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정재동(Jae Dong Chung),이주명(Ju Myoung Lee),이준식(Joon Sik Lee) 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2001 No.3
This paper presents a numerical analysis on the solidification characteristics in twin-roll strip casting. Unstructured fixed-grid system was employed to deal with phase change. Melting of pure gallium was analyzed to confirm the validity of present program in both structure and unstructured grid system. An algorithm for simultaneous calculation of the temperature in the roll and the molten metal pool was developed. The flow field in the pool and heat transfer features between pool and roll were showed. The effect of process parameters was also studied. Since the geometry of the molten metal pool significantly deforms along the casting direction, unstructured grid system is more efficient. The unstructured grid system gives almost the same accuracy, even though the number of grids is only 60% of the structured one.
Phonon Dispersion이 열전달 모델에 미치는 영향
정재동(Jae Dong Chung) 대한기계학회 2003 대한기계학회 춘추학술대회 Vol.2003 No.4
The effect of (1) phonon dispersion in thermal conductivity model and (2) the differentiation of<br/> group velocity and phase velocity for Ge is examined. The results show drastic change of thermal<br/> conductivity regardless of using same relaxation time model. Also the contribution of transverse acoustic<br/> (TA) phonon and longitudinal acoustic (LA) phonon is changed by considering more rigorous dispersion<br/> model. Holland model underestimates the scattering rate for high frequency TA, so misleading<br/> conclusion, i.e. TA is dominant heat transfer mode at high temperature. But the actual reduction of<br/> thermal conductivity is much larger than the estimation by Holland model and high frequency TA is<br/> no more dominant heat transfer mode. Another heat transfer mechanism may exist for high temperature.<br/> Two possible explanations are (1) high frequency LA by Umklapp scattering and (2) optical phonon.