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Molecular Dynamic Simulation of Melting/Solidification Rate of Ar
정재동(Jae Dong Chung) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Molecular Dynamics (MD) simulations have been conducted to look at the melting and solidification of Lennard-Jones argon (100) interface at small amounts of undercooling and superheating, 6.0K. By combining the fully equilibrated bulk phases of liquid and solid in one simulation box and counting the number of solid - like particle, the interface velocity, i.e. growth rate or melting rate, as a function of temperature was obtained. The melting temperature where no growth or melting of crystal particle is expected T<SUB>m</SUB><SUP>*</SUP> =0.668which is close to that of Gibbs free energy calculation. Linear slope dependency on temperature was found except for high superheating, △ T>6K. Thus the high superheating is believed as the main source of slope discontinuity in the rate, not the misuse of initial regime.
정재동(Jae Dong Chung) 대한설비공학회 2010 설비공학 논문집 Vol.22 No.7
paper deals with approximate integral solutions to the one-dimensional model describing the charging process of stratified thermal storage tanks. Temperature is assumed to be the form of Fermi-Dirac distribution function, which can be separated to two sets of cubic polynomials for each hot and cold side of thermal boundary layers. Proposed approximate integral solutions are compared to the previous works of the approximate analytic solutions and show reasonable agreement. The approach, however, has benefits in mathematical difficulties, complicated solution form and unstable convergence of series solution founded in the previous analytic solutions. Solutions for a semi-infinite region, which have simple closed form solutions, give close agreement to those for a finite region. Thermocline thickness is obtained in closed form and shows proportional behavior to the square root of time and inverse proportional behavior to the square root of flow rate.
정재동(Jae Dong Chung) 대한기계학회 2008 대한기계학회 춘추학술대회 Vol.2008 No.5
Molecular Dynamic Simulation has been conducted for the melting process of Ar and the effect of defect on the melting temperature was examined. Drastic change of volume and energy is expected to be involved with phase change. In pure crystal, hysteresis is found due to the superheating and supercooling, but a defect decreases the superheating. Asymptotic behavior is found as the strength of defects increases the temperature where the volume changes drastically approaches to the experimental value of melting temperature. Thus the melting point can be expected by observing the change of drastic volume change.