Cylindrical cyclones are always used in the petroleum industry to separate the oil-water two-phase mixtures or treatment the waste water. Here, we use dimensional analysis and multiphase flow numerical simulation to analyze the separation process in a cylindrical cyclone with a vortex finder to better understand the theory and characteristics of separation. In the dimensional analysis, we consider all structural, flow, and operating parameters. A multiphase mixture model is used to simulate oil-water two-phase flow and separation in a cylindrical cyclone. There is a vortex in the core of the cylinder, and its structure is influenced by the diameter of the overflow pipe, the inlet velocity, and the flow split ratio. However, the influence of these three factors on the equivalent diameter of the vortex core can be ignored. Moreover, the inlet velocity has little influence on the equivalent length of the vortex core. Therefore, the structure of the vortex core can be calculated from the diameter and flow split ratio of the up-outlet of the cylindrical cyclone. Oil-water separation increases as the diameter of the oil droplet increases. The separation efficiency of the cylindrical cyclone with vortex can reach 80% if the inlet dispersion droplet diameter is larger than 1 mm. The oil volume fractions in the up- and down-outlets decrease as the overflow split ratio increases. The flow split ratio is the only operating parameter to consider to obtain the best separation results for a cylindrical cyclone with a fixed inlet oil-water mixture.

A gas–liquid swirling flow with shear-thinning liquid rheology exhibits complex behavior. In order to investigate its flow characteristics, experiments and computational fluid dynamics (CFD) simulations are conducted based on dimensional analysis. A Malvern particle size analyzer and electrical resistance tomography are applied to obtain the bubble size distribution and section void fraction. A Coriolis mass flowmeter is applied to obtain the mixture flow rate and mixture density for an entrance gas volume fraction smaller than 7%. The CFD coupled mixture multiphase model and large eddy simulation model are applied, considering the liquid shear-thinning power-law rheology. The results show that the swirling flow can be divided into developing and decaying sections according to the swirl intensity evolution in the axial direction. A gas–liquid swirl flow with shear-thinning liquid prohibits a core-annulus flow structure. A smaller index n contributes to maintaining the development of the swirl flow field and its core-annulus flow structure so that the swirl flow can form over a shorter distance with a stronger intensity. For a more uniform distribution of the apparent viscosity, the gas column in the pipe center is thinner. On the other hand, a larger consistency k enlarges the stress tensor. The amplitude of the velocity and the pressure of the core-annulus flow structure are reduced. A weaker swirl intensity appears with a wider gas column appearing as a consequence. Furthermore, the swirl number decays with an exponential behavior with parameters sensitive to the consistency k and index n of the decaying section of the swirling flow field. These are beneficial to gas–liquid separator design and optimization when encountering the shear-thinning power-law liquid phase in the petroleum industry.