Molecular Dynamics Simulation Of Phase Change Of Alkane Binary Mixed System

Phase change energy storage technology, which is a storing and releasing energy technology by phase change material's reception and release of heat, is used widely in solar energy, building energy conservation, industrial exhaust heat and textile industry. Paraffin made up of straight chain hydrocarbon is one of the organic phase change materials. Its general expression is CnH2n+2. In the practical application, phase change temperature must consistent with different working conditions and can be changed by adjusting constituent of organic mixture. Therefore, it is important to study how to gain the special phase change temperature by adjusting constituent of mixture. Comparing with the tradition method differential scanning caborimetry and dynamic thermomechametry, molecular dynamics simulation is used as the main study method in this article.The potential function is ORGANIC which includes inter-molecular force L-J and intra-molecular force OPLS. Predictor-corrector method is undertaken to compute equation of motion. Velocity scaling method is used to control temperature. Parrinello-Rahman is used to control pressure and periodic boundary condition is undertaken in every simulation system.There are two parts in this paper.In the first part, molecular dynamics simulation (NTP ensemble) is adopted to study the melt behavior of Heptadecane, Pentadecane and Heptadecane-Pentadecane mixed system (six systems in all, 530 particles). Self-diffusion coefficient and specific volume changing along with temperature are drafted by collecting the movement locus of particles to determine the phase change temperature of every system. At the same time, Bond length, Bond angle and Dihedral angle changing along with temperature are drafted by collecting the internal coordinate of particles to study material microscopic structure of Heptadecane in melting process.In the second part, molecular dynamics simulation (NTV ensemble) is adopted to study the melt behavior of Heptadecane, Eicosane and Heptadecane-Eicosane mixed system (eleven systems in all, 3100 particles). Phase temperatures of these systems are gained by self-diffusion coefficient changing along with temperature. The results show that different phase transition temperatures can be gained to fit different working conditions by adjusting constituent of mixture.