Study of the Ignition Behavior in Slender Packed Bed Reactors Using Direct Numerical Simulation and 1D Phenomenological Models

Packed bed reactors are widely used in the chemical process industry. This study compares particle-resolved computational fluid dynamics (PR-CFD) with 1D models to analyze ignition phenomena in slender packed beds under varying column-to-particle ratios (N = 7, 5.25, 4.2), Reynolds numbers (Re = 20, 50, 100), and Thiele moduli (ϕ₀ = 0.5, 1.0, 3.0). Higher inlet velocity produces weaker ignition, whereas the opposite is found for faster reactions. In adiabatic operation, ignition location is independent of N, whereas in wall-cooled cases, lower N shifts ignition downstream and reduces its intensity. Three ignition regimes are identified: no ignition, downstream ignition, and inlet ignition. While the 1D model captures ignition behavior in adiabatic cases, it fails in wall-cooled conditions due to its inability to resolve radial profiles and intraparticle temperature asymmetry. These findings quantify the intrinsic failure modes of 1D models under wall-cooled conditions and identify when higher-dimensional models become necessary.