Mechanisms for thermal conduction in hydrogen hydrate

Abstract

Extensive equilibrium molecular dynamics (MD) simulations have been performed to investigate thermal conduction mechanisms via the Green-Kubo approach for (type II) hydrogen hydrate, at 0.05 kbar and between 30 and 250 K, for both lightly-filled H 2 hydrates (1s4l) and for more densely-filled H 2 systems (2s4l), in which four H 2 molecules are present in the large cavities, with respective single-and doubleoccupation of the small cages. The TIP4P water model was used in conjunction with a fully atomistic hydrogen potential along with long-range Ewald electrostatics. It was found that substantially less damping in guest-host energy transfer is present in hydrogen hydrate as is observed in common type I clathrates (e.g., methane hydrate), but more akin in to previous results for type II and H methane hydrate polymorphs.This gives rise to larger thermal conductivities relative to common type I hydrates, and also larger than type II and H methane hydrate polymorphs, and a more crystallike temperature dependence of the thermal conductivity. a) Corresponding author.

Molecular Dynamics Study of Propane Hydrate Dissociation: Nonequilibrium Analysis in Externally Applied Electric Fields

“…Least-squares regression fits of eq were performed for the first régime of dissociation, and the calculated rate constants and those standard deviations in addition to goodness-of-fit R 2 values are reported in Table . However, the assumption of a constant thermal conductivity in the model would be expected to become invalid as the number and extent of contributing phonon modes thereto decline upon shrinkage of the planar crystallite along the z axis; ,,− this is a flaw that may well explain the lack of near- (or semi-)­quantitative agreement at later times when this disparity is at its greatest.…”

Structural and dynamical properties of methane clathrate hydrates from molecular dynamics: Comparison of atomistic and more coarse-grained potential models

“…17 Such an understanding of equilibrium dynamical properties and phonon scattering offered by molecular dynamics (MD) has indeed led to progress in recent years in enhancing our understanding of thermalconduction processes in clathrate hydrates. [18][19][20][21][22] Also, with increasing computer power and advances in Density Functional Theory (DFT) and its relative computational M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT 3 tractability, ab-initio MD has also offered progress in dynamical properties, such as intramolecular vibations of the guest and host molecules in hydrates. [23][24][25] Naturally, however, despite the community's increasingly sophisticated arsenal of simulation methods, the potential model [26][27][28] or functional 23 used in dynamics will of course affect directly the fidelity (or lack thereof) for predicting equilibrium properties (whether structural, dynamical, thermal, etc).…”

Molecular Simulation of the Phase Diagram of Methane Hydrate: Free Energy Calculations, Direct Coexistence Method, and Hyperparallel Tempering

“…For instance, many porous materials, such as zeolites and metal organic frameworks, are synthesized by crystallizing cages around an organic template, therefore sharing some important features with hydrates. In addition, owing to their nonstoichiometric nature, gas hydrates can be considered as prototypical examples of confined solids which also possess varying compositions with temperature and pressure (even though their bulk counterpart exhibits constant stoichiometry). , As a result, owing to its importance for both fundamental and practical sciences, methane hydrate receives increasing attention with significant effort devoted to better understanding their physical and physicochemical properties. ,− …”