Filter Cake Formation: Porous Medium, Multiphase Flow

Multiphase Flow in Porous Medium, Filter Cake Formation, ANSYS Fluent CFD Simulation Training

Description

This project simulates multiphase flow through a porous medium using ANSYS Fluent. The model consists of two regions: an upper column section containing water-soluble particles suspended in water, and a lower section containing the porous medium itself. The initial mixture carries a particle volume fraction of 0.185. As water flows in from the top of the column, it applies pressure to the mixture and drives it through the pores of the porous medium below — separating the soluble particles from the water flow in the process.

The 2D geometry was designed in Design Modeler as a vertical column measuring 0.08 m in height and 0.0125 m in width, divided into two regions with the porous medium occupying the lower section. Given the model's symmetrical structure, only half the geometry was modeled, with a symmetry boundary condition applied. The domain was meshed in ANSYS Meshing using a structured grid totaling 572,852 elements.

Methodology

Water enters from the top of the vertical column at a relative pressure of 100,000 Pa and a temperature of 288.15 K, flowing downward into the porous medium at the column's base. This porous medium is modeled as aluminum, with a porosity coefficient of 0.6 (the ratio of void/fluid space to total volume).

Since this problem involves two mixed phases, a multiphase model was required — specifically the Eulerian multiphase model, the most comprehensive multiphase approach available, capable of solving separate momentum and energy equations for each phase individually. This model is well-suited to a wide range of multiphase phenomena, including bubble flows, droplet flows, vertical risers, cyclones, fluidized beds, bubble columns, slurry flows, sedimentation, and particle suspension — the filtration process modeled here falls within this same category.

The primary phase was defined as liquid water, with the secondary phase representing the water-soluble particles (sludge), defined with a density of 2400 kg/m³, specific heat capacity of 4180 J/kg·K, thermal conductivity of 0.0454 W/m·K, and a viscosity following a power-law model. The simulation was run as transient.

Conclusion

Results include 2D contours of mixture pressure, along with velocity, temperature, and volume fraction for both the primary (water) and secondary (particle) phases. As the water flow moves downward through the column toward the porous medium, the results show that the water-soluble particles are unable to pass through the pores, while the water itself passes through freely.

This selective separation — water passing through while particles are retained — confirms that the porous medium successfully filters the soluble particles out of the flow, producing the characteristic filter cake buildup at the medium's surface as particles accumulate and are progressively separated from the water stream.