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과냉수 내부 슈평튜브 외면에서의 국소 풀비등 열전달계수
강명기(Myeong-Gie Kang) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.10
Subcooled pool boiling of water has been tested at atmospheric pressure to determine local heat transfer coefficients on the outside surface of a horizontal tube of 51 ㎜ diameter. The local values were determined at every 45˚ from the very bottom to the uppermost of the tube periphery and a representative value was suggested. The maximum and the minimum local coefficients were observed at the azimuthal angles of 45˚ and 180˚, respectively, from the tube bottom. The representative value was at the azimuthal angle of 90˚. The major mechanisms affecting the heat transfer on a horizontal tube were liquid agitation generated by the sliding bubbles and bubble coalescence.
핵비등에서 열전달 특성과 기포발생의 광학적 관찰에 관한 연구
윤준규,임종한 한국기계기술학회 2009 한국기계기술학회지 Vol.11 No.1
This study is experimentally to analyze the heat transfer characteristics and photographic observation of bubble generation in saturated nucleate pool boiling. The photographs were taken of water boiling from heated nickel wires. The attempts is made to explain the different nucleate boiling of water. Some of the bubbles photographed were very close to the spherical shape, while others were close to the hemispherical. Also, a number of bubble had intermediate shapes that were called oblate bubbles. At least, heat transfer regions of three and possibly four were found to exist in nucleate boiling depended upon the mode of vapor generation. The vapor structure on the surface progressed through a sequence of first discrete bubbles, then vapor columns and vapor mushrooms, and finally vapor paths, as the surface temperature was increased. These individual vapor structures or combinations of them determine the mechanism of heat transfer in the four nucleate boiling regions.
과냉 비등유동에 대한 CFD 모의계산에서의 벽 인접격자 영향
인왕기(W.K. In),신창환(C.H. Shin),전태현(T.H. Chun) 한국전산유체공학회 2010 한국전산유체공학회 학술대회논문집 Vol.2010 No.5
A multiphase CFD analysis is performed to investigate the effect of near-wall grid for simulating a subcooled boiling flow in vertical tube. The multiphase flow model used in this CFD analysis is the two-fluid model in which liquid(water) and vapor(steam) are considered as continuous and dispersed fluids, respectively. A wall boiling model is also used to simulate the subcooled boiling heat transfer at the heated wall boundary. The diameter and heated length of tube are 0.0154 m and 2 m, respectively. The system pressure in tube is 4.5 MPa and the inlet subcooling is 60 K. The near-wall grid size in the non-dimensional wall unit (y<SUB>w</SUB><SUP>+</SUP>) was examined from 64 to 172 at the outlet boundary. The CFD calculations predicted the void distributions as well as the liquid and wall temperatures in tube. The predicted axial variations of the void fraction and the wall temperature are compared with the measured ones. The CFD prediction of the wall temperature is shown to slightly depend on the near-wall grid size but the axial void prediction has somewhat large dependency. The CFD prediction was found to show a better agreement with the measured one for the large near-wall grid, e.g., y<SUB>w</SUB><SUP>+</SUP> > 100.
벽 비등모델을 이용한 과냉비등 유동에 대한 CFD 모의계산에서 벽 인접격자의 영향
인왕기(W.K. In),신창환(C.H. Shin),전태현(T.H. Chun) 한국전산유체공학회 2010 한국전산유체공학회지 Vol.15 No.3
A multiphase CFD analysis is performed to investigate the effect of near-wall grid for simulating a subcooled boiling flow in vertical tube. The multiphase flow model used in this CFD analysis is the two-fluid model in which liquid(water) and gas(vapour) are considered as continuous and dispersed fluids, respectively. A wall boiling model is also used to simulate the subcooled boiling heat transfer at the heated wall boundary. The diameter and heated length of tube are 0.0154 m and 2 m, respectively. The system pressure in tube is 4.5 ㎫ and the inlet subcooling is 60 K. The near-wall grid size in the non-dimensional wall unit for lqiuid phase (y?<SUB>w,l</SUB>) was examined from 101 to 313 at the outlet boundary. The CFD calculations predicted the void distributions as well as the liquid and wall temperatures in tube. The predicted axial variations of the void fraction and the wall temperature are compared with the measured ones. The CFD prediction of the wall temperature is shown to slightly depend on the near-wall grid size but the axial void prediction has somewhat large dependency. The CFD prediction was found to show a better agreement with the measured one for the large near-wall grid, e.g., y?<SUB>w,l</SUB> > 300 at the tube exit.
임태우(Tae-Woo Lim),유삼상(Sam-Sang You),최형식(Hyeung-Sik Choi) 한국마린엔지니어링학회 2009 한국마린엔지니어링학회 학술대회 논문집 Vol.2009 No.-
Experiments were conducted to evaluate pool boiling heat transfer performance between plain and micro finned surfaces with FC-72, which is chemically and electrically stable. Three kinds of micro fins with the dimension of 100㎛×10㎛, 150㎛×10㎛ and 200㎛×10㎛ ( width x height ) were fabricated on the surface of a silicon chips. The experiments were carried out on the liquid subcooling of 5, 10 and 15 K under the atmospheric condition. The micro finned surface with a larger fin width of 200㎛ provided a better pool boiling heat transfer performance. Also, the micro finned surfaces showed a sharp increase in heat flux with increasing wall superheat and a large heat transfer enhancement compared to a plain surface.
차상진(Sangjin Cha),이재호(Jae ho Lee),변호원(Ho Won Byun),이을종(Eul jong Lee),김내현(Nae Hyun Kim) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.5
본 연구에서는 자연순환형 수직증발기 내의 과냉비등 열전달 계수는 검토하였다. 실험을 위해 작은 크기의 모델이 사용되었다. 압력손실계산에 Ueda의 마찰손실 상관식, Saha and Zuber의 건도와 기공율 상관식을 적용하고 열전달 계산에는 Roshenow의 중첩모델을 적용한 결과 모형실험데이터를 잘 예측하였다. In this study, an effort has been made to analyze the subcooled boiling heat transfer in a natural circulation vertical evaporator. To verify the analysis, a small-scale model was made and tested. The friction correlation by Ueda, void fraction and quality correlation by Saha and Zuber along with the superposition heat transfer model by Rohsenow yielded a satisfactory agreement with the model test data.
차상진(Sang-jin Cha),김내현(Nae-Hyun Kim),유진상(Jin-Sang Ryu) 대한설비공학회 2011 설비공학 논문집 Vol.23 No.9
In this study, an effort has been made to analyze the subcooled boiling heat transfer in a natural circulation vertical evaporator. To verify the analysis, a small-scale model was made and tested. The friction correlation by Ueda, void fraction and quality correlation by Saha and Zuber along with the superposition heat transfer model by Rohsenow yielded a satisfactory agreement with the model test data. The analysis was extended to simulate a 1 ton/day concentration system. Comparison with the test results of 1 ton/day prototype revealed that the data were overpredicted by 13%. The capacity of the prototype was 1.2 ton/day with COP of 5.77.