Thermal conductivity of gas hydrates

The thermal conductivity of gas hydrates is dependent on temperature, but has no pressure dependence. Table 10.4 shows the thermal conductivities of ice, water, CO2 hydrates, and methane hydrates. 

It is clear that the thermal conductivity of gas hydrates is much less than that of ice, but similar to hquid water. Furthermore, when it comes to hydrate/gas/water or hydrate/gas/water/sediment systems, the thermal properties are usually determined as the average values of the properties of the components by considering their saturation (volumetric fraction) in the sample. Because of the paucity of data of CO2 hydrates, the heat capacities of ice, methane and ethane hydrates are shown in Table 10.5. Considering the similarity between CO2 hydrates and other gas hydrates, the heat capacity of CO2 hydrates is certainly less than that of liquid water and may be similar to that of ice. 

The calculation of the thermal conductivity of gas hydrate using EMD and the Green-Kubo linear response theory was repeated recently. In that work, convergences of the relevant quantities were monitored carefully as a function of the model size. Subtleties in the numerical procedures were also carefully considered. The thermal conductivity of methane hydrate was found to converge within numerical accuracy for 3 x 3 x 3 and 4x4x4 supercells. In the calculation of the heat flux vector there is an interactive term that is a pairwise summation over the forces exerted by atomic sites on one another. The species (i.e., water and methane) enthalpy correction term requires that the total enthalpy of the system is decomposed into contributions from each species. Because of the partial transformation from pairwise, real-space treatment to a reciprocal space form in Ewald electrostatics, it is necessary to recast the diffusive and interactive terms in this expression in a form amenable for use with the Ewald method using the formulation of Petravic. ... 

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