Multi-phase Turbulent Rayleigh–Bénard convection with Bubbles

We report a direct numerical simulation of multiphase turbulent Rayleigh–Bénard convection to investigate the heat transfer mechanism and flow modulations. The numerical simulations are performed in a three-dimensional domain at Prandtl number Pr = 4 (water), Rayleigh number 10⁸ ≤ Ra ≤10⁹, and Weber number We = 6000. We recently found that when non-colloidal, rigid spherical particles are present in this flow, the heat transfer rate is enhanced. However, beyond a threshold particle volume fraction value, the Nusselt number exhibits a substantial drop due to the dense particle layering in the near-wall region which results in reducing the convection in that region and prevents the formation of any coherent structures within one particle diameter from the wall. In this work, by considering bubbles (as the secondary phase) inside the fluid flow, we aim to investigate the effects of deformability of the secondary phase on the heat transfer rate. For this purpose, a parametric study of the effects of bubble volume fraction (0 < α < 0.4) and the dynamic viscosity ratio (0.01 < µ_d /µ_c < 100) is performed and the results presented in details.