 실험 데이터, 실험의 경험식 및 3D 예측 방법이 잘 예측되는 것을 확인하였다. 이러한 결과로 검증된 3D 시뮬레이션을 통해 기어의 구체적인 윤활 유동 연구가 가능할 것이다. The gear is one of the vital components of power transmission, and its churning loss is a significant factor that determines the efficiency of the mechanical system when it is operated without a load. The gear churning loss has long been analyzed using empirical correlations with experiment; however, computational performance has recently improved and has enabled 3D CFD (three-dimensional computational fluid dynamics). In this study, analyses to predict the gear churning loss were performed using a 1D method and 3D simulation. Two techniques for the rotating motion of the gear, namely the sliding grid technique and MRF (multiple reference frames), were adopted. A multi-phase model with the VOF (volume of fluid) method was used out to predict the interfacial flows. A good agreement was obtained by comparing experimental data, empirical relation, and 3D analysis results at a rotation speed of 5,000 rpm. From the results, further study on the detailed lubricant flow is possible through validated 3D CFD simulation.
대구지하철 화재 경우의 환기에 따른 열 및 연기 거동변화의 수치해석 연구
최종락(Jongrak Choi),허남건(Nahmkeon Hur) 대한설비공학회 2013 대한설비공학회 학술발표대회논문집 Vol.2013 No.6
The Daegu subway station fire on February 18th, 2003, was a disastrous incident that killed the lives of 192 people in Korea. In the present study, a detailed simulation was carried out to investigate the flows of fire and smoke in the underground subway station with consideration to factors including fire development, air flow induced by the moving train, and buoyancy of the fire. From the simulation results, higher concentrations of smoke were found to be near the staircase areas where many of the casualties were reported in the real disaster. The effect from ventilation operation in the station on the movement of smoke is studied to explore ways to reduce otherwise higher smoke concentrations in critical locations, such as staircases. The results of the present study provide suggestions on proper design of subway ventilation systems in case of a fire, in order to control smoke dispersion and ultimately assist in the safe evacuation of passengers.