Origin of Self-preservation Effect for Hydrate Decomposition: Coupling of Mass and Heat Transfer Resistances
Gas hydrates could show an unexpected high stability at conditions out of thermodynamic equilibrium, which is called the self-preservation effect. The mechanism of the effect for methane hydrates is here investigated via molecular dynamics simulations, in which an NVT/E method is introduced to represent different levels of heat transfer resistance. Our simulations suggest a coupling between the mass transfer resistance and heat transfer resistance as the driving mechanism for self-preservation effect. We found that the hydrate is initially melted from the interface, and then a solid-like water layer with temperature-dependent structures is formed next to the hydrate interface that exhibits fractal feature, followed by an increase of mass transfer resistance for the diffusion of methane from hydrate region. Furthermore, our results indicate that heat transfer resistance is a more fundamental factor, since it facilitates the formation of the solid-like layer and hence inhibits the further dissociation of the hydrates. The self-preservation effect is found to be enhanced with the increase of pressure and particularly the decrease of temperature. Kinetic equations based on heat balance calculations is also developed to describe the self-preservation effect, which reproduces our simulation results well and provides an association between microscopic and macroscopic properties.
Methane Hydrate Intrinsic Dissociation Kinetics Measured in a Microfluidic System by Means of in Situ Raman Spectroscopy
The present work investigates the dissociation kinetics of methane (sI) hydrate in a thermoelectrically cooled microfluidic system with in situ Raman spectroscopy. The dissociation profile of methane (sI) hydrate was measured under different Reynolds numbers (0.42–4.16), pressures (60.2 to 80.1 bar), and temperature driving force ([Teq – 0.1 K] to [Teq + 0.3 K]). A theoretical model was derived from first-principles to describe the contributions of heat transfer and intrinsic kinetics on the dissociation rate of methane hydrate. It was observed that the dimensionless ratio of heat transfer to the intrinsic dissociation rate depended on the initial thickness of methane hydrate, temperature driving force, pressure, and the time. Intrinsic kinetics dominated where the initial thickness of methane hydrate was in the range of 10 μm and the temperature driving force was low. Increasing initial thickness of methane hydrate resulted in a switch to a heat-transfer-limited dissociation. Our results support that the...
The quantum particle in a box: what we can learn from classical electrodynamics
The problem of a charged particle enclosed in an infinite square potential well is analysed from the point of view of classical theory with the addition of the electromagnetic zero-point radiation field, with the aim to explore the extent to which such an analysis can contribute to enhance our understanding of the quantum behavior. First a proper treatment is made of the freely moving particle subject to the action of the radiation field, involving a frequency cutoff ωc. The jittering motion and the effective structure of the particle are sustained by the permanent action of the zero-point field. As a result, the particle interacts resonantly with the traveling field modes of frequency ωc in its proper frame of reference, which superpose to give rise to a modulated wave accompanying the particle. This is identified with the de Broglie wave, validating the choice of Compton’s frequency for ωc. For the stationary states of particles confined in the potential well, the Lorentz force produced by the accompanying field is shown to lead to discrete values for the mean speed and to an uneven probability distribution that echoes the corresponding quantum distribution. The relevance of the results obtained and the limitations of the classical approach used, are discussed in the context of present-day stochastic electrodynamics.