Heat transfer enhancement in turbulent Rayleigh Bénard convection with liquid-liquid emulsions*

In this study, we investigate the heat transfer in a liquid-liquid emulsion and flow properties in a three-dimensional Rayleigh-Bénard convection cell at fixed Ra = 1e8 and Pr = 4. By varying the droplet volume fraction (Φ) from 0 to 0.5, while keeping thermophysical property ratios constant at unity, we uncover intriguing insights. The introduction of droplets into the single-phase flow significantly enhances heat transfer between the plates, resulting in a remarkable 9% increase in the Nusselt number for Φ = 0.5. This enhancement is attributed to augmented diffusion near the walls and convection in the central region due to the presence of dispersed droplets, more at higher volume fractions. Despite the decrease in carrier-phase diffusion and convection heat transfer at higher Φ, droplets exhibit increased rates of diffusion and convection, leading to an overall enhancement in total diffusion and convection. Moreover, we examine turbulent kinetic energy budgets, providing deeper insights into the emulsion dynamics in the Rayleigh-Bénard convection cell. At higher concentrations of secondary phase, we observe a simultaneous increase in both production and energy dissipation. Finally, we investigate the influence of different viscosity ratios on heat transfer rates. Remarkably, utilizing more viscous droplets (μd / μc = 10) in a moderately concentrated flow (Φ = 0.2) shows a significant enhancement in heat transfer rate, which becomes less pronounced as the droplet volume fraction increases (Φ = 0.5).