Separator CFD Simulation, Three-Phase Flow, ANSYS Fluent Training

Separator Problem Description

The 3-Phase Horizontal Separator works based on density differences of fluids. The mixture of fluids inter through the inlet vessel and, after collision with the inlet diverter, enters the tank. In reality, the Separator is equipped with sensors to control oil and water level and then control mass flow.

Therefore, controlling the mass flows is a challenge in the simulation. In this project, the density of air, water, and oil is assumed to be 1.2, 998 & 689 kg/m^3, respectively. Also, the VOF Multiphase model is used.

Geometry & Mesh

The 3D geometry is modeled in Ansys Design Modeler software. A cylindrical zone with a 1m diameter extended for 8 meters with two caps. Also, the mesh grid is carried out using Ansys Meshing software.

Furthermore, an unstructured grid is generated, and in total, 7166267 elements established the fluid domain, which is depicted in the following figure.

CFD Simulation

Several assumptions have been considered to simulate the horizontal 3-phase separator, including:

• The simulation is steady.
• The pressure-based solver type is used due to the incompressibility of the working fluids.
• Gravitational acceleration effects are applied in –y-direction.

The following table represents a summary of the solution:

Models(Viscous)
Viscous	K-epsilon	Realizable
Multiphase	Type	VOF
	Formulation	Implicit
	Primary Phase Secondary Phase Secondary Phase	Air Oil Water-liquid
Materials
Fluid	Definition method	Fluent database
	Material name	Air
		Engine-oil
		Water-liquid
Cell zone condition
	Material name	Mixture-template
Boundary condition
Inlet	Type	Mass-flow-inlet
	Gas-phase	0.005 kg/s
	Oil-phase	2 kg/s
	Water-phase	3 kg/s
Outlet-gas   Outlet-oil   Outlet-water   Wall-shell Oil-Bucket Diverter Separator	Type	Mass-flow-outlet
		0.005 kg/s
	Type	Mass-flow-outlet
		2 kg/s
	Type	Mass-flow-outlet
		3 kg/s
	Type	Wall (Stationary – No-slip condition)
Solver configuration
Pressure-velocity coupling	Scheme	Coupled
Spatial Discretization	Gradient	Least squares cell-based
	Pressure	PRESTO!
	Momentum	First-order upwind
	Volume Fraction	Modified HRIC
	Turbulent kinetic energy	First-order upwind
	Turbulent dissipation rate	First-order upwind
Initialization	Initialization methods	Standard Initialization
Run Calculation
	Number of time steps	1000

 

Separator Results

After the simulation process, the two & three-dimensional contours are extracted. It is evident that high inlet velocity could increase the mixing rate, which is not our interest and aim. So by using an inclined diverter, the velocity decreases and enters the fluid domain.

Due to the density gradient, the dense fluid (water) remains at the bottom of the tank and oil on top to reach the oil bucket level and leaves the tank. The volume fraction contours corroborate the claim.

You can obtain Geometry & Mesh file and a comprehensive Training Movie that presents how to solve the problem and extract all desired results.