Multiphase Vertical Slug Flow Hydrodynamics with Hydrate Phase Transition

Hydrate phase transition may pose risks in pipeline blockage and severe challenges for offshore natural gas hydrate production. The present work involves the development of a multiphase gas-liquid-solid vertical slug flow hydrodynamic model considering hydrate phase transition kinetics with heat and mass transfer behaviors. The varying gas physical properties due to pressure and temperature variations are also introduced to evaluate vertical slug flow characteristics. The proposed model is used to carry out a series of numerical simulations to examine the interactions between hydrate phase transition and vertical slug flow hydrodynamics. Furthermore, the hydrate volumetric fractions under different pressure and temperature conditions are predicted. The results reveal that hydrate formation and gas expansion cause the mixture superficial velocity, and the gas and liquid fractions, void fraction in liquid slug, and unit length tend to decrease. The increase in outlet pressure leads to an increased hydrate formation rate, which not only increases the hydrate volumetric fraction along the pipe but also causes the upward shift of the hydrate phase transition critical point.