正二十四烷烃石蜡/膨胀石墨复合相变材料分子动力学模拟

Molecular dynamics simulation of n-tetracosane paraffin/expanded graphite composite phase change materials

相变材料(PCMs)在相变时的恒温、高能量密度等特性,经常应用于设备的热管理,但是PCMs导热系数低的缺点影响了其使用范围.本文采用分子动力学方法,模拟了在正二十四烷烃石蜡PCMs中添加不同结构(层状、交叉状)的膨胀石墨(EG)之后构成的复合PCMs的物性.文章通过径向分布函数(RDF)、声子态密度(PDOS)、比热容和导热系数这四个指标,分析了夹角为0°的层状结构,夹角为45°、90°的交叉状EG添加物对于石蜡热物性的影响.EG(0°、45°、90°)添加使得石蜡的原子分布在不同程度上变得更加均匀、紧密,使得石蜡的比热容有所增加.同时,两种类型的添加物提高了石蜡的PDOS,提高了导热系数.其中,EG(90°)添加物对于石蜡导热系数的提升最为明显,石蜡/EG(0°、45°、90°)模型中EG的含量分别为33.63 wt%、30.86 wt%和23.20 wt%,相比于的石蜡的导热系数分别提升了417.1%、345.7%和522.9%.EG的添加能够提高石蜡的导热系数,不同结构的EG对石蜡导热系数的影响有着较大的区别.

The properties of phase change materials(PCMs),such as constant temperature and high energy density during phase change,are often used for thermal management of equipment,but the drawback of low thermal conductivity of PCMs affects their scope of use.In this paper,the molecular dynamics method is used to simulate the physical properties of composite PCMs composed of n-tetracosane paraffinic PCMs after adding different structures(layered and crossed)of expanded graphite(EG)to the PCMs.The effects of the laminar structure with 0°angle and the crossed EG additions with 45°and 90°angles on the thermal properties of the paraffinic were analyzed by four indexes:radial distribution function(RDF),phonon density of states(PDOS),specific heat capacity and thermal conductivity.The EG(0°,45°,90°)additions made the atomic distribution of paraffin more uniform and compact in different degrees,which led to an increase in the specific heat capacity of paraffin.At the same time,both types of additions increased the PDOS of paraffins and im-proved the thermal conductivity.Among them,the EG(90°)additive has the most obvious improvement on the thermal conductivity of paraffins.The contents of EG in the paraffin/EG(0°,45°,90°)models were 33.63 wt%,30.86 wt%and 23.20 wt%,respectively,which improved the thermal conductivity of paraffin by 417.1%,345.7%and 522.9%,respectively,compared with those of paraffins.The addition of EG could improve the thermal conductivity of paraffins,and the effect of different structures of EG on the thermal conductivity of paraffins had a large difference.