Direct numerical simulation of flow past a reactive/inert mixed particle pair

During the pyrolysis and gasification processes inside fluidized bed reactors, a single reactive particle is generally surrounded by multiple inert heat carrier particles. In this work, we focus on the simplest mixed particle pair (one reactive particle: P-1, and one inert particle: P-2) to investigate the joint effects of the Stefan Reynolds number (Re-sf), the particle Reynolds number (Re), separation distance normalized by particle diameter (L), and relative orientation (a) on the drag force exerting on each particle by particle-resolved direct numerical simulations. The results show that when particles are placed in a tandem arrangement, the blocking effect on P-2 is weakened/strengthened with negative/positive Stefan flow since the effective diameter of P-1 is smaller/larger than its real diameter. When L = 1.25, Re = 3, and particles are placed in tandem, the drag force of P-1 decreases as Re-sf increases, but the reduction of the drag force decreases as Re increases. Under such conditions, the positive Stefan flow induces the repulsion between the two particles; thus, the drag force of P-2 increases as Re-sf increases. When Re-sf = 3 and P-2 is located downstream, the repulsive force felt by P-1 can partially offset the drag force at L = 1.25, Re = 3. Moreover, the negative/positive Stefan flow enhances/weakens the drag force of P-2 when it is located upstream. The Stefan flow has a negligible effect on the drag force of P-2 when L = 3.

Automated summary

In this study, particle-resolved direct numerical simulations were conducted to investigate the combined effects of Stefan Reynolds number, particle Reynolds number, separation distance, and relative orientation on the drag force exerted on particles in fluidized bed reactors. The results show that the blocking effect on inert particles in a tandem arrangement is weakened/strengthened with negative/positive Stefan flow due to the difference between the effective diameter and the real diameter of reactive particles. The drag force on the reactive particle decreases as Stefan Reynolds number increases, but the rate of reduction decreases as particle Reynolds number increases. The positive Stefan flow induces repulsion between the particles, leading to an increase in drag force on the inert particle. The Stefan flow has a negligible effect on the drag force of the inert particle when the separation distance is 3 times the particle diameter.