Molecular Dynamics Simulations Of Thermal Transport In Gas Hydrate

Gas hydrate is ideal alternative energy for their huge storage and large energy density.At present,experiment researches have already make great progress in hydrate's thermal properties,as well as composition and decomposition.While it is difficult to get an explicit interpretation of the thermal transport process because of the limits of experiment.The studies of thermal transport in hydrate have a lot of significance in hydrate exploitation and gas hydrate storage and transport.This thesis focus on calculating the thermal transport process in gas hydrate with equilibrium and non-equilibrium molecular dynamic method.Both effects of temperature,crystal cave occupation and interaction strength are simulated with non-polarized potential.Thermal transport process in methane hydrate from 30 K to 265 K is calculated.The TIP4 P model can describe radial distribution function,lattice constant and change of heat conductivity precisely.The density of state of carbon atom and oxygen atom is coincide in the low frequency region which means strong couple between host and guest motion.The phonon relaxation time shows a decrease with increasing temperature.The acoustic phonon contributes most to heat conductivity.There are water and methane molecule in hydrate,we decompose total heat conductivity into contribution of water,contribution of methane and contribution of both them in order to investigate effect of each molecule.It turns out contribution of water is biggest,then contribution of methane and contribution of both them are smaller.With the increasing occupation,heat conductivity decreasing,the same as phonon mean free path and overlapped phonon energy of vibrational density of states.With the increasing interaction,couple between carbon and oxygen become stronger,and the heat conductivity increase.Both SPC/E and TIP4 P model can describe radial distribution function fine,while density of state with TIP4 P is closer to some early paper and SPC/E model can get the heat conductivity more close to the experiment.We obtain the thermal conductivity much closer to experiments results with quantum correlation.The minimum thermal conductivity increase with temperature,and reach a plateau when the temperature beyond the Debye temperature.The non-equipment method can predict heat conductivity well just as equipment method,and both can get correct structure and density of state.Mean free path decreases as temperature increase from 50 K and 150 K,as well as phonon mean speed and phonon relaxation time.