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In-line separators separate substances, like liquids or solids, from a fluid stream as it flows through a pipeline. These separators are frequently employed in a wide range of industrial processes and applications to effectively eliminate contaminants or unwanted substances from a fluid stream. The axial-flow swirl generator is a specialized component commonly used in in-line oil separators to improve their efficiency in separating oil from the water stream.

The present project has tried to eliminate the oil phase from the water phase inside an in-line separator with the help of an axial-flow swirl generator. To consider correct and proper assumptions, the reference paper entitled “Performance Characteristics of In-Line Oil Separator with Various Airfoil Vane Configurations of the Axial-Flow Swirl Generator” is selected as the reference, so most of the parameters are taken from it.

• Referennce [1]: Je, Yeong-Wan, Jong-Chul Lee, and Youn-Jea Kim. “Performance characteristics of in-line oil separator with various airfoil vane configurations of the axial-flow swirl generator.” Processes5 (2022): 948.

Simulation Process

One of the most significant challenges of the present project is the complex geometry, which is tackled using Solidworks software. It requires endeavour and hard work to design the generator’s blades properly. Then, it is imported into Spaceclaim software to combine with the in-line separator and produce the final geometry. Figure 1 shows the computational domain. Then, the model is divided into poly-hexacore elements in Fluent Meshing software. In total, 3310421 cells are generated with admissible quality. Figure 2 depicts the cells around the swirling generator.

Figure 1- Geometry of in-line separator and swirling generator created by Solidworks and ANSYS Spaceclaim

Then, the model is divided into poly-hexacore elements in Fluent Meshing software. In total, 3310421 cells are generated with admissible quality. Figure 2 depicts the cells around the swirling generator.

Figure 2- Poly-hexacore elements around the swirling generator

Based on the reference paper, Reynolds Stress Model (RSM) is used to solve turbulence effects. It is one of the comprehensive models provided in Ansys Fluent, which considers 7 equations. More importantly, two phases are modeled using the Eulerian Multiphase module. Note that the usage of the correct drag law model and accurate surface tension is of the essence. Water is the primary phase, and oil is the secondary one.

Post-processing

Complex flow patterns and phase separation methods are revealed by the two-phase in-line separator’s computational fluid dynamics (CFD) research. With tangential velocities as high as 2.5 m/s, the streamline visualization shows how well the axial-flow swirl generator produces a strong helical flow pattern. The efficacy of phase separation depends on the strong centrifugal forces produced by this induced swirling motion, which are around three to four times stronger than gravity forces. The turbulent kinetic energy distribution and intricate secondary flows are captured by the Reynolds Stress Model (RSM) turbulence modeling, especially in the wake zone of the swirl generating blades. According to the flow structure analysis, an effective separation process is achieved by optimizing the blade geometry and angle of attack to enhance tangential momentum transfer while reducing pressure losses.

Figure 3-Oil Velocity Streamline

The volume fraction contours, which display clear phase stratification patterns, offer quantitative proof of the separation effectiveness. While the lighter oil phase (ρ = 900 kg/m³) accumulates in the the center region with volume fractions above 0.85, the water phase, which has a higher density (ρ ≈ 998 kg/m³), experiences larger centrifugal forces and concentrates along the separator walls. The interface dynamics between the two phases, including surface tension effects and phase interaction forces, are captured by the Eulerian multiphase simulation. The equilibrium between centrifugal forces and turbulent dispersion is demonstrated by the radial distribution of phases, with the separation efficiency being especially sensitive to the swirl intensity and inlet flow conditions. This analysis offers useful information for improving in-line separator designs for a range of industrial uses, such as wastewater treatment systems and oil-water separation in petroleum refining.

Figure 4- Volume fraction of a) water b) oil phase