Effect of particle diameter ratio and density ratio on Rayleigh- Bénard convection

We investigate the flow structures, dynamic behaviors of particles and heat transfer in turbulent Rayleigh–Bénard convection laden with inertial particles. Direct numerical simulations using IB-LBM are presented in the range of diameter ratios 1.5% ≤ D *≤ 5.6% and density ratios −7 × 10 -4 ≤ Δ ρ ≤ 7 × 10 -4 , at Rayleigh number Ra = 10 8 and Prandtl number Pr = 1. A four-way coupling model was adopted, where particles were treated as rigid bodies, and the momentum exchange between discrete particles and the carrier fluid was fully accounted for. We found that the added mass M *, a dimensionless parameter, can serve as a criterion for judging the particle motion and turbulent heat transfer performance. For M * < M c , where M c denotes the critical added mass, the particles feature a small diameter ratio ( D *≤ 3%) and a density close to the carrier fluid. Under the influence of the preferential sweeping effect, the particle clusters mainly move along the vortex edges. The strong coupling interaction between particles and vortices can perturb the thermal boundary layer, enhance turbulent mixing, and thereby improve the turbulent heat transfer performance. For M * > M c , corresponding to particles with a large diameter ratio ( D * ≥ 3%) or extreme density ratio, their motion is no longer confined to the vortex edges, resulting in a more uniform spatial distribution. Meanwhile, large-scale deposition of particle clusters occurs on the top and bottom plates. This phenomenon hinders the development and stability of large-scale circulation and impairs the turbulent heat transfer performance.