PFR Flow Simulation

Overview

This case study models fluid transport through the packed-bed section of a Plug Flow Reactor (PFR) using ANSYS Fluent. The project builds directly on my earlier physical PFR design and demonstrates how porous materials regulate velocity, pressure, and residence time inside environmental treatment systems.

Using Fluent’s porous-media model, I simulated laminar flow entering a cylindrical reactor, passing through a porous zone (porosity = 0.4), and exiting through a contracted outlet. The results closely match theoretical expectations from Darcy-Forchheimer behavior and validate the flow-conditioning effects of porous internals in environmental reactors.

Tools & Software

• ANSYS Workbench 2025 R2

• ANSYS DesignModeler for geometry

• ANSYS Meshing for volume discretization

• ANSYS Fluent (3D) for CFD simulation and visualization

Geometry Design

The model was built to reflect the dimensions of my previously constructed PFR:

• Inlet pipe → contraction → porous cylindrical reactor body → contraction → outlet pipe

• Length: ~0.3 m

• Porous zone located centrally

• Smooth transitions to avoid artificial separation

The geometry was created based on the profile shown in DesignModeler

Model Setup (Fluent)

Flow Regime: Laminar

Inlet: Velocity inlet, 25 m/s

Outlet: Pressure outlet, 0 Pa gauge

Porous Zone Properties:

• Porosity = 0.4

• Permeability: 3.8 x 10^7

• Viscous and inertial resistances defined according to the Darcy–Forchheimer model

Solver Settings:

• Pressure-velocity coupling (SIMPLE)

• Second-order spatial discretization

• Residual convergence monitored to <10⁻³ for all components

Results

Convergence Behavior

Residuals decreased several orders of magnitude over ~600 iterations with stable late-stage behavior. Minor mid-simulation oscillations correspond to model stabilization at the porous interface, normal for Darcy-Forchheimer models.

Velocity Contour

The flow accelerates at the inlet contraction, rapidly decelerates upon entering the porous media, and re-accelerates at the outlet.

Velocity Vectors

Velocity vectors show jet entry, energy dissipation inside the porous zone, and smooth flow recovery toward the outlet.

Engineering Interpretation

1. Pressure Drop & Energy Loss

The sharp deceleration at the porous entrance confirms significant viscous resistance. This corresponds to the steep pressure gradient predicted by Darcy’s Law. Inside the packed bed, energy losses stabilize and the flow becomes more uniform.

2. Flow Uniformity

Velocity contours show the hallmark of plug-like flow:

• High-speed jet → dissipated rapidly

• Near-uniform velocities within the porous region

• Controlled outlet acceleration

This is desirable in PFR systems that rely on consistent residence time.

3. Influence of Porous Media

Porous structures dampen turbulence and reduce velocity gradients. The simulation illustrates how reactor internals modify mixing patterns and flow distribution, which are key for treatment efficiency in filtration, adsorption, or biological reactors.

4. Model Validity

The results match expected porous media behavior, aligning with theory and my prior experimental PFR work. This confirms the correctness of the setup and supports future optimization of media selection and geometry.

Skills Demonstrated

• 3D reactor geometry modeling

• Mesh generation & quality control

• Porous media modeling in Fluent

• Laminar/Darcy–Forchheimer flow simulation

• Interpretation of CFD results (pressure drop, streamlines, velocity distribution)

• Environmental reactor design principles

• Integration of CFD with physical design