MHD & EHD: Spiral Magnetic Separator

Spiral Magnetic Separator CFD Simulation Using ANSYS Fluent

Introduction

This study investigates the performance of a spiral magnetic separator using computational fluid dynamics to understand the complex interactions between fluid flow, magnetic particles, and an applied magnetic field within the separator. Water enters the domain from the upper boundary carrying both magnetic particles and SiO2 particles, while an applied magnetic field, represented through user-defined functions for the Bx, By, and Bz components, influences the trajectory of the magnetic particles and enables their separation from the non-magnetic SiO2 particles. By combining turbulence modeling, discrete phase modeling, and magnetohydrodynamics, this research provides valuable insight into the separation efficiency and flow behavior characteristic of magnetic separation systems.

Geometry and Mesh

The geometry consists of a spiral-shaped separator with multiple turns, designed in ANSYS SpaceClaim and meshed in ANSYS Meshing to promote effective particle separation along the spiral flow path. The simulation was conducted using a steady-state, pressure-based solver in ANSYS Fluent to capture the coupled flow and particle behavior throughout the domain.

Methodology

Turbulent flow within the separator was resolved using the Realizable k-epsilon model with standard wall functions. A two-way coupled Discrete Phase Model was implemented to simulate the behavior of both magnetic and SiO2 particles, capturing the interaction between the particles and the continuous water phase. Group injection was defined for both particle types, with diameter distributions specified using the Rosin-Rammler model. The Magnetic Induction MHD method was enabled with a DC field type to simulate the effects of the applied magnetic field on both the flow and particle trajectories, with several user-defined functions implemented to define the source terms for the Bx, By, and Bz magnetic field components.

Results and Conclusion

The magnetic field components exhibit alternating positive and negative regions along the spiral path, with By ranging from -1.5347×10⁻¹⁵ to 1.7298×10⁻¹⁵ T, Bz ranging from -1.0879×10⁻¹⁴ to 8.7105×10⁻¹⁶ T, and Bx displaying a more complex distribution between -3.79×10⁻¹⁵ and 4.40×10⁻¹⁵ T. Static pressure within the separator ranges from -0.84606 to 4.6414 Pa, with higher pressures concentrated near the outer walls of the spiral, while velocity magnitude varies from 0 to 0.13735 m/s, with higher velocities observed near the inner walls. Particle tracks reveal a polydisperse mixture with diameters ranging from 1.00×10⁻⁴ to 2.96×10⁻⁴ m, experiencing static pressures between -8.94380 and 9.69623 Pa as they travel through the domain. Pathlines colored by Bx and velocity magnitude illustrate the complex spiral flow pattern, with velocities along the pathlines reaching up to 0.181 m/s in the upper turns of the spiral. The particle tracks further indicate a gradual separation of particles based on their magnetic properties and size, with larger and more strongly magnetic particles tending to concentrate toward the outer walls of the spiral. These results confirm the effectiveness of the spiral design in creating an extended separation path, where the combined variation in magnetic field strength and flow velocity along the spiral drives progressive particle segregation based on each particle's position within the separator.