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Chiller용 냉매 CFC-11과 대체냉매 HCFC-123의 전기장을 사용한 핵비등 열전달 촉진에 관한 연구
곽태희,김주형,정동수,김종보,차태우,한창섭,Kwak, T.H.,Kim, J.H.,Jung, D.S.,Kim, C.B.,Cha, T.W.,Han, C.S. 대한설비공학회 1994 설비공학 논문집 Vol.6 No.4
Pool boiling experiments were carried out to study the effect of electric field on nucleate boiling heat transfer. CFC-11 and its alternative HCFC-123 were used as working fluids. Boiling on both single tube and a bundle of five tubes was investigated. Heat flux varied from 5 to $25kW/m^2$ while the applied voltage changed from 0 to 1kV. The results showed that at low heat flux where boiling was not present or very weak, electric field-induced forced convection helped increase the heat transfer coefficients of CFC-11 and HCFC-123 significantly(4-15 times increase). However, at higher heat flux, nucleate boiling of CFC-11 which is a highly dielectric fluid, was not affected significantly by the application of electric field. In contrast to CFC-11, even at high heat flux, nucleate boiling of CFC-11 which has a relatively larger electric conductivity than CFC-11, was vigorously increased up to 2-4 times. The additional power required to apply the electric field was 1-2% of the total power consumption by the heater. The increase in overall heat transfer coefficient of evaporators with HCFC -123 was about 40%, suggesting a considerable reduction in evaporator size with EHD technique.
전기자동차 모터 유냉식 방열성능 향상을 위한 열전달 해석 및 최적화
장준호(J.H. Jang),오근우(G.W. Oh),Xiang Sun,김종수(J.S. Kim),곽태희(T.H. Kwak),최정일(J.-I. Choi) 한국전산유체공학회 2020 한국전산유체공학회지 Vol.25 No.4
This paper presents the heat transfer analysis of the electric vehicle motor and optimization of an operating parameter for improving the performance of the motor with an oil cooling system. The homogeneous multi-phase flow model in commercial software, ANSYS CFX, is applied to solve the flow of mixture, including oil and air. We mainly focus on the influence of operating (oil level) and driving conditions (roll and pitch angles) on the cooling system. Several CFD simulations are performed with various input parameters (oil level, roll, and pitch angles) generated from the Latin Hypercube Sampling method. Based on the CFD results, we built a Polynomial Chaos Expansions based surrogate model to predict the temperature distribution, maximum temperature, and torque loss, which respond to the input parameters. Sensitivity analysis indicates that the oil level significantly affects system performance (maximum temperature and torque loss). Finally, the optimal range of oil level is estimated, considering the maximum allowable temperature of the motor.
하이브리드 자동차용 모터 내부의 오일 냉각 시스템에 대한 수치해석
김종수(J.S. Kim),문정욱(J.W. Moon),곽태희(T.H. Kwak),강태곤(T.G. Kang) 한국전산유체공학회 2017 한국전산유체공학회지 Vol.22 No.3
This paper presents the numerical study on the flow and heat transfer in an oil cooling system for the motor employed in a hybrid vehicle. The heat sources in the motor are identified by conducting numerical simulations for the electromagnetic field. Then, they are used as input parameters in the thermal analysis. The multiple reference frame(MRF) scheme in a commercial software, ANSYS CFX, is used to treat the rotating rotor. A separated flow model is employed to solve the non-isothermal two-phase flow of the oil-air mixture. We mainly focus on the influence of the oil injection and the fluid flow caused by rotating parts on the performance of the oil cooling system. At two typical operating points of the motor, it is found that the temperature distribution in the motor is highly affected by the injection rate of the oil. In addition, the convective heat transfer caused by the secondary flows occurring in the gap between the stator and rotor also contribute to cooling.