Effect of particle holdup on bubble formation in suspension medium by VOF–DPM simulation

A numerical simulation based on volume-of-fluid and discrete particle method has been accomplished to analyze the effect of particle holdup on bubble formation in suspension medium. A two-way coupled model involving some essential interphase forces (liquid-particle suspension inertial force, particle-bubble contact force, Basset force, bubble inertial force, virtual mass force, pressure gradient force, etc.) is firstly set up and validated with the experimental and simulation results. On the basis of the analysis on two-stage bubble formation, some potential influence factors (bubble neck length, bubble detachment size and period, bubble shape and wakes) are discussed. The results show that the neck length of bubble detachment increases with the increase of particle holdup due to the greater drag coefficient. For 0.6% < ε _p < 0.8%, the neck length at t/ t _det = 1 varies greatly due to a significant increase in apparent viscosity at ε _p = 0.55%. Additionally, the trajectory instability of the bubble is attributed to the increase of bubble aspect ratio, leading to a strong entrainment ability and transport enhancement in gas–liquid–solid medium. The particles can weaken the entrainment of bubble-induced flow to the surrounding fluid, thus the influence of shortening the detachment period caused by the wake weakening is weakened.