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착상에 의한 휜관형 열교환기의 성능변화에 관한 실험적 연구
김정국(Jungkuk Kim),小山繁(Shigeru Koyama),桑原憲(Ken Kuwahara),박병덕(Byung-Duck Park),김동휘(Dong-Hwi Kim),사용철(Yang-Cheal Sa) 대한설비공학회 2009 설비공학 논문집 Vol.21 No.2
The present study was investigates the effect of the parameters on the frost formation and heat transfer performance such as fin shape, air temperature and air velocity. Heat transfer rate and pressure drop by frost were experimentally investigated. Effect of the wet blub temperature and air velocity on the heat transfer performance has been also investigated. The heat transfer performance of the louver fin and tube type heat exchanger was higher by maximum of 0.85% than the corrugate fin type at the air temperature of 2.0/1.5℃. As the wet blub temperature of air were increased, the heat transfer rate, pressure drop and mass of frost of three test models were increased. Especially, the maximum heat transfer rate and maximum pressure drop were shown for the Type B louver fin heat exchanger. As an experimental result, the enhancement factor(EF) of louver fin and tube type heat exchanger was only 0.2 - 0.4 due to the high pressure drop.
확대 모델을 이용한 루버 휜의 국부 열전달 특성변화에 관한 연구
김정국(Jungkuk Kim),小山繁(Shigeru Koyama),桑原憲(Ken Kuwahara),박병덕(Byung-Duck Park),김동휘(Dong-Hwi Kim),사용철(Yong-Cheol Sa) 대한설비공학회 2008 대한설비공학회 학술발표대회논문집 Vol.2008 No.2
The present study was investigated the local heat transfer characteristics and temperature distribution on the louver fin by using the expansion model. Heat transfer rate, frost mass and temperature distribution of the louver fin under frosting condition were experimentally investigated. Local heat transfer rate and heat flux on the louver were analyzed by the conduction heat transfer between top and lower part of the louver. The experimental key parameter was brine inlet temperature(-5, -10, -15℃). The heat transfer performance and frost mass at brine temperature of -15℃ were increased by maximum 3 time than the brine temperature of -5℃. At all experimental case, local heat transfer rate and heat flux of the louver were almost symmetry at the louver number of 6. Especially, local heat transfer rate and heat flux were maximum increased on the louver number of 4 and 8.
수직 액막 흡수관의 유동변화에 따른 흡수성능 변화에 관한 해석적 연구
김정국(Jungkuk Kim),조금남(Keumnam Cho) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.11
Numerical analyses have been performend to the absorption heat and mass transfer coeffieients and the absorption mass flux from a falling film of LiBi solution. Inthe present study, the behavior of laminar-wavy falling film in the vertical absorber was studied analytically and experimentally. The change of absorption performanse on mean film thickness, wave celerity was analysed. The heat and mass transfer equations are solved simuktanwously to give the temperature and concentration variation at the LiBr solve solution/refrigeration vapor interface and at wall. Effects of uniform film, wavy film and film Reynolds number on the heat mass transfer coefficients have been estimated. The analytical results of the uniform and wavy falling film in the bare tube was higher than experimental result for re<100.The absorption performance showed the maximun at the wavy film by the insert device(spring).
수치해석적 방법을 통한 저토피 및 암질불량구간의 터널 안정성 검토
김정국(Jungkuk Kim),김희수(Heesu Kim),반호기(Hoki Ban),김동규(Donggyou Kim) 한국지반환경공학회 2021 한국지반환경공학회논문집 Vol.22 No.11
우리나라는 국토 전체 면적 중 70% 이상 산악지형으로 철도공사 시 주행성능 확보를 위해 터널 공사가 매년 증가하고 있다. 터널공사가 증가함에 따라 터널굴착 방법 또한 다양해지고 있다. 굴착부의 지반이 풍화암으로 구성되어있으면 다양한 터널굴착 공법이 적용될 수 있지만 굴착부가 파쇄대를 지나거나 저토피의 계곡부를 지나는 경우 터널 굴착 시 붕괴의 위험성을 지니고 있다. 따라서 본 연구에서는 다양한 지반에서의 보강공법을 제시하고자 저토피 및 암질불량구간의 굴착 중인 대표터널을 선정하였다. 수치해석은 암질불량구간일 때 강관을 미적용한 경우와 적용한 경우, 저토피 구간일 때 터널 상부에 고화토를 성토한 경우 강관 보강을 적용하여 수치해석을 통해 안정성 분석을 수행하였다. Tunneling is widely increased in rail-road construction due to the large portion of mountainous regions in Korea as well as the improving running performance of train. Tunneling under poor rock condition, shallow overburden, or existing fault zone has high risk for collapse. Therefore, this study presents the stability of tunnel under unfavorable geological conditions using finite element methods.