A fixed-grid model to track the interface and porosity of a chemically reacting moving char particle

•A new method for a reacting particle interface and particle porosity tracking has been presented.•The Stefan flow suppress the ambient gas penetration into the pores.•The Stefan flow modifies the hydrodynamic boundary layer around the particle.

The main objectives of this work are to present a new CFD-based model for tracking the chemically reacting particle interface and particle porosity, and to numerically explore the influence of particle velocity on the dynamics of the particle porosity. As an illustrative example we consider the gasification of a single spherical particle moving in a hot CO2 gas. The interface tracking model has been validated against a moving-grid method using a commercial CFD software. Excellent agreement has been achieved. Several cases for a moving porous particle have been studied numerically. Simulation results showed that the Stefan flow inside the gasifying particle plays a significant role in the mass transfer governed by the Thiele modulus. Besides this, we show that the Stefan flow significantly modifies the hydrodynamic boundary layer around the particle at low values of the Reynolds number corresponding to unity order of magnitude. Finally, we show that in all regimes (from kinetically controlled to diffusion controlled), particle porosity is at a minimum in the center of the particle, and increases towards its outer surface at all stages of particle conversion. Additionally, we found out that the diffusion-controlled regime is characterized by the particle porosity gradient reaching higher values in comparison to the pore diffusion regime.