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Fluid-particle and particle-particle drag forces in moderate-Reynolds-number bidisperse suspensions
- Fan DUAN Xuan HE Qiang ZHOU
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The Chinese Journal of Process Engineering. 2024, 24(3):
297-314.
DOI: 10.12034/j.issn.1009-606X.223212
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A set of fully resolved numerical methods are employed to simulate the bidisperse suspensions where the particles are free to translate and rotate according to the effects of the surrounding fluid, and the fluid-particle and particle-particle drag relations in the literature are examined. Three overall solid volume fractions of 0.1, 0.2, and 0.3, two diameter ratios of 1.5 and 2, three small-particle-phase fractions of 0.1, 0.3, and 0.5, four particle-to-fluid density ratios of 10, 100, 500, and 1000, and three overall particle Reynolds numbers of 10, 20, and 50 are chosen. Simulation results show that, among the fluid-particle drag relations available in the literature, in terms of the model accuracy, the relations obtained from static homogeneous systems are the best, the next are those of dynamic suspensions, and the monodisperse drag extended relations are the worst. Based on the simulation data, a new fluid-particle drag relation that meets all physical requirements is proposed. Further analysis reveals that the fluid-particle drag of bidisperse suspensions is influenced by five factors, that is the local solid volume fraction, the slip velocity between different particle phases, the granular temperature, the particle Stokes number, and the particle microstructure. Under the action of these factors, the change of the fluid-particle drag is not significant as the particle-fluid density ratio varies, and the difference of the fluid-particle drag between small and large particle phases is smaller than that in static homogeneous systems. For the particle-particle drag, when the particle-fluid density ratio equals 10 or 100, the collision numbers are unevenly distributed between different particle pairs because of the lubrication force. This uneven distribution of the collision numbers leads to the invalid of the assumption of molecular chaos, and for this reason, the particle-particle drag is highly overestimated by the relation derived from the kinetic theory of granular flow.