Abstract
Nanobubbles have attracted wide scientific attention due to their large number of potential applications in nanotechnology, and they are ubiquitous during natural gas hydrates (NGHs) mining which is one of the strategic energy resources. Molecular dynamic simulations were performed to investigate CH4 nanobubble characteristics during NGHs dissociation. The nucleation mechanism and evolution characteristics of nanobubbles vary with hydrate dissociation temperature. The higher the temperature, the earlier the bubble nucleation, the more small methane clusters are produced, and the more complex the evolution path of nanobubbles, the initial position of bubble nucleation is closer to the decomposition interface. The gas reservoir can provide another possibility for methane molecules to overcome solubility barriers to avoid the formation of nanobubbles at lower dissociation temperature. CH4 nanobubble evolution was found to be governed by the gas supersaturation and the diffusion of CH4 molecules. The self-diffusion coefficient of CH4 molecules near the decomposition interface area is small due to the adsorption effect of the incomplete cages, nanobubbles are more likely to form outside the adsorption zone where the CH4 diffusion coefficient is larger at a lower temperature. A direct proof of speeding up of hydrate dissociation by nanobubble growth was given. The acceleration of dissociation is later than nanobubble growth and the accumulation of nanobubbles on dissociation interface may have a negative influence. The new findings on nanobubble evolution may help design and optimize nanobubble formation techniques in nanotechnology and efficient gas hydrate production protocols.
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