Turbulent convection in emulsions: the Rayleigh-Bénard configuration

This study explores heat and turbulent modulation in three-dimensional multiphase Rayleigh-B & eacute;nard convection using direct numerical simulations. Two immiscible fluids with identical reference density undergo systematic variations in dispersed-phase volume fractions, 0.0 <=Phi <= 0.5, and ratios of dynamic viscosity, lambda(mu), and thermal diffusivity, lambda(alpha), within the range [0.1-10]. The Rayleigh, Prandtl, Weber and Froude numbers are held constant at 108, 4, 6000 and 1, respectively. Initially, when both fluids share the same properties, a 10 % Nusselt number increase is observed at the highest volume fractions. In this case, despite a reduction in turbulent kinetic energy, droplets enhance energy transfer to smaller scales, smaller than those of single-phase flow, promoting local mixing. By varying viscosity ratios, while maintaining a constant Rayleigh number based on the average mixture properties, the global heat transfer rises by approximately 25 % at Phi=0.2 and lambda(mu)=10. This is attributed to increased small-scale mixing and turbulence in the less viscous carrier phase. In addition, a dispersed phase with higher thermal diffusivity results in a 50 % reduction in the Nusselt number compared with the single-phase counterpart, owing to faster heat conduction and reduced droplet presence near walls. The study also addresses droplet-size distributions, confirming two distinct ranges dominated by coalescence and breakup with different scaling laws.