Abstract: The morphology characteristics of CH₄, CO₂, and CO₂+N₂ hydrate film forming on the suspending gas bubbles are studied using microscopic visual method at supercooling conditions from 1.0 to 3.0 K. The hydrate film vertical growth rate and thickness along the planar gas-water interface are measured to study the hydrate formation kinetics and mass transfer process. Adding N₂ in the gas mixture plays the same role as lowering the supercooling conditions, both retarding the crystal nucleation and growth rates, which results in larger single crystal size and rough hydrate morphology. N₂ in the gas mixture helps to delay the secondary nucleation on the hydrate film, which is beneficial to maintain the pore-throat structure and enhance the mass transfer. The vertical growth rate of hydrate film mainly depends on the supercooling conditions and gas compositions but has weak dependence on the experimental temperature and pressure. Under the same gas composition condition, the final film thickness shows a linear relationship with the supercooling conditions. The mass transfer coefficient of CH₄ molecules in hydrates ranges from 4.54×10^-8 to 7.54×10^-8 mol·cm^-2·s^-1·MPa^-1. The maximum mass transfer coefficient for CO₂ + N₂ hydrate occurs at the composition of 60% CO₂ + 40% N₂, which is 3.98×10^-8 mol·cm^-2·s^-1·MPa^-1.

Key words: Gas hydrate, Morphology, Secondary nucleation, Formation kinetics, Mass transfer

摘要： The morphology characteristics of CH₄, CO₂, and CO₂+N₂ hydrate film forming on the suspending gas bubbles are studied using microscopic visual method at supercooling conditions from 1.0 to 3.0 K. The hydrate film vertical growth rate and thickness along the planar gas-water interface are measured to study the hydrate formation kinetics and mass transfer process. Adding N₂ in the gas mixture plays the same role as lowering the supercooling conditions, both retarding the crystal nucleation and growth rates, which results in larger single crystal size and rough hydrate morphology. N₂ in the gas mixture helps to delay the secondary nucleation on the hydrate film, which is beneficial to maintain the pore-throat structure and enhance the mass transfer. The vertical growth rate of hydrate film mainly depends on the supercooling conditions and gas compositions but has weak dependence on the experimental temperature and pressure. Under the same gas composition condition, the final film thickness shows a linear relationship with the supercooling conditions. The mass transfer coefficient of CH₄ molecules in hydrates ranges from 4.54×10^-8 to 7.54×10^-8 mol·cm^-2·s^-1·MPa^-1. The maximum mass transfer coefficient for CO₂ + N₂ hydrate occurs at the composition of 60% CO₂ + 40% N₂, which is 3.98×10^-8 mol·cm^-2·s^-1·MPa^-1.

关键词: Gas hydrate, Morphology, Secondary nucleation, Formation kinetics, Mass transfer