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In this paper, the geometric design of a gravity-based separator is studied with a computational fluid dynamics method. ANSYS Fluent (18.2) is used to model the ratio of horizontal and vertical lengths with three dimensionless groups. A dimensional analysis method is used to develop a new correlation of separator geometric design. Corresponding plots were created and analyzed using nonlinear regression on the x-y Cartesian coordinate system. Also, manual iterations were performed to determine the coefficients in the general correlation relationship. The dimensional analysis results show that the Reynolds and Euler numbers have a direct correlation with separator design, which means increasing the Reynolds and Euler numbers require a separator with a larger length to height ratio to achieve the same separation efficiency. However, the Weber number has an inverse correlation with separator design, which means an increase in the Weber number requires a separator with a smaller length to height ratio. The new correlation developed in this paper can be used as a reference for separator geometry design to separate immiscible fluids with a wide range of fluid properties.

In this paper, experimental and numerical methods are used to investigate the separation of an oil / water mixture. An American Petroleum Institute (API) gravity-based separator was built to conduct the experimental studies. The numerical simulations were developed with the same geometry as the experimental setup. The effect of inlet velocity and the oil volume fraction on the separation process is investigated with the new numerical predictions. Validations of the simulation model show that the numerical predictions of the multiphase Volume of Fluid (VOF) model with the laminar viscosity model agree well with the experimental results. The results of oil volume fraction and velocity vector distribution in the separator showed that there was a mixing zone located at the entrance, which had a lower relative oil volume fraction and a higher velocity. The study of the inlet velocity effect on the mixing length of the entrance mixing zone shows that when the fluid in the separator is in the laminar range, the mixing length is less than 40% of the total separator length. However, when the inlet velocity was increased until the fluid in the separator reached the transient range, the mixing length occupied 90% of the total separator length.

In this paper, a new correlation is developed to predict liquid / liquid separation dynamics with a focus on a water / oil mixture. The correlation employs a force balance on the droplets to predict the rising velocity of the oil phase. The effect of droplet coalescence on the droplet’s rising velocity is investigated, and the new correlation predicts the coalescence rate based on the oil / water volume fraction, as well as the initial droplet diameter. To develop the correlation for droplet coalescence, a series of new numerical simulations of a batch oil / water separation process were conducted. An equivalent experiment was conducted, the results of which agree well with the numerical predictions (relative error of 13.39%). The new correlation can predict the rate of separation with a relative error of 6.35% compared to numerical predictions.

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