In thermal multiphase flows, the modulation in the heat transfer rate due to the presence of finite-size solid particles attract growing interest in recent years. This study focuses on developing a robust and efficient simulation method for particle-laden Rayleigh-Bénard convection. We utilize the double distribution function-based thermal lattice-Boltzmann method (TLBM), which enables successful simulations of multiphase fluid-thermal interactions. The no-slip boundary of the moving solid particles is handled by the interpolated bounce-back scheme. Additionally, Galilean invariant momentum exchange and heat exchange approaches are employed for hydrodynamic force and heat transfer calculation at the solid boundaries. The accuracy of the current method is verified first with several benchmark cases. Then, we explore the modulation of Rayleigh-Bénard flows due to the presence of freely moving finite-size particles. The effects of finite-size solid particles on the overall heat transfer efficiency and modulation to the flow field in three-dimensional particle-laden turbulent Rayleigh-Bénard convection are discussed. The results show that addition of solid particles causes a moderate increase in the overall Nusselt number, and this enhancement is mainly due to the increased heat flux transported by the particles, associated with the large-scale and vertical transport modes of particle motion and particle-induced thermal plumes. This enhancement is seen at low to moderate Rayleigh numbers, and disappears at high Rayleigh numbers.

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