Packed Bed Reactor: Particles Modeling

Packed Bed Reactor with Particles, CFD Simulation Training with ANSYS Fluent

Description

Reactor models range from pseudo-homogeneous to heterogeneous, from one-dimensional to three-dimensional, and from assumed flow patterns to fully computed flow and transport fields. Among these, packed bed reactors (also known as fixed-bed reactors) are widely used for catalytic processes, particularly favored for heterogeneous reactions where solid-fluid contact strongly influences reaction rate. A packed bed reactor consists of a cylindrical vessel filled with solid reactant material, with a second reactant entering through the inlet face and flowing through the packed solids.

Compared to fluidized bed reactors — which typically achieve near-isothermal conditions and more uniform product output — packed bed reactors generally experience a temperature drop near the reactor inlet regardless of the wall temperature profile, along with comparatively poorer mixing and more heterogeneous behavior.

This project simulates a packed bed reactor using ANSYS Fluent. The 2D geometry was designed in Design Modeler as a rectangle measuring 120 mm long and 40 mm wide, meshed in ANSYS Meshing using a structured quad mesh totaling 5,000 elements.

Methodology

Several assumptions were applied to the simulation: a pressure-based solver was used, only fluid behavior was examined (no heat transfer was modeled), the simulation was run as unsteady, and gravitational effects were included at -9.81 m/s² along the y-axis.

Key simulation settings included:

• Viscous model: SST k-omega, with a mixture turbulence multiphase model

• Multiphase model: Eulerian, with implicit formulation across two phases — gas (flow) and solid particles

• Boundary conditions: Velocity inlet with the flow phase at 0.05 m/s (volume fraction 1) and particles at 0 m/s (volume fraction 0); pressure outlet at 0 Pa gauge pressure; stationary upper and lower walls

• Solution methods: Phase Coupled SIMPLE for pressure-velocity coupling, PRESTO! for pressure discretization, and first-order upwind schemes for momentum, turbulent dissipation rate, turbulent kinetic energy, and volume fraction

• Initialization: Standard method with a patch applied to define the packed particle region, setting particle volume fraction to 0.65 within that patched zone

Conclusion

Results include 2D contours of pressure, velocity, and volume fraction for both the water flow and the alumina particles. Water enters the reactor and passes through the particles — packed and fixed within the lower half of the reactor — ultimately exiting at the same velocity as the inlet flow.

The static pressure contour further shows a clear pressure drop as flow passes through the packed particle region, after which pressure remains constant at zero through to the outlet face — confirming that the packed bed of particles introduces the expected flow resistance while the reactor otherwise maintains steady, consistent flow behavior downstream.