Thermal Conductivity of Methane Hydrate from Experiment and Molecular Simulation

Abstract

A single-sided transient plane source technique has been used to determine the thermal conductivity and thermal diffusivity of a compacted methane hydrate sample over the temperature range of 261.5-277.4 K and at gas-phase pressures ranging from 3.8 to 14.2 MPa. The average thermal conductivity, 0.68 +/- 0.01 W/(m K), and thermal diffusivity, 2.04 x 10(-7) +/- 0.04 x 10(-7) m2/s, values are, respectively, higher and lower than previously reported values. Equilibrium molecular dynamics (MD) simulations of methane hydrate have also been performed in the NPT ensemble to estimate the thermal conductivity for methane compositions ranging from 80 to 100% of the maximum theoretical occupation, at 276 K and at pressures ranging from 0.1 to 100 MPa. Calculations were performed with three rigid potential models for water, namely, SPC/E, TIP4P-Ew, and TIP4P-FQ, the last of which includes the effects of polarizability. The thermal conductivities predicted from MD simulations were in reasonable agreement with experimental results, ranging from about 0.52 to 0.77 W/(m K) for the different potential models with the polarizable water model giving the best agreement with experiments. The MD simulation method was validated by comparing calculated and experimental thermal conductivity values for ice and liquid water. The simulations were in reasonable agreement with experimental data. The simulations predict a slight increase in the thermal conductivity with decreasing methane occupation of the hydrate cages. The thermal conductivity was found to be essentially independent of pressure in both simulations and experiments. Our experimental and simulation thermal conductivity results provide data to help predict gas hydrate stability in sediments for the purposes of production or estimating methane release into the environment due to gradual warming.

Heat Transfer Related to Gas Hydrate Formation/Dissociation

“…With same technique, thermal conductivities of several other gas hydrates, such as tetrohydrofuran (THF) hydrate (Cortes et al, 2009), xenon hydrate (Krivchikov et al, 2006), HCFC-141b hydrate , and CFC-11 hydrate ) have been measured. Transient plane source (TPS) technique in double-and single-sided configurations has been used more recently to measure thermal conductivity of gas hydrates Li et al, 2010;Rosenbaum et al, 2007). This technique is based on the transient method and the needle probe, but it has a very small probe (Gustafsson et al, 1979(Gustafsson et al, , 1986.…”

“…With respect to temperature effect, many studies found that hydrates exhibit a glass-like temperature dependence of thermal conductivity (Andersson and Ross, 1983;Handa and Cook, 1987;Krivchikov et al, 2005Krivchikov et al, , 2006Ross et al, 1981;Ross and Andersson, 1982;Tse and White, 1988). Among these studies, the works of Krivchikov et al (2005Krivchikov et al ( , 2006 are interesting as they found that both methane and xenon hydrates show crystal-like temperature dependence below 90 K, while exhibiting glass-like behavior above 90 K. The effect of pressure has also been investigated by many groups (Andersson and Ross, 1983;Rosenbaum et al, 2007;Waite et al, 2007). Only weak pressure dependency was observed by them.…”

Mechanisms for thermal conduction in hydrogen hydrate

“…Experimental measurements of thermal conductivity in (type I) methane hydrate exhibit a crystal-like temperature dependence below 90 K, with glass-like behaviour above this temperature [24], while similar low-temperature behaviour is observed in some semi-conductor clathrates [25]. In addition to various recent molecular dynamics (MD) studies estimating methane hydrate thermal conductivities [26][27][28][29][30][31][32][33][34], and those of other clathrates [29,34], progress has been made towards elucidating the underlying mechanisms governing thermal conduction in methane hydrates of various polymorphs [31][32][33]. It was found that a greater extent of damping in guest-host energy transfer in type I methane hydrates as higher temperatures (above 150 K), is responsible for the more glass-like temperature dependence of the thermal conductivity, whereas more harmonic energy transfer at lower temperatures results in the experimentally observed crystal-like behaviour [31][32][33].…”

“…The JACF was defined for 100 ps at 30 K, for 50 ps at 100 and 150 K and for 20 ps at 200 K and above; a sampling ratio of approximately 20:1 or higher is recommended for a robust definition of the ACF [26]. These durations were found to be more than sufficient to provide a reliable estimate of the thermal conductivity at each temperature: the JACF had decayed essentially to zero within less than a quarter of the sampled time scales, and oscillated about zero thereafter.…”

“…Prior to discussing the conductivity results, however, it is worthwhile making some general remarks about crystalline thermal conductivity behaviour, the temperature profile of which is wellknown: above half the Debye temperature,  D /2, the thermal conductivity exhibits a dependence, determined mainly by boundary scatterings. Therefore, experimental determination of thermal conductivity is highly dependent on samples" nature and quality, as outlined in some detail for hydrates [26][27][28][29][30][31][32][33][34], which serves to emphasise the difficulty in direct, quantitative comparisons of theoretical and experimental values, as previous research for hydrates has shown . It must also be borne in mind that experimental measurements of hydrogen hydrate thermal conductivity have not been reported.…”