Particle properties influence on the borderline between gas-dispersed flows with high and low particle concentrations

Computational fluid dynamics (CFD) methods were used to analyze the flow around two sequentially arranged bodies. A comparative assessment was conducted to determine the conditions under which hydrodynamic instability may occur in low-concentration gas-dispersed flows. Variations in the physical properties of particles, typical of those found in industrial biomass and fossil fuel energy installations, were considered in this assessment. The numerical model for laminar flow around individual particles was validated using the experimental data of Rowe and Henwood for dimensionless intersphere distance of 5, 11, 17, and 23. It was demonstrated that the velocity profile upstream of the first sphere influences the ratio of forces acting on each sphere. The critical dimensionless center-to-center distance (x/d)_кр was calculated, at which the ratio of the force acting on the second particle (F₂) to that on the first particle (F₁) equals 0,95 (indicating the onset of convergence), under steady uniform gas flow conditions in an elemental streamtube of an ideal entrained-flow reactor for particles of spherical and plate-like shapes. Within the Reynolds number range 2,0·10^-1…3,2·10³, the influence of particle density, size, and shape on the corresponding critical volume concentration φ_кр and (x/d)_кр was determined. Additionally, for spheres, the force ratio F₂/F₁ = 0,90 was considered, which allowed to establish the transition zone between entrained-flow systems and circulating fluidized bed (CFB) boilers. Simulations of gas flow around two plates with three different orientations relative to the incoming flow were conducted. The results demonstrate that the mutual orientation of plate-like particles in the flow affects their hydrodynamic interaction. Specifically, compared to the scenario of flow around two spheres of equivalent diameter, the risk of convergence increases when the particles are oriented with their largest face perpendicular to the incoming flow, and decreases when they are oriented with their smallest face perpendicular to the incoming flow. The effectiveness of the proposed method was verified by analyzing a range of systems, including power boilers, industrial gasifiers, and large-scale test installations.

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