高温热管内钠蒸发冷凝特性分子动力学研究

Molecular Dynamics Study of Characters of Evaporation and Condensation of Sodium inside High Temperature Pipe

高温钠热管是热管堆中进行非能动热量传输的核心部件。为深入理解热管内工质钠的蒸发机理及气液交界的传热传质特性,用分子动力学软件LAMMPS模拟了600 K下钠的蒸发,统计了质量调节系数,定为0.3887。随后变更壁温,打破体系内热质输运平衡,进行非平衡态模拟,观察液膜变化,求解气液交界处的净蒸发通量和换热系数。结果表明,9~10 ns后,底部的液膜厚度、气液交界处的净蒸发通量及换热系数分别在0.1~0.52 nm、0.03~0.07 kg/(m^(2)·s)、2.2~3.9 kW/(m^(2)·K)范围波动,此时上部液膜厚度在6 nm左右,其气液交界的净蒸发通量在10^(-4)量级,换热系数为0.028 kW/(m^(2)·K),至末期降为0.0035 kW/(m^(2)·K)。本文为钠热管启动阶段的数值模拟提供了参考。

The high temperature sodium heat pipe is the key component in the heat pipe reactor.It is used for passive heat transportation.For deeply understanding working media’s evaporation mechanism and characters of heat and mass transfer at liquid-gas interface,the molecular dynamics software LAMMPS was adopted to simulate the evaporation of liquid sodium film in 600 K.The mass accommodation coefficient was obtained and its value was 0.3887.The wall temperature was changed and non-equilibrium simulation was run.The change of liquid film in non-equilibrium were observed,and the net evaporation mass flux and heat transfer coefficient at liquid-gas interface were acquired.The results show that after 9-10 ns,the bottom liquid film thickness,net evaporation mass flux and heat transfer coefficient at liquid-gas interface fluctuate repeatedly in 0.1-0.52 nm,0.03-0.07 kg/(m^(2)·s)and 2.2-3.9 kW/(m^(2)·K),while the net evaporation mass flux at upper liquid-gas interface approaches 10^(-4) magnitude and the heat transfer coefficient is 0.028 kW/(m^(2)·K)and finally decreases to 0.0035 kW/(m^(2)·K).The results provide reference to numerical simulation of sodium heat pipe in startup phase.