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The gas-liquid two-phase swirl flow can increase the gas-liquid two-phase contact area and enhance the heat and mass transfer efficiency between gas and liquid. The swirl flow has important practical application value for promoting gas hydrate formation and ensuring the flow safe of natural gas hydrate slurry. The experimental section was made of plexiglass pipe and the experimental medium was air and water. The flow pattern of the gas-liquid two-phase swirl flow in the horizontal pipe was divided, according to a high-definition camera and the overall characteristics of the gas-liquid interface. The flow pattern map of the gas-liquid two-phase swirl flow in a horizontal pipe was studied. The influence of the flow velocity and vane parameters on pressure drop was investigated. Two types of gas-liquid two-phase swirl flow pressure drop models was established. The homogeneous-phase and split-phase pressure drop models have good prediction on swirl bubble flow, swirl dispersed flow, swirl annular flow and swirl stratified flow, and the predictive error band is not more than 20%.

The supersonic separation is a novel technology in the natural gas dehydration for its compact design and fewer emissions. The other fascinating advantage is that the diffuser can convert kinetic energy into pressure energy to improve the energy efficiency. The mechanism of the pressure recovery is not well understood for the various flow conditions in supersonic velocities. The maximum pressure recovery coefficient (PRC) was estimated in theory and a theoretical equation was obtained with the ideal gas assumption. The theoretical results indicated that the PRC depended on the gas adiabatic exponent and Mach number in the upstream of the shock wave. A computational fluid dynamics model was developed to evaluate the gas dynamic parameters with various Mach numbers and their effects on the PRC. We found that a higher adiabatic exponent induced a larger PRC when the gas Mach number is more than 1.3. The PRC declined with the increase of the Mach number in the upstream of the shock wave both in the theoretical and numerical predictions. The numerical results are smaller than the ideal data with the maximum error of about 8.69% in the whole computed gas Mach number from 1.15 to 1.87. These results have suggested that the derived theoretical equation can be employed to estimate the PRC in the supersonic separation process to improve the design efficiency.

The real gas effects on natural gas supersonic separation were investigated using a computational fluid dynamics approach with ideal gas and real gas models. The computed results showed that the fluid properties calculated by the ideal gas law diverged significantly from the real gas cases in the supersonic zones, while the real gas models predicted a similar result from one to the other. The deviation of the gas Mach number between the ideal and real gas models was about 13.50% at the nozzle exit, while the error in the gas density was more than 20% in the whole supersonic separators. The shock wave position calculated by the real gas model was ahead of the one calculated by the ideal gas law. The shock position moved forward with the increasing inlet pressure, while the real gas predicted value was always in front of the ideal gas value. The relative error of the gas Mach number exceeded 15% with an inlet temperature of 283 K.

The liquid slug formation in a hilly-terrain pipeline is simulated using the Volume of Fluid model and RNG k-ε turbulence model. The numerical model is validated by the experimental data of the horizontal slug flow. The influence of pipe diameter on liquid slug formation is discussed in detail. The results show that the pipe is blocked by the liquid slug at the moment of slug formed. The pipe pressure suddenly increases, and then decreases gradually in the process of liquid slug formation and motion. The pipe diameter has little effect on liquid slug formation, while the pipe pressure drop and liquid holdup change small.

The gas-liquid two-phase flow within a double inlet cyclone for natural gas separation was numerically simulated using the discrete phase model. The numerical approach was validated with the experimental data, and the comparison results agreed well with each other. The simulation results showed that the strong swirling flow produced a high centrifugal force to remove the particles from the gas mixture. The larger particles moved downward on the internal surface and were removed due to the outer vortex near the wall. Most of the tiny particles went into the inner vortex zones and escaped from the up-outlet. The swirling flow was concentric due to the design of the double inlet for the cyclonic separator, which greatly improved the separating efficiency. The separating efficiency was greater than 90% with the particle diameter of more than 100 μm.

A supersonic separator has been introduced to remove water vapour from natural gas. The mechanisms of the upstream and downstream influences are not well understood for various flow conditions from the wellhead and the back pipelines. We used a computational model to investigate the effect of the inlet and outlet flow conditions on the supersonic separation process. We found that the shock wave was sensitive to the inlet or back pressure compared to the inlet temperature. The shock position shifted forward with a higher inlet or back pressure. It indicated that an increasing inlet pressure declined the pressure recovery capacity. Furthermore, the shock wave moved out of the diffuser when the ratio of the back pressure to the inlet one was greater than 0.75, in which the state of the low pressure and temperature was destroyed, resulting in the re-evaporation of the condensed liquids. Natural gas would be the subsonic flows in the whole supersonic separator, if the mass flow rate was less than the design value, and it could not reach the low pressure and temperature for the condensation and separation of the water vapor. These results suggested a guidance mechanism for natural gas supersonic separation in various flow conditions.

A differential mathematical model for hollow fiber membrane gas seperator was established and used for multi-component gas separation, especially natural gas. The influences of the characteristics of feed gas, pressure drop within the hollow fibers and concentration polarization were taken into consideration. We developed a computing software for gas membrane separation with LabVIEW. This software can be used for hollow fiber membrane separation of gases, continuous membrane column cascade operation and multi-level membrane modules in designing and checking calculations, can replace the tedious manual calculations, and has a great reference value in laboratory testing and industrial design applications.