甲烷水合物导热机理的分子动力学模拟

甲烷水合物导热系数是甲烷水合物勘探、开采、储运以及其他应用过程中一个十分重要的物理参数.我们采用平衡分子动力学（EMD）方法Green-Kubo理论计算温度203.15～263.15K、压力范围3～100MPa、晶穴占有率为0～1的sI甲烷水合物的导热系数,采用的水分子模型包括TIP4P、TIP4P-Ew、TIP4P-FQ、TIP4P/2005、TIP4P/Ice.研究了主客体分子、外界温压条件等对甲烷水合物导热性能的影响.研究结果显示甲烷水合物的低导热性能由主体分子构建的sI笼型结构决定,而客体分子进入笼型结构后,使得笼型结构导热性能增强,同时进入笼型结构的客体分子越多,甲烷水合物导热性能越强.研究结果还显示在高温区域（T〉TDebye/3）内不同温度作用下,所有sI水合物具有相似的导热规律.压力对导热系数有一定影响,尤其是在较高压力条件下,压力越高,导热系数越大.而在不同温度和不同压力作用过程中,密度的改变对导热系数的增大或减小几乎没有影响.

Molecular dynamics simulation on the mechanisms of thermal conduction in methane hydrates

Thermal conductivity of methane hydrate is an important physical parameter serving in processes of methane hydrate exploration,mining,gas hydrate storage and transportation as well as other applications.In this paper,equilibrium molecular dynamics simulation and the Green-Kubo method for the systems of from fully occupied to vacant occupied sI methane hydrate have been performed to estimate their thermal conductivity.The estimation was carried out at temperatures about 203.1-5263.15 K and at pressures around 3-100 MPa.Potential models selected for water were TIP4P,TIP4P-Ew,TIP4P/2005,TIP4P-FQ and TIP4P/Ice.Effects of composition in the host and guest molecules and the outside thermobaric condition on the methane hydrate heat performance were studied.Results indicate that the thermal conduction of methane hydrate is determined by framework of cage which constitutes the hydrate lattices and,in reverse,framework of cage has slightly higher thermal conductivity after the presence of the guest molecules.Further,more guest molecules enclosed the cage improve on the poor thermal conduction of methane hydrate.It is also revealed that all sI hydrate has the similar heat performance with the effect of high temperature（T TDebye/3）.Pressure has certain effect on the thermal conductivity,particularly under the higher pressure.As the pressure increases,it encounters slightly higher thermal conductivity.With the effects of temperatures and pressures,density shift has little impact on thermal conductivity from methane hydrate.