Investigation of Fire Rate in a Porous Media Reactor with Hollow Spheres as Packed Bed

Inert porous media reactors made up of solid spheres are widely recognized for their high performance and easy manipulation. The main objective of this work is to investigate the effects of fire rate (FR) on the combustion wave temperature and its propagation rate in a porous media reactor composed of hollow alumina spheres. Experimental data were recorded at a range of FRs from 755 kW/m2 to 3776 kW/m2 for an equivalence ratio of 0.55 and 0.7. A 2D two temperature model based on the heat transfer mechanism is developed. The heat transfer mechanism considers convection, conduction of each phase, thermal radiation between the external surface of the sphere and internal radiation exchange inside the hollow sphere, where three gasses are tested as enclosed fluid: air, carbon dioxide, and water. The numerical model uses a one-step combustion for methane oxidation in lean conditions. The results of the numerical model are found to be in a good agreement with experimental data. Upstream and stagnated combustion waves are obtained in the range of FRs studied. The experimental results expose their maximum combustion wave velocity around the FR of 1500 kW/m2 and 1800 kW/m2 for an equivalence ratio of 0.55 and 0.7, respectively. Numerical results indicate that the internal radiation inside the hollow sphere is the predominant component in the heat transfer mechanism on the temperature and propagation rate of the combustion wave. It was found that reducing particle diameter of the hollow sphere and the thickness of its shell enlarge the surface area for convection, increasing the solid phase temperature. © 2025 Elsevier Ltd